NASASpaceFlight.com Forum

SpaceX Vehicles and Missions => SpaceX Starship Program => Topic started by: Chris Bergin on 06/13/2015 06:13 pm

Title: MCT Speculation and Discussion Thread 4
Post by: Chris Bergin on 06/13/2015 06:13 pm
Thread 4 for the discussions of SpaceX MCT.

Thread 1:
http://forum.nasaspaceflight.com/index.php?topic=33494.0

Thread 2:
http://forum.nasaspaceflight.com/index.php?topic=35424.0

Thread 3:
http://forum.nasaspaceflight.com/index.php?topic=36805.0

Main NSF Articles:

http://www.nasaspaceflight.com/2014/03/spacex-advances-drive-mars-rocket-raptor-power/

http://www.nasaspaceflight.com/2014/07/spacex-roadmap-rocket-business-revolution/

http://www.nasaspaceflight.com/2014/08/battle-heavyweight-rockets-sls-exploration-rival/

And http://www.nasaspaceflight.com/?s=Raptor

L2 Info and Evaluations:
http://forum.nasaspaceflight.com/index.php?topic=35419.0 (Menu links in the opening post).

L2 MCT Rending Effort (ongoing, large collection):
http://forum.nasaspaceflight.com/index.php?topic=35307.0

--


Remember to be civil and to stay on topic.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 06/14/2015 08:34 am
From the last thread:

So I propose that we actually refuel the MCT in LEO (something we would already routinely do) for partially propulsive Earth Entry.

Your fuel needs to get into LEO. If other MCTs on BFRs are launching fuel to LEO depots, then, pretty much by definition, those MCTs will need to be able to handle a full LEO reentry, so the TPS problem would need to be solved before you can use this to solve the program that you are trying to solve by using this. (So to speak.)

As Jim said earlier somewhere, Dragon is too small to have a rover.

Jim was wrong. Dragon's side hatch is too small for a rover like MSL, but the internal volume and modelled payload capacity to Mars is more than sufficient. Even without changing the hatch-size, you can still fit in a rover around 0.6x0.7x2m, which is large enough for the job since you will want to offload as much of the computation, power and communications to the capsule itself.

Moreso, if you want to propose using a Dragon for site-surveying for MCT landings, then even the above size limitation doesn't apply. After all, on the scale of the development costs for MCT and BFR, making a few structural modifications to a Dragon capsule is going to be a rounding off error. (Certainly less than your proposed alternative.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/14/2015 03:35 pm
From the last thread:

So I propose that we actually refuel the MCT in LEO (something we would already routinely do) for partially propulsive Earth Entry.

Your fuel needs to get into LEO. If other MCTs on BFRs are launching fuel to LEO depots, then, pretty much by definition, those MCTs will need to be able to handle a full LEO reentry, so the TPS problem would need to be solved before you can use this to solve the program that you are trying to solve by using this. (So to speak.)


Only if one tries to imagine that MCT is used as a Tanker to LEO, which is very silly and wasteful.  Tankers will be a stretched upper stage of the BFR without any cargo on top and will use its low ballistic coefficient and retro-propulsion with residual propellents and likely some parachutes to perform re-entry and landing, all while delivering far MORE propellents.

Lots of people have been pushing this idea of MCT is the ONLY thing that BFR will ever have placed on top of it and that is must do EVERYTHING we want done from LEO all the way to Mars, this is completely unrealistic and dose not save any money as the MCT would be 10x harder to design and build when it has so many requirements put on it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Krevsin on 06/14/2015 05:38 pm
From the last thread:

So I propose that we actually refuel the MCT in LEO (something we would already routinely do) for partially propulsive Earth Entry.

Your fuel needs to get into LEO. If other MCTs on BFRs are launching fuel to LEO depots, then, pretty much by definition, those MCTs will need to be able to handle a full LEO reentry, so the TPS problem would need to be solved before you can use this to solve the program that you are trying to solve by using this. (So to speak.)


Only if one tries to imagine that MCT is used as a Tanker to LEO, which is very silly and wasteful.  Tankers will be a stretched upper stage of the BFR without any cargo on top and will use its low ballistic coefficient and retro-propulsion with residual propellents and likely some parachutes to perform re-entry and landing, all while delivering far MORE propellents.
Why bother with the cargo?
Just leave the cargo bay empty and send up an empty MCT. Less payload to LEO = more leftover fuel in the tanks.

Lots of people have been pushing this idea of MCT is the ONLY thing that BFR will ever have placed on top of it and that is must do EVERYTHING we want done from LEO all the way to Mars, this is completely unrealistic and dose not save any money as the MCT would be 10x harder to design and build when it has so many requirements put on it.
While MCT will most likely be supplanted by a dedicated reusable tanker in the long run, in the short run its capabilities make it good enough for the task. Or a really simple, cheap, disposable tanker stage (a glorified fuel tank with a docking port and a single raptor engine).

The idea that early MCTs be used as both a tanker vehicle and an MCT stems from a very real and present fact that SpaceX does not have infinite money and thus cannot really afford development and manufacturing of multiple different reusable, earth-landable and rapidly reusable vehicle designs.

Just make one that is good enough and build as many as you can. An MCT without the cargo will do just fine for refuelling. Not perfect, but good enough.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/14/2015 05:42 pm
Take a BFR which is equivalent to 300 tonnes to LEO as an ELV.

As a two stage fully reusable launcher this can place about 150 tonnes of payload into LEO (+ the mass of the reusable upper stage + landing fuel).

As a two stage launcher with only the first stage reused it could place about 210 tonnes of payload into LEO + the mass of the upper stage (say about 30 tonnes).

If the MCT acts as its own upper stage, then MCT + payload can be up to 240 tonnes. This allows the MCT to have significant mass growth margin.

If the MCT were just payload to a fully reusable two stage BFR, the BFR would have to be 60% larger.

A larger BFR would cost significantly more to develop, not only is it larger and development and intrastructure cost scales more than linearly with size but a separate reusable upper stage would need to be developed. It would have the advantage of needing few tanker flights per MCT flight to Mars. A tanker based on the upper stage is probably going to be more efficient than one based on the MCT (but see mission kit discussion below). Having a MCT act as its own upper stage also has the disadvantage of putting extra design constraints on the MCT which might tip it from being difficult to design to being impossible.

If possible I think SpaceX will optimise for low development cost, even at the expense of some loss of efficiency.

One possibility for the MCT is that it is basically just an upper stage + fairing to which mission kits can be added. So there would be a tanker mission kit, a propellant mission kit and a Mars mission kit (other possible mission kits are long duration, lunar landing, science lab, etc.). The crew and cargo MCT to Mars would be identical with differences being confined to the payload.

If this is the correct way of looking at the MCT, the tanker mission kit would not be that much more inefficient than a dedicated tanker second stage, while the cost of developing a dedicated tanker would be considerably more.

Although I've used a 300 tonne ELV equivalent BFR in the example above, it looks like it could be 10% smaller and still allow adequate mass for the MCT. My guess is that BFR will be 270 tonnes to LEO ELV equivalent with a MCT which acts as its own upper stage, but there are significant factors which are unknown to anyone outside SpaceX and it is still possible that a bigger two stage reusable BFR might be used.

A more radical suggestion for the MCT is to have it having a payload of only 50 tonnes. Two of these mini-MCT would be launched they would join up in orbit, refuel and then each perform half of the TMI burn. The advantage of this arrangement is that there are always 2 independent habitats available to the crew and in an emergency all the crew could land on Mars in one of these MCT. Cargo missions would not need to join up in LEO and can do the TMI independently. This would greatly increase safety and significantly reduce development costs as the BFR and MCT would only need to be half the size. The cost would be a less efficient MCT (due to scaling and the need for a docking port) and more complex LEO operations. If SpaceX went this route than the BFR would be only about 135 tonnes to LEO ELV equivalent, barely bigger than SLS block II.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/14/2015 05:58 pm
MCT and BFR are supposed to be based on the same kind of platform. MCT will HAVE to have similar mass efficiency of an upper stage (in fact Musk has said MCT needs to be capable of Mars surface to earth in a SINGLE stage, though with far less payload), and essentially that's what it is. So whether you call the tanker a modified MCT or a stretched BFR upper stage may be a distinction without much difference.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/14/2015 06:59 pm
Dang it, we really need one spot that has all known information about MCT that comes from SpaceX. I'm not sure if he said 80-100 or 50-100. Not that it makes an enormous difference, but it's annoying.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Llian Rhydderch on 06/14/2015 08:01 pm
Dang it, we really need one spot that has all known information about MCT that comes from SpaceX. I'm not sure if he said 80-100 or 50-100. Not that it makes an enormous difference, but it's annoying.

If it is info based on some sort of "reliable source" (news article, speech captured on video and available on the web, etc.), then wikis seem much better than discussion board threads for compiling the info. 

Wikipedia has such an article:  Mars Colonial Transporter (https://en.wikipedia.org/wiki/Mars_Colonial_Transporter).  (also, a section of that article has it's own link for the BFR:  MCT launch vehicle  (https://en.wikipedia.org/w/index.php?title=MCT_launch_vehicle).

If people don't want to actually add text and a source to the article in that encyclopedia, then just summarize the factoid and add the source in raw URL on the Talk page associated with the MCT:  the  Mars Colonial Transporter (Talk page) (https://en.wikipedia.org/wiki/Talk:Mars_Colonial_Transporter)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/14/2015 08:36 pm
Dang it, we really need one spot that has all known information about MCT that comes from SpaceX. I'm not sure if he said 80-100 or 50-100. Not that it makes an enormous difference, but it's annoying.

My recollection is 80-100 people but my memory is not a very safe source.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/15/2015 01:26 am
A second attempt at a Mars Colonial Transporter.  Not a first generation ship, but perhaps second or third generation of 10m core rockets.  Youtube playlist should show 18 little videos covering the whole trip.  A few very speculative items have crept in, for fun.
For some unknown reason, you need to restart the playlist after the first video. Sorry.

https://youtu.be/s0zokCWXYE4?list=PLBU9UJfqaRooKnHY8QtQ399qqRwBqU6W3

Michel Lamontagne
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/15/2015 05:15 am
MCT and BFR are supposed to be based on the same kind of platform. MCT will HAVE to have similar mass efficiency of an upper stage (in fact Musk has said MCT needs to be capable of Mars surface to earth in a SINGLE stage, though with far less payload), and essentially that's what it is. So whether you call the tanker a modified MCT or a stretched BFR upper stage may be a distinction without much difference.

Show me the quote for this, because I've never heard any such thing.  Rather I think direct single stage Earth return is rather a possible (and the most aggressive possible) interpretation of some of Musks statements but it is far from set in stone.

And even if Elon had said this was his goal we should have SERIOUS doubts if such a goal would survive contact with real engineering as the vehicle capable of doing all that would put a single stage to Earth orbit vehicle to shame.  You can hand wave away the incredible difficulty and mass costs of EDL on Mars and Earth and the costs of keeping a vehicle alive during interplanetary transit.

All this talk about avoiding costs by not developing a 2nd stage are silly, SpaceX MUST have a use for the BFR other then launching for Mars related travel.  The rocket would be completely useless for any other purpose if it's payloads were volumetricly constrained by needing to be inside a MCT cargo-hold which is likely no more then 500 m^3,  SLS should have a payload fairing in excess of 2000 m^3.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sublimemarsupial on 06/15/2015 05:47 am
MCT and BFR are supposed to be based on the same kind of platform. MCT will HAVE to have similar mass efficiency of an upper stage (in fact Musk has said MCT needs to be capable of Mars surface to earth in a SINGLE stage, though with far less payload), and essentially that's what it is. So whether you call the tanker a modified MCT or a stretched BFR upper stage may be a distinction without much difference.

Show me the quote for this, because I've never heard any such thing.  Rather I think direct single stage Earth return is rather a possible (and the most aggressive possible) interpretation of some of Musks statements but it is far from set in stone.

And even if Elon had said this was his goal we should have SERIOUS doubts if such a goal would survive contact with real engineering as the vehicle capable of doing all that would put a single stage to Earth orbit vehicle

Do you anything more than handwaving to support this? Because the people on this site that have tried to put numbers to this have shown that such a stage has a LESS demanding dry mass fraction than an SSTEO vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Krevsin on 06/15/2015 07:05 am
MCT and BFR are supposed to be based on the same kind of platform. MCT will HAVE to have similar mass efficiency of an upper stage (in fact Musk has said MCT needs to be capable of Mars surface to earth in a SINGLE stage, though with far less payload), and essentially that's what it is. So whether you call the tanker a modified MCT or a stretched BFR upper stage may be a distinction without much difference.

Show me the quote for this, because I've never heard any such thing.  Rather I think direct single stage Earth return is rather a possible (and the most aggressive possible) interpretation of some of Musks statements but it is far from set in stone.
It will have to be a Mars SSTO in any case, which means 4.5 km/s of delta V minimum. That's very much in 2nd stage territory.

All this talk about avoiding costs by not developing a 2nd stage are silly, SpaceX MUST have a use for the BFR other then launching for Mars related travel.  The rocket would be completely useless for any other purpose if it's payloads were volumetricly constrained by needing to be inside a MCT cargo-hold which is likely no more then 500 m^3,  SLS should have a payload fairing in excess of 2000 m^3.
But what will use that excessive volumetric capability? The BA2100? Who would use a BA2100 and why? Would you ever need to launch multiple BA2100s? If so, for what reason? If you need something big put in space, wouldn't you rather design it according to the volumetric constraints of the vehicle you'll be using instead of the other way around?

In any case, the bread and butter of most commercial launch service companies is and has always been communication satellites.

A cargo bay which can hold 100 tonnes of cargo for mars can most definitely hold a comms satellite, and the excessive delta V that a MCT is required to pull (even/especially if it doesn't act as its own 2nd stage or do a one burn from Mars to Earth since it still needs at least 4.5 km of delta V to rendezvous with a transfer tug in LMO) make it more than capable of acting as a GTO delivery vehicle.

The volume constraint argument is a red herring. If something big enough to fill the volume constraints of a SLS fairing comes along and requires a launch it might as well get a stage specifically designed for it or even the SLS, if that ever goes into commercial launches. You design things based on the constraints you are given, not the other way around.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/15/2015 07:40 am
A second attempt at a Mars Colonial Transporter.  Not a first generation ship, but perhaps second or third generation of 10m core rockets.  Youtube playlist should show 18 little videos covering the whole trip.  A few very speculative items have crept in, for fun.
For some unknown reason, you need to restart the playlist after the first video. Sorry.

Michel Lamontagne

A lot of thought and work has gone into this. The engineering of an MCT like this would be formidably difficult, but it addresses concerns about zero gravity and abort that other conceptual designs do not.

One improvement might be to have the capsule part of the MCT nominally land attached to the cargo/transit part. Then it can perform an abort during landing.

Do you have mass estimates to go with the animations?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/15/2015 07:59 am
All this talk about avoiding costs by not developing a 2nd stage are silly, SpaceX MUST have a use for the BFR other then launching for Mars related travel.  The rocket would be completely useless for any other purpose if it's payloads were volumetricly constrained by needing to be inside a MCT cargo-hold which is likely no more then 500 m^3,  SLS should have a payload fairing in excess of 2000 m^3.

I disagree. Estimates in other threads have about 22 m^3 per person of pressurised volume, so for 100 passengers that is 2200 m^3. If the crew accommodations are payload to MCT, this means that the payload volume would need to be 2500 m^3 or above.

With suitable mission kits MCT could perform the following missions:

- Tanker flights to LEO
- Propellant depot
- Satellite and space station (up to BA 2100 size at least) delivery
- Tourist launch to LEO (~300 passengers)
- Cargo/crew delivery to space stations anywhere in cis-lunar space
- Moon landings
- NEO visits.

MCT may not be the most efficient system to perform such missions, but it is capable enough. Capability will win out over efficiency in my opinion because dedicated efficient systems of the size of MCT will cost a lot to develop. The one exception to this might be a dedicated tanker because of the large number of tanker flights required for anything beyond LEO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/15/2015 11:34 am
MCT and BFR are supposed to be based on the same kind of platform. MCT will HAVE to have similar mass efficiency of an upper stage (in fact Musk has said MCT needs to be capable of Mars surface to earth in a SINGLE stage, though with far less payload), and essentially that's what it is. So whether you call the tanker a modified MCT or a stretched BFR upper stage may be a distinction without much difference.

Show me the quote for this, because I've never heard any such thing.  Rather I think direct single stage Earth return is rather a possible (and the most aggressive possible) interpretation of some of Musks statements but it is far from set in stone.

And even if Elon had said this was his goal we should have SERIOUS doubts if such a goal would survive contact with real engineering as the vehicle capable of doing all that would put a single stage to Earth orbit vehicle to shame.  You can hand wave away the incredible difficulty and mass costs of EDL on Mars and Earth and the costs of keeping a vehicle alive during interplanetary transit.

All this talk about avoiding costs by not developing a 2nd stage are silly, SpaceX MUST have a use for the BFR other then launching for Mars related travel.  The rocket would be completely useless for any other purpose if it's payloads were volumetricly constrained by needing to be inside a MCT cargo-hold which is likely no more then 500 m^3,  SLS should have a payload fairing in excess of 2000 m^3.
The quote is in the thread the moderators deleted for some reason.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 06/15/2015 11:42 am
With suitable mission kits MCT could perform the following missions:
- Tanker flights to LEO
- Propellant depot
- Satellite and space station (up to BA 2100 size at least) delivery
- Tourist launch to LEO (~300 passengers)
- Cargo/crew delivery to space stations anywhere in cis-lunar space
- Moon landings
- NEO visits.
MCT may not be the most efficient system to perform such missions, but it is capable enough.

Hmmm, it looks like many people (myself included) are reading into MCT that it will be what the Space Shuttle was supposed to be. A low-cost, general-purpose, reusable space truck.

Others, like Impaler, are (perhaps more realistically) assuming it will be a specialised single-purpose vehicle, barely capable of what is being asked of it.

Not specifying which group you fall into is bound to result in pointless arguing past each other.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/15/2015 11:58 am
What difference is there between MCT and a reusable upper stage? Just the habitable portion on top. They will need similar performance (~6.5-7km/s). Both need reentry and landing capability (legs, etc).

The problem with Shuttle is there were only a few of them made, no custom ones. With MCT, thousands will be made, so no problem making some that lack the habitable portion or that act as tankers or that are only used for cargo. The requirements for these things are similar but the MCTs can be modified to fit the purpose instead of having one vehicle type do everything at once.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/15/2015 12:11 pm
Imagine a reusable F9 upper stage and Dragon melded together into a more structurally efficient whole and using methane instead of kerosene (slightly stretched to compensate for the lower bulk density of methane/oxygen). That would have roughly 7km/s of performance, which is basically what you need for Mars surface to Earth. Make that bigger, and you have a rough sketch of MCT.

(And MCT will need it's crew quarters to be far lower density than Dragon... Dragon is 500-1000kg per m^3 of pressurized volume. MCT will need to be more like 120-250kg per m^3, comparable to a passenger jet.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/15/2015 12:14 pm
I do expect the tanker to be different. No payload or crew quarters. Just stretched main tanks. That's a lot more mass efficient. But early on for the first few missions or in a test phase they may use MCT for that purpose too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 06/15/2015 03:25 pm
What difference is there between MCT and a reusable upper stage? Just the habitable portion on top. They will need similar performance (~6.5-7km/s). Both need reentry and landing capability (legs, etc).

The problem with Shuttle is there were only a few of them made, no custom ones. With MCT, thousands will be made, so no problem making some that lack the habitable portion or that act as tankers or that are only used for cargo. The requirements for these things are similar but the MCTs can be modified to fit the purpose instead of having one vehicle type do everything at once.

I don't know about THOUSANDS of MCT's being built, dozens and maybe hundreds, but by that time, I expect newer designs will superceed the current design scheme.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/15/2015 03:25 pm
One way of taking the multiple configurations is to divide the MCT up into 2 parts: the theater specific buss and the payload specific canister. Since the payload "canister" would sit on top of the buss with a common interface plane (mechanical and electrical), 3 canister types (Cargo, HSF, Tanker) and 2 buss types (Earth reentry and Mars Reentry and Launch) would give you 6 configurations. This would also allow for additional canister types (I can't think of any right now that could be possibly used except possibly very custom canister payloads) to be developed as needed. All canisters since they remain attached are reusable.

All busses for a specific theater of operations are identical. So in ground processing a failed buss can have a canister type removed and fitted to another working bus. For Mars this becomes important in that a lot of basically one way cargo MCT's busses could be used with a HSF canister to make a working HSF MCT. Just remove the canisters and place the HSF canister on the working buss.

For all intents and purposes the reusable buss looks like a stage but without provisions for the payload canister to be deployed in space. The canister must remain in order for the buss to reenter the atmosphere.

The buss would have the engines, computers, communications, landing hardware, RCS, and reentry shield. All this does not change regardless of the type of "canister" sitting on top. The canisters must fit a specific form factor of shape, size, weight limits and CG. This means that a general aero qualification of the MCT shape would include all the configurations of canister types used on a buss.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/15/2015 04:05 pm
Why do you differentiate between Earth reentry and Mars reentry? I like most people assume it is one and the same. Some disagree, I know.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/15/2015 04:16 pm
Very different in velocity on approach, and because of the very different ground level density, going from super sonic to landing on Mars presents very different requirements than Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/15/2015 04:47 pm
This concept of 2 parts allows the solving of a specific engineering problem to be done only once. Such as the Mars reusable MCT and the Earth Reusable MCT are separate specific engineering problems (launch, in-space operations, reentry, and landing) whereas the "containers" solve a different engineering problem such as the ECLSS and equipment for a long duration in space support of people, the launch of them into space, and the landing back onto a surface is a problem that is nearly identical for either the Earth scenario or the Mars scenario. By solving this problem such that it is inclusive of the parameters for each scenario creates a single HSF canister design. The same can be done for the tanker design and the cargo design. 5 separate engineering problems instead of 6. This is a development cost savings as well could save a lot later as new canister designs are made without having to resolve the buss engineering problems.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/15/2015 05:09 pm
A second attempt at a Mars Colonial Transporter.  Not a first generation ship, but perhaps second or third generation of 10m core rockets.  Youtube playlist should show 18 little videos covering the whole trip.  A few very speculative items have crept in, for fun.
For some unknown reason, you need to restart the playlist after the first video. Sorry.

Michel Lamontagne

A lot of thought and work has gone into this. The engineering of an MCT like this would be formidably difficult, but it addresses concerns about zero gravity and abort that other conceptual designs do not.

One improvement might be to have the capsule part of the MCT nominally land attached to the cargo/transit part. Then it can perform an abort during landing.

Do you have mass estimates to go with the animations?
Yes, there is a spreadsheet here:

https://docs.google.com/spreadsheets/d/11edSaSqnDQeWBPgz1XMa4E3X0R7hPWcTS5EYxe853U8/edit?usp=sharing

Copy at will, if you like :-)

It's a two stage rocket, that reaches orbit almost empty.  It refuels with 800 tons of oxygen and methane.  This has been delivered to orbit by 7 previous cargo launches, that lift 120 tons of fuel per trip.  So eight launches are required per trip.  The ship lands in two parts because a paper I read suggested an upper limit of about 80 tons per ship for a 10m diameter thermal shield on Mars, and I like having the abort capability.  The design presupposes the 'second stage re entry problem' has been solved.  The ship carries 50 tons of water as shielding, but only shields a 300 m3 area in the capsule, for just under 20 g/cm2 of radiation protection. The water is also added in orbit. 

The capsule includes an empty fuel tank, that can be filled to provide SSTO capability to the capsule.  This may be overkill, since as a second generation ship one might expect a complete assembly building to have been built on Mars.  I would expect the first generation ship to be simpler, without the fancy rotation, but in about the same proportions.  And a first generation capsule would need to be SSTO to provide the 'advertised' return capability. 
A cargo version should also exist, although without paying passengers, the costs per kg to Mars would be pretty impressive.  Definitively an incentive for local production!

If anyone wants the 3D model, just let me know.  It's made with Sketchup.

Michel Lamontagne
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/15/2015 05:21 pm
What difference is there between MCT and a reusable upper stage? Just the habitable portion on top. They will need similar performance (~6.5-7km/s). Both need reentry and landing capability (legs, etc).

The problem with Shuttle is there were only a few of them made, no custom ones. With MCT, thousands will be made, so no problem making some that lack the habitable portion or that act as tankers or that are only used for cargo. The requirements for these things are similar but the MCTs can be modified to fit the purpose instead of having one vehicle type do everything at once.

I don't know about THOUSANDS of MCT's being built, dozens and maybe hundreds, but by that time, I expect newer designs will superceed the current design scheme.

Sharing the development costs between a large number of ships is a key requirement.  A 10 billion dollar development cost over 100 ships is 'only' 100 million dollars per ship, and if each ship can do 50 trips, then it's 2 million $ per trip, and a small portion of the 50 million dollar fare per ship.  So perhaps 100 ships per design generation?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/15/2015 05:56 pm
All this talk about avoiding costs by not developing a 2nd stage are silly, SpaceX MUST have a use for the BFR other then launching for Mars related travel.  The rocket would be completely useless for any other purpose if it's payloads were volumetricly constrained by needing to be inside a MCT cargo-hold which is likely no more then 500 m^3,  SLS should have a payload fairing in excess of 2000 m^3.

I disagree. Estimates in other threads have about 22 m^3 per person of pressurised volume, so for 100 passengers that is 2200 m^3. If the crew accommodations are payload to MCT, this means that the payload volume would need to be 2500 m^3 or above.



Nice post.  One nit.  I see the MCT as having no crew per se.  How & why?  Because many functions like astrogation are automated.  But things break.  What kinds of people and what skill sets will be in the 100 passengers?  It would be astounding were there not will over a half dozen or so passengers with the skill sets to be trained as flight engineers to maintain and troubleshoot systems.  Somebody has to be doing this on Mars too.  I see "astronaut" as an anachronism superceded by what I call flight systems engineers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/15/2015 06:24 pm
What difference is there between MCT and a reusable upper stage? Just the habitable portion on top. They will need similar performance (~6.5-7km/s). Both need reentry and landing capability (legs, etc).

The problem with Shuttle is there were only a few of them made, no custom ones. With MCT, thousands will be made, so no problem making some that lack the habitable portion or that act as tankers or that are only used for cargo. The requirements for these things are similar but the MCTs can be modified to fit the purpose instead of having one vehicle type do everything at once.

I don't know about THOUSANDS of MCT's being built, dozens and maybe hundreds, but by that time, I expect newer designs will superceed the current design scheme.

Sharing the development costs between a large number of ships is a key requirement.  A 10 billion dollar development cost over 100 ships is 'only' 100 million dollars per ship, and if each ship can do 50 trips, then it's 2 million $ per trip, and a small portion of the 50 million dollar fare per ship.  So perhaps 100 ships per design generation?
50 reuses is far too many. My guess is the MCTs may last about 3 decades, one reuse every ~2 years (every synod), so only 12-15 reuses is practical.

Musk has said 80,000 people per year (and ten times as many cargo shipments), which is 1000 Passenger MCTs at once, plus 10,000 cargo MCTs (or actually, there ways around this, but it remains to be seen if they're worth it). So yeah, at any one time, there would need to be thousands of MCTs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/15/2015 09:29 pm
What difference is there between MCT and a reusable upper stage? Just the habitable portion on top. They will need similar performance (~6.5-7km/s). Both need reentry and landing capability (legs, etc).

The problem with Shuttle is there were only a few of them made, no custom ones. With MCT, thousands will be made, so no problem making some that lack the habitable portion or that act as tankers or that are only used for cargo. The requirements for these things are similar but the MCTs can be modified to fit the purpose instead of having one vehicle type do everything at once.

I don't know about THOUSANDS of MCT's being built, dozens and maybe hundreds, but by that time, I expect newer designs will superceed the current design scheme.

Sharing the development costs between a large number of ships is a key requirement.  A 10 billion dollar development cost over 100 ships is 'only' 100 million dollars per ship, and if each ship can do 50 trips, then it's 2 million $ per trip, and a small portion of the 50 million dollar fare per ship.  So perhaps 100 ships per design generation?
50 reuses is far too many. My guess is the MCTs may last about 3 decades, one reuse every ~2 years (every synod), so only 12-15 reuses is practical.

Musk has said 80,000 people per year (and ten times as many cargo shipments), which is 1000 Passenger MCTs at once, plus 10,000 cargo MCTs (or actually, there ways around this, but it remains to be seen if they're worth it). So yeah, at any one time, there would need to be thousands of MCTs.
I was thinking of reuse for the first stage and cargo modules to Earth orbit.  I agree the MCT itself will not have so many runs. Thousands of ships is fine with me, the important concept is the reduction of cost by using large production numbers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/15/2015 09:40 pm
That is larger than most airline fleets.  The first stage might get more use.  Launch and MCT to Mars, land, load, and launch another one in what a week or two.  In the 18 months when Mars is not close to earth, maybe SEP tugs can transfer lots of cargo, and MCT's can be used to refuel large fuel depots for the next 6 month launch window.  If the MCT can get to mars in say 4 months, launch, land, refuel and launch once a week will only get you 8 launches per rocket per window. 

For hundreds, there will have to be several launch pads with facilities.  There would also have to be several large fuel depots.  Probably several large SEP tugs to transfer non perishable cargo.  For SEP tugs, there may be a need to leave MCT's at Mars for picking up SEP cargo, and taking it to Mars surface, thus becoming reusable landers.  The 10-1 cargo-people may require cargo be shipped during the 18 months when people are not coming. 

Just getting the BFR and the MCT is one thing.  The MCT might have to fill several roles.  Second stage for BFR for LEO refueling depots.  Cargo reusable lander left on Mars to retrieve SEP cargo.  Then the people carrier in the 6 month window.

A ship or plane can be made to do multiple roles.  Thus the MCT might have to do multiple roles.  Cargo planes, refueling planes, and passenger airliners.  MCT the same, Cargo carrier, Fuel carrier, reusable lander, and people carrier.  Thus about 3-4 MCTs per BFR.  One MCT might be used as a reusable lander for moon projects also. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/15/2015 10:01 pm
Lots of people have been pushing this idea of MCT is the ONLY thing that BFR will ever have placed on top of it and that is must do EVERYTHING we want done from LEO all the way to Mars, this is completely unrealistic and dose not save any money as the MCT would be 10x harder to design and build when it has so many requirements put on it.
While MCT will most likely be supplanted by a dedicated reusable tanker in the long run, in the short run its capabilities make it good enough for the task. Or a really simple, cheap, disposable tanker stage (a glorified fuel tank with a docking port and a single raptor engine).

The idea that early MCTs be used as both a tanker vehicle and an MCT stems from a very real and present fact that SpaceX does not have infinite money and thus cannot really afford development and manufacturing of multiple different reusable, earth-landable and rapidly reusable vehicle designs.

Just make one that is good enough and build as many as you can. An MCT without the cargo will do just fine for refuelling. Not perfect, but good enough.

@This.

Again, There is nothing completely unrealistic about this.  In fact, it's quite plausible with many cost-development benefits.  Obviously SpaceX will be the ones to decide their design, but there's nothing unrealistic about it.

As discussed before, but it bears repeating...MCT being it's own 2nd stage is the easiest of the multiple capabilities it will need to have anyway.  Even if it gets to LEO as it's own 3rd stage, as you've often postulated, it still needs to be it's own EDS stage, it's own Mars lander, it's own Mars ascent vehicle, it's own Earth return vehicle (perhaps with LMO refueling, perhaps without), and it's own Earth lander.
Being it's own 2nd stage to LEO would be a capability it would pretty much have by default....unless SpaceX has some very different method of propulsion like SEP, LMO refueling, or something where it won't need large tank capacity. 
Having a version without any of it's crew accommodations installed, which will in effect just carry residual propellants to LEO isn't any amazing stretch of technology or capability like you seem to imply it is.  Any more than making tankers and depot modules and lander modules out of an ACES stage didn't appear to be a major stretch for ULA....had there been a demand for such.




Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/15/2015 10:13 pm

All this talk about avoiding costs by not developing a 2nd stage are silly, SpaceX MUST have a use for the BFR other then launching for Mars related travel.  The rocket would be completely useless for any other purpose if it's payloads were volumetricly constrained by needing to be inside a MCT cargo-hold which is likely no more then 500 m^3,  SLS should have a payload fairing in excess of 2000 m^3.

Who says it would be useless for anything else?  See SpaceX's F9US reusable concept video.  You see quite clearly there's a payload (Dragon in the video) on top of the reusable F9US. 

And even if MCT isn't the 2nd stage, but a spacecraft/EDS stage, you'd still have the problem of a 2nd stage that will need to get to Orbit, and then need to get itself back to the landing site...just as MCT would...and you'd still need to put a payload on -that-.  So I'm not quite sure what you think you'll solve by having a dedicated reusable 2nd stage vs. an MCT variant as it's own 2nd stage?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/15/2015 10:31 pm
What difference is there between MCT and a reusable upper stage? Just the habitable portion on top. They will need similar performance (~6.5-7km/s). Both need reentry and landing capability (legs, etc).

The problem with Shuttle is there were only a few of them made, no custom ones. With MCT, thousands will be made, so no problem making some that lack the habitable portion or that act as tankers or that are only used for cargo. The requirements for these things are similar but the MCTs can be modified to fit the purpose instead of having one vehicle type do everything at once.

Well said.

One point of note.  Although no custom Shuttle's were made per se, you could think of the Shuttle itself like an MCT, with it's payload bay being the configurable option.  It could haul sats+kick stages (as MCT would likely have to possibly externally in a PLF), it could haul cargo, it could carry SpaceLab....which was essentially a crew hab which tied into the Shuttle's base hab system, or other things.  The Shuttle -could- have hauled up a liquid rocket stage as Centaur-G Prime (if not for the Challenger incident), and likewise, it could have hauled up a basic liquid propellant tank to fuel up a depot...had the Challenger accident not happened and there had been a need for that.
The basic shuttle needed a crew to land, so it's base platform had to have that crew accomodations.  MCT wouldn't, so it's base platform wouldn't need that.  So MCT can be more "basic" in it's base platform.  And MCT will have integral cryo propellant tanks unlike the Shuttle, so as long as it has the capability to offload that propellant in space, a tanker would be it's most basic level configuration.

So the shuttle was configurable, in a sense, and could perform a variety of missions.  More than it actually ever did.  Just that it's base configuration was pretty heavy, and included crew accommodations. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/15/2015 10:35 pm
I do expect the tanker to be different. No payload or crew quarters. Just stretched main tanks. That's a lot more mass efficient. But early on for the first few missions or in a test phase they may use MCT for that purpose too.

Why stretched main tanks?

The lighter that configuration of MCT would be without any crew accomodations, the more propellant it has left when arriving in LEO.  No need to stretch the tanks.  Plus better to keep the basic tank/skin/structure common over all variants, I would think. 

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/15/2015 11:22 pm
Stretching probably does make sense. At least, once we're talking hundreds of MCTs per synod.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/15/2015 11:48 pm
Stretching probably does make sense. At least, once we're talking hundreds of MCTs per synod.

The volume of the fuel for a given mass is much less than the volume required for the crew, so a tanker stage should always be much shorter than an MTC stage.
Liquid methane is only 2.3 m3 per tonne and oxygen is 0,84 m3 per tonne, so 150 tonnes of propellant in a 3.4 ratio is 110 tons of oxygen (50 m3) and 40 tons of methane (100 m3) or about 150 m3 total. For a 10m core, 5^2xpi= 78m3 per m of length, it's barely 2 meters of length.  Of course other types of cargo can take up more volume.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/15/2015 11:56 pm
Stretching probably does make sense. At least, once we're talking hundreds of MCTs per synod.

Possibly down the road.  At first I think they'd want to stick with one common vehicle platform and not have to reengineer it too much. 

And you'd be limited on how much of a stretch you could do, before that extra propellant mass is exceeding the capacity of the booster and MCT/upper stage to be able to get itself into LEO.  Although I'm sure there'd be margin that would be worked within.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 06/16/2015 12:15 am
Stretching probably does make sense. At least, once we're talking hundreds of MCTs per synod.

The volume of the fuel for a given mass is much less than the volume required for the crew, so a tanker stage should always be much shorter than an MTC stage.
Liquid methane is only 2.3 m3 per tonne and oxygen is 0,84 m3 per tonne, so 150 tonnes of propellant in a 3.4 ratio is 110 tons of oxygen (50 m3) and 40 tons of methane (100 m3) or about 150 m3 total. For a 10m core, 5^2xpi= 78m3 per m of length, it's barely 2 meters of length.  Of course other types of cargo can take up more volume.
Do we have any authoritative optimal fuel:oxidizer mass ratio estimates for FFSC methalox?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/16/2015 02:01 am

But what will use that excessive volumetric capability? The BA2100? Who would use a BA2100 and why? Would you ever need to launch multiple BA2100s? If so, for what reason? If you need something big put in space, wouldn't you rather design it according to the volumetric constraints of the vehicle you'll be using instead of the other way around?

In any case, the bread and butter of most commercial launch service companies is and has always been communication satellites.

A cargo bay which can hold 100 tonnes of cargo for mars can most definitely hold a comms satellite, and the excessive delta V that a MCT is required to pull (even/especially if it doesn't act as its own 2nd stage or do a one burn from Mars to Earth since it still needs at least 4.5 km of delta V to rendezvous with a transfer tug in LMO) make it more than capable of acting as a GTO delivery vehicle.

The volume constraint argument is a red herring. If something big enough to fill the volume constraints of a SLS fairing comes along and requires a launch it might as well get a stage specifically designed for it or even the SLS, if that ever goes into commercial launches. You design things based on the constraints you are given, not the other way around.

Commercial communication satellites are LOW DENSITY, just look at the size of current payload fairing and you can see that their is no way you could put 100 mT of satellites into the kind of volumes were looking at for a MCT cargo-hold.

Falcon 9 payload fairing has a volume of ~275 m^3 and it launches only 5 mT to GTO, Ariane 5 has ~390 m^3 and launches a maximum of 12 mT to GTO.  Shuttle had ~300 m^3 payload bay and could carry 24 mT to LEO. 

At these kinds of packaging densities you would need 1200-5000 m^3 to use that mass effectively for launching satellites.  But their is no way the vehicle can have such a huge cargo hold, it would make the overall vehicle too large and require too much structural mass to make it survive re-entry.

Volume is VERY important, MANY space launch systems face volume limitations, Dragon capsule for example is volume rather then mass limited for most cargoes that need to be launched to ISS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/16/2015 02:33 am
I do expect the tanker to be different. No payload or crew quarters. Just stretched main tanks. That's a lot more mass efficient. But early on for the first few missions or in a test phase they may use MCT for that purpose too.

Why stretched main tanks?

The lighter that configuration of MCT would be without any crew accomodations, the more propellant it has left when arriving in LEO.  No need to stretch the tanks.  Plus better to keep the basic tank/skin/structure common over all variants, I would think.

The cargo should be shorter, except for light high volume payloads.  A bit like the joined image
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/16/2015 03:28 am
Why do you differentiate between Earth reentry and Mars reentry? I like most people assume it is one and the same. Some disagree, I know.

No these aren't comparable at all, in fact their are perhaps 6 different entry scenarios.  http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040086716.pdf


Mars from LMO                           3.5 kms

Mars from Interplanetary Slow      6 kms
Earth from LEO                           7.5 kms
Mars from Interplanetary Fast      8 kms

Earth from Interplanetary Slow    12 kms !
Earth from Interplanetary Fast     14 kms !!


Any Mars Entry also requires significant rocket retro-propulsion to not crash, where as on Earth you can basically just do very small amounts of touchdown retro-propulsion because terminal falling velocity in the lower atmosphere is subsonic.

That brutal 12-14 kms entry to Earth is something everyone who is talking about this direct Earth return is glossing over, that is beyond Apollo speeds, the only thing that can survive that kind of heat, dynamic pressure and g-force is a dense capsule with thick heavy ablatives.

This is why it is not valid to design spacecraft by only looking at Delta-V and tank sizes and imagining that a giant 2nd stage can do the job of direct Earth return from Mars surface just because it can hold the propellents to launch to Earth.  It would literally be crushed like an empty beer can against ones forehead when it hits the Earth's atmosphere.

A 2nd stage that can return from Earth orbit is a vastly simpler thing to do because the speed is half (and the energy is a quarter), and it is fairly easy to slow down the 2nd stage by several kms with residual propellents, and to employ disposable things like parachutes because it only needs to perform ONE landing before servicing rather then two, and lastly it can be made much less reliable in landing because it's unmanned, no one dies horribly if it crashes or burns up on reentry unlike MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/16/2015 03:41 am
Why do you differentiate between Earth reentry and Mars reentry? I like most people assume it is one and the same. Some disagree, I know.

No these aren't comparable at all, in fact their are perhaps 6 different entry scenarios.  http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040086716.pdf


Mars from LMO                           3.5 kms

Mars from Interplanetary Slow      6 kms
Earth from LEO                           7.5 kms
Mars from Interplanetary Fast      8 kms

Earth from Interplanetary Slow    12 kms !
Earth from Interplanetary Fast     14 kms !!

Once supersonic retropropulsion is used, the differences become much smaller. The hardest reentry is back to earth. If it can do that, Mars speed is no problem. Negative lift is needed on Mars. but that is no more than some attitude control. Also much more fuel. If the vehicle has that fuel = delta v Mars landing is no problem. On earth landing needs a lot less fuel due to the dense atmosphere.

So there are the two major differences. More attitude control for Mars EDL, more capacity of the heatshield for earth reentry.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/16/2015 04:48 am
The hardest reentry is back to earth. If it can do that, Mars speed is no problem.

But it CAN'T that's the rub, the vehicle can't be the large low density tank people are imagining, it would be crushed.  The Apollo heat shield alone was 15% of the mass, the structure was 27% and this was to for a compact and easy to protect shape.  So we can't just wave our arms and say MCT will be able to do this.

How much retro-propulsion do you think we can do upon return to Earth?  Any propellent to do this with is added to our DeltaV from Mars surface which is already 6-7 kms for a direct Earth return.  The propellent fraction is already near the limits of credibility.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Krevsin on 06/16/2015 05:50 am

At these kinds of packaging densities you would need 1200-5000 m^3 to use that mass effectively for launching satellites.  But their is no way the vehicle can have such a huge cargo hold, it would make the overall vehicle too large and require too much structural mass to make it survive re-entry.
This is an entirely wrong assumption. An Ariane V, per your words, has ~390 cubic meters of volume and can manage to bring two satellites into GTO and costs about $200 million per launch, at a price of $100 million per satellite. A falcon 9 has ~275 cubic meters and can get a single satellite into GTO in fully expendable mode at a price of $90 million per launch/satellite.

Therefore, the only thing a MCT needs to do in order to be competitive as a satellite delivery platform is lower the cost of getting satellites into GTO, not increase the amount of satellites into GTO and since the goal of the MCT is to be rapidly reusable, a "gas & go" type of system, the only costs involved with the launch would be processing, operation and the cost of the methalox rather than building an entire vehicle, the MCT is cheaper and if the internal volume of its cargo bay is only equal to that of an Ariane V fairing, it can still get two satellites into GTO so the only way a MCT is not competitive is if the cost of its launch approaches the $200 million mark.

And given the MCT's much touted price tag of $50 million per 100 people ($500 000 per passenger) I just don't see that as a likely event.
Commercial communication satellites are LOW DENSITY, just look at the size of current payload fairing and you can see that their is no way you could put 100 mT of satellites into the kind of volumes were looking at for a MCT cargo-hold.

Falcon 9 payload fairing has a volume of ~275 m^3 and it launches only 5 mT to GTO, Ariane 5 has ~390 m^3 and launches a maximum of 12 mT to GTO.  Shuttle had ~300 m^3 payload bay and could carry 24 mT to LEO. 

At these kinds of packaging densities you would need 1200-5000 m^3 to use that mass effectively for launching satellites.  But their is no way the vehicle can have such a huge cargo hold, it would make the overall vehicle too large and require too much structural mass to make it survive re-entry.

Volume is VERY important, MANY space launch systems face volume limitations, Dragon capsule for example is volume rather then mass limited for most cargoes that need to be launched to ISS.
You would never pack 100 metric tonnes' worth of satellites in a MCT.

Mostly because an MCT without refuelling can do much less than that in tonnes to GTO. (I remember that a number of 10-15 tonnes was mentioned somewhere in the previous topic, which amounts to 2 conventional satellites or 3-4 SEP ones, so about an Ariane 5 worth of payload to GTO). The reason why you'd want to do this without refuelling is to lower operating costs and complexity of the mission.

So you pack it with as many satellites as you can given the volume and mass constraints and that still makes the volume of the MCT a non-issue because it's still cheaper than the alternatives and has enough of a capability for at least 2 satellites.

The only time when the volume of a MCT becomes an issue is if you consider a commercial depot stationed in LEO, to which the MCT could deliver its full payload in mass and from which tugs would take over. But even then it'd still be cheaper
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 06/16/2015 06:51 am

But it CAN'T that's the rub, the vehicle can't be the large low density tank people are imagining, it would be crushed.  The Apollo heat shield alone was 15% of the mass, the structure was 27% and this was to for a compact and easy to protect shape.  So we can't just wave our arms and say MCT will be able to do this.

How much retro-propulsion do you think we can do upon return to Earth?  Any propellent to do this with is added to our DeltaV from Mars surface which is already 6-7 kms for a direct Earth return.  The propellent fraction is already near the limits of credibility.

What about retro burning before the MTC hits the troposphere - how much of a burn would that require to be effective? Is there any way lunar gravity could be helpful for negating some of that velocity?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/16/2015 07:13 am
How much retro-propulsion do you think we can do upon return to Earth?  Any propellent to do this with is added to our DeltaV from Mars surface which is already 6-7 kms for a direct Earth return.  The propellent fraction is already near the limits of credibility.

None, of course. It will all be done by the heat shield. None, that is, except the few seconds landing burn, maybe 200m/s delta-v. And PicaX is not only vastly better than Avcoat, it is also vastly lighter.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/16/2015 11:15 am
MCT is a radical design. Acknowledge that and move on.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 06/16/2015 12:06 pm
Using a BFR and MCT to launch satellites is comparable to using the Queen Mary as an ore barge.
We should also acknowledge that and move on.

It will also refuel at least twice, so Apollo-like 'missions' to Mars are off the table... for SpaceX anyway.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/16/2015 12:37 pm
Using a BFR and MCT to launch satellites is comparable to using the Queen Mary as an ore barge.
We should also acknowledge that and move on.

It will also refuel at least twice, so Apollo-like 'missions' to Mars are off the table... for SpaceX anyway.
I'm sure you would be better off using the Queen Mary to haul ore than throwing away part of an ore ship each time. You can always build a freighter version, just like the cargo 747 or whatever.

But yeah, MCT will be refueled at least twice. (well, once for sure... Has to be refueled on Mars... But a lightweighted version could possibly take a slow trip to Mars on a single shot.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/16/2015 12:40 pm
This is why it is not valid to design spacecraft by only looking at Delta-V and tank sizes and imagining that a giant 2nd stage can do the job of direct Earth return from Mars surface just because it can hold the propellents to launch to Earth.  It would literally be crushed like an empty beer can against ones forehead when it hits the Earth's atmosphere.

Try crushing a beer can containing several bars of pressure against your forehead.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/16/2015 12:49 pm
Try crushing a beer can containing several bars of pressure against your forehead.

Or better - don't.  :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/16/2015 01:50 pm
If the MCT is completely refueled on Mars for launch back to earth, all of the fuel will not be needed to get the TEI burn.  There will be quite a bit of fuel left.  So the MCT could fire and slow down before earth reentry, or it could slow down using aerocapture for a few orbits to slow down.  Also, there will probably be only a crew return, not 100 people. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/16/2015 02:19 pm
No. Retropulsion before reentry on Earth isn't going to happen with chemical propulsion. It's always better to improve the heatshield.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 06/16/2015 02:44 pm
No. Retropulsion before reentry on Earth isn't going to happen with chemical propulsion. It's always better to improve the heatshield.

Why?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/16/2015 02:55 pm
Mass penalty is way too high. Increasing the required delta-v for the Mars stage from 7-7.5km/s to ~10km/s would double the required mass, and that's assuming no increase in tankage mass.

Just no.

PICA-X is crazy awesome stuff. Just use a little more of it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 06/16/2015 02:59 pm
Take advantage of Earth's thick atmosphere. A PICA-X heatshield can handle the high speed reentry and will be lighter, less complicated, and cheaper than any retropulsion system.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/16/2015 03:07 pm
Mass penalty is way too high. Increasing the required delta-v for the Mars stage from 7-7.5km/s to ~10km/s would double the required mass, and that's assuming no increase in tankage mass.

Just no.

PICA-X is crazy awesome stuff. Just use a little more of it.

Might it be possible to refuel the MCT in Mars orbit?  Not the first ones, but once the transit system is set up?  There could be a few ships permanently at Mars, operating as SSTO's hauling up fuel, and a used MCT would make a good orbital tanker, as it already has the cooling systems required to prevent evaporation.  If the MCT (most of the times) goes back empty of crew, with no radiation shielding, that should allow for pretty high deltaV?

Depends a lot on how complicated orbital refueling turns out to be, I expect.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/16/2015 03:09 pm
The first stage is a different story. The delta-v penalty is far less for first stage retropulsion and RTLS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Doesitfloat on 06/16/2015 03:10 pm
Yeah but,..
Any chance they would use both.  We have seen the results of firing an engine in a braking burn. (F-9 booster recovery attempts)  Also they showed computer modeling of hypersonic reentry with engine firing.  ISTM the results show the engine pushes the superheated plasma from reentry, away from the spacecraft.

So say they use an appropriately sized engine to push the plasma away from the spacecraft, but the majority of the braking is done by the atmosphere.  Would lead to less wear on the pica-X heat shield and is reusable by refueling the engine.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/16/2015 03:32 pm
If the MCT is completely refueled on Mars for launch back to earth, all of the fuel will not be needed to get the TEI burn.  There will be quite a bit of fuel left.  So the MCT could fire and slow down before earth reentry, or it could slow down using aerocapture for a few orbits to slow down.  Also, there will probably be only a crew return, not 100 people.

Crew?
Why?
MCT should be able to return to Earth empty.  (And as needed provide occasional return transport for humans needing to return)

On the way out assuming several 10s of passengers it would be astounding if there were not several engineers capable of specialized training as "flight engineers" to repair anything repairable by humans.  No astronaut corps test pilots needed, just FEs similar to on the shuttle.

Crew mass & life support is wasted mass and money. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/16/2015 03:39 pm
Yeah but,..
Any chance they would use both.  We have seen the results of firing an engine in a braking burn. (F-9 booster recovery attempts)  Also they showed computer modeling of hypersonic reentry with engine firing.  ISTM the results show the engine pushes the superheated plasma from reentry, away from the spacecraft.

So say they use an appropriately sized engine to push the plasma away from the spacecraft, but the majority of the braking is done by the atmosphere.  Would lead to less wear on the pica-X heat shield and is reusable by refueling the engine.
The wear on the PICA-X is infinitesimal compared to the propellant needed to prevent it. If you already have a heatshield, you should be maximizing it's use when possible. For Mars entry, you'll still need retropropulsion while supersonic, but for Earth you should be subsonic before you start the landing burn.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/16/2015 04:16 pm
I think one of the previous concerns was the high speed reentry from Mars vs orbital reentry.  They were thinking of the MCT crushing itself with the high g slowdown.  That was the reason for some retro burn before entering the atmosphere, not really about the heat shield.  From the moon the reentry was 25,000 mph while orbital it is 17,000 mph.  The MCT could be built with titanium supports to be held together, or it might require slowing down to 17,000 mph before atmospheric entry so it wouldn't be a slam into the atmosphere.  For a large spacecraft reentry from Mars, this is a concern. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 06/16/2015 04:28 pm
Try crushing a beer can containing several bars of pressure against your forehead.

Or better - don't.  :)

But if you do, make sure it's empty first!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 06/16/2015 04:40 pm
The hardest reentry is back to earth. If it can do that, Mars speed is no problem.

But it CAN'T that's the rub, the vehicle can't be the large low density tank people are imagining, it would be crushed.  The Apollo heat shield alone was 15% of the mass, the structure was 27% and this was to for a compact and easy to protect shape.  So we can't just wave our arms and say MCT will be able to do this.

How much retro-propulsion do you think we can do upon return to Earth?  Any propellent to do this with is added to our DeltaV from Mars surface which is already 6-7 kms for a direct Earth return.  The propellent fraction is already near the limits of credibility.

     If you're applying the Cube Square law directly and we hadn't had over fifty years of materials technology advancement behind us, you'd possibly be correct, but as the newer designs can take advantage of engineering advances, plus, structures can be made VASTLY stronger for less than half the mass that was required in the past, plus the reusable TPS system is lower mass than the TPS system that Apollo required, I think that it's likely that the craft, while heavier than Gucky seems to think it'll be, will still be far lighter than you suspect it'll be.

     As is, I suspect that SpaceX will most likely use a multiple pass aerobraking maneuver to achieve orbit and reentry.  This would reduce the requirements for a retropropulsive burn for Earth entry, and as the craft will be FAR lower mass than when it originally launched, (Having shed the 100 colonists and all of their associated cargo) actual fuel requirements for both the return trip and actual landing will like wise be far lower.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/16/2015 04:40 pm
I think that is what he was referring to, and empty MCT.  Empty of fuel and cargo, thus being much lighter and easier to crush when slamming into the earths atmosphere, even with a good heat shield.  Thus the idea of a retro burn to slow down before entering earths atmosphere.  Also, coming from Mars one MCT at a time, an orbit or two would help in enabling a more precise landing at the launch site, instead of the middle of the ocean or the jungle somewhere. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 06/16/2015 04:45 pm
I think that is what he was referring to, and empty MCT.  Empty of fuel and cargo, thus being much lighter and easier to crush when slamming into the earths atmosphere, even with a good heat shield.  Thus the idea of a retro burn to slow down before entering earths atmosphere.  Also, coming from Mars one MCT at a time, an orbit or two would help in enabling a more precise landing at the launch site, instead of the middle of the ocean or the jungle somewhere.

Being empty will not make the structure weaker. MCT isn't an Atlas fuel tank.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 06/16/2015 04:47 pm
If the MCT is completely refueled on Mars for launch back to earth, all of the fuel will not be needed to get the TEI burn.  There will be quite a bit of fuel left.  So the MCT could fire and slow down before earth reentry, or it could slow down using aerocapture for a few orbits to slow down.  Also, there will probably be only a crew return, not 100 people.

Crew?
Why?
MCT should be able to return to Earth empty.  (And as needed provide occasional return transport for humans needing to return)

On the way out assuming several 10s of passengers it would be astounding if there were not several engineers capable of specialized training as "flight engineers" to repair anything repairable by humans.  No astronaut corps test pilots needed, just FEs similar to on the shuttle.

Crew mass & life support is wasted mass and money.

     You may be correct aboutthe need for a crew, but people are still a bit primitive.  They'd be more than a bit nervous to trust their lives to nothing more than machines.  I'm pretty sure that they'd want at least a minimal crew orf pilot, navigator/copilot and at least one engineer.  (A dedicated doctor/medic would also likely be a good idea).  If nothing else, to keep the passengers calm during the flight.

     While machines are pretty good at doing their jobs, nobody will want to risk a several billion dollar investment on the possibility that a IC chip will fry because of a stray cosmic ray and send the craft wandering off into space or worse, come c rashing down on Earth at 6 to 7 KMS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/16/2015 04:59 pm
I think that is what he was referring to, and empty MCT.  Empty of fuel and cargo, thus being much lighter and easier to crush when slamming into the earths atmosphere, even with a good heat shield.  Thus the idea of a retro burn to slow down before entering earths atmosphere.  Also, coming from Mars one MCT at a time, an orbit or two would help in enabling a more precise landing at the launch site, instead of the middle of the ocean or the jungle somewhere.

Being empty will not make the structure weaker. MCT isn't an Atlas fuel tank.
Atlas stages aren't weak when empty, they're weak when not pressurized. If MCT isn't pressurized, there would be other, bigger problems to worry about.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/16/2015 05:03 pm
While machines are pretty good at doing their jobs, nobody will want to risk a several billion dollar investment on the possibility that a IC chip will fry because of a stray cosmic ray and send the craft wandering off into space or worse, come c rashing down on Earth at 6 to 7 KMS.

90% may be cargo flights and those will not carry any crew. So that is no reason for crew to return on a crew vehicle. True, maybe a technician and a medic might be on board in the unlikely case no one of the settlers would be capable of filling that function. This is assuming they are flights with settlers. An exploration crew will be even more likely to have those skills.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/16/2015 05:10 pm
If MCT isn't pressurized, there would be other, bigger problems to worry about.

This discussion gets me to another thought. I had anticipated cargo flights might not be pressurized. But they will likely need to be pressurized, not only for the benefit of the cargo but to give them stability.

Getting slightly OT, I wonder if equipment will have to be pressurized all the way, which would make unloading quite difficult. Or if it could be exposed to the near vacuum of Mars for a short time during unloading. Some equipment would be designed to work on the surface, no problem there. But a lot of stuff would go into habitats.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/16/2015 05:19 pm
The hardest reentry is back to earth. If it can do that, Mars speed is no problem.

But it CAN'T that's the rub, the vehicle can't be the large low density tank people are imagining, it would be crushed.  The Apollo heat shield alone was 15% of the mass, the structure was 27% and this was to for a compact and easy to protect shape.  So we can't just wave our arms and say MCT will be able to do this.

How much retro-propulsion do you think we can do upon return to Earth?  Any propellent to do this with is added to our DeltaV from Mars surface which is already 6-7 kms for a direct Earth return.  The propellent fraction is already near the limits of credibility.

Quote
It would literally be crushed like an empty beer can against ones forehead when it hits the Earth's atmosphere.

Is there any reason the tanks couldn't be pressurized for EDL?  As was done with Atlas SM-65 to keep it from collapsing under it's own weight, or Centaur to keep the payload from crushing it like a beer can, prior to fueling?
Probably use GOX and GCH4 rather than GN2 as was done with Atlas and Centaur though.  Just allow some boiloff of each to adequate pressure.

Beer cans don't crush against one's forehead if they are pressurized.  (Even if they are gas only with no liquid)





Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/16/2015 05:31 pm

At these kinds of packaging densities you would need 1200-5000 m^3 to use that mass effectively for launching satellites.  But their is no way the vehicle can have such a huge cargo hold, it would make the overall vehicle too large and require too much structural mass to make it survive re-entry.
This is an entirely wrong assumption. An Ariane V, per your words, has ~390 cubic meters of volume and can manage to bring two satellites into GTO and costs about $200 million per launch, at a price of $100 million per satellite. A falcon 9 has ~275 cubic meters and can get a single satellite into GTO in fully expendable mode at a price of $90 million per launch/satellite.

Therefore, the only thing a MCT needs to do in order to be competitive as a satellite delivery platform is lower the cost of getting satellites into GTO, not increase the amount of satellites into GTO and since the goal of the MCT is to be rapidly reusable, a "gas & go" type of system, the only costs involved with the launch would be processing, operation and the cost of the methalox rather than building an entire vehicle, the MCT is cheaper and if the internal volume of its cargo bay is only equal to that of an Ariane V fairing, it can still get two satellites into GTO so the only way a MCT is not competitive is if the cost of its launch approaches the $200 million mark.

And given the MCT's much touted price tag of $50 million per 100 people ($500 000 per passenger) I just don't see that as a likely event.
Commercial communication satellites are LOW DENSITY, just look at the size of current payload fairing and you can see that their is no way you could put 100 mT of satellites into the kind of volumes were looking at for a MCT cargo-hold.

Falcon 9 payload fairing has a volume of ~275 m^3 and it launches only 5 mT to GTO, Ariane 5 has ~390 m^3 and launches a maximum of 12 mT to GTO.  Shuttle had ~300 m^3 payload bay and could carry 24 mT to LEO. 

At these kinds of packaging densities you would need 1200-5000 m^3 to use that mass effectively for launching satellites.  But their is no way the vehicle can have such a huge cargo hold, it would make the overall vehicle too large and require too much structural mass to make it survive re-entry.

Volume is VERY important, MANY space launch systems face volume limitations, Dragon capsule for example is volume rather then mass limited for most cargoes that need to be launched to ISS.
You would never pack 100 metric tonnes' worth of satellites in a MCT.

Mostly because an MCT without refuelling can do much less than that in tonnes to GTO. (I remember that a number of 10-15 tonnes was mentioned somewhere in the previous topic, which amounts to 2 conventional satellites or 3-4 SEP ones, so about an Ariane 5 worth of payload to GTO). The reason why you'd want to do this without refuelling is to lower operating costs and complexity of the mission.

So you pack it with as many satellites as you can given the volume and mass constraints and that still makes the volume of the MCT a non-issue because it's still cheaper than the alternatives and has enough of a capability for at least 2 satellites.

The only time when the volume of a MCT becomes an issue is if you consider a commercial depot stationed in LEO, to which the MCT could deliver its full payload in mass and from which tugs would take over. But even then it'd still be cheaper

If SpaceX were to plan to put an expendable (or parachute recoverable) PLF on the front of MCT, like they would have with F9US-R, then volume will be immense, depending on PLF length.

Additionally, if MCT is just dropping the payload and a kick stage off in LEO, and then returning to the launch site, the kick stage would be very low volume compared to it's mass.  Whether that's a liquid kick stage like the F9US, or a solid one like the Intertial Upper stage the Shuttle dropped off in LEO with sats like Magellan and Galileo.

If talking about some sort of multi-purpose internal payload area inside of MCT which could carry a sat, or cargo to Mars, or a hab with crew to Mars, etc, then it would most likely be much more volume constrained.  As well as tricky to deploy remotely.  Which is why a traditional PLF on the nose as they envisioned doing with F9US-R seems like it would me more reliable, simple, and versatile (larger volume). 
MCT could still have an internal area which could be configured for cargo for the Mars surface, or crew.  But it doesn't necessary have to try to make that work for deploying unmanned sats.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/16/2015 05:41 pm
Using a BFR and MCT to launch satellites is comparable to using the Queen Mary as an ore barge.
We should also acknowledge that and move on.

It will also refuel at least twice, so Apollo-like 'missions' to Mars are off the table... for SpaceX anyway.

It all depends on cost.  It will be reusable.  Which means, the more it flies, the cheaper per launch overall it will be. 

I couldn't see SpaceX really delaying their plans just so sats could fly on MCT.  But SpaceX is a private company, and a paying customer is a paying customer, whether it's putting NASA astronauts on the Moon or putting a load of bricks into LEO.  As long as SpaceX is making a profit on each launch and it's not interferring with their own Mars plans...why wouldn't they use it to launch sats that would otherwise need possibly a more expensive expendable FH?

At the end of they day, F9R and FHR will be doing the vast bulk of the sat launches.  But I'd expect if there's a rare paylaod that would need a fully expendable FH, then they could launch it with MCT...assuming MCT is designed with the capability to do so...which it may or may not be.

But anything that can fly on F9R and FHR will do so, I'm sure.  SpaceX isn't investing in all of those F9/FH pads for nothing.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/16/2015 06:08 pm


That brutal 12-14 kms entry to Earth is something everyone who is talking about this direct Earth return is glossing over, that is beyond Apollo speeds, the only thing that can survive that kind of heat, dynamic pressure and g-force is a dense capsule with thick heavy ablatives.

This is why it is not valid to design spacecraft by only looking at Delta-V and tank sizes and imagining that a giant 2nd stage can do the job of direct Earth return from Mars surface just because it can hold the propellents to launch to Earth.  It would literally be crushed like an empty beer can against ones forehead when it hits the Earth's atmosphere.

A 2nd stage that can return from Earth orbit is a vastly simpler thing to do because the speed is half (and the energy is a quarter), and it is fairly easy to slow down the 2nd stage by several kms with residual propellents, and to employ disposable things like parachutes because it only needs to perform ONE landing before servicing rather then two, and lastly it can be made much less reliable in landing because it's unmanned, no one dies horribly if it crashes or burns up on reentry unlike MCT.

The thing is....this is all a moot point to your argument.  Whether MCT is it's own 2nd stage to LEO or it sits atop a dedicated unique 2nd stage won't change the fact that MCT will need to have -large- tanks.  It will be mostly propellant tank by volume just to do the TMI burn and Mars EDL retropropulsion....and to get itself off the surface of Mars, even if it were only going to LMO before getting refueled there rather than all the way back in one shot.
It will be mostly a large propellant tank, with some legs, engines, and some cargo or hab internal volume.

Having MCT be it's own 2nd stage rather than having a separate dedicated 2nd stage won't change that.  MCT can't then become just a simple larger Dragon capsule. 
With a dedicated reusable 2nd stage, then it's just a giant 3rd stage, rather than a giant 2nd stage.  Maybe a little smaller.  Not much else changes.  So it's a bit of a moot argument.

Yes, designing a vehicle that is returning just form LEO is vastly more simple than designing one that's coming back from interplanetary speeds.  You are correct.  But, there's not an either/or option.  SpaceX must figure out how to get a large rocket stage back from Mars and land it on Earth.  They already need to solve that long pole issue.  A vehicle they design to handle that, can already return to Earth from LEO easily enough, without the [easy] development of a separate LEO only vehicle even necessary. 


Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/16/2015 06:29 pm
What difference is there between MCT and a reusable upper stage? Just the habitable portion on top. They will need similar performance (~6.5-7km/s). Both need reentry and landing capability (legs, etc).

The problem with Shuttle is there were only a few of them made, no custom ones. With MCT, thousands will be made, so no problem making some that lack the habitable portion or that act as tankers or that are only used for cargo. The requirements for these things are similar but the MCTs can be modified to fit the purpose instead of having one vehicle type do everything at once.

I don't know about THOUSANDS of MCT's being built, dozens and maybe hundreds, but by that time, I expect newer designs will superceed the current design scheme.

Sharing the development costs between a large number of ships is a key requirement.  A 10 billion dollar development cost over 100 ships is 'only' 100 million dollars per ship, and if each ship can do 50 trips, then it's 2 million $ per trip, and a small portion of the 50 million dollar fare per ship.  So perhaps 100 ships per design generation?
50 reuses is far too many. My guess is the MCTs may last about 3 decades, one reuse every ~2 years (every synod), so only 12-15 reuses is practical.

Musk has said 80,000 people per year (and ten times as many cargo shipments), which is 1000 Passenger MCTs at once, plus 10,000 cargo MCTs (or actually, there ways around this, but it remains to be seen if they're worth it). So yeah, at any one time, there would need to be thousands of MCTs.

Once you get to this level you are talking about huge cycler vehicles ->40,000 persons in a 15m diameter tube at 1000m diameter wheel with .5g at a rotation rate of 1RPM. This configuration has over 2 million m^3 of volume. 4 of these would be launched every 2 years during the 2 month Mars departure window. In order to stop the spin or start it takes 100m/sec delta V. Spin must be stopped when the vehicle is realigned for a major burn. There would be 560 100mt propellant tanks (arranged in groups of 8 every 15m along a support structure 1050m long that stick 500 m out to each side of the wheel and 50 Raptor engines at each end for doing the orbit change burns

For cargo, there would be a vehicle tug 1800m long that can carry 4000 100mt cargo containers on a similar propulsion arrangement as the habitat cycler. 5 of these would be launched during the 2 month Mars departure window oin order to deliver the 10,000 100mt cargo deliveries.

The MCT's and BFR's except for just a handful of emergency vehicles HSF MCT's to transfer personnel between habitats and 8 on each cargo cycler for the operations and maintenance crew. The rest of 100's of MCT's at Earth and Mars are used only locally for ferry to and from orbit the personnel and cargo. In order to get all this into orbit would take about 3000 flights of BFR and MCT's out to L2 every year or about 8 every day. With a 50 flight usage for the propulsion busses and BFR stages and 100 flight usage for the personnel container and a 500 usage for the cargo and tanker containers: 60 MCT busses and BFR's manufacture each year; 30 personnel carriers manufacture each year , 6 cargo and 6 tankers carriers manufacture each year. the cycler vehicles have a 30-50 year life with good maintenance. representing 5-8 round trips. The vehicle has to stay at each destination 2 years for unloading and loading.

Edit fixed a value from 4 years to 2 years.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/16/2015 07:17 pm
Just to shake things up a bit and challenge some of the preconceptions here:

Assuming that for each MCT departure to Mars there are several BFR launches for the MCT itself, Fuel, and maybe more cargo, and some FH launches for personnel for those MCT's that carry passengers (at least initially as it maybe a while before the BFR is human rated).

Do we have a propellant depot in LEO?  If yes I suspect that it will have an attached/nearby habitat.  If not the logistics of launching to Mars will be constrained around the refueling procedures I imagine and will only take place serially with a 'launch season' seeing launches one after another, each on a somewhat different course. Yes a rendezvous between MCT's on the way might be possible, but mainly with ones relatively close in the launching order without using up the ΔV needed for Mars landing. This may constrain manned MCTs to launching in the middle of the 'launch season' for safety protocols.  There may be other constraints. Certainly it means that each MCT must be rendezvoused with several times, with a depot, the depot is the rendezvous point, could even be for people transiting. The Mars bound MCTs could launch, fill completely with fuel, board passengers if manned, take on any last minute cargo if there was any then head out.  I favour the depot, but for another reason too.

On returning from Mars the MCT, at a LEO periapsis is moving about 2kms faster than escape velocity, to shed just a little more than that in an aerocapture maneuver requires far more TPS than all of Mars entry from the interplanetary speeds there, but still significantly less than going in for landing. Subsequent aerobraking maneuvers could shed velocity in smaller increments and each would start at a much less energetic state (relative the atmosphere it would be braking in). So going back to the idea that MCTs might not return to earth to be recycled, what if, as well as being a propellant depot, we also had MCTs parked where they could have their TPS refreshed, and engines inspected, and if any were not good for at least 2 more flights, have it replaced (there would be a steady stream of vehicles coming up with new or recently Earth refurbished engines they could swap with) designing the engine and pump system to be space or Mars swapable only makes sense.  I also take it as a given that at least initially many MCTs would be staying on (or at) Mars at least for a few years. They might be a source of spare engines too if some didn't pass inspection on Mars.

This would suggest that although we intend to ramp up cargo and personnel flights to Mars with each successive launch season, we could do it with a steady state of MCT production, say one a month or less. That makes planning production simple.

Now as soon as we have a few spare MCT's hanging around in LEO waiting for launch season, someone else might want to lease a few to start up lunar ISRU for fuel and maybe something else.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/16/2015 07:41 pm
Do we have a propellant depot in LEO?

It is part of the plan laid out by Elon Musk. However for the first few conjunctions when only 2-4 flights go to Mars, it may be easier to just refuel directly in LEO. When the number of flights increases, depots will soon become necessary.

Edit: I could imagine that a manned MCT would be refuelled draining a full cargo MCT that would then be fuelled up for a second time. That may count as a kind of depot and avoid a delay for the crew.

I also take it as a given that at least initially many MCTs would be staying on (or at) Mars at least for a few years. They might be a source of spare engines too if some didn't pass inspection on Mars.

Nothing to have a disagreement on but I believe only the first 2 or 3 would stay, probably forever. I believe it is safer to send them back after unloading and only a few weeks stay on Mars rather than having them there for a full synod and then relying on their continued function and safety without means for a thorough inspection.

This would suggest that although we intend to ramp up cargo and personnel flights to Mars with each successive launch season, we could do it with a steady state of MCT production, say one a month or less. That makes planning production simple.

Now as soon as we have a few spare MCT's hanging around in LEO waiting for launch season, someone else might want to lease a few to start up lunar ISRU for fuel and maybe something else.

Sounds good. I would guess though that it will be some time until production rate is ramped up to one a month. Depending on funds.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/16/2015 08:31 pm
Do we have a propellant depot in LEO?

It is part of the plan laid out by Elon Musk. However for the first few conjunctions when only 2-4 flights go to Mars, it may be easier to just refuel directly in LEO. When the number of flights increases, depots will soon become necessary.

Edit: I could imagine that a manned MCT would be refuelled draining a full cargo MCT that would then be fuelled up for a second time. That may count as a kind of depot and avoid a delay for the crew.


I can imagine that the first 'launch season' where an MCT is launched sees only 2-4 go. But by even the next one I expect that they have at least a dozen if not twice that, more built. Depending when the first MCTs go, and how much preparation might have been done in the launch season before the previous conjunction, there might or might not be people going in that first wave. However, baring serious complications, I am certain that the second wave will have people, and with those people both those who intend to stay and build up the outpost, as well as those there for one or two synods worth of scientific study.

I also don't believe that an MCT acting as fuel freighter, or for that matter any upper stage for a BFR, can carry enough propellant to fully fuel an MCT bound for Mars, which if it massed 160mt dry weight would have to mass a minimum 600mt fully fueled with the most optimistic landing maneuver planned. 440mt seems to be at the absolute minimum 4 BFR and MCT used as tanker launches or 2 dedicated expendible tanker BFR US or 3 reusable ones.

While a depot isn't absolutely needed, I think at the scale even of sending 10 MCTs over a 3 month period (the 2nd launch season) it would save on total launch mass.  A LEO depot, or MCT waiting for days partly fueled needs to be able to actively cool propellant far more than the MCT does once it leaves LEO. Rather than equipping each MCT with the ability to do that level of active cooling lets go with the depot and only design into the MCT the cooling required once heat radiated from Earth is no longer a factor.

I also take it as a given that at least initially many MCTs would be staying on (or at) Mars at least for a few years. They might be a source of spare engines too if some didn't pass inspection on Mars.

Nothing to have a disagreement on but I believe only the first 2 or 3 would stay, probably forever. I believe it is safer to send them back after unloading and only a few weeks stay on Mars rather than having them there for a full synod and then relying on their continued function and safety without means for a thorough inspection.

I am thinking that some would be used point to point and surface to orbit as well. Potentially these could be used dozens of times from a TPS point of view, but might no longer, after a few uses have the TPS level required for return to Earth.



This would suggest that although we intend to ramp up cargo and personnel flights to Mars with each successive launch season, we could do it with a steady state of MCT production, say one a month or less. That makes planning production simple.

Now as soon as we have a few spare MCT's hanging around in LEO waiting for launch season, someone else might want to lease a few to start up lunar ISRU for fuel and maybe something else.

Sounds good. I would guess though that it will be some time until production rate is ramped up to one a month. Depending on funds.

Well how about this timeline for you (totally ex cathedra from my belly button and as chock full of assumptions and extrapolations as popular breakfast cereals have calories and artificial flavours):

2019: Raptor ready for flight test, first 4 flight ready are put on a mock up MCT for initial hover and landing tests
2020: MCT with TPS tested in suborbital flight to an ASDS, First suborbital tests of BFR.
2021: Raptor production now at 10 per month; first orbital tests.
2022: October launch of first MCT To Mars 4 more in the next three months.

by the 2025 launch season a full expedition of 12 MCT's ready to go.

Optimistic yes. Impossible no. Including raptor development I think it could be accomplished with $3 - $4B by the end of the 2025 launch season not including payloads.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 06/16/2015 08:36 pm
This discussion gets me to another thought. I had anticipated cargo flights might not be pressurized. But they will likely need to be pressurized, not only for the benefit of the cargo but to give them stability.

Getting slightly OT, I wonder if equipment will have to be pressurized all the way, which would make unloading quite difficult. Or if it could be exposed to the near vacuum of Mars for a short time during unloading. Some equipment would be designed to work on the surface, no problem there. But a lot of stuff would go into habitats.

Cargo handling will be complicated and require tradeoffs.

If the cargo hold on the MCT needs to stay pressurized, then some sort of pressurized truck will be needed to move the cargo from the MCT to the habitats. The truck would dock with the MCT and the habitats. This requires a special vehicle for cargo handling.

If cargo is packed in pressurized containers, say pallet sized, then the containers could be exposed to Martian atmosphere or even vacuum during flight. These containers could be transported to the habitats by various means. This requires special pressurized containers and would not be mass efficient. The containers would pickup dust from the outside and may need cleaning before being unloaded.

Equipment could be made to survive low pressure or vacuum. Even packaging for items such as food or clothing. That would increase mass due to packaging and get back to the dust and cleaning issue. On the plus side, if a module depressurized, items packed like this would still be usable once the module was repaired and re-pressurized.

The entire pressurized MCT cargo hold could be a removable module. The module could be added to the current base and converted to whatever living or workspace the base needs. Remove the cargo to other sections of the base and refit the module. But how do you move something that large?

I'm sure there are many other possible scenarios. Each potentially has an impact on MCT design.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/16/2015 08:44 pm
If the MCT is completely refueled on Mars for launch back to earth, all of the fuel will not be needed to get the TEI burn.  There will be quite a bit of fuel left.  So the MCT could fire and slow down before earth reentry, or it could slow down using aerocapture for a few orbits to slow down.  Also, there will probably be only a crew return, not 100 people.

Crew?
Why?
MCT should be able to return to Earth empty.  (And as needed provide occasional return transport for humans needing to return)

On the way out assuming several 10s of passengers it would be astounding if there were not several engineers capable of specialized training as "flight engineers" to repair anything repairable by humans.  No astronaut corps test pilots needed, just FEs similar to on the shuttle.

Crew mass & life support is wasted mass and money.

     You may be correct aboutthe need for a crew, but people are still a bit primitive.  They'd be more than a bit nervous to trust their lives to nothing more than machines.  I'm pretty sure that they'd want at least a minimal crew orf pilot, navigator/copilot and at least one engineer.  (A dedicated doctor/medic would also likely be a good idea).  If nothing else, to keep the passengers calm during the flight.

     While machines are pretty good at doing their jobs, nobody will want to risk a several billion dollar investment on the possibility that a IC chip will fry because of a stray cosmic ray and send the craft wandering off into space or worse, come c rashing down on Earth at 6 to 7 KMS.

Huh?  I said that trained Flight Engineer passengers would be aboard. They are better at fixing the IC chip problem than pilots and/or setting a new heading.  Pilots, co-pilots and navigators are not needed.  Engineers can easily learn nav functions, not that they'd ever need to perform them. Realize that these flights will occur in a decade when driverless trucks & autos are commonplace.  It's not the 1960s in space.

Good point about the MD.  I should have also mentioned that out of the 50 or 100 passengers there should be one doctor passenger or at least EMT/nurse.  I would expect the colony to want such medical folks as well as engineers so that requirement should not be a problem.  STEM folk by necessity will comprise the majority of colonists.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/16/2015 09:09 pm
A single MCT won't be billions of dollars of investment or the $500k per passenger figure will be impossible. An order of magnitude less like $100-400 million. Also, electronics can easily be made reliable enough. We have lots an lots of experience running spacecraft for years at a time without maintenance. 6-9 months won't be a challenge for a company that will launch thousands of satellites into LEO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 06/16/2015 09:52 pm
At the end of they day, F9R and FHR will be doing the vast bulk of the sat launches.

Surely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)

[I would think the customers would end up forcing the decision. In much the same way that few were interested in F1 when they could fly as a secondary payload on F9 for half the price.]
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/16/2015 10:30 pm
At the end of they day, F9R and FHR will be doing the vast bulk of the sat launches.

Surely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)

[I would think the customers would end up forcing the decision. In much the same way that few were interested in F1 when they could fly as a secondary payload on F9 for half the price.]

Only SpaceX knows their long term plans for sure, obviously.  But I can't imagine they have any plans of retiring FH or F9 once MCT starts flying.  For several reasons.
When you have a hammer, everything looks like a nail.  But not everything is a nail.

They're investing a lot of money into the F9/FH infrastructure.  And they'll want to get an ROI on that.  All the tooling and production for Falcon already exists so all you save by shutting down Hawthorne is the overhead there.

And I think it's just a matter of the right tool for the job.  Most commercial comsats will be able to fly on F9R v1.2.  The F9US is cheap.  That'll be a cheap launch.  It's hard to imagine them launching a big Saturn V size (or larger) LV for such a comsat, even if it's fully reusable. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/17/2015 01:07 am


That brutal 12-14 kms entry to Earth is something everyone who is talking about this direct Earth return is glossing over, that is beyond Apollo speeds, the only thing that can survive that kind of heat, dynamic pressure and g-force is a dense capsule with thick heavy ablatives.

This is why it is not valid to design spacecraft by only looking at Delta-V and tank sizes and imagining that a giant 2nd stage can do the job of direct Earth return from Mars surface just because it can hold the propellents to launch to Earth.  It would literally be crushed like an empty beer can against ones forehead when it hits the Earth's atmosphere.

A 2nd stage that can return from Earth orbit is a vastly simpler thing to do because the speed is half (and the energy is a quarter), and it is fairly easy to slow down the 2nd stage by several kms with residual propellents, and to employ disposable things like parachutes because it only needs to perform ONE landing before servicing rather then two, and lastly it can be made much less reliable in landing because it's unmanned, no one dies horribly if it crashes or burns up on reentry unlike MCT.

The thing is....this is all a moot point to your argument.  Whether MCT is it's own 2nd stage to LEO or it sits atop a dedicated unique 2nd stage won't change the fact that MCT will need to have -large- tanks.  It will be mostly propellant tank by volume just to do the TMI burn and Mars EDL retropropulsion....and to get itself off the surface of Mars, even if it were only going to LMO before getting refueled there rather than all the way back in one shot.
It will be mostly a large propellant tank, with some legs, engines, and some cargo or hab internal volume.

Having MCT be it's own 2nd stage rather than having a separate dedicated 2nd stage won't change that.  MCT can't then become just a simple larger Dragon capsule. 
With a dedicated reusable 2nd stage, then it's just a giant 3rd stage, rather than a giant 2nd stage.  Maybe a little smaller.  Not much else changes.  So it's a bit of a moot argument.

Yes, designing a vehicle that is returning just form LEO is vastly more simple than designing one that's coming back from interplanetary speeds.  You are correct.  But, there's not an either/or option.  SpaceX must figure out how to get a large rocket stage back from Mars and land it on Earth.  They already need to solve that long pole issue.  A vehicle they design to handle that, can already return to Earth from LEO easily enough, without the [easy] development of a separate LEO only vehicle even necessary.

Ok beer can metaphor was not a good one because folks are interpreting it as implying that tanks would not have ANY internal pressure.  That's not what I was trying to imply, pressurizing the tank to give it more rigidity is always a good idea and would only require a modest amount of gas to be reserved for that purpose.

But I'm doubtful that their can be enough internal pressure in the tank to allow it to withstand the dynamic pressure of reentry, which is intense.  The formula is 1/2 * Ballistic coefficient * velocity ^2, thus a direct interplanetary Earth reentry is on the order of x10 higher pressure then an Entry from Mars orbit.


And please stop repeating that big-tank are the ONLY way, I have shown you several times how the vehicle can designed with much smaller tanks, your not a fan of these options but it is dishonest to begin your argument with your preferred solution as the only option, it is simply begging the question.

First off you can go to LMO and then dock with a transit vehicle like Mars Semi-Direct, no one here can claim that they are unfamiliar with Semi-Direct.  Second, inflatable tanks in the cargo-hold, even rigid tanks in the cargo hold if you think inflatables are to low TRL.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 06/17/2015 01:32 am
Surely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)

....I can't imagine they have any plans of retiring FH or F9 once MCT starts flying.  For several reasons.
When you have a hammer, everything looks like a nail.  But not everything is a nail.  it's...a matter of the right tool for the job...It's hard to imagine them launching a big Saturn V size (or larger) LV for such a comsat, even if it's fully reusable.

Agreed. Semi trucks haul mail cross country because that's the most cost efficient truck for that task. Jeep sized vehicles deliver to local mailboxes because that is the most cost efficient vehicle for that task. You don't use a maul when driving a finish nail. You use a finish nail hammer. Vice versa when demolishing a wall. You use the right tool for the job, and there is no single tool that does every job.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 06/17/2015 02:11 am
Surely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)
[...] Semi trucks haul mail cross country because that's the most cost efficient truck for that task. Jeep sized vehicles deliver to local mailboxes because that is the most cost efficient vehicle for that task. You don't use a maul when driving a finish nail. You use a finish nail hammer. Vice versa when demolishing a wall. You use the right tool for the job, and there is no single tool that does every job.

That seems to be what SpaceX thought with Falcon 1 and Falcon 9. But the F9 quickly ate the F1's market, so they cancelled it to save money.

I can't imagine a client wanting to use a semi-expendable rocket when a cheaper secondary/tertiary payload slot is available on a fully reusable HLV. People seem hung up over the size, all that matters is the price.

(Those semis will often carry many small packages because the per-item cost is lower than carrying them individually in a smaller vehicle.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/17/2015 03:42 am

I can't imagine a client wanting to use a semi-expendable rocket when a cheaper secondary/tertiary payload slot is available on a fully reusable HLV. People seem hung up over the size, all that matters is the price.

(Those semis will often carry many small packages because the per-item cost is lower than carrying them individually in a smaller vehicle.)

People seem to be trying to compare BFR cost to launch satellites with other existing or near term launchers (Ariane 5, SLS, F9 etc etc).  But that is not what my argument is about, it is about which VISION FOR BFR is cheaper to launch satellites with.  Musk's goal is not to slightly undercut existing launchers, it is to create massive paradigm-shifting reductions in $ to LEO, even if BFR launch blows every other launch vehicle out of the water it still needs to compete with variants of itself.

I'm arguing that BFR with mostly normal reusable 2nd stage is better at launching satellites then BFR with the giant MCT combo 2nd stage.  These latter will cost LESS because a 2nd stage even reusable is a much simpler and lower mass vehicle then the whole MCT which has MUCH more demanding requirements on lifespan, reentry heat, lifespan etc etc. 

The first stage is identical and presumably all other logical and launch related costs are too, so the only difference is in the 2nd stages, one which is conventional with a voluminous payload fairing which is light and designed for optimal mass delivery to orbit, the other is a huge heavy vehicle totally over engineered for this job and has a small cargo hold. 

Their is no contest the normal 2nd stage will out perform the giant vehicle to any orbit, just as an EELV booster outperformed the shuttle at launching satellites.  And the normal 2nd stage is going to be vastly cheaper to develop as well, the only argument that anyone has left is that because Elon absolutely MUST have his Mars oriented vehicle he will choose to shoehorn it into every possible usage even for things it is not optimized for so as to amortize the cost over as many flights as possible.  I don't recall that strategy working well for Shuttle. 

Musk is blessed with inordinate patience, he could have blown his money on a stunt ages ago but has always focused on building a viable BUSINESS first and foremost.  In pursuit of greater revenue he is now getting into the satellite business.  He doesn't leave any potential revenue source on the table.  Se Musk is not going to pass on designing the best conventional satellite launcher simply because he also wants to use the vehicle for Mars adventures, he knows that it must be a viable vehicle in it's own right.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 06/17/2015 03:59 am
EDIT: moved to MCT thread, where it's more appropriate
500 m^3 is a reasonable cargo-hold but their would be no integral habitat as many have speculated, it makes much mores sense to load a large module into the cargo-hold which can be removed and left on the Mars surface to minimize the return mass.  This also has the advantage of eliminating separate crew and cargo variants.

It is also extremely inefficient in structural mass. MCT is all about efficiency in structural mass.

The most mass efficient thing is to NOT make it integral to the MCT.  The time when structural mass efficiently maters most is take off, and if we indent to me offloading people and not taking them back to Earth then all that habitat mass would be pure dead-weight on take off.
A single MCT won't be billions of dollars of investment or the $500k per passenger figure will be impossible. An order of magnitude less like $100-400 million. Also, electronics can easily be made reliable enough. We have lots an lots of experience running spacecraft for years at a time without maintenance. 6-9 months won't be a challenge for a company that will launch thousands of satellites into LEO.
Of course, transit time is just ~3 months, not 8, so that's a big difference right there. Additionally, they likely did not sleep in shifts like you would on MCT colonization runs.
MCT is a radical design. Acknowledge that and move on.

Okay, this meme has reached an extreme.  We need to do some scoping.

Do you guys think we could separate, semantically:

A) A Gemini/Apollo-grade opposition-class mission to Mars.  Flags, footprints, a 1-4 weeks EVAs, and imported propellant.  At the end of this, we should have the technology for landing on Mars and returning to Earth at best-case unimproved sites.  May end up doing weak ISRU, but only with pre-landed hardware.  Population of 1's of people.

B) The sensible conjunction-class mission to Mars.  ~18 months on the surface, capable of weak ISRU return, experimenting with strong ISRU.  At the end of this, we should have the technology for landing on Mars and returning in a robust manner, pioneered experimentally at a range of unimproved sites.  Population of 10's of people.

C) The next step after that, a larger crew charged with maximizing geological exploration and innovating construction & ISRU techniques;  At the end of this, we should have the technology for landing on Mars and returning iteratively improved, and standardized at unprepared sites with 'strong' (hydrogen-harvesting) ISRU.  We should be able to mine ice, and bury habitats.  We should be able to reuse as much of the mission hardware as possible.  Population of 100's of people.

D) The next step after that, a mission charged with delivering and building Antarctica-grade accommodations for permanent scientific bases;  At the end of this, we should have the technology for landing on Mars and returning streamlined and improved with a ground-based ISRU system and ground-based habitats, as well as experimental agriculture, and should be able to deploy the first synod-round inhabited Mars bases, with people serving spaced tours of duty.  An ISRU station on Phobos/Deimos begins to become feasible to assist in providing return propellant at this point.  Population of 1000's of people.

E) The next step after that, a mission charged with delivering people to a permanent scientific base and building out industrial capacity, fleshing out most of the mass balance remaining between the station and self-sufficiency;  At the end of this, we should have the capacity to send people to Mars for permanent habitation at multiple sites, with only a modest, steady number of supply vessels per year.  Landing and takeoff should be routinized at Mars-side spaceports, and brought down to affordable levels with use of Aldrin cycler habitats and steerage-grade rendezvous capsules.  With this load it starts to make sense to begin to build small NTRs for crew capsule transfers.  Population of 10,000's of people.

F) Bootstrapping self-sufficiency and economic productivity with a population of 100,000's of people.  Domestic production of necessities.  Ability to sustain internal supplychain independently until the durable goods wear out.

G) Some exports, able to support unrestricted internal population growth, and sufficient industry to serve as a backup for human society, 1,000,000's of people.

Now: NASA's traditional approach is to try and cost out a series of missions that go beyond A (after carefully examining it for merit), and deep into B, with 4-6 people.  Right now their official line is 'we can do B on the current budget in 2037... maybe?' while their unofficial belief seems to be 'all we can show without doubling or tripling the HSF budget is increasingly advanced Powerpoints and progressively delayed 20-years-off launch times'. 

Musk appears to want, for SpaceX's first mission, to go straight through and complete all of B and straight through into C, with hardware that might still be useful for the first part of D.  This is an extremely ambitious, many would say non-credible plan.  It would certainly require NASA to increase its HSF budget by a factor of 10, and maybe more than that, for them to accomplish this;  Musk has been wildly successful with Falcon relative to what NASA expected its development costs to be, however, so we're unwilling to say he can't do it for only what NASA would pay him, a few billion a year, to outsource its HSF development (by leapfrogging their tech readiness until Congress breaks down and cancels the current path).

Now, Musk made comments about how far he eventually wanted to go with SpaceX's Mars program, and what it should cost and he said:
Quote
Musk’s $500,000 ticket price for a Mars trip was derived from what he thinks is affordable.

"The ticket price needs to be low enough that most people in advanced countries, in their mid-forties or something like that, could put together enough money to make the trip," he said, comparing the purchase to buying a house in California. [Photos: The First Space Tourists]

He also estimated that of the eight billion humans that will be living on Earth by the time the colony is possible, perhaps one in 100,000 would be prepared to go. That equates to potentially 80,000 migrants.

Musk figures the colony program — which he wants to be a collaboration between government and private enterprise — would end up costing about $36 billion. He arrived at that number by estimating that a colony that costs 0.25 percent or 0.5 percent of a nation’s gross domestic product (GDP) would be considered acceptable.

The United States' GDP in 2010 was $14.5 trillion; 0.25 percent of $14.5 trillion is $36 billion. If all 80,000 colonists paid $500,000 per seat for their Mars trip, $40 billion would be raised.

"Some money has to be spent on establishing a base on Mars. It’s about getting the basic fundamentals in place," Musk said. "That was true of the English colonies [in the Americas]; it took a significant expense to get things started. But once there are regular Mars flights, you can get the cost down to half a million dollars for someone to move to Mars. Then I think there are enough people who would buy that to have it be a reasonable business case."

He was, to my eye, pretty clearly talking about phases E, F, and G, and not on a design basis.  He has no mission plan for those phases, but $500k is what he thinks is required to achieve G on a private basis simply because there aren't enough people in the world with more than $500k to spend if G is available, to support those numbers of passengers.

To *get* from where we are in 2015, to phases E, F, and G, there's going to need to be vehicles that come first, vehicles that accomplish the earlier phases of a Mars program.  Vehicles that ride a 10-20m BFR in the 2020's-2030's.  I ask again that you find a way to distinguish between the earlier vehicles, and the later vehicles, because they will have wildly different technological capabilities and requirements.  Saying "But SpaceX is magic and MCT is an ambitious project!" only gets you so far - it doesn't get you to $500k/passenger, 3 month transits, and, for that matter, giant domed cities filled with one-way-ticket passengers.  I'm ready to extend an order of magnitude of credulity given Musk's track record, but there's too many orders of magnitude of progress there, relative to where we are now: It's portraying a future where we're 1,000 to 10,000 times more efficient at this than we are currently.  If Musk does eventually get there, he's certainly not going to start there from day 1.

So: We're talking about different vehicles and mission paradigms, some that come earlier and some that come later. "MCT" is no longer sufficient if you want to talk about the latter.  What do you guys want to call them?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/17/2015 04:41 am
You're now inventing some new whole bunch of vehicles from whole cloth? Not interested. We have very little to go on for the Mars Colonial Transporter, but that's what we have to go on for this thread, not inventing something new. There are other threads for what SpaceX might do before MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Krevsin on 06/17/2015 05:41 am

I can't imagine a client wanting to use a semi-expendable rocket when a cheaper secondary/tertiary payload slot is available on a fully reusable HLV. People seem hung up over the size, all that matters is the price.

(Those semis will often carry many small packages because the per-item cost is lower than carrying them individually in a smaller vehicle.)

People seem to be trying to compare BFR cost to launch satellites with other existing or near term launchers (Ariane 5, SLS, F9 etc etc).  But that is not what my argument is about, it is about which VISION FOR BFR is cheaper to launch satellites with.  Musk's goal is not to slightly undercut existing launchers, it is to create massive paradigm-shifting reductions in $ to LEO, even if BFR launch blows every other launch vehicle out of the water it still needs to compete with variants of itself.

I'm arguing that BFR with mostly normal reusable 2nd stage is better at launching satellites then BFR with the giant MCT combo 2nd stage.  These latter will cost LESS because a 2nd stage even reusable is a much simpler and lower mass vehicle then the whole MCT which has MUCH more demanding requirements on lifespan, reentry heat, lifespan etc etc. 

The first stage is identical and presumably all other logical and launch related costs are too, so the only difference is in the 2nd stages, one which is conventional with a voluminous payload fairing which is light and designed for optimal mass delivery to orbit, the other is a huge heavy vehicle totally over engineered for this job and has a small cargo hold. 

Their is no contest the normal 2nd stage will out perform the giant vehicle to any orbit, just as an EELV booster outperformed the shuttle at launching satellites.  And the normal 2nd stage is going to be vastly cheaper to develop as well, the only argument that anyone has left is that because Elon absolutely MUST have his Mars oriented vehicle he will choose to shoehorn it into every possible usage even for things it is not optimized for so as to amortize the cost over as many flights as possible.  I don't recall that strategy working well for Shuttle. 

Musk is blessed with inordinate patience, he could have blown his money on a stunt ages ago but has always focused on building a viable BUSINESS first and foremost.  In pursuit of greater revenue he is now getting into the satellite business.  He doesn't leave any potential revenue source on the table.  Se Musk is not going to pass on designing the best conventional satellite launcher simply because he also wants to use the vehicle for Mars adventures, he knows that it must be a viable vehicle in it's own right.
Again, while SpaceX is comprised of brilliant engineers and has an insane(ly dedicated) leader, it isn't made entirely out of money, nor does it have infinite time. Making and improving on the MCT will take up a lot of their money and time (in fact I'm pretty sure all of it) which they won't be able to spend on reusable BFR upper stage design.

Unless the MCT simply refers to a specific combination of a BFR reusable upper stage and payload which I think is an entirely viable option.

So they'll either use a modified MCT design for their comsat launch operations, or they will maintain their F9R and FHR lines.

Funnily enough, with a depot in space, the Falcon 9 and Falcon Heavy can go fully reusable without even needing a tug.

Comparing the shuttle to the MCT is not a valid comparison (yet) because the shuttle never really optimized for cost and because we do not know the specifics of the MCT outside its target preformance and cost figures (both of which are supremely vague and general) while having perfect retrospective view on both of those figures for the STS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: fast on 06/17/2015 01:48 pm
And back to design concepts, it is the most fun  :)

What if BFR and MCT will be the essentially same thing?
Kind of universal module sized similar to S-IC, 9 Raptors at the bottom, with lending legs, around 1900mt.
 
Than all thing will be three core (I know, Elon said one-core, but look at F5), MCT in the center will have less fuel load replaced by cargo bay and improved thermal protection, and probably have less than 9 Raptors(3?).

Just a thought to standardize and reduce cost...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/17/2015 04:12 pm

And please stop repeating that big-tank are the ONLY way, I have shown you several times how the vehicle can designed with much smaller tanks, your not a fan of these options but it is dishonest to begin your argument with your preferred solution as the only option, it is simply begging the question.

First off you can go to LMO and then dock with a transit vehicle like Mars Semi-Direct, no one here can claim that they are unfamiliar with Semi-Direct.  Second, inflatable tanks in the cargo-hold, even rigid tanks in the cargo hold if you think inflatables are to low TRL.

I -did- say your concept might be smaller.  But you seemed to be implying that by putting MCT on top of a dedicated 2nd stage, then it won't be a flying gas tank any more.  It'll be just a giant Dragon or something, and you'll avoid the issues of getting a large fuel tank through EDL.
That's incorrect.   You may have smaller tanks, but they'll still be large in relation to the overall vehicle. 
It's not what I am or am not a fan of, but what must be at a minimum.  MCT must be a single stage to Mars orbit vehicle at a minimum.  And thus, it will still be a big gas can that must get through EDL, whether it does direct return or not...whether it's it's own 2nd stage on Earth ascent or not.

:-)
 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/17/2015 04:19 pm
The key item that will stabilize the designs of the BFR and MCT is the Raptor. Once a Raptor test article exists then design values with low technical risks for bell size, engine weight, thrust, and ISP will exist along with an low risk model for manufacturing costs for a production Raptor based on the test article. Once SpaceX has that the 1st stage can be designed with low technical risk (low variation of its actual production version capabilities). With a 1st stage then the US or MCT designs can be done because the diameter and capabilities of the 1st stage are a known in a tradeoff engineering model.

So until that first test article enters testing on a test stand SpaceX itself only will have engineering goals for the system and few actual specifications: diameters, GLOW, payload weights, etc.

Our excursion into BFR/MCT design is only a fleshing out of the design scope (architectures and capabilities) and issues with design, development and operations of such a vehicle will be a help to SpaceX but in the end it will be a SpaceX design to meet their goals of cost (development, manufacture, operations[reuse number of times]) and capability (size, destinations, in-space operations [single vs multi launch to reach destination], reentry, landing, and reuse).

We may only have to wait 2 years for that Raptor test article to reach the test stand. Until then all we can do is highly speculate as to what SpaceX will do.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/17/2015 04:29 pm
And back to design concepts, it is the most fun  :)

What if BFR and MCT will be the essentially same thing?
Kind of universal module sized similar to S-IC, 9 Raptors at the bottom, with lending legs, around 1900mt.
 
Than all thing will be three core (I know, Elon said one-core, but look at F5), MCT in the center will have less fuel load replaced by cargo bay and improved thermal protection, and probably have less than 9 Raptors(3?).

Just a thought to standardize and reduce cost...

Setting aside Elon's actual words aside for a moment about it being single core, the 2-piece concept myself and a few others have been debating about would do what you are doing, but with just two pieces rather than 3.  One big monolithic RTLS booster, and one combo upperstage/spacecraft that can get itself to LEO where it will be refueled prior to going to Mars. 

If there were to be 3 pieces, then probably the concept Impaler has been advocating would be better, with a dedicated reusable 2nd stage between the booster and MCT/Spacecraft.  Then you essentially have a big dumb 2-stage LV that can be used a little more readily for other purposes than putting MCT in LEO.

Additionally, such a tri-core concept would have what engines on the central core/MCT?  Sea level Raptors as they'd be igniting at sea level.  Or vacuum Raptors as they'll be going to LEO and doing in-space burns?  Or would it launch without the central core lighting, like Titan III/IV?  And ignite the central core after booster sep?  I think that'd probably be the best way to approach such a concept, then you can have your vacuum Raptors on it. 
But then, each core would be narrower than a monolithic, and if MCT were core diameter, it'd be narrower too.  I think it'd be better for MCT to be as wide as feasible to help make it shorter and more stable when landing on the MArs surface.  Such a tri-core MCT would mean a pretty tall and skinny MCT.  Might look like the F9R booster when landing.  ;-)



Title: Re: MCT Speculation and Discussion Thread 4
Post by: Sohl on 06/17/2015 05:35 pm
Try crushing a beer can containing several bars of pressure against your forehead.

Sheesh!  There's easier ways to enjoy a beer! :P

;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/17/2015 05:50 pm
And back to design concepts, it is the most fun  :)

What if BFR and MCT will be the essentially same thing?
Kind of universal module sized similar to S-IC, 9 Raptors at the bottom, with lending legs, around 1900mt.
 
Than all thing will be three core (I know, Elon said one-core, but look at F5), MCT in the center will have less fuel load replaced by cargo bay and improved thermal protection, and probably have less than 9 Raptors(3?).

Just a thought to standardize and reduce cost...

Setting aside Elon's actual words aside for a moment about it being single core, the 2-piece concept myself and a few others have been debating about would do what you are doing, but with just two pieces rather than 3.  One big monolithic RTLS booster, and one combo upperstage/spacecraft that can get itself to LEO where it will be refueled prior to going to Mars. 

Actually this looks to me like the first innovative new idea for a while.

Elon Musk said single core. But the idea behind that was to my understanding, not a 3 core heavy configuration because the central core would go too fast for easy RTLS and would incur heavy payload loos for reuse. This concept avoids that problem.

This concept would be like a first stage in two parts, something completely different. The "central core" would be the MCT. The vac engine problem might be solvable with a retractable engine bell extension. The mechanism shown in that Falcon Heavy animation seems to allow fast efficient reconnection so should not be a major problem for simple operation.

Two side cores with 9 engines each plus a central core with 5? engines would give a total number of engines 23 for lift off. Most of them would be switched off as soon as the T/W ratio allows it to retain fuel for reaching orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/17/2015 06:08 pm
And back to design concepts, it is the most fun  :)

What if BFR and MCT will be the essentially same thing?
Kind of universal module sized similar to S-IC, 9 Raptors at the bottom, with lending legs, around 1900mt.
 
Than all thing will be three core (I know, Elon said one-core, but look at F5), MCT in the center will have less fuel load replaced by cargo bay and improved thermal protection, and probably have less than 9 Raptors(3?).

Just a thought to standardize and reduce cost...

Setting aside Elon's actual words aside for a moment about it being single core, the 2-piece concept myself and a few others have been debating about would do what you are doing, but with just two pieces rather than 3.  One big monolithic RTLS booster, and one combo upperstage/spacecraft that can get itself to LEO where it will be refueled prior to going to Mars. 

Actually this looks to me like the first innovative new idea for a while.

Elon Musk said single core. But the idea behind that was to my understanding, not a 3 core heavy configuration because the central core would go too fast for easy RTLS and would incur heavy payload loos for reuse. This concept avoids that problem.

This concept would be like a first stage in two parts, something completely different. The "central core" would be the MCT. The vac engine problem might be solvable with a retractable engine bell extension. The mechanism shown in that Falcon Heavy animation seems to allow fast efficient reconnection so should not be a major problem for simple operation.

Two side cores with 9 engines each plus a central core with 5? engines would give a total number of engines 23 for lift off. Most of them would be switched off as soon as the T/W ratio allows it to retain fuel for reaching orbit.

It is innovative (good job fast).  And it could work for the reason you say.  It eliminates the central core that's staging too fast.  There's also be a booster core for the intermediate size LV that's been discussed over on the SFR thread.

But, I just don't know that it has advantages over an in-line wider core?  Do you see where this would be an advantage?  Maybe if they weren't planning to build the cores near the launch facility, this concept would result in thinner cores that are more easily transported.  But that's really not a problem unless SpaceX changes from what they've stated.

And it'd result in a tall and skinny MCT.  That's probably the major issue with it vs. monolithic, that I see.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/17/2015 06:27 pm
Here goes. After calculating from chemical rockets only the weights needed to get cargo to mars surface and for a Human visit mission the following was the result. ISP of Vacuum Raptor 385. All tankers return to Earth. They need ~8mt of prop to do the return.

Cargo Mission:
1) 100mt payload at Mars surface
2) 140mt MCT dry weight at Mars surface (payload + vehicle)
-> 1.2km/s
3) 200mt wet weight at Deimos arrival
-> 3km/s
4) 440mt wet weight leaving L2 (300mt of propellant)
->13.3km/s
5) The cargo direct from Earth surface (140mt) + 3 tanker flights to L2 (delivering 100mt prop each)

Human Mission
1) 140mt Earth return MCT on Earth surface
->3.7km/s
2) 375mt Earth return MCT at departure from Deimos
3) 120mt dry weight at Deimos
->6km/s
4) 600mt wet weight at Mars surface fueled with 480mt of propellant from ISRU
5) 140mt dry weight landing
->1.2km/s
6) Mars SSTO 200mt wet weight arrival at Deimos
7) Earth return MCT 375mt wet weight at Deimos arrival
->3km/s
8 ) 1180mt MCT pair wet weight departure from L2
->13.3km/s
9) Direct from Earth 140mt Mars SSTO MCT, 140mt Earth Return MCT, 9 MCT Tankers to L2

Edit: added the Delta V values used in the calculations.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 06/17/2015 06:32 pm
A single MCT won't be billions of dollars of investment or the $500k per passenger figure will be impossible. An order of magnitude less like $100-400 million. Also, electronics can easily be made reliable enough. We have lots an lots of experience running spacecraft for years at a time without maintenance. 6-9 months won't be a challenge for a company that will launch thousands of satellites into LEO.

As these craft are supposed to effectively be the DC-3s of space, acting as both cargo and passenger carriers, Billions would be possible.  After all, airliners cost tens of millions of dollars and most airline tickets are less than $400.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 06/17/2015 06:59 pm
A single MCT won't be billions of dollars of investment or the $500k per passenger figure will be impossible. An order of magnitude less like $100-400 million. Also, electronics can easily be made reliable enough. We have lots an lots of experience running spacecraft for years at a time without maintenance. 6-9 months won't be a challenge for a company that will launch thousands of satellites into LEO.

As these craft are supposed to effectively be the DC-3s of space, acting as both cargo and passenger carriers, Billions would be possible.  After all, airliners cost tens of millions of dollars and most airline tickets are less than $400.

Airliners fly multiple flights per day to achieve their low cost per passenger. An MCT will make one Earth to Mars flight about every two years. That will be about 15 flights over the life of the MCT. With 100 passengers per flight at $500k each, the lifetime gross revenue of an MCT will be $750M. The MCT cost and all operating and maintenance costs had better be less than that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/17/2015 07:06 pm
A single MCT won't be billions of dollars of investment or the $500k per passenger figure will be impossible. An order of magnitude less like $100-400 million. Also, electronics can easily be made reliable enough. We have lots an lots of experience running spacecraft for years at a time without maintenance. 6-9 months won't be a challenge for a company that will launch thousands of satellites into LEO.

As these craft are supposed to effectively be the DC-3s of space, acting as both cargo and passenger carriers, Billions would be possible.  After all, airliners cost tens of millions of dollars and most airline tickets are less than $400.
No, billions would not be possible. 15 reuses for passenger MCTs, 100 passengers max, $500k per passenger yields a maximum cost per MCT of $750m. But you also have the BFR (first stage) and refueling flights plus operations and refurb cost, etc, plus cargo (although some of that will be funded in other ways perhaps), cost of capital over 30 years, plus the desire to reduce costs to below $500k, and you really, really need to get costs to around $200-400m per MCT. Which also means lightweighting the heck out of it, using as small of volume as you can get away with, etc.

But if each MCT cost billions (not counting BFR), Musk's goals are impossible to reach. But good news is that it shouldn't be anywhere near that expensive. A good rule of thumb for aerospace hardware like launch vehicles or airplanes is about $1k-4k/kg empty (True for Delta IV, Falcon 9, 747, 737, Bombardier, etc). If MCT has an empty mass of 50-100t, that gives a price range of about $50-400m per MCT (given the costs for F9v1.1, it'd be $100-200m per MCT, but MCT will be produced at a much greater rate than F9, so it could get down to $50-100m). Spacecraft are usually more expensive than this, but I think economies of scale (both production rate and size of the vehicle) can reduce the cost to somewhere in that range.

BFR first stage may be reused hundreds or even thousands of times.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 06/17/2015 07:30 pm
Don't forget that your income calculation is only for colonists. There will also be a market for cargo on the MCT as well, which may well be able pull in more per KG (scientific payloads etc). I reckon you might be able to pull in $1B on each MCT trip.

How much does it currently cost to put a 100kg payload on Mars?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/17/2015 08:35 pm
Don't ask how much it costs, ask what the total market size is likely to be. Sending 80k colonists per year at $500k each is just $40B per year, which is over twice NASA's budget. NASA is not going to get a huge funding increase any time soon and neither is NASA going to devote all their money to SpaceX. And NASA is the largest such organization by far. So initially, yes scientific payloads could be a significant source of income, but not for colonization and $500k per passenger stage. And Musk doesn't think there's anything worthwhile exporting from Mars, so MCT has to be able to pay for itself.

The base itself, however, may be built using revenues from the SpaceX constellation which would dwarf the revenue of even the full-swing colonization stage of $40B/year. The Constellation when built and fully populated should see revenues of $50B-$500B per year.

Satellite telecomm is hundreds of billions per year industry and growing at a fairly good clip... If all of a sudden you can compete for much of the business of Comcast--$65B--and Verizon at $145B and AT&T at $132B... But all over the world including the fast growing developing world, then over a trillion dollars in revenue is possible (not at all guaranteed) although that would take decades and likely require climbing up the value chain to mobile services as well (with requisite ground and/or air infrastructure).

But this is the sort of thing that may help pay for the Mars colony. Scientific payloads on MCT will be a pittance in comparison.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/17/2015 08:49 pm
Don't forget that your income calculation is only for colonists. There will also be a market for cargo on the MCT as well, which may well be able pull in more per KG (scientific payloads etc). I reckon you might be able to pull in $1B on each MCT trip.

How much does it currently cost to put a 100kg payload on Mars?
About once a decade, NASA might spend a billion dollars to put a fancy rover on Mars. Maybe $1-4 billion per year to transport stuff for a crewed research outpost, I don't imagine much more than that. But that's still only a tiny fraction of the $500k per person ticket price. At such high flight rates, a single MCT will not be able to command anywhere near $1B.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/17/2015 09:01 pm
If the reusable BFR and MCT are eventually built, NASA will probably abandon SLS and use the money to pay SpaceX to launch their payloads for whatever they are doing.  It was stated about 10 years ago that NASA needed to get out of the launch vehicle building business and build payloads and bid out the launch services as rockets were getting bigger and cheaper.  For what they have spent on Constellation and SLS, they could have built and launched Nautilis X and we would probably be on Mars now at least with flags and footprints. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/17/2015 09:59 pm
Unfortunately, NASA's funding is not purely for exploration, science, tech, etc, it is also a regional development program for Dixie and a couple other places. So you can have the coolest spaceship ever imagined for super cheap and amazing capability, and it still won't get but a small fraction of funding from NASA. Additionally, NASA is so much more than human spaceflight and launch services. $4 billion annually is the max possible I can imagine anything like BFR/MCT ever getting from NASA (in the next half century), with maybe $1-2 billion being far more likely.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/17/2015 11:53 pm
You may have smaller tanks, but they'll still be large in relation to the overall vehicle. 
It's not what I am or am not a fan of, but what must be at a minimum.  MCT must be a single stage to Mars orbit vehicle at a minimum.  And thus, it will still be a big gas can that must get through EDL, whether it does direct return or not...whether it's it's own 2nd stage on Earth ascent or not.

:-)

Mars Orbit needs a 66% propellent fraction, 33% dry, if takeoff weight is 150 mT then we need 300 mT propellent and this would be about 300 m^3.  Were both assuming a vehicle of ~1500 m^3 so were talking about tank sizes that are 1/5 of total volume.  Hardly large relative to the whole vehicle.

I'm looking at a Bi-conic with the following dimensions, at the tip a half-sphere with 6.5 m diameter, first frustum with 17 degree wall slope 8.5 m tall and with an 11 m diameter base, second frustum 8 degree slope 7.5 m tall with a 13 m diameter base, 2 meter cylindrical unpressurized skirt divided into control flaps.

Volumes are 72 m^3 for half-sphere, 453 m^3 for the first frustum, 819 m^3 for second frustum, 265 m^3 for skirt.  Total volume 1609 m^3 including volume in the skirt.  In addition the 4 Raptor engine bells would extend 2 meters beyond the skirt.

Cargo hold is inside the second frustum, 7 m wide, 13 meters long at the base (running fully from the from one side of the vehicle to the other) and it's belly extends into the skirt area making it 8.5 m tall totaling ~700 m^3.  It would accommodate 9 standard 20ft shipping containers stacked 3 wide and 3 tall.  A folding ramp forms the first few meters of the floor and can reach the ground which would be some 5 meters below the floor upon landing.  Containers would be offloaded to the ground with an on-board gantry crane in the roof of the cargo hold which would telescope out only a meter or two to clear the edge of the vehicle.

The cords to the side of the cargo-hold hold the landing gear legs (6) which are simple tube-rod pneumatically extended, rocket plumbing, and possibly additional propellent tanks or storage compartments. 

The upper frustum and half-sphere would be tanks, probably in the form of carbon fiber wrapped spheres or ellipsoids as in Dragon.  Two weights on semicircular tracks allow the vehicle to adjust center of mass for reentry and to compensate for variations in cargo density that might offset the center of mass.  Their may also be a small manned compartment (it might or might not separate in emergencies) for return to orbit of 6-8 persons at a time and an external docking mechanism to transfer them to a waiting transit vehicle.

Outer skin and TPS are integrated and metallic, titanium skin on the majority of the vehicle, inconel or ceramics on the hottest parts aka nose cone and control flaps.  Maximum entry speed is 4 kms, with a L/D of >1 it would experience no more then 2 g's (very important for our potentially weakend astronauts) resulting in considerable savings in mass.  Structures are carbon fiber as well.  Estimated mass is under 100 mT with plenty of growth margin.


Flight for Early exploration would be as follows

Launching without crew but with a monolithic surface habitat in cargo-hold and small propellent load used for either abort or as 3rd stage to reach higher orbit and rendezvous with a SEP transit vehicle.  The combined vehicle moves to Lagrange or LDRO, crew is send by taxi craft and enter habitat.  Combined vehicle transits and captures to LMO from which lander enters.  Surface stay and early base aggregation using surface habitats which are on wheels to facilitate removal from lander and high mobility exploration, it is left behind to establish a perment base.  Crew returns to orbit in landers small compartment and docks with the SEP and a pre-placed return habitat which was stocked with sufficient provisions should the landing have been aborted.  This combined vehicle transits back to High earth orbit and meets another taxi craft which returns the crew to Earth, the Lander is return to LEO refueled by tanker and performs a braking maneuver to allow a low speed entry and landing, the SEP is also re-propellented and ready for another round.

Flight for Cargo (Early)

Launch with cargo and same small propellent load, rendezvous with SEP vehicle in LEO, slow high ISP transit to low Mars orbit.  Entry and landing, cargo unloaded, refuel and launch.  Dock with SEP return to LEO, refuel and land.

Flight for Cargo (Late)

Cargo containers are launched in a payload fairing rather then the lander itself and are pushed all the way to Mars from LEO by SEP (this should be nearly 2 lander loads worth per launch).  At LMO they are loaded into the lander which land and immediately relaunch to orbit to take down more cargo, lander returns to Earth periodically for inspection after making many cargo landings in a single synod.

Flight for mass colonization would be modified as follows

Launch with a monolithic high-density 'sleeper-car' like module holding 100 passengers, same abort propellents.  Rendezvous in LEO with a 2nd stage that has been refilled by several other similar 2nd stages acting as tankers.  The combined vehicle is propelled to Lagrange/DLRO rendezvous with a large inflatable (BA 2100) transit habitat placed earlier by SEP, passengers transfer to habitat.  The lander and habitat are pushed to Mars by two separate SEP vehicles, upon reaching LMO passengers transfer back to the lander for entry and landing.  Passenger modules is returned to orbit with any return passengers and it and the transit habitat are returned to Earth orbit.  The lander is returned to LEO and as usual refueled for Earth landing and the habitat is only returned to high orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 12:30 am
Except Musk, in the biography, said MCT would go from the surface of Mars to Earth (in a single stage). But what does he know.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/18/2015 12:41 am
Again please link me to this quote.

Musk has said a lot of stuff that did not survive contact with reality, and we know they are looking at SEP right now.  So this is very much a viable profile and frankly it is FAR superior to a direct return.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 02:22 am
Again please link me to this quote.
http://www.amazon.com/Elon-Musk-SpaceX-Fantastic-Future/dp/0062301233
And here: http://forum.nasaspaceflight.com/index.php?topic=37839.msg1390934#msg1390934

Quote
Musk has said a lot of stuff that did not survive contact with reality
And? You've done better? Musk and occasionally Shotwell are basically the ONLY source for anything about MCT. So like it or not, that's all we've got right now.
Quote
and we know they are looking at SEP right now.
And one of the best ways of using SEP is to haul propellant around, from LEO to EML1/2 (or high Earth orbit).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CuddlyRocket on 06/18/2015 03:16 am
And Musk doesn't think there's anything worthwhile exporting from Mars, so MCT has to be able to pay for itself.

That's not entirely true - there are things that might be available on Mars whose value on Earth would exceed the marginal cost of transporting them via the MCT - but it's unlikely that they'd make a significant contribution to defraying the MCT's operational costs. But hey, every little helps!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Darkseraph on 06/18/2015 03:20 am
I've extremely high doubts that once the BFR/MCT package is complete, SpaceX will just cancel its breadwinning Falcon9/Falcon Heavy lines and launch all commercial satellites on a Saturn V class rocket. Mostly for the same reason that Boeing doesn't cancel the 737 regional jets because, hey they have a shiny new 787, and its fuel economy, reusuability and scale will make it more attractive for flying a few people 400kms away :P

The Falcon 1 analogy is bad here. It wasn't cancelled because the Falcon 9 could do those missions cheaper as such..it was cancelled because there wasn't a huge market for small satellites to low earth orbit in the late 00s. It was the wrong time for such a vehicle.

My own guess on this is that the Raptor engine is put on a ~5 meter reusable vehicle comparable in stats to Vulcan, for human launches to LEO, Military, commercial satellites and other bread-winning applications. I wouldn't be surprised if we even see this vehicle first, before the BFR, as a step on the way. I think it will be a long while before the Falcon line is discontinued.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: QuantumG on 06/18/2015 03:26 am
I've extremely high doubts that once the BFR/MCT package is complete, SpaceX will just cancel its breadwinning Falcon9/Falcon Heavy lines and launch all commercial satellites on a Saturn V class rocket.

.. and assuming that's the case, what's BFR for? Annual (at best) launches of MCTs?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/18/2015 03:42 am
I've extremely high doubts that once the BFR/MCT package is complete, SpaceX will just cancel its breadwinning Falcon9/Falcon Heavy lines and launch all commercial satellites on a Saturn V class rocket.

.. and assuming that's the case, what's BFR for? Annual (at best) launches of MCTs?

For every MCT going to Mars there will be 4 BFR launches. At a guess the first MCTs going to Mars will be preceded by more than 12 months by a first orbital flight, by 6-12 months the establishment of a propellant depot (4 BFR flights), then when the first MCTs go to Mars there will be 4 or more MCTs and for each MCT 3 tanker flights of the BFR with a reusable tanker upper stage. Then in the 22 months that follow the last of the MCTs from the first wave at least 10 more MCTs will have been built, maybe a few of them are contracted to others who want to establish a lunar mining operation, L2 L4 or L5 base. The depot is probably expanded, maybe someone contracts the BFR and MCTs just to built their own LEO or even GEO station.  At the price point of the BFR maybe the Clarke vision of 3 to 6 huge communications stations in GEO makes sense.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 03:43 am
I've extremely high doubts that once the BFR/MCT package is complete, SpaceX will just cancel its breadwinning Falcon9/Falcon Heavy lines and launch all commercial satellites on a Saturn V class rocket.

.. and assuming that's the case, what's BFR for? Annual (at best) launches of MCTs?
You would be sending up cargo and propellant flights all year round, waiting in Earth orbit for the departure window, not waiting on the ground. (Or possibly more exotic ballistic trajectories.)

Dark seraph:
But anyway, all these analogies are silly. Who cares about the relative power or size, what matters is cost. If you are comparing the cost of pizza delivery in a Ferrari vs a Camry that needs to be half replaced each time, the Ferrari will be cheaper.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/18/2015 03:45 am
Thanks for the link, this seems to be the key quote.

“And then one of the key questions is can you get to the surface of Mars and back to Earth on a single stage. The answer is yes, if you reduce the return payload to approximately one-quarter of the outbound payload, which I thought made sense because you are going to want to transport a lot more to Mars than you’d want to transfer from Mars to Earth. For the spacecraft, the heat shield, the life support system, and the legs will have to be very, very light."


It's largely as I suspected, Musk is describing what COULD be done and the constraints he would face in doing it, but it is by no means a commitment that this is how he will proceed even with the initial design.  I think the incredible lightness necessary to make it work will prove too risky of a development challenge, he could end up in Venture Star territory if just one of his lightening strategies fails to work the whole thing could collapse.

By setting low bars like Mars surface to Low Mars orbit and low entry velocity the whole design process becomes a much less risky and cutting edge.  SpaceX has traditionally not done high risk designs so I think it is far more likely that in the end he chooses the safer design even if it dose require a second SEP vehicle to function and a good deal of rendezvous in space for refueling.

And? You've done better? Musk and occasionally Shotwell are basically the ONLY source for anything about MCT. So like it or not, that's all we've got right now.

Actually their is a LOT of information on rocketry out their on the inter-webs and we can and should do our own research if we expect to speculate with any kind of informed way.  If Musk & Shotwell quotes were the only permissible source material then this thread would be nothing more then a religious war between the SpaceX fan-boys and the SpaceX haters.  If my analysis disagrees with anyone else's, even Musk's I have every right and indeed the responsibility to point that out and I will not heckled by you or anyone else simply because I don't own a rocket company.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 03:55 am
Extreme lightness is a SpaceX specialty. That is one area we can assume they'll do better than the status quo, certainly much better than is typically assumed for Mars architecture.

SpaceX boosters can do on the order of 30 mass ratio. The shell of MCT may be similarly constructed. I think this is quite doable with the right design.

Just by pressured volume, we'd be talking about approximately 16 tons for the crew section, another 16 tons of the engines and propellant tanks, plus the TPS and legs to support it all (of course the legs only need to support a 100 payload plus dry mass on Mars, not on Earth since a smaller payload would be sent to Earth. 50 tons dry mass should be more than doable, if you strip out the cheap stuff.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 03:57 am
BTW, nobody is stopping you, Impaler, from starting a new thread with your own idea of how to transport people to Mars if you don't like how Musk is doing it or think it's unworkable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: SLC17A5 on 06/18/2015 06:58 am
In 2016 SpaceX has bookings for ~$1.3B of rockets (22 at $57m via Google and the US launch schedule thread).  They receive about $650M annually from the CCtCap award ($2.6B through 2019) and about $200M from CRS, that's about $2.15B in revenues.  A very cursory search suggests that Tesla and Google both have 25% profit margins so let's assume that SpaceX gets the same and makes a profit of ~$550M.  Suppose half that profit goes into funding private Mars work, so that 1/8th of all revenue is being spent on internal Mars R&D and mission costs.  That's a $275m annual budget for Mars efforts, on the order of half their yearly costs on the CCtCap award.

A doubling of commercial sales -- 50 launches a year -- adds about $170m to this estimate and puts the effort at $450M yearly.  A great success of reuse might drastically affect profit margins, or it might not, since now you need to build fewer rockets for the same flight rate, but you also need to maintain reflown stages, and you might end up discounting your launch price anyways.  Imagining a 50% profit margin and doubled sales, SpaceX can spend $900M on Mars work yearly.

What I am getting at is that the scale of SpaceX's commercial rocketry business is borderline in terms of building and operating individual exploration craft.  Fleets of $500M MCTs are beyond SpaceX's independent means, even under optimistic expectations.

I am also skeptical of SpaceX trying to switch horses in midstream between kerolox Falcon and methalox BFR architectures with this cost structure.  Before they had an order book and DoD certification, they had a lot of freedom to change rocket configurations.  Now, they have an ongoing business of maintaining Falcon service and associated Falcon costs.  If SpaceX tries to leap directly to methalox and BFR in one go, that adds on Raptor costs and BFR costs and MCT costs all at once.  These are going to be Large Rocket Costs, much larger than those incurred for Falcon.  I am skeptical that the existing business can bear them.  SLS costs are $2.2b/year, and BFR is larger than SLS.  I don't see how SpaceX can develop a rocket larger than SLS and a very advanced upper stage / spacecraft capable of Mars EDL/ascent for a small fraction of the price.

I think Musk's comments about a "single monster boost stage" can encompass a range of monstrosity.  A single core equivalent of Falcon Heavy would, after all, be at least a smidge monstrous.  A craft that delivers "100 metric tons of useful payload to the surface of Mars" can be assembled in Earth orbit and does not need to launch intact from Earth's surface.

Ultimately I think that SpaceX might well achieve a manned Mars landing, but I am doubtful of their ability to independently fund a major colonization architecture. It does make me wonder if SpaceX might try to get into the satellite business to scale up their revenues in order to better follow up on the Mars goal.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 06/18/2015 07:52 am
In 2016 SpaceX has bookings for ~$1.3B of rockets (22 at $57m via Google and the US launch schedule thread).  They receive about $650M annually from the CCtCap award ($2.6B through 2019) and about $200M from CRS, that's about $2.15B in revenues.  A very cursory search suggests that Tesla and Google both have 25% profit margins so let's assume that SpaceX gets the same and makes a profit of ~$550M.  Suppose half that profit goes into funding private Mars work, so that 1/8th of all revenue is being spent on internal Mars R&D and mission costs.  That's a $275m annual budget for Mars efforts, on the order of half their yearly costs on the CCtCap award.
>

We should also note that the new Tesla Energy Corporation scored $800 million in orders for Powerwall (home) and Powerpack (business & utility) power storage packs in its first week,

Bloomberg.... (http://www.bloomberg.com/news/articles/2015-05-08/tesla-s-battery-grabbed-800-million-in-its-first-week)

They're gonna need more Gigafactories (and they're already planned).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: fast on 06/18/2015 08:48 am
And back to design concepts, it is the most fun  :)

What if BFR and MCT will be the essentially same thing?
Kind of universal module sized similar to S-IC, 9 Raptors at the bottom, with lending legs, around 1900mt.
 
Than all thing will be three core (I know, Elon said one-core, but look at F5), MCT in the center will have less fuel load replaced by cargo bay and improved thermal protection, and probably have less than 9 Raptors(3?).

Just a thought to standardize and reduce cost...

Setting aside Elon's actual words aside for a moment about it being single core, the 2-piece concept myself and a few others have been debating about would do what you are doing, but with just two pieces rather than 3.  One big monolithic RTLS booster, and one combo upperstage/spacecraft that can get itself to LEO where it will be refueled prior to going to Mars. 

Actually this looks to me like the first innovative new idea for a while.

Elon Musk said single core. But the idea behind that was to my understanding, not a 3 core heavy configuration because the central core would go too fast for easy RTLS and would incur heavy payload loos for reuse. This concept avoids that problem.

This concept would be like a first stage in two parts, something completely different. The "central core" would be the MCT. The vac engine problem might be solvable with a retractable engine bell extension. The mechanism shown in that Falcon Heavy animation seems to allow fast efficient reconnection so should not be a major problem for simple operation.

Two side cores with 9 engines each plus a central core with 5? engines would give a total number of engines 23 for lift off. Most of them would be switched off as soon as the T/W ratio allows it to retain fuel for reaching orbit.

It is innovative (good job fast).  And it could work for the reason you say.  It eliminates the central core that's staging too fast.  There's also be a booster core for the intermediate size LV that's been discussed over on the SFR thread.

But, I just don't know that it has advantages over an in-line wider core?  Do you see where this would be an advantage?  Maybe if they weren't planning to build the cores near the launch facility, this concept would result in thinner cores that are more easily transported.  But that's really not a problem unless SpaceX changes from what they've stated.

And it'd result in a tall and skinny MCT.  That's probably the major issue with it vs. monolithic, that I see.



Proportion of MCT module (same as side booster modules), as I mentioned can be similar to S-1C, which are ~10m diameter and ~40m long, but can be wider. It is not anywhere as skinny as F9 :)d.

Advantage of the concept is this one standard core module (with features) can give SpaceX one universal reusable LV of reasonable size. And Falcons could be discontinued.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/18/2015 09:28 am
But, I just don't know that it has advantages over an in-line wider core?  Do you see where this would be an advantage? 

It would use all engines at launch, including those MCT will bring to Mars. That might make for a better T/W if the use of two tanks does not eat that advantage. But it should not since a smaller diameter tank can be thinner. Higher production on the production line.

Plus, as you mentioned already. A single core may make a more cost effective launch vehicle for everything that now goes on Falcon 9 and Falcon Heavy with much smaller development cost.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 10:37 am
In 2016 SpaceX has bookings for ~$1.3B of rockets (22 at $57m via Google and the US launch schedule thread).  They receive about $650M annually from the CCtCap award ($2.6B through 2019) and about $200M from CRS, that's about $2.15B in revenues.  A very cursory search suggests that Tesla and Google both have 25% profit margins so let's assume that SpaceX gets the same and makes a profit of ~$550M.  Suppose half that profit goes into funding private Mars work, so that 1/8th of all revenue is being spent on internal Mars R&D and mission costs.  That's a $275m annual budget for Mars efforts, on the order of half their yearly costs on the CCtCap award.

A doubling of commercial sales -- 50 launches a year -- adds about $170m to this estimate and puts the effort at $450M yearly.  A great success of reuse might drastically affect profit margins, or it might not, since now you need to build fewer rockets for the same flight rate, but you also need to maintain reflown stages, and you might end up discounting your launch price anyways.  Imagining a 50% profit margin and doubled sales, SpaceX can spend $900M on Mars work yearly.

What I am getting at is that the scale of SpaceX's commercial rocketry business is borderline in terms of building and operating individual exploration craft.  Fleets of $500M MCTs are beyond SpaceX's independent means, even under optimistic expectations.

I am also skeptical of SpaceX trying to switch horses in midstream between kerolox Falcon and methalox BFR architectures with this cost structure.  Before they had an order book and DoD certification, they had a lot of freedom to change rocket configurations.  Now, they have an ongoing business of maintaining Falcon service and associated Falcon costs.  If SpaceX tries to leap directly to methalox and BFR in one go, that adds on Raptor costs and BFR costs and MCT costs all at once.  These are going to be Large Rocket Costs, much larger than those incurred for Falcon.  I am skeptical that the existing business can bear them.  SLS costs are $2.2b/year, and BFR is larger than SLS.  I don't see how SpaceX can develop a rocket larger than SLS and a very advanced upper stage / spacecraft capable of Mars EDL/ascent for a small fraction of the price.

I think Musk's comments about a "single monster boost stage" can encompass a range of monstrosity.  A single core equivalent of Falcon Heavy would, after all, be at least a smidge monstrous.  A craft that delivers "100 metric tons of useful payload to the surface of Mars" can be assembled in Earth orbit and does not need to launch intact from Earth's surface.

Ultimately I think that SpaceX might well achieve a manned Mars landing, but I am doubtful of their ability to independently fund a major colonization architecture. It does make me wonder if SpaceX might try to get into the satellite business to scale up their revenues in order to better follow up on the Mars goal.
They have enough revenues to develop Raptor and perhaps the first few MCT/BFR, but Mars will not be paid for by Dragon or F9/FH, but according to Musk, Mars will be paid for by new growth from the SpaceX constellation. Did you miss that?

The revenue from the constellation would be at least an order of magnitude (and perhaps 2-3 orders of magnitude) higher than launch revenues right now.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/18/2015 10:44 am
In 2016 SpaceX has bookings for ~$1.3B of rockets (22 at $57m via Google and the US launch schedule thread).  They receive about $650M annually from the CCtCap award ($2.6B through 2019) and about $200M from CRS, that's about $2.15B in revenues.  A very cursory search suggests that Tesla and Google both have 25% profit margins so let's assume that SpaceX gets the same and makes a profit of ~$550M.  Suppose half that profit goes into funding private Mars work, so that 1/8th of all revenue is being spent on internal Mars R&D and mission costs.  That's a $275m annual budget for Mars efforts, on the order of half their yearly costs on the CCtCap award.

...

SpaceX probably do not need to fund Raptor/BFR/MCT completely out of earnings. With investment funding they can probably spend about $7B on them over the next 5-6 years. That should be enough to get basic versions of them designed and built, but probably not enough for a full manned Mars architecture (long duration crew and propellant depots, etc.). Long term revenue from their constellation will help, but there won't be much revenue this decade.

I would not use SLS as a benchmark of what BFR/MCT costs might be, SpaceX have proven low cost development.

I can't see BFR/MCT replacing F9R/FHR, but any FH (expendable) payloads would probably be cheaper on BFR.

Long term I think that F9R/FHR will be replaced by a methalox rocket, sized at about 15 tonnes to LEO fully reusable and using a smaller full flow staged combustion engine in the Raptor family. But that is many years down the road, and the road may diverge from that track.

Assembly in LEO is not feasible in my opinion, it has proved extremely expensive to do any assembly in space. However docking might be possible. Splitting the MCT into two parts which are then docked might work, especially if those two parts are identical mini-MCT which then dock nose to nose.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Eerie on 06/18/2015 11:43 am
Assembly in LEO is not feasible in my opinion, it has proved extremely expensive to do any assembly in space.

What are you talking about? It was proven that ISS is expensive, but that's basically it. ISS is the second modular space station to ever exist, and it used the most expensive launch vehicle (STS).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 12:43 pm
Salyut 7 was modular, too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/18/2015 12:57 pm
Thanks for the link, this seems to be the key quote.

“And then one of the key questions is can you get to the surface of Mars and back to Earth on a single stage. The answer is yes, if you reduce the return payload to approximately one-quarter of the outbound payload, which I thought made sense because you are going to want to transport a lot more to Mars than you’d want to transfer from Mars to Earth. For the spacecraft, the heat shield, the life support system, and the legs will have to be very, very light."


It's largely as I suspected, Musk is describing what COULD be done and the constraints he would face in doing it, but it is by no means a commitment that this is how he will proceed even with the initial design.  I think the incredible lightness necessary to make it work will prove too risky of a development challenge, he could end up in Venture Star territory if just one of his lightening strategies fails to work the whole thing could collapse.

By setting low bars like Mars surface to Low Mars orbit and low entry velocity the whole design process becomes a much less risky and cutting edge.  SpaceX has traditionally not done high risk designs so I think it is far more likely that in the end he chooses the safer design even if it dose require a second SEP vehicle to function and a good deal of rendezvous in space for refueling.

And? You've done better? Musk and occasionally Shotwell are basically the ONLY source for anything about MCT. So like it or not, that's all we've got right now.

Actually their is a LOT of information on rocketry out their on the inter-webs and we can and should do our own research if we expect to speculate with any kind of informed way.  If Musk & Shotwell quotes were the only permissible source material then this thread would be nothing more then a religious war between the SpaceX fan-boys and the SpaceX haters.  If my analysis disagrees with anyone else's, even Musk's I have every right and indeed the responsibility to point that out and I will not heckled by you or anyone else simply because I don't own a rocket company.

One question this raises for me is just how many people is the MCT supposed to bring back?  Because if we just bring back the ship for reuse, automatically, and do not have return passengers, we can do without the radiation protection.  As Musk mentioned it would be mostly water (how many tonnes?  I've been using 50), so it can be drained easily.  We can also do away with 20 to 25 tonnes of food, and 10 tonnes of crew and personal luggage.  So the return MCT could be 80+ tons lighter than in the other direction.  My other question : is the radiation shield a type of payload?  Because the hydrogen can be used as seed for fuel production, and the clean water can be used directly at the colony.  Even the food might be considered payload, since by the end of the trip it could be on the way to becoming valuable organic compost.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 02:07 pm
Actually, you probably want to dump the water shielding before Mars entry. Mars has lots of water, and it will be absolutely essential to tap that water for any of this to work.

Additionally, clever arrangement of propellant tanks (and surface tension devices) could use your propellant as shielding. Methane is actually significantly more efficient than water for radiation shielding (Water has an average atomic mass of 6, while methane has an average of ~3). Only hydrogen is superior.

That would probably shift the expected fuel:oxidizer ratio to be more fuel rich than it otherwise would be (if you could adjust that ratio on the fly, you may depart EML1/2 with a more stoich ratio but do final burn above Mars with significantly more fuel rich).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/18/2015 02:17 pm
In 2016 SpaceX has bookings for ~$1.3B of rockets (22 at $57m via Google and the US launch schedule thread).  They receive about $650M annually from the CCtCap award ($2.6B through 2019) and about $200M from CRS, that's about $2.15B in revenues.  A very cursory search suggests that Tesla and Google both have 25% profit margins so let's assume that SpaceX gets the same and makes a profit of ~$550M.  Suppose half that profit goes into funding private Mars work, so that 1/8th of all revenue is being spent on internal Mars R&D and mission costs.  That's a $275m annual budget for Mars efforts, on the order of half their yearly costs on the CCtCap award.
Note that there are 3 CRS flights in 2016 and that is $400M

I would work on the assumption of a $10M margin per launch right now for commercial flights of the F9, and maybe double that for FH.




What I am getting at is that the scale of SpaceX's commercial rocketry business is borderline in terms of building and operating individual exploration craft.  Fleets of $500M MCTs are beyond SpaceX's independent means, even under optimistic expectations.

I am certain that the first MCT costs effectively a lot more than $500M, but I certainly don't expect them to cost that much after the first. I would also break down the cost between booster ($250M maybe) and MCT $100M and reusable tanker US $50M and resuable payload lofter $50M. The large fleet needs to be of MCTs, much smaller fleet of BFR boosters.

I am also skeptical of SpaceX trying to switch horses in midstream between kerolox Falcon and methalox BFR architectures with this cost structure.  Before they had an order book and DoD certification, they had a lot of freedom to change rocket configurations.  Now, they have an ongoing business of maintaining Falcon service and associated Falcon costs.  If SpaceX tries to leap directly to methalox and BFR in one go, that adds on Raptor costs and BFR costs and MCT costs all at once.  These are going to be Large Rocket Costs, much larger than those incurred for Falcon.  I am skeptical that the existing business can bear them.  SLS costs are $2.2b/year, and BFR is larger than SLS.  I don't see how SpaceX can develop a rocket larger than SLS and a very advanced upper stage / spacecraft capable of Mars EDL/ascent for a small fraction of the price.

Not sure of your logic here, it was not easier to develop Falcon 1 along with 2 engines, and design the F9 with a lot of latitude and zero cash flow. F9 development was paid for by NASA under COTS and one thing that F9 demonstrated was the fact that F9 development could be done at 1/3rd the costs of similar developments in the past.

As far as "leap directly to methalox and BFR in one go" I assure you that doing it in 2 steps would cost more both in $ and time.  There will be no issue on the F9/FH business as BFR/MCT is being developed.  There will be little ongoing development in F9/FH by 2018 it will have hit maturity.  Dragon is another story.  BFR/MCT will be manufactured in a new centre and that will cost money, but I am certain Elon will find a source for the capital to gear up for that either with new equity or more likely a deal that brings other sponsorship.


Ultimately I think that SpaceX might well achieve a manned Mars landing, but I am doubtful of their ability to independently fund a major colonization architecture. It does make me wonder if SpaceX might try to get into the satellite business to scale up their revenues in order to better follow up on the Mars goal.

No argument there but if SpaceX can fund all of the set up and demonstrate the will to go to Mars anyway,  I can't imagine that they aren't years ahead of anyone else and that the can sell participation to other groups, probably sell enough to actually pay for the first manned expedition even though the other groups are a small part of it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/18/2015 02:32 pm
Actually, you probably want to dump the water shielding before Mars entry. Mars has lots of water, and it will be absolutely essential to tap that water for any of this to work.

Additionally, clever arrangement of propellant tanks (and surface tension devices) could use your propellant as shielding. Methane is actually significantly more efficient than water for radiation shielding (Water has an average atomic mass of 6, while methane has an average of ~3). Only hydrogen is superior.

That would probably shift the expected fuel:oxidizer ratio to be more fuel rich than it otherwise would be (if you could adjust that ratio on the fly, you may depart EML1/2 with a more stoich ratio but do final burn above Mars with significantly more fuel rich).
So I guess it might be a good idea to jettison the water before the final injection burn to Mars orbit, that might reduce the fuel required for that manoeuver.  A linked question is would we want to jettison the waste, or is the compost value higher than the value of fuel saving?  Is the injection burn a large part of the overall fuel use for Mars transfer?  My understanding is the faster we go, the more fuel is required to stop at Mars, but for a 6 month mission, is the Mars burn a large portion of the deltaV requirement?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/18/2015 02:39 pm
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/18/2015 02:42 pm
So I guess it might be a good idea to jettison the water before the final injection burn to Mars orbit, that might reduce the fuel required for that manoeuver.  A linked question is would we want to jettison the waste, or is the compost value higher than the value of fuel saving?  Is the injection burn a large part of the overall fuel use for Mars transfer?  My understanding is the faster we go, the more fuel is required to stop at Mars, but for a 6 month mission, is the Mars burn a large portion of the deltaV requirement?

I don't anticpate any Mars injection burn. MCT will come in hot for aerobraking, doing only a landing burn.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/18/2015 03:00 pm
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
Thanks, this is a great summary.   I guess this means not much water based radiation shielding?  And if as Guckyfan proposes there is no final injection burn, not much fuel at the end for radiation protection either?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/18/2015 03:05 pm
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
Thanks, this is a great summary.   I guess this means not much water based radiation shielding?  And if as Guckyfan proposes there is no final injection burn, not much fuel at the end for radiation protection either?

One item I forgot to mention was the number of Raptors on MCT would be 5 to give a 3g liftoff at Mars with immediate 1 engine out continue mission capability. Later in Mars launch even 2 engines out would still enable continue mission. A very low risk value for mission success results from this.

Edit added: GLOW at Mars liftoff would be 965mt or 2.135Mlb more than 2x the GLOW of the F9v1.0. (65mt dry weight [40mt vehicle 25mt payload]). The MCT is not a small vehicle. It could conceivably reach Earth orbit as an SSTO witha  little payload about 20mt.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 03:29 pm
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
15m diameter and other such details have not been mentioned. Please cite your sources and put the source quote in the MCT source thread so we know exactly what was said: http://forum.nasaspaceflight.com/index.php?topic=37839.0
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/18/2015 03:44 pm
- Vehicle structure+engines+ shield =40mt

I think you are being rather optimistic here, compared to the F9 upper stage 10x the dry mass for 10x the propellant mass is quite reasonable, but the MCT would need heat shield and other reuse components, long duration features (propellant cooling), beyond earth orbit features (solar panels, better comms) and a large fairing to encapsulate the payload (perhaps 2500 m^3 of volume).

I've guestimated 90 tonnes, others have guestimated down to about 50 tonnes, but this is the lowest I've seen.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/18/2015 03:46 pm
The MCT is not a small vehicle. It could conceivably reach Earth orbit as an SSTO with a  little payload about 20mt.

20 tonnes to LEO is not a little payload.

If the MCT could really achieve a dry mass of 40 tonnes it would make a very useful reusable SSTO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 03:56 pm
Except the Vac-optimized Raptors may not have enough thrust to get it off the ground nor the Isp to get to orbit. Just because it might conceivably get 9km/s in free space doesn't mean it is a SSTO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/18/2015 04:06 pm
I've extremely high doubts that once the BFR/MCT package is complete, SpaceX will just cancel its breadwinning Falcon9/Falcon Heavy lines and launch all commercial satellites on a Saturn V class rocket.

.. and assuming that's the case, what's BFR for? Annual (at best) launches of MCTs?

If MCT basically gets itself plus 100mt of payload to LEO, and gets refueled there, that means it'll take several tanker flights per mission to fill up one MCT prior to departure.  If two MCT's are going, then double that.  If there's just one MCT pad initially, that could keep pretty busy just supporting that.  I think a depot (basically an MCT modified for extra low boiloff and long LEO loiter) would allow for regular flights during the time between syniods.  So that the MCT facility can work and launch regularly, rather than in a flurry once every two years, with lag time in between.

In addition to that, I think any large payloads that might otherwise require an expendable FH could be launched on the MCT stack, as well as anything larger, if there is anything larger. 

I think all of that in the aggregate could keep an MCT construction/landing/launch facility busy year-round, with F9/FH taking care of payloads EELV-class and below.  Realistically, a single HIF probably isn't going to handle more than one MCT per month.  A single pad could be used for multiple HIF's, and thus it could launch a few a month possibly, depending on how much pad damage there is between launches.  A launch complex could be pretty busy then, year round.

Once things ramp up for full colonization down the road, probably additional pads would be needed with multiple depots needing filled up between synoids to fuel up multiple MCT's heading to Mars each launch window.

So it's not the 1 or 2 or 3 MCT's per synoid going to Mars that will keep the hardward and facilities busy, it's staging all that propellant in LEO for those MCT's that will keep them busy.  With some other non Mars related payloads sprinkled in there.  If MCT were to take on F9 and FH payloads too, they'd need quite a large complex for that sort of launch rate.  And then there's the issue of how they'd get some MCT's from their main East Coast facility to VAFB for West coat launches and Falcon would be otherwise handling.

I'd also not be surprised if NASA hired SpaceX to do some lunar missions ahead of getting on board with them for the early Mars missions, assuming MCT is capable of lunar missions.  Elon seemed to indicate he thought it would be.  MCT will still need to be fully fueled in LEO for a lunar mission, and possibly get some more propellant in lunar orbit, as it might not be able to get from LEO to the surface of the moon, and then back to the surface of Earth all on one tank.  So that'd also be a nice testbed for SpaceX to refine their operations and methods and launch rates and hardware before sending MCT with a crew all the way to Mars.  So they'd have a vested interest in doing it aside from profit, if NASA were to hire them for that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/18/2015 04:14 pm
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
15m diameter and other such details have not been mentioned. Please cite your sources and put the source quote in the MCT source thread so we know exactly what was said: http://forum.nasaspaceflight.com/index.php?topic=37839.0
I like the quote page, thanks!  the 15m had a qualifying text with it :-)  so I'm keeping with my own ideas for a 10m core for the moment.  Although the 15m core is a tempting design basis.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/18/2015 04:16 pm
Except the Vac-optimized Raptors may not have enough thrust to get it off the ground nor the Isp to get to orbit. Just because it might conceivably get 9km/s in free space doesn't mean it is a SSTO.

Btw how would MCT land on Earth if it had vac-Raptors?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/18/2015 04:22 pm
Except the Vac-optimized Raptors may not have enough thrust to get it off the ground nor the Isp to get to orbit. Just because it might conceivably get 9km/s in free space doesn't mean it is a SSTO.

5 Raptors probably would not have enough thrust for Earth launch (depending on what their SL thrust is), but landing on Earth would need a SL engine so at least one of them might have altitude compensation.

I'm really sceptical myself, if SpaceX could really bring in an MCT at 40 tonnes, they would be able to achieve what I have long considered impossible using near term technology - an economically viable reusable SSTO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/18/2015 04:23 pm
I was just thinking, what if the side-boosters of Falcon Heavy are used a boosters to the BFR (like 8-10 of them).  Like any rocket you need more liftoff thrust then you need to sustain and the side-boosters would simply drop off and do the normal return to launch site or down-range landing as that would be a well established practice by then (I'd imagine they don't all drop off at once, early drops RTLS, late ones land down range). 

The side-booster would continue to use Kerolox and 9 Merlin engines which means you would be using two fuels but Kerosine is easy to handle.  Structural attachment to the core might prove tricky and the reintegration of the overall vehicle also be annoying and far short of 'gas-and-go' so it might be much like Atlas V, the rocket can launch without boosters but adding them gives higher payload which would allow SpaceX to design a smaller launcher that is more economical for small launches while still performing the few actual launches of massive vehicle while being fully reusable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/18/2015 04:31 pm
The MCT is not a small vehicle. It could conceivably reach Earth orbit as an SSTO with a  little payload about 20mt.

20 tonnes to LEO is not a little payload.

If the MCT could really achieve a dry mass of 40 tonnes it would make a very useful reusable SSTO.

Now this is an interesting bit, if accurate.  For those looking at commonality with MCT to replace Falcon, here you have it.  Not a new Raptor powered SFR.  The MCT spacecraft acting as a SSTO LV.
Of course, most unmanned paylaods are not just going to LEO, so a kick stage or something would need to be used for BLEO trajectories.  And that kick stage would need to be significantly cheaper than F9US to make any economic advantage over F9R or FHR.
But interesting, nontheless.

Except the Vac-optimized Raptors may not have enough thrust to get it off the ground nor the Isp to get to orbit. Just because it might conceivably get 9km/s in free space doesn't mean it is a SSTO.

If there was a cluster of 5 Raptors, they could do something clever like making the four outer engines sea level Raptors, and just the central engine vacuum Raptor.  The outer booster engines would be shut down at the optimal point during ascent and the rest of ascent done on just the central vacuum Raptor.  By that point enough propellant would likely have been burned so that the single 500klb upper stage engine can finish the job.

Again, unless only going to LEO, I don't know that this gains anything over Falcon.  But interesting.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 06/18/2015 04:32 pm
Quote
15m diameter vehicle (this was hited at not actually specified by SpaceX

How and where (by whom) was this "hinted at"? What was the actual wording?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/18/2015 04:35 pm
I have just noticed this year's number for the raptor engine, at 230 tonnes rather than 820 tonnes (Raptor engine Wikipedia article).  As this is a direct quote from Musk, it seems cannon.  That means something like 28+ engines for the fully fuelled ship on Earth.  That probably doesn't fit on a 10m core.  So the single core design would have to be larger, leading to a very short rocket, 35 to 40 m high for a 15m core, for example.  Is that the present consensus, more or less?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/18/2015 04:38 pm
Now this is an interesting bit, if accurate.  For those looking at commonality with MCT to replace Falcon, here you have it.  Not a new Raptor powered SFR.  The MCT spacecraft acting as a SSTO LV.
Of course, most unmanned paylaods are not just going to LEO, so a kick stage or something would need to be used for BLEO trajectories.  And that kick stage would need to be significantly cheaper than F9US to make any economic advantage over F9R or FHR.
But interesting, nontheless.

As I said above, not likely to be feasible in my opinion, as 40 tonnes seems too little mass for MCT. However, if it was possible, it would be in a universe of propellant transfer in LEO (probably from a depot) and so ability to only get to LEO would be no handicap, no kick stage needed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/18/2015 04:53 pm
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
Thanks, this is a great summary.   I guess this means not much water based radiation shielding?  And if as Guckyfan proposes there is no final injection burn, not much fuel at the end for radiation protection either?

One item I forgot to mention was the number of Raptors on MCT would be 5 to give a 3g liftoff at Mars with immediate 1 engine out continue mission capability. Later in Mars launch even 2 engines out would still enable continue mission. A very low risk value for mission success results from this.

Edit added: GLOW at Mars liftoff would be 965mt or 2.135Mlb more than 2x the GLOW of the F9v1.0. (65mt dry weight [40mt vehicle 25mt payload]). The MCT is not a small vehicle. It could conceivably reach Earth orbit as an SSTO witha  little payload about 20mt.

Atlas,

Hmmm...this all looks pretty familiar.  :-)

Thanks for fleshing that concept of mine out a bit more.  Putting some numbers with concept is interesting.

I too have been speculating the advantages of a 5-engine cluster on MCT, for reasons of engine-out.  It would basically allow for an engine out during Earth ascent to LEO (although an engine out then would likely result in that MCT being recalled and mission aborted).  Obviously it'd allow for engine out during TMI.  It would allow for an engine out during Mars liftoff and ascent, or at TEI burn.
And -if- MCT were to land on Raptor vs. dedicated landing thrusters, it would allow various engine out contingency options during EDL.

Seems like a good bit of backup.

I do agree that 40mt is probably too optimistic.  The S-II stage was about 45mt dry, and it had a volume of ~1800m^3 as well.  If SpaceX were making an equivalent expendable stage to the S-II, I'm sure they could make it lighter, given modern methods and materials.  But Making it a reusable spacecraft I think it would be at least somewhat heavier.
If it's dry mass were 100mt (as has been often guestimated as a nice round number in this thread), what would the performance numbers be then?  Just to make a more conservative number, for the sake of discussion?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/18/2015 04:55 pm
I have just noticed this year's number for the raptor engine, at 230 tonnes rather than 820 tonnes (Raptor engine Wikipedia article).  As this is a direct quote from Musk, it seems cannon.  That means something like 28+ engines for the fully fuelled ship on Earth.  That probably doesn't fit on a 10m core.  So the single core design would have to be larger, leading to a very short rocket, 35 to 40 m high for a 15m core, for example.  Is that the present consensus, more or less?

Note Elon said "Thrust to weight is optimizing for a surprisingly low thrust level, even when accounting for the added mass of plumbing and structure for many engines. Looks like a little over 230 metric tons (~500 klbf) of thrust per engine, but we will have a lot of them :)"

Don't read into it more than he said. There are other things to optimise, including cost, reliability, maintainability and manufacturing. When these and other factors are taken into account they may decide to go for a bigger engine.

That said my opinion is that they will end up with a slightly larger engine at maybe 250-270 tonnes. The size will be driven mainly by using 5 (which would give the best balance or T/W and engine out IMHO) of them on the MCT.

A short stubby BFR seems to be the consensus, with MCT on top it is still going to be pretty tall, perhaps 60-70m in total.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/18/2015 05:13 pm
For an MCT that has a vehicle weight of 90mt (the heavy pessimistic version vs the light weight optimistic version)

-Mars liftoff GLOW 1265mt (1150mt of propelant)
-Earth liftoff GLOW (on top of BFR 1st stage) 1340mt with a delta v of 7.3km/s (which is still > 6.5km/sec needed on top of the 1st stage 3km/s capability to reach LEO + margins)

Would need ~8 tankers to load prop for Mars departure in 100mt increments. Needs additional prop to do the remaining 5.8km/s delta v that its residual prop capability of about 1km/s cannot meet the 6.8km/s for TMI (using direct entry no orbiting Mars).

As for the 15m diameter this was established because of the bell size (calculated from the rocket equation for 1atm) of a 500klbf Raptor and the number of them required (~31) in order to get ~200mt into LEO. 12m is just not big enough. Plus for this heavier MCT (90mt vehicle dry weight) a diameter of 20m would work better giving it a 20m diameter and 30m height in capsule like shape where it would have up to 2500m^3 of payload volume. A 15m diameter  lighter MCT would have only about 1500m^3 of payload volume.

BTW a Earth SSTO version (90mt dry weight) with 5 340 ISP Raptors and 15mt of payload could do ~8.5km/s. A very minimal orbit that would quickly decay. A 2mt kick motor would turn this vehicle into a F9R sized payload vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/18/2015 05:27 pm
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
That gives you and MCT with a ΔV of 7.475 km/s (380 isp) I am under the impression that ΔV budget of 4.5km/s worst case for LEO-Mars TMI and that variably we have been discussing needs in the order of 1kms for EDL presuming Aerocapture/braking.  That leave us with a need for about 5.5km/s, since making LEO as a 2nd stage for F9 needs about 5.9, I am happy with making 6.2km/s the round number leaving a healthy margin of fuel for Earth EDL.  At 6.2km/s and 380isp I see the amount of propellant needed for the dry weight and payload you mentioned being 600t at launch, and 472t leaving LEO.
However, personally, even with the smaller propellant load, I would presume MCT's dry weight (which includes potentially some active cooling for propellant and/or sun shades/reflectors, solar power, a higher proportion of RCS than your average US, and several other systems not seen on upper stages) is 60t.
I see it launching with less than full cargo though and having a full tank for the TMI burn.

Can you tell me where your 7.475km/s came from (or where I might have made an assumption about your vehicle concept that reduces its ΔV)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/18/2015 05:41 pm
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
That gives you and MCT with a ΔV of 7.475 km/s (380 isp) I am under the impression that ΔV budget of 4.5km/s worst case for LEO-Mars TMI and that variably we have been discussing needs in the order of 1kms for EDL presuming Aerocapture/braking.  That leave us with a need for about 5.5km/s, since making LEO as a 2nd stage for F9 needs about 5.9, I am happy with making 6.2km/s the round number leaving a healthy margin of fuel for Earth EDL.  At 6.2km/s and 380isp I see the amount of propellant needed for the dry weight and payload you mentioned being 600t at launch, and 472t leaving LEO.
However, personally, even with the smaller propellant load, I would presume MCT's dry weight (which includes potentially some active cooling for propellant and/or sun shades/reflectors, solar power, a higher proportion of RCS than your average US, and several other systems not seen on upper stages) is 60t.
I see it launching with less than full cargo though and having a full tank for the TMI burn.

Can you tell me where your 7.475km/s came from (or where I might have made an assumption about your vehicle concept that reduces its ΔV)

The higher values are for worst case scenarios etc in departures other than the lowest delta v departure dates + the vehicles capabilities was based on using an ISP of 385 (upgraded version of Raptor) to see how much it could do). The 380 ISP values is much less delta V capability for same prop amounts. The real key is the amount of delta  v required to leave Mars surface and head for earth, nearly 9km/s. That is what governs the MCT prop load amounts. Use as its own 2nd stage needs less propellant load so the extra propellant increases the delta v capability as a 2nd stage. So size the propellant load to get the vehicle off Mars and headed back to Earth. The 2nd stage required amount is actually less.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 05:57 pm
Mars surface to earth is much less than 9km/s. More like 7-7.5km/s.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BobHk on 06/18/2015 05:57 pm
Except the Vac-optimized Raptors may not have enough thrust to get it off the ground nor the Isp to get to orbit. Just because it might conceivably get 9km/s in free space doesn't mean it is a SSTO.

Btw how would MCT land on Earth if it had vac-Raptors?

By designing both into one engine:  https://en.wikipedia.org/wiki/Expanding_nozzle (https://en.wikipedia.org/wiki/Expanding_nozzle)

Hard to make it work but beneficial if you can.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/18/2015 06:09 pm
Mars surface to earth is much less than 9km/s. More like 7-7.5km/s.

But still the largest delta v requirement. At some point for growing vehicle dry weight other delta v requirements become larger. A 90mt vehicle weight may even be beyond that point. But leaving Mars surface it would be prudent to have significantly more capability than just the minimum. The item here is that use as 2nd stage to LEO, use as EDS and the use as direct return all have close to the same propellant requirements. The vehicle dry weight minus the payload weight drives which one is the driver for the amount the MCT must hold.

My values gives the information that it is doable and the reasoning behind some of the speculation on what the MCT would do.  For Earth departure you just keep filling the tanks until you get enough prop. Note here is that you need also prop for the landing phase on Mars of ~1km/s or more based on the vehicle shape and weight.

Edit: Difference between 2nd stage or EDS and Mars liftoff is payload size 100mt vs 25mt.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/18/2015 06:23 pm
So, a few thoughts on MCT's TPS system.  Impaler has made the point that if coming in from interplanetary speeds, a metallic heat-absorption type TPS probably won't be able to handle that direct entry head load without the heat bleeding through and melting the structure.  And that the shuttle had ground support equipment to circulate cooling behind the TPS to prevent this from happening, which MCT won't have on Mars....at least for some time.

Now if you look at the SpaceX F9US-R concept, and the Rocketplane Kistler K-1 concept, they both only had a heat shield on a blunted nose.  Presumably that'd be an ablator as it'd be a relatively small surface area to take a large heat load.  But presumably enough engineering went into both to give the idea that the concept would work.

So, what if MCT basically looked like F9US-R and the K-1 (as I've speculated in the past), with a replaceable ablator on the nose, but fully reusable metallic TPS around everything else, which would pretty much compromise the skin.  Rather than the traditional biconic concepts with the TPS on just one half, this metallic would wrap the entire vehicle.  The ablator nose would take the severe heat load, but after a certain amount of deceleration, MCT would pitch over and start to "fly" like a biconic as it continued to decelerate.  That way the metallic TPS wouldn't get overheated for it's head absorption capacity.  Also, the primary reentry forces would be transferred directly along the axis, where a pressurized cylinder is the strongest, and not have the bending forces subjected to it like for a full "belly" reentry.

Moreover, for this we'd put the crew/cargo at the bottom, between the engine and the bottom of the tanks. in this way, the metallic TPS is backed by the tank skin all the way to very back of the vehicle, which has cryogenic temp residual liquids in it, which could absorb excess heat bleeding through the TPS system, and vent off the boiloff gasses, or collect it and use it for the RCS thrusters.  (Obviously you must be sure to not boiloff too much so there's enough liquid propellant to land).  So it'd be hard to soak enough heat into the structural tank to cause a problem because of the cold liquids and gases on the other side, I would think.
And the ablator on the nose would be backed by the pressurized tank dome, rather than by an unpressurized cargo hold or a crew cabin.  So it'd have a nice, evenly distributed support behind it from that.  Not mention the advantages of having the crew/cargo down at that bottom once on the surface.

Possibly, if there's a full wrap around engine skirt so the engines would be protected on all sides, if needed, perhaps MCT could roll over during EDL do actually distribute the heating evenly around the full circumference.  Do a "rotisserie" maneuver as the Apollo astronauts called what they did with the CSM during the transits.  (The crew may not be a fan of that however, heh)

The metallic panels would be attached to the cryogenic tank wall as part of an integrated airframe concept, as talked about in this paper which can be Googled to find...the link is too long to post.

AIAA 2002-0502
Metallic Thermal Protection System
Technology Development: Concepts,
Requirements And Assessment Overview

Quote
The TPS is attached to the tanks and intertank structures through the TPSS. Depending on the tank structural concept and stiffening arrangement, the TPSS may be attached to external stiffeners, such as ring frames and longerons, or to the outer skin of a sandwich tank structure.

So something like that.

Finally, if MCT were a symetrical cylinder with a bunt nosed ablator on top, that means theoretically, all such metallic TPS panels would be identical.  If you had a multi sloped biconic or triconic, or an asymmetrical biconic or lifting body of some sort, you'd have tiles of various shapes depending on their location...not unlike the Shuttle's.  But if you just have a basic cylinder, every tile should be the same shape no matter where it goes.  Which would make fabrication and repair much cheaper and more simple between missions, or possibly even on Mars.

Bottom pic is the 5-engine Raptor cluster on MCT with wrap around protective skirt.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 06:30 pm
Yeah, I agree it probably I the largest delta-v requirement. Although 100-120 day Earth to Mars transits are pretty brutal, it helps a lot if you fill up last at high orbit like EML1/2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 06:34 pm
MCT will only be reused 15-30 times (once each for Mars entry and Earth entry), so for the crew version, PICA-X may be fine, perhaps with TPS replacement every decade or so. Metallic TPS probably doesn't make sense for MCT, except for perhaps a tanker or cargo version that would just travel to LEO but could be reused hundreds or even thousands of times and which isn't as mass-sensitive.

PICA-X should be just fine for MCT, though, if it works as good as SpaceX says it does. metallic would be suboptimal except for tanker/cargo duty.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/18/2015 06:36 pm
As a note, it occured to me where Rocketplane Kistler must have gotten then idea for the shape of the K-1.

;-)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/18/2015 06:55 pm
As a note, it occured to me where Rocketplane Kistler must have gotten then idea for the shape of the K-1.

;-)

George Mueller has been around for a long time (96yrs old!). He was there to manage things when Saturn V was being stacked before becoming Kistler Aerospace CEO. Also many other guys in Kistler had roots back to Redstone age. It was the newoldspace :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 06/18/2015 07:10 pm
Mars surface to earth is much less than 9km/s. More like 7-7.5km/s.

But still the largest delta v requirement. At some point for growing vehicle dry weight other delta v requirements become larger. A 90mt vehicle weight may even be beyond that point. But leaving Mars surface it would be prudent to have significantly more capability than just the minimum. The item here is that use as 2nd stage to LEO, use as EDS and the use as direct return all have close to the same propellant requirements. The vehicle dry weight minus the payload weight drives which one is the driver for the amount the MCT must hold.

My values gives the information that it is doable and the reasoning behind some of the speculation on what the MCT would do.  For Earth departure you just keep filling the tanks until you get enough prop. Note here is that you need also prop for the landing phase on Mars of ~1km/s or more based on the vehicle shape and weight.

Edit: Difference between 2nd stage or EDS and Mars liftoff is payload size 100mt vs 25mt.

     I'm thinking that there may be more involved with the Fairing recovery concept than simply holding down launch costs.  It could be that any fuel tankage launched into orbit by SpaceX would be designed with minimal RCS, TPS, avionics and recovery equipment (parachute) for reuse.

    I'm also wondering about their choice to launch the pad abort with the trunk still attached.  Stability could be the reason, but one would think that with computer controlled throttling, that really shouldn't be an issue.  If the MCT lander is essentially a scaled up Crew Dragon, it could be that the main cargo and habitat for the passengers would be carried in a "trunk" style structure, to be released to it's own soft landing after atmospheric interface.  A strictly cargo and habitat module could take a rougher ride to landing, using Soyuz style retrothrust in the last seconds before landing, while the MCT itself would accomplish a propulsive landing after seperating from the Hab/cargo trunk.

     The habitat/cargo section can be made lighter than the MCT itself, as it is designed to be kept on Mars and won't have to go through launch and landing stresses more than one time.  (It may also be made as a specialized Bigelow Olympus class inflatible with seperate modules that could be linked to it as well).     
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/18/2015 07:17 pm
MCT will only be reused 15-30 times (once each for Mars entry and Earth entry), so for the crew version, PICA-X may be fine, perhaps with TPS replacement every decade or so. Metallic TPS probably doesn't make sense for MCT, except for perhaps a tanker or cargo version that would just travel to LEO but could be reused hundreds or even thousands of times and which isn't as mass-sensitive.

PICA-X should be just fine for MCT, though, if it works as good as SpaceX says it does. metallic would be suboptimal except for tanker/cargo duty.

So how would the PICA-X be arranged?  Just on the nose like F9USR and K-1?  Or on the nose and along one half of the cylinder like most biconic concepts?
And how long would/could the PICA-X be made to last?  Assuming two EDL's per round trip, and no more than 1 trip every 2 years, would mean 5 trips per decade max per MCT, and 10 EDL's?  I think Dragon's PICA-X is supposedly good for 10 EDL's, but that's from LEO reentry speeds. 
The idea is to not have to replace the whole TPS system too often.  If it only needed replaced once a decade, that wouldn't seem to be too cumbersome.

A tanker MCT could do several LEO EDL's per year though.  Then again, from LEO, metallic TPS should be adequate without the overheating issues of interplanetary return?

But do they want two different TPS configurations?  I would think they might rather go with a common platform.  Would replacing a PICA-X TPS on a cargo/tanker MCT be too cumbersome to do every 10 missions? (which could be within one year theoretically)  Can PICA-X tiles be made to last more than 10 LEO reentries?  Or would that be overly heavy?

Maybe a cargo/tanker MCT could have the PICA-X just on the nose like F9US-R and K-1, as it would be coming back only from LEO speeds like them, and would be uncrewed, so fairly high g-loading for that reentry profile wouldn't be a problem for humans.  That's be a pretty ballistic reentry without much lift vs. a belly entry.  But SpaceX and Rocketplace Kistler seemed to think it would work without crushing their beer cans.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/18/2015 07:28 pm
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
15m diameter and other such details have not been mentioned. Please cite your sources and put the source quote in the MCT source thread so we know exactly what was said: http://forum.nasaspaceflight.com/index.php?topic=37839.0

I remember Shotwell I think saying something about 15m.  I think it was in the context of a question comparing it's scale to Saturn V.  I think she said it'll be wider than Saturn V, maybe as much as 15m wide.

But the reference was from awhile ago, if memory serves, before she made the comment about it being too big for pad 39A even.  And as we know, MCT's design appears to be very much in flux, so it may not be relevant any more, but I Think that's what Atlas was referring to by 15m being "hinted at". 

If I can dig up her actual quote somewhere, I'll post it on your other thread.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/18/2015 07:47 pm
I really don't understand why SpaceX would not limit the BFR to 12 million lbs thrust to take advantage of the Kennedy, then so what if they can only get 75 tons to Mars on MCT instead of 100.  Once this BFR/MCT gets going, it will put SLS out of business since it will cost less and the entire Kennedy facility with 4 high bay doors and room for 6 BFR/MCT rockets at a time.  That would save SpaceX a ton of money, it seems to me, building the infrastructure for such a large rocket.  What would Kennedy be limited to 14m in diameter and 12 million lbs thrust?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 07:55 pm
MCT will only be reused 15-30 times (once each for Mars entry and Earth entry), so for the crew version, PICA-X may be fine, perhaps with TPS replacement every decade or so. Metallic TPS probably doesn't make sense for MCT, except for perhaps a tanker or cargo version that would just travel to LEO but could be reused hundreds or even thousands of times and which isn't as mass-sensitive.

PICA-X should be just fine for MCT, though, if it works as good as SpaceX says it does. metallic would be suboptimal except for tanker/cargo duty.

So how would the PICA-X be arranged?  Just on the nose like F9USR and K-1?  Or on the nose and along one half of the cylinder like most biconic concepts?
And how long would/could the PICA-X be made to last?  Assuming two EDL's per round trip, and no more than 1 trip every 2 years, would mean 5 trips per decade max per MCT, and 10 EDL's?  I think Dragon's PICA-X is supposedly good for 10 EDL's, but that's from LEO reentry speeds. 
The idea is to not have to replace the whole TPS system too often.  If it only needed replaced once a decade, that wouldn't seem to be too cumbersome.

A tanker MCT could do several LEO EDL's per year though.  Then again, from LEO, metallic TPS should be adequate without the overheating issues of interplanetary return?

But do they want two different TPS configurations?  I would think they might rather go with a common platform.  Would replacing a PICA-X TPS on a cargo/tanker MCT be too cumbersome to do every 10 missions? (which could be within one year theoretically)  Can PICA-X tiles be made to last more than 10 LEO reentries?  Or would that be overly heavy?

Maybe a cargo/tanker MCT could have the PICA-X just on the nose like F9US-R and K-1, as it would be coming back only from LEO speeds like them, and would be uncrewed, so fairly high g-loading for that reentry profile wouldn't be a problem for humans.  That's be a pretty ballistic reentry without much lift vs. a belly entry.  But SpaceX and Rocketplace Kistler seemed to think it would work without crushing their beer cans.
Basically, yes, this is my thought process.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/18/2015 08:00 pm
I really don't understand why SpaceX would not limit the BFR to 12 million lbs thrust to take advantage of the Kennedy, then so what if they can only get 75 tons to Mars on MCT instead of 100.  Once this BFR/MCT gets going, it will put SLS out of business since it will cost less and the entire Kennedy facility with 4 high bay doors and room for 6 BFR/MCT rockets at a time.  That would save SpaceX a ton of money, it seems to me, building the infrastructure for such a large rocket.  What would Kennedy be limited to 14m in diameter and 12 million lbs thrust?
They may have some clever ideas about how're get beyond usual limits, maybe how to reduce acoustic loads, as we already heard from what's his name's LC39A pad tour. Additionally, they could operate at lower thrust initially.

But only for initial flights. They will want their own launch facility.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/18/2015 11:41 pm
A small forward facing heat-shield won't present enough surface area to slow down on Mars, you would probably impact the surface at high speed, also the L/D ratio would be very low or possibly nill in this configuration which results in even worse heat and g-forces.  A smaller ballistic coefficient works on Earth because we have a much deeper atmosphere to slow down in.

I don't know  how to calculate the ballistic coefficient of a bi-conic though, I think it is more complex then simply the cross-sectional area which is itself highly dependent on angle of attack.

I have to agree with earlier statements that a 40 mT MCT that dose single stage Earth return is not realistic. The 'long poles' are 7.5 kms DeltaV (btw did anyone account for landing on Earth in this math) and 14 kms Entry velocity both of which are HUGE.

My own conservative thought is for 5.1 kms DeltaV (launch and land on Mars) and 3.5 kms Entry velocity, both radically lower demands and I'd allocate 75-100 mT for it to allow for generous mass growth.

If SpaceX could build the first vehicle for 40 then they can certainly do the latter for even less which translates to even more cargo, safety margin and lower cost.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/19/2015 12:19 am
A small forward facing heat-shield won't present enough surface area to slow down on Mars, you would probably impact the surface at high speed.  A smaller ballistic coefficient works on Earth because we have a much deeper atmosphere to slow down in.

My original thought was such a shield could do the initial deceleration and ablate enough of the thermal energy that the cylinder wrapped in a metallic TPS could then take the remaining heat load while MCT were to transition from ballistic entry to "belly" entry.  It could then present enough surface area to get down to supersonic terminal velocity.  Essentially the PICA-X nose would shunt enough heat that the metallic TPS wouldn't get over heated, as you were saying it likely would if coming directly in with only metallic TPS.  I'm not sure it would work, but was just thinking aloud.  In this way, only the relatively small and simple geometry of the nose would need to be periodically replaced, rather than a whole half of a cylinder or biconic.

But, as Robot pointed out, MCT heading to Mars physically could never do more than two EDL's every two years.  Maybe more like four if they need to be staged Mars Direct style where the arriving crew transfer to an MCT already on the surface and fueled, while theirs begins fueling itself for the next crew.  Depnding on refueling times and mission options.
So an ablative full belly/nose TPS could potentially go for a decade before being replaced if it could handle 6 or 8 EDL's before it ablated too far.

MCT's (or dedicated upper stages in your scenario) only going back and forth to LEO could then use just a metallic TPS, as they'll only see LEO reentry speeds, but could go through 10-12 reentries per year potentially. 
Or, theoretically, it could have just an ablator on the nose as it'll only be coming back from LEO speeds.  RPK and SpaceX seemed to think a ballistic entry like that would work, rather than needing to to a belly entry.

So some interesting options, if LEO MCT's/upper stages and Mars MCT's were to have a bit different TPS configuration from each other.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/19/2015 12:45 am
Peak heat is also peak deceleration, small forward face delays deceleration in time and in depth into the atmosphere so the time remaining to do any other deceleration is reduced even if your able to increese your cross-sectional area and create more drag.  It's the same principle as opening a parachute on Mars, if your too late you impact the surface so I favor presenting maximum surface area as soon as possible.

And even under my lower velocity entry assumption something like ceramic tiles may be needed on the nose and control flaps, stagnation point temperatures can still be quite high. 

I don't favor any kind of ablative because I believe we can eventually do more then 2 EDL per synod by sending cargo containers outside of a vehicle and loading them into the lander in Low Mars orbit.  Then landing unloading refueling and returning to orbit with enough propellent to land again.  At a generous 1 week turn around one landing can bring down ~100 cargo loads per synod, so an indefinite lifespan TPS would be needed for that.  While only applicable to cargo this would be a huge improvement in efficiency over the baseline of 1 cargo in 1 lander in 1 synod.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/19/2015 01:03 am

- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume


Your volume estimate is badly off, I calculate your segments are from bottom to top 1060 m ^3 for the cylinder, 1244 m ^3 for the first frustum, 261 m^3 for the top cone (which would in reality need to be blunted to some degree).

Total 2565 m^3, a 60% increase over the vehicle size I'm proposing.

Keep in mind that a F9 first stage has a volume of 480 m^3 and has dry masses of 25 mT and holds just shy of 400 mT of propellents, this should really show how absurd a vehicle with 5 times the volume holding more then twice the propellent and with all the heat shields necessary to do high speed EDL could possibly have a mass only 15 mT more then a F9 first stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/19/2015 07:19 pm
Peak heat is also peak deceleration, small forward face delays deceleration in time and in depth into the atmosphere so the time remaining to do any other deceleration is reduced even if your able to increese your cross-sectional area and create more drag.  It's the same principle as opening a parachute on Mars, if your too late you impact the surface so I favor presenting maximum surface area as soon as possible.

You are probably right.  I'm no expert on Mars EDL.  My thought was mainly an easily replaceable ablator nose cap used in conjunction with metallic TPS behind it could perhaps operate as a hybrid system that would be easier to maintain than all ablative, but not overheat at interplanetary entry speeds as metallic might.  I don't know how long it would take from the time a conical shape presented it's full cross section during EDL until it reaches it's terminal velocity, which is what's needed before the final retro propulsion and landing.  If it could reach terminal velocity after presenting just it's nose, then transition to belly presenting it's full cross section and also reach terminal velocity in time to do the retro burn and landing, then that was my thinking.
Of course, if it's still has not slowed down to terminal velocity by the time it needs to do the final burn and landing, then as you say, this won't work and will crash, or would need more retro propulsion, which defeats the purpose.
Again, just thinking aloud.

And even under my lower velocity entry assumption something like ceramic tiles may be needed on the nose and control flaps, stagnation point temperatures can still be quite high. 

The problem with ceramic, as with the shuttle as I understand, is they are relatively fragile and more subject to MMOD strikes than metallic or ablator.  MCT will have it's TPS exposed to open space far more than the Shuttle, as well as on the surface stay.  But if you kept the amount to a minimum, the dangers are more minimized.

I don't favor any kind of ablative because I believe we can eventually do more then 2 EDL per synod by sending cargo containers outside of a vehicle and loading them into the lander in Low Mars orbit.  Then landing unloading refueling and returning to orbit with enough propellent to land again.  At a generous 1 week turn around one landing can bring down ~100 cargo loads per synod, so an indefinite lifespan TPS would be needed for that.  While only applicable to cargo this would be a huge improvement in efficiency over the baseline of 1 cargo in 1 lander in 1 synod.

In your preferred method that'd be a valid concern. 
With the direct approach Robot and I have been preferring, MCT would only do 1 EDL every synoid.  (1 Mars EDL during one synoid, and 1 Earth EDL for the next synoid, then back to Mars the next synoid, repeat).
So that'd be just one EDL every 2 years.  Just 6 in 12 years/3 round trips, with only 3 of them being the hotter Earth EDL's.  So as an example, assuming a single PICA-X ablator TPS can withstand 3 Mars EDL's and 3 Earth EDL's from direct entry from interplanetary speeds, it would only need replaced every 12 years.  That Particular MCT may even be ready to be retired at that point just due to 12 years of improvements/developments, and just the riggers of such lone periods in space and on the Mars surface.  So depending on the situation, it may never need to be actually replaced, and would last the service life of the Mars-MCT.
I think SpaceX has said the Dragon ablator is good for 10 Earth EDL's form LEO.  So 3 Mars EDL's and 3 Earth EDL's from BLEO speeds should be plausible, with perhaps a bit more thickness if necessary.  Then again, it could be thinner than Dragon due to the much larger surface area of MCT and much more "fluffy" density than Dragon.  As mass will be a premium on a Mars MCT, they may make it only thick enough to handle one round trip, and then just plan to replace it every time it comes home, to save every kg on a Mars MCT.  This K-1/F9USR geometry I've mentioned would be beneficial in that case, as it seems like it'd be far easier to replace PICA-X panels on it than on a non-uniform geometry like the space shuttle belly or the belly/nose of a true biconic or triconic.  So it wouldn't necessarily have to be an expensive or laborious thing.

Now, for the direct approach Robot and I have been favoring, there would be a depot, with many tanker missions to fill it up in preparation for a Mars MCT launch.  So there'd be a valid issue about the TPS system on those, and if they'd be any different than Mars MCT?  Would it be better to have a common system, and just accept the maintenance of replacing that Ablator every 10 missions or so? (That could be once a year)  And if so, maybe they could put just an ablative nosecap like K-1 and F9USR, which would be easier than doing the whole belly of it like the Mars MCT would need.  Just pull the whole nose cap off and have a new one that drops right in.  So replacement nosecaps can be prepared ahead of time to maintain these tankers.  In this way it wouldn't be much different than replacing a Dv1 heat shield.

Or go a whole different approach like metallic TPS? where you'd never have to replace the whole TPS, just individual panels that might be damaged.  That would make the tanker MCT at least somewhat different externally than the Mars MCT.  And may or may not be worth the trouble to have two different TPS systems.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/19/2015 10:38 pm
Unfortunately, NASA's funding is not purely for exploration, science, tech, etc, it is also a regional development program for Dixie and a couple other places. So you can have the coolest spaceship ever imagined for super cheap and amazing capability, and it still won't get but a small fraction of funding from NASA. Additionally, NASA is so much more than human spaceflight and launch services. $4 billion annually is the max possible I can imagine anything like BFR/MCT ever getting from NASA (in the next half century), with maybe $1-2 billion being far more likely.
This is a good point.  But it's also of note that ~$2B/year flowing into the coffers of SpaceX would really help with expeneses.  If they made $50M profit per Falcon launch, $2B would be the equivalent of about 40 Falcon launches per year worth of profit.

So I think it'd certainly help things out to have that, and provide maybe 2 lunar missions per year intially with 1-2 Mars missions per synoid later that NASA has seats on and input into where they land, etc.

The Mars missions would really be the deal, as SpaceX would be going there anyway.  They just have say 4 NASA astronauts along with say 3 SpaceX astronauts/spacecraft specialists on the early missions (7 total, so that a single F9/Dv2 can bring the whole crew up in one launch after MCT has docked with the depot and is all fueled up and ready to depart.  I think most NASA DRM missions were 4-6 crew, so 7 should work pretty well for the initial missions, then maybe expanding to 14...two Dv2 crew launches...for phase 2 once they start to get things figured out better, and maybe want to try to start an outpost.).

So that would be pretty much just all profit for SpaceX.

$2B/year could go a long way to aid SpaceX.  In return, NASA not only gets a HLV, they get a spacecraft, and the door to the Moon and Mars opened up to them.  A pretty good bargain for them!



Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/20/2015 05:57 am
I put this here because it seems the thread where it is least OT.

Then there's the 1st stage with expen$ive 10-15 meter tooling

It is always argued that a new tooling for a large diameter would be very expensive. But is it really true? I understand the common method is first make a circular barrel of a very thick aluminium sheet and then machine the structure in to make it light and robust. Bending a very thick sheet I imagine is expensive indeed. However with friction stir welding the sheet will be quite thin and the structure to make it robust is then welded on. Still expensive but a lot less so.

Any comments?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/20/2015 02:25 pm

- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume


Your volume estimate is badly off, I calculate your segments are from bottom to top 1060 m ^3 for the cylinder, 1244 m ^3 for the first frustum, 261 m^3 for the top cone (which would in reality need to be blunted to some degree).

Total 2565 m^3, a 60% increase over the vehicle size I'm proposing.

Keep in mind that a F9 first stage has a volume of 480 m^3 and has dry masses of 25 mT and holds just shy of 400 mT of propellents, this should really show how absurd a vehicle with 5 times the volume holding more then twice the propellent and with all the heat shields necessary to do high speed EDL could possibly have a mass only 15 mT more then a F9 first stage.

Thank you for the correction I noticed the error in the calculation of the second section and have corrected it in my spreadsheet for later use.

On weights it would be better to use Dragon and scale it up to see where the maximum weight of MCT would end up. Actual could be a value more or less than that but this estimate would be a good place to start. The weight scales with surface area increase not volume increase. The surface area increase of the MCT over a Dragon is ~ 19=exp(ln(2565/30)*2/3)^10 [Dragon having a volume defined by the surface skin of ~30m^3 (3.6m diameter in a cone 6m tall)].

Dragon weighs ~4.2mt so scaled up dry weight for MCT comes to about 80mt.

Edit: corrected math
BTW a 480m^3 1st stage weighing 25mt would give a scaled up weight for MCT of 76mt an even lighter value.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/20/2015 02:31 pm
It's a pressure vessel (and internal equipment needs internal supports) so weight scales with volume, not just area.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/20/2015 02:53 pm
It's a pressure vessel (and internal equipment needs internal supports) so weight scales with volume, not just area.

Almost half the volume of the MCT is the prop tanks. So the scaling is very complex. So if the prop tank 1000m^3 section is scaled using an F9 1st stage and the upper capsule part is scaled based on volume increase of that section over that of a Dragon the result is 41mt for the tank portion and 215mt for the other non prop section. 215mt is a very high value and the actual as you suggest will be greater than the surface area increase derived weight for the "crew" section of 58mt and probably less than this volume derived weight of 215mt. So weights using this divide and conquer method is a range of 99-256mt for the MCT weight range.

An actual vehicle weight still maybe less than the lower value so we have an upper limit but not really any lower limit except maybe the 76mt value as the absolute best possible. Also note is that the F9 1st stage weight also includes engine weight which is 9 engines at ~.8mt each or 7.2mt of that 25mt of engines and tank.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/20/2015 05:49 pm
I've seen steel pipe being made from 1/4" thick steel plate.   The plate steel is a huge roll brought in by rail.  They have rollers that can bend this plate into a long tube for 16" diameter pipe.  It is electric resistance welded without a seam down the middle.  Then it is cut to 42' lengths, beveled on the ends.  Then they sand blast to clean the pipe and a powder vinyl coating is put on the pipe to protect it from corrosion.  Then it is shipped to the gas pipeline companies.  If they can bend 1/4" thick plate steel, surely they can bend softer aluminum into a 15m diameter tube, that is a lesser bend.  Even the mill making the Falcon 9 could probably used the same bending tools, just using larger rollers for a larger diameter.  After initial investment, they can crank out rocket tubes fairly fast.  SpaceX has proven they can make a rocket far cheaper than Atlas or Delta.  So I think the BFR/MCT can be made far cheaper than SLS and in far less time, since it isn't political.   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/20/2015 06:05 pm
Perhaps a mass estimate based on adding up the parts of the MCT would be more reasonable.

You'll need,

# of Raptors and mass of Raptor (lets assume 100:1 thrust:weight which would make them 2.3 mT each.
Thrust structure mass, probably proportional to thrust, few good examples to base a comparison on
Tank volume and tankage fraction, F9 tanks are reasonable basis for comparison
Surface Area and mass per unit area of Thermal protection
Structural mass, probably proportional to internal volume and peak g-forces.
Landing legs, I've read that these are generally 10% of touch down mass.
Auxiliary systems, solar panels, radiators, batteries, avionics etc etc, again hard to estimate.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/20/2015 07:14 pm
Raptors would likely have a thrust to weight ratio at least competitive with Merlin 1D. They will be high pressure staged combustion, so although they'll be methane-fueled (not kerosene), they should still get at least Merlin 1D's level of performance. Merlin 1D has a thrust-to-weight-ratio of about 150.

The first stage should have a mass ratio of about 25 (including the landing legs, assuming propellant densification).

Assuming 15 million pounds of thrust (source is here: http://forum.nasaspaceflight.com/index.php?topic=37839.msg1391925#msg1391925 ), and 500klbf thrust per Raptor (source: http://forum.nasaspaceflight.com/index.php?topic=37839.msg1390942#msg1390942 ), then 30 Raptors looks reasonable. Note that these two figures weren't given at the same time, so it's possible the thrust of BFR/MCT will be different (and also number of Raptors), but my bet is they're likely to be fairly close to what BFR/MCT was supposed to be at the time of the AMA, based on other things mentioned there.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/20/2015 08:38 pm
The reason the MCT dry weight is so important is that everything else is dependent on that. The 1st stage must be able when combined with the MCT spacecraft be able to put the MCT into orbit with 100mt of payload. Without the dry weight of the MCT you cannot specify how much propellant the MCT must hold (this is an iterative process with dry weight) and thus how large and how many engines are necessary for the 1st stage BFR. Everything returns back to the dry weight. The Raptors have less unknowns than the MCT dry weight. For the most part 5 Raptors on the MCT itself should be able to support quite a range of MCT weight unless it gets to heavy then the number would probably increase to 7 or 9 if things are really bad. Once you get to 9 that means that 15m for the diameter of the 1st stage is not going to be large enough you will need significantly more than 30 engines.

When I broke out everything except the heat shield as separate estimates the estimate did not change very much it reduced to 97mt from the 99mt earlier value. Unless there is some magic weight savings from somewhere I think the dry weight is going to be close to 100mt. It has been estimated way back that the reason SpaceX has hinted at the BFR being able to orbit 200+mt is that the MCT will weigh 100mt and carry a 100mt payload. I am beginning to believe that may be the right value to use since our estimates are narrowing in on the same value of ~100mt for the MCT dry weight.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/20/2015 08:45 pm
Why would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?

I would guess more like 30-35 tons.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 06/20/2015 08:49 pm


Perhaps a mass estimate based on adding up the parts of the MCT would be more reasonable.

You'll need,

# of Raptors and mass of Raptor (lets assume 100:1 thrust:weight which would make them 2.3 mT each.
Thrust structure mass, probably proportional to thrust, few good examples to base a comparison on
Tank volume and tankage fraction, F9 tanks are reasonable basis for comparison
Surface Area and mass per unit area of Thermal protection
Structural mass, probably proportional to internal volume and peak g-forces.
Landing legs, I've read that these are generally 10% of touch down mass.
Auxiliary systems, solar panels, radiators, batteries, avionics etc etc, again hard to estimate.
I like this method for estimation better than just scaling up Dragon (or just random guessing ;) .)

Was that 10% of touch down mass or touchdown weight?  On Mars, it will have 100 tons of cargo but at a fraction of the gravity.  Earth landing should be less 0-20 tons of cargo.

The structural mass depends a lot on design details.  For example if the crew/cargo section is below the propellant tanks, the walls have to be beefed up to support the full propellant load (~1000 tons) through max Q.  Also, having the TPS somewhere other than the bottom (top or side), requires it to be beefed up further to handle load in multiple directions.

I think that there will only be a pressurized version (as opposed to an un-pressurised cargo version) for reasons of the cargo/crew pressure vessel doing double duty as the support structure, just like the propellant tanks.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/20/2015 09:07 pm
Why would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?

I would guess more like 30-35 tons.

Just the propellant tank portion, 5 Raptor engines and possibly landing legs too would weight ~40mt. Now add the reentry shield and the cargo bay structure. Of course the cargo variant will not have as high a dry weight as the crew variant but where is the tradeoff in crew payload size and crew vehicle dry weight increase. If you could get the cargo variant to have a dry weight as low as 60mt then reduce the payload size of the crew variant (crew + supplies) to only 60mt on a crew variant that dry weight 100mt things will work out better in that the overall system becomes smaller. You shrink the size and maybe some savings on the propellant tank dry weight due to smaller tanks.

My only problem with the estimates is that the more detail we go the heavier the MCT gets.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oceanbluesky on 06/20/2015 09:30 pm
Sorry this is a basic but what are "rendings"? Illustrated separations of rocket stages and their components (or should the links at the top of these threads read "renderings")??

Quote
L2 MCT Rending Effort (ongoing, large collection):
http://forum.nasaspaceflight.com/index.php?topic=35307.0

Thanks for the clarification
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oceanbluesky on 06/20/2015 09:45 pm
Musk has said 80,000 people per year (and ten times as many cargo shipments), which is 1000 Passenger MCTs at once, plus 10,000 cargo MCTs (or actually, there ways around this, but it remains to be seen if they're worth it). So yeah, at any one time, there would need to be thousands of MCTs.

No, he has suggested a mature colony developed over decades would reach a population of 80k, not that eighty thousand settlers would be sent every year....
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/20/2015 09:54 pm
It shouldn't have worse dry mass per wet ton than a Falcon 9 first stage plus the fairing (not counting the heatshield).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/20/2015 09:56 pm
No, he has suggested a mature colony developed over decades would reach a population of 80k, not that eighty thousand settlers would be sent every year....

Incorrect.

https://twitter.com/elonmusk/status/273483420468932608
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oceanbluesky on 06/20/2015 11:05 pm
Incorrect.
https://twitter.com/elonmusk/status/273483420468932608

Wow!! Thanks so much for taking your time to link to his tweet. (If it were not his account I wouldn't believe he'd said that - especially after reading the article he links to in various venues several times...it seems as if the author of that article is unclear as to the timeframe of 80k and Musk is tweeting a correction. Amazing! Sorry to have wasted your time, much appreciated. 

This is a phenomenal figure. Doable, but, ten times the passenger capacity of Disney's entire cruise fleet. Their largest ship carries about four thousand passengers in luxury for a couple of weeks, with quite a bit of superfluous amenities...eventually humanity will create interplanetary cruise lines but that is still a staggering figure. Glad someone is thinking boldly.

Did this figure initially take you aback?? Were you surprised by it?? (Jeez I must be thinking small in so much of my life...that still shocks me! Anyways thank you for your time!)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/21/2015 02:24 am
Did this figure initially take you aback??

Honestly it still does.

But see it that way: combine 80000 people a year, 10 cargo flights for each colonist flight and 50 Million $ per flight the total cost of 440 Billion $ would still be below the present US military budget so certainly doable if there is a sufficiently strong motivation, like impending destruction of the earth. In that case this number could even be exceeded. But short of that?

I believe however that colonization and forming of a truly self sustaining civilization can be achieved with much more modest numbers IF the effort is sustained for a sufficiently long period. Like the present NASA budget for 100 years should be enough.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/21/2015 04:20 am


I like this method for estimation better than just scaling up Dragon (or just random guessing ;) .)

Was that 10% of touch down mass or touchdown weight?  On Mars, it will have 100 tons of cargo but at a fraction of the gravity.  Earth landing should be less 0-20 tons of cargo.

The structural mass depends a lot on design details.  For example if the crew/cargo section is below the propellant tanks, the walls have to be beefed up to support the full propellant load (~1000 tons) through max Q.  Also, having the TPS somewhere other than the bottom (top or side), requires it to be beefed up further to handle load in multiple directions.

I think that there will only be a pressurized version (as opposed to an un-pressurised cargo version) for reasons of the cargo/crew pressure vessel doing double duty as the support structure, just like the propellant tanks.

The landing gear mass is almost certainly driven by the force of impact with the surface NOT the static weight of the vehicle, in other words objects still have inertia irregardless of gravity.  And even if static weight weight were the concern you would need to size the legs based on the gross take off weight which we all agree will be greater then landing weight.

F9 first stage has 8% of dry mass in the leg system, and this is designed for flat artificial surfaces and is not carry precious human cargo.  The LEM had around 3% of touch down mass in legs, but that was a soft-touchdown with a deeply throttling engine, not the SpaceX 'hover-slam'.

I think Gross take off Weight will be ~450 mT total, not these monstrous 1000 ton figures.  And their would not be any kind of integral habitat in a 'crew' version.  Their will just be a single version with an unpressurized cargo bay into which a habitat module would be placed.

Max Q is aerodynamic pressure peak, in the Martian atmosphere it is an almost irrelevant force compared to the force experienced during launch from Earth, it is not the same as max g-forces which is what would be relevant for not crushing the vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/21/2015 09:09 am
Did this figure initially take you aback??

Honestly it still does.

But see it that way: combine 80000 people a year, 10 cargo flights for each colonist flight and 50 Million $ per flight the total cost of 440 Billion $

So .. uh .. the cargo is free?


Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/21/2015 09:20 am
So .. uh .. the cargo is free?

You are right, I miscalculated by one order of magnitude, sorry. Yes it is much higher than the US defense budget. Corrected my post.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/21/2015 09:47 am
So .. uh .. the cargo is free?

You are right, I miscalculated by one order of magnitude, sorry. Yes it is much higher than the US defense budget. Corrected my post.

Your original flight cost was calculated correctly (800 passenger flights, 8000 cargo flight, 8800 total at $50M a pop yields the $440B.

The cost of the cargo is presently unknown. My gut feeling is that the answer to question "what do you have to pack  in order to live on Mars" is quite lengthy, complex and thus expensive.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/21/2015 10:12 am

Your original flight cost was calculated correctly (800 passenger flights, 8000 cargo flight, 8800 total at $50M a pop yields the $440B.

The cost of the cargo is presently unknown. My gut feeling is that the answer to question "what do you have to pack  in order to live on Mars" is quite lengthy, complex and thus expensive.

True, I did not include the material value of the cargo.

Edit: Seems I am seriously slow this morning. Of course R7 was referring to the value of the cargo. I included only the cost of the flights.

It is really hard to make an educated guess. But it would be nowhere near the cost of present NASA payloads. Much would be COTS equipment, maybe slightly modified. Also what is dedicated Mars would not be single production items but produced in quantities for so many people.

Sometimes I use a first approximation and say the cargo is as much as transport cost. That would average 500000 $ for one t. Averaged between simple tools and Intel CPUs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 06/21/2015 04:19 pm
I would think once the flight rate of 80, 000 colonists per year is reached, the cargo requirements per colonist fight will be much less than 10:1.

By that time, the mars industrial base should be able to produce anything they need short of integrated circuits.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/21/2015 04:30 pm
I would think once the flight rate of 80, 000 colonists per year is reached, the cargo requirements per colonist fight will be much less than 10:1.

By that time, the mars industrial base should be able to produce anything they need short of integrated circuits.
See this earlier post
 http://forum.nasaspaceflight.com/index.php?topic=37808.msg1390322#msg1390322 (http://forum.nasaspaceflight.com/index.php?topic=37808.msg1390322#msg1390322)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/21/2015 04:35 pm
I would think once the flight rate of 80, 000 colonists per year is reached, the cargo requirements per colonist fight will be much less than 10:1.

By that time, the mars industrial base should be able to produce anything they need short of integrated circuits.

You may well be right. A colony needs to be well advanced to be able to absorb that many people per year. I really don't see that mass exodus happen, ever. It is just that it is not completely impossible with available ressources.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/21/2015 05:14 pm
I would think once the flight rate of 80, 000 colonists per year is reached, the cargo requirements per colonist fight will be much less than 10:1.

By that time, the mars industrial base should be able to produce anything they need short of integrated circuits.

You may well be right. A colony needs to be well advanced to be able to absorb that many people per year. I really don't see that mass exodus happen, ever. It is just that it is not completely impossible with available ressources.

As I outlined earlier it is possible with using just the BFR/MCT as the workhorse for getting to and from he Earth and Mars gravity wells in the 100mt increments. Fo getting to amd from Earth and Mars a bigger/safer vehicle with better mass/people or mass/cargo ratios would bring down costs tremendously and since the MCT's would be used almost exclusively as a quick up/down vehicle with high reuse the whole endever remains fairly cheap.

A follow on to the MCT weight design issue I developed this chart to get a handle on the design space relative to propellant and dry weights relationships for the various profiles that the MCT would have to be capable of. The highest delta v of 9km/s is a L2 return from Mars and the 7.5km/s is a direct fiery reentry return from Mars. I also added the estimated tank prop amount based on a prop tank weighing 25% of the total dry weight of the MCT. This seems to be good guideline in the MCT design. Some iteration to optimize from that point would get an accurate weight model.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/21/2015 05:32 pm
Why would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?

I would guess more like 30-35 tons.

Just the propellant tank portion, 5 Raptor engines and possibly landing legs too would weight ~40mt. Now add the reentry shield and the cargo bay structure. Of course the cargo variant will not have as high a dry weight as the crew variant but where is the tradeoff in crew payload size and crew vehicle dry weight increase. If you could get the cargo variant to have a dry weight as low as 60mt then reduce the payload size of the crew variant (crew + supplies) to only 60mt on a crew variant that dry weight 100mt things will work out better in that the overall system becomes smaller. You shrink the size and maybe some savings on the propellant tank dry weight due to smaller tanks.

My only problem with the estimates is that the more detail we go the heavier the MCT gets.

My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.

My visualization for a reusable Earth orbit tanker Upper Stage for the BFR is a slightly smaller volume all fuel vehicle that adds little to the launch weight of the BFR and has about 10% lower dry weight than the MCT cargo. Running some numbers this morning I am only seeing 120mt of propellant left over (after margins) to transfer to a depot.  Note the idea is that there doesn't need to be active cooling on the tanker since it goes immediately to its offload rendezvous.  I want this vehicle to be specially designed because operationally it flies the most. With 4.1 flights per MCT going to Mars, plus whatever flights get made to satisfy other BLEO business the depot, MCTs and other LEO and Earth based Mars infrastructure gets used for.  So a small fleet of these makes sense. Cargo MCTs may well work for just launching cargo bound anywhere in LEO or beyond and I suspect that there will  be far less volume of this than keeping the depot topped up so no need to specifically develop a LEO cargo MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/21/2015 05:52 pm
Why would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?

I would guess more like 30-35 tons.

Just the propellant tank portion, 5 Raptor engines and possibly landing legs too would weight ~40mt. Now add the reentry shield and the cargo bay structure. Of course the cargo variant will not have as high a dry weight as the crew variant but where is the tradeoff in crew payload size and crew vehicle dry weight increase. If you could get the cargo variant to have a dry weight as low as 60mt then reduce the payload size of the crew variant (crew + supplies) to only 60mt on a crew variant that dry weight 100mt things will work out better in that the overall system becomes smaller. You shrink the size and maybe some savings on the propellant tank dry weight due to smaller tanks.

My only problem with the estimates is that the more detail we go the heavier the MCT gets.

My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.

My visualization for a reusable Earth orbit tanker Upper Stage for the BFR is a slightly smaller volume all fuel vehicle that adds little to the launch weight of the BFR and has about 10% lower dry weight than the MCT cargo. Running some numbers this morning I am only seeing 120mt of propellant left over (after margins) to transfer to a depot.  Note the idea is that there doesn't need to be active cooling on the tanker since it goes immediately to its offload rendezvous.  I want this vehicle to be specially designed because operationally it flies the most. With 4.1 flights per MCT going to Mars, plus whatever flights get made to satisfy other BLEO business the depot, MCTs and other LEO and Earth based Mars infrastructure gets used for.  So a small fleet of these makes sense. Cargo MCTs may well work for just launching cargo bound anywhere in LEO or beyond and I suspect that there will  be far less volume of this than keeping the depot topped up so no need to specifically develop a LEO cargo MCT.
Yes, the depot could be a specially equipped MCT for 0 boil-off since it would have large enough tanks to refuel 1+ MCT's for Earth departure. This would make it easy to orbit the depots since they are just another cargo specialized version of the MCT which are then manufactured in the 10's to 100's.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/21/2015 06:05 pm
Why would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?

I would guess more like 30-35 tons.

Just the propellant tank portion, 5 Raptor engines and possibly landing legs too would weight ~40mt. Now add the reentry shield and the cargo bay structure. Of course the cargo variant will not have as high a dry weight as the crew variant but where is the tradeoff in crew payload size and crew vehicle dry weight increase. If you could get the cargo variant to have a dry weight as low as 60mt then reduce the payload size of the crew variant (crew + supplies) to only 60mt on a crew variant that dry weight 100mt things will work out better in that the overall system becomes smaller. You shrink the size and maybe some savings on the propellant tank dry weight due to smaller tanks.

My only problem with the estimates is that the more detail we go the heavier the MCT gets.

My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.

My visualization for a reusable Earth orbit tanker Upper Stage for the BFR is a slightly smaller volume all fuel vehicle that adds little to the launch weight of the BFR and has about 10% lower dry weight than the MCT cargo. Running some numbers this morning I am only seeing 120mt of propellant left over (after margins) to transfer to a depot.  Note the idea is that there doesn't need to be active cooling on the tanker since it goes immediately to its offload rendezvous.  I want this vehicle to be specially designed because operationally it flies the most. With 4.1 flights per MCT going to Mars, plus whatever flights get made to satisfy other BLEO business the depot, MCTs and other LEO and Earth based Mars infrastructure gets used for.  So a small fleet of these makes sense. Cargo MCTs may well work for just launching cargo bound anywhere in LEO or beyond and I suspect that there will  be far less volume of this than keeping the depot topped up so no need to specifically develop a LEO cargo MCT.
Yes, the depot could be a specially equipped MCT for 0 boil-off since it would have large enough tanks to refuel 1+ MCT's for Earth departure. This would make it easy to orbit the depots since they are just another cargo specialized version of the MCT which are then manufactured in the 10's to 100's.

I see the depot as much larger than that. I would prefer to see passenger carrying MCT's launch in pairs as close to simultaneously as possible. Also because of the intensity of the black body radiation of the earth and its daytime reflection of heat, I see the depot needing far more active cooling than the MCT which will only need to keep its propellant from boiling off near Mars and between Mars and Earth but will not need to keep it cool for long in the 10 radii range of the Earth. I also see the depot with a hab as transit station, and a place where PicaX can be recoated on MCT's along with engine swaps (engines taken off BFR tanker stages)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/21/2015 06:06 pm


My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.


I don't believe integrated habitat and direct Earth-reutrn are compatible.

The problem I see is that the mass of the habitat if it is a module or integrated will be considerably above the 25% return payload limit which Musk stated was needed to make the direct earth-return possible, and I don't think anyone can claim that Musk is being conservative in this number.

Their is simply no way to offload 75% of the mass of an integrated habitat, all the passengers, all their baggage and personal effects, even all the waste products accumulated during transit wouldn't be 75%.  You would need to actually strip out most or all the ECLSS equipment from the vehicle which really defeats the purpose of having an integrated habitat.

If it's going to be left on Mars (which is a win-win by both providing needed equipment and reducing costly return mass) then a module designed to be removed is the way to go.  I would even go so far as to advocate for a large wheeled vehicle/habitats to make removal from the lander and aggregation easier, much like this concept

(https://www.teachengineering.org/collection/cub_/lessons/cub_images/cub_mars_lesson06_figure2web.jpg)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/21/2015 06:30 pm


My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.


I don't believe integrated habitat and direct Earth-reutrn are compatible.


An integrated hab for 6-10 people could probably mass less than 25 tonnes, so it seems possible for initial missions. Later missions with more would need a larger hab and that could not be integrated.

So I believe you have made an important point, integrated habs have no long term future on the MCT, so will probably not be designed in the first place.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/21/2015 07:00 pm
Related, but going off in a slightly different direction:

My favorite,

Quote from: Musk

I mean, if you do a densified liquid methalox rocket with on-orbit refueling, so like you load the spacecraft into orbit and then you send a whole bunch of refueling missions to fill up the tanks and you have the Mars colonial fleet - essentially - that gets built up during the time between Earth-Mars synchronizations, which occur every 26 months, then the fleet all departs at the optimal transfer point.

Elon Musk at MIT
http://shitelonsays.com/transcript/elon-musk-at-mits-aeroastro-centennial-part-2-of-6-2014-10-24

One of the issues that has been discussed many times is reducing passenger travel times from the amount of time the lowest energy Hohman orbit takes, however, when you consider the launch windows for Mars, each launch window leaves you the opportunity for higher and lower energy launches that vary in flight duration by as much as 3 months more or less than the ideal Hohmann orbit. However at any time during the approximately 3 month long launch window there is an optimum energy launch to Mars and the flight profile of that launch in terms of flight duration and arrival time will have significant impact on the logistics of Mars operations:

Roughly speaking any launch that flies the optimum(for ΔV) course for its launch time that occurs before the date of the optimum Hohmann orbit launch date arrives as many days later than the Hohmann transfer would as it departs early. So if you launch 2 weeks before the optimum Hohmann orbit launch date and take the optimum orbit for that time (which goes a little outside Mars orbit then comes back to meet Mars) you travel for 4 weeks longer than the Hohmann orbit. Contrawise those launches that occur after the date of the optimum Hohmann orbit launch also have an apoapsis further out than Mars but they pass Mars long before their apoapsis. So a craft leaving 2 weeks after the optimum Hohmann orbit to Mars on the optimum path for that time, arrives 2 weeks before a flight on the Hohmann transfer.  You can cut the flight time to Mars down to about 5 months without too much extra ΔV, however if you are doing that just for passenger carrying MCT's you have to realize that he cargo launched at that time would be (if launched on the most energy efficient orbit) will be arriving much later than the people (6-7 weeks for cargo on a Hohmann transfer).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/21/2015 10:02 pm


My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.


I don't believe integrated habitat and direct Earth-reutrn are compatible.


An integrated hab for 6-10 people could probably mass less than 25 tonnes, so it seems possible for initial missions. Later missions with more would need a larger hab and that could not be integrated.

So I believe you have made an important point, integrated habs have no long term future on the MCT, so will probably not be designed in the first place.

I should have been more clear, an integrated habitat that carries all the OUTBOUND passengers (nominally 100) would be incompatible with direct Earth-return.

A small one would not be physically impossible but it would cut into outbound mass and be a poor idea, I favor simply using a smaller return module which would be landed as part of preparatory cargo missions.

Ultimately if we are talking about multiple hundreds or even thousands of colonists per year then then the only architecture that makes sense is a large 'space-liner' and 'space-freighter' transit vehicle with electric propulsion combined with much smaller landing craft that can cycle rapidly between orbit and surface at Mars and Earth. 

That's why I'm looking at much smaller landers, they flow much more easily into the kind of future high volume system that would ultimately be necessary while still being viable early exploration vehicles when paired with modest SEP stages that we can produce now.  Direct-return vehicles are essentially a dead-end configuration because they have a low maximum flight rate, so why go down that path.

Lastly you have a low risk spiral development path, as follows

1) BFR with reusable 2nd stage - Compete with SLS, launch constellation sats to LEO, multiple large satellites to GTO, larger LEO station construction, revenue streams secured immediatly.

2)  MCT lander, do some lunar landings for NASA as shake-down cruises, or as a large crew delivery vehicle to LEO stations if they are getting big enough.

3)  Develop in-situ propellent production, send it to Mars on a one way lander, retire lots of risk.

4)  SEP pusher stage that can take the lander to and from Mars, now all the parts are ready for an initial Mars landing with the crew traveling in a habitat in the lander that remains on the surface.

5) Develop a BIG transit habitat, or just buy it from Bigelow, build up a much larger base and send more people by using the transit hab and a denser 'sleeper-car' module in the lander just for brief launch-landing.

6)  Make a much bigger SEP vehicle with orbital assembly, stick 6-8 of the big transit habs on it along with hundreds of cargo containers.  Use the landers multiple times per trip to take cargo and passengers down from the larger transit vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 06/21/2015 11:30 pm

The landing gear mass is almost certainly driven by the force of impact with the surface NOT the static weight of the vehicle, in other words objects still have inertia irregardless of gravity.  And even if static weight weight were the concern you would need to size the legs based on the gross take off weight which we all agree will be greater then landing weight.

F9 first stage has 8% of dry mass in the leg system, and this is designed for flat artificial surfaces and is not carry precious human cargo.  The LEM had around 3% of touch down mass in legs, but that was a soft-touchdown with a deeply throttling engine, not the SpaceX 'hover-slam'.

I think Gross take off Weight will be ~450 mT total, not these monstrous 1000 ton figures.  And their would not be any kind of integral habitat in a 'crew' version.  Their will just be a single version with an unpressurized cargo bay into which a habitat module would be placed.

Max Q is aerodynamic pressure peak, in the Martian atmosphere it is an almost irrelevant force compared to the force experienced during launch from Earth, it is not the same as max g-forces which is what would be relevant for not crushing the vehicle.
You are correct about mass vs. weight, but I would think the Martian landing will be at lower speed due to the lower gravity (wider tolerance for v=0 altitude=0 point).  Good point about Mars GLOW though I think we would both agree that that should not be the peak force on the legs (Earth landing will).

Good comparison on the lunar lander vs F9 S1 legs.  The F9 legs had the additional constraints of having to be deployable, aerodynamic when folded, support a higher COV vehicle, and as you mentioned a higher speed impact (through the nominal should be close to 0).  Probably all the same constraints the MCT legs will have.

The reason I think they will all be pressurized is that I think having an aero shell and a separate pressure vessel is a waste of mass.  The exception to this would be if you are leaving the habitat behind on mars.  With a top or side TPS I think a pressurized volume is all but required. Are you assuming a capsule design with the TPS on the bottom? 

Regarding max Q and max Gs.  I agree with you in the general sense, but I think we may be talking past each other.  Different phases of flight have different masses, and a larger mass at a given G load requires more structure.  There are also different "sources" of force acting on the MCT (inner stage, engine thrust structure, TPS, nose).  The highest G phase will be the peak pressure on most structural members, but not all.

At max Q (earth assent) the MCT structure has to support the aerodynamic pressure plus the payload mass (times Gs) plus the full propellant mass (times Gs) (yes I'm assuming combined S2, you might not be).  My point was that certain structural members will see a higher pressure at max Q than at higher G phases of the flight (MECO, SECO, mars assent, and mars or earth entry)

Edit: spelling
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/22/2015 01:42 am

You are correct about mass vs. weight, but I would think the Martian landing will be at lower speed due to the lower gravity (wider tolerance for v=0 altitude=0 point).  Good point about Mars GLOW though I think we would both agree that that should not be the peak force on the legs (Earth landing will).

Agree that static weight is not an issue, it is speed of impact with the surface.  But I disagree that gravity will be the main determinant of that, on both Mars and Earth the vehicle will be under propulsive decent and gravity is simply a part of that 'dance' the Raptor engine is TOO MUCH thrust to hover on at either Earth or Mars (230 mT hover on Earth, 605 mT on Mars), no one belives MCT would have that much mass at touchdown.  I favor a set of vernier engines specifically to make a softer touchdown (and avoid cratering the surface)

Good comparison on the lunar lander vs F9 S1 legs.  The F9 legs had the additional constraints of having to be deployable, aerodynamic when folded, support a higher COV vehicle, and as you mentioned a higher speed impact (through the nominal should be close to 0).  Probably all the same constraints the MCT legs will have.

LEM landing legs deployed too, though not nearly as much as F9, I think Apollo was also trying DESPERATELY to shave mass on everything, often leaving little or no safety margin.  SpaceX is going to make more robust systems as they want these things to not break which makes them both safe and reusable.  A comparison of the actual design threshold impact speed would be an interesting comparison.  Lastly the F9 landing legs have to have a very wide stance to accommodate the tall slender vehicle (and it is still falling over as of the last attempt), LEM was very squat which it needed because it landed on some considerable slope angles.

The reason I think they will all be pressurized is that I think having an aero shell and a separate pressure vessel is a waste of mass.  The exception to this would be if you are leaving the habitat behind on mars.  With a top or side TPS I think a pressurized volume is all but required. Are you assuming a capsule design with the TPS on the bottom?

I have never heard of an space vessel in which the outer aero shell IS the pressure vessel, I would speculate that it presents for too much of a thermal pathway into the vessel and would literally COOK the passengers, note that reentry capsules get quite warm inside during re-entry and this is with considerable insulation between the TPS and pressure vessel.  So I do not believe what your describing is possible.

Leaving habitats on surface is exactly what I proposed.  The overall shape I'm going with (originally Lobo's configuration) is that of a biconic with TPS on the top/sides, engines and legs on the bottom and an unpressurized cargo-bay door on the side.

Regarding max Q and max Gs.  I agree with you in the general sense, but I think we may be talking past each other.  Different phases of flight have different masses, and a larger mass at a given G load requires more structure.  There are also different "sources" of force acting on the MCT (inner stage, engine thrust structure, TPS, nose).  The highest G phase will be the peak pressure on most structural members, but not all.

At max Q (earth assent) the MCT structure has to support the aerodynamic pressure plus the payload mass (times Gs) plus the full propellant mass (times Gs) (yes I'm assuming combined S2, you might not be).  My point was that certain structural members will see a higher pressure at max Q than at higher G phases of the flight (MECO, SECO, mars assent, and mars or earth entry)

Edit: spelling

I see your point, both forces are unique and would need to be evaluated separately on each part of the ship.  G-force max is generally right before 'burn out' aka at the last bit of propellent being used, a throttle down on the engines is typically employed to limit this g-force.  As the MCT will have less cargo on Mars launch it is likely that max g-force is felt on Mars assent, or alternatively they simply do a deeper throttle-down to keep the peak comparable to the peak experienced at Earth.  I think the force limit will be comparable to what a Dragon capsule experiences.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 06/22/2015 02:27 am
A 5-person crew's luxurious tourist hab is a 25-person crew's adequate expedition hab is a 100-person crew's short-term transfer hab.  Design once, and use it for multiple campaigns.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/22/2015 02:45 am
A 5-person crew's luxurious tourist hab is a 25-person crew's adequate expedition hab is a 100-person crew's short-term transfer hab.  Design once, and use it for multiple campaigns.

The only thing that would be common to all three of these would be the pressure vessel and the means of securing it inside the vessel (assuming your talking about a removable module), everything internal would need to be radically different due to the ECLSS needs, the floor layouts, bunks etc etc.

Still I agree you would save money and development time by having at least that level of commonality and the reuse of a proven design would likely be desirable from a safety standpoint too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 06/22/2015 03:15 am


Agree that static weight is not an issue, it is speed of impact with the surface.  But I disagree that gravity will be the main determinant of that, on both Mars and Earth the vehicle will be under propulsive decent and gravity is simply a part of that 'dance' the Raptor engine is TOO MUCH thrust to hover on at either Earth or Mars (230 mT hover on Earth, 605 mT on Mars), no one belives MCT would have that much mass at touchdown.  I favor a set of vernier engines specifically to make a softer touchdown (and avoid cratering the surface)
Agreed on the terminal landing thrusters.  On my design back in the first thread I actually used pressure fed metholox thrusters for the entire EDL (Earth and Mars) without using raptor at all.  I am re-thinking that, especially now that raptor is smaller.  Raptor would have an ISP advantage in the super-sonic retro-propulsion.  Terminal landing is where raptor is far from ideal.

Landing with raptor alone on Mars would be very difficult and risky.  Impossible without a prepared surface.  Earth landing would require the flow separation issues to be solved.

I have never heard of an space vessel in which the outer aero shell IS the pressure vessel, I would speculate that it presents for too much of a thermal pathway into the vessel and would literally COOK the passengers, note that reentry capsules get quite warm inside during re-entry and this is with considerable insulation between the TPS and pressure vessel.  So I do not believe what your describing is possible.

Leaving habitats on surface is exactly what I proposed.  The overall shape I'm going with (originally Lobo's configuration) is that of a biconic with TPS on the top/sides, engines and legs on the bottom and an unpressurized cargo-bay door on the side.

You are correct about the thermal issues  but I wasn't clear enough in my description. I was also toying with the same TPS configuration for my next design (top and side).  The integrated pressure vessel I proposed would double as the load bearing structure behind the TPS.  I think this would save several tons over your proposal, but your proposal saves tens of tons by having the hab pull double duty as cargo.  Then saves several hundred tones of ISRU propellant on mars per return flight.  So you might have converted me. ;) 

Your rigid hab left behind has a lot of merit, especially in the first dozens or hundreds of flights.  A few months back I proposed an inflatable hab used in transit being left behind for the same effect.  I also had sketched a 180ş side door for an unpressurized cargo version before, though I can't remember if I posted it here.  When I have time to sit down with excel and cad again and turn my hand-waving into something concrete, we will see what I come up with.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/22/2015 04:38 am
I'm all for integrating some of the layers that normally make up a space craft, metallic TPS which I favor can be combined with the aero-shell and would be right over the skeletal frame members which take the dynamic pressure and g-forces.  As I favor an unpressurized cargo-bay the interior is all just tanks, plumbing, framing and some sheet-metal to nominally separate the cargo-hold from the rest of the interior.

The habitat I'm envisioning might make use of an inflatable section, such as a loft or water tank on the top that would only be expanded once on Mars.  NASA has built similar concept habitats.  The rigid portion would be 2 floors and mounted on set of wheels that can squat down and lower the vehicles height to allow it to fill as much of the cargo hold as possible.  Functionally it is a trailer that is ment to be towed by a second large vehicle 'locamotive' which would be sent ahead on a cargo flight.

The great height of the cargohold above the ground (largely due to the need to accommodate the Raptor nozzle bells above the surface means that it might be necessary to build up some earthen ramps to get the large vehicles in and out.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/22/2015 07:37 am
Direct-return vehicles are essentially a dead-end configuration because they have a low maximum flight rate, so why go down that path.

But SEP stages and transit habs also have a low flight rate. So replacing a direct-return MCT with SEP, transit hab and a smaller MCT lander does not seem to be a win.

The main advantage of a direct-return MCT is that it can be maintained, refurbished and upgraded on Earth.

Any architecture which involves space-only or Mars-only stages has to explain how they will be maintained in space or on Mars. This is not an easy problem to solve, especially if we assume new and upgraded versions of SEP, transit hab and MCT lander are produced every few years. Earth has so many advantages, presence of jigs and tooling, unlimited supplies of water and other working fluids, a full local supply chain, local presence of the design engineers, clean rooms, large hangers under pressure, etc.

I think that the overheads of maintaining equipment off-earth removes any advantage your architecture might have in terms of lower initial mass in LEO,  at least until we reach colony sizes of 100,000.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/22/2015 08:23 am
Sometimes I use a first approximation and say the cargo is as much as transport cost. That would average 500000 $ for one t. Averaged between simple tools and Intel CPUs.

The overall expense for an aspiring colonist has mushroomed into $10,500,000  :-\

Middle class no longer need to apply, very/ultra high networth individuals only.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/22/2015 02:46 pm
I think large SEP tugs should be to take a lot of cargo and disposable landers to Mars since the cargo is 10:1 colonists.  MCT would be for colonists, larger cargo and time sensitive cargo.  Disposable landers could be designed to be salvaged for colonists building materials.  For instance legs could hold up solar panels.  Fuel tanks could be salvaged and grouped together for a fuel depot, or habitats, or the smaller landers could be refueled to launch argon from the Martian atmosphere to refuel SEP tugs, then re-land for refueling again and launching again. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/22/2015 06:03 pm
Direct-return vehicles are essentially a dead-end configuration because they have a low maximum flight rate, so why go down that path.

But SEP stages and transit habs also have a low flight rate. So replacing a direct-return MCT with SEP, transit hab and a smaller MCT lander does not seem to be a win.

The main advantage of a direct-return MCT is that it can be maintained, refurbished and upgraded on Earth.

Any architecture which involves space-only or Mars-only stages has to explain how they will be maintained in space or on Mars. This is not an easy problem to solve, especially if we assume new and upgraded versions of SEP, transit hab and MCT lander are produced every few years. Earth has so many advantages, presence of jigs and tooling, unlimited supplies of water and other working fluids, a full local supply chain, local presence of the design engineers, clean rooms, large hangers under pressure, etc.

I think that the overheads of maintaining equipment off-earth removes any advantage your architecture might have in terms of lower initial mass in LEO,  at least until we reach colony sizes of 100,000.

No the flight rate is considerably higher for the lander because it is being loaded in Mars orbit and cycle rapidly between the surface and back to orbit, 100 flights per synod would easily be achievable.  That is 100 times more then the direct return lander.   A large frighter would carry mostly cargo and just 1 or 2 landers and it could easily take the lander back to Earth to land there and be serviced if needed once every synod.

The SEP vehicle itself dose 1 round trip per synod, but it is not being landed and relaunched, were only launching new cargo and propellent to it in LEO, this will utilize the launch vehicle far more efficiently.  With cargo inside landers and an all chemical TMI your looking at 1/6th of launch mass being usable cargo, 1/6th being the lander and 2/3rds propellents.   The efficiency of the SEP would make this 2/3rds cargo, 1/3 propellents.

Inspection and maintenance are important functions and will be done for landers on Earth, do not confuse the 'stay at Mars' normal operational practice with removing the vehicle from service for maintenance, airplanes are not maintained in the air or on the runway or at the terminal gate.  The SEP vehicle is effectivly a space-station and would have a life-span and maintenance needs much like ISS, if parts wear out they are replaced either internally or externally.

Upgrading of any significant parts (engines, structures, Thermal protection) is rarely done to vehicles of any kind.  As we expect a growing fleet you will simply see new models added to the fleet while older ones continue to serve until they are deemed obsolete or worn out (like airplanes).  The landers design is likely too interconnected to allow significant upgrading outside of engine upgrades as we saw in Merlin.  The SEP might see upgrades or replacement of it's thrusters as that technology improves, this would be done by spacewalk to detach and reattach a new engine block, so long as it is designed to be replaced it wouldn't be a problem.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 06/22/2015 11:20 pm
Impaler and CyclerPilot, this idea should be compatible with the CONOPS you are developing:

Consider the passenger  version of MCT, the trans-Hab and the surface-Hab to be all the same unit. By this I mean that the passenger section and the propulsion section of MCT would be separate and functionally independent units, i.e. propulsion avionics entirely in the propulsion unit and ECLSS components entirely within the passenger unit.. The passenger unit would sit on top of the propulsion unit, which sports a wide heat shield on its underbelly for EDL. The bottom rim of the passenger unit would be joined to the top rim of the propulsion unit only by a ring of bolts through both rims.

Passengers would ride in this vehicle from Earth and land on Mars' surface. A mobile robotic arm that was previously deployed onto Mars' surface would remove the bolts holding the units together. Then a pre-deployed crane would raise the passenger unit and place it on the ground in a desirable location. The passengers have now landed on Mars along with a permanent habitat unit complete with ECLSS. The propulsion unit, now rather lightweight, could then be launched back to Earth and reused. Note that the heat shield on the underbelly also returns.

This system could also pre-deploy habitats on Mars prior to the first human landing.

As more colonists arrive and build ISRU-based habitats, these original habs would continue to be employed as backup in case of emergency or simply additional housing to give colonists more living space. Also note that not all habs would be permanently located on Mars; some would be launched back to Earth with persons wishing to return.

A cargo version of MCT could also perform double-duty. Once landed, the cargo unit would likewise be removed and set on the ground. Unloading cargo would proceed from ground level to ground level. After unloading, the cargo hatch door(s) would be closed and permanently welded shut, both the interior pressure vessel and the exterior shell. Now we have a sizable tank for storing propellants or other liquids produced on Mars.

Do you think this is feasible?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 06/23/2015 01:53 am
Impaler and CyclerPilot, this idea should be compatible with the COOPS you are developing:

Consider the passenger  version of MCT, the trans-Hab and the surface-Hab to be all the same unit. By this I mean that the passenger section and the propulsion section of MCT would be separate and functionally independent units, i.e. propulsion avionics entirely in the propulsion unit and ECLSS components entirely within the passenger unit.. The passenger unit would sit on top of the propulsion unit, which sports a wide heat shield on its underbelly for EDL. The bottom rim of the passenger unit would be joined to the top rim of the propulsion unit only by a ring of bolts through both rims.

Passengers would ride in this vehicle from Earth and land on Mars' surface. A mobile robotic arm that was previously deployed onto Mars' surface would remove the bolts holding the units together. Then a pre-deployed crane would raise the passenger unit and place it on the ground in a desirable location. The passengers have now landed on Mars along with a permanent habitat unit complete with ECLSS. The propulsion unit, now rather lightweight, could then be launched back to Earth and reused. Note that the heat shield on the underbelly also returns.

This system could also pre-deploy habitats on Mars prior to the first human landing.

As more colonists arrive and build ISRU-based habitats, these original habs would continue to be employed as backup in case of emergency or simply additional housing to give colonists more living space. Also note that not all habs would be permanently located on Mars; some would be launched back to Earth with persons wishing to return.

A cargo version of MCT could also perform double-duty. Once landed, the cargo unit would likewise be removed and set on the ground. Unloading cargo would proceed from ground level to ground level. After unloading, the cargo hatch door(s) would be closed and permanently welded shut, both the interior pressure vessel and the exterior shell. Now we have a sizable tank for storing propellants or other liquids produced on Mars.

Do you think this is feasible?
Possible yes.  Here is a LINK (http://forum.nasaspaceflight.com/index.php?topic=35424.0) to my old design with one big raptor.  Very similar to what you proposed.  My hab was detachable but for purposes of a LAS.  I never thought of leaving it behind.

The design (yours or mine) has a few shortcomings.

A bottom heat shield has to have a very large diameter to provide enough deltaV for 100 tons of cargo and the craft that contains it.  It also has too many seams to leave an opening for the engine bell and inner stage.  These seams need to be closed in space.  This adds a huge LOC risk.

A new (but modest) aero shell would be needed for mars assent.

Need to leave the hab on some return flight to return humans.

LAS escape pod is pretty heavy on mine(contains all cargo, ECLSS, ect).  Non existent on yours as far as I can tell.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/23/2015 02:41 am
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.  Likewise their would need to be yet more on the now exposed top of the propulsion stage to allow it to land on Earth.  Lastly their is no way to send anyone or anything back to Earth which is required.

The crane necessary to remove this habitat would be monstrous, and it would need to be mobile both before and AFTER picking up the habitat for it to do anything other then put it on the ground right next to the propulsion section which needs to blast off again, a very bad place to be.  The crane would have a higher mass then what it is lifting and would be extremely dangerous.


I'm proposing a habitat that is INSIDE the lander and deployed by WHEELS down a ramp, I can't see anything being simpler then that, and am perplexed why anyone feels this needs improving.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 06/23/2015 03:38 am
Direct-return vehicles are essentially a dead-end configuration because they have a low maximum flight rate, so why go down that path.

But SEP stages and transit habs also have a low flight rate. So replacing a direct-return MCT with SEP, transit hab and a smaller MCT lander does not seem to be a win.

Any architecture which involves space-only or Mars-only stages has to explain how they will be maintained in space or on Mars.

- How about not having to design a huge jack of all trades space vehicle with razor thin margins? I think there's a history of great ambition leading to such projects in space flight. We all know how they ended.

- I think NASA considers reusing Habitat, SEP and pressure-fed hypergolic propulsion because these technologies have proven their durability respectively in-space maintainability. I'd say expendable Mars landers would be perfectly fine until a Mars colony is big enough to refurbish them with spare parts delivered from Earth.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 06/23/2015 01:41 pm
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.  Likewise their would need to be yet more on the now exposed top of the propulsion stage to allow it to land on Earth.  Lastly their is no way to send anyone or anything back to Earth which is required.

The crane necessary to remove this habitat would be monstrous, and it would need to be mobile both before and AFTER picking up the habitat for it to do anything other then put it on the ground right next to the propulsion section which needs to blast off again, a very bad place to be.  The crane would have a higher mass then what it is lifting and would be extremely dangerous.

I'm proposing a habitat that is INSIDE the lander and deployed by WHEELS down a ramp, I can't see anything being simpler then that, and am perplexed why anyone feels this needs improving.
I value your critique.
 
You mentioned needing TPS on all sides of the MCT; I am only familiar with TPS on one side, where it serves as a leading edge during aerobraking on Mars,i.e. Design Reference Architecture 5A. Is the all-around TPS now a requirement for all Mars landers? Did your design include this?

I have seen a suggested design for MCT that is an enlarged version of a Dragon V.2, which sports a 15 m shield on the bottom and heat-resistant metal or composite for the rest of the "capsule'". Is this approach now obsolete?

The system I suggested could have TPS on all surfaces, but that would probably be expensive. If so, it would be less desirable to leave a whole section on Mars permanently. The large crane I suggested could be replaced by a different, low-mass system. But the first issue is TPS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 06/23/2015 03:25 pm
...
...
I'm proposing a habitat that is INSIDE the lander and deployed by WHEELS down a ramp, I can't see anything being simpler then that, and am perplexed why anyone feels this needs improving.
Your proposal is excellent and should be employed. I would add only this:
After you have unloaded your habitat, now go back and unload the whole top section of the MCT as another habitat.

Maximum cargo delivered in just one trip of the MCT.  Win-win for SpaceX!

###
[Edit: A bonus -- we will be returning to Earth the absolute minimum mass that is physically possible.]
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/23/2015 04:22 pm
...
...
I'm proposing a habitat that is INSIDE the lander and deployed by WHEELS down a ramp, I can't see anything being simpler then that, and am perplexed why anyone feels this needs improving.
Your proposal is excellent and should be employed. I would add only this:
After you have unloaded your habitat, now go back and unload the whole top section of the MCT as another habitat.

Maximum cargo delivered in just one trip of the MCT.  Win-win for SpaceX!

###
[Edit: A bonus -- we will be returning to Earth the absolute minimum mass that is physically possible.]

Except that the proposals are in headon conflict with two basic principles Elon Musk has stated over and over again.

One is mass fraction. Best possible mass fraction is required for full reusability. Having an outer shell capable of withstanding atmospheric reentry at interplanetary speeds and the resultant heating plus an inner habitat capable of holding pressure for crew is extremely mass inefficient.

The second is full reusability. I think it might be possible that some low value but heavy equipment not needed for a smaller return crew might be removed if necessary. Especially if they can be reused on Mars. But except early on as a special startup arrangement the complete MCT will go back to reach the cost goals.

I have suggested before, that the whole cabin or cargo compartment may be removable and reused as habitat space on Mars. But that as an initial method. Not in a later stage when large numbers of colonists are transfered, that means the 100 people per flight are actually transported. At that stage the colony needs to be able to provide habitats and work places for all the arriving colonists.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: cambrianera on 06/23/2015 04:36 pm
First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars. 

One of his early Apollo design questions was how much heat shielding to install on the lee side of the Apollo capsule to protect it when it reentered the earth's atmosphere upon returning from the moon. "Based on intuition, not calculations, I said you didn't need to put anything on it," Faget says. "But the people who were doing calculations were ultraconservative. They put about an inch of ablative material on the lee side. Sure enough, when the thing reentered, it still had its thin mylar dust sheet. So my intuition would have saved at least four or five pounds a square foot, carried all the way to the moon and back, absolutely useless.

Max Faget: Master Builder
http://www.astronautix.com/articles/maxilder.htm
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 06/23/2015 04:57 pm
...
...
...
I have suggested before, that the whole cabin or cargo compartment may be removable and reused as habitat space on Mars. But that as an initial method. Not in a later stage when large numbers of colonists are transfered, that means the 100 people per flight are actually transported. At that stage the colony needs to be able to provide habitats and work places for all the arriving colonists.
I agree. And I bow to your earlier posting (reference?)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/23/2015 05:40 pm

I agree. And I bow to your earlier posting (reference?)

No need for that. I mentioned it only to show that I am not generally against it. It is quite long ago and I would be hard pressed to find it now. The idea was to remove the whole upper part and have another heatshield on the tank dome of the propulsion section for earth reentry.

It may be most efficient to remove the cargo hold of some cargo MCT and use them as pressurized habitat. The ECLSS would be mostly not suited for Mars surface operation as that would be based on biological, plant ECLSS. So better send that back to earth for reuse.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/23/2015 06:52 pm
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.  Likewise their would need to be yet more on the now exposed top of the propulsion stage to allow it to land on Earth.  Lastly their is no way to send anyone or anything back to Earth which is required.

The crane necessary to remove this habitat would be monstrous, and it would need to be mobile both before and AFTER picking up the habitat for it to do anything other then put it on the ground right next to the propulsion section which needs to blast off again, a very bad place to be.  The crane would have a higher mass then what it is lifting and would be extremely dangerous.

I'm proposing a habitat that is INSIDE the lander and deployed by WHEELS down a ramp, I can't see anything being simpler then that, and am perplexed why anyone feels this needs improving.
I value your critique.
 
You mentioned needing TPS on all sides of the MCT; I am only familiar with TPS on one side, where it serves as a leading edge during aerobraking on Mars,i.e. Design Reference Architecture 5A. Is the all-around TPS now a requirement for all Mars landers? Did your design include this?

I have seen a suggested design for MCT that is an enlarged version of a Dragon V.2, which sports a 15 m shield on the bottom and heat-resistant metal or composite for the rest of the "capsule'". Is this approach now obsolete?

The system I suggested could have TPS on all surfaces, but that would probably be expensive. If so, it would be less desirable to leave a whole section on Mars permanently. The large crane I suggested could be replaced by a different, low-mass system. But the first issue is TPS.

No, the issue that killed the idea for me was the crane which is huge and dangerous, the TPS is just added inefficiency on top of that.

I think DRM 5 was for some kind of high-altitude airobraking shield far wider then the payload to create low ballistic coefficient, where as your proposing a Dragon/Soyuz shaped capsule in which the sides are quite exposed to hot air flow, and I doubt the DRM ideas were actually analyzed to account for back-side heating.  Every probe sent to Mars has had a back-shell to protect it.  This is not to say that it is impossible or even prohibitively heavy, you just don't get to ignore the entry heating on this habitat or the back side of the propulsion unit which is what it seemed to me your were doing.

The crane is what I find totally impractical and I do not see how it is replaced by a 'low mass system', if your hab is just sitting on top of a rocket stage their is no way to get it down without using either a crane or a second rocket or legs with wheels that extend all the way around and past the propulsion stage.  All of which look extremely impractical compared to simple ramp+wheels deployment.

Now to be clear cranes CAN be useful if they are the right TYPE, specifically gantry cranes in the room of the payload bay are an excellent means of loading and unloading containerized cargo.  They use the vehicle itself for support and for achieving a wide base and only need to have rails that telescope out a few meters to clear the edge of the vehicle and deposit containers into waiting ground vehicles.


Your proposal is excellent and should be employed. I would add only this:
After you have unloaded your habitat, now go back and unload the whole top section of the MCT as another habitat.

Maximum cargo delivered in just one trip of the MCT.  Win-win for SpaceX!

###
[Edit: A bonus -- we will be returning to Earth the absolute minimum mass that is physically possible.]

Huuu??  The top section of the lander I've been proposing is propellent tanks, why on Earth would their be a second habitat of any kind on the vehicle.  If I'm deploying by ramp and wheels I would put EVERYTHING on thouse wheels to maximize it's efficiency and operational simplicity.  Anything that is returned to Earth will be loaded back in as cargo, NOTHING should be integrated into the vehicle which is not physically necessary for launch and landing.



Except that the proposals are in headon conflict with two basic principles Elon Musk has stated over and over again.

One is mass fraction. Best possible mass fraction is required for full reusability. Having an outer shell capable of withstanding atmospheric reentry at interplanetary speeds and the resultant heating plus an inner habitat capable of holding pressure for crew is extremely mass inefficient.

The second is full reusability. I think it might be possible that some low value but heavy equipment not needed for a smaller return crew might be removed if necessary. Especially if they can be reused on Mars. But except early on as a special startup arrangement the complete MCT will go back to reach the cost goals.

I have suggested before, that the whole cabin or cargo compartment may be removable and reused as habitat space on Mars. But that as an initial method. Not in a later stage when large numbers of colonists are transfered, that means the 100 people per flight are actually transported. At that stage the colony needs to be able to provide habitats and work places for all the arriving colonists.

If your saying that the Thermal protection can be integrated with the pressure hull then that's a non-starter for the simple reason that it provides a direct heat path into the interior and will COOK people.  The pressure hull has to have a stand-off gap between it and the TPS, likewise for propellent tanks.

Thus a removable habitat inside of an unpressurized bay is hardly any less efficient then an integrated one, the only extra mass is a little sheet metal wall for the payload bay and the system to secure the payload during launch and landing.  The benefits are getting BIG habitats deployed on the surface for early missions and reducing the mass at launch from Mars surface to a minimum.

What is inefficient is doing high speed entry from interplanetary speeds, I'm advocating for much much lower speeds which will tax the vehicle design far less, which should more then make up for mass costs of a removable hab.  And it will also allow a single type of lander to do both crew and cargo flights, a key factor in making it cheaper to develop, manufacture and operate.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/23/2015 07:21 pm
Why would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?

I would guess more like 30-35 tons.

Just the propellant tank portion, 5 Raptor engines and possibly landing legs too would weight ~40mt. Now add the reentry shield and the cargo bay structure. Of course the cargo variant will not have as high a dry weight as the crew variant but where is the tradeoff in crew payload size and crew vehicle dry weight increase. If you could get the cargo variant to have a dry weight as low as 60mt then reduce the payload size of the crew variant (crew + supplies) to only 60mt on a crew variant that dry weight 100mt things will work out better in that the overall system becomes smaller. You shrink the size and maybe some savings on the propellant tank dry weight due to smaller tanks.

My only problem with the estimates is that the more detail we go the heavier the MCT gets.

The Saturn SII was about 45mt dry, including give J2 engines.  I think a similar expendable stage built today would be somewhat lighter.  So 40mt is probably a good conservative number. 30-35mt is more aggressive, but plausible.  Of course, it depends on what such a stage would be volume-wise compared to the SII.  Less efficient engines (but only about 40s less), but more dense fuel.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/23/2015 07:36 pm

F9 first stage has 8% of dry mass in the leg system, and this is designed for flat artificial surfaces and is not carry precious human cargo.  The LEM had around 3% of touch down mass in legs, but that was a soft-touchdown with a deeply throttling engine, not the SpaceX 'hover-slam'.

Only the F9 booster hoverslams.  We don't know that they'd do that for a crewed vehicle.  Which is why although there's certain advantages to landing on Raptors if they can manage it, I think we can't rule out dedicated landing thrusters with soft landing ability.  Dv2 will land pretty softly as it seems, and that will have people.


And their would not be any kind of integral habitat in a 'crew' version.  Their will just be a single version with an unpressurized cargo bay into which a habitat module would be placed.


That's what I've been wondering too, although that comes back to my favored concept of a common basic MCT platform that would be configured for various roles like tanker, instead of a dedicated 2nd stage.
But essentially a basic cylindrical aeroshell with a blunted nose as the outer mold line.  All of these platforms would look like that from the outside. Inside there's tanks and a space for installing things.  Tankers would have nothing there.  Depots would have perhaps active cryogenic refrigerators there to reduce boiloff during it's long stay in LEO.  Later people movers would have a large hab module with accommodations for 100 people there.  Cargo movers would have accommodations for stowing and locking in 100mt of cargo containers/rovers/etc.
Whatever you put in this modular volume would total 100mt.  100mt of cargo, 100mt large pressurized hab plus 100 people plus provisions for them, etc,

But the initial MCT's would have that space with more of a combination of small exploration crew accommodations and cargo area for equipment and supplies.  With probably a Sabatier reactor and rolls of solar film cells?  Whatever's needed for support a crew of 7-14 and do surface exploration and refueling, without any prepositioned support like later missions would likely have.
So maybe a 25mt hab+7 crew+provisions, and 75mt worth of cargo and supplies.  Or something.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/23/2015 08:07 pm
If you have to have 10 flights of cargo with 1 passenger flight of 100 with say 4 crew, why not have a crew of 4 with 10 passengers on each flight.  Have the rest as cargo.  That way every MCT would be identical, and so it only carries about 80-90 tons of cargo.  However, the cargo could be loaded in modules, that could be unloaded and when emptied can be used for habitat.  No need for separate cargo and human flights.  The 10 colonists could stay on Mars to work, build habitats, landing pads, solar power stations, and maintain ISRU equipment.  10 MCT's would get you 100 colonists. 

Cargo modules could be made from Falcon 9 cores with openings on each end.  Once emptied of solar panels, a rover or so, the inside can have modular rooms/furniture installed for living quarters.  They could be laid down and covered with Martian soil for radiation protection, except on the openings to the outside.  Or, Bigelow inflatable habitats could be used until more permanent cover can be made. 

Having 14 in an oversized capsule similar to Dragon would allow and extra layer of safety during launches on earth and Mars. 

On another note, several MCT's with minimum crew only would have to land first to set up fueling for return, that way the colonists would have a way to escape Mars in case of some unforeseen calamity. 

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/23/2015 08:25 pm
So, as a thought for the layout of MCT itself, I'm still favoring this basic cylinder, with a blunted nose cap or nose cone on it.  Probably with ablative TPS on the nose and along the ventral half of it.  But we need a way to deploy fairly large solar arrays for the cruise each way, which can then be retracted.  We've kicked this around a few times, but here's a perhaps simple and plausible method.

So to this cylindrical MCT, picture a raised blister along it's whole dorsal side on the cylinder body, and the modular compartment on the bottom, between the tanks and engines (although it could be at the top of putting it at the bottom was too problematic with design).
That raised blister is a long series of mini cargo bay doors housing retracted solar arrays, similar to how the ISS arrays looked when they were stowed.  Once the blister doors are open, the arrays, which are fixed in position, extend directly out to the sides.  Not nearly as far as the ISS's, probably just far enough to block the sun hitting the MCT hull.  So once MCT does the TMI burn, it flips to put it's "back" to the sun and then these arrays both shade MCT do reduce solar energy absorption, and they'll always be facing the sun for maximum electricity production.

So, you have a combo solar array and sun shield (acting like the one they installed on Skylab to get the temperatures down).  And they don't have much in the way of moving parts.  little doors that fold down, and rectangular arrays that simply extend out stretching out folded solar panels, and then pull back in at the end of the cruise and the blister doors are closed.

I think this would be far more simple method than deploying a large array out of a cargo bay door like X-37B does, and reduces the heat loads on MCT that must be compensated for with radiators.  They would also help reduce boiloff in transit as the tanks are shaded. 

This system would be independent of what that MCT platform was configured as.  It'd be an integral part of the platform, as no matter what it's doing, it'll need power.  A depot would need power (and benefit greatly from shading).  Even just a simple tanker would probably need power, or a lot of batteries.

I suppose even -more- clever than this would be just to coat the whole dorsal side of the MCT cylinder with solar panels, like Dv2's trunk or HTV.  But could such a system be made that could withstand EDL?  And would there be the same sunlight blocking advantages as there would be to separate physical arrays crating actual shade?  The temps the arrays might get to really wouldn't be transferred to MCT, where they would with integrated solar panels on MCT's surface through conduction.  And a deployable separate arrays would be flat for maximum exposure instead if curved around half of a cylinder. 

But, there'd be a nice advantage to such a static/passive system if possible.  It's why JAXA went with it on HTV and why SpaceX went to it on Dv2.



As an interesting note, if the designers are clever, such an array could possibly be deployed after landing on Mars...although they wouldn't be much use if you were close to the equator unless they could rotate up some too.  Probably not enough power to fuel up MCT, but should be enough to provide system power.  Which would be useful until larger surface arrays are deployed. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/23/2015 08:28 pm

Yes, the depot could be a specially equipped MCT for 0 boil-off since it would have large enough tanks to refuel 1+ MCT's for Earth departure. This would make it easy to orbit the depots since they are just another cargo specialized version of the MCT which are then manufactured in the 10's to 100's.

Bingo.

Plus it'd be a depot that could periodically return to Earth for repair/refurbishment and then be relaunched for another tour of duty.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/23/2015 08:41 pm
So it would take one MCT depot to refuel one MCT going to Mars.  The Depot if emptied each time it goes up could come back to be refueled and checked out then.  No need to worry about boil off.  Launch the Fuel depot, launch the MCT to dock, refuel and head to Mars.  Fuel depot returns, refuels, and relaunches with the next MCT. 

I too like the idea of a cylinder MCT. It could be stretched for a fuel depot without much expense. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: rklaehn on 06/23/2015 08:58 pm
So it would take one MCT depot to refuel one MCT going to Mars.  The Depot if emptied each time it goes up could come back to be refueled and checked out then.  No need to worry about boil off.  Launch the Fuel depot, launch the MCT to dock, refuel and head to Mars.  Fuel depot returns, refuels, and relaunches with the next MCT. 

I too like the idea of a cylinder MCT. It could be stretched for a fuel depot without much expense.

I think a depot needs to be larger than a MCT. The economics are much better if you can fill the depot over the two years of a mars synodic cycle where there is no good launch window to mars, and the MCT fleet is somewhere in transit.

If you would refuel the MCT from another tanker MCT, you would have to do all your launches in the few weeks per synod or so that have good launch opportunities.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/23/2015 11:01 pm


My visualization for the MCT version of the BFR upper stage is 4 raptors, but the hardware to cant them for Mars landing/take off.   I think 60t works for the dry weight of a cargo only version, and I am not committed one way or the other yet as to whether the passenger ECLSS and quarters are just cargo 'modules' that fit on an otherwise standard MCT or a seperately designed and built MCT.  What I do expect is that a passenger MCT is less loaded with payload than the cargo only one so that it has more ΔV partly for slighlty shorter transit time, partly for more safety margin.


I don't believe integrated habitat and direct Earth-reutrn are compatible.


An integrated hab for 6-10 people could probably mass less than 25 tonnes, so it seems possible for initial missions. Later missions with more would need a larger hab and that could not be integrated.

So I believe you have made an important point, integrated habs have no long term future on the MCT, so will probably not be designed in the first place.

Yup.   See the Bigelow BA-330.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/23/2015 11:27 pm
So it would take one MCT depot to refuel one MCT going to Mars.  The Depot if emptied each time it goes up could come back to be refueled and checked out then.  No need to worry about boil off.  Launch the Fuel depot, launch the MCT to dock, refuel and head to Mars.  Fuel depot returns, refuels, and relaunches with the next MCT. 

Bingo.

I too like the idea of a cylinder MCT. It could be stretched for a fuel depot without much expense.

Yup, nice and simple geometry.  Makes the potential of TPS panels/tiles all one uniform size and shape possible around most of MCT, aside from the nose. 

It could be stretched, but that's a different spacecraft with different EDL profile, etc. 
But I don't think a Mars bound MCT will need full fuel in LEO, if we assumed direct return, as direct return will be the greatest dV requirement I suspect.  So a full depot wouldn't need the ability to transfer every drop of it's propellant into Mars-MCT necessarily.  Perhaps it'd transfer over enough propellant for TMI and Mars EDL, and have enough left so it can do it's own Earth EDL. 

And assuming it stays in orbit for 1-1.5 years receiving regular tanker offloads, and then pumps up one Mars-MCT per synoid, it could then come home, spend a few months getting refurbished, and then get relaunched and start taking tanker deliveries for the next 1-1.5 years in preparation for another Mars-MCT departure the next synoid.

I see the depot as much larger than that. I would prefer to see passenger carrying MCT's launch in pairs as close to simultaneously as possible. Also because of the intensity of the black body radiation of the earth and its daytime reflection of heat, I see the depot needing far more active cooling than the MCT which will only need to keep its propellant from boiling off near Mars and between Mars and Earth but will not need to keep it cool for long in the 10 radii range of the Earth. I also see the depot with a hab as transit station, and a place where PicaX can be recoated on MCT's along with engine swaps (engines taken off BFR tanker stages)

My response to Spacenut applies here too. Why a larger Depot?  If you are launching two MCT in a synoid, then place two MCT-depots in LEO a year or so ahead of time and then launch enough tankers to fill them both up ahead of the MCT-Mars launch.  Where they will dock with their respective depots, tank up, and burn for Mars together.

As for active cooling, see my earlier post about MCT having dorsal solar/shade arrays.  In place of "cargo" it could have the refrigerators and run off those solar arrays.

Now, all of that said, if you wanted to make a much larger depot that never came back down, that might be an application for the flexible tanks Impaler has been talking about?
I wonder if they could be set up with some sort of air bladder that could be inflated to push the propellant to the Mars MCT, and then pumped down again.  Like an air diaphram pump? Of course the MCT's deliverying the propellant would be in rigid tanks and would need some method of pumping propellant out of them, so that might not necessary accomplish much.  However, of the inflatable tanks were cheap, maybe such a depot could be cheap and thus expendable?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/24/2015 02:48 am
One of the advantages of a SEP transit vehicle is that all this depot stuff largely goes away.  The vehicle itself would hold all the propellents needed, it would not be cryogenic and the 'fleet' would be stationed at high Earth orbit so the small amounts of chemical propellents in the landing craft are much easier to keep refrigerated.  Filling this fleet of vehicles is just a matter of putting propellents in LEO and having members of the fleet shuttle it up to high orbit.

Each synod the fleet departs for Mars and a few months later the empty return vessels arrive as they depart for Earth at approximately the same time.  Assuming 3 month transfer this means 23 months of loiter at Earth which means the fleet available 88% of the time for receiving propellents and non-perishable cargo as well.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 06/24/2015 02:54 am
If you have to have 10 flights of cargo with 1 passenger flight of 100 with say 4 crew, why not have a crew of 4 with 10 passengers on each flight.  Have the rest as cargo.  That way every MCT would be identical, and so it only carries about 80-90 tons of cargo.  However, the cargo could be loaded in modules, that could be unloaded and when emptied can be used for habitat.  No need for separate cargo and human flights.  The 10 colonists could stay on Mars to work, build habitats, landing pads, solar power stations, and maintain ISRU equipment.  10 MCT's would get you 100 colonists. 
Lots of reasons this is less efficient.

The opportunity cost of those 36 seats that could have been paying customers.  The substantial salaries of those 36 extra crew.

The added safety margins, colonist accommodations, and extra propellant for a faster transit that were not necessary on 90% of flights but now are.

This also makes earth orbit operations harder because now you either have to launch everything near the TMI window instead of having the freedom to launch cargo MCTs months or years ahead of time.

Edit: spelling
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 06/24/2015 03:07 am
So it would take one MCT depot to refuel one MCT going to Mars.  The Depot if emptied each time it goes up could come back to be refueled and checked out then.  No need to worry about boil off.  Launch the Fuel depot, launch the MCT to dock, refuel and head to Mars.  Fuel depot returns, refuels, and relaunches with the next MCT. 

I too like the idea of a cylinder MCT. It could be stretched for a fuel depot without much expense.
Not clear from your post that you need multiple refuel flights.  A single launch does not have enough propellant for a MCT TMI.  Even the most optimistic mission designs require at least 3 refuel flights.  I have seen some estimates as high as 8.

Having the depot semi-permanently in orbit with good insulation / shading and active cooling allows the operational freedom to launch propellant all throughout the synod.  As opposed to a high flight rate sprint followed by 20 months of inactivity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 06/24/2015 04:01 am


If your saying that the Thermal protection can be integrated with the pressure hull then that's a non-starter for the simple reason that it provides a direct heat path into the interior and will COOK people.  The pressure hull has to have a stand-off gap between it and the TPS, likewise for propellent tanks.

Thus a removable habitat inside of an unpressurized bay is hardly any less efficient then an integrated one, the only extra mass is a little sheet metal wall for the payload bay and the system to secure the payload during launch and landing.  The benefits are getting BIG habitats deployed on the surface for early missions and reducing the mass at launch from Mars surface to a minimum.

What is inefficient is doing high speed entry from interplanetary speeds, I'm advocating for much much lower speeds which will tax the vehicle design far less, which should more then make up for mass costs of a removable hab.  And it will also allow a single type of lander to do both crew and cargo flights, a key factor in making it cheaper to develop, manufacture and operate.
If there is an issue with thermal flux to the structure / pressure vessel, a layer of insulation could be added between them over most of the area.  If it gets as hot as you say, your design will probably need this insulation layer too because your load bearing layer will lose strength at elevated temperatures.

In your design isn't the "little sheet metal wall for the payload bay" a critical and heavy load bearing member?  It has to support the load of the propellant tanks, propellant, TPS, and aerodynamic drag during launches.  If it is a combined S2 on earth launch (full prop tanks at max Q and MECO) I would say the added mass requirement is a non-starter.  If your MCT launches as an empty S3 then the load is much less but still significant.  Hard to say if Earth or Mars launch would be a higher peak load without doing the math.

For nose first reentry that wall has to support the load of the engines and cargo during max G.  You said you were using a low speed entry, so probably not a major constraint.  Are you accomplishing this propulsively with an oberth burn at Mars?  SEP deceleration?  Slower transits?  Aerobraking?  EM drive?

I think your design would be much better and lighter if you made your crew pressure vessel (and cargo containers) load bearing. They could still be modular and removable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/24/2015 04:08 am
PICA-X is a very good insulator.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/24/2015 04:36 am

If there is an issue with thermal flux to the structure / pressure vessel, a layer of insulation could be added between them over most of the area.  If it gets as hot as you say, your design will probably need this insulation layer too because your load bearing layer will lose strength at elevated temperatures.

In your design isn't the "little sheet metal wall for the payload bay" a critical and heavy load bearing member?  It has to support the load of the propellant tanks, propellant, TPS, and aerodynamic drag during launches.  If it is a combined S2 on earth launch (full prop tanks at max Q and MECO) I would say the added mass requirement is a non-starter.  If your MCT launches as an empty S3 then the load is much less but still significant.  Hard to say if Earth or Mars launch would be a higher peak load without doing the math.

For nose first reentry that wall has to support the load of the engines and cargo during max G.  You said you were using a low speed entry, so probably not a major constraint.  Are you accomplishing this propulsively with an oberth burn at Mars?  SEP deceleration?  Slower transits?  Aerobraking?  EM drive?

I think your design would be much better and lighter if you made your crew pressure vessel (and cargo containers) load bearing. They could still be modular and removable.

Structural framework would be be in the gap between the TPS and the bay wall, the TPS system would be connected to the frame at only a few points that are designed to minimized heat-transfer.

The rest of your questions indicate that your confusing my proposal with that of Lobo and the differences would easily be answered by going back a few pages and reading my posts just a few pages prior in which I provide a full description.

http://forum.nasaspaceflight.com/index.php?topic=37808.msg1390895#msg1390895
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 06/24/2015 04:38 pm
So it would take one MCT depot to refuel one MCT going to Mars.  The Depot if emptied each time it goes up could come back to be refueled and checked out then.  No need to worry about boil off.  Launch the Fuel depot, launch the MCT to dock, refuel and head to Mars.  Fuel depot returns, refuels, and relaunches with the next MCT. 

I too like the idea of a cylinder MCT. It could be stretched for a fuel depot without much expense.
Not clear from your post that you need multiple refuel flights.  A single launch does not have enough propellant for a MCT TMI.  Even the most optimistic mission designs require at least 3 refuel flights.  I have seen some estimates as high as 8.

Having the depot semi-permanently in orbit with good insulation / shading and active cooling allows the operational freedom to launch propellant all throughout the synod.  As opposed to a high flight rate sprint followed by 20 months of inactivity.

A permanent depot infrastructure is the optimum as discussed frequently on this and other strings.  LEO ZBO depots are much tougher technically than HEO/EML-1/2 depots, and you are still stuck with the delta-v problem of getting out of Earth's gravity well. 

Not sure if this has been posted elsewhere or of the veracity of the quote (bold mine):
Quote
Musk and his team have already designed a methane-based rocket for the job, and the idea would be it for it to refuel once outside of the Earth’s orbit at a type of fueling station and then make a high-speed journey to Mars in three months.

http://www.bloomberg.com/news/articles/2015-06-24/elon-musk-first-martian-a-serious-conversation-about-the-future-in-space

If the quote is true, which I cannot determine independently, then it shows that there will be a DEPOT SYSTEM... deliver fuel to LEO, say with FH-R in 50mT increments, and then transfer it to outside of the Earth's orbit as staging for the MCT.  This is exactly the concept published by ULA for their ACES depot system.  (Ref below)

http://www.ulalaunch.com/uploads/docs/Published_Papers/Exploration/DepotBasedTransportationArchitecture2010.pdf

EML-2 is the optimum location delta-v-wise for depots, exploration outpost(s), and Mars departures.  EML-1 is almost as good.  I have proposed EML-1 as the refit location and EML-2 as fuel topping and departure staging point for the fleet.  Some of the fuel could be loaded in LEO, and then the vehicle immediately departs for EML-1/2 for fit-out as a hybrid approach.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 06/24/2015 05:04 pm
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/24/2015 05:07 pm
Question:
Why do we cite EM-L1/L2 which require active stationkeeping propulsion instead of the more stable EM-L4/5 points for orbital depots?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 06/24/2015 05:15 pm
Question:
Why do we cite EM-L1/L2 which require active stationkeeping propulsion instead of the more stable EM-L4/5 points for orbital depots?

Because the goal is to get MCT to Mars. Less delta-v from L1 and especially L2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 06/24/2015 05:50 pm
Question:
Why do we cite EM-L1/L2 which require active stationkeeping propulsion instead of the more stable EM-L4/5 points for orbital depots?

Because the goal is to get MCT to Mars. Less delta-v from L1 and especially L2.

Here is an easy table:
https://en.wikipedia.org/wiki/Delta-v_budget

LEO to EML-1  3.77 (km/s)
LEO to EML-2  3.43
LEO to EML-4/5  3.97

Escape from EML-1  0.14
Escape from EML-2  0.14
Escape from EML-4/5  0.43
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/24/2015 06:15 pm
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)

Don't be pedantic.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/24/2015 06:29 pm
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)

Don't be pedantic.
It is not pedantic, as was pointed out earlier in the thread by the quote from Max Faget TPS is unnecessary because there in fact is no such flow of matter dense enough to provide any convective heating.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/24/2015 06:56 pm
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: UberNobody on 06/24/2015 07:48 pm
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

The modifications to do that would be significant.  Rockets aren't legos, after all.  Not saying it isn't possible, but I think it's unlikely.

Elon was at one point considering refueling in a high elliptical orbit, which has delta-v advantages, but launch opportunity is more limited.  Who knows if he has switched to LEO or L2.  It's anybody's guess.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/24/2015 08:15 pm
A modified first stage seems like it would only require 3-4 vacuum Raptors instead of about 30, and no landing legs.  Once in orbit, it can be filled by any number of ways and rockets, with universal docking adapters and connections.  A full first stage size tank could probably refuel 2-3 MCT's and can be filled during the off synod.  L2 would lesson boiloff, LEO might need some shading, insulation, and/or solar powered refrigerating equipment. 

ESA, Russia, China, NASA, or any private company who wants a share of colonizing Mars might pay by helping fuel the depot(s). 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/24/2015 09:09 pm
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)

Don't be pedantic.
It is not pedantic, as was pointed out earlier in the thread by the quote from Max Faget TPS is unnecessary because there in fact is no such flow of matter dense enough to provide any convective heating.

Yes it is pedantic, he is not disputing the content, he is nitpicking my use of terms, hot air vs plasma.  He fails to considered that I might have been using simplified terms because I'm responding to someone who doesn't have all the basics on re-entry and I might not be try to intimidate people with technical terms like describing detached shock-layers and radiative heating which DOSE heat the back side of the vehicle.

Some decade old sour-grapes quotes from Max Faget dose not constitute a counter argument to the fact that EVERY entry vehicle has had a back-shell with thermal protection.

http://www.parabolicarc.com/2014/09/01/heat-shield-installed-orion-spacecraft/

Quote
But the space shuttles traveled at 17,000 miles per hour, while Orion will be coming in at 20,000 miles per hour on this first flight test. The faster a spacecraft travels through Earth’s atmosphere, the more heat it generates. So even though the hottest the space shuttle tiles got was about 2,300 degrees Fahrenheit, the Orion back shell could get up to 3,150 degrees, despite being in a cooler area of the vehicle. - See more at: http://www.parabolicarc.com/2014/09/01/heat-shield-installed-orion-spacecraft/#sthash.eNwEh6dP.dpuf
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/24/2015 09:18 pm
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

The modifications to do that would be significant.  Rockets aren't legos, after all.  Not saying it isn't possible, but I think it's unlikely.

Elon was at one point considering refueling in a high elliptical orbit, which has delta-v advantages, but launch opportunity is more limited.  Who knows if he has switched to LEO or L2.  It's anybody's guess.
When did he mention an elliptical orbit? I had considered that as well, but have never seen Musk mention a kind of orbit. Please put it in the MCT source quotes thread.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 06/24/2015 09:39 pm
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)

Don't be pedantic.
It is not pedantic, as was pointed out earlier in the thread by the quote from Max Faget TPS is unnecessary because there in fact is no such flow of matter dense enough to provide any convective heating.

Well, I kinda was being pedantic.  Sorry Impaler.

Sometimes a simplified explanation becomes technically incorrect, but still can be useful.  (Full disclosure: I do this all the time with non-technical listeners to get the big picture point across.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/24/2015 09:50 pm
No, not remotely.

First off, all sides of an object doing reentry need Thermal protection systems because hot air swirls around the back of a capsule shaped vehicle, so the habitat your placing on the top would need extensive TPS which then gets left on Mars.

hot air => plasma
swirls around => not at hypersonic/supersonic speeds (hot air/plasma basically limited to sonic velocities)

Don't be pedantic.
It is not pedantic, as was pointed out earlier in the thread by the quote from Max Faget TPS is unnecessary because there in fact is no such flow of matter dense enough to provide any convective heating.

Yes it is pedantic, he is not disputing the content, he is nitpicking my use of terms, hot air vs plasma.  He fails to considered that I might have been using simplified terms because I'm responding to someone who doesn't have all the basics on re-entry and I might not be try to intimidate people with technical terms like describing detached shock-layers and radiative heating which DOSE heat the back side of the vehicle.

Sorry but simplifying (which might mean explaining the process) and simply misinforming (inventing an analogy to something that is in fact completely dissimilar and creates a false idea of the physics and then not even identifying the inaccuracy) is not the same.  Radiative heating is real but is protected against quite differently than convective.  If someone explained a Tesla or Prius braking as winding up a spring to slow the car down then reversing that spring to start it up again I would not feel it was pedantic to correct that.


Some decade old sour-grapes quotes from Max Faget dose not constitute a counter argument to the fact that EVERY entry vehicle has had a back-shell with thermal protection.

http://www.parabolicarc.com/2014/09/01/heat-shield-installed-orion-spacecraft/

Quote
But the space shuttles traveled at 17,000 miles per hour, while Orion will be coming in at 20,000 miles per hour on this first flight test. The faster a spacecraft travels through Earth’s atmosphere, the more heat it generates. So even though the hottest the space shuttle tiles got was about 2,300 degrees Fahrenheit, the Orion back shell could get up to 3,150 degrees, despite being in a cooler area of the vehicle. - See more at: http://www.parabolicarc.com/2014/09/01/heat-shield-installed-orion-spacecraft/#sthash.eNwEh6dP.dpuf

And if you read that article it is saying "could" and "will be tested" to actually determine how much heating those areas get and whether micro meteoroid impacts will affect it.

Note that the Max Faget comments are relevant as they were about the Apollo capsule which also re-entered at the speeds in question from your quote.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/24/2015 10:36 pm
Some decade old sour-grapes quotes from Max Faget dose not constitute a counter argument to the fact that EVERY entry vehicle has had a back-shell with thermal protection.

Apollo imagery of people fishing out the capsules with leeward side in near pristine condition proves that Faget was right.

India's SRE-1 (https://en.wikipedia.org/wiki/Space_Capsule_Recovery_Experiment) proves that you are wrong.

(https://upload.wikimedia.org/wikipedia/commons/thumb/b/be/ISRO-SCRE-1-Spacecraft-1.jpg/319px-ISRO-SCRE-1-Spacecraft-1.jpg)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 06/24/2015 10:57 pm
Impaler, let me push back a bit against the premise of what you are pushing.  If I understand you correctly, you advocate lower speed reentry, such as from an orbit (both on Mars and Earth) than direct reentry for the MCT, primarily because then one could use metallic TPS rather than ablative TPS (i.e. PICA-X).  And that this is practically necessary to ensure high reusability and high flight rates.  Do I have that right?

But is avoiding ablative TPS really that important in the grand scheme?  Doesn't SpaceX intend to rapidly and frequently reuse the Dragon 2, which will surely have PICA-X.  What do we suppose is the answer here?  Is PICA-X something that can be de-ablated (reblated?) back on to the bottom of a capsule without too much hassle.  I'm imagining that there is an inch or so of the material, and half an inch ablates off during reentry (a little more some places, a little less others) and then then additional PICA-X is applied and added to what remains before the next flight - sort of like retreading a tire.  Or conversely, the entire backshell of PICA-X is designed and installed as a bolt on module, and a new one will be bolted onto the capsule for each flight (i.e. changing the tires).  I ask because I don't know.

But in any case, this seems to solve the problem fully, without a great deal of bother.  Surely a simpler solution than radically modifying the flight profiles to include orbital insertion on each end, which requires a great deal of additional fuel, don't you think?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/24/2015 10:57 pm


Not sure if this has been posted elsewhere or of the veracity of the quote (bold mine):
Quote
Musk and his team have already designed a methane-based rocket for the job, and the idea would be it for it to refuel once outside of the Earth’s orbit at a type of fueling station and then make a high-speed journey to Mars in three months.

http://www.bloomberg.com/news/articles/2015-06-24/elon-musk-first-martian-a-serious-conversation-about-the-future-in-space

If the quote is true, which I cannot determine independently, then it shows that there will be a DEPOT SYSTEM... deliver fuel to LEO, say with FH-R in 50mT increments, and then transfer it to outside of the Earth's orbit as staging for the MCT.  This is exactly the concept published by ULA for their ACES depot system.  (Ref below)

http://www.ulalaunch.com/uploads/docs/Published_Papers/Exploration/DepotBasedTransportationArchitecture2010.pdf

EML-2 is the optimum location delta-v-wise for depots, exploration outpost(s), and Mars departures.  EML-1 is almost as good.  I have proposed EML-1 as the refit location and EML-2 as fuel topping and departure staging point for the fleet.  Some of the fuel could be loaded in LEO, and then the vehicle immediately departs for EML-1/2 for fit-out as a hybrid approach.

Outside of Earth's orbit?  As in outside of the Earth's orbit around the sun?  That'd have to be Earth-Sun L-2.  The Earth-Moon L-points are inside Earth's orbit half the time.  ESL1 is inside Earth orbit as well.  I Guess EML1 or EML2 work when the moon is in the correct spot.  Or outside of the orbit around the Earth?

Or was it just a misstatement, and they meant something like "out in Earth's orbit"?  A depot outside of LEO would change the look of the mission profiles as most of us have been assuming a LEO depot. 
Also means MCT would need to be able to put 100mt plus the dry mass of MCT-spacecraft into whatever L-point they are looking at.  Or would they be now looking at staging a SEP MTV like in Boeing's proposal, with the spacecraft really only then needing to get itself form Mars orbit down to the Mars surface, refuel, and back up to MArs orbit fro MOR with the MTV for the trip back to the Earth L-point, and then get itself back down on the Earth's surface? 
I guess that would mean MCT-spacecraft wouldn't need much fuel when at EArth's L-point, just enough for Mars EDL outbound, and Earth EDL inbound.  Then it fills up for Mars Ascent on the surface. 
It'd be more efficient, but also require more new hardware development. 
Although I suppose the Mars-MCT, if full at the L-point, could be the kick stage that Boeing proposed using a DCSS or something for to get the big MTV/Lander stack moving.

Also means a pretty big booster to get an MCT spacecraft plus 100mt payload all the way out to an L-point in one shot.  Or would there be LEO refueling, before heading out to the L-point?

Hmmmm...sure like to get some more on this to support or refute this.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: UberNobody on 06/25/2015 12:53 am
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

The modifications to do that would be significant.  Rockets aren't legos, after all.  Not saying it isn't possible, but I think it's unlikely.

Elon was at one point considering refueling in a high elliptical orbit, which has delta-v advantages, but launch opportunity is more limited.  Who knows if he has switched to LEO or L2.  It's anybody's guess.
When did he mention an elliptical orbit? I had considered that as well, but have never seen Musk mention a kind of orbit. Please put it in the MCT source quotes thread.

I can't figure out how to quote myself, so here is a link
http://forum.nasaspaceflight.com/index.php?topic=36805.msg1352680#msg1352680

I'll put the info into the quotes thread.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/25/2015 02:11 am
Would something like the joined picture be a good fuel depot?

It's essentially two BFR second stages configured for fuel storage.  The are added docking points, the same solar panels as the MCT for power, compressors for fuel cooling, radiators for the compressor heat, added gold foil insulation and shadow shields that also have solar cells on the other side to power the compressors.
There is a Bigelowe module for a maintenance crew stayover, but it should usually be automatic.
It's in LEO, and can boost itself up from time to time.  It's a bit shorter than the MCT, since it desn't need the volume for crew accomodation.  The faring protecting the compressor module has been returned to Earth  It takes about 12 tanker trips to fill, and it can service two MCT for a Mars transfer.  Dockind and fuelling is available for other types of ships as well.  The extended structure may be overkill, but seems safer somehow.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/25/2015 03:29 am
Some decade old sour-grapes quotes from Max Faget dose not constitute a counter argument to the fact that EVERY entry vehicle has had a back-shell with thermal protection.

Apollo imagery of people fishing out the capsules with leeward side in near pristine condition proves that Faget was right.

India's SRE-1 (https://en.wikipedia.org/wiki/Space_Capsule_Recovery_Experiment) proves that you are wrong.


First off trying to use your EYE as a after-the-fact calorimeter on a surface that was heat-shielded is a profoundly flawed.  You have no idea what surface temperature it reached nor do you have any idea if it is truly pristine, that would take chemical analysis after-the-fact or ideally a temperature probe during the entry itself. 

Second, vehicles have to be designed for the worst possible entry profile expected, just because you may have had AN entry with low heating dose not mean you can strip the vehicle of TPS and remove all the margin because you raise the chance of a deadly burn-up.

Third this ISRO vehicle is radically different in shape (it basically looks like a low drag ICBM re-entry vehicle) then what the poster I was replying to was asking about which was the traditional blunted capsule.  Narrow conical entry vehicles have very different in thermal profile, they go much deeper in the atmosphere and are not viable for Mars entry.  Also this vehicle did an 8 kms re-entry, which is not even lunar return speed and far below any kind of direct Mars return speed.

The rear of this IRSO vehicle looks to be composed of small solar panels, solar panel are covered with glass which has a high melting point, we would not expect this to blacken or char, the forward TPS is non-ablative ceramic tile which would not deposit black char streaks.  The shuttle didn't LOOK chared when it returned from orbit but the top of it had TPS of a thinner, lower temperature type, but TPS none the less.  What is behind the panels? you have no idea.  Present some engineering documentation on this vehicle and data on what kind of heating regime it went through and you might have something.  I myself was unable to find any technical details on this vehicle.




Well, I kinda was being pedantic.  Sorry Impaler.

Sometimes a simplified explanation becomes technically incorrect, but still can be useful.  (Full disclosure: I do this all the time with non-technical listeners to get the big picture point across.)

No problem, nothing wrong with expanding a simple explanation and getting into the details so long as it's for the purpose of educating and avoiding confusion.  The actual mechanisms of heat transfer and airo-thermics around an entry vehicle are VERY complex, we could easily go on for pages so some brevity is needed, though I may have been excessive.   What I've read is that you actually get an area of secondary compression behind the vehicle and this area heats the back of the vehicle via radiation.  And I am fairly sure their is a vortex between the sides of the capsule and the shock-layers coming off the edges of the forward heat-shield this delivers convective heat to the sides.



Impaler, let me push back a bit against the premise of what you are pushing.  If I understand you correctly, you advocate lower speed reentry, such as from an orbit (both on Mars and Earth) than direct reentry for the MCT, primarily because then one could use metallic TPS rather than ablative TPS (i.e. PICA-X).  And that this is practically necessary to ensure high reusability and high flight rates.  Do I have that right?

But is avoiding ablative TPS really that important in the grand scheme?  Doesn't SpaceX intend to rapidly and frequently reuse the Dragon 2, which will surely have PICA-X.  What do we suppose is the answer here?  Is PICA-X something that can be de-ablated (reblated?) back on to the bottom of a capsule without too much hassle.  I'm imagining that there is an inch or so of the material, and half an inch ablates off during reentry (a little more some places, a little less others) and then then additional PICA-X is applied and added to what remains before the next flight - sort of like retreading a tire.  Or conversely, the entire backshell of PICA-X is designed and installed as a bolt on module, and a new one will be bolted onto the capsule for each flight (i.e. changing the tires).  I ask because I don't know.

But in any case, this seems to solve the problem fully, without a great deal of bother.  Surely a simpler solution than radically modifying the flight profiles to include orbital insertion on each end, which requires a great deal of additional fuel, don't you think?

Well first off their are likely to be advantages outside of the thermal protection in the vehicle being designed for low entry speed, lower g-forces which mean a lighter structural frame.  As this is integral to the vehicle any gain/loss in mass is permanent and will have to be hauled around for the whole vehicle life-span.

Second, the low-entry system is also paired with a lower DeltaV demand placed on the vehicle by offloading heliocentric transport to a second vehicle, this is in opposition to direct-Earth-return.  This reduces the tank volume needed on the lander, which then compounds to lighter structures, smaller surface areas for TPS, lower liftoff mass etc etc. 

Third the Mars surface propellent production demands are MUCH less under this proposal by something like 60-80%, we don't know exactly WHAT that process will be but it will certainly require a lot of pre-positioned equipment and power sources.  Regardless of how efficient it is (and my own estimates are that we can get 3x to 4x the equipment mass in propellents produced per synod) the less propellent we need the more usable cargo can be sent instead, or the propellents can be used locally for any number of purposes.

Lastly while I think it is reasonable to expect SpaceX to re-apply PICAX to a vehicle that uses it (reused Dragon would be great to see), the process would likely be possible only on Earth.  Where as my intent was to evolve the lander into a rapid mars-surface 2 mars orbit cargo hauler that performs ~100 such round trips per synod before returning to Earth, a PICAX shield with that many layers sounds like it would be more massive then the metallic TPS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/25/2015 06:59 am
First off trying to use your EYE as a after-the-fact calorimeter on a surface that was heat-shielded is a profoundly flawed.  You have no idea what surface temperature it reached nor do you have any idea if it is truly pristine, that would take chemical analysis after-the-fact or ideally a temperature probe during the entry itself.

...


The rear of this IRSO vehicle looks to be composed of small solar panels, solar panel are covered with glass which has a high melting point, we would not expect this to blacken or char, the forward TPS is non-ablative ceramic tile which would not deposit black char streaks.  The shuttle didn't LOOK chared when it returned from orbit but the top of it had TPS of a thinner, lower temperature type, but TPS none the less.  What is behind the panels? you have no idea.


Look closer. The electrical wiring for the solar panels is still there in its bright red attachment points.

https://upload.wikimedia.org/wikipedia/commons/b/be/ISRO-SCRE-1-Spacecraft-1.jpg
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Andy Smith on 06/25/2015 10:43 am
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

Given the speculated mass fractions, isn't the actual first stage just about capable of SSTO if it doesn't have a second stage or any payload attached?

It may need a pre-launched second stage to dock and act as a shepherd, raising it to its working location - but that should be do-able?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/25/2015 11:55 am
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

Given the speculated mass fractions, isn't the actual first stage just about capable of SSTO if it doesn't have a second stage or any payload attached?

It may need a pre-launched second stage to dock and act as a shepherd, raising it to its working location - but that should be do-able?

Yes but it would mean sending a lot of expensive Raptors on a one off mission. If inflatable LOX/methane tanks are possible it seems like the more cost efficient solution to me.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/25/2015 12:01 pm
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

Given the speculated mass fractions, isn't the actual first stage just about capable of SSTO if it doesn't have a second stage or any payload attached?

It may need a pre-launched second stage to dock and act as a shepherd, raising it to its working location - but that should be do-able?
Very good point! And a much better idea than mine. Especially a huge first stage with no legs. Because it's big, low drag loss. Because no upper stage, low gravity losses. f9 v1.2-like mass fractions and propellant densification. Raptor's high Isp. All those engines allow you to have ability to throttle way down to prevent crushing your stage due to over acceleration of such a light stage. Just put an aerodynamic fairing on top, and yeah, it should have no problem reaching orbit.

But if it's going to be a depot, it might need better insulation than a first stage usually has. That might be a major reason why you wouldn't do this, since you might need to fly it inside a fairing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Andy Smith on 06/25/2015 01:05 pm
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

Given the speculated mass fractions, isn't the actual first stage just about capable of SSTO if it doesn't have a second stage or any payload attached?

It may need a pre-launched second stage to dock and act as a shepherd, raising it to its working location - but that should be do-able?

Yes but it would mean sending a lot of expensive Raptors on a one off mission. If inflatable LOX/methane tanks are possible it seems like the more cost efficient solution to me.

That's a good point. Of course if this depot had appropriate fuel levels it could later de-orbit and land for servicing - say every two years following the mars departure window. It is no longer a one off mission, just another part of the reusable infrastructure?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/25/2015 01:10 pm
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

Given the speculated mass fractions, isn't the actual first stage just about capable of SSTO if it doesn't have a second stage or any payload attached?

It may need a pre-launched second stage to dock and act as a shepherd, raising it to its working location - but that should be do-able?

Yes but it would mean sending a lot of expensive Raptors on a one off mission. If inflatable LOX/methane tanks are possible it seems like the more cost efficient solution to me.

That's a good point. Of course if this depot had appropriate fuel levels it could later de-orbit and land for servicing - say every two years following the mars departure window. It is no longer a one off mission, just another part of the reusable infrastructure?

But it would need significant modifications to handle re-entry as it was designed for something like 2.5 km/s re-entry.  Another possibility though would be to retrieve the engines only or keep them as a stock of on orbit spares for replacements (or even ship them to Mars as a pool of spares there).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/25/2015 01:13 pm
Or use end of life Raptors.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Andy Smith on 06/25/2015 01:33 pm
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

Given the speculated mass fractions, isn't the actual first stage just about capable of SSTO if it doesn't have a second stage or any payload attached?

It may need a pre-launched second stage to dock and act as a shepherd, raising it to its working location - but that should be do-able?
Very good point! And a much better idea than mine. Especially a huge first stage with no legs. Because it's big, low drag loss. Because no upper stage, low gravity losses. f9 v1.2-like mass fractions and propellant densification. Raptor's high Isp. All those engines allow you to have ability to throttle way down to prevent crushing your stage due to over acceleration of such a light stage. Just put an aerodynamic fairing on top, and yeah, it should have no problem reaching orbit.

But if it's going to be a depot, it might need better insulation than a first stage usually has. That might be a major reason why you wouldn't do this, since you might need to fly it inside a fairing.

I can see the insulation being an issue - perhaps I was being too optimistic - would it depend on where the depot was located, raise it sufficiently far that the Earth isn't adding to the heat load, then "end on" to the sun?

If its using the methane / oxygen to power itself, run the refrigeration plant etc. Then it would need some detailed maths to balance heat loads and fuel being used vs the cost of additional insulation / infrastructure (ie one launch vs a depot requiring multiple launches for a non-returnable asset).

One other problem would be where do we install radiators? It would increase the valve and plumbing complexity - but (wild suggestion I know) how about using the engine bells?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/25/2015 01:37 pm
  Another possibility though would be to retrieve the engines only or keep them as a stock of on orbit spares for replacements (or even ship them to Mars as a pool of spares there).

Scratch the part that suggests using them as spares on orbit or at Mars, wrong engines, though the concept works with MCT derived depots. A variant of Lamontagne's design seems most likely. Start with one, and build up to 2, 4, or even more as demand dictates. One thing I see is having liquid hydrogen at this depot as the "refrigerant" and of course potentially to sell to other customers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Andy Smith on 06/25/2015 01:40 pm
Use a modified first stage as a giant depot. Launch it partially filled (to reach orbit dry, so acting as its own upper stage) on top of another first stage.

Given the speculated mass fractions, isn't the actual first stage just about capable of SSTO if it doesn't have a second stage or any payload attached?

It may need a pre-launched second stage to dock and act as a shepherd, raising it to its working location - but that should be do-able?

Yes but it would mean sending a lot of expensive Raptors on a one off mission. If inflatable LOX/methane tanks are possible it seems like the more cost efficient solution to me.

That's a good point. Of course if this depot had appropriate fuel levels it could later de-orbit and land for servicing - say every two years following the mars departure window. It is no longer a one off mission, just another part of the reusable infrastructure?

But it would need significant modifications to handle re-entry as it was designed for something like 2.5 km/s re-entry.  Another possibility though would be to retrieve the engines only or keep them as a stock of on orbit spares for replacements (or even ship them to Mars as a pool of spares there).

Isn't it just fuel? If it can get to orbit then it can propulsively slow down, it doesn't need to re-enter at orbital speeds - whether fuelling the depot in order to bring it home is cost effective I don't know. But I could see the benefits of being able to inspect it before launching the next iteration as being useful?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: ArbitraryConstant on 06/25/2015 02:11 pm
Also because of the intensity of the black body radiation of the earth and its daytime reflection of heat, I see the depot needing far more active cooling than the MCT which will only need to keep its propellant from boiling off near Mars and between Mars and Earth but will not need to keep it cool for long in the 10 radii range of the Earth.
Not sure this is a problem. Other depot studies have noted this as an issue for hydrogen but methane is quite a mild cryogen in comparison. With solar power a methane prop depot should be able to be zero boiloff anywhere.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/25/2015 02:42 pm
Yes boiling points are:

-252.8 degrees C for hydrogen
-182.9 degrees C for oxygen
-162 degrees C for methane. 

Hydrogen is much harder to keep from boiling off. 

I worked for a natural gas company and we liquefied natural gas in the summer for winter peeks.  Boil off was not that big of a problem on the ground, and space is colder.  Tanks on the ground were doubled like a thermos bottle, with a vacuum pulled between the inner storage tank and outer shell.  There was about 3' of space between them (1m), so keeping cold wasn't hard, and that is in the deep south. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/25/2015 02:52 pm
I do like the idea of using a BFR first stage for a refueling depot for the MCT's.  Seems like it wouldn't be such a problem with removal of all but 4-5 Raptor engines to get it into orbit.  Also removal of landing legs unless one wants to deorbit it.  Then installing extra insulation on the tanks, add solar panels and shading panels if necessary, and adding docking facilities like previously proposed. 

The only thing I see, is in a Boeing proposal was to have the depot spin slowly to make the fuel stay on the end being pumped from, especially when near empty.  So the depot tanks might have to be in a circle with docking in the center, then spin slowly while fueling and refilling.  Say have an x shape, 3 tanks on three legs, with the 4th leg for refueling and refilling, with the ability to spin slowly, (SEP thrusters maybe attached to create spin and to stop spin) or use boil off for thrusters. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: ArbitraryConstant on 06/25/2015 03:10 pm
Your original flight cost was calculated correctly (800 passenger flights, 8000 cargo flight, 8800 total at $50M a pop yields the $440B.

The cost of the cargo is presently unknown. My gut feeling is that the answer to question "what do you have to pack  in order to live on Mars" is quite lengthy, complex and thus expensive.
I think Musk is assuming most things will be manufactured locally before flights reach that level.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 06/25/2015 03:35 pm
Yes boiling points are:

252.8 degrees C for hydrogen
182.9 degrees C for oxygen
162 degrees C for methane. 

Hydrogen is much harder to keep from boiling off. 

I worked for a natural gas company and we liquefied natural gas in the summer for winter peeks.  Boil off was not that big of a problem on the ground, and space is colder.  Tanks on the ground were doubled like a thermos bottle, with a vacuum pulled between the inner storage tank and outer shell.  There was about 3' of space between them (1m), so keeping cold wasn't hard, and that is in the deep south.
You forgot negative signs.  Also: Please just use kelvins.  It's much easier.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/25/2015 03:52 pm
Also because of the intensity of the black body radiation of the earth and its daytime reflection of heat, I see the depot needing far more active cooling than the MCT which will only need to keep its propellant from boiling off near Mars and between Mars and Earth but will not need to keep it cool for long in the 10 radii range of the Earth.
Not sure this is a problem. Other depot studies have noted this as an issue for hydrogen but methane is quite a mild cryogen in comparison. With solar power a methane prop depot should be able to be zero boiloff anywhere.


There was a paper I read in the last month (and I know it is linked to here on NSF and I will look for it later) that suggested LOX and Methane would be fine more than 10 radii from Earth at Earth's distance from the sun with simply passive cooling, but that near Earth and potentially Mars more cooling would be required. And remember a LEO depot will spend roughly half its time above a sunlit Earth that is radiating significantly more than its black body night time amount and that it will cover a significant fraction of the visible area around the depot.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: ArbitraryConstant on 06/25/2015 04:07 pm
And remember a LEO depot will spend roughly half its time above a sunlit Earth that is radiating significantly more than its black body night time amount and that it will cover a significant fraction of the visible area around the depot.
I could say the same of LNG depots on the ground.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 06/25/2015 04:09 pm
Also because of the intensity of the black body radiation of the earth and its daytime reflection of heat, I see the depot needing far more active cooling than the MCT which will only need to keep its propellant from boiling off near Mars and between Mars and Earth but will not need to keep it cool for long in the 10 radii range of the Earth.
Not sure this is a problem. Other depot studies have noted this as an issue for hydrogen but methane is quite a mild cryogen in comparison. With solar power a methane prop depot should be able to be zero boiloff anywhere.


There was a paper I read in the last month (and I know it is linked to here on NSF and I will look for it later) that suggested LOX and Methane would be fine more than 10 radii from Earth at Earth's distance from the sun with simply passive cooling, but that near Earth and potentially Mars more cooling would be required. And remember a LEO depot will spend roughly half its time above a sunlit Earth that is radiating significantly more than its black body night time amount and that it will cover a significant fraction of the visible area around the depot.
True, it is much more difficult in LEO, but an actuated passive system is very flexible, and even a static passive system can be done.  Mount a cone-shaped reflective thermal shroud around the tanks, and point it normal to the orbital plane, and so long as your choice of orbital plane isn't very far from the ecliptic, you can be mostly in radiative thermal contact with deep space rather than the Earth or the Sun.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/25/2015 04:18 pm
Sorry about the negative signs.  I'm not a rocket scientist and have never used kelvin.  When I looked up the temps, they were not listed in kelvin but C and F.  I know kelvin is from absolute zero, but a lot of people here are not rocket scientists but all should know degrees C or F. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 06/25/2015 04:19 pm
I worked for a natural gas company and we liquefied natural gas in the summer for winter peeks.  Boil off was not that big of a problem on the ground, and space is colder.  Tanks on the ground were doubled like a thermos bottle, with a vacuum pulled between the inner storage tank and outer shell.  There was about 3' of space between them (1m), so keeping cold wasn't hard, and that is in the deep south.

Taking advantage of the vacuum of space, a sunshield keeping the tanks in the shade would have the same effect. It shouldn't be difficult to minimize boil off for LOX and liquid methane.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/25/2015 04:28 pm
On another question, could one of these large fuel depots be towed to L1 or L2 for say fueling some MCT's going to and from Mars without them landing every time?  Seems like a lot of cargo, in cargo containers that could fit in an MCT could be brought up in Falcon Heavies, say two 50 ton containers.  Then towed with SEP tugs to L1 or L2 to be loaded into an MCT to be sent back to Mars.  Fuel and LOX in 50 ton units could also be towed to the fuel depot for refilling.  If Vulcan comes on line, it too, could send up shipments of cargo/fuel to be loaded and sent to Mars.  SpaceX wouldn't have to provide everything.  Everyone might eventually get involved in Mars colonization, ESA, Russia, China, India, Japan, NASA, and other American companies.  SpaceX just seems to be leading the way. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/25/2015 04:52 pm
Also because of the intensity of the black body radiation of the earth and its daytime reflection of heat, I see the depot needing far more active cooling than the MCT which will only need to keep its propellant from boiling off near Mars and between Mars and Earth but will not need to keep it cool for long in the 10 radii range of the Earth.
Not sure this is a problem. Other depot studies have noted this as an issue for hydrogen but methane is quite a mild cryogen in comparison. With solar power a methane prop depot should be able to be zero boiloff anywhere.


There was a paper I read in the last month (and I know it is linked to here on NSF and I will look for it later) that suggested LOX and Methane would be fine more than 10 radii from Earth at Earth's distance from the sun with simply passive cooling, but that near Earth and potentially Mars more cooling would be required. And remember a LEO depot will spend roughly half its time above a sunlit Earth that is radiating significantly more than its black body night time amount and that it will cover a significant fraction of the visible area around the depot.

Only had to go back 119 posts to find where I replied to a message with the excerpt from that paper quoted:

http://www.permanent.com/space-transportation-propellants.html (http://www.permanent.com/space-transportation-propellants.html)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/25/2015 05:01 pm
True, it is much more difficult in LEO, but an actuated passive system is very flexible, and even a static passive system can be done.  Mount a cone-shaped reflective thermal shroud around the tanks, and point it normal to the orbital plane, and so long as your choice of orbital plane isn't very far from the ecliptic, you can be mostly in radiative thermal contact with deep space rather than the Earth or the Sun.

So, basically use Webb telescope shielding technology to build a "crater" in orbit, well insulated from Earth. Place propellant tanks in the bottom of that crater.  Add a sun shield to make it permanently shadowed and you're set. Illustrated simple setting with articulating boom. Some other geometry might not even need that. Having openings to "vent" the thermal radiation into 2.7K space improves shield efficiency a lot. In regular MLI it just bounces between layers without escape.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 06/25/2015 05:18 pm
True, it is much more difficult in LEO, but an actuated passive system is very flexible, and even a static passive system can be done.  Mount a cone-shaped reflective thermal shroud around the tanks, and point it normal to the orbital plane, and so long as your choice of orbital plane isn't very far from the ecliptic, you can be mostly in radiative thermal contact with deep space rather than the Earth or the Sun.

So, basically use Webb telescope shielding technology to build a "crater" in orbit, well insulated from Earth. Place propellant tanks in the bottom of that crater.  Add a sun shield to make it permanently shadowed and you're set. Illustrated simple setting with articulating boom. Some other geometry might not even need that. Having openings to "vent" the thermal radiation into 2.7K space improves shield efficiency a lot. In regular MLI it just bounces between layers without escape.

That's one way, but you would have to actuate that every orbit.  A non-actuated passive thermal shield is also possible so long as you control orientation, tightly in LEO and less tightly as you gain altitude.  It would get a *little* incident radiation, but not enough to matter.  This is a matter of proportions: You can tolerate small amounts of boiloff, a 99% reduction is fine.

Attachment has reflective thermal shield as a gold conical foil around a blue-grey tank.  Emission direction is towards the normal of the orbital plane, the only area that remains non-occluded by the Earth for the whole orbit.  The orbital plane is chosen so the Sun never drifts into this narrow beam of heat emission/absorption.

An elliptical reflector would work better (for the same reasons spotlight reflectors and other reflective geometrical optics work), but may have issues with structural packing.  The cone illustrated is probably not long enough to work well, but suffices to show the concept.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/25/2015 06:11 pm
That shields the sun completely but the "mouth" of the cone still sees half of earth. Wondering if some finetuning would help that. Might be quite sufficient for methalox but passive LEO system capable to cope with hydrogen would be nice too.

Extend a flat reflector (normal pointing towards earth) from the earth-side lip of the cone? If the orbit is at ecliptic it won't reflect sunshine into the cone.

Fancier would be to do elliptical conical cut, the longer "lip" facing earth. Sun would shine into the cone but it should reflect it away before it reaches the bottom of it, no? (Not sure, seems that way)

With elliptical reflector do you mean those which attempt to focus the beam  (parabola being optimal) ? Wondering if inverted shape would be even better, like a trumpet? After all the goal is a shape which rejects radiation fed to it from all angles as much as possible before it reaches the "bottom" where the tank(s) are, which see only black space.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/25/2015 06:43 pm
Sorry about the negative signs.  I'm not a rocket scientist and have never used kelvin.  When I looked up the temps, they were not listed in kelvin but C and F.  I know kelvin is from absolute zero, but a lot of people here are not rocket scientists but all should know degrees C or F.

Too funny Just asked 6th grade daughter and she knows the Kelvin scale 😀
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 06/25/2015 09:04 pm
Sorry about the negative signs.  I'm not a rocket scientist and have never used kelvin.  When I looked up the temps, they were not listed in kelvin but C and F.  I know kelvin is from absolute zero, but a lot of people here are not rocket scientists but all should know degrees C or F.

Too funny Just asked 6th grade daughter and she knows the Kelvin scale 😀

Yes, you don't have to be a rocket scientist to use Kelvin, but most here do have some kind of STEM background and fully understand it. Kelvin is taught in the younger grades and it is the metric used in high school sciences. In high school chemistry, basic calorimetry is measured in Kelvin. Thermal calculations in high school physics are done in Kelvin. Celsius and Kelvin both have a 100 degree difference between the state change temperatures of pure H2O @ STP (Standard Temperature and Pressure), i.e. solid/liquid and liquid/gas. Thus, Celsius and Kelvin scale on a 1:1 ratio. Since absolute zero is 273.15C below the first state change temperature of pure H2O @ STP, given y = temp K and x = temp C, y = x +273.15. Kids do learn how to do this in middle school.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 06/25/2015 09:25 pm
On another question, could one of these large fuel depots be towed to L1 or L2 for say fueling some MCT's going to and from Mars without them landing every time?  Seems like a lot of cargo, in cargo containers that could fit in an MCT could be brought up in Falcon Heavies, say two 50 ton containers.  Then towed with SEP tugs to L1 or L2 to be loaded into an MCT to be sent back to Mars.  Fuel and LOX in 50 ton units could also be towed to the fuel depot for refilling.  If Vulcan comes on line, it too, could send up shipments of cargo/fuel to be loaded and sent to Mars.  SpaceX wouldn't have to provide everything.  Everyone might eventually get involved in Mars colonization, ESA, Russia, China, India, Japan, NASA, and other American companies.  SpaceX just seems to be leading the way.

Fuel depots would optimally have their own vacuum engines (and they already have plenty fuel).  This would allow one to be filled in LEO and then cruise on to EML-1/2 to either await customers or transfer its load to another depot.  The ULA-proposed ACES model, adjusted to store liquid methane instead of liquid hydrogen, is the best example I've seen of a functional system.  Additionally, a full depot at EML-2 would be only 0.14km/s from Earth departure, so could also reposition itself to Mars orbit for fueling ops there.

Cargo would be tougher to move than fuel, so modular containers/tugs could work well.  This presupposes that the MCTs don't land on Earth to load cargo...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/25/2015 09:51 pm
I too know the kelvin scale and I too have used formulas for gas flows using the kelvin scale.  I was just trying to keep it simple and I saw the degrees C and just transferred it in my text.  Most people here at lest can relate to 0 deg C to freezing water.  However there are a lot of newbees, and a lot of foreign people reading this and know centigrade and do not use the F scale.  Some of you guys obviously are just plain rude and don't care if a lot of people read this forum.  I for one, would like for more to read it and get interested because they VOTE and can have a say in how much is spent on the space program.  It has to be focused and exciting for most to understand.  Sorry if I have offended you Kelvin only users. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 06/25/2015 10:18 pm
Lets just correct the signs if they are wrong and not mock people for their chosen temperature scales. An american using celsius has already shown generosity towards rest of the world. Not long ago I read scientific paper about gas turbines which had temperatures in rankines.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/25/2015 10:44 pm
Sorry about the negative signs.  I'm not a rocket scientist and have never used kelvin.  When I looked up the temps, they were not listed in kelvin but C and F.  I know kelvin is from absolute zero, but a lot of people here are not rocket scientists but all should know degrees C or F.

Too funny Just asked 6th grade daughter and she knows the Kelvin scale 😀

Yes, you don't have to be a rocket scientist to use Kelvin, but most here do have some kind of STEM background and fully understand it. Kelvin is taught in the younger grades and it is the metric used in high school sciences. In high school chemistry, basic calorimetry is measured in Kelvin. Thermal calculations in high school physics are done in Kelvin. Celsius and Kelvin both have a 100 degree difference between the state change temperatures of pure H2O @ STP (Standard Temperature and Pressure), i.e. solid/liquid and liquid/gas. Thus, Celsius and Kelvin scale on a 1:1 ratio. Since absolute zero is 273.15C below the first state change temperature of pure H2O @ STP, given y = temp K and x = temp C, y = x +273.15. Kids do learn how to do this in middle school.

Real rocket scientists use Rankine. 

;-)

Lets just correct the signs if they are wrong and not mock people for their chosen temperature scales. An american using celsius has already shown generosity towards rest of the world. Not long ago I read scientific paper about gas turbines which had temperatures in rankines.

Well said.  You don't need to be a rocket scientist to use kelvin, and rocket scientist I'm sure use celsius and Fahrenheit an Rankine depending on how old they are, where they are located in the world, and person preference. 

I had a Mechanics of Materials professor who hated all metric scales and so often had Imperial/US Standard on his tests, under the premise that we here (in the Northwest US) don't have a feel for metric units. They're just numbers with no "gut check" ability.  If we got an answer in pounds, we had a feel of our result was withing the ballpark, or completely out of whack meaning we probably screwed up a calculation somewhere, and needed to go back and check our work.  But what does a Newton feel like? What does 21,409 Newtons feel like?  Do you have an idea right off the top of your head?  Does your answer feel right?  Probably not, if you grew up in the US.
But you do if it's 1 pound or 21,409 pounds. 

Or a Pascal vs. a PSI.  or an acre vs. a hectare, etc.

I know that will make some people's head's explode here, but he was a PhD in Mechanical Engineering and a very big brain.  It was his personal preference because he noticed student working in metric who made a calculation error usually had no feel for if their answer made any sense or not, as they usually did with US Standard/Imperial.
And I had other professors who were dead set on making sure we all -only- used SI units, because they thought America should already be using them.

So...use of units isn't any indication of anything other than preference usually.  Nothing to get hung up on.  :-)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 06/26/2015 01:37 am
I'm retired and grew up on the English system.  I even had a professor who would not let me use my new $100 calculator in class, had to use a slide rule.  Said the slide rule didn't use batteries and always worked.  I also worked most of my career using paper drawings instead of computer.  I was only trying to use what I thought most who might read these forums would use, Centigrade.  I try to be simple so MOST people can easily understand.  There are thousands of people who access these forums who are not scientists or engineers, but who just are interested in the space program.  Also, this is s Speculation thread, not one working out problems.  I saw that someone posted about not using methane for rocket fuel because of the DEEP cyro cooling of methane which is warmer than lox.  Hydrogen is the problem, not methane.  I worked as an engineer with a natural gas company for 39 years, and we liquefied natural gas on the ground in large tanks, no problem.  Just trying to let him know space could be easier since it is colder. 

I have two college professor relatives, and they don't use kelvin as their fields are not engineering or physics, but they are interested in what NASA is doing. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 06/29/2015 09:22 am
When I was in primary school, sometime around Grade 3, as part of our science class we measured out 1 kg of sand in a plastic bag and passed it around, getting the heft of it. That stuck with me throughout my life, although it weighs "less" now that I'm an adult. Amusingly, I was also about 1 metre tall at the time. I don't remember learning about Kelvin, it must have been in Jerry Pournelle's A Step Farther Out which taught me a lot of my physics before I learned it in the classroom.

How much does a kilo weigh? Same as a litre of coke. How much is a Newton? A 100gm bag of chips. Metric's great if you grow up with it.

Back on topic, metholox is also a lot less volume to shade than LH2... but you will have to reboost against atmospheric drag in LEO, which counts against your boiloff issues. Staging from L2 you could use the recovered spent stages

The size of depot you're going to be looking at to support (eventually) 800 transports is huge. O'Neill colony huge. So after the first few depots you want something that is pretty daunting, and the economics will only work if you scale up quickly. Maybe a long chain of these things (although tidal effects come into play here too - maybe vertically oriented). Debris is also going to be a consideration. It would probably have to be manned anyway, and with so many stages coming and going shouldn't be a problem. There's going to be all sorts of work needed to be done all the time and robotics won't be able to handle all of it, not beyond the first dozen or so tanks.

So perhaps a popcorn box-shaped sunshield, with a reinforced "fore" panel and removable "aft" panel that simply gets transferred rearwards as the depot grows.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/29/2015 10:06 am
With the size of a large depot the boiloff problem in LEO may go away. The square cube law helps. Plus constantly arriving sub cooled propellant. What's left of boiloff may justbe accepted for the sake of simplicity of operations.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/29/2015 11:44 am
If you have a sunshade you also automatically have a place for solar cells.  You can use these to power compressors than can cool the fuel and eliminate boil off altogether.  Boil off is using phase change to cool the fuel to offset solar gains.  It seems better to me to do this in a controlled way, that will eventually offset the cost of lifting the compressors to orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 06/29/2015 01:34 pm
With the size of a large depot the boiloff problem in LEO may go away. The square cube law helps. Plus constantly arriving sub cooled propellant. What's left of boiloff may justbe accepted for the sake of simplicity of operations.

True but your tank size is going to be constrained by the size of the launch vehicle payload, unless you weld it together in orbit (also a possibility). A 12m diameter tank should be fine though - and hold plenty of propellant.

Plus you have to make ullage burns to get the stuff flowing, or else use something clever like low-temperature bladders. Rotate for (very weak) artificial gravity? That'll probably cause more problems than it solves.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/29/2015 02:21 pm
True but your tank size is going to be constrained by the size of the launch vehicle payload, unless you weld it together in orbit (also a possibility). A 12m diameter tank should be fine though - and hold plenty of propellant.

There are ways around that. One, it was mentioned somewhere on the forum that inflatable tanks for LOX and methane are possible. The second, the square cube law still applies if you bundle tanks. They see the temperature of the fuel everywhere, where a tank is.

Plus you have to make ullage burns to get the stuff flowing, or else use something clever like low-temperature bladders. Rotate for (very weak) artificial gravity? That'll probably cause more problems than it solves.

You are right, I forgot ullage. If the tank becomes really large that becomes an issue.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/29/2015 03:15 pm
Plus you have to make ullage burns to get the stuff flowing, or else use something clever like low-temperature bladders. Rotate for (very weak) artificial gravity? That'll probably cause more problems than it solves.

You are right, I forgot ullage. If the tank becomes really large that becomes an issue.

A very large tank will have a significant gravity gradient (and by design could have a larger one), I don't known whether this is significant enough to avoid needing other forms of settling.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/29/2015 03:22 pm
With the size of a large depot the boiloff problem in LEO may go away. The square cube law helps. Plus constantly arriving sub cooled propellant. What's left of boiloff may justbe accepted for the sake of simplicity of operations.

True but your tank size is going to be constrained by the size of the launch vehicle payload, unless you weld it together in orbit (also a possibility). A 12m diameter tank should be fine though - and hold plenty of propellant.

Plus you have to make ullage burns to get the stuff flowing, or else use something clever like low-temperature bladders. Rotate for (very weak) artificial gravity? That'll probably cause more problems than it solves.
With two sets of tanks, it should be possible to arrange for flow of the liquid in the tanks using low velocity mixers.  If the mixers were contra rotating, the angular acceleration would tend to cancel out.  It would be important to keep velocities low, and to be able to vary the velocity of the mixers for operation with mixed phase fluids.  Rotating the whole tank seems complex, and might require rotating joints for fluid transfer, which are weak points.
As a negative point the mixers would add energy and possible increase boil off because there would be constant friction, but this could be offset by using active mechanical cooling of the fuel.  Careful operation should create laminar flow; that would create the lowest friction.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: wes_wilson on 06/29/2015 03:52 pm
With the size of a large depot the boiloff problem in LEO may go away. The square cube law helps. Plus constantly arriving sub cooled propellant. What's left of boiloff may justbe accepted for the sake of simplicity of operations.

True but your tank size is going to be constrained by the size of the launch vehicle payload, unless you weld it together in orbit (also a possibility). A 12m diameter tank should be fine though - and hold plenty of propellant.

Plus you have to make ullage burns to get the stuff flowing, or else use something clever like low-temperature bladders. Rotate for (very weak) artificial gravity? That'll probably cause more problems than it solves.
With two sets of tanks, it should be possible to arrange for flow of the liquid in the tanks using low velocity mixers.  If the mixers were contra rotating, the angular acceleration would tend to cancel out.  It would be important to keep velocities low, and to be able to vary the velocity of the mixers for operation with mixed phase fluids.  Rotating the whole tank seems complex, and might require rotating joints for fluid transfer, which are weak points.
As a negative point the mixers would add energy and possible increase boil off because there would be constant friction, but this could be offset by using active mechanical cooling of the fuel.  Careful operation should create laminar flow; that would create the lowest friction.

Following on to the talk about having the depot behind a sunshade; a less mechanically complex possibility might be to move the O as solid bricks from the depot to the spacecraft fuel tanks; then move the spacecraft into the sun to liquefy the O in the fuel tanks.   

Oxygen solidifies at 54K under 1 atm pressure.

Nasa's site says the JWST sunshield allows passive cooling to 39K. 
http://jwst.nasa.gov/sunshield.html
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/29/2015 04:30 pm
Rather than guessing this or that, how about some math?

The solar constant is about 1300 W/m2.  Since the depot is in the Earth's shadow 50% of the time this can be reduced to 650 W/m2 average.  A good reflector foil wrap with a low emissivity of e=0.1 will reduce this to 65 W/m2. Depending on insulation effectiveness, this energy will either be absorbed into the fuel, or radiated back out into space.  If the insulation was 100% effective, the exterior hull temperature would be determined by Q=Be(Ts^4-ta^4), where B is 5.7e-8, e is the emissivity of 0.1 and ta is the average ambient temperature in earth orbit, that I believe NASA usually sets at about 200°K.  Solving this gives a surface temperature of 337°K, or 65°C.
On the other hand, if the thermal resistance is 0, all the energy goes into the fuel and it boils off at the phase change rate of oxygen or methane; using 480 kJ/kg for methane, that's about 0.000135 kg/s/m2 of exposed hull area.
So you want to reduce boil off, and for this you need to insulate the tank.  To know the insulation effectiveness you can use the equation for multilayer insulation, where Q=UAdt, in which U is the insulation value, and is calculated by U=4BT^3 * (1/(N(2/e)-1)+1) where n is the number of layers.  dt is the difference between surface temperature and fuel temperature, T is the average temperature in the insulation.

If you wanted to reduce the heat gain to, let's say, 6,5 W/m2, or a factor of 10, you need an insulation value of 6.5 / (300K - 108 K) = 0,03 W/m^2K.  (300 K is an initial guess, this usually gets solved by iteration)

Knowing that T = 204K

Then 0.03=4*5.7e-8*204*(1/(N(2/e)-1)+1)
You just need to isolate N and you get the number of layers required.
Calculating N is left as an algebra exercise for the reader  ;-) .  It's my lunch break after all.  but it should be about 3 or 4.

In a sense, a shadow shield is simply a extra layer of reflective insulation, put further away in space. 
Eventually, residual heat gain can be removed by mechanical compression. This in a very inefficient process, specially at low temperatures, where Qcold = Qhot*(Tcold/Thot).
For a residual load of 6.5 W tcold at 108K and thot at 324 K, Qhot =3*6.5 = 19.5W, and the total energy radiated out by the cooling system will be 26 Watts, using 19,5 watts of electrical energy.  This is an ideal Carnot process, in the real world it should be about twice that, or about 40 W per m2 of hull area.  Since solar cells can deliver 1300 *.2*.5=325 watts on average, they can provide the required energy.

Although this is full  of outrageous simplifications, I hope this helps.
Michel Lamontagne


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 06/30/2015 09:45 pm
That's pretty good mathery.

I'll chip in that the ULA ACES depot architecture wasn't trying to achieve zero boiloff becuase it had station keeping needs.  So they just needed to mitigate the boiloff until it was about equal to what was needed for station keeping.  Methalox RCS thrusters would burn those boiloff gasses to keep the depot in proper orbit and position.

I'd assume that'd be the case here, but easier to do with LCH4 instead of LH2.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 06/30/2015 10:05 pm
Rather than guessing this or that, how about some math?

The solar constant is about 1300 W/m2.  Since the depot is in the Earth's shadow 50% of the time this can be reduced to 650 W/m2 average.  A good reflector foil wrap with a low emissivity of e=0.1 will reduce this to 65 W/m2. Depending on insulation effectiveness, this energy will either be absorbed into the fuel, or radiated back out into space.  If the insulation was 100% effective, the exterior hull temperature would be determined by Q=Be(Ts^4-ta^4), where B is 5.7e-8, e is the emissivity of 0.1 and ta is the average ambient temperature in earth orbit, that I believe NASA usually sets at about 200°K.  Solving this gives a surface temperature of 337°K, or 65°C.

I don't quite understand this.  The effective temperature (https://en.wikipedia.org/wiki/Effective_temperature) of a blackbody at 1AU should be 254K (https://en.wikipedia.org/wiki/Black-body_radiation#Temperature_of_Earth).  You can set the emissivity fairly high (for rocky Earth, emissivity approaches 1.0), but albedo is the variable you can tweak heavily, and with higher albedo should come lower hull temperatures.

In Low Earth Orbit, you have the added factor of a hemisphere radiating at ~288K (may be subject to some corrections).  But nothing, as far as I understand it, should raise the hull temperature up to 337K.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 07/01/2015 12:36 am
Rather than guessing this or that, how about some math?

The solar constant is about 1300 W/m2.  Since the depot is in the Earth's shadow 50% of the time this can be reduced to 650 W/m2 average.  A good reflector foil wrap with a low emissivity of e=0.1 will reduce this to 65 W/m2. Depending on insulation effectiveness, this energy will either be absorbed into the fuel, or radiated back out into space.  If the insulation was 100% effective, the exterior hull temperature would be determined by Q=Be(Ts^4-ta^4), where B is 5.7e-8, e is the emissivity of 0.1 and ta is the average ambient temperature in earth orbit, that I believe NASA usually sets at about 200°K.  Solving this gives a surface temperature of 337°K, or 65°C.

I don't quite understand this.  The effective temperature (https://en.wikipedia.org/wiki/Effective_temperature) of a blackbody at 1AU should be 254K (https://en.wikipedia.org/wiki/Black-body_radiation#Temperature_of_Earth).  You can set the emissivity fairly high (for rocky Earth, emissivity approaches 1.0), but albedo is the variable you can tweak heavily, and with higher albedo should come lower hull temperatures.

In Low Earth Orbit, you have the added factor of a hemisphere radiating at ~288K (may be subject to some corrections).  But nothing, as far as I understand it, should raise the hull temperature up to 337K.

The fuel depot has low emissivity and likely fairly high albedo, these are usually more or less inversely proportional.  So it reflects a lot of radiation (high albedo), and therefore absorbs very little , but for the radiation it doesn't reflect, it had a lot of difficulty getting rid of, so it has to heat up quite a bit.  That is why you can burn yourself on a piece of aluminium left in the sun.  The depot is very far from a black body, in that sense.  My use of e only in the calculations was just a quick simplification.  But the surface temperature can get quite hot.

Here is a little spreadsheet, see the cooling tab.
https://docs.google.com/spreadsheets/d/11edSaSqnDQeWBPgz1XMa4E3X0R7hPWcTS5EYxe853U8/edit#gid=2038396500
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 07/01/2015 06:46 am
The fuel depot has low emissivity and likely fairly high albedo, these are usually more or less inversely proportional.  So it reflects a lot of radiation (high albedo), and therefore absorbs very little , but for the radiation it doesn't reflect, it had a lot of difficulty getting rid of, so it has to heat up quite a bit. 

In another discussion it was mentioned that there is something as simple as a paint that combines both properties. It is high albedo - white - in the visible spectrum where the sun emits most of its energy and at the same time low albedo in infrared where a depot needs to get rid of excess energy.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 07/02/2015 12:15 am
The fuel depot has low emissivity and likely fairly high albedo, these are usually more or less inversely proportional.  So it reflects a lot of radiation (high albedo), and therefore absorbs very little , but for the radiation it doesn't reflect, it had a lot of difficulty getting rid of, so it has to heat up quite a bit. 

In another discussion it was mentioned that there is something as simple as a paint that combines both properties. It is high albedo - white - in the visible spectrum where the sun emits most of its energy and at the same time low albedo in infrared where a depot needs to get rid of excess energy.

Yes, high albedo paint is readily available for roofing.  Commercial sites rate this paint at 0,9 emissivity and 0,9 albedo.  However, it seems that it breaks down somewhat with time and that a more reasonable value for the albedo would be 0,5 or 0,6.  This still brings down the surface temperature to something like 240K, or -32C. 
But that doesn't tell the whole story, because as aluminium is very conductive, and in space there is no external surface convection to insulate it, it will lose (or gain) energy at a rate of 200 W/m2K.  So what happens then is that the surface temperture goes down to an equilibrium value between the fuel temperature and temperture from the solar heat gain, and the tank loses energy.  With the methane fuel at 160K, even a surface temperature as low as 161K would mean 200W/m2 of heat gain! (in a detailled analysis, the methane itself is not such a good conductor, and will not provide heat at this rate; in a sense the methane will act as its own insulator). Therefore, some form of insulation is needed, no matter what .  The good news is that even a thin sheet of aluminised mylar will reduce the heat gain significantly or any form of trapped gas in a foam or blanket will quicly bring this down one or 2 orders of magnitude.
 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 07/02/2015 08:01 pm
One way to speculate about the BFR launcher for the MCT is to look at mass fraction to LEO efficiency.  The F9 has a mass fraction of ~2.7% to LEO.  Despite full re-usability most of us amazing peoples/girls here expect that SX will somehow improve on that with the fully re-useable BFR. The tables below 1st assume 180mT to LEO with the dry MCT massing 80mT and the 2nd table assumes a dry MCT at 100mT.  Various optimistic mass fractions yield different BFR takeoff weights.  A T/W ratio of 1.2 is assumed yielding 1st stage thrust and dividing by 500KLBs/Raptor, the # of Raptors needed.

MCT + Payload = 180mT to LEO 

MASS FRACTION   BFR         BFR TAKEOFF      
TO LEO          WEIGHT mT      WEIGHT M LBS   THRUST M LBS     # RAPTORS @ 500KLB
5.0%                3500              7.7                     9.2                       19
                     
4.5%                3889              8.6                    10.3                       21
                     
4.0%                4375              9.6                    11.6                       23
                     
3.5%                5000            11.0                    13.2                       26
                     
3.0%                5833            12.8                    15                         31
                     
MCT + Payload = 200mT to LEO                    
MASS FRACTION                  
TO LEO        BFR                 BFR TAKEOFF      
                WEIGHT mT          WEIGHT M LBS     THRUST M LBS       # RAPTORS
5.0%                4000               8.8                   10.6                      21
                     
4.5%                4444               9.8                   11.7                      24
                     
4.0%                5000             11.0                   13.2                      26
                     
3.5%                5714             12.6                   15.1                      30

Assuming Raptor engine bells are ~1.6m wide, it's likely that 1st stage diameters of over 10m are preferred with 12.5m or even better 13.5m best to allow for max # of engines in case mass fraction drops.  A smaller MCT dry weight really helps reduce BFR mass & # of engines as would be expected.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/03/2015 05:16 pm
For comparison here are the numbers for SLS

70 mT to LEO

MASS FRACTION   SLS         SLS TAKEOFF     
TO LEO          WEIGHT mT      WEIGHT M LBS   THRUST M LBS     

2.8%                2500              5.5                    8.4 

130 mT to LEO

MASS FRACTION   SLS         SLS TAKEOFF     
TO LEO          WEIGHT mT      WEIGHT M LBS   THRUST M LBS     

4.3%                3000              6.5                    9.2                     
                     
                   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 07/04/2015 05:11 pm
Great perspective with the SLS #s.
Going with the 200mT to LEO target or possibly less it looks as if the BFR will have somewhere in the mid to high 20s # of 1st stage engines.  This likely means a single core (Musk's statement) would have over 10m diameter to house the # of engines.  Around 12.5 to 13.5m seems like a reasonable guess.  As stated by Elon, the BFR mainframe will be manufactured "close" to the launch site. This BFR will likely be a short squat looking beast compared to the taller Falcon 9.  The next question is...how wide is the upper stage, assumed to be the MCT itself?  Rockets like the Falcon & others have wide "payload" fairings. Wider is better for carrying several tens of people for several months along with many tens of metric tons of cargo.  But atmospheric entry requirements will likely drive  MCT form factor design decisions for a vehicle that goes to Mars & back from the Earth's surface.

Of course this assumes that the whole thing (MCT) goes to Mars & lands, the most conservative assumption based on what little has been said.  I would not be surprised if a very different approach was announced later this year or next year such as a SEP planetary transit vehicle. Right now, BFR & MCT have to be on Elon's back burner.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 07/04/2015 07:36 pm
The clearest proof that landing is the plan was the statement that for the first crews MCT would be the habitat on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/05/2015 06:00 am
The clearest proof that landing is the plan was the statement that for the first crews MCT would be the habitat on Mars.

And their is nothing inconsistent with that statement and having a SEP transit stage.  Musk calls it the "Mars Colonial transport SYSTEM" which clearly implies multiple parts such as the BFR first stages and what ever LEO propellent depots are need, neither of which will go to Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 07/05/2015 06:21 am
The clearest proof that landing is the plan was the statement that for the first crews MCT would be the habitat on Mars.

And their is nothing inconsistent with that statement and having a SEP transit stage.  Musk calls it the "Mars Colonial transport SYSTEM" which clearly implies multiple parts such as the BFR first stages and what ever LEO propellent depots are need, neither of which will go to Mars.

True, but it is by no means a positive proof for that concept. The infrastructure of depots in LEO and ISRU propellant production on Mars is a system by itself.

I recall Elon Musk saying something like it can be done with chemical propulsion, no advanced propulsion systems are necessary. As far as I know he never repeated that statement and it does not preclude SEP. I would not be too surprised if it is added at some point in time to improve efficiency. But I am very sure it will not be part of the initial system at the time when a first base is set up because it adds complexity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 07/05/2015 12:24 pm
...
...
I recall Elon Musk saying something like it can be done with chemical propulsion, no advanced propulsion systems are necessary. As far as I know he never repeated that statement and it does not preclude SEP. I would not be too surprised if it is added at some point in time to improve efficiency. But I am very sure it will not be part of the initial system at the time when a first base is set up because it adds complexity.
Given the depot system discussed here and given that Elon thinks an all propulsive system could work, consider the following:

Four fully-fueled Tanker-MCT (TMCT) are clustered around and attached to a Mars-Bound-MCT (MBMCT). The engines of the four TMCTs are lit and push the cluster to HEO using about 1/2 of their fuel. The MBMCT is released and begins its TMI burn while the remaining four return to LEO and then individually RTLS. Alternatively, just to a fuel depot in LEO.

Feasible?

Edit: Starting point is LEO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 07/05/2015 12:39 pm
Gwenn Shotwell in a 2015 video interview, "We're looking at SEP"

Anyone who thinks that any aspect of MCT is cast in stone right now is likely mistaken.  It's in the concept stage where many alternatives are considered, not deep into the design stage.

I took the conservative approach following Musk's long ago , "Land the whole thing" remark.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 07/05/2015 01:56 pm
Four fully-fueled Tanker-MCT (TMCT) are clustered around and attached to a Mars-Bound-MCT (MBMCT). The engines of the four TMCTs are lit and push the cluster to HEO using about 1/2 of their fuel. The MBMCT is released and begins its TMI burn while the remaining four return to LEO and then individually RTLS. Alternatively, just to a fuel depot in LEO.

Feasible?

Edit: Starting point is LEO.

I don't think it is a very efficient architecture. It means several MCT with all their mass would need to be accelerated a significant part of TMI. Also you mention using half of their fuel. It would not be necessary to reserve half of the fuel for return. Injecting into a highly ellicptic orbit would give the Mars bound MCT much of the needed delta-v and brings the booster MCT back to earth basically free.

Why do you propose to get them back to LEO? More efficient to land them for a new launch with payload.

I think the most efficient way is giving MCT tanks large enough to do TMI burn and Mars EDL by themselves. Use tanker MCT to refuel in LEO either directly fuelling up an MCT or filling depots. They need that tankage and the delta-v to get back to earth from the Mars surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 07/05/2015 05:14 pm
...
...
I don't think it is a very efficient architecture. It means several MCT with all their mass would need to be accelerated a significant part of TMI. Also you mention using half of their fuel. It would not be necessary to reserve half of the fuel for return. Injecting into a highly ellicptic orbit would give the Mars bound MCT much of the needed delta-v and brings the booster MCT back to earth basically free.

Why do you propose to get them back to LEO? More efficient to land them for a new launch with payload.

I think the most efficient way is giving MCT tanks large enough to do TMI burn and Mars EDL by themselves. Use tanker MCT to refuel in LEO either directly fuelling up an MCT or filling depots. They need that tankage and the delta-v to get back to earth from the Mars surface.
You are right, it's not the most fuel efficient. But it might be a method for reaching Mars faster than the least-energy transfer orbit to reach Mars, perhaps in in 3-4 months rather than 6. Also a method that would represent a non-SEP architecture if Elon is serious about it. I am sure this has already been addressed somewhere and lies on someone's spreadsheet.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 07/06/2015 06:00 am
Plus you have to make ullage burns to get the stuff flowing, or else use something clever like low-temperature bladders. Rotate for (very weak) artificial gravity? That'll probably cause more problems than it solves.

Maybe a totally crazy idea. But could a fan be used to herd the propellant to the pumps? That would save the need to accelerate a depot with thousands of tons of propellant so it can settle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 07/07/2015 01:36 am
Plus you have to make ullage burns to get the stuff flowing, or else use something clever like low-temperature bladders. Rotate for (very weak) artificial gravity? That'll probably cause more problems than it solves.

Maybe a totally crazy idea. But could a fan be used to herd the propellant to the pumps? That would save the need to accelerate a depot with thousands of tons of propellant so it can settle.
Good ideas.  I would think the fan could work if it covered most of the diameter.  It could be an interesting ISS or Dragon lab experiment.

I was trying to come up with a KISS transfer solution that could work between MCTs.  If one tank was actively heated/boiled and the other actively cooled to below boiling, it would all transfer except the residual gas.  There would be a constant pressure differential and flow which should keep the cold liquid on its own side.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 07/07/2015 01:52 am


...
...
I don't think it is a very efficient architecture. It means several MCT with all their mass would need to be accelerated a significant part of TMI. Also you mention using half of their fuel. It would not be necessary to reserve half of the fuel for return. Injecting into a highly ellicptic orbit would give the Mars bound MCT much of the needed delta-v and brings the booster MCT back to earth basically free.

Why do you propose to get them back to LEO? More efficient to land them for a new launch with payload.

I think the most efficient way is giving MCT tanks large enough to do TMI burn and Mars EDL by themselves. Use tanker MCT to refuel in LEO either directly fuelling up an MCT or filling depots. They need that tankage and the delta-v to get back to earth from the Mars surface.
You are right, it's not the most fuel efficient. But it might be a method for reaching Mars faster than the least-energy transfer orbit to reach Mars, perhaps in in 3-4 months rather than 6. Also a method that would represent a non-SEP architecture if Elon is serious about it. I am sure this has already been addressed somewhere and lies on someone's spreadsheet.
There have been several MCT designs that had large enough tanks to do the 4 month transfer direct from LEO.  (I think the jump from 4 to 3 months is pretty insane most synods).

If you think those tanks are too large, and want to transfer to a higher energy orbit before TMI, you should just use one extra MCT instead of 4.  That will save hundreds of tons of propellant because you are moving less dry mass.  A reusable SEP tug is another popular option.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 07/07/2015 10:45 pm
...
...
There have been several MCT designs that had large enough tanks to do the 4 month transfer direct from LEO.  (I think the jump from 4 to 3 months is pretty insane most synods).

If you think those tanks are too large, and want to transfer to a higher energy orbit before TMI, you should just use one extra MCT instead of 4.  That will save hundreds of tons of propellant because you are moving less dry mass.  A reusable SEP tug is another popular option.
Excellent. I have seen a lot of discussion with the SEP option, but not the propellant only option. Do you know where I could find those designs -- on this forum?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 07/07/2015 10:50 pm
One way to speculate about the BFR launcher for the MCT is to look at mass fraction to LEO efficiency.  The F9 has a mass fraction of ~2.7% to LEO.  Despite full re-usability most of us amazing peoples/girls here expect that SX will somehow improve on that with the fully re-useable BFR. The tables below 1st assume 180mT to LEO with the dry MCT massing 80mT and the 2nd table assumes a dry MCT at 100mT.  Various optimistic mass fractions yield different BFR takeoff weights.  A T/W ratio of 1.2 is assumed yielding 1st stage thrust and dividing by 500KLBs/Raptor, the # of Raptors needed.

MCT + Payload = 180mT to LEO 

MASS FRACTION   BFR         BFR TAKEOFF      
TO LEO          WEIGHT mT      WEIGHT M LBS   THRUST M LBS     # RAPTORS @ 500KLB
5.0%                3500              7.7                     9.2                       19
                     
4.5%                3889              8.6                    10.3                       21
                     
4.0%                4375              9.6                    11.6                       23
                     
3.5%                5000            11.0                    13.2                       26
                     
3.0%                5833            12.8                    15                         31
                     
MCT + Payload = 200mT to LEO                    
MASS FRACTION                  
TO LEO        BFR                 BFR TAKEOFF      
                WEIGHT mT          WEIGHT M LBS     THRUST M LBS       # RAPTORS
5.0%                4000               8.8                   10.6                      21
                     
4.5%                4444               9.8                   11.7                      24
                     
4.0%                5000             11.0                   13.2                      26
                     
3.5%                5714             12.6                   15.1                      30

Assuming Raptor engine bells are ~1.6m wide, it's likely that 1st stage diameters of over 10m are preferred with 12.5m or even better 13.5m best to allow for max # of engines in case mass fraction drops.  A smaller MCT dry weight really helps reduce BFR mass & # of engines as would be expected.

Are you counting the mass of MCT as payload, or as the stage itself?  If it is it's own 2nd stage, then you should figure 180 or 200mt -gross- to LEO.

It'd be a heavy stage with a bad mass fraction obviously, but a stage nonetheless.

For example, STS could only delivery about 23mt net payload into LEO.  But it could deliver ~90mt gross mass into LEO.   And actually more if you factor in the ~27mt dry ET which was dropped just prior to circular LEO.

Direct's J130 advertised it could put about 70mt into LEO.  But the core went almost to LEO, and it  would have massed about 71mt at burnout (according to Direct's baseball cards).  SO the J130 was pushing upwards of 140mt gross towards LEO (unsure the actual net payload it could have delivered to a fully circular LEO).  And it would have had less than 7Mlbs of thrust at take off.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 07/08/2015 01:57 am
One way to speculate about the BFR launcher for the MCT is to look at mass fraction to LEO efficiency.  The F9 has a mass fraction of ~2.7% to LEO.  Despite full re-usability most of us amazing peoples/girls here expect that SX will somehow improve on that with the fully re-useable BFR. The tables below 1st assume 180mT to LEO with the dry MCT massing 80mT and the 2nd table assumes a dry MCT at 100mT.  Various optimistic mass fractions yield different BFR takeoff weights.  A T/W ratio of 1.2 is assumed yielding 1st stage thrust and dividing by 500KLBs/Raptor, the # of Raptors needed.

MCT + Payload = 180mT to LEO 

MASS FRACTION   BFR         BFR TAKEOFF      
TO LEO          WEIGHT mT      WEIGHT M LBS   THRUST M LBS     # RAPTORS @ 500KLB
5.0%                3500              7.7                     9.2                       19
                     
4.5%                3889              8.6                    10.3                       21
                     
4.0%                4375              9.6                    11.6                       23
                     
3.5%                5000            11.0                    13.2                       26
                     
3.0%                5833            12.8                    15                         31
                     
MCT + Payload = 200mT to LEO                    
MASS FRACTION                  
TO LEO        BFR                 BFR TAKEOFF      
                WEIGHT mT          WEIGHT M LBS     THRUST M LBS       # RAPTORS
5.0%                4000               8.8                   10.6                      21
                     
4.5%                4444               9.8                   11.7                      24
                     
4.0%                5000             11.0                   13.2                      26
                     
3.5%                5714             12.6                   15.1                      30

Assuming Raptor engine bells are ~1.6m wide, it's likely that 1st stage diameters of over 10m are preferred with 12.5m or even better 13.5m best to allow for max # of engines in case mass fraction drops.  A smaller MCT dry weight really helps reduce BFR mass & # of engines as would be expected.

Are you counting the mass of MCT as payload, or as the stage itself?  If it is it's own 2nd stage, then you should figure 180 or 200mt -gross- to LEO.


Yes the MCT itself plus the 100mT "payload? Elon mentioned has a gross mass to LEO of 180mT or 200mT in my above examples.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 07/08/2015 06:25 am
F9R 1.1 can put approx 13.1mT to LEO with recovery of the first stage. That might improve for 1.2 but we dont have numbers on that yet.
Second stage weights around 3.9mT while F9R weights about 505mT at launch. That makes a gross mass to orbit of about 3.36%.

But that is with KeroLOX all the way. With MethaLOX, alone that number would increase significantly. So yes, I guess it is safe to assume that the mass to orbit fraction will be around 4 to 5 % as you listed in your table. If SpaceX has enough unicorn hair and ferry dust left from their Dragon production, it might even go higher than 5%, simply because there is no payload adapter, fairings or what have you necessary.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: symbios on 07/08/2015 11:13 am
I think this is interesting because everything hangs on the mass "budget" (gross weight to LEO).

I think that Mr Musk is not going for a high mass fraction but rather price and re-usability.

That means that he might be forced to add things that will prolong the life of the booster and MCT.

To compensate he will have to go for a higher thrust on the booster. Maybe that is why he has mentioned 15 mlbs rather then 12 mlbs. He has to have a margin for things always get more heavy in production than originally planed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: symbios on 07/08/2015 11:33 am
Another interesting discussion is how much of the total delta V budget of the total LV is going into the booster and how much is going into the MCT (second stage)?

I think that there will be a big difference from EELV LV's where most of the fuel is in the booster with a small second stage.

1. You will not be able to land the booster on a barge, it has to come back to a well prepared and solid landing site. This means you cant get to far away (unless you have an island to land on).

2. You will have to have more thrust capacity on the MCT (second stage). But you will need this anyway if you are going to get of Mars.

3. The MCT (second stage) is going to need a high delta-V both for high energy transfer to Mars (3-4 month as stated by Elon) and to get from Mars (delta-v budget of 6-9 km/s). This means you can take advantage of this when staging to LEO.

Is there any flaws in my reasoning or mayor points I have missed?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 07/08/2015 02:42 pm
F9R 1.1 can put approx 13.1mT to LEO with recovery of the first stage. That might improve for 1.2 but we dont have numbers on that yet.
Second stage weights around 3.9mT while F9R weights about 505mT at launch. That makes a gross mass to orbit of about 3.36%.

But that is with KeroLOX all the way. With MethaLOX, alone that number would increase significantly. So yes, I guess it is safe to assume that the mass to orbit fraction will be around 4 to 5 % as you listed in your table. If SpaceX has enough unicorn hair and ferry dust left from their Dragon production, it might even go higher than 5%, simply because there is no payload adapter, fairings or what have you necessary.

Yes.  Thank you for correcting my oversight on computing mass fraction for F9.  It is ~ 3.4% not ~2.7% when you add the mT for stage 2 which reaches LEO.  4% for BFR/MCT may be achievable even with a robust design.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 07/08/2015 02:56 pm
Another interesting discussion is how much of the total delta V budget of the total LV is going into the booster and how much is going into the MCT (second stage)?

I think that there will be a big difference from EELV LV's where most of the fuel is in the booster with a small second stage.

1. You will not be able to land the booster on a barge, it has to come back to a well prepared and solid landing site. This means you cant get to far away (unless you have an island to land on).

2. You will have to have more thrust capacity on the MCT (second stage). But you will need this anyway if you are going to get of Mars.

3. The MCT (second stage) is going to need a high delta-V both for high energy transfer to Mars (3-4 month as stated by Elon) and to get from Mars (delta-v budget of 6-9 km/s). This means you can take advantage of this when staging to LEO.

Is there any flaws in my reasoning or mayor points I have missed?

First, I am not an aerospace engineer (I'm a EE) so I'm not sure I know what I'm doing. 

I have reached the exact same conclusions you cite above. 
Unlike the F9, the BFR/MCT will probably have a 1st stage that stages "low & slow" making boostback to launch site a given.  And yes, the 2nd stage, a.k.a. MCT will after orbital re-fueling need sufficient delta V to escape LEO & transit to Mars in a few months and will also later need sufficient delta v to launch from Mars (having refueled again on the surface) and return to Earth or HEO.  All these requirements dictate a high delta v capability and consequently a larger 2nd stage to 1st stage weight & propellant capacity design point than required for a simple LEO/GEO launcher.  My latest models have a 1st stage with 14-15 million LBS thrust & 7 Raptors (slight overkill) powering the 2nd stage.  The Vacuum Raptors are assumed to have ~610 thousand pounds thrust following the same 1.22 vac/sea level thrust ratios of the Falcon 9.

Think of the MCT as a near SSTO that fell short but gets enough boost from the stage one BFR such that it's good to go.



Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 07/08/2015 03:41 pm
Another interesting discussion is how much of the total delta V budget of the total LV is going into the booster and how much is going into the MCT (second stage)?

I think that there will be a big difference from EELV LV's where most of the fuel is in the booster with a small second stage.

1. You will not be able to land the booster on a barge, it has to come back to a well prepared and solid landing site. This means you cant get to far away (unless you have an island to land on).

2. You will have to have more thrust capacity on the MCT (second stage). But you will need this anyway if you are going to get of Mars.

3. The MCT (second stage) is going to need a high delta-V both for high energy transfer to Mars (3-4 month as stated by Elon) and to get from Mars (delta-v budget of 6-9 km/s). This means you can take advantage of this when staging to LEO.

Is there any flaws in my reasoning or mayor points I have missed?

First, I am not an aerospace engineer (I'm a EE) so I'm not sure I know what I'm doing. 

I have reached the exact same conclusions you cite above. 
Unlike the F9, the BFR/MCT will probably have a 1st stage that stages "low & slow" making boostback to launch site a given.  And yes, the 2nd stage, a.k.a. MCT will after orbital re-fueling need sufficient delta V to escape LEO & transit to Mars in a few months and will also later need sufficient delta v to launch from Mars (having refueled again on the surface) and return to Earth or HEO.  All these requirements dictate a high delta v capability and consequently a larger 2nd stage to 1st stage weight & propellant capacity design point than required for a simple LEO/GEO launcher.  My latest models have a 1st stage with 14-15 million LBS thrust & 7 Raptors (slight overkill) powering the 2nd stage.  The Vacuum Raptors are assumed to have ~610 thousand pounds thrust following the same 1.22 vac/sea level thrust ratios of the Falcon 9.

Think of the MCT as a near SSTO that fell short but gets enough boost from the stage one BFR such that it's good to go.

Yes, this has been my thinking.

A relatively large MCT/upper stage that will take it from "low and slow" booster staging to LEO.  It will refuel there and do a fast transit to Mars.  After refueling on the surface of Mars it will lift off and do a direct return to Earth on a slower transit.  The multiple engines (5 or 7) will give engine out contingency during the various phases of the mission after TMI, as well as during LEO ascent.  (although I'm sure if there were an engine out during LEO ascent, the mission would be scrubbed and the vehicle returned.  But it still should be able to do a safe abort to orbit)

The MCT/upper stage will be large and "fluffy" during EDL, with a large cylindrical cross section, but not overly long so as to not be too tall when landing. 

Not sure it'll need to be quite 14-15Mlbs of thrust on the booster though.  May be possible to get away with less, depending.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 07/08/2015 04:00 pm
If MCT plus 100mT payload is less than 200mT the required 1st stage thrust will drop.  See spreadsheet posted.
If a really innovative design allows 4% mass fraction or better, 1st stage thrust will drop.

Make it so, Elon!

(I just hope that the 2nd stage doesn't have that explode just before staging feature thingy the F9R has)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 07/08/2015 04:20 pm
(I just hope that the 2nd stage doesn't have that explode just before staging feature thingy the F9R has)

Assuming that event has something to do with the helium pressurization, it won't. Both methane and LOX tank will have self pressurization, no helium involved, I am sure.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 07/08/2015 04:34 pm
(I just hope that the 2nd stage doesn't have that explode just before staging feature thingy the F9R has)

Assuming that event has something to do with the helium pressurization, it won't. Both methane and LOX tank will have self pressurization, no helium involved, I am sure.

That would also make a lot of sense so the tanks could be pressurized at all times to provide structural integrity during EDL, landing, etc.   They'd want the tanks pressurized with GCH4 and GOX I'd imagine.  If the pressure got too high, they could collect some and compress into smaller GCH4 and GOX tanks to operate the methalox RCS thrusters. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 07/08/2015 06:02 pm


...
...
There have been several MCT designs that had large enough tanks to do the 4 month transfer direct from LEO.  (I think the jump from 4 to 3 months is pretty insane most synods).

If you think those tanks are too large, and want to transfer to a higher energy orbit before TMI, you should just use one extra MCT instead of 4.  That will save hundreds of tons of propellant because you are moving less dry mass.  A reusable SEP tug is another popular option.
Excellent. I have seen a lot of discussion with the SEP option, but not the propellant only option. Do you know where I could find those designs -- on this forum?

In the old MCT threads.

my design (http://forum.nasaspaceflight.com/index.php?topic=35424.msg1288500.msg#1288500)

design by Malu from thread 1 (http://forum.nasaspaceflight.com/index.php?topic=33494.msg1225313.msg#1225313)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 07/22/2015 04:30 am
I am not sure where to put this.

Yesterday there was an interview with Hans Koenigsmann in german TV ZDF. He repeated the argument that rockets need to be reusable like airplanes. He added that planes fly for decades and rockets will not fly that much but it should be 100 flights. He did not specify if this would be the Falcon Family or the goal for BFR/MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 07/23/2015 10:49 am
I am not sure where to put this.

Yesterday there was an interview with Hans Koenigsmann in german TV ZDF. He repeated the argument that rockets need to be reusable like airplanes. He added that planes fly for decades and rockets will not fly that much but it should be 100 flights. He did not specify if this would be the Falcon Family or the goal for BFR/MCT.

Do you happen to know the show he said that in? It might be possible to still see it in the zdf mediathek from within Germany.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 07/23/2015 11:06 am
Do you happen to know the show he said that in? It might be possible to still see it in the zdf mediathek from within Germany.

It is available.

http://www.zdf.de/ZDFmediathek#/beitrag/video/2452860/ZDF-heute-journal-vom-21-Juli-2015

The part with Hans Koenigsmann is near the end. Skip through most of it.

Edit: It's at 21:40
Title: Re: MCT Speculation and Discussion Thread 4
Post by: marcon on 07/23/2015 11:56 pm
Do you happen to know the show he said that in? It might be possible to still see it in the zdf mediathek from within Germany.

It is available.

http://www.zdf.de/ZDFmediathek#/beitrag/video/2452860/ZDF-heute-journal-vom-21-Juli-2015

The part with Hans Koenigsmann is near the end. Skip through most of it.

Edit: It's at 21:40

For all non-German speakers:
The segment is really a short introduction of SpaceX to the German news audience and reasonably well done at that. The recent anomaly is shown, with the broken strut in the second stage getting called out. They also show the latest landing attempt and the Merlin engine is mentioned as a core competency, with competitors using Russian rocket engines.   There is a very short interview in German with Koenigsmann as employee No. 4 and now one of the vice presidents. He re-tells the old (for us) comparison with reusable aircraft and mentions the eventual goal of 100 reuses. He also talks about the early decision to do as much in-house and independently from other companies as possible and how they felt as newcomers at Cape  Canaveral.

(just to elaborate on what was mentioned above)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: ciscosdad on 07/24/2015 12:51 am
Thank you Marcon

This summary of a foreign language news segment is very welcome. Thank you. Feel free to do this for us at any time.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 07/24/2015 06:23 am
For all non-German speakers:
[...]
(just to elaborate on what was mentioned above)

Thx Marcon. I thought about writing a translated transcript but decided its not worth it since he doesnt mentions anything new. Your summary is way better than either nothing or a transcript. Thx.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 07/24/2015 07:19 am
We know now first hand that they are not aiming low. 2-5 reuses would only help to make their competetive situation better which is already very good.

100 or more is what they need to get prices anywhere near what Elon Musk has proposed for his Mars architecture.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: marcon on 07/24/2015 09:09 pm
For all non-German speakers:
[...]
(just to elaborate on what was mentioned above)

Thx Marcon. I thought about writing a translated transcript but decided its not worth it since he doesnt mentions anything new. Your summary is way better than either nothing or a transcript. Thx.
Thank you. I usually do enjoy reading transcripts done by other people ;-), but you are right, there wasn't really anything new.

It is such a pity they didn't ask Koenigsmann more personal questions about the early days.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/25/2015 02:02 am
We know now first hand that they are not aiming low. 2-5 reuses would only help to make their competetive situation better which is already very good.


Are you referring to some new information?  If so it should get posted in http://forum.nasaspaceflight.com/index.php?topic=37839.0
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 08/13/2015 10:48 pm
Will the MCT need a nuclear reactor? Zubrin thought that Mars Direct's ERV would need a 100 kW nuclear reactor to power the ISRU plant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/14/2015 01:41 am
NO, even Zubrins idea's were for a reactor to be cargo not integral to the vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 08/14/2015 02:01 am
Again, using existing solar panels on Mars, how big an area would 100kw of solar panels cover?  Of course it will only work effectively 8-10 hours a day whereas a small nuke unit will go 24-7. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/14/2015 05:46 am
Again, using existing solar panels on Mars, how big an area would 100kw of solar panels cover?  Of course it will only work effectively 8-10 hours a day whereas a small nuke unit will go 24-7.

Insolation on Mars will be roughly 400W/m˛. Calculate with 25% efficiency for low efficiency but very low weight solar foils and you get 100W/m˛. That's 1000m˛ for 100kW peak output. More if you want that power for 8-10 hours/day.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/14/2015 05:52 am
Realistically you'd probably also want more to allow for high atmospheric opacity during dust storms. But thin films can be VERY thin and light.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 08/14/2015 09:45 pm
Add lightweight reflectors which can also be used to cover the array during dust storms which will more than double the isolation to possibly as high as 1000w/m^2 for the array itself. So the array with its fold out reflectors would need to be 400m^2 for 100kw for about a 30% equivalent daily power level. so increase the size of the arrays to 1500m^2 to handle the short daylight charging duration where the panels peak output is 375kw. With a good lithium rechargeable batteries you may get as good as up to 100kw continuous power. 1500m^2 is a set of arrays that folded would be 30m X 50m. Unfolded they would cover an area of 70m X 50m. That is actually a fairly large area about twice the size of a football field. So besides the panels there will be a need for structures to mount the panels and wiring for connecting the panels back to the power management systems (batteries and power conditioners). All of which adds weight. At 10kg per m^2 (that includes the reflectors) just the arrays will weigh 15mt. Now add structures wiring and storage batteries and your up to something around 50mt for a 24/7 100kw power system.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/14/2015 11:42 pm
10kg per m^2 for just the arrays sounds really high given modern thin films.

Thin films just placed on the ground would have lower efficiency per square meter due to dust and lack of reflectors... but probably significantly better per kilogram.

The cells in IKAROS were 25 micrometers thick - if they were amorphous silicon, that's something like 58 grams per m^2!

It might need to be somewhat thicker on Mars due to wind, but even so, I think you could do way better than 10kg per m^2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jcc on 08/14/2015 11:58 pm
10kg per m^2 for just the arrays sounds really high given modern thin films.

Thin films just placed on the ground would have lower efficiency per square meter due to dust and lack of reflectors... but probably significantly better per kilogram.

The cells in IKAROS were 25 micrometers thick - if they were amorphous silicon, that's something like 58 grams per m^2!

It might need to be somewhat thicker on Mars due to wind, but even so, I think you could do way better than 10kg per m^2.

For an initial robotic mission, thin film arrays that can unroll themselves are probably the best bet. With human labor, simple reflectors could be added that require people to assemble them to minimize weight and complexity. If a reflector weighs more than the array per sq meter, it's not worth using it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/15/2015 05:26 am
Reflectors may not be that much lighter than thin film arrays. More importantly they don't work well during dust storms. Overall it is IMO better to increase solar cell array size.

Initially they would be deployed flat on the ground which is easy to automate. When humans arrive they may go on frames which gets them into the best angle and minimizes dust accumulation.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jimmy Murdok on 08/15/2015 12:00 pm
If you want high solar panels you can use poles and ropes, no need of heavy structures. The weight will come more from good uv protection than the panel itself. No need of reflectors just more light panels.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/15/2015 12:39 pm
The weight will come more from good uv protection than the panel itself.

Not necessarily. UV protective coating can be thin and invisible. I learned that when I built a roof for my terrace. The transparent polycarbonate panels come with an UV coating on one side. You don't even see that. The panels need a marking for the side that goes up. If you mount them wrong side up they don't last.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 08/15/2015 12:56 pm
So, the first few MCT's might have to be expendable or will have to stay until everything is set up for fuel production.  It would probably take two or more to just land and maybe using robotics deploy the first solar panels and power station for fuel production and power for habitats.  Then the passengers can come and start setting things up that cannot be done with robot deployment.  So it might be months before the first MCT can return.   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/15/2015 01:17 pm
So it might be months before the first MCT can return.

I don't see less than a full cycle, so more than two years, if everything goes right. But they would have consumables for twice that in case something goes wrong and replacements for fuel ISRU need to be sent.

This would be done with long time stays in mind from the beginning. Just remember Aldrin. He proposes sending people without even the means in place to get them back and work that out later. I don't support that but see initial missions with 2 years or more on the surface of Mars as the way to go if you want to start a settlement.

Edit: Not that much is needed, assuming that at least water is available and air for breathing can be sourced locally. Inspiration Mars calculated with 300 or 500g per day per person. That may be too low. If you calculate 10 persons with 2kg/day/person that's  ~30t for four years. That much can be carried on the crew MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/15/2015 06:06 pm
It hinges on the mass of the ISRU equipment and power systems.  If a complete automated deployment turn-key system capable of refueling the MCT-Lander in 1 synod will fit within one such Lander then I see no reason to ever abandon any mechanically sound lander.

Rather you go right into propellant production, return the first vehicle and leave the ISRU equipment in place.  This achieves the two most important goals, 1) Have propellant in place before crew is risked, 2) Validate the entire round-trip flight of the vehicle before crew is risked.

The only reason to temporarily or permanently 'strand' an expensive vehicle on Mars is if the ISRU equipment is so massive that it needs to be broken-up over multiple landers, but all of my estimates show that it should easily fit within one landers 100 mT capacity (and finish in 1 synod), provided that the return propellant mass is not some absurd amount like 1000 mT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/15/2015 06:14 pm
The weight will come more from good uv protection than the panel itself.

Not necessarily. UV protective coating can be thin and invisible. I learned that when I built a roof for my terrace. The transparent polycarbonate panels come with an UV coating on one side. You don't even see that. The panels need a marking for the side that goes up. If you mount them wrong side up they don't last.

Not that I know much about this, but hard UV straight from the Sun is rather different from the bit of it that gets through our atmosphere.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/15/2015 07:02 pm
Not that I know much about this, but hard UV straight from the Sun is rather different from the bit of it that gets through our atmosphere.

Sure but I think we can make better coatings than the one on my panels without putting thick glass over the solar arrays.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 08/15/2015 07:31 pm
It hinges on the mass of the ISRU equipment and power systems.  If a complete automated deployment turn-key system capable of refueling the MCT-Lander in 1 synod will fit within one such Lander then I see no reason to ever abandon any mechanically sound lander.

Rather you go right into propellant production, return the first vehicle and leave the ISRU equipment in place.  This achieves the two most important goals, 1) Have propellant in place before crew is risked, 2) Validate the entire round-trip flight of the vehicle before crew is risked.

The only reason to temporarily or permanently 'strand' an expensive vehicle on Mars is if the ISRU equipment is so massive that it needs to be broken-up over multiple landers, but all of my estimates show that it should easily fit within one landers 100 mT capacity (and finish in 1 synod), provided that the return propellant mass is not some absurd amount like 1000 mT.

About 700 metric tons.  So semi absurd  ;-)
One of the MCT will make a good storage tank.  It has the storage capacity required for the second MCT.  If you don't keep an MCT in place where will you store the fuel?  So the first MCT of all will stay in place, roll out large solar arrays to get power and produce and store fuel for the second ship's return. Or it could switch out with the second ship, as long as it leaves all the production equipment in place. 

Personally, I expect the first 2, possible the first 3 MCT to be entirely remote controlled and to not return.
How much energy does it take to extract the fuel from the air and water, and how quickly do we want to do it?  That is what fundamentaly sets the power required, isn't it?  So many many solar arrays at first, because there will not be a nuclear reactor developped in the next few years, unless things change dramatically on the energy front.


Here is a possible MCT propellant tank arrangement, CH4 and O2.





Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/15/2015 08:24 pm
  This achieves the two most important goals, 1) Have propellant in place before crew is risked, 2) Validate the entire round-trip flight of the vehicle before crew is risked.

Is that actually necessary? It might be easier just to carry, say, 3 synodic periods' worth of life support supplies...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 08/15/2015 08:49 pm
  This achieves the two most important goals, 1) Have propellant in place before crew is risked, 2) Validate the entire round-trip flight of the vehicle before crew is risked.

Is that actually necessary? It might be easier just to carry, say, 3 synodic periods' worth of life support supplies...
Shouldn't the fuel production operation be validated before sending crew, because without in situ production Mars return is extremely difficult, and a rescue mission would need huge amounts of fuel and organisation.  On the other hand if the fuel is already there, rescue isn't a likely developement.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/15/2015 09:37 pm
Shouldn't the fuel production operation be validated before sending crew, because without in situ production Mars return is extremely difficult, and a rescue mission would need huge amounts of fuel and organisation.  On the other hand if the fuel is already there, rescue isn't a likely developement.

The only thing that needs to be validated is the availability of water. Everything else is definitely doable. I am just trying to avoid "trivial". I would not send crew until a large source of water is proven and redundant means of getting it is available.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 08/15/2015 09:41 pm
To produce hydrogen we need about 120 MJ/kg. (Wikipedia). For 200 tons of CH4, we need 50 tons of H, so 50000 x 120 MJ is 6 000 000 MJ. If we produce  100 kW, that means 6 000 000 000 kJ / 100 kW = 60 000 000 second or 17000 hours, or 2 years.  Since availability may only be 25%, we would need 400 kW installed, or if we want to do it in a year 800 kW installed, perhaps 10000 m2, at 10 kg/m2 = 100 tons, so one MCT load?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/15/2015 10:42 pm

About 700 metric tons.  So semi absurd  ;-)
One of the MCT will make a good storage tank.  It has the storage capacity required for the second MCT.  If you don't keep an MCT in place where will you store the fuel?  So the first MCT of all will stay in place, roll out large solar arrays to get power and produce and store fuel for the second ship's return. Or it could switch out with the second ship, as long as it leaves all the production equipment in place. 

Personally, I expect the first 2, possible the first 3 MCT to be entirely remote controlled and to not return.
How much energy does it take to extract the fuel from the air and water, and how quickly do we want to do it?  That is what fundamentaly sets the power required, isn't it?  So many many solar arrays at first, because there will not be a nuclear reactor developped in the next few years, unless things change dramatically on the energy front.


Here is a possible MCT propellant tank arrangement, CH4 and O2.

I think your assuming direct Earth return, but I believe just return to orbit and docking with an ERV is the way to go and would put propellant needs at ~400 mT.

The use of the lander vehicle as the storage tank is good and something I've been assuming for initial missions, eventually a tank farm would be set up but that's likely to be after permanent habitation has begun.  Likewise the 'swap' of returning in a different vehicle then the one landed in is a strategy I've advocated for.

2-3 autonomous landings prior to first manned landing is a perfectly reasonable number, but I see no reason why these are not returning.  No one seems to ever explain their logic here for NOT returning these vehicles, it just seems to be a reflex assumption that autonomous = no return.  Remember the actual vehicle used in both the autonomous and follow up manned missions will be IDENTICAL, it is only the cargo that's going to differ.  An autonomously deployed payload doesn't infringe on the vehicles ability to return any more then having passengers or cargo being delivered to an operation outpost on board and we know SpaceX wants thouse vehicle back.


  This achieves the two most important goals, 1) Have propellant in place before crew is risked, 2) Validate the entire round-trip flight of the vehicle before crew is risked.

Is that actually necessary? It might be easier just to carry, say, 3 synodic periods' worth of life support supplies...

This makes no sense, if we have not validated the vehicles ability to return to Earth (as in if it will SURVIVE re-entry at Earth) then the risk to the crew is not mitigated by giving them more supplies.  Also 3 synod periods is 6.5 YEARS, this is absolutely beyond the limits of our ability to keep food from spoiling, not to mention the MASS, at 5 kg a day of consumables a 4 person crew would need nearly 50 mT of supplies.  And 5 kg a day is conservative when you realize it includes all your spare for fixing EVERYTHING.

Lastly we can not expect a crew to be in remotely sane or healthy after that time period, regardless of what a certain Sci-Fi movie remake of Robinson Crusoe might have lead people to believe any person stranded on Mars is as good as dead.  We are going to be stretching all our technology and physiological means to the maximum just to do a mission of 1 synod.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Soralin on 08/16/2015 03:48 am

About 700 metric tons.  So semi absurd  ;-)
One of the MCT will make a good storage tank.  It has the storage capacity required for the second MCT.  If you don't keep an MCT in place where will you store the fuel?  So the first MCT of all will stay in place, roll out large solar arrays to get power and produce and store fuel for the second ship's return. Or it could switch out with the second ship, as long as it leaves all the production equipment in place. 

Personally, I expect the first 2, possible the first 3 MCT to be entirely remote controlled and to not return.
How much energy does it take to extract the fuel from the air and water, and how quickly do we want to do it?  That is what fundamentaly sets the power required, isn't it?  So many many solar arrays at first, because there will not be a nuclear reactor developped in the next few years, unless things change dramatically on the energy front.


Here is a possible MCT propellant tank arrangement, CH4 and O2.

I think your assuming direct Earth return, but I believe just return to orbit and docking with an ERV is the way to go and would put propellant needs at ~400 mT.

The use of the lander vehicle as the storage tank is good and something I've been assuming for initial missions, eventually a tank farm would be set up but that's likely to be after permanent habitation has begun.  Likewise the 'swap' of returning in a different vehicle then the one landed in is a strategy I've advocated for.
And where does the ERV get its propellant from, to get everything from Mars orbit back to Earth?  Any propellant you bring along for a return trip essentially counts as payload mass.  (a bit less than 1-1 for payload to Mars surface, since you don't have to take it down to mars and back up again, but you do have to carry it all the way from Earth surface to Mars orbit)

The lander part to mars, would have to be capable of landing 100 tons down on the surface, and, after being refueled, do a single-stage flight back up to meet with the ERV.  Which means the lander is going to be the bulk of the spacecraft, and the ERV would essentially just be an extra fuel tank, dropped off in orbit, and picked up again for the return trip.

Which essentially reduces the question down to:  Is it more efficient to bring a full fuel tank from Earth surface to Mars orbit, or to bring an empty fuel tank from Earth surface to Mars surface, and then fill it there?  Lifting fuel from Mars surface to Mars orbit is significantly less delta-v than moving fuel from Earth surface to Mars orbit is.  Fuel is a lot easier to produce on Earth than it is on Mars, but the whole point of ISRU is to change that equation, to increase Mars production enough that it's easier to produce things there than it is to bring them from Earth.  And really, that's the long term strategy that you want to go for.  Bringing ISRU equipment from Earth for extra fuel production only has to be done once, and once it's done, it makes every flight from then on out more efficient.  (except for replacements and such, the longer-term step would be to be to bring the equipment needed to make more ISRU equipment to mars).

(I also realized, after writing this, that I was assuming an ERV would have fuel at all.  If you had something like long-term life support and crew quarters, that you just picked up and dropped off in Mars orbit, and then dropped off and picked up in Earth orbit, and repeat, then something like that could potentially be more efficient.  Assuming that you already have sufficient life-support built and set up on Mars.  Basically, the stuff it could be useful to leave in orbit would be non-consumables)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/16/2015 07:23 am
I'm in favor of SEP for all in space propulsion, this reduces round trip propellant needs to a fraction of what they would be if chemical propulsion is used, all the studies on SEP show significant reduction in IMLEO for the same delivered payload that's why they are becoming the standard for mission planning.

Also it allows delivery of the landing craft to a low orbit at both Mars and Earth making entry velocity a fraction of what a direct entry would require, and this means hugely reduced heat, stress, weight and wear & tear on the lander.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/16/2015 07:37 am
I'm in favor of SEP for all in space propulsion, this reduces round trip propellant needs to a fraction of what they would be if chemical propulsion is used, all the studies on SEP show significant reduction in IMLEO for the same delivered payload that's why they are becoming the standard for mission planning.

SEP from LEO means slow spiralling out of LEO through the van Allen belts. BFR will make fuel in LEO really cheap. ISRU makes fuel on Mars cheap. I don't see SEP as competetive.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 08/16/2015 04:45 pm
And where does the ERV get its propellant from, to get everything from Mars orbit back to Earth?

Impaler apparently meant SEP, but there is another alternative. You fuel the ERV in Mars orbit from the surface ISRU facility. (Similar to the fuel depot on the Earth side.) The SSTO cargo-landers ferry fuel up to the ERV. By leaving most of your long-duration, heavily shielded, interplanetary infrastructure in orbit, you can reduce the dry-mass of the landers to the bare minimum. The ERV is the "ship", the landers are "boats" used only for the initial and final legs. This also means that you can use fewer smaller landers doing multiple trips to ferry the cargo/passengers down to Mars, rather than one-big-lander-per-100t of payload. Again, that may let you reduce the size of the SSTOs to something more manageable.

Even better, if you can put enough prop in Mars orbit, your incoming cargo-landers can do a deorbit burn that is a significant proportion of the entry velocity, several km/s, greatly simplifying the design of the landers.

["Ah", you say, "but when ferrying fuel, the landers will still have to reenter at full orbital velocity!" Yes, but they will be empty. As, most likely, will any MCTs used as shuttles/ferries to LEO on the Earth side; launch full, reenter empty. But on the Mars side, the cargo MCTs need to carry the full 100t payload down to the surface.]

Obviously, I don't think this is the model that Musk is going for, judging by the clues that have been dropped. But this concept may still allow an increase in scale after the basic (self-contained) MCTs have established the core infrastructure on Mars. Let those giant, 100 tonne MCTs become the mere surface ferries for an even larger main interplanetary transport. That's how you go from 50-100 hundred colonists per synod, to "a million in my lifetime".
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/16/2015 07:44 pm
I'm in favor of SEP for all in space propulsion, this reduces round trip propellant needs to a fraction of what they would be if chemical propulsion is used, all the studies on SEP show significant reduction in IMLEO for the same delivered payload that's why they are becoming the standard for mission planning.

SEP from LEO means slow spiralling out of LEO through the van Allen belts. BFR will make fuel in LEO really cheap. ISRU makes fuel on Mars cheap. I don't see SEP as competetive.

Reducing IMLEO by 1/3rd to 1/2 saves money no matter what the cost to orbit is, and when you reuse SEP the savings are huge.  For a Chemical mission you need a minimum of 3x propellant mass to cargo meaning 25% of IMLEO is cargo.  With SEP the ratio would about 1:1 propellant:cargo meaning your cargo efficiency shoots up to 50% and it has the potential to rise even higher with higher power and ISP systems in the future.

And where does the ERV get its propellant from, to get everything from Mars orbit back to Earth?

Impaler apparently meant SEP, but there is another alternative. You fuel the ERV in Mars orbit from the surface ISRU facility. (Similar to the fuel depot on the Earth side.) The SSTO cargo-landers ferry fuel up to the ERV. By leaving most of your long-duration, heavily shielded, interplanetary infrastructure in orbit, you can reduce the dry-mass of the landers to the bare minimum. The ERV is the "ship", the landers are "boats" used only for the initial and final legs. This also means that you can use fewer smaller landers doing multiple trips to ferry the cargo/passengers down to Mars, rather than one-big-lander-per-100t of payload. Again, that may let you reduce the size of the SSTOs to something more manageable.

Even better, if you can put enough prop in Mars orbit, your incoming cargo-landers can do a deorbit burn that is a significant proportion of the entry velocity, several km/s, greatly simplifying the design of the landers.

["Ah", you say, "but when ferrying fuel, the landers will still have to reenter at full orbital velocity!" Yes, but they will be empty. As, most likely, will any MCTs used as shuttles/ferries to LEO on the Earth side; launch full, reenter empty. But on the Mars side, the cargo MCTs need to carry the full 100t payload down to the surface.]

Obviously, I don't think this is the model that Musk is going for, judging by the clues that have been dropped. But this concept may still allow an increase in scale after the basic (self-contained) MCTs have established the core infrastructure on Mars. Let those giant, 100 tonne MCTs become the mere surface ferries for an even larger main interplanetary transport. That's how you go from 50-100 hundred colonists per synod, to "a million in my lifetime".

That scenario would be a bit more efficient even under chemical propulsion but only if their is an in-space habitat module as you describe with the lander being a rapid cycle 'ferry'.

I think that this is likely to be the 'evolved' mission profile once significant propellant infrastructure is in place on the order of multiple tons per day allowing the lander to be sent back to orbit on a short cycle of a month to a week to disembark large numbers of passengers into an existing base.  Earlier missions are likely to be singular landings and singular assents due to propellant limitations.

Still this same architecture works even better under SEP, the propellant delivered to the ERV in low Mars orbit could be Argon and only a small fraction would be needed relative to chemical.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/16/2015 09:16 pm
Also 3 synod periods is 6.5 YEARS, this is absolutely beyond the limits of our ability to keep food from spoiling, not to mention the MASS, at 5 kg a day of consumables a 4 person crew would need nearly 50 mT of supplies.  And 5 kg a day is conservative when you realize it includes all your spare for fixing EVERYTHING.

Lastly we can not expect a crew to be in remotely sane or healthy after that time period, regardless of what a certain Sci-Fi movie remake of Robinson Crusoe might have lead people to believe any person stranded on Mars is as good as dead.  We are going to be stretching all our technology and physiological means to the maximum just to do a mission of 1 synod.

While I don't agree particularly with many of your other points you are making some assertions here that really are not defensible:

We can and do preserve foods for more than 6.5 years.

5kg a day is not conservative for food, water and air. In fact it presumes that just about everything is permanently broken and there weren't enough spares. Water for example will be supplied by several redundant systems extracting it from the ECLSS, waste products, from ISRU. These systems should start out with redundancy. I still advocate planning to mitigate disaster early on.

As much as possible vital systems spare parts will be stored digitally and in raw materials for additive manufacturing.

This is in the context of an MCT based Mars expedition mission so this is heading for a permanent settlement and we will see more than 4 people on the first expedition, we probably saw at least 1 MCT and in total 3 or more craft landed at the first settlement location the synod before people get there. Then there will be at least 3 MCT's when the people land and my guess is 10 - 20 people that synod. There will be at least 3 more MCT's coming the next synod that are not launched until after the previously launched group has seen how the settlelment is shapping up meaning that there is the option a few months after the first manned landing to reprioritize what gets shipped that synod.  While I don't expect there to be a gap in coverage for a full evacuation until hundreds of people live on Mars, operating so that there is enough margin to stretch all vital systems through just over 1.5 full synods makes sense until enough redundancy exists to ensure there is always spare capacity on vital systems.

And as for the state of physical and  mental health after 6.5 years, you are putting to high a value on them having a bland and boring existence on Mars. Most of us routinely take a chance of experiencing serious trauma that may or may not adversely affect us. Having to cope with being in a situation with a dozen other people for 6.5 years, cut off, not knowing if you are going to survive and not able to communicate with anyone else is not an expected outcome of the establishment of the outpost, but as risks of establishing the outpost, well it is no worse than the risks associated with sailing small craft in the open ocean, flying and potentially being adrift in a life raft or reaching shore somewhere. If you told me that you expect people to be unaffected by a disaster that they survive through, I would say that is unreasonable. So expecting new people and cargo every synod and the ability at least once every two years and a few months to decide whether or not to return to Earth is something that should not drive people mad, but if they were cut off and potentially unable to return and might have to last 6 years or more on their own, then sure they might not be mentally (or physically) healthy, in fact a few may have died for a variety of reasons by then, but that was an emergency situation, just like getting into the liferaft that an airliner carries. Airlines carry them, but they don't expect their use to be a natural and healthy outcome.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sghill on 08/16/2015 09:56 pm
I was in institution-scale solar for years. There's a bunch of over thinking the MCT ground use-panels on this thread (plus it's OT, we have a thread for solar panels on Mars in that area).

Instead of complicated schemes to deploy PV panels or schemes like reflectors to get more power out them, it is far easier and cheaper to just have a longer spool of thin film panels to make up for inefficiencies.

Additionally,  no automated unfurling system is needed. Just set the spool on the ground and roll it out- over the rocks and everything, then plug it in to the junction box (on board power will be DC). Hammer in some ground stakes every 2m.

A UV coating will be needed. They make that stuff in "space application" strength, so there's no new technology there.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/17/2015 04:05 am
and a rescue mission would need huge amounts of fuel and organisation.  On the other hand if the fuel is already there, rescue isn't a likely developement.

Well, I was assuming there would be one or more missions coming the next synod anyway. MCT isn't for one-off missions, it's meant to be a colonization infrastructure.

In a one-off mission scenario, yes it needs to be self-sufficient. But that's not MCT.

This makes no sense, if we have not validated the vehicles ability to return to Earth (as in if it will SURVIVE re-entry at Earth) then the risk to the crew is not mitigated by giving them more supplies.

Sure it does as we are talking about a colony, thus return to Earth is not necessary for survival.

Quote
Also 3 synod periods is 6.5 YEARS, this is absolutely beyond the limits of our ability to keep food from spoiling,

No, it isn't.

Quote
not to mention the MASS, at 5 kg a day of consumables a 4 person crew would need nearly 50 mT of supplies. 

The 5 kg number assumes zero recycling, which pretty much can't be the case for a MCT that will be capable of carrying 50-100 people.

Quote
Lastly we can not expect a crew to be in remotely sane or healthy after that time period, regardless of what a certain Sci-Fi movie remake of Robinson Crusoe might have lead people to believe any person stranded on Mars is as good as dead.  We are going to be stretching all our technology and physiological means to the maximum just to do a mission of 1 synod.

Well, that's the difference in assumptions then... MCT is for permanent colonization.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/17/2015 05:02 am
Additionally,  no automated unfurling system is needed. Just set the spool on the ground and roll it out- over the rocks and everything, then plug it in to the junction box (on board power will be DC). Hammer in some ground stakes every 2m.

I agree. However Elon Musk mentioned it so naturally it gets discussed.

A UV coating will be needed. They make that stuff in "space application" strength, so there's no new technology there.

Good to hear. I assume that you don't mean adding a glass panel on the front but some surface coating with not too much weight.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/17/2015 05:56 am
Well, I was assuming there would be one or more missions coming the next synod anyway. MCT isn't for one-off missions, it's meant to be a colonization infrastructure.

In a one-off mission scenario, yes it needs to be self-sufficient. But that's not MCT.
Quote

MCT is not part of some MarsOne no-return suicide pact, people are going to do exploration missions first and they will come home promptly.  Even once a base is established people will rotate in and out for a long time before anyone even thinks about settling permanently.  A return option MUST exist at the time the first person sets foot on Mars.

Also 3 synod periods is 6.5 YEARS, this is absolutely beyond the limits of our ability to keep food from spoiling,

No, it isn't.

You have no idea what your talking about.  If you have some notion of canned or frozen food then you've completely blown the mass budget on the food alone as that would be ~75% water, the only practical way to send food is dry and that reduces it's self-life, even a conjunction mission to Mars spanning 1 synod pushes our tech to the limits.

The 5 kg number assumes zero recycling, which pretty much can't be the case for a MCT that will be capable of carrying 50-100 people.

You know nothing about ECLSS is you think 5 kg a day is zero recycling, it is ISS current tech level based on nearly full closure of water and would be conservative once you factor in all the redundancy in parts and equipment needed.  The MarsOne nonsense got shot down by MIT for exactly the same failure to consider spares.

http://sites.nationalacademies.org/cs/groups/depssite/documents/webpage/deps_063596.pdf

Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/17/2015 06:34 am
The ISS has a lot of recycling, true. However on Mars there is plenty of water and air available. Also gravity will allow normal cooking. The ISS has MREs. On Mars you can have flour, noodles, rice, cooking oil to work with. That's vastly more mass efficient, also more tasty. Especially with growing even a limited amount of herbs and vegetables which would be part of any long term expedition. Also there will be washing of clothes, not discarding. Two kg/person/day is easily achievable under such conditions.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Owlon on 08/17/2015 06:57 am
You have no idea what your talking about.  If you have some notion of canned or frozen food then you've completely blown the mass budget on the food alone as that would be ~75% water, the only practical way to send food is dry and that reduces it's self-life, even a conjunction mission to Mars spanning 1 synod pushes our tech to the limits.

The shelf life of the powdered Soylent* in my pantry is two years, and you could theoretically live on nothing but that indefinitely at 500-750g a day. Bland, sure, but you could get something like 80% of your calories from Soylent and the rest from more traditional (and flavorful) dry and/or canned foods. And I'm sure changes could be made to add fairly significant time to the shelf life of Soylent with dedicated effort. You run into trouble when you start talking about 2+ synods, but I would hardly call a 2.5 year shelf life on dry food pushing our technology to the limits.

You know nothing about ECLSS is you think 5 kg a day is zero recycling, it is ISS current tech level based on nearly full closure of water and would be conservative once you factor in all the redundancy in parts and equipment needed

Assuming 4 liters of water, 1 kg of oxygen, and .75 kg of food, you don't even break 6 kg/day with zero recycling. The page you linked gives about 2.2 kg per man day with a state-of-the-art, partially closed ECLSS including throwaway clothing and wipes. Somehow I feel like a water-efficient microgravity washing machine and shower should be achievable with modern technology, and much of the mission would be spent under Mars gravity. Big engineering projects, sure, but not outlandish.

Spares and redundant equipment aren't exactly consumables. They don't linearly scale (or necessarily scale at all) with the number of people you bring or the length of the mission, so I'm not sure x kg/day is a good way to quantify them. You want more redundancy as your mission gets longer, but it's not like you're going to want to add a whole backup ECLSS for every two years your mission lasts. You might only, say, double your spares going from a 60 day to 600 day mission, or from 600 to 2000 (pulling these numbers out of nowhere).

*not that I'm endorsing Soylent as the perfect space food, I'm just giving an example of an existing widely available product that fits the role well enough
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 08/17/2015 04:09 pm
Wait but Why post

http://waitbutwhy.com/2015/08/how-and-why-spacex-will-colonize-mars.html

Quote
No one’s exactly sure how the transportation will work, but it’ll likely be something like this: the Mars Colonial Transporter will consist of two pieces—the giant, powerful first stage, and the second stage, which will also be the spacecraft. The first stage will launch a spacecraft into orbit, then come back down (landing propulsively), refuel, undergo a bit of maintenance, and head back up with another spacecraft. This will go on for a while in the weeks leading up to the point where Earth and Mars are next to each other in orbit. Then SpaceX will send up a tanker of some kind to refuel the orbiting spacecraft (which also functions as the second stage rocket, so it’ll have spent a lot of its fuel getting itself into orbit).

By the time the planets are in place, there will be a group of MCT spacecraft—what Musk calls the “colonial fleet”—orbiting the Earth, fueled up and ready to go, and at just the right moment, the fleet will take off for Mars.

Three-to-six months later, the spacecraft will get to Mars, descend through the atmosphere, and land propulsively. The people will get out, probably to a fun welcome celebration put on by the existing residents, and unload everything over the next few weeks.

About two years later, when the planets are again aligned, right around the time Earth is launching the next colonial fleet, the group of spacecraft that came to Mars two years earlier will head back to Earth, carrying anyone on Mars who’s over it.

Three-to-six months later, the spacecraft will arrive back on Earth, land propulsively, and head in for maintenance so they’ll be ready to head back to Mars in two more years.

A good secondary source about how the MCT might work. I wish it had more direct quotes.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 08/17/2015 05:13 pm
Minimum consumables requirements are something like:
–Water: 2 kg/person/day drinking + 0.2 kg/person/day for minimal washing. Probably more on long trips for better hygiene
–Oxygen: 0.8 kg/person/day for metabolic consumption (assumes exercise) + leaks + repressurization
–Nitrogen: mostly driven by leak rates, repressurization (e.g. for airlocks)
–Food: 1.8 kg/person/day (includes meal-level packaging) at ~380 kg/m3 density
–Be sure to account for both mass and volume

(copy pasted from a Phobos mission presentation).

Also see attached image from http://www.nasa.gov/pdf/146558main_RecyclingEDA(final)%204_10_06.pdf.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sghill on 08/17/2015 05:24 pm
A UV coating will be needed. They make that stuff in "space application" strength, so there's no new technology there.

Good to hear. I assume that you don't mean adding a glass panel on the front but some surface coating with not too much weight.

Yes.  There are a number of manufacturers of flexible coatings for optical photovoltaic applications.  The two big differences are that the space application stuff generally has a wider temperature range it can survive in without degrading, and it is applied "fully-densified," meaning the coating material is prepared with absolutely no air bubbles that will expand and ruin the coating when exposed to space vacuum.

Of course none of this stops cosmic rays, but we already know how to make solar panels that can survive in space for decades...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/17/2015 05:51 pm
Minimum consumables requirements are something like:
–Water: 2 kg/person/day drinking + 0.2 kg/person/day for minimal washing. Probably more on long trips for better hygiene
–Oxygen: 0.8 kg/person/day for metabolic consumption (assumes exercise) + leaks + repressurization
–Nitrogen: mostly driven by leak rates, repressurization (e.g. for airlocks)
–Food: 1.8 kg/person/day (includes meal-level packaging) at ~380 kg/m3 density
–Be sure to account for both mass and volume

That's great. Sounds like my estimate of 2kg/person/day was very generous. Getting water and nitrogen from ISRU on Mars is a safe assumption. Also meal-level packaging would add a lot of unnecessary weight. For a long stay under gravity food can be stored in bulk. Maybe I should adjust my estimate from 2 kg to 1 kg for the duration of the surface stay.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/17/2015 06:16 pm
Minimum consumables requirements are something like:
–Water: 2 kg/person/day drinking + 0.2 kg/person/day for minimal washing. Probably more on long trips for better hygiene
–Oxygen: 0.8 kg/person/day for metabolic consumption (assumes exercise) + leaks + repressurization
–Nitrogen: mostly driven by leak rates, repressurization (e.g. for airlocks)
–Food: 1.8 kg/person/day (includes meal-level packaging) at ~380 kg/m3 density
–Be sure to account for both mass and volume

That's great. Sounds like my estimate of 2kg/person/day was very generous. Getting water and nitrogen from ISRU on Mars is a safe assumption. Also meal-level packaging would add a lot of unnecessary weight. For a long stay under gravity food can be stored in bulk. Maybe I should adjust my estimate from 2 kg to 1 kg for the duration of the surface stay.

The question is what provisions for systems failures do you make?

I think it is credible to have a large water, oxygen and food store in the early settlement stages, and plenty of margin on any exploratory expeditions to remote locations the evacuation might be delayed in the case of some sort of system failure. However, at an early settlement, I believe if there were 3 sources of water (ISRU, recycled from air from what we exhale, recycled waste) and that each of those systems was redundant and repairable then water supply storage does not need to stretch beyond a safety margin for the settlement and whatever stores need to be sent with a return craft, stock the evacuation craft, go out on missions, and feed propellant manufacture and agricultural activity.

Oxygen, very similar, there will need to be a couple of processes to generate it anyway (there will be excess from propellant manufacture for example) so as long as there is redundant capacity to generate, the margins needed for potential systems outages and flushing/rebooting the habitats a couple of times and of course any ammounts needed to be sent with exploration craft, return craft or maintaining the stock on evacuation craft.

Nitrogen would definitely need to have some storage, and needs to be produced as a supplement to agricultural activity, so here I would suggest a substantial reserve based on the need to reboot agriculture after a disaster as well as whatever atmospheric needs are in the habitats.  Nitrogen will probably only have one type of system for ISRU based on the small percentage in the atmosphere and this might actually be a more vulnerable commodity than any of the others mentioned so far to an outage. However less of it needs to be stored for a return craft, expedition or evacuation craft.

Food, well there is one that is more of an issue. Going from zero to hero in the self-supporting food department, will take a long time for a settlement, and must as an ultimate goal be aimed to produce packaged, preserved food that can be used on expeditions, return craft, evacuation craft. So reliance on some imported food elements will exist for many synods even if the basics are provided locally. Agricultural systems will need to be redundant and as they are power intense there is the most potential for downtime from a disaster, needing reboot after a plant disease related flushing so food production and storage will only offset needs from stored imported foods partially and therefore it will be relatively easy to see large stores of food that could keep the incumbent population alive for several years always present in the major settlements even as the populations and safety levels go beyond the strict need for it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 08/17/2015 06:19 pm
Minimum consumables requirements are something like:
–Water: 2 kg/person/day drinking + 0.2 kg/person/day for minimal washing. Probably more on long trips for better hygiene
–Oxygen: 0.8 kg/person/day for metabolic consumption (assumes exercise) + leaks + repressurization
–Nitrogen: mostly driven by leak rates, repressurization (e.g. for airlocks)
–Food: 1.8 kg/person/day (includes meal-level packaging) at ~380 kg/m3 density
–Be sure to account for both mass and volume

That's great. Sounds like my estimate of 2kg/person/day was very generous. Getting water and nitrogen from ISRU on Mars is a safe assumption. Also meal-level packaging would add a lot of unnecessary weight. For a long stay under gravity food can be stored in bulk. Maybe I should adjust my estimate from 2 kg to 1 kg for the duration of the surface stay.

That sounds reasonable. If water isn't a concern, many long-term food storage items are highly dehydrated. That plus the reduced packaging due to bulk storage should make it take up less mass. Some freeze-dried foods have a 25 year shelf life.

A single serving of a freeze-dried entree is about 53g, without packaging.

If you have ever had a LRP or freeze-dried meals for hiking, you know they make an MRE look like a gourmet meal. However, it beats starving. But you have to a reliable water supply or it's like eating salty sand and gravel.

Hopefully, the crew wouldn't have to resort to the emergency rations.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/17/2015 07:41 pm

If you have ever had a LRP or freeze-dried meals for hiking, you know they make an MRE look like a gourmet meal. However, it beats starving. But you have to a reliable water supply or it's like eating salty sand and gravel.

Hopefully, the crew wouldn't have to resort to the emergency rations.

Actually, I am a back packer and a couple of times on longer trips I dehydrated a few ingredients to make better meals (my friends and I often do a 'meal plan' where each person is assigned a set number of meals to provide for all so that we can benefit from economies of scale at each meal) and I would make soups and pasta sauces that way. After a couple of trips with things like linguine with clam sauce and chicken mushroom soup, my friends pitched in and bought me a dehydrator and I managed to make a lot more variety of really good meals.

My points are that: dehydrated foods don't have to be terrible even if the packaged stuff made for back packers is less than ideal; given the cost of shipping foods from the emergency stores should be eaten before they deteriorate and replaced with new; locally produced food should as soon as possible be packaged for long term storage and eventually even exported.

Note one of the non edible products that early Mars agriculture needs to address is growing feed stocks for cellophane and the coating to make it non permeable to water vapor.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/17/2015 08:34 pm
ISRU dose almost nothing to reduce consumables because our consumable budget is dominated by PROCESSED FOOD AND SPARE EQUIPMENT.  Not water, nitrogen or any simple elements that could be collected from Mars air or soil.


If you people would read the literature on the current state of the art ECLSS (http://sites.nationalacademies.org/cs/groups/depssite/documents/webpage/deps_063596.pdf) before shooting from the hip you would see that water needs are only 0.25 kg per person day.  The water closure problem is almost a solved problem (the new Pyrolysis process being added now to the ISS to combine methane and CO2 will likely give us the last bit of closure needed).  Some of you are talking about stored OXYGEN like you were reading  Buck Rogers pulp-sci-fi paperbacks from the 50's, we haven't used stored oxygen for breathing since Apollo, all oxygen has been provided by electrolysis of condensed water vapor for decades now, please get with the times.

The total for physiological maintenance of crew comes out to 2.2 kg per person day and while it might be possible to greatly reduce this it would involve things like a completely closed loop agriculture system, clothing that can be worn for weeks without washing, human waste incineration and recycling, the ability to both manufacture and recycle all paper and packaging materials.  In other words very advanced stuff that might be part of a permanent base but that you won't see on the very first manned landing of 4-6 people which is the context in which Vultur proposed just sending 'more supplies' rather then actually having a safe return option.

And again SPARE PARTS are the killer because you have to maintain the machines as well as the people, MIT estimated the need at 3.5 - 4.6 kg per person day (depending on if the food system is open or closed respectively)  for the Mars One concept which is based current state of the art.  So again I reiterate 5 kg is optimistic when you look at the total picture.  Thus trying to simply bring masses of supplies for a crew to say an additional synod or two if they can't return to Earth is a terrible misallocation, the mass would be much better spent on the systems to ensure they actually get back to Earth on time.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/17/2015 09:02 pm
Why do you dismiss 3D printing as a primary source of spare parts?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/17/2015 09:12 pm
Why do you dismiss 3D printing as a primary source of spare parts?

To be honest I would dismiss it for the moment too. However the food assumed by Impaler does not take into account bulk packing as we did. Also I don't see it as a valid assumption that an ECLSS completely new designed for MCT with all knowledge and experience available will need the same amount of spare parts as the present ISS systems do. It will be designed to be more robust and needing less spares. ECLSS on Mars is another item again. It is not part of what we discuss as consumables. It will be designed for Mars with completely different methods, mostly biological. More volume, more initial weight but more efficient to run for a long time.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/17/2015 09:52 pm
Why do you dismiss 3D printing as a primary source of spare parts?

To be honest I would dismiss it for the moment too. However the food assumed by Impaler does not take into account bulk packing as we did. Also I don't see it as a valid assumption that an ECLSS completely new designed for MCT with all knowledge and experience available will need the same amount of spare parts as the present ISS systems do. It will be designed to be more robust and needing less spares. ECLSS on Mars is another item again. It is not part of what we discuss as consumables. It will be designed for Mars with completely different methods, mostly biological. More volume, more initial weight but more efficient to run for a long time.

Well if it is designed between now and when they start launching, I think it will be designed with 3D printable spares in mind.

One thing we haven't discussed is CO2 scrubbing and parts/consumables there.

Oh and as important as food is going to be, I think growing fiber for clothing and other non-edible things will be important too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/17/2015 11:46 pm
Why do you dismiss 3D printing as a primary source of spare parts?

Because I come from a family that has been in the tool-and-die, plastic injection molding and quality control industries for 3 generations, we know that these additive processes complement but do not replace traditional manufacturing processes.

Furthermore the reactions happening in most ECLSS equipment are high temperature and energy chemistry, that means metal and ceramic vessels, valves and catalysts, they can not be replaced with plastic widgets.

While their is some limited potential for packaging materials to be a source of plastic feed-stocks as soon as you start talking about metallic part printing your looking at bring large amounts of metallic feed-stock, and large amounts of secondary equipment for finishing, measuring and testing the parts created.

In summary 3D printing is not a Star Trek Replicator.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/18/2015 12:02 am
Why do you dismiss 3D printing as a primary source of spare parts?

Because I come from a family that has been in the tool-and-die, plastic injection molding and quality control industries for 3 generations, we know that these additive processes complement but do not replace traditional manufacturing processes.

Furthermore the reactions happening in most ECLSS equipment are high temperature and energy chemistry, that means metal and ceramic vessels, valves and catalysts, they can not be replaced with plastic widgets.

While their is some limited potential for packaging materials to be a source of plastic feed-stocks as soon as you start talking about metallic part printing your looking at bring large amounts of metallic feed-stock, and large amounts of secondary equipment for finishing, measuring and testing the parts created.

In summary 3D printing is not a Star Trek Replicator.

I believe rather than plastic it will be a material that can be produced on Mars (there are some cellulose additive manufacturing efforts going on right now) and definitely metal, and probably ceramic. If you design the equipment with the intent for having the vast majority of replaceable parts with what can be produced with relative ease then there is a small subset of parts that require unique materials or production techniques that can't be made locally and those will have to have spares on hand to last until replacements can be ordered and delivered from Earth.  Metal is not impossible today, nor is ceramic, the possibilities in the next 5 years are immense considering how far additive manufacturing has come so far. For the first wave though the cut off is likely going to be where additive manufacturing is by 2020 to have ECLSS equipment designed and built by the 2025 launch window. But it isn't just ECLSS, it is every system that will be used in a settlement that needs to be optimized for locally sourced spares.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/18/2015 02:13 am
I don't think food production via agriculture need be either complex/difficult or especially fragile.

Agricultural systems will need to be redundant and as they are power intense there is the most potential for downtime from a disaster, needing reboot after a plant disease related flushing

Why power intense? Mars gets sufficient sunlight for plant growth -- probably more than, say, the Pacific Northwest temperate rainforests or England (due to clouds) which are both rather lush.

It should be rather simple to eliminate all plant diseases by not bringing them from Earth. Even if this fails, plant disease doesn't usually mean complete collapse of the system, as you'd have multiple species.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/18/2015 02:14 am
Your saying an entire mining industry needs to be established to support manufacturing of spare parts, to keep the ECLSS running to keep the FIRST LANDING of 4-6 astronauts alive for multiple synods so we can postpone having to figure out how to do a return trip???

Did you not pay attention to the original premise of this tangent?  I have been talking this ENTIRE time about initial landings of small numbers for exploratory purposes, you seem to be talking about Blue Mars level end-state total self sufficiency a century from now.  Your scale and time range are so out of step with what I'm talking about it's like talking about how the James town settlers will will generate electricity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/18/2015 02:20 am
MCT is not part of some MarsOne no-return suicide pact,

-MCT will definitely return (Musk said to reuse the spacecraft if nothing else) but given its expected size and payload capacity I see no reason why the first crew wouldn't intend to stay permanently.


(And "Mars to Stay" plans aren't inherently suicidal. Risky, but not insanely so, and they actually make a lot of sense given a limited-per-year budget).


Quote
Even once a base is established people will rotate in and out for a long time before anyone even thinks about settling permanently.  A return option MUST exist at the time the first person sets foot on Mars.

Based upon what?


You have no idea what your talking about.  If you have some notion of canned or frozen food then you've completely blown the mass budget on the food alone as that would be ~75% water, the only practical way to send food is dry and that reduces it's self-life,

What about freeze-dried, vacuum-packed?

Quote
You know nothing about ECLSS is you think 5 kg a day is zero recycling,

5 kg number doesn't include spares or anything else mechanical, it's food+water+oxygen use.

Quote
The MarsOne nonsense got shot down by MIT for exactly the same failure to consider spares.

I wouldn't use that paper as a source, given that it assumed a wheat/soy based agriculture system which is a terrible choice when space is a constraint.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/18/2015 05:53 am
I don't think food production via agriculture need be either complex/difficult or especially fragile.

Agricultural systems will need to be redundant and as they are power intense there is the most potential for downtime from a disaster, needing reboot after a plant disease related flushing

Why power intense? Mars gets sufficient sunlight for plant growth -- probably more than, say, the Pacific Northwest temperate rainforests or England (due to clouds) which are both rather lush.

It should be rather simple to eliminate all plant diseases by not bringing them from Earth. Even if this fails, plant disease doesn't usually mean complete collapse of the system, as you'd have multiple species.

You know microbes and virus mutate, something in human intestinal flora and fauna might mutate and become a pathogen to the plants. Or anything else that gets there.

If you are doing hydro or Aero 'ponics you have a fair bit of energy in the system, artificial light will be more, if you don't want radiation to require potential resets to the growing environment, and if you want to not rely on always going back to unmutated seed stock you need your growing getting its light indirectly being radiation shielded from the light and the incident cosmic rays. So underground, artificially lit, recirculation systems, filters, pumps it is all energy intensive.

Maximum credible disaster is that the growing environment needs to be flushed and reset. Lets provision for it. Not a big deal but pretending it might not be necessary is foolhardy.

Same thing with whatever the largest pressurized area is. Presume you might need to maintain pressure during a leak, presume it might completely depressurize and need to be repressurized.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/18/2015 05:59 am
Your saying an entire mining industry needs to be established to support manufacturing of spare parts, to keep the ECLSS running to keep the FIRST LANDING of 4-6 astronauts alive for multiple synods so we can postpone having to figure out how to do a return trip???
I am presuming 10 - 20 on the first expedition. I expect human exploration to branch out from the first landing site in the first synod by rover, maybe the 2nd, or 3rd synod will bring secondary settlements, Also by the 3rd synod the equipment to travel to other locations via high inclination orbit to refuel at a depot then land at any point on Mars and take off again to land at one of the settlements with propellant ISRU. At that point real exploration starts to happen, and by then the population is around 50 with maybe 20 or so of the people who had travelled to Mars having returned.

By the 10th synod of human occpuation maybe the population is up over 500 and 100 passenger MCT's start to arrive.
Did you not pay attention to the original premise of this tangent?  I have been talking this ENTIRE time about initial landings of small numbers for exploratory purposes, you seem to be talking about Blue Mars level end-state total self sufficiency a century from now.  Your scale and time range are so out of step with what I'm talking about it's like talking about how the James town settlers will will generate electricity.
And I have been pointing out for almost as long that this is a thread about MCT and that is not about a few boots and flags - it is about settling Mars from the get go.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/18/2015 06:44 am
You seem to be throwing your lot in with Vultur and the MarsOne nonsense of immediate colonization from the first footprint.  This is not going to happen, it's like saying that Neil Armstrong should have colonized the moon rather then coming back.

Any logical sequence would consist of first exploratory scouting missions, followed by outposts with personnel cycling in and out and then finally a permanent settlement once lots of infrastructure is built up and optimum sites are found.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/18/2015 06:58 am
Any logical sequence would consist of first exploratory scouting missions, followed by outposts with personnel cycling in and out and then finally a permanent settlement once lots of infrastructure is built up and optimum sites are found.

It seems you don't comprehend what the availability of a transport system for 100t payload combined with abundant local resources like water, CO2 and nitrogen means. Especially combined with the aim for colonizing driving development.

I am absolutely convinced that beginning with the first landing there will be a permanent presence. Some will go back after 2 years, some will stay longer, some may stay for the rest of their lives.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/18/2015 02:36 pm
You seem to be throwing your lot in with Vultur and the MarsOne nonsense of immediate colonization from the first footprint.  This is not going to happen, it's like saying that Neil Armstrong should have colonized the moon rather then coming back.

No I am saying what I believe is the intent of use of MCT. We have many threads discussing other Mars mission styles, and while I would be very sad if we just did an Apollo style sortie on Mars, that is the context of many of those threads (we also have specific threads to discuss agriculture, aspects of ISRU whose context implies longer term missions).


Any logical sequence would consist of first exploratory scouting missions, followed by outposts with personnel cycling in and out and then finally a permanent settlement once lots of infrastructure is built up and optimum sites are found.

And here we can agree to disagree, my best case scenario for the economics of exploring Mars includes settling Mars.  Some surveying will happen by unmanned probes (and effectively that has already started), and the first settlement may not end up being the epicentre of Martian colonization, but it will provide the base to start really exploring Mars from. The one alternative I can see is if we do ISRU on Phobos or Deimos and supply many manned sorties to the surface of Mars before building the first settlements. This would still involve a permanent presence and the one reason I don't really elaborate on it here is the idea that it doesn't work all that well with the MCT model driving Mars settlement.

As for people cycling in and out, of course they will, but not everyone. A high percentage of the first few hundred people to visit Mars will be scientists and explorers supporting them, some colonists but chosen for their ability to build settlements and the needed infrastructure and not operate it. But of the first few hundred people to go my bet is that some of them would have gone intending to stay but end up returning to Earth, and some will have gone intending to return to Earth but stay instead.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/18/2015 02:59 pm
The one alternative I can see is if we do ISRU on Phobos or Deimos and supply many manned sorties to the surface of Mars before building the first settlements. This would still involve a permanent presence and the one reason I don't really elaborate on it here is the idea that it doesn't work all that well with the MCT model driving Mars settlement.

This may or may not warrant an extended discussion. I do like that idea as I was always thinking of fuel ISRU at Phobos or Deimos. Do we know if MCT would be able to land with  enough fuel to lift off again? It probably should not be much heavier than on a normal landing with 100t supplies. So with minimal life support for a small crew and very little cargo to maximise fuel. Still seems not enough with less than 100t to lift off and reach Phobos. Maybe entry from orbit at lower speed allows for some more payload.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Nilof on 08/18/2015 03:44 pm
New info from Musk about the Raptor and MCT(and sorry about the crossposting):

Quote from: Elon Musk
Yeah, these are seemingly absurd percentage improvements, however not impossible. The critical elements of the solution are rocket reusability and low cost propellant (CH4 and O2 at an O/F ratio of ~3.8 ). And, of course, making the return propellant on Mars, which has a handy CO2 atmosphere and lots of H2O frozen in the soil.

The design goal is technically 100+ metric tons of useful cargo per flight, so maybe more than 100 people can be taken. Depends on how much support mass is needed per person and the luggage allowable.

Avionics, sensors, communications, aspects of vehicle structure, landing pads and a few other things get better with scale, plus it is more fun to be on a cruise ship than a bus, so I suspect that the 100 people per flight number grows a lot over time, maybe to several hundred. Also, we could subsidize the equivalent of economy by charging a lot more for first class.

Factor in all of the above and getting below $100k/ton or person eventually is conceivable, as the trip cost is then dominated by propellant, which is mostly liquid oxygen at a mere $40/ton (although a lot of it is needed per useful ton of cargo). That would be really awesome!

Looks like the Raptor will run oxidizer rich. That puts its niche even closer to the BE-4.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 08/18/2015 03:46 pm
The one alternative I can see is if we do ISRU on Phobos or Deimos and supply many manned sorties to the surface of Mars before building the first settlements. This would still involve a permanent presence and the one reason I don't really elaborate on it here is the idea that it doesn't work all that well with the MCT model driving Mars settlement.

This may or may not warrant an extended discussion. I do like that idea as I was always thinking of fuel ISRU at Phobos or Deimos. Do we know if MCT would be able to land with  enough fuel to lift off again? It probably should not be much heavier than on a normal landing with 100t supplies. So with minimal life support for a small crew and very little cargo to maximise fuel. Still seems not enough with less than 100t to lift off and reach Phobos. Maybe entry from orbit at lower speed allows for some more payload.

Known 'facts' about MCT you can fit on the back of a stamp. A small one, that already has writing on the back.

Even things Musk has already said (which is practically nothing anyway) are liable to significant change. Just like most other things SpaceX have done. They are happy to change as they go along, as they discover more stuff.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/18/2015 03:59 pm
Known 'facts' about MCT you can fit on the back of a stamp. A small one, that already has writing on the back.

Even things Musk has already said (which is practically nothing anyway) are liable to significant change. Just like most other things SpaceX have done. They are happy to change as they go along, as they discover more stuff.

Actually performance data for MCT have been very consistent over time. Data on Raptor have changed but they said, less thrust of a single Raptor, more Raptors, total thrust and performance a constant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sghill on 08/18/2015 04:06 pm
IMHO, a reality check on MCT has been long overdue as this thread wanders all over the place because there are no facts to pin us down. 

SpaceX can't even build Dragon 2 without public support, and it's been delayed for years because of a lack of internal funding to make up for shortfalls in public funding measured in millions of dollars.  Yet somehow SpaceX is going to commit to actually building and flying BFR and MCT with billions of their own dollars and no contracted return on the investment?  I don't think so.  Not a snowball's chance in Hades.

More likely IMHO is that we'll see a fleshed-out paper concept similar to Hyperloop.  Then they will go fishing for governments to pony up the development costs in order to be occupants on the actual spacecraft.

That tactic may work, but SpaceX doesn't have that many supporters in Congress as a consequence of making everything under one roof. 

Even if money does come in from a government source, which won't be possible to even have allocated until 2017 at the extreme earliest, we won't see parts manufactured for the spacecraft until sometime in the mid to late 2020's.

Now, could I be entirely wrong? Sure I could, I'd love to be wrong on this! But the Dragon2 development experience is telling me I'm not.

On the gripping hand, a large well-funded religious group could put up a few billion to have a planet all their own for their more fervent adherents with no problem at all.  It worked for the Pilgrims, why not Scientologists!?!

Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/18/2015 04:27 pm
New info from Musk about the Raptor and MCT(and sorry about the crossposting):

Quote from: Elon Musk
Yeah, these are seemingly absurd percentage improvements, however not impossible. The critical elements of the solution are rocket reusability and low cost propellant (CH4 and O2 at an O/F ratio of ~3.8 ). And, of course, making the return propellant on Mars, which has a handy CO2 atmosphere and lots of H2O frozen in the soil.

The design goal is technically 100+ metric tons of useful cargo per flight, so maybe more than 100 people can be taken. Depends on how much support mass is needed per person and the luggage allowable.

Avionics, sensors, communications, aspects of vehicle structure, landing pads and a few other things get better with scale, plus it is more fun to be on a cruise ship than a bus, so I suspect that the 100 people per flight number grows a lot over time, maybe to several hundred. Also, we could subsidize the equivalent of economy by charging a lot more for first class.

Factor in all of the above and getting below $100k/ton or person eventually is conceivable, as the trip cost is then dominated by propellant, which is mostly liquid oxygen at a mere $40/ton (although a lot of it is needed per useful ton of cargo). That would be really awesome!

Looks like the Raptor will run oxidizer rich. That puts its niche even closer to the BE-4.

No 3.8 O/F is fuel rich, 16 units of mass of CH4 combines with 64 units of mass of O2 for a stoichiometric reaction which would be a ratio of 4.0 - this makes 3.8 slightly fuel rich but not by much.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/18/2015 05:15 pm
IMHO, a reality check on MCT has been long overdue as this thread wanders all over the place because there are no facts to pin us down. 

True, but as is pointed out, the design isn't finalized yet and lots can change. And while many here might disagree with me, I think even the target payload could change if a bunch of good engineering shows a "sweet" spot of overall design that makes a different payload range than 100t have a higher overall system performance.

SpaceX can't even build Dragon 2 without public support, and it's been delayed for years because of a lack of internal funding to make up for shortfalls in public funding measured in millions of dollars.  Yet somehow SpaceX is going to commit to actually building and flying BFR and MCT with billions of their own dollars and no contracted return on the investment?  I don't think so.  Not a snowball's chance in Hades.

While I have no proof to the contrary for BFR, I rush to point out how much SpaceX has funded from their own pocket so far, and shown that they can continue to raise equity to fund their portion of developments (they just raised $1B). As for the pace of the Dragon 2, it does have a customer and that customer is as much setting the pace as SpaceX cash flow is. Neither Dragon were built for SpaceX internal projects, they were developed for a client with a schedule worked out mutually. The fact that there were slips in that schedule can be attributed to both sides, but there was no motivation to move either faster than the pace needed to meet the client schedule so, any delay on the client side or the SpaceX side pushed that schedule further to the right.  If SpaceX never had a client for a Dragon the design and the crafts life cycle would have been completely different, the first version would probably have been designed for passengers, and it would have launched much later than it did, but they might have flown a manned one by now.  The way things are happening however they are getting to do all the engineering they need to develop a passenger carrying spacecraft paid for, and they get a craft that, hopefully is a superset of their requirements and NASA's requirement.

For BFR and MCT it is believable to me that SpaceX will spend several billion of money raised from: investors, cash flow from their cash flow positive activities, possibly even debt as SpaceX matures its other businesses. In fact it seems far more believable than a company with less a little over $100M in cash and only the almost empty pockets of a dot com boom instant millionaire wiz kid for more capital making a brand new rocket using two new liquid fuel engines, their own avionics, tanks etc.  SpaceX has far more wherewithal and potential funding sources proportionally to attack this problem than it did when it was founded.


More likely IMHO is that we'll see a fleshed-out paper concept similar to Hyperloop.  Then they will go fishing for governments to pony up the development costs in order to be occupants on the actual spacecraft.
Actually that would be very inconsistent with everything that Elon Musk has done to date. From the start hyperloop was an Elon concept looking for a non Elon home. He introduced it that way and described his process for arriving at the idea publicly. He has been as open about his intent to colonize Mars. His first plan was to inspire people to want it by sending a greenhouse experiment to Mars. He even tried to make that work, and I suspect somewhere early on, he will pay homage to that original idea in some early launch of an unmanned craft to Mars, but if he does it will be as significant as the wheel of cheese on the first Dragon flight. He publicly explained each of the step changes in his rational towards getting people on Mars, and has all along since starting to build rockets said that he is building towards creating the infrastructure needed to settle Mars. If you consider his actions with Tesla and Solar City in the way he announces business development, everything he has done suggests that what he is doing right now with SpaceX includes several money making adjuncts that also carry it towards its ultimate goal. SpaceX also exists to help Tesla and Solar city if you haven't noticed, and if needed they will help SpaceX.

The idea that Musk will only develop BFR/MCT if he can sell it to a public funded agency is not consistent with what he has done to date. However, if he can get that funding or more likely he makes a change to the way this sort of project interacts with goverments and NGO's and gets a new model of corporate and philanthropic exploration to come about, he will. His is probably the only person who can make that change work even. However, if he does make it work many will say that it only worked because he conned others into following his flawed vision, rather than acknowledging that while many elements of his vision are arbitrary rather than optimum, it is his ability to create the organization that transforms his vision into reality that is making it happen rather than flaws and disingenuity.

That tactic may work, but SpaceX doesn't have that many supporters in Congress as a consequence of making everything under one roof. 

Even if money does come in from a government source, which won't be possible to even have allocated until 2017 at the extreme earliest, we won't see parts manufactured for the spacecraft until sometime in the mid to late 2020's.

So does the Raptor count as a "part"?

Now, could I be entirely wrong? Sure I could, I'd love to be wrong on this! But the Dragon2 development experience is telling me I'm not.

As could I, but I would bet on several elements of my views on this and it is the SpaceX track record to date, and Elon's consistent communications style about what he does, that make me feel as I do about it.

On the gripping hand, a large well-funded religious group could put up a few billion to have a planet all their own for their more fervent adherents with no problem at all.  It worked for the Pilgrims, why not Scientologists!?!
I hope it doesn't come to that. I personally would like to see only humanist motivations organizing off Earth communities and their rules and customs (and on Earth communities for that matter). Let us please avoid bringing prejudice and hate into space (eliminating nationalism as well as religion).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: enzo on 08/18/2015 10:27 pm
I rush to point out how much SpaceX has funded from their own pocket so far, and shown that they can continue to raise equity to fund their portion of developments (they just raised $1B).
Like Tesla, SpaceX's 'pocket' is rapidly running out. The $1B was allocated to general funds, not just the satellite venture where it is much needed, which speaks to the shallow depth of the general funds. It is clear that the larger SpaceX plan depends on satellite income, much like Tesla's larger plan depends on model X, and then the model after that. And like Tesla, raising funds by diluting ownership is not sustainable at the level needed to compensate for foundering profits. I do think both companies can stay afloat, but this dangerous game was Musk's plan all along, and we should recognize how dangerous it is.

I personally would like to see only humanist motivations organizing off Earth communities and their rules and customs (and on Earth communities for that matter). Let us please avoid bringing prejudice and hate into space (eliminating nationalism as well as religion).
Aldrin took communion on the moon, read the words of Jesus, and planted the American flag. This did not preclude the trip from being for all mankind. We should let our rules and customs be what they are, wherever we are, in the spirit of individual freedom.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/18/2015 11:08 pm
I rush to point out how much SpaceX has funded from their own pocket so far, and shown that they can continue to raise equity to fund their portion of developments (they just raised $1B).
Like Tesla, SpaceX's 'pocket' is rapidly running out. The $1B was allocated to general funds, not just the satellite venture where it is much needed, which speaks to the shallow depth of the general funds. It is clear that the larger SpaceX plan depends on satellite income, much like Tesla's larger plan depends on model X, and then the model after that. And like Tesla, raising funds by diluting ownership is not sustainable at the level needed to compensate for foundering profits. I do think both companies can stay afloat, but this dangerous game was Musk's plan all along, and we should recognize how dangerous it is.

Dangerous as in has a high risk of failing? Well not doing it that way gives it a 100% chance of failing. Or do you do you mean dangerous to bystanders somehow?

I certainly think Musk has plans to raise more equity in all of his companies. My third post on NSF outlines one possibility of how he uses an IPO of SpaceX to both increase the value of SpaceX and create the funding for another private venture (possibly even a not for profit) to hire SpaceX to colonize Mars: http://forum.nasaspaceflight.com/index.php?topic=35529.msg1250251#msg1250251 (http://forum.nasaspaceflight.com/index.php?topic=35529.msg1250251#msg1250251)
I personally would like to see only humanist motivations organizing off Earth communities and their rules and customs (and on Earth communities for that matter). Let us please avoid bringing prejudice and hate into space (eliminating nationalism as well as religion).
Aldrin took communion on the moon, read the words of Jesus, and planted the American flag. This did not preclude the trip from being for all mankind. We should let our rules and customs be what they are, wherever we are, in the spirit of individual freedom.

I really don't want respond to the religion part but it really offends me that someone can imagine that those actions (and plenty of others) did not help keep it from being for all mankind.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 08/19/2015 10:33 am
I rush to point out how much SpaceX has funded from their own pocket so far, and shown that they can continue to raise equity to fund their portion of developments (they just raised $1B).
Like Tesla, SpaceX's 'pocket' is rapidly running out. The $1B was allocated to general funds, not just the satellite venture where it is much needed, which speaks to the shallow depth of the general funds. It is clear that the larger SpaceX plan depends on satellite income, much like Tesla's larger plan depends on model X, and then the model after that. And like Tesla, raising funds by diluting ownership is not sustainable at the level needed to compensate for foundering profits. I do think both companies can stay afloat, but this dangerous game was Musk's plan all along, and we should recognize how dangerous it is.

Not as dangerous as the time when he needed to fund both SpaceX and Tesla at the last minute....

Although I would comment that what you say above is pretty much how many big companies work...they sell stuff to keep going. They invest money so that can make stuff they can sell.  SpaceX and Tesla are investing a lot, but the payoffs could be massive (esp. Tesla and the next couple of models). That should encourage investors should they need them.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 08/19/2015 02:00 pm
Has anyone here considered to take Tim Urban's drawings of the MCT a bit more serious as a possible sneak peak from Musk's side regarding the final design? After all, the publication of the article was delayed because of something that was outside of Tim's control - but the cause for the delay was never really identified. In the "waiting" post, the stick figure is shown drawing an MCT fleet approaching Mars... Was Tim perhaps waiting for a rendering of the planed look of the MCT? If you look at the drawn MCTs, they look very detailed for being purely generic, e.g., look at this angled, extensible (?) solar panel on the "thick" left part of the MCT. And could the dark end (right part) be a heat shield? If we take this speculation serious for a moment - can we make sense of this design?

See: http://28oa9i1t08037ue3m1l0i861.wpengine.netdna-cdn.com/wp-content/uploads/2015/08/SpaceX-F-782x530.jpg
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/19/2015 03:37 pm
I'm confused again.  Do folks here believe that Musk has said the MCT is 200mT to LEO (then refueled and onto Mars' surface) with 100mT useful payload?  Or is it 100mT useful payload with X mT more being the Dry Mass of what it takes to carry that payload...airframe, empty fuel tanks, re-entry shield, engine tonnage?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/19/2015 03:47 pm
I'm confused again.  Do folks here believe that Musk has said the MCT is 200mT to LEO (then refueled and onto Mars' surface) with 100mT useful payload?  Or is it 100mT useful payload with X mT more being the Dry Mass of what it takes to carry that payload...airframe, empty fuel tanks, re-entry shield, engine tonnage?

Recently he was very clear on this. It is 100t pure payload, to be unloaded and left on Mars while the whole vehicle flies back. Earlier statements were less clear and one could think it includes the empty vehicle but no longer.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/19/2015 04:06 pm
I'm confused again.  Do folks here believe that Musk has said the MCT is 200mT to LEO (then refueled and onto Mars' surface) with 100mT useful payload?  Or is it 100mT useful payload with X mT more being the Dry Mass of what it takes to carry that payload...airframe, empty fuel tanks, re-entry shield, engine tonnage?

I think that Musk has said that the MCT will deliver 100t to Mars via a trip to Earth orbit for refueling. How much it can put into LEO was not a matter of record from Elon and speculation here has been anything from 70t to LEO to 200t to LEO.

My personal expectation is that MCT will have an dry weight around 50t, carry 100t of payload, 670t of propellant and that a tanker version that is reusable to LEO has a dry weight of 30t, carries virtually no payload but 800t of propellant at launch and can nominally deliver 130t of that to a depot. Thus 5 to 6 tanker flights per MCT launch to Mars (note that I am presuming a ΔV budget of 6km/s).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: su27k on 08/19/2015 04:47 pm
IMHO, a reality check on MCT has been long overdue as this thread wanders all over the place because there are no facts to pin us down. 

SpaceX can't even build Dragon 2 without public support, and it's been delayed for years because of a lack of internal funding to make up for shortfalls in public funding measured in millions of dollars.  Yet somehow SpaceX is going to commit to actually building and flying BFR and MCT with billions of their own dollars and no contracted return on the investment?  I don't think so.  Not a snowball's chance in Hades.

They don't have enough money for Dragon 2 because Falcon 9 (and Dragon 1) has a low launch rate, and their engineering resources are focused on Falcon 9, Falcon Heavy and Dragon 2. If they can get their launch rate up, their cash flow situation would improve. And after F9/FH/DV2 are completed, they would have the engineering resources for BFR and MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/19/2015 04:53 pm
Someone from SpaceX, not sure who, said the design of MCT is changing because they learn so much from Dragon 2. Everything they do is part of the learning curve.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/20/2015 01:48 am
I'm confused again.  Do folks here believe that Musk has said the MCT is 200mT to LEO (then refueled and onto Mars' surface) with 100mT useful payload?  Or is it 100mT useful payload with X mT more being the Dry Mass of what it takes to carry that payload...airframe, empty fuel tanks, re-entry shield, engine tonnage?

I think that Musk has said that the MCT will deliver 100t to Mars via a trip to Earth orbit for refueling. How much it can put into LEO was not a matter of record from Elon and speculation here has been anything from 70t to LEO to 200t to LEO.

My personal expectation is that MCT will have an dry weight around 50t, carry 100t of payload, 670t of propellant and that a tanker version that is reusable to LEO has a dry weight of 30t, carries virtually no payload but 800t of propellant at launch and can nominally deliver 130t of that to a depot. Thus 5 to 6 tanker flights per MCT launch to Mars (note that I am presuming a ΔV budget of 6km/s).

Appreciate the response.  Makes sense.  Agree with the tanker #s.
Your delta V budget seems a little low from LEO.
Figures I've seen for reaching Mars surface from LEO run higher...aerobraking away a Km/sec or two?

http://www.lr.tudelft.nl/index.php?id=29335&L=1

Then the return trip to Earth from Mars' surface runs almost up to 8Km/sec.  Of course the returning MCT will only have the 50mT dry weight plus say just 10-20mT "payload resulting in "only" a mass of 60-70mT.  Using the rocket equation, that MCT won't even need a full load of ISRU propellant to meet delta V return needs from Mars to Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/20/2015 04:22 am
You seem to be throwing your lot in with Vultur and the MarsOne nonsense of immediate colonization from the first footprint.  This is not going to happen, it's like saying that Neil Armstrong should have colonized the moon rather then coming back.

Apollo was designed for brief forays, MCT will presumably be designed for colonization. It's not comparable.

EDIT: Also, a Mars mission is going to be 2-3 years anyway so you need long term life support even for "flags and footprints". So the difficulty gap between "flags and footprints" and colonization is much smaller for Mars than the Moon.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/20/2015 06:16 am
Your delta V budget seems a little low from LEO.
Figures I've seen for reaching Mars surface from LEO run higher...aerobraking away a Km/sec or two?

http://www.lr.tudelft.nl/index.php?id=29335&L=1

Your link gives 5,7km/s for LEO to LMO. Landing should require less. That's assuming the LMO figure is with propulsive braking. Not going into LMO saves a lot and much of the braking for landing is done with aerobraking. If I remember correctly usually 1km/s propulsive braking was usually assumed for Mars landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 08/20/2015 09:31 am
[Here is an update of a post of mine from 4th April on thread 3]

Lets sum up what  know (or at least reasonably can expect) of MCT.

Payload to Mars surface 100 tonnes - initial flights are likely to have lower payload mass, perhaps as low as 50 tonnes.

Up to 100 passengers and crew - initial flights are likely to carry far less, perhaps around 10, later flights perhaps a few more.

100 SUV volume - it is unclear if this is external volume which could be 2000m3 or internal volume perhaps 700m3. It is also unclear if this refers to total MCT volume or usable cargo volume or pressurized volume.

Something like 2-10 cargo flights to each crew flight - cargo flights are the major cost driver. Elon says 10 cargo flights, but that seems more than is needed.

Launched on a 100-150 tonne BFR (fully reusable) - equivalent to 200-300 tonnes expendable rocket. It is probably possible to go as low as 50 or as high as 600 tonnes (reusable) and still make the architecture work, but these seem to go away from the optimum. A fully reusable BFR with return to launch site (RTLS) would place 190-280 tonnes into LEO. So that with the MCT as its own second stage, MCT+payload is a bit less than BFR expendable payload.

MCT is its own second stage. This seems to be confirmed by WaitButWhy blog.

There is also a tanker second stage.

Cargo and crew flights will use a similar MCT configuration - technologies that are only useful for crew flights are unlikely.

MCTs to be returned to Earth so that they can be reused within 1 synod. This might not apply to early flights, some might be left on Mars, others might be returned later. WaitButWhy blog says 2 synod reflight.

Reflight within 1 synod implies fast cargo flights. Most architectures employ low energy cargo flights which save on IMLEO.

Crew accommodations are just cargo. It seems likely that crew and cargo MCT are almost identical with all additions for crew being treated as cargo.

Methane/Oxygen main fuel and lots of it.

Main engine is raptor. Used for TMI, Mars ascent, TEI, also probably used for Mars landing.

Raptor size is in the range 500-1500klb. Optimisation still probably taking place, but 500-700klb seems most likely. Landings on Mars using Raptor at higher thrusts would be 'sporty', but not impossible given the range of potential MCT masses and throttling levels.

Fully reusable - both MCT and BFR. This has implications for Mars and Earth entry descent and landing.

Land the whole MCT on Mars. The simplest architecture. Given that the MCT will be large and fully reusable and uses Mars derived propellants it is difficult to improve on this.

Propellant transfer in LEO, either from tankers to MCT, or from tankers to propellant depot to MCT.

Multiple tanker flights per MCT. Could be as high has 12 or as low as 3 depending on BFR size, MCT size, etc. perhaps 6 is a reasonable estimate.

Multiple constraints means that the MCT design is hard. All aspects of the flight (Earth launch, TMI/TEI, transit, Mars EDL, Mars surface ops, Earth EDL) put constraints on the MCT, it is a very difficult problem to satisfy them all. Finding it impossible to meet all of them would be the most likely reason to change from a land-it-all, return-it-all in 1 synod using methane architecture.

It is highly probable that Solar power will be used during transit. Lightest and cheapest solution, but it does create difficulties in furling the solar sails for landing.

It is likely that Solar power will be used during surface ops. Cheap and easy to scale.

Electric Propulsion may be used during transit. But probably only as a secondary propulsion system for attitude control, course corrections. Large SEP stages do not fit well with a land-it-all, return-it-all in 1 synod architecture.

There seem to be 3 possible shapes for the MCT:
1. Capsule - similar to Dragon - SpaceX has lots of experience in this, but perhaps not enough lift for Mars to give a reasonable payload fraction landed - scaling Red Dragon would give a heat shield over 20m in diameter.
2. Bullet - similar to fairing - most space efficient, used on DRM 5.0, but perhaps too tail-heavy either during Mars descent or Earth descent. Actual shape may be a biconic/triconic.
3. Semi-lifting - something like ESA's IXV perhaps, gives more lift than capsules.
All three have advantages and disadvantages.

Vertical landing is likely. As this avoids the problems with horizontal landings -  load paths in 2 directions, a separate set of landing engines and does not need raising to the vertical for launch from Mars.

Separate landing engines are possible. Better match to thrust required, could possibly be used for LAS, keeps exhaust well away from martian surface which reduces debris, also might be used as a launch abort system. But add extra mass and complexity.

No Nuclear. There are no suitable reactors off-the-shelf, creating one would be time consuming, very costly and impose great regulatory burdens on the entire architecture.

Initial crews live in the MCT.

Early designs of the MCT are likely to be quite different from those at the colony stage. More experience, better technology, economies of scale and competition will all affect the MCT over several generations. 100 people for $500k each is likely 50 years away, lots can happen in that time.

The MCT and BFR factory will be built near the launch site. If there are more than one launch site, probably near water as well.

The launch site location is unknown. Noise is a major constraint, few if any places on the coast are suitable, perhaps launch from a short distance off-shore.

Two possible configurations of BFR/MCT:
1. MCT is the second stage of the BFR, with mission kits for tanker, propellant depot, crew and cargo roles.
2. MCT is payload on a two stage BFR. It would then probably make sense for the tanker and propellant depot roles to be a stretched upper stage variant, while the MCT takes on other roles.
The first option allows a larger MCT (+payload) for the size of BFR at the expense of even more constraints on the MCT design. The second option is more flexible and probably easier, but at the expense of designing an extra reusable stage.

LEO rendezvous. Use of L1 does not seem to be part of the plan. Putting the mission together at L1 gives the advantage of staging, but it seems unlikely that BFR can get a fully loaded MCT to L1 in a single launch, even with a SEL tug. Assuming BFR launch is cheap, the added complexity of L1 does not seem worth it.

No use of Lunar propellants. Production of lunar propellants and launch are highly likely to be more expensive than using BFR tanker flights. Depending on lunar propellants puts lots of unknowns on the critical path.

Direct return injection. The MCT launches and directly injects into an Earth return orbit. No stops in low Mars orbit, no propellant depot on a Mars moon. A MCT sized to go from LEO to the Mars surface is also sized correctly to go from the Mars surface back to Earth in one go (perhaps with a smaller but still substantial payload). Schemes to refuel in Mars orbit, may save a bit of propellant production on Mars but only at the expense of increased complexity.

Testing. The MCT will be thoroughly tested in LEO before flights are attempted to Mars. Multiple landings on Mars will be made before the first crew landing, multiple return flights will be made before the first crew return.

Early MCT crew may be launched on Dragon. Early crews are likely to be in the order of 10 people, it is likely that it will be cheaper to launch them on Dragon than to man rate the BFR/MCT. The MCT can also be refuelled over months using tankers without needing the crew on board (this stops the propellant depot becoming a gating item).

The cost of moving to Mars will be higher than $500k. Add in necessary equipment and supplies and cost to expand the base/colony to accommodate one more person and the true cost (long term) is probably an order of magnitude higher.

The BFR and MCT may have other uses. Other short term uses might be one way of paying for the development. SpaceX have a record of getting customers to pay for development flights.

Development over the next 5 years will not be payed for from the satellite constellation. It will take at least that long for the satellite business to be profitable, in the mean time that will be a vast capital expense.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/20/2015 10:05 am
I'm confused again.  Do folks here believe that Musk has said the MCT is 200mT to LEO (then refueled and onto Mars' surface) with 100mT useful payload?  Or is it 100mT useful payload with X mT more being the Dry Mass of what it takes to carry that payload...airframe, empty fuel tanks, re-entry shield, engine tonnage?

First: "200mT to LEO" is something that probably corresponds to BFR the launch vehicle rather than to MCT the upper stage & lander.  Anything which lands 100mT of useful payload on the Martian surface, will be much higher than 200mT IMLEO, and this implies that one MCT mission will be the culmination of multiple propellant-carrying, and possibly multiple payload-carrying launches.

With that said, there are still big questions.

The core of the capability falls on several questions
1) Is MCT's structural/rocket-stage mass counted within this 100 tons?
2) How many pieces on the board are there: Will non-landed transit habitats be used?
3) Is MCT's human cargo, life support, & food counted within this 100 tons?
3.5) Is MCT's habitat integral to the design?
4) Is MCT's ISRU gear counted within this 100 tons?
4.5) Is MCT's ISRU gear integral to the design?
5) Does MCT need to *return* 100 tons of cargo to Earth orbit?
5.5) Is MCT's ISRU gear returned?

I think we can answer 1) with a definite 'No' based on the repetition of 'useful cargo'.

We have very little idea about how to answer 2), and there are a spectrum of possibilities: In the extreme case, MCT could just be a short-term launcher/lander attached to a very large transit habitat, whether on a cycler trajectory or a semi-cycler which remains in high Mars orbit.

Answering 3) with 'Yes' is less definite, but implied by Musk not knowing how many people could be moved within a 100 ton payload envelope, which is what it sounds like he's saying.

I would probably answer 4.5) with 'No', in the long run, but 'Yes' in the short run - I think they're trying to design a rocket that remains useful over several stages of colonization.  That doesn't provide any insight into how to answer 4) though.

My inclination is that 5.5) should be 'No', because landed ISRU gear can be useful for future missions, even just as spares, and designing a dual deployer / retractor has to be orders of magnitude harder than designing a lightweight deployer.

I really want 4) to be 'No' and 5) to be 'Yes', but a lot of that is aspirational: Apollo-style exploration of multiple locations is something I see as a required capability for a mission ( which sets up a colony initially AND reuses its landers ), and I think if you're going to send hundreds of people to Mars, it's best not to design an entirely separate spacecraft just to venture to the other side of the planet.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/20/2015 10:22 am
Excellent post Mike, with a few reservations.

The one I want to tackle first is 1-synod operation.

By what mission plan can an MCT be used once per synod?  Would this be an opposition-class mission that refuels from prelanded ISRU assets?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Owlon on 08/20/2015 10:23 am
The core of the capability falls on several questions
5) Does MCT need to *return* 100 tons of cargo to Earth orbit?

I believe Musk said in the past year or so that MCT would be able to carry about 25 tons back to Earth, which adds up pretty nicely if you assume the 4 month Marsbound trajectory that he has talked about and a 75ish ton dry mass.

Although, it's quite possible I'm misremembering something.

Regardless, it really doesn't make sense to design for 100 tons both ways because the return flight is more demanding in delta-V.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/20/2015 11:17 am
The core of the capability falls on several questions
5) Does MCT need to *return* 100 tons of cargo to Earth orbit?

I believe Musk said in the past year or so that MCT would be able to carry about 25 tons back to Earth, which adds up pretty nicely if you assume the 4 month Marsbound trajectory that he has talked about and a 75ish ton dry mass.

Although, it's quite possible I'm misremembering something.

Regardless, it really doesn't make sense to design for 100 tons both ways because the return flight is more demanding in delta-V.

I believe 2kg/day is the baseline assumption on consumables, from ISS/Shuttle accommodations, with a reasonably complete ECLSS closure on water and breathing gas.

(A 200-day Mars->Earth transit * 2kg/day/person food & sanitary) + 100kg/person bodyweight, clothing, personal items, & spacesuits ) * 100 persons works out to 50 tons needed just to get the purported number of living humans from Mars orbit to Earth orbit, before approaching any durable goods or return cargo (Marsrocks) counted within the 100 tons.

For that matter, ( (a 200 day Earth->Mars transit + a 600-day Mars surface deployment ) * 2kg/day/person food & sanitary) + 100kg/person bodyweight, clothing, personal items, & spacesuits ) * 100 persons  works out to 170 tons before durable goods or deployable hardware.

Potential interpretations:
A)
the consumable budget is going to be considerably closer to refined food powder & oils than ISS' partially-dehydrated whole food panty (or the two levels I thought were plausible upgrades on this, US MRE-grade rations or a kitchen with a freezer & perhaps even toaster oven), and daily consumables mass is going to be closer to 500g-750g than 2000g, despite the harsher psychological impact of long duration mission, & the increased sanitary & clothing needs
B)
The 100 tons refers to returned mass
C)
There are additional complications, like having "up to 25 tons on the MAV", which proceeds to rendezvous with a food-packed transit hab in LMO within a week.

I think A) is unreasonable, but there have been vocal disagreements in prior threads.  If A) is false, that leads one to believe either B or C or both have to be true.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/20/2015 12:43 pm
@Burninate

I vote for D) None of the above. 100 is the number of people going to Mars in colonization mode. It is not anticipated and planned for that so many people will ever go back to earth. That number may be closer to 10 max. That could be provided for with 25t return mass. Provided the ECLSS for 100 people does not have too much weight by itself which could reduce the max number of people going back further or part of the ECLSS would need to be removed and go back on empty cargo MCT to maximize passenger capacity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 08/20/2015 12:57 pm
Excellent post Mike, with a few reservations.

The one I want to tackle first is 1-synod operation.

By what mission plan can an MCT be used once per synod?  Would this be an opposition-class mission that refuels from prelanded ISRU assets?

The 1-synod operation comes from the requirement to reuse the MCT as much as possible. If the MCT has a 30 year life (comparable to commercial planes - yes I know they can last longer, but most are retired after 30 years), then 2-synod reuse leads to 15 flights, it is hard to see how costs could be kept low enough for a $500,000 trip. Something Elon Musk said also indicated that he was keen to have reuse asap.

I think that with higher delta-v, fast transits and fast turn-around on Mars 1-synod are possible. If I have time I might try and work out if this is actually true, and how large the delta-v, transit time and entry velocities are.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 08/20/2015 01:02 pm
@Burninate

I vote for D) None of the above. 100 is the number of people going to Mars in colonization mode. It is not anticipated and planned for that so many people will ever go back to earth. That number may be closer to 10 max. That could be provided for with 25t return mass. Provided the ECLSS for 100 people does not have too much weight by itself which could reduce the max number of people going back further or part of the ECLSS would need to be removed and go back on empty cargo MCT to maximize passenger capacity.

I agree D)

Also note that there will be many cargo trips per crew flight, so the crew could return on a cargo MCT, if the cargo and crew MCT are similar enough.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 08/20/2015 01:13 pm
The core of the capability falls on several questions
1) Is MCT's structural/rocket-stage mass counted within this 100 tons?
2) How many pieces on the board are there: Will non-landed transit habitats be used?
3) Is MCT's human cargo, life support, & food counted within this 100 tons?
3.5) Is MCT's habitat integral to the design?
4) Is MCT's ISRU gear counted within this 100 tons?
4.5) Is MCT's ISRU gear integral to the design?
5) Does MCT need to *return* 100 tons of cargo to Earth orbit?
5.5) Is MCT's ISRU gear returned?

My answers:
1) No
2) BFR booster, MCT (cargo+crew which are similar as crew hab mainly acts as cargo), tanker. No
3) Yes - MCT payload is either cargo or hab + crew + consumables
3.5) Partly - the hab is plumbed in for crew flights, it can be removed/replaced but only with considerable effort, cargo MCT would not have the hab, but would have some cargo containment system.
4) No - some of the initial flights have as cargo ISRU
4.5) No - no reason to carry ISRU back to Earth, many reasons not to.
5) No - only 25 tonnes. Aborts might return a full 100 tonnes.
5.5) No - ISRU remains on Mars were it forms part of a ISRU farm.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/20/2015 01:58 pm
I want to comment on 3.5)

I imagine there is no crew hab inside MCT. MCT has a pressure hull and the whole thing is pressurized and habitable. BTW I prefer passenger MCT. :) The difference between cargo and passenger MCT would be the ECLSS and interior outfit for crew or cargo. Cargo will need a large SpaceShuttle style cargo door. Passenger MCT will likely not have that. Otherwise they would be very similar.

Recently I was also thinking about stabiity of MCT for reentry. A capsule like Dragon is strong and heavy. Mass budget for MCT will likely not allow this. Maybe they pressurize the interior more like the tanks of an ascent stage for stability. That would mean maybe 3 times earth normal pressure during EDL. Sounds off even for myself, maybe totally wrong but new solutions will be needed or mass of MCT gets too high.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/20/2015 02:38 pm
The core of the capability falls on several questions
1) Is MCT's structural/rocket-stage mass counted within this 100 tons?
2) How many pieces on the board are there: Will non-landed transit habitats be used?
3) Is MCT's human cargo, life support, & food counted within this 100 tons?
3.5) Is MCT's habitat integral to the design?
4) Is MCT's ISRU gear counted within this 100 tons?
4.5) Is MCT's ISRU gear integral to the design?
5) Does MCT need to *return* 100 tons of cargo to Earth orbit?
5.5) Is MCT's ISRU gear returned?

My answers:
1) No
2) BFR booster, MCT (cargo+crew which are similar as crew hab mainly acts as cargo), tanker. No
3) Yes - MCT payload is either cargo or hab + crew + consumables
3.5) Partly - the hab is plumbed in for crew flights, it can be removed/replaced but only with considerable effort, cargo MCT would not have the hab, but would have some cargo containment system.
4) No - some of the initial flights have as cargo ISRU
4.5) No - no reason to carry ISRU back to Earth, many reasons not to.
5) No - only 25 tonnes. Aborts might return a full 100 tonnes.
5.5) No - ISRU remains on Mars were it forms part of a ISRU farm.

FWIW:
My preference/prediction is for a spacecraft that is capable of, but does not mandate, 100 tons within these parameters:
1) No
2) Yes, SEP and hab stay in Mars orbit
3) Yes
3.5) Yes.  If pure cargo shipments are required at some point, they will use alternate spacecraft, not MCT;  If alternate spacecraft are not available, stripping the hab section of gear and using prelanded ISRU for return is a possibility, albeit a wasteful one.
4) No, and it is surprisingly heavy;  MCT will not be a small spacecraft.
4.5) No.  Leaving the ISRU gear in modular cargo pods permits the same vehicle to eventually be used both for exploration of new sites, and landings at established sites with preexisting ISRU setups.  This will not be useful in the first few tens of missions, however - backups are more valuable for established sites, and exploring new sites will be an important component of exploration.
5) Yes.  50 tons minimum for people & food need to arrive in Earth orbit, anyhow - ideally some rocks and reusable gear get brought back as well.  Unclear how this meshes with strictly orbital assets, or with a 'split lander' concept I've been toying with
5.5) No.  Rolling up solar panels and returning cargo pods & vehicles to the lander is less practical with the designs I'm interested in than building new ones for every mission.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/20/2015 02:43 pm
I think that with higher delta-v, fast transits and fast turn-around on Mars 1-synod are possible. If I have time I might try and work out if this is actually true, and how large the delta-v, transit time and entry velocities are.
I understand the desire, in the same way that I understand the desire for quarter-synod operations.

My question is: How?

Doesn't this presume:
1) No ISRU gear aboard the lander, strictly refueling from landed assets
2) A short-stay opposition-class mission, days to weeks on the ground, then return to orbit;  To avoid 'flags and footsteps', the MCT acts are a transit shuttle to a surface station where people live, rather than a self-contained mission
And maybe even 3) Confining operations to low-dV synods, where Mars is near perihelion (I think?)

Designing MCT to my concept ("18 month surface mission in a can, maximum reuse, one round trip every 2 or 3 synods") permits it to eventually, tens of missions in, start to shift to missions of your concept ("Bus to Mars station, one round trip every synod")... but not the other way around.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/20/2015 02:55 pm
Your delta V budget seems a little low from LEO.
Figures I've seen for reaching Mars surface from LEO run higher...aerobraking away a Km/sec or two?

http://www.lr.tudelft.nl/index.php?id=29335&L=1

Your link gives 5,7km/s for LEO to LMO. Landing should require less. That's assuming the LMO figure is with propulsive braking. Not going into LMO saves a lot and much of the braking for landing is done with aerobraking. If I remember correctly usually 1km/s propulsive braking was usually assumed for Mars landing.

5.7 includes a propulsive Mars capture maneuver. My 6km/s budget presumes Aerocapture/braking but it also assumes a slightly faster than Hohmann orbit (6-7 month transit time) with 1km/s reserved for Mars landing and 300m/s contingency.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/20/2015 04:18 pm
I'm confused again.  Do folks here believe that Musk has said the MCT is 200mT to LEO (then refueled and onto Mars' surface) with 100mT useful payload?  Or is it 100mT useful payload with X mT more being the Dry Mass of what it takes to carry that payload...airframe, empty fuel tanks, re-entry shield, engine tonnage?

First: "200mT to LEO" is something that probably corresponds to BFR the launch vehicle rather than to MCT the upper stage & lander.  Anything which lands 100mT of useful payload on the Martian surface, will be much higher than 200mT IMLEO, and this implies that one MCT mission will be the culmination of multiple propellant-carrying, and possibly multiple payload-carrying launches.

That seems to be consistent with everything that Musk has said about MCT in the last year or more as well as the WBW article.


With that said, there are still big questions.

The core of the capability falls on several questions
1) Is MCT's structural/rocket-stage mass counted within this 100 tons?
2) How many pieces on the board are there: Will non-landed transit habitats be used?
3) Is MCT's human cargo, life support, & food counted within this 100 tons?
3.5) Is MCT's habitat integral to the design?
4) Is MCT's ISRU gear counted within this 100 tons?
4.5) Is MCT's ISRU gear integral to the design?
5) Does MCT need to *return* 100 tons of cargo to Earth orbit?
5.5) Is MCT's ISRU gear returned?

First let me add another few questions that I feel are vital:

A) Are there going to be a propellant depots, or are MCT's going to be refueled by a succession of tanker rendezvous?
B) does each MCT have regenerative ZBO or does it rely on passive cooling?
C) where would propellant depots be located?
D) where will BFR launch from?

Now my take on answering what I think we can infer about your questions:

1) No, nothing that went to Mars and returns as part of the craft is included in the 100t
2) Pieces: well I see MCT as the 2nd stage of BFR, but that BFR can also use alternate upper stages such as a tanker upper stage and a LEO bulk transport upper stage meant just to bring a large cargo to LEO. I also see MCT as having several designs, the first being an autonomous cargo to Mars surface version that precedes any manned operations by 1 synod or more. The 2nd design is going to be the cargo version that has a 10 round trip life span or more and is the basis of the bulk cargo transit for the short and medium term of Martian settlement. The 3rd design will be the first passenger carrying iteration. This version will probably only see 5 cycles and there may only be a handful of them built. While I expect them to only carry 16 - 20 passengers maximum they will be over provisioned by at least 100% for ECLSS. They will have a lot of room for cargo. And I see two of them sent out on the first synod of manned presence. The next version would be in the 50 passenger size range and still over engineered for ECLSS. These for MCT version would, in my mind account for all the MCT use over the first 10-15 synods of Martian settlement. At a guess no more than 5 of the first version will be built. At least a dozen of the 2nd version, 5 of the 3rd, 5 - 10 of the 4th version. So a build rate of about 2 MCT's a year maybe.
3) Yes and see above, there are different version of MCT
3.5) definitely but it represents a different design from a cargo MCT.
4 and 4.5) Yes and while it may be integrated into the design of the first few MCTs, after the first few larger ISRU systems will be built from delivered subsystems and cargo MCTs that return will not have ISRU systems built in but get fuel from the settlement where they deliver cargo.
5) No, and the only way it could do that is if it were partially refueled in Mars orbit. Note while I doubt that there will ever be an MCT dispatched from Mars to Earth with full cargo, I can see MCTs being sent from Mars to the Asteroids with cargo to support an operation there (fuel, food and maybe Mars built solar panels as the cargo)
5.5) no the early MCTs with ISRU will be just there to produce propellant for the early passenger MCTs - they might later be cannibalized for parts (engines particularly) to refurbish other MCT's.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/20/2015 06:02 pm

First let me add another few questions that I feel are vital:

A) Are there going to be a propellant depots, or are MCT's going to be refueled by a succession of tanker rendezvous?
B) does each MCT have regenerative ZBO or does it rely on passive cooling?
C) where would propellant depots be located?
D) where will BFR launch from?

A) Elon Musk mentioned depots. They will be needed when many flights go every launch window. However I believe that they won't need them early on. Two or three MCT, one of them passenger, can easily be fuelled directly.

B) ZBO can be achieved completely passive during interplanetary flight. There may be some boiloff in LEO but that is probably acceptable. So IMO no active cooling

C) Depots would be in LEO for all we know.

D) Good question. My personal opinion on a platform a few km off the coast of Brownsville, Texas.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/20/2015 10:01 pm

MCT is its own second stage. This seems to be confirmed by WaitButWhy blog.


I have the disagree with the very idea that this WaitButWhy blog can be considered a confirmation of ANYTHING.  The writer doesn't claim any privileged access to information beyond what we have on these forums and I strongly think that everything they described came FROM this forums speculation or the speculation of similar forums.  Even if the author independently arrived at similar conclusions that's nothing more then another 'vote' for one a particular configuration.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/20/2015 10:05 pm

MCT is its own second stage. This seems to be confirmed by WaitButWhy blog.


I have the disagree with the very idea that this WaitButWhy blog can be considered a confirmation of ANYTHING.  The writer doesn't claim any privileged access to information beyond what we have on these forums and I strongly think that everything they described came FROM this forums speculation or the speculation of similar forums.  Even if the author independently arrived at similar conclusions that's nothing more then another 'vote' for one a particular configuration.

No he discussed this at length with Elon.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/20/2015 11:49 pm

MCT is its own second stage. This seems to be confirmed by WaitButWhy blog.


I have the disagree with the very idea that this WaitButWhy blog can be considered a confirmation of ANYTHING.  The writer doesn't claim any privileged access to information beyond what we have on these forums and I strongly think that everything they described came FROM this forums speculation or the speculation of similar forums.  Even if the author independently arrived at similar conclusions that's nothing more then another 'vote' for one a particular configuration.

No he discussed this at length with Elon.

I don't think Elon let slip all that much privileged information.  Hell, I don't think Elon has finalized all that much information, but that's another matter.  He's organizing the community's conjectures, that's all.  Plus a 3.8 F/O ratio.  He quotes Elon where Elon provides info.

Note he says "No one’s exactly sure how the transportation will work, but it’ll likely be something like this: "
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/21/2015 12:01 am

MCT is its own second stage. This seems to be confirmed by WaitButWhy blog.


I have the disagree with the very idea that this WaitButWhy blog can be considered a confirmation of ANYTHING.  The writer doesn't claim any privileged access to information beyond what we have on these forums and I strongly think that everything they described came FROM this forums speculation or the speculation of similar forums.  Even if the author independently arrived at similar conclusions that's nothing more then another 'vote' for one a particular configuration.

No he discussed this at length with Elon.

I don't think Elon let slip all that much privileged information.  Hell, I don't think Elon has finalized all that much information, but that's another matter.  He's organizing the community's conjectures, that's all.  Plus a 3.8 F/O ratio.  He quotes Elon where Elon provides info.

Note he says "No one’s exactly sure how the transportation will work, but it’ll likely be something like this: "

Elon had a veto on what went in the article and certainly provided plenty of background that counts as access to me. No this article did not say that a two stage design was set in stone, but neither is it something that he just got by reading the forum here or guessing.

Note that Elon has endorsed the latest WBW article by tweeting a link to it twice. He has not to my knowledge ever tweeted a link to speculation we have on this site saying "oh hey they are pretty close"
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/21/2015 03:23 am
I find it unlikely that Elon would specifically request that some piece of speculation be cut from an article (who has the time to wade through that morass of an article), especially when it is many others have already been speculating the exact same thing and he is is still entertaining it himself.  We know Elon has through about direct Earth return and might PREFER that, but it doesn't prove it will work and if it can't work then he can't use it.  It is the idea that this configuration was in anyway CONFIRMED that is bogus.

The only bit of information that has any provenance back to Elon is the O/F ratio and that's an extremely minor detail.  If their was a 'long discussion' it must have consisted of either Musk describing his dreams of colonization without going into detail, or the author asking every basic 3rd grader question that could have been answered by reading 'shit that Elon says'.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/21/2015 06:30 am
I find it unlikely that Elon would specifically request that some piece of speculation be cut from an article (who has the time to wade through that morass of an article), especially when it is many others have already been speculating the exact same thing and he is is still entertaining it himself.  We know Elon has through about direct Earth return and might PREFER that, but it doesn't prove it will work and if it can't work then he can't use it.  It is the idea that this configuration was in anyway CONFIRMED that is bogus.

The only bit of information that has any provenance back to Elon is the O/F ratio and that's an extremely minor detail.  If their was a 'long discussion' it must have consisted of either Musk describing his dreams of colonization without going into detail, or the author asking every basic 3rd grader question that could have been answered by reading 'shit that Elon says'.

Of course it has provenance back to Elon and since he commissioned the articles from this source in the first place, since he asked that it be reviewed before being published in the 2nd place, and since he promoted it in the third place he wants it written the way it is. Is 100% sure no, but did it come from him yes.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 08/21/2015 07:14 am

MCT is its own second stage. This seems to be confirmed by WaitButWhy blog.


I have the disagree with the very idea that this WaitButWhy blog can be considered a confirmation of ANYTHING.  The writer doesn't claim any privileged access to information beyond what we have on these forums and I strongly think that everything they described came FROM this forums speculation or the speculation of similar forums.  Even if the author independently arrived at similar conclusions that's nothing more then another 'vote' for one a particular configuration.

No he discussed this at length with Elon.

I don't think Elon let slip all that much privileged information.  Hell, I don't think Elon has finalized all that much information, but that's another matter.  He's organizing the community's conjectures, that's all.  Plus a 3.8 F/O ratio.  He quotes Elon where Elon provides info.

Note he says "No one’s exactly sure how the transportation will work, but it’ll likely be something like this: "

Elon had a veto on what went in the article and certainly provided plenty of background that counts as access to me. No this article did not say that a two stage design was set in stone, but neither is it something that he just got by reading the forum here or guessing.

Note that Elon has endorsed the latest WBW article by tweeting a link to it twice. He has not to my knowledge ever tweeted a link to speculation we have on this site saying "oh hey they are pretty close"

MCT is its own second stage. This seems to be confirmed by WaitButWhy blog.

I chose my words carefully, if I thought WaitButWhy was authoritative I would have used is confirmed.

Lets get back to speculation and discussion about MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MickQ on 08/21/2015 10:22 am
@Burninate

I vote for D) None of the above. 100 is the number of people going to Mars in colonization mode. It is not anticipated and planned for that so many people will ever go back to earth. That number may be closer to 10 max. That could be provided for with 25t return mass. Provided the ECLSS for 100 people does not have too much weight by itself which could reduce the max number of people going back further or part of the ECLSS would need to be removed and go back on empty cargo MCT to maximize passenger capacity.

If the ECLSS on passenger MCT was made up of, say, 5 identical modules then after arrival on Mars, 3 modules could be removed for use in ground habitats leaving the other 2 for the return trip.  Saves weight and also rotates new equipment on every subsequent flight.  Similarly, gas and water storage tanks.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 08/21/2015 11:08 am
Potential interpretations:
A)
the consumable budget is going to be considerably closer to refined food powder & oils than ISS' partially-dehydrated whole food panty...

Is the food really that bad on the ISS? Are they that desperate with the cargo ship losses?

j/k, couldn't resist.

But in all seriousness, remember that the ships will not fly on their own but launched as a rag-tag fugitive fleet. There is no need for there to be any food at all on the passenger MCTs. One logistics MCT would provide enough chow for the entire 1000 person fleet. The passengers could also fly in cold sleep, which I see as a viable option as far as colonisation goes.

@Burninate

I vote for D) None of the above. 100 is the number of people going to Mars in colonization mode. It is not anticipated and planned for that so many people will ever go back to earth. That number may be closer to 10 max. That could be provided for with 25t return mass. Provided the ECLSS for 100 people does not have too much weight by itself which could reduce the max number of people going back further or part of the ECLSS would need to be removed and go back on empty cargo MCT to maximize passenger capacity.

If the ECLSS on passenger MCT was made up of, say, 5 identical modules then after arrival on Mars, 3 modules could be removed for use in ground habitats leaving the other 2 for the return trip.  Saves weight and also rotates new equipment on every subsequent flight.  Similarly, gas and water storage tanks.

The 100 passenger phase is likely to be deep into the 21st century, 2070 or thereabouts. Rocketry has seen very little radical development since the 60s so we could be seeing the MCT still flying, but there could also be a whole host of unforeseen events. Bigelow building a cycler to serve the Earth-Mars routes.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/21/2015 12:05 pm
If the ECLSS on passenger MCT was made up of, say, 5 identical modules then after arrival on Mars, 3 modules could be removed for use in ground habitats leaving the other 2 for the return trip.  Saves weight and also rotates new equipment on every subsequent flight.  Similarly, gas and water storage tanks.

I agree that everything really useful on Mars would be removed. Quite possibly storage tanks and bunks and dividers for the passengers may be useful. The ECLSS units not so much. ECLSS on Mars would be based on plants. Greenhouses that produce food enough to eat will also produce enough oxygen. Technical recycling like on spacecraft is not needed. So even if some of them need to be removed to maximise passenger capacity they would go back on cargo MCT for reuse unless single components like pipes, valves or fans are valuable on Mars.

It also depends on how much the weight of this equipment is. If the 25t return mass allow return of everything to earth and 10 people and supplies they may remove very little, only items of really high value on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 08/21/2015 12:29 pm
If the ECLSS on passenger MCT was made up of, say, 5 identical modules then after arrival on Mars, 3 modules could be removed for use in ground habitats leaving the other 2 for the return trip.  Saves weight and also rotates new equipment on every subsequent flight.  Similarly, gas and water storage tanks.

I agree that everything really useful on Mars would be removed. Quite possibly storage tanks and bunks and dividers for the passengers may be useful. The ECLSS units not so much. ECLSS on Mars would be based on plants. Greenhouses that produce food enough to eat will also produce enough oxygen. Technical recycling like on spacecraft is not needed. So even if some of them need to be removed to maximise passenger capacity they would go back on cargo MCT for reuse unless single components like pipes, valves or fans are valuable on Mars.

It also depends on how much the weight of this equipment is. If the 25t return mass allow return of everything to earth and 10 people and supplies they may remove very little, only items of really high value on Mars.

Primary O2 source would likely be plants, but you must have a secondary system in case you have a plant disease issue.

Everything on an MCT will be high value to Mars, at least for some decades!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/21/2015 02:12 pm
Secondary source would be the fuel ISRU. Plenty of oxygen and nitrogen produced there. Some CO2 scrubbing would be needed.

Some ECLSS units may be needed at outlying mining or research stations without their own plant LSS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/21/2015 04:02 pm
The 100 passenger phase is likely to be deep into the 21st century, 2070 or thereabouts. Rocketry has seen very little radical development since the 60s so we could be seeing the MCT still flying, but there could also be a whole host of unforeseen events. Bigelow building a cycler to serve the Earth-Mars routes.

My impression was, this design exercise was for a vehicle & mission architecture which would work without thus-far-imaginary technologies like induced torpor, would be capable of equipping for 100-person missions and most of Musk's other requirements, and would have first mission in the 2030's and first launch in the 2020's.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 08/21/2015 04:21 pm
The 100 passenger phase is likely to be deep into the 21st century, 2070 or thereabouts. Rocketry has seen very little radical development since the 60s so we could be seeing the MCT still flying, but there could also be a whole host of unforeseen events. Bigelow building a cycler to serve the Earth-Mars routes.

My impression was, this design exercise was for a vehicle & mission architecture which would work without thus-far-imaginary technologies like induced torpor, would be capable of equipping for 100-person missions and most of Musk's other requirements, and would have first mission in the 2030's and first launch in the 2020's.

Agreed, but that doesn't mean SpaceX can pull it off from an engineering or cost point of view. We might see a smaller first generation MCT to get things rolling and a later second generation MCT that can handle 100-person missions.

Until SpaceX releases a PowerPoint showing what they really have in mind, we don't have much to go on.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/21/2015 07:04 pm
What if, some 100t cargo deliveries to Mars were made with a one way EDL system but launched from LEO with a reusable booster that could put 50 modules on a course to Mars each Synod?

So I have been assuming that a first generation Cargo MCT would be something like:

Dry weight 50t
Payload 100t
ISP 360
ΔV  6000m/s
Propellant 670t

And I presumed that at first several are sent that won't ever be returning (though their raptors and other systems could be spares to service future vehicles and their tanks the first local propellant stores).  However in this assumption I also assumed that we would have passenger carrying MCTs that had a significant enough different design that many systems and even possibly vehicle shape might be different.

Along with these I presumed an alternate BFR 2nd stage that was a reusable tanker, also presumed a LEO depot probably built from tankers, or even possibly a BFR first stage launched with no payload as an SSTO.

But lets imagine if we go this route:

A tanker, cylindrical with an aerodynamic fairing.

An MCT, the first version 10 - 20 passenger model that also carries significant amount of cargo.

And rather than sending cargo MCTs, imagine a cargo "capsule" that weighs in at 25t dry and includes the TPS just capable of the one way over Mars escape velocity entry and landing and has 100t of cargo. The total weight of this unit is 200t with 75t of propellant for 1300m/s ΔV (ISP 280). It is launched with full cargo and no fuel as the payload of a regular tanker craft. A stripped down tanker is used on orbit (2 engines instead of 4 or 5, no TPS) it is partially fueled (about 650t out of 800) and the 75t of propellant is loaded on the cargo pod. It boosts to TMI (4300m/s roughly) lets the cargo pod go, immediately boosts most of the velocity off backwards and does a little maneuver at apogee around 12,000km or so for a near rendezvous perigee and then rendezvous at perigee. As long as the fuel was ready at the depot and there were cargo pods to go it could do 50 launches per synod easily.

So I figure the pod would have some super draco style landing engines though fueled by Methalox, however it would save significant structural and equipment mass being designed for the one way trip and not be carrying raptors, as much reduced TPS, and even less robust landing gear. So I envisage 25t dry weight, 100t cargo and 75t propellant. The vehicle that launches it is based on a tanker and can be loaded with the appropriate amount of propellant for the mission requirement (based on when in the launch window the individual pod is going).  In the long run MCTs will bring most of the people and freight but in that initial build up period for the first few synods this might be an effective supplement.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/22/2015 03:43 am
I don't see how any large lander can avoid having large amounts of retro-propulsion, a few Draco's might be nice for toughing down on at a thrust level just equal to gravity, but they can't exert enough force during the short time before impacting the surface.  Raptor rockets are definitively going to be necessary for something of that tonnage.

People keep throwing out this idea of some kind of vehicle which is designed to be expendable maximum efficiency cargo haulers, that's not going to happen.  If their are vehicles that don't come back to Earth it will be because they are demonstration vehicles (probably sub-scale) for gathering data and testing concepts.  Falcon-1 equivalents designed to be pathfinders rather then haulers, they will be overbuilt as an expendable and will try to incorporate and test return capabilities as soon as possible and any cargo they bring will be part of testing and perfecting return rather then trying to deliver any supplies for people.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 08/23/2015 01:50 pm
A) Are there going to be a propellant depots, or are MCT's going to be refueled by a succession of tanker rendezvous?
A) Elon Musk mentioned depots. They will be needed when many flights go every launch window. However I believe that they won't need them early on. Two or three MCT, one of them passenger, can easily be fuelled directly.
That's consistent with the Wait-but-Why article, which says that Elon described the early process as sending up the MCT, returning the BFR and sending up tankers to refuel. With more MCTs it'll make sense to make a depot so that this can allow the MCT to be sent up last, getting a refuel quickly before departing. But at the beginning using small reusable tankers makes more sense.

Early missions:
a) BFR launches the MCT then BFR returns
b) BFR launches tanker then returns
c) Tanker refuels the MCT then returns for another run
Repeat b-c
d) BFR launches another MCT.

1 BFR, 1 Tanker, 2 or 3 early version MCTs.
I know others frequently say reusability is key, and it was clear to me (I thought), but the effect on the early planning only really just dawned on me.

Q: "How do you launch your fleet"
A: "We have a rocket, a big one"
Q: "Just one rocket?"
A: "Yes. And one tanker".
Q: "So you're sending just one spacecraft"
A: "No, we're sending 5".

Of course the reality is that redundancies are needed (though in today's world if one crashes it will hold up the sister rockets enough to miss the Mars window anyway).

Really once SpaceX builds a single BFR and tanker they can launch and relaunch, and relaunch. That first one will be expensive. When they have prototype MCTs they can launch them and refuel them. This could be a fun time for Elon :) And except for manned MCTs, other MCTs can stay in orbit a year waiting for the Mars window, to depart.

Getting a brilliant BFR and tanker early is more important than the MCT... with the exception that the BFR needs to know the MCT mass etc. That's why the Falcon reusability results are critical (while Dragon v2 can be a few years behind). And perhaps the early BFR and tanker can help with a Dragon mission to Mars.

(edit: sorry if that's really obvious!)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/23/2015 08:51 pm
I’ve been running spreadsheets & rocket equation calcs to speculate about the MCT. I’ve taken these Musk’s statements as a given.
100mT land on Mars cargo
Land the whole thing and re-use it; i.e. return it to Earth
Raptor thrust over 230mT; use a lot of them.
363 seconds ISP vacuum

10 meter stage 1 diameter won’t get it done; we need a bigger boat.
BFR is 12.5m diameter, making a relatively squat vehicle just over 50m tall, no worries about pad towers for 100m high rockets.  BFR is shorter than F9 but 10 times more massive.  BFR’s 12.5m diameter is a nice size to fit living quarters and various colonial heavy equipment.

Don’t need 15 million LBS thrust, but with mass ratios 4.25% range need just over 11 million LBS (50 million newtons) thrust, 21engines.  CORRECTION:  Typo should be 22 engines

Given the huge delta V requirements for both Mars departure from refueling at LEO AND later functioning as a SSTO taking off from Mars’ surface and return to Earth, I put the Km/sec budget into the 2nd stage.  Stage one goes Low & Slow, just 3.4 Km/sec boosting the heavy 2nd stage before return to launch site, RTLS.

Total BFR mass 4100mT or 9 million LBS.  LEO mass fraction 4.25%.

Stage One:
12.5m diameter with 21m length propellant tanks
2950mT  6.5 million LBS  1st stage fueled mass
230mT thrust engines  506K LBS
21 engines 50 million Newtons  11.1 million LBS Thrust; T/W 1.23
Rings of 14 engines, 7 engines, plus a center engine
Avg ISP from sea level to vacuum 325
Only 3.4 Km/sec Delta V via Rocket equation
0.5 Km/sec additional Delta V for RTLS

Stage Two The MCT:
Dry Mass 175mT; 100mT is cargo
12.5m diameter with 7.5 m length propellant tanks. 
Cargo/passengers 12m; 1470 m3 volume
1150mT fueled mass (2.5 million LBS)
363 seconds ISP vac; Rvac engines 10% higher thrust as with F9
6 Rvac engines   3.3 million LBS Thrust
6.7Km/sec Delta V capability, via Rocket eq.

About 8 fuel cargo MCTs needed to refuel the MCT for LEO Mars departure

S1 avg ISP    325   
S2 vac ISP   363   
1st Stage T/W   1.23   
BFR DIA   12.5   m
MCT Mass   175   mT
1st Stage Tank Length   21.0   m
S1 Propellant Volume    2576   m3
1st Stg Airframe Weight   190   mT
Propellant Weight   2731   mT
S1 Engines Weight   33   mT
S1 Total Weight mT   2954   mT
S1 Total Weight LBS   6.5   Million LBS
S1 empty + S2   1373   mT
DRY Weight   223   mT
%  DRY WEIGHT     7.5%    %
RTLS Propellant   40   mT
RTLS Delta V   0.53   Km/sec
Stage One Km/sec   3.40   Km/sec Rocket Equation
2nd Stage Tank Length   7.5   m
Propellant Volume   920   m3
Propellant Mass   975   mT
S2/S1 mass   0.39   
S2 Mass w/MCT   1150   mT
S2 Mass w/MCT   2.5   Million LBS
Calc # Vac Raptors   6.00   1.32
Stage 2 Thrust   3.3   Million LBS
Stage 2 Km/sec   6.70   Km/sec Rocket Equation
S2 Mars 25mT Cargo    8.7   Km/sec Rocket Equation
TOTAL WT mT   4104   mT
TOTAL WT LBS    9.0   Million LBS
THRUST Needed    11.1   Million LBS
THRUST Needed    49.5   Million Newtons
1st STAGE # ENG    21.9    
Eng 14+7+1 = 22
LEO Mass Fract   4.26%   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/23/2015 09:13 pm
I am quite sure I recall ISP of the Raptor vac engine as 380 which would make it somewhat less heavy. Can someone confirm or correct me?

Edit: here the reference, planned ISP is 380

http://forum.nasaspaceflight.com/index.php?topic=37839.msg1390942#msg1390942

It is interesting to hear that 15 million pound thrust are on the high side. 11 and a smaller number of engines are certanly preferable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/24/2015 12:13 am
380 vacuum ISP will definitely reduce both stage's mass.  Rocket equation.  i'll update.
Any other errata?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/24/2015 03:23 am
I'm doubtful this 2nd stage can be built, the vehicle mass is a mere 6.5% of the liftoff mass, while a F9 first stage with legs is 6% without anywhere near the entry velocity demands, and SpaceX has a lot of trouble getting that first stage to not "explode on impact with the atmosphere" at a mere 1.3 km/s and that's with retro-propulsion.  This vehicle would need to survive re-entry at Earth of at least 11 km/s possibly more.

If the vehicle is cylindrical and comes into the atmosphere like a bullet with either the top or bottom facing forward it could conceivably get away with having TPS on only that side and it would be compressed along the naturally strong long axis.  But it would probably not decelerate fast enough and either impact the martian surface or 'impact' the lower atmosphere on Earth and be crushed by dynamic pressure.  On the other hand if the vehicle comes in on it's side it needs TPS over a much larger area and is being compressed on a much weaker axis again causing it to buckle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Owlon on 08/24/2015 04:11 am
380 vacuum ISP will definitely reduce both stage's mass.  Rocket equation.  i'll update.
Any other errata?

380 vacuum ISP for the vacuum Raptor, 363 vacuum ISP for the sea level Raptor. I'm pretty sure the 363 just came from forum estimates (albeit probably from actual propulsion engineers).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/24/2015 01:07 pm
Revised the #s based on comments.  Changed ISPs for S1 average, sea level to vac & S2 ISP vac.
S2 added 5mT for TPS to the MCT and reduced the mass of S2 so that the ratio was more realistic. Side benefit was eliminating one Rvac engine so nearly another couple mT added for S2 TPS as well.  So S2 now has "only" 5 Rvac engines.  The 150mT MCTs cited here that carried 100mT cargo seem infeasible.

Added S1 propellant mass & adjusted dry mass to near 7%.  Added 5mT to RTLS propellant since I am clueless as to how much Delta V is needed.

S1 avg ISP SL to MECO   330   
S2 vac ISP    380   
1st Stage T/W   1.25   
BFR DIA   12.5   m
MCT Mass   180   mT
1st Stage Tank Length   21.5   m
S1 Propellant Volume   2637   m3
1st Stg Airframe Weight   175   mT
Propellant Weight   2796   mT
S1 Engines Weight   33   mT
S1 Total Weight mT   3004   mT
S1 Total Weight LBS   6.6   Million LBS
S1 empty + S2   1233   mT
DRY Weight   208   mT
%  DRY WEIGHT     6.9%   
RTLS Propellant     45   mT
RTLS Delta V   0.63   Km/sec
Stage One Km/sec   3.71   Km/sec Rocket Equation
2nd Stage Tank Length   6.5   m
Propellant Volume   797   m3
Propellant Mass   845   mT
S2/S1 mass   0.34   
S2 Mass w/MCT   1025   mT
S2 Mass w/MCT   2.3   Million LBS
Calc # Vac Raptors   4.98   1.23 T/W
Stage 2 Thrust   2.8   Million LBS
Stage 2 Km/sec   6.48   Km/sec Rocket Equation
S2 Mars 25mT Cargo    8.5   Km/sec Rocket Equation
TOTAL WT mT   4029   mT
TOTAL WT LBS   8.9   Million LBS
THRUST Needed    11.1   Million LBS
THRUST Needed    49.4   Million Newtons
1st STAGE # ENG    21.9     Eng 14+7+1 = 22
LEO Mass Fract   4.47%   
MCT Payload length   12   m
MCT Payload Vol m3   1472   m3
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 08/24/2015 02:15 pm
MCT Mass   180   mT

S2 Mass w/MCT   1025   mT

S2 Mars 25mT Cargo    8.5   Km/sec Rocket Equation

I don't think those three go together.

A stage with 180mt dry mass, 8.5km/s delta v and 25mt payload has a wet mass of 1980mt.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/24/2015 02:48 pm
MCT Mass   180   mT

S2 Mass w/MCT   1025   mT

S2 Mars 25mT Cargo    8.5   Km/sec Rocket Equation

I don't think those three go together.

A stage with 180mt dry mass, 8.5km/s delta v and 25mt payload has a wet mass of 1980mt.

In the context of what he wrote it was 80t dry mass and 100t cargo outbound and 25t cargo inbound
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 08/24/2015 02:54 pm
MCT Mass   180   mT

S2 Mass w/MCT   1025   mT

S2 Mars 25mT Cargo    8.5   Km/sec Rocket Equation

I don't think those three go together.

A stage with 180mt dry mass, 8.5km/s delta v and 25mt payload has a wet mass of 1980mt.

In the context of what he wrote it was 80t dry mass and 100t cargo outbound and 25t cargo inbound

80t dry mass for landing 100t on the surface? That's impossible.

Not with a blunt body, certainly not with a slender body.

In fact you get only close to that with HIAD.

The problem is, going with retropropulsion instead of more aerobraking (e.g. with HIAD) does not reduce your dry mass, to the contrary, because you're coming in heavier and consequently your structural mass increases.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/24/2015 04:12 pm
So we're saying that the oft stated 200mT MCT landing on Mars is impossible?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/24/2015 04:18 pm
MCT Mass   180   mT

S2 Mass w/MCT   1025   mT

S2 Mars 25mT Cargo    8.5   Km/sec Rocket Equation

I don't think those three go together.

A stage with 180mt dry mass, 8.5km/s delta v and 25mt payload has a wet mass of 1980mt.

In the context of what he wrote it was 80t dry mass and 100t cargo outbound and 25t cargo inbound

That was what I was attempting to say. 

I am correcting a spreadsheet formula error (rocket equation) for Mars takeoff.  EDIT formula was OK.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/24/2015 05:07 pm
MCT Mass   180   mT

S2 Mass w/MCT   1025   mT

S2 Mars 25mT Cargo    8.5   Km/sec Rocket Equation

I don't think those three go together.

A stage with 180mt dry mass, 8.5km/s delta v and 25mt payload has a wet mass of 1980mt.

Dry mass return from Mars is 80mT + 25mT payload = 105mT
Total fueled mass is 1025 yielding nearly 8.5 Km/sec with Elon's cited ISP of 380



Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/24/2015 05:12 pm
So we're saying that the oft stated 200mT MCT landing on Mars is impossible?

We aren't, Oli is, I am sure some agree with him. As opposed, I believe 50t could be the dry mass of a 820t fully loaded and fueled MCT, note that at most there would be 1.3km/s of ΔV or so a re-entry mass around 230t, and a landing mass approaching 150t.

Note my overall mission requirement ΔV is 6km/s.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 08/24/2015 05:23 pm
So we're saying that the oft stated 200mT MCT landing on Mars is impossible?

Looking at 5 different 20t+ lander concepts with only supersonic retropropulsion I can find in my pdf collection (:) ), the best payload / structural mass ratio is ~0.7. And that's for an expendable lander with 13m diameter blunt body and a payload of 52t (from austere human mission to Mars, 2009).

Slender bodies are worse, for example the lander from DRM5 has a ratio of 0.41.

100 / 80 is 1.25.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/25/2015 01:10 am
I think we need to consider entry velocity when looking at any lander, it's the #1 driver of TPS, structural mass and retro-propulsion needs.  Most lander heritage involves direct entry from interplanetary transit and very high entry velocity.  The Viking lander was the exception and is probably the best comparison because it doesn't drop nearly as many parts along the way.  It had a landed mass of 62% of entry mass compared with 10% for the Phoinex lander.

If the requirement is scaled down to ~3.6 km/s as you would have from an entry from Mars orbit then the entry becomes exceedingly gentle, combined with a lifting body shape to further lengthen and distribute the heating load should put it well within the range of radiative metallic systems which would be negligible in additional mass because they would simply BE the outer skin of the vehicle.  G-forces would be reduced to under 1.5 g's meaning the vehicle doesn't need to be anywhere near as strong.  Retro-propulsion needs should be on the order of ~800 m/s.


http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100017668.pdf  (Se slide 14)

http://www.ssdl.gatech.edu/papers/conferencePapers/IAC-2008-D2.3.9.pdf (see page 7)

So I propose a vehicle designed to act as a ferry between the surface and orbit, able to land 100 mt and return to orbit with 25 mt PLUS enough propellant to make another landing on Mars.  At 75 mt dry mass for the vehicle the landing requires 40 mt of propellants.  The launch mass is 400 mt of which 260 is assent (4.1 km/s) propellant, 25 cargo, 40 return propellant (.8 km/s) and 75 the vehicle dry mass.  Total propellant load is just 300 mt meaning propellant production on Mars can be a fraction of that needed for Direct return.  The structural mass fraction at launch is a very conservative 18.75% and payload is 46% of entry mass (including propellant) both very reasonable figures.

The lander would launch from Earth atop a 2 stage launch vehicle and would be loaded with ~50 mt of propellants providing ~900 m/s DeltaV to be used for emergency separation and propulsive landing in the even of an abort.  This would put the total launch mass at 225 mt.  And the lander could then be fully topped off via another launch of and transfer of 250 mt or propellant from a stretched 2nd stage tanker.  Transit to Mars is then done via a hybrid propulsion system, first a large SEP vehicle would slow push the lander to high Earth orbit where crew would board via a dragon capsule.  Then the SEP would separate and the lander would make a lunar-Earth slingshot burn of ~1 km/s for fast transit to Mars and use propulsive capture and perhaps some airobraking to reach low mars orbit leaving just enough propellant for landing.  On the surface the cargo is unloaded and a 25 mt return cabin is loaded in it's place.  The SEP system would make a slow transit to mars arriving well after the lander and wait in low orbit for rendezvous after which it would bring the lander back to high Earth orbit, crew would disembark again via Dragon capsule and then the unoccupied combined vehicle would do a down-spiral to low Earth orbit where it would be refueled again and use it's propulsive capacity to reduce entry velocity to the 3.6 km/s velocity it can tolerate followed by landing on Earth for reloading and reintegration, SEP remains in orbit ready to be reused.


Total BFR launches would be 6, one for the lander, 2 tankers of chemical propellant, 1 for SEP hardware, 2 estimated for SEP propellant.  In addition 2 trans-lunar Dragon capsule launches likely on Falcon Heavy.  Each subsequent launch would need 5 launches when SEP is reused.  The cycle would be one round trip every 2 synods.  If philw1776 can run the numbers of the size of the BFR needed to do a 225 mt launch that would be most informative to see how it compares.

As the Mars colony is built up the small SEP transit vehicle would be replaced with a large more powerful cargo hauler with extensive habitats aka the mother-ship.  The lander would be fueled in LEO and used to rapidly deliver passengers (100 at a time) to the waiting mother-ship in high orbit and would then travel attached too it as the mother-ships speed is expected to be competitive with the earlier direct flight.  At mars the lander is used to repeatedly ferry between surface and low orbit with containerized cargo being reloaded in orbit.  At Earth the launch of chemical propellant and landers is almost eliminated in favor of launching naked cargo containers and SEP propellant to be loaded onto the mother-ship.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/25/2015 01:26 am
Isn't PICA supposed to be significantly better than previous TPS materials though? Would that reduce the required dry mass?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 08/25/2015 02:27 am
I think we need to consider entry velocity when looking at any lander, it's the #1 driver of TPS, structural mass and retro-propulsion needs.  Most lander heritage involves direct entry from interplanetary transit and very high entry velocity.  The Viking lander was the exception and is probably the best comparison because it doesn't drop nearly as many parts along the way.  It had a landed mass of 62% of entry mass compared with 10% for the Phoinex lander.

The human lander concepts I referred to are all designed for either entry from Mars orbit or aerocapture into orbit + entry from Mars orbit. Granted, gs, heat peak rate and heat load are significantly higher in the aerocapture phase than in the entry phase, although its a lot better than direct entry.

"Parts dropped along the way" are part of the structural mass at entry, which I was refering to. I.e. the entry mass minus the fuel and payload.

The best lander in terms of payload to structural entry mass I cound find is in the pdf attached on page 15, top left. A value of ~1.2. With SIAD, from orbit. It has a total entry mass of only 20t though. The higher the entry mass the worse usually.

With HIAD it may get better, haven't seen the mass break down of such a lander yet. HIAD could be interesting for MCT.

The lander would launch from Earth atop a 2 stage launch vehicle and would be loaded with ~50 mt of propellants providing ~900 m/s DeltaV to be used for emergency separation and propulsive landing in the even of an abort.  This would put the total launch mass at 225 mt.  And the lander could then be fully topped off via another launch of and transfer of 250 mt or propellant from a stretched 2nd stage tanker.  Transit to Mars is then done via a hybrid propulsion system, first a large SEP vehicle would slow push the lander to high Earth orbit where crew would board via a dragon capsule.

Wait, you want to use SEP for transfering a 475t payload from LEO to HEO (e.g. LDHEO)? That would take about 8 years with a 300kw SEP.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/25/2015 02:57 am
It's late but a quick run on a 225mT to LEO, i.e. >10Km/sec allowing for gravity losses, looks like a 25 engine 12.7 million LBS thrust BFR stage one and a 7 engine stage 2.  Don't like this solution because mass fraction to LEO seems too high, but it's bed time.

S1 avg ISP SL to MECO  330   
S2 vac ISP    380   
1st Stage T/W   1.21   
BFR DIA   12.5   m
MCT Mass   225   mT
1st Stage Tank Length   24.5   m
S1 Propellant Volume   3005   m3
1st Stg Airframe Weight   205   mT
Propellant Weight   3186   mT
S1 Engines Weight   33   mT
S1 Total Weight mT   3424   mT
S1 Total Weight LBS   7.5   Million LBS
S1 empty + S2   1568   mT
DRY Weight   238   mT
%  DRY WEIGHT    7.0%    %
RTLS Propellant   45   mT
RTLS Delta V   0.56   Km/sec
Stage One Km/sec   3.50   Km/sec Rocket Equation
2nd Stage Tank Length   8.5   m
Propellant Volume   1043   m3
Propellant Mass   1105   mT
S2/S1 mass   0.39   
S2 Mass w/MCT   1330   mT
S2 Mass w/MCT   2.9   Million LBS
Calc # Vac Raptors   6.83   1.3 T/W
Stage 2 Thrust   3.8   Million LBS
Stage 2 Km/sec   6.62   Km/sec Rocket Equation
S2 Mars 25mT Cargo    8.1   Km/sec Rocket Equation
TOTAL WT mT   4754   mT
TOTAL WT LBS   10.5   Million LBS
THRUST Needed   12.7   Million LBS
THRUST Needed   56.4   Million Newtons
1st STAGE # ENG    25.0   Eng 16+8+1 = 25
LEO Mass Fract   4.73%    %

I think that even the 1st MCT architecture revealed by SX will be somewhat different than Musk has said so far and by the time it's built, quite different again.  I think the Raptor engine will have 20% or so more thrust than ~ 500 KLBS leading to somewhat fewer engines but still "a lot".
I like the SEP interplanetary haulers myself.  It's just not the "land the whole thing" paradigm that we think Musk was speculating.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/25/2015 04:00 am
Isn't PICA supposed to be significantly better than previous TPS materials though? Would that reduce the required dry mass?

PICA is the best ablative, but I intend for the lander to do repeated rapid cargo flights between mars surface and low orbit maybe as many as 100 such round trips before returning to Earth, no ablative can go through that many cycles so I reject it as an option.

The human lander concepts I referred to are all designed for either entry from Mars orbit or aerocapture into orbit + entry from Mars orbit. Granted, gs, heat peak rate and heat load are significantly higher in the aerocapture phase than in the entry phase, although its a lot better than direct entry.

"Parts dropped along the way" are part of the structural mass at entry, which I was refering to. I.e. the entry mass minus the fuel and payload.

The best lander in terms of payload to structural entry mass I cound find is in the pdf attached on page 15, top left. A value of ~1.2. With SIAD, from orbit. It has a total entry mass of only 20t though. The higher the entry mass the worse usually.

With HIAD it may get better, haven't seen the mass break down of such a lander yet. HIAD could be interesting for MCT.

Yes the aerocapture is worse then the subsequent entry, Ideally I would like to avoid it to keep thermal and load requirements to a bare minimum.

The HIAD dose look like it saves a lot of propellant, but I'm concerned that it's basically a disposable system and I'm looking for a repeatable surface-2-orbit shuttle for mars which rules out any disposable systems.  One alternative I'm considering is if an HIAD like equivalent can be produced via a circle of body flaps at the rear of a biconic vehicle.  I'm looking at 13 m diameter with flaps 2 -4 m long effectively creating a diameter of 15-17 m, the flaps would also provide control authority possibly saving more propellant.

Wait, you want to use SEP for transfering a 475t payload from LEO to HEO (e.g. LDHEO)? That would take about 8 years with a 300kw SEP.

Who said 300 kw?  I said large and that it would have DRY mass of up to 250 mt aka an entire BFR launch load, that's a lot more then 300 kw, though I have not done the full number crunch on this vehicle it is by no means ARM or anything that small.  Both the spiral to HEO and the transit to mars could be more then a year.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Owlon on 08/25/2015 04:44 am
Isn't PICA supposed to be significantly better than previous TPS materials though? Would that reduce the required dry mass?

PICA is the best ablative, but I intend for the lander to do repeated rapid cargo flights between mars surface and low orbit maybe as many as 100 such round trips before returning to Earth, no ablative can go through that many cycles so I reject it as an option.

I'm actually pretty sure Elon Musk said at one point (probably the Dragon 2 unveiling) that version 3 of PICA-X would be good for at least 10 Dragon flights, and that they were shooting for as many as 100 in the long term (presumably a version 4 of something). PICA-X version 3 is debuting with Dragon 2, and they were planning on switching to the then-new PICA-X version 2 on Dragon 1 whenever this was said. If they can achieve those sorts of numbers, they can probably get something that works for the necessary 30ish Earth+Mars reentries for MCT or many hundreds from LMO.

Additionally, I'm pretty sure it each version of PICA developed by SpaceX has been lighter than the previous.

Most of that comes from the Dragon 2 unveiling, and I'm thinking the 10/100 flights bit came from a video at the same event with some Q&A recorded by a forum member here.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 08/25/2015 05:51 am
As the Mars colony is built up the small SEP transit vehicle would be replaced with a large more powerful cargo hauler with extensive habitats aka the mother-ship.  The lander would be fueled in LEO and used to rapidly deliver passengers (100 at a time) to the waiting mother-ship in high orbit and would then travel attached too it as the mother-ships speed is expected to be competitive with the earlier direct flight.  At mars the lander is used to repeatedly ferry between surface and low orbit with containerized cargo being reloaded in orbit.  At Earth the launch of chemical propellant and landers is almost eliminated in favor of launching naked cargo containers and SEP propellant to be loaded onto the mother-ship.

Why not start this way?

Following elements:

- 1.5MW SEP tug capable of transporting 100mt from HEO to Mars orbit (e.g. 1 sol). The SEP tug in the Raftery concept can do that.
- 100mt reusable Mars lander.
- 100mt Habitat.
- 100mt Cargo "container".

A colonial fleet starts in HEO with:

- Cargo containers.
- 1 Habitat.
- 1 brand new Mars lander.

Each with its own SEP tug. All elements are being transfered to Mars. Then:

- Crew lands with brand new lander.
- People from the surface come up with the lander.
- Habitat plus all SEP tugs head home to HEO.
- Lander continues to "ship" Cargo containers from Mars orbit to the surface.

Requires some sort of Lander maintenance on the surface, but the idea is to fly it until its broken. Better start with the high value Cargo :).

Obvious advantages:

- The Lander is far better utilized.
- Far simpler. Only entry from Mars orbit and back.
- Doesn't spend years in deep space.
- No huge volume (living space, space for supplies) required for the crew, as the crew only lands in it.

Anyway, I guess that wouldn't be MCT anymore so its OT  ;).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/25/2015 05:59 am
PICA is the best ablative, but I intend for the lander to do repeated rapid cargo flights between mars surface and low orbit maybe as many as 100 such round trips before returning to Earth

Ah, I was assuming one landing, one launch direct to Earth.

MCT is supposed to be "land the whole thing".

So only one Earth launch, one Mars entry, one Mars launch, and one Earth entry between servicings (on Earth).

I think PICA-X will be used for MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: llanitedave on 08/25/2015 06:06 am

PICA is the best ablative, but I intend for the lander to do repeated rapid cargo flights between mars surface and low orbit maybe as many as 100 such round trips before returning to Earth, no ablative can go through that many cycles so I reject it as an option.



The same flights that bring up fuel and cargo to MCTs in orbit could also bring up replacement heat shields as necessary.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/25/2015 06:24 am
As opposed, I believe 50t could be the dry mass of a 820t fully loaded and fueled MCT, note that at most there would be 1.3km/s of ΔV or so a re-entry mass around 230t, and a landing mass approaching 150t.

Does it really need that much delta-v to go from terminal velocity to landing?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Rocket Surgeon on 08/25/2015 06:26 am
With regards to testing the BFR before flight, is it possible for the Launch Pad to double as the full first stage testing site? It could possibly save on costs rather than having to develop new sites. The main hangar could also be used as the final production facility ala the N1 (except this time, with pre-launch testing).

Depending on costs you could build the BFR pieces off site, ship them to the launch pad, and assemble/test them there.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/25/2015 06:36 am
PICA is the best ablative, but I intend for the lander to do repeated rapid cargo flights between mars surface and low orbit maybe as many as 100 such round trips before returning to Earth

Ah, I was assuming one landing, one launch direct to Earth.

MCT is supposed to be "land the whole thing".

So only one Earth launch, one Mars entry, one Mars launch, and one Earth entry between servicings (on Earth).

I think PICA-X will be used for MCT.

It is supposed to get the mission done as efficiently as possible, I'm making the case that this hybrid architecture is 1) Actually achievable without using pixie-dust and 2) more efficient to boot.  Compared to that any 'supposed to be' is moot.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/25/2015 06:49 am
It is supposed to get the mission done as efficiently as possible, I'm making the case that this hybrid architecture is 1) Actually achievable without using pixie-dust and 2) more efficient to boot.  Compared to that any 'supposed to be' is moot.

To be clear on this. You are arguing that you know better than SpaceX and Elon Musk?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 08/25/2015 07:15 am
So I propose a vehicle designed to act as a ferry between the surface and orbit, able to land 100 mt and return to orbit with 25 mt PLUS enough propellant to make another landing on Mars.  At 75 mt dry mass for the vehicle the landing requires 40 mt of propellants.  The launch mass is 400 mt of which 260 is assent (4.1 km/s) propellant, 25 cargo, 40 return propellant (.8 km/s) and 75 the vehicle dry mass.  Total propellant load is just 300 mt meaning propellant production on Mars can be a fraction of that needed for Direct return.  The structural mass fraction at launch is a very conservative 18.75% and payload is 46% of entry mass (including propellant) both very reasonable figures.

The lander would launch from Earth atop a 2 stage launch vehicle and would be loaded with ~50 mt of propellants providing ~900 m/s DeltaV to be used for emergency separation and propulsive landing in the even of an abort.  This would put the total launch mass at 225 mt.  And the lander could then be fully topped off via another launch of and transfer of 250 mt or propellant from a stretched 2nd stage tanker.  Transit to Mars is then done via a hybrid propulsion system, first a large SEP vehicle would slow push the lander to high Earth orbit where crew would board via a dragon capsule.  Then the SEP would separate and the lander would make a lunar-Earth slingshot burn of ~1 km/s for fast transit to Mars and use propulsive capture and perhaps some airobraking to reach low mars orbit leaving just enough propellant for landing.  On the surface the cargo is unloaded and a 25 mt return cabin is loaded in it's place.  The SEP system would make a slow transit to mars arriving well after the lander and wait in low orbit for rendezvous after which it would bring the lander back to high Earth orbit, crew would disembark again via Dragon capsule and then the unoccupied combined vehicle would do a down-spiral to low Earth orbit where it would be refueled again and use it's propulsive capacity to reduce entry velocity to the 3.6 km/s velocity it can tolerate followed by landing on Earth for reloading and reintegration, SEP remains in orbit ready to be reused.


Total BFR launches would be 6, one for the lander, 2 tankers of chemical propellant, 1 for SEP hardware, 2 estimated for SEP propellant.  In addition 2 trans-lunar Dragon capsule launches likely on Falcon Heavy.  Each subsequent launch would need 5 launches when SEP is reused.  The cycle would be one round trip every 2 synods.  If philw1776 can run the numbers of the size of the BFR needed to do a 225 mt launch that would be most informative to see how it compares.

I really like this architecture. It has high reusability and great flexibility, obvious changes for lunar, asteroid and Mars moons missions.

Perhaps you should write it up as a paper.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/25/2015 08:59 am
It is supposed to get the mission done as efficiently as possible, I'm making the case that this hybrid architecture is 1) Actually achievable without using pixie-dust and 2) more efficient to boot.  Compared to that any 'supposed to be' is moot.

To be clear on this. You are arguing that you know better than SpaceX and Elon Musk?

I'm confident they will reach the same conclusion I have after figuring out (possibly the hard way) that Direct Earth return is impossible.  People are being way to fast to grasp at nebulous ideas and speculations even if they come from Musk as THE ONE AND ONLY way it will be done,  Musk like any good programmer tries to think of the simplest possible system he thinks could possibly work, we saw that with F9 reuse plans, they are now WAY more complex then originally planned, MCT will be the same.




Perhaps you should write it up as a paper.

I might do that, though I still need to work out the SEP transit vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 08/25/2015 09:17 am
It is supposed to get the mission done as efficiently as possible, I'm making the case that this hybrid architecture is 1) Actually achievable without using pixie-dust and 2) more efficient to boot.  Compared to that any 'supposed to be' is moot.

To be clear on this. You are arguing that you know better than SpaceX and Elon Musk?

Since the amount of information known about MCT outside of SpaceX can fit on a postage stamp, written with a crayon, and that SpaceX plans change considerable over time, how do we know this isn't the plan? No point in saying "MUSK SAID THIS", because aforesaid plans change.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/25/2015 09:39 am
To be clear on this. You are arguing that you know better than SpaceX and Elon Musk?

Since the amount of information known about MCT outside of SpaceX can fit on a postage stamp, written with a crayon, and that SpaceX plans change considerable over time, how do we know this isn't the plan? No point in saying "MUSK SAID THIS", because aforesaid plans change.

I hear that argument a lot. But it really is not true. There is a lot of info that is consistent over time.

My base argument is that complex architectures are not likely to get anywhere near the aimed for cost level. At least not before hundreds if not thousands of MCT go to Mars at every synod. SpaceX is aiming to build at least a permanently manned base and they could not afford designing and building such a complex architecture.

I don't deny that your architecture is an interesting one. I only say it is not compatible with what we know about the SpaceX architecture and this is the MCT thread. We have a whole section on this forum for Mars. Your Mars architecture should be discussed there IMO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 08/25/2015 11:28 am
I'm confident they will reach the same conclusion I have after figuring out (possibly the hard way) that Direct Earth return is impossible.  People are being way to fast to grasp at nebulous ideas and speculations even if they come from Musk as THE ONE AND ONLY way it will be done,  Musk like any good programmer tries to think of the simplest possible system he thinks could possibly work, we saw that with F9 reuse plans, they are now WAY more complex then originally planned, MCT will be the same.

I am with Gucky on this one. I dont think that the mission plan you described is realistic at the beginning.
1. Aerobraking has never been used before, for good reason.
2. SEPs are for small payloads, not ones of many mT. The amount of solar arrays needed to get any meaningful thrust would be ginormous.
3. Using first SEP and then chemical propulsion is really inefficient.
4. Your mission plan is as complicated as it possibly can get. Simple is most often more important than efficient. Any complication in the flight plan means a rats hole of additional design and engineering work and launch mass to avoid failures. The more things you have the more things can break. And if anything breaks, your mission is toast.
5. The answer to "direct return is impossible" would not be to make the plan more complicated but to reduce the payload mass. The 100 persons per MCT figure is probably something for the far future. Not something for the first try.

The plan you described is maybe something for the far future, when Humanity has figured Mars transport out and is on its way to optimize the process. When failure modes are known and engineers learn to cut the right corners. I am very skeptical for the beginning though.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/25/2015 01:50 pm
As opposed, I believe 50t could be the dry mass of a 820t fully loaded and fueled MCT, note that at most there would be 1.3km/s of ΔV or so a re-entry mass around 230t, and a landing mass approaching 150t.

Does it really need that much delta-v to go from terminal velocity to landing?

Note "At most there would be 1.3km/s of ΔV" my mission 'plan' was leaving Earth orbit with enough 'hyperbolic' velocity (600 m/s or so over escape TMI, varies between launch windows greatly) to leave 1.3 km/s of ΔV which includes the 1km/s I am expecting is needed for landing and 300m/s for margin/contingency.

EDIT: originally had BF and typed escape instead of TMI
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/25/2015 05:51 pm

I am with Gucky on this one. I dont think that the mission plan you described is realistic at the beginning.
1. Aerobraking has never been used before, for good reason.

MCT will require at least 10 things that have never been done and Airobraking HAS been done with satellites, your thinking of Airocapture (which NASA is studying heavily and will probably do soon) but I am base lining propulsive capture with the airobraking just for scrubbing off some additional velocity.

2. SEPs are for small payloads, not ones of many mT. The amount of solar arrays needed to get any meaningful thrust would be ginormous.

I find it quite odd that people who don't bat an eyelash as SpaceX designing and building the largest launch vehicle in history, an interplanetary spacecraft larger then the shuttle and EDL technology able to land more then 3 orders of magnitude more mass then has ever been put on Mars suddenly go into conniptions at the idea that SEP vehicles might be made plus size as well.

3. Using first SEP and then chemical propulsion is really inefficient.

Yes their is an inefficiency their, but resent papers on Hybrid propulsion have shown considerable savings in time and required SEP power levels when chemical propulsion is narrowly focused on fly-by escape maneuvers and propulsive capture.  And obviously we must have propellant for landing.

4. Your mission plan is as complicated as it possibly can get. Simple is most often more important than efficient. Any complication in the flight plan means a rats hole of additional design and engineering work and launch mass to avoid failures. The more things you have the more things can break. And if anything breaks, your mission is toast.

I find this statement ridiculous, it is no more complex then Apollo and involves only 2 vehicles and 1 mission critical rendezvous at Mars.  Their are Earth orbital rendezvouses but these are so routine now I don't see how they can be considered a barrier, not to mention their are fewer of them when you realize that every tanker visiting the giant alternative 1000 mt MCT vehicle is a rendezvous too.

5. The answer to "direct return is impossible" would not be to make the plan more complicated but to reduce the payload mass. The 100 persons per MCT figure is probably something for the far future. Not something for the first try.

Payload is irreverent because it is a question of dry mass fraction being impossibly low, that comes from the DeltaV and the Earth Entry velocity requirements.

The plan you described is maybe something for the far future, when Humanity has figured Mars transport out and is on its way to optimize the process. When failure modes are known and engineers learn to cut the right corners. I am very skeptical for the beginning though.

The second part with the 'mother-ship' would be for a far future, but the same basic landing ferry is going to be needed in both architectures.  The future improvements will all be in SEP as chemical performance is basically maxed out so we can create now a lander which will not become obsolete for decades.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 08/25/2015 06:29 pm
I agree with having large SEP tugs.  Why not?  Only the solar panels would be the limiting factor.  A Falcon Heavy could deliver 50 tons of propellant to a large SEP tug after an earlier Falcon Heavy delivered a 50 ton tug to LEO.  With one docking maneuver to either attach the propellant, or load the propellant.  Then this 100 ton tug could take a large cargo to Mars, especially a cargo that is not affected by the radiation belt. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/25/2015 06:54 pm
Posting my spreadsheet for fun & amusement "designing" various BFRs
Please inform me of any errata.  Thanks!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/25/2015 06:58 pm
This has been posted previously but here's two nice papers describing SEP/Chemical hybrid approach to Mars vehicles. 

I believe Gwenn Shotwell when she said "We're looking at SEP" for the MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 08/25/2015 07:51 pm
Ok, lets make a back-of-the-envelope calculation.

A recent all-electric satellite Eutelsat  115 WEST B (2,205 kg) uses about 18 kW (4x 4.5 kW thrusters) to reach GSO. It takes 8 Month, so that is a reasonable timeframe for the not yet crewed MCT. Each thruster weights below 16 kg, say 15. So the mass of the spacecraft without the thrusters is 2141 kg. The solar arrays provide 18 kW of power for the thrusters. Wikipedia says that one gets about 300W/kg and 300W/m^2. That makes 60 kg of solar panels and 60 m^2 area. So the spacecraft without the engines and without the panels is 2081 kg.

Now, scaling that to the mass of the MCT of about 475mT in your design. Then the SEP tug would need 475/2* 18 kW= 4.25MW of solar, or 472/2 * 60kg approx 14 mT of solar panels which have a surface area of about 14000 m^2. Say launch that thing with an BFR that has a payload bay of 20m hight. Then the solar arrays need to have a wing span of about 700m. Since the individual elements cant be larger than the diameter, say 10m, that are 70 segments. Say we have 2 equal sized 350m panels (one on either side) and you use ISS type solar arrays, that would fill two boxes of about 5m height each.

I admit, I thought that the solar panels alone would be far larger than that. I thought that this alone would invalidate your concept. It is at these considerations borderline possible. But I did not include everything that needs to be included. I did not include the Xenon mass, the mass of the SEP tug structure, any electronics or transformers. No heat control system or other things that are needed.

sources:
https://directory.eoportal.org/web/eoportal/satellite-missions/a/all-electric
https://en.wikipedia.org/wiki/Solar_panels_on_spacecraft
https://en.wikipedia.org/wiki/Integrated_Truss_Structure#Truss_subsystems
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/25/2015 11:14 pm
Ok, lets make a back-of-the-envelope calculation.

A recent all-electric satellite Eutelsat  115 WEST B (2,205 kg) uses about 18 kW (4x 4.5 kW thrusters) to reach GSO. It takes 8 Month, so that is a reasonable timeframe for the not yet crewed MCT. Each thruster weights below 16 kg, say 15. So the mass of the spacecraft without the thrusters is 2141 kg. The solar arrays provide 18 kW of power for the thrusters. Wikipedia says that one gets about 300W/kg and 300W/m^2. That makes 60 kg of solar panels and 60 m^2 area. So the spacecraft without the engines and without the panels is 2081 kg.

Now, scaling that to the mass of the MCT of about 475mT in your design. Then the SEP tug would need 475/2* 18 kW= 4.25MW of solar, or 472/2 * 60kg approx 14 mT of solar panels which have a surface area of about 14000 m^2. Say launch that thing with an BFR that has a payload bay of 20m hight. Then the solar arrays need to have a wing span of about 700m. Since the individual elements cant be larger than the diameter, say 10m, that are 70 segments. Say we have 2 equal sized 350m panels (one on either side) and you use ISS type solar arrays, that would fill two boxes of about 5m height each.

I admit, I thought that the solar panels alone would be far larger than that. I thought that this alone would invalidate your concept. It is at these considerations borderline possible. But I did not include everything that needs to be included. I did not include the Xenon mass, the mass of the SEP tug structure, any electronics or transformers. No heat control system or other things that are needed.

sources:
https://directory.eoportal.org/web/eoportal/satellite-missions/a/all-electric
https://en.wikipedia.org/wiki/Solar_panels_on_spacecraft
https://en.wikipedia.org/wiki/Integrated_Truss_Structure#Truss_subsystems

Your basing your calculations on a freight SEP vehicle on a com-sats performance?  That's like using a water bottle rocket to estimate the performance of a launch vehicle.  Try using one of a million SEP design concepts for lunar tugs, ARM or Boeing's recent paper rather then this nonsense.  I'll get back with a concept of my own shortly.

Second who said anything about payload doors on the BFR, I said BFR would be a conventional 2 stage rocket which means normal clam-shell payload fairings probably on the order of 15 m diameter and >40 m long, the thing would have the same launch configuration as ARM with solar arrays on long boom arms that simply fold out.  And as for propellants I said they would be on a separate launch and are almost certainly going to be Krypton, as their is not enough production of Xenon to supply this vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Rocket Surgeon on 08/26/2015 04:36 am
Something I haven't seen many discussions on: Abort Modes
Is this somewhere where SEP may be superior? If you use a 6 months fast Hohmann transfer, you will naturally return to Earth in 2 years if you miss Mars for what ever reason. Swing out to 2 AU then back in again to meet up with Earth (source: the Case for Mars/Mars Direct).

This is fine for initial exploration, as you will only have a small crew (~4 people) as you only need to carry 2 years worth of supplies for 4, and you would arguable have to do that anyway.

But trying to carry 2 years worth of supplies for 100 people, and things get out of hand. Roughly 1000kg per person of supplies and you're looking at over 100 tonnes of just food, water and oxygen. We could just assume that nothing will go wrong, but it's not going to be fun when something does.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 08/26/2015 04:44 am
Something I haven't seen many discussions on: Abort Modes
Is this somewhere where SEP may be superior? If you use a 6 months fast Hohmann transfer, you will naturally return to Earth in 2 years if you miss Mars for what ever reason. Swing out to 2 AU then back in again to meet up with Earth (source: the Case for Mars/Mars Direct).

This is fine for initial exploration, as you will only have a small crew (~4 people) as you only need to carry 2 years worth of supplies for 4, and you would arguable have to do that anyway.

But trying to carry 2 years worth of supplies for 100 people, and things get out of hand. Roughly 1000kg per person of supplies and you're looking at over 100 tonnes of just food, water and oxygen. We could just assume that nothing will go wrong, but it's not going to be fun when something does.

That's why IMO it makes sense to launch several MCT's in the same launch window - a small fleet - that way they could support and assist each other if a problem should occur.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/26/2015 05:24 am

That's why IMO it makes sense to launch several MCT's in the same launch window - a small fleet - that way they could support and assist each other if a problem should occur.

Yes in the first few synods with human presence I expect the crewed MCTs to be launched with enough extra room that a single one could be lost and everyone be accommodated on the remaining ones. For example, the first crewed expedition, I see two MCTs with about 10 people on each launched at almost exactly the same time, and each capable of providing ECLSS for 20.  At the first return window those short timers (scientists maybe 6 to 8 ) would return on one, but leave a craft behind that could still evac everyone there. The next arrivals would have at least as many people and and ships and as few returning.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TetraOmni on 08/26/2015 07:21 am
Not sure this has been discussed here. Is there a chance BFR gets a grasshopper type development vehicle?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 08/26/2015 09:05 am
Your basing your calculations on a freight SEP vehicle on a com-sats performance?  That's like using a water bottle rocket to estimate the performance of a launch vehicle. Try using one of a million SEP design concepts for lunar tugs, ARM or Boeing's recent paper rather then this nonsense.

In the contrary. I am basing my calculations on what I know is not nonsense but existing technology. Also can you please refer to the paper?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/26/2015 01:51 pm
Ok, lets make a back-of-the-envelope calculation.

A recent all-electric satellite Eutelsat  115 WEST B (2,205 kg) uses about 18 kW (4x 4.5 kW thrusters) to reach GSO. It takes 8 Month, so that is a reasonable timeframe for the not yet crewed MCT. Each thruster weights below 16 kg, say 15. So the mass of the spacecraft without the thrusters is 2141 kg. The solar arrays provide 18 kW of power for the thrusters. Wikipedia says that one gets about 300W/kg and 300W/m^2. That makes 60 kg of solar panels and 60 m^2 area. So the spacecraft without the engines and without the panels is 2081 kg.

Now, scaling that to the mass of the MCT of about 475mT in your design. Then the SEP tug would need 475/2* 18 kW= 4.25MW of solar, or 472/2 * 60kg approx 14 mT of solar panels which have a surface area of about 14000 m^2. Say launch that thing with an BFR that has a payload bay of 20m hight. Then the solar arrays need to have a wing span of about 700m. Since the individual elements cant be larger than the diameter, say 10m, that are 70 segments. Say we have 2 equal sized 350m panels (one on either side) and you use ISS type solar arrays, that would fill two boxes of about 5m height each.

I admit, I thought that the solar panels alone would be far larger than that. I thought that this alone would invalidate your concept. It is at these considerations borderline possible. But I did not include everything that needs to be included. I did not include the Xenon mass, the mass of the SEP tug structure, any electronics or transformers. No heat control system or other things that are needed.

sources:
https://directory.eoportal.org/web/eoportal/satellite-missions/a/all-electric
https://en.wikipedia.org/wiki/Solar_panels_on_spacecraft
https://en.wikipedia.org/wiki/Integrated_Truss_Structure#Truss_subsystems
What you did is assume away several factors: required delta V & burn duration, which determine both required power and required propellant.  The SEP mass fraction of the MCT being identical to the 702SP is not a safe assumption.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 08/26/2015 02:58 pm
Ok, lets make a back-of-the-envelope calculation.

A recent all-electric satellite Eutelsat  115 WEST B (2,205 kg) uses about 18 kW (4x 4.5 kW thrusters) to reach GSO. It takes 8 Month, so that is a reasonable timeframe for the not yet crewed MCT. Each thruster weights below 16 kg, say 15. So the mass of the spacecraft without the thrusters is 2141 kg. The solar arrays provide 18 kW of power for the thrusters. Wikipedia says that one gets about 300W/kg and 300W/m^2. That makes 60 kg of solar panels and 60 m^2 area. So the spacecraft without the engines and without the panels is 2081 kg.

Now, scaling that to the mass of the MCT of about 475mT in your design. Then the SEP tug would need 475/2* 18 kW= 4.25MW of solar, or 472/2 * 60kg approx 14 mT of solar panels which have a surface area of about 14000 m^2. Say launch that thing with an BFR that has a payload bay of 20m hight. Then the solar arrays need to have a wing span of about 700m. Since the individual elements cant be larger than the diameter, say 10m, that are 70 segments. Say we have 2 equal sized 350m panels (one on either side) and you use ISS type solar arrays, that would fill two boxes of about 5m height each.

I admit, I thought that the solar panels alone would be far larger than that. I thought that this alone would invalidate your concept. It is at these considerations borderline possible. But I did not include everything that needs to be included. I did not include the Xenon mass, the mass of the SEP tug structure, any electronics or transformers. No heat control system or other things that are needed.

sources:
https://directory.eoportal.org/web/eoportal/satellite-missions/a/all-electric
https://en.wikipedia.org/wiki/Solar_panels_on_spacecraft
https://en.wikipedia.org/wiki/Integrated_Truss_Structure#Truss_subsystems
What you did is assume away several factors: required delta V & burn duration, which determine both required power and required propellant.  The SEP mass fraction of the MCT being identical to the 702SP is not a safe assumption.

I know, its a back of the envelope analysis. Its quick and dirty, thats what estimations are for. Its a calculation to see if the concept makes sense in the most simplistic way. I expected that an SEP tug for such a huge payload is physically impossible to launch and I tried to prove that. I did not achieve that goal.
But that is not a prove that the concept works. Its just a failure to prove that it does not work. I hope you understand the difference.

Also, my initial information on Impalers design did only state "from LEO to HEO" which is as fuzzy as it can get and I cant possibly deduce dV requirements from that. I just assumed that GSO is roughly equivalent to what he envisions as HEO.

I still dont like Impalers concept for the other reasons I stated, even if a SEP tug is physically possible.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Manabu on 08/26/2015 09:00 pm
Not sure this has been discussed here. Is there a chance BFR gets a grasshopper type development vehicle?
It has been discussed here: Developing BFR reusability first (http://forum.nasaspaceflight.com/index.php?topic=34665.0)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/27/2015 01:02 am
I know, its a back of the envelope analysis. Its quick and dirty, thats what estimations are for. Its a calculation to see if the concept makes sense in the most simplistic way. I expected that an SEP tug for such a huge payload is physically impossible to launch and I tried to prove that. I did not achieve that goal.
But that is not a prove that the concept works. Its just a failure to prove that it does not work. I hope you understand the difference.

Also, my initial information on Impalers design did only state "from LEO to HEO" which is as fuzzy as it can get and I cant possibly deduce dV requirements from that. I just assumed that GSO is roughly equivalent to what he envisions as HEO.

I still dont like Impalers concept for the other reasons I stated, even if a SEP tug is physically possible.

Ok, so you admit that you've already decided you don't like my proposed mission architecture before you did any actual research (and regardless of what the research says), and are now trying to 'prove' it is not feasible via some sloppy back of a napkin calculations that seem to be uninformed by ANY actual studies on large SEP vehicles of which their are dozens.  And you expect me to do your research for you by providing these links?  I think not.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 08/27/2015 08:06 am
Ok, so you admit that you've already decided you don't like my proposed mission architecture before you did any actual research (and regardless of what the research says), and are now trying to 'prove' it is not feasible via some sloppy back of a napkin calculations that seem to be uninformed by ANY actual studies on large SEP vehicles of which their are dozens.  And you expect me to do your research for you by providing these links?  I think not.

Well in that case, go on. I have nothing to say to you on that level.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/27/2015 11:28 pm
Here are some of my initial thoughts on a large SEP tug.  First off Alpha should be around 5 kg/kw by combining 300 W/kg solar and 1.5 kg/kw Nested Hall thrusters with power processing units.  Sizing would be 5.75 MW which is admittedly very big.  29 of the X3 Hall thrusters would be used and the total hardware mass would be some 28 mt, possibly small enough to fit on a F9H launch depending on the packing density of solar arrays.

SEP Propellants would be delivered by a BFR flight which delivers a single propellant unit (likely a series of spherical tanks inside a cage frame) massing 215 mt total or which 183 is propellant and 32 are tanks which is 30% of departure mass.  This would be enough to get do the whole round trip.

Transit times would be around 400 days to spiral up from LEO, the lander would then travel to mars in around 200 days and stay 500 days on the surface, meanwhile the SEP tug would take about 600 days to travel to mars and reach low orbit.  After rendezvousing in Mars orbits the combined vehicle would take just 200 days to return to low Earth orbit due to the greatly reduced mass which will be just in time to leave again.

I'll do a more detailed breakdown and examine the area of panels needed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/30/2015 06:47 am
I don't see why direct earth return is impossible.

Even if it really is 8 km/s, that's not at all unachievable with chemical -- due to the exponential nature of the rocket equation, that's much easier than the ~ 9.5 km/s for SSTO (which is clearly possible).

If the return delta-v is that high, the vehicle would only ever be fully fueled on Mars, as it doesn't need nearly as much delta-v to get to Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/30/2015 07:05 am
If the return delta-v is that high, the vehicle would only ever be fully fueled on Mars, as it doesn't need nearly as much delta-v to get to Mars.

It would likely be fully fueled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: symbios on 08/30/2015 09:12 am
If the return delta-v is that high, the vehicle would only ever be fully fueled on Mars, as it doesn't need nearly as much delta-v to get to Mars.

It would likely be fully fueled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.

Also you could utilize the extra delta-v to make the booster a little smaller and maybe make the trip to Mars  take less time.

It is the leg that requires most delta-v that steers the parameters of the rest.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 08/30/2015 05:07 pm
If the return delta-v is that high, the vehicle would only ever be fully fueled on Mars, as it doesn't need nearly as much delta-v to get to Mars.

It would likely be fully fuelled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.

Also you could utilize the extra delta-v to make the booster a little smaller and maybe make the trip to Mars  take less time.

It is the leg that requires most delta-v that steers the parameters of the rest.

Actually, the dry weight of the MCT (and total mass on a return flight) also is very important in this equation since the ΔV budget of a fully fuelled craft could be significantly different when it departs LEO from when it departs Mars surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/30/2015 05:43 pm
If the return delta-v is that high, the vehicle would only ever be fully fueled on Mars, as it doesn't need nearly as much delta-v to get to Mars.

It would likely be fully fueled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.

Maybe, but the return payload has to be large enough to accommodate people + life support according to Musk, and less fuel means fewer tanker launches needed to fuel up the vehicle going to Mars.

Assuming vacuum* Isp of 380 s it needs a mass ratio of 8.57 for 8 km/s, vs. about 5.01 for 6 km/s.

*Mars' atmosphere is close enough to vacuum that the numbers shouldn't be too far off.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/30/2015 06:10 pm
It would likely be fully fueled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.

Maybe, but the return payload has to be large enough to accommodate people + life support according to Musk, and less fuel means fewer tanker launches needed to fuel up the vehicle going to Mars.

Yes, people need to go back, but it would not be 100 like on the flight out. The 100 is a value for colonization and going back is the exception. Recently from SpaceX a number was given of 20 or 25t return cargo.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/31/2015 05:25 am
If the return delta-v is that high, the vehicle would only ever be fully fueled on Mars, as it doesn't need nearly as much delta-v to get to Mars.

It would likely be fully fuelled in both directions. However the payload back to earth would be much lower to achieve the higher delta-v with the same amount of fuel.

Also you could utilize the extra delta-v to make the booster a little smaller and maybe make the trip to Mars  take less time.

It is the leg that requires most delta-v that steers the parameters of the rest.

Actually, the dry weight of the MCT (and total mass on a return flight) also is very important in this equation since the ΔV budget of a fully fuelled craft could be significantly different when it departs LEO from when it departs Mars surface.

This, the dry weight is too small and encloses too large of a volume (spreading it very thin) to be able to survive re-entry on Earth which is a minimum of 11 km/s.  Even once we take into account for the 75% reduction in cargo on the Earth return leg.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/31/2015 05:57 am
This, the dry weight is too small and encloses too large of a volume (spreading it very thin) to be able to survive re-entry on Earth which is a minimum of 11 km/s.  Even once we take into account for the 75% reduction in cargo on the Earth return leg.

The volume would be pressurized so is stable when reentering head on. Only when it has slowed down a lot it would pivot over for flying engines first for landing. I have speculated before that they may pressurize for more than 1000 millibar for reentry.

Going for good mass fraction prohibits massive walls like on capsules.

And one of my standard arguments. :) The designers at SpaceX are certainly aware of that problem and have at least tentatively a solution. A Falcon 9 first stage cannot do it because it is too long and slender. A second stage or a MCT has different proportions.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/31/2015 07:12 am
This, the dry weight is too small and encloses too large of a volume (spreading it very thin) to be able to survive re-entry on Earth which is a minimum of 11 km/s.  Even once we take into account for the 75% reduction in cargo on the Earth return leg.

The volume would be pressurized so is stable when reentering head on. Only when it has slowed down a lot it would pivot over for flying engines first for landing. I have speculated before that they may pressurize for more than 1000 millibar for reentry.

Going for good mass fraction prohibits massive walls like on capsules.

And one of my standard arguments. :) The designers at SpaceX are certainly aware of that problem and have at least tentatively a solution. A Falcon 9 first stage cannot do it because it is too long and slender. A second stage or a MCT has different proportions.
This was proposed on one of these threads, but I have no data on its plausibility.  Can you provide any references on the concept of superpressure as lighter-weight substitute for structural strength during reentry?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/31/2015 07:25 am
This was proposed on one of these threads, but I have no data on its plausibility.  Can you provide any references on the concept of superpressure as lighter-weight substitute for structural strength during reentry?

We do know pressurization greatly increases strength. It is done for launch loads on tanks routinely. Why would it not apply during reentry? I have not done engineering calculations on it.

Edit: it is my own idea. I did not get it from anywhere. So it may not be practical but I am quite confident.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/31/2015 08:30 am
Internal pressure doesn't prevent you from burning up which is my main concern.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/31/2015 08:43 am
Internal pressure doesn't prevent you from burning up which is my main concern.

That's what PicaX is for. At its size I think MCT would be lighter per volume and per surface than a Dragon capsule. Especially with a small cargo entering earth's atmosphere at high speed. The shield would be thick and strong on the tip but could be thin at the sides.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 09/01/2015 01:14 am
I'm sure MCT will have significant PICA-X TPS.

How heavy is a Dragon heat shield?

Googling I find 848 kg for Apollo heat shield, and PICA-X is supposed to be better than previous materials.

Would it necessarily flip over though? The engines are cooled during firing aren't they... maybe it will have engines sticking out of a PICA-X base and enter tail first?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/01/2015 03:10 am
>
How heavy is a Dragon heat shield?

Googling I find 848 kg for Apollo heat shield, and PICA-X is supposed to be better than previous materials.
>

This old pdf lists the original PICA-X as having a density of 0.27g / cm^3, and cork is about 0.24. Dragon 2 uses PICA-X version 3.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/01/2015 04:52 am
Internal pressure doesn't prevent you from burning up which is my main concern.

That's what PicaX is for. At its size I think MCT would be lighter per volume and per surface than a Dragon capsule. Especially with a small cargo entering earth's atmosphere at high speed. The shield would be thick and strong on the tip but could be thin at the sides.

Volume density is irrelevant, it is the Ballistic coefficient which matters and it would almost certainly be higher then Dragon capsule, show me some calculations to the contrary if you have done some.

It sounds like your proposing a tubular body doing some kind of ballistic plunge directly into the atmosphere like the F9 first stage.  That would result in almost inconceivable dynamic pressure and crushing forces when it reaches the lower atmosphere or Earth.  The star-dust entry capsule for example entered at 11 km/s and experienced ~40g.  And if you tried a similar entry on Mars you'd probably impact the surface.  A slender body vehicle has to use it's sides to get enough drag and that means thermal protection is heavy on the side/s (potentially just one side as with the shuttle).  This trajectory will be longer and actually result in more integrated heat load then the ballistic entry.

PICAX is nice stuff but no one even knows how to seal seems in it yet so it can only be used in monolithic pieces, assuming this limitation is over come their are other issues.  While it is low density it is ablative and will need to be able to withstand 2 entries which means making it thicker as the erosion rate looks to be around 1 - 0.5 centimeters on each entry from interplanetary speeds.  The bonding of all ablatives is basically done with adhesives and isn't designed to be modified so if the vehicle survived and lands on Earth it would mean a complete disassemble of the outer skin and replacement with a new one, a process likely to kill any chance at quick turnaround times.

http://www.academia.edu/10188019/Defining_Ablative_Thermal_Protection_System_Margins_for_Planetary_Entry_Vehicles

This paper looks to be the latest work on modeling for PICA based heat-shields and the necessary safety margins, it looks like new modeling had significantly reduced the need from the conservative Stardust mission.  Estimates are now at 3.5 cm thickness for a comparable single-use mission.  But note that this is not the only mass contributor, their are adhesives, back skins and aluminum honeycombs so total mass will be greater then the ~10 kg/ m2 that the PICA alone accounts for, by how much I don't know.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sublimemarsupial on 09/01/2015 06:02 am

PICAX is nice stuff but no one even knows how to seal seems in it yet so it can only be used in monolithic pieces, assuming this limitation is over come their are other issues. 

I guess these don't count as seams then? SpaceX figured out how to seal PICAX seams on their very first cargo dragon flight back in 2010.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 09/01/2015 06:07 am
Peak heat rates and heat loads of 5g-limited trajectories for various entry velocities and vehicle shapes. One can see that heat loads/peak rates are massively higher for Moon/Mars entry than LEO entry. On the other hand, their estimates for TPS mass do not seem to increase much with velocity ("the TPS mass is derived by assuming a constant thickness forebody heatshield sized to the stagnation-point heating environment, a conservative assumption"). Needless to say the TPS won't be reusable.

From: Entry System Options for Human Return from the Moon and Mars

Note that Mars entry is a lot less demanding in comparison, closer to LEO entry.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/01/2015 06:14 am
Based on http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20000062016.pdf

It looks like metallic TPS would have a mass of 5 kg/m2 in low temperature areas and 10 kg/m2 in high temperature area and this is a fully inclusive mass down to where the TPS meets an aluminum based vehicle structure or tank wall.

My vehicle concept would have a surface area of 650 m^2 of which 150 should be high and 500 low temperature.  Total mass would be 4 mT which is then padded to 5.  This would be the same average density as shuttle but less total mass due to lower surface area, and remember this is intended for an entry speed half that of the shuttle.  The vehicles total entry mass of 215 mT would yield a 2.5% TPS mass which is consistent with the Viking lander.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 09/01/2015 06:21 am

PICAX is nice stuff but no one even knows how to seal seems in it yet so it can only be used in monolithic pieces, assuming this limitation is over come their are other issues. 

I guess these don't count as seams then? SpaceX figured out how to seal PICAX seams on their very first cargo dragon flight back in 2010.

Yes, I'm not sure where this idea comes from. PICA-X does not have to be monolithic. Statements like this makes me question your other assertions, Impaler.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/01/2015 07:22 am

PICAX is nice stuff but no one even knows how to seal seems in it yet so it can only be used in monolithic pieces, assuming this limitation is over come their are other issues. 

I guess these don't count as seams then? SpaceX figured out how to seal PICAX seams on their very first cargo dragon flight back in 2010.

Yes, I'm not sure where this idea comes from. PICA-X does not have to be monolithic. Statements like this makes me question your other assertions, Impaler.

It comes from the fact that NASA rejected PICA for the use of the Orion capsule due to not being able to make the gap fillers work and they have said this in publications discussing their design choices, they may be suffering from 'not-invented-here' syndrome but it is something they say which is where the idea comes from. 

I expected it to be a solvable problem in any case so if you want to nitpick this tangential remark rather then looking at the core points go right ahead.  I've provided the links to the relevant papers so you can question the assertions of the authors who wrote them as I'm not asserting anything without a source.

No one advocating for these huge MCT concepts had done any kind of TPS mass estimates, they simply chant PICAX and think they are done, even though they can't even site a mass for the Dragon capsule heat-shield.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/01/2015 04:22 pm
Here's a fully fueled 180mT MCT outbound from LEO (100mT cargo) compared with the launch back from Mars' surface with "only" 25 mT cargo

MCT Dry Wt & Cargo   180   mT
S2 Mass w/MCT   1025   mT  LEO departure.  Mars Return is 75 mT less
S2 Mass w/MCT   2.3   Million LBS
Stage 2 Km/sec    6.48   Km/sec Rocket Equation  LEO
S2 Mars Return 25mT Cargo  8.5Km/sec Rocket Equation

Exponentials help when you reduce the mass.  Just refuel with less propellant to reduce "excess" Km/sec.
The technical challenge is a lightweight MCT vehicle able to withstand Earth re-entry if that is the goal rather than return to some high Earth/moon orbit.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/02/2015 03:10 am
philw1776:  Did you take into account some propellant for landing on Earth?  In a simple direct Earth return this would be needed and in a return that tries to capture into an orbit would also need some propellant or an airo-capture maneuver. 

The easiest capture orbit would be an elliptical one, come in just above the atmosphere and do a braking burn at perigee, this should be much lower deltaV then doing the same kind of capture at Mars because Earth's gravity well it so much stronger.  I'd estimate ~1 km/s as that about what you need to do an Earth escape from a high orbit and this is basically the time-reversal of that maneuver.  From this orbit a refueling could be done and then the vehicle can do a retro-propulsion assisted decent and landing from a lower orbit and speed which would hugely reduce the difficulty.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 09/02/2015 05:48 am
S2 Mars Return 25mT Cargo  8.5Km/sec Rocket Equation

For a 80t dry mass that would mean a prop. mass fraction of 92% (with isp of 380, assuming you can fit such huge nozzles into MCT). That's what you optimally get for an expendable methalox upper stage, not for a deep space SSTE monstrosity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/02/2015 03:28 pm
There should be no problem fitting the 5 Rvac nozzles into the 12.5m MCT or even inside a 10m.

8.5 Km/sec is probably a half Km/sec too low
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 09/02/2015 04:05 pm
There should be no problem fitting the 5 Rvac nozzles into the 12.5m MCT or even inside a 10m.

8.5 Km/sec is probably a half Km/sec too low

I think 7.5km/s for the return has 300m/s margin after gravity loss of 400m/s

Can someone who is saying 8.5km/s or more give me a break down of where they are budgeting the extra ΔV?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/02/2015 04:17 pm
Now I'm confused.  Just calculated Mars' escape velocity and it's only ~5 Km/sec without needed allowance for gravity losses. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 09/02/2015 04:26 pm
Now I'm confused.  Just calculated Mars' escape velocity and it's only ~5 Km/sec without needed allowance for gravity losses.

Yes but being lower escape velocity you get a lower benefit from hyperbolic velocity (Oberth effect) so you need more ΔV over escape for trans Earth injection from low Mars orbit than you do for trans Mars injection from low Earth orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 09/02/2015 04:28 pm
But I still feel 7.5km/s ΔV is sufficient, 8.5 or 9 should actually allow a much faster return if it was available.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/02/2015 04:31 pm
But I still feel 7.5km/s ΔV is sufficient, 8.5 or 9 should actually allow a much faster return if it was available.

Agree with prior comments re:oberth effect.  Still can't find citable source for total Km/sec budget.

I did find a spreadsheet formula error on my Mars return rocket equation delta V.  Now 8.2 Km/sec.
Fixed in attached.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/02/2015 06:26 pm
Now I'm confused.  Just calculated Mars' escape velocity and it's only ~5 Km/sec without needed allowance for gravity losses.

Yes but being lower escape velocity you get a lower benefit from hyperbolic velocity (Oberth effect) so you need more ΔV over escape for trans Earth injection from low Mars orbit than you do for trans Mars injection from low Earth orbit.

Humm, if I am launching from Mars surface and I want to enter an elliptical hohoman transfer around the sun I need to decrease my heliocentric velocity aka I need to be going slower then Mars itself after having left it's sphere of influence.  Thus gravity loss incurred during escape may actually be beneficial IF it results in the loss in heliocentric velocity that one needs to reach Earth.

This is just the opposite of leaving Earth in which In need to have excess velocity relative to the Earth and gravity loss while escaping the Earth is counter productive.

At the NASA trajectory browser it looks like they have DeltaV between 800 and 1000 m/s for Earth return but this is from a C3=0 Mars orbit aka escape.

http://tinyurl.com/p88y3co

According to https://en.wikipedia.org/wiki/File%3aDelta-Vs_for_inner_Solar_System.svg you need 5.5 km/s DeltaV to reach escape so an additional 1 km/s would mean a total of 6.5 km/s which looks to be the best case lowest DeltaV for Earth return.  BUT it should be noted that this trajectory doesn't match Musk's stated goal of a one Synod round trip nor is it particularly fast as the return transit legs are around 240 days, the ones below 200 days are usually above 1 km/s so their is a trade off.  IF you were trying to meet all of Musk's goals the DeltaV would be significantly higher and the dry mass fraction into unrealistic areas, so some kind of descoping is needed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 09/02/2015 08:18 pm
I do not intend to interrupt your current dV conversation. Its very interesting, so please go on. But I want to make a point that bugs me quite some time already.

There is one thing, I do see not enough in L2 and here in the open forums BFR/MCT designs.
They do not seem that anyone takes an evolution of the BFR+MCT design into account. I would suspect that the first versions of the BFR+MCT are much less fleshed out, much less capable than the announced 100mT cargo / 100 passengers to Mars surface. In fact, I would expect them to have less than half of that.

Just an example for early missions that do not need the full, stated MCT capacity. Its just an example, it does not need to go down that way.
* The first MCT goes to Mars and stays there. Having a fuel production plant on board. But no people and no intention to get back. It would require a way to collect water, witch probably is the largest challenge.
* The second MCT would be dedicated to make it back. Using the fuel production of the first lander, store some food, a precursor for Humens. On its way back, it might bring some rocks as well. But really, it would be a demonstrator of getting back.
* The third might be a ship that brings furthe supplies as a precurser to human arrival. It could function as an MCT in case one of the next human rated MCTs can not make it back.
* The forth might have some humans on board. The mission would be: survive and come back. And the equipment would be triple and quadruple redundant to make that happen. No base as of yet. No habitat, MCT will have to do. That and the last MCT in case something breaks.
* The fifth MCT might get the first crew that stays longer. With the mission to create a base. It might be accompanied by 2-3 cargo MCTs. That all are intended to get back.

All this will likely happen with a less capable craft, as explained above. I would expect a major redesign of the magnitude F9 to F9 1.1 and Dragon to Dragon2. But still after this redesign, BFR and MCT might not have the capability that Musk is promising and that you are guys designing right now.

My arguments completely neglects the uses of BFR/MCT for LEO. At the current state, I would expect a precursor to BFR+MCT that is capable of payload to LEO of around 70 to 100 mT. It might be enough for the Mars missions stated above after one evolution step. It also might well be used to phase out FH and be used to deploy large satellite constellations that SpaceX and others are planning. I do not believe that SpaceX will come up with a BFR+MCT design that fulfils Elons statements in the next 20 years.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/03/2015 12:49 am
Could not agree more that the real life BFR/MCT will be an evolutionary design.  I've always said so.
I do think BFR starts out with more tons to LEO then you speculate but even Elon's #s today will likely be revised by flight time.  First crew #s to Mars will be around 8-12. my guess. Summer 2033.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 09/03/2015 04:02 pm
I do not intend to interrupt your current dV conversation. Its very interesting, so please go on. But I want to make a point that bugs me quite some time already.

There is one thing, I do see not enough in L2 and here in the open forums BFR/MCT designs.
They do not seem that anyone takes an evolution of the BFR+MCT design into account. I would suspect that the first versions of the BFR+MCT are much less fleshed out, much less capable than the announced 100mT cargo / 100 passengers to Mars surface. In fact, I would expect them to have less than half of that.

Just an example for early missions that do not need the full, stated MCT capacity. Its just an example, it does not need to go down that way.
* The first MCT goes to Mars and stays there. Having a fuel production plant on board. But no people and no intention to get back. It would require a way to collect water, witch probably is the largest challenge.
* The second MCT would be dedicated to make it back. Using the fuel production of the first lander, store some food, a precursor for Humens. On its way back, it might bring some rocks as well. But really, it would be a demonstrator of getting back.
* The third might be a ship that brings furthe supplies as a precurser to human arrival. It could function as an MCT in case one of the next human rated MCTs can not make it back.
* The forth might have some humans on board. The mission would be: survive and come back. And the equipment would be triple and quadruple redundant to make that happen. No base as of yet. No habitat, MCT will have to do. That and the last MCT in case something breaks.
* The fifth MCT might get the first crew that stays longer. With the mission to create a base. It might be accompanied by 2-3 cargo MCTs. That all are intended to get back.

All this will likely happen with a less capable craft, as explained above. I would expect a major redesign of the magnitude F9 to F9 1.1 and Dragon to Dragon2. But still after this redesign, BFR and MCT might not have the capability that Musk is promising and that you are guys designing right now.

My arguments completely neglects the uses of BFR/MCT for LEO. At the current state, I would expect a precursor to BFR+MCT that is capable of payload to LEO of around 70 to 100 mT. It might be enough for the Mars missions stated above after one evolution step. It also might well be used to phase out FH and be used to deploy large satellite constellations that SpaceX and others are planning. I do not believe that SpaceX will come up with a BFR+MCT design that fulfils Elons statements in the next 20 years.

The question is what is the point of developing an intermediate capacity rocket for SpaceX?  The goal is a fully recoverable rocket. That's what drops the prices by orders of magnitude and makes Mars even thinkable. Once you stop destroying the rocket at each launch, then the cost become much closer to the fuel costs+ development costs.  the development costs are a huge portion for rockets that aren't used much.  So I would expect that Spacex to develop a single large core, and then use that for all possible variants.  The BFR could be used with only partial loads and part of its fuel, for example.  Or for smaller loads is could fly back to the launch pad, since this cuts down on payload by almost 50%.  125 tons with fly back, 250 tons with barge or a remote landing area.  That's a wide range of payloads.  As for the MCT itself, whatever extra capacity it has can be filled with spare parts, or even just stock materials; we're going to need a lot of spare parts for this program  :-)

If a market develops, a modification of the second stage could carry up many different payloads using adapted fairings, without breaking the bank in development costs.

In a similar vein, the shuttle almost never flew fully loaded, and increased capacity by various optimisations with the external tank and the tiles, but it always remained outwardly identical.

Michel Lamontagne
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 09/03/2015 04:28 pm
One precursor mission I would like to see discussed is a launch of an MCT carrying nothing more than a probe launcher and a set of landers and solar powered rovers.  If we remove the crew, stores and most of the radiation protection, how many landings could we have on Mars in a single shot?  How about 100 Mars rovers running about and looking for landing spots and such?  This is figuring 20 tons for the storing and handling mechanism, which is perhaps a bit short. 

Do 100 lander/rovers fit into a 500m3 of cargo space?

We could probably fit in a Mars sample return mission at the cost of 20 rovers!  So 80 rovers+mars sample return.
Would lose the MCT itself though.  It would become a rather nice space station in mars orbit, and a relay station for the coms.

All with a single launch.
How would that compare to sending any number of falcon Heavy missions?

Regards

M Lamontagne
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/03/2015 05:01 pm
Why only 500 cubic meters storage?  Seems way too small by over a factor of 2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 09/03/2015 06:04 pm
Why only 500 cubic meters storage?  Seems way too small by over a factor of 2.
Just a stretch goal. Total internal volume should be between 1000 to 1500, but some of it is in impractical shapes for storing vehicles, and we might want to keep some of the furnished areas for living space latter, or storing multiple communication antennas, or whatever.  5m3 per lander seemed ample.

ML
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 09/03/2015 06:27 pm
Why only 500 cubic meters storage?  Seems way too small by over a factor of 2.
Just a stretch goal. Total internal volume should be between 1000 to 1500, but some of it is in impractical shapes for storing vehicles, and we might want to keep some of the furnished areas for living space latter, or storing multiple communication antennas, or whatever.  5m3 per lander seemed ample.

ML
Even 1000-1500m^3 is still too small for a volume needed to hold 100 people. It needs to be >2000m^3 or about 2500m^3.  A 15m diameter MCT with a 30m tall payload section has about 2000m^3. This is what I expect this section of the MCT to be like. Plus larger diameters solves some other problems such as Mars entry terminal velocity values. In general it makes the height of the MCT a lot shorter and manageable. Larger diameters also increases prop tank volume for a specified height and decrease the ratio of tank weight to volume.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 09/03/2015 08:58 pm
The question is what is the point of developing an intermediate capacity rocket for SpaceX?  The goal is a fully recoverable rocket. That's what drops the prices by orders of magnitude and makes Mars even thinkable. Once you stop destroying the rocket at each launch, then the cost become much closer to the fuel costs+ development costs.  the development costs are a huge portion for rockets that aren't used much.  So I would expect that Spacex to develop a single large core, and then use that for all possible variants.  The BFR could be used with only partial loads and part of its fuel, for example.  Or for smaller loads is could fly back to the launch pad, since this cuts down on payload by almost 50%.  125 tons with fly back, 250 tons with barge or a remote landing area.  That's a wide range of payloads.  As for the MCT itself, whatever extra capacity it has can be filled with spare parts, or even just stock materials; we're going to need a lot of spare parts for this program  :-)

If a market develops, a modification of the second stage could carry up many different payloads using adapted fairings, without breaking the bank in development costs.

In a similar vein, the shuttle almost never flew fully loaded, and increased capacity by various optimisations with the external tank and the tiles, but it always remained outwardly identical.

Michel Lamontagne

Well, many reasons why I believe there will be an incremental approach.
1. SpaceX always did an incremental approach. The didnt start with Falcon 9 1.1 when they developed their first rocket. Same holds true for the BFR. They need to learn to manufacture, launch, etc. such big rockets and thats easier if they dont jump into it with both feat.
2. There is a business case. They can probably much more cheaply launch large constellations of satellites. Like one or more of the internet constellations. Maybe even modules of a new space station. Maybe even a commercial space station, serviced by Dragon2 for space tourists.
3. All the key technologies for BFR+MCT can be tested on a smaller rocket with a smaller MCT precursor. That includes:
* landing on Mars
* large scale energy production on Mars
* water production on Mars
* methane/oxygen production on Mars
* landing, retanking and MCT (precursor) return to Earth
* flight operations and trajectory execution
* communications
* high bandwidth, high latency internet access on Mars
* booster launch and recovery (using Raptor)
* second stage recovery (if any)
* re-tanking in LEO
* first human on Mars and survivability
* first habitat on Mars
* first plant growth on Mars using Mars soil
* first sustainable food growth on Mars
And that are just the biggies. All this needs to be ready for colonization. And all this is easier with a smaller version of BFR/MCT than the ultimate goal noted by Musk.
Once these technologies are in place and tested and ready, a full size MCT makes sense. I would not be surprised that after the logistical hassles are overcome with the first missions, a bigger version of MCT are produced, one that is closer or even capable of 100 humans to Mars. Even though this particular capability would not be used.
4. I dont think that SpaceX will have the funds to do it alone. They will need the help of governments, NASA might not even be enough. When in cooperation with space agencies, pork needs to be provided. That is far easier with a precursor MCTs that focus on technology development and science rather than direct colonization of a naked planet.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 09/03/2015 09:04 pm
Well, isn't Falcon Heavy,  fully recoverable, the perfect precursor?  Why another model in between? It can get some nice experimental payloads to Mars.

I indeed hope there is a case! More ships=less cost. I just question the need for an intermediate step between a fully recoverable Heavy and the BFR.

About deltaV, can aerobraking reduce the deltaV required at Earth return or does it have too great a time penalty?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 09/03/2015 09:10 pm
Why only 500 cubic meters storage?  Seems way too small by over a factor of 2.
Just a stretch goal. Total internal volume should be between 1000 to 1500, but some of it is in impractical shapes for storing vehicles, and we might want to keep some of the furnished areas for living space latter, or storing multiple communication antennas, or whatever.  5m3 per lander seemed ample.

ML
Even 1000-1500m^3 is still too small for a volume needed to hold 100 people. It needs to be >2000m^3 or about 2500m^3.  A 15m diameter MCT with a 30m tall payload section has about 2000m^3. This is what I expect this section of the MCT to be like. Plus larger diameters solves some other problems such as Mars entry terminal velocity values. In general it makes the height of the MCT a lot shorter and manageable. Larger diameters also increases prop tank volume for a specified height and decrease the ratio of tank weight to volume.

Nasa papers are available quoting 4 m3 per person as viable for a temporary stay in a rad shelter, 10 m3 per person an the minimum livable and 18 m3 per person as ideal. Google habitability in spacecraft design.  All intermediate values are ok to me.  My question was is 100 rovers an interesting idea, or not viable?  Put them in 2000m if you want ;-)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 09/03/2015 10:11 pm
Well, isn't Falcon Heavy,  fully recoverable, the perfect precursor?  Why another model in between? It can get some nice experimental payloads to Mars.

I indeed hope there is a case! More ships=less cost. I just question the need for an intermediate step between a fully recoverable Heavy and the BFR.

About deltaV, can aerobraking reduce the deltaV required at Earth return or does it have too great a time penalty?
Falcon Heavy will do somewhere in the vicinity of 35-40 tons to LEO semi-reusably.  BFR + MCT will allegedly do somewhere in the vicinity of 200 tons to LEO reusably.  FH is a good precursor for unmanned missions that test single subsystems, but some intermediate LV *would* be useful for less ambitious goals and larger subsystems, I suspect.  4.6m of payload fairing isn't a lot to play with.

However, I think that's out of the scope of this conversation.  MCT is "The vehicle that can land 100 tons of payload , to include 100 passengers, on Mars".  BFR is the large-diameter LV that launches MCT.  Other launch / transfer vehicles / experimental platforms of more modest aims may come into existence, but they don't really belong in the MCT thread unless they're involved in MCT's mission architecture.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 09/03/2015 10:35 pm
Note I don't think they will do any intermediate steps between FH and BFR, however, if they did (and note at one time they definitely were planning to) this is how I think it would go (cue to the band to start playing Flash's Theme by Queen  (https://www.youtube.com/watch?v=P2QJj3Nbyb0) while you read this):

So after they have the FH working with the two side cores doing RTLS and the centre core being recovered down range by an ASDS, they develop an alternate 2nd stage with about 2.2 times the current tank volume, probably a 5 meter diameter, and that stage runs with a single Raptor Vac. It masses about 200t.  This would be the workhorse to iron out the design of a Methalox space stage that can re-enter and be reused. As such it might never fly in a configuration that outperformed (in total payload to LEO, GTO, GSO etc) the current FH flight profiles, but while the upper stage would cost a lot more than the existing Falcon upper stage, the goal would be for it to be reusable. It might well drop the price per kilo to orbit somewhat but probably not enough to justify it on its own, but that would not be the main motivation. This stage would allow work on propellant depot/transfer, high energy methalox stage re-entry, and possibly be a working step towards an intermediate man rated vehicle capable of lofting more than 7 but much less than 100 passengers.

Now if you go to that amount of work to build the 5M diameter upper stage running methalox, why not make an intermediate step towards a BFR that is more or less a 5M diameter first stage with the same fineness ratio of an F9 so 5M diameter 70M high first stage with about 2.5x the mass of fuel as the existing first stage and an upper stage that is about twice the mass of the current upper stage so: 1500t take off weight 9 Raptors. This would be destined to become the workhorse to LEO with the new, reusable upper stage that was developed first.

Then what if you did the three, four or five core versions of this? That gets you to BFR size booster. Finally you go with a 10m upper stage replacement, that would be your MCT (and tanker).

This is of course not how things will evolve


Well, many reasons why I believe there will be an incremental approach.
1. SpaceX always did an incremental approach. The didnt start with Falcon 9 1.1 when they developed their first rocket. Same holds true for the BFR. They need to learn to manufacture, launch, etc. such big rockets and thats easier if they dont jump into it with both feat.

And it was also the original path they offered us a few years ago, but have adamantly changed that and insisted it was a straight to BFR in the last 2 years or so.

2. There is a business case. They can probably much more cheaply launch large constellations of satellites. Like one or more of the internet constellations. Maybe even modules of a new space station. Maybe even a commercial space station, serviced by Dragon2 for space tourists.

I don't see a business case that couldn't be met with FH until the BFR is there. Since there is no customer today asking for even 50t to LEO that the FH can do, making a 70 to LEO intermediate step does not show any business case. HOWEVER, whether they create a 70t to LEO NFR or 120t to LEO BFR next, once in place it may develop its own new market.

3. All the key technologies for BFR+MCT can be tested on a smaller rocket with a smaller MCT precursor. That includes:
Sure they can, but they can also be tested with an FH - at most making a new methalox upper stage.

* landing on Mars
Avionics, precursor aerodynamics of shape if not total mass, autonomous operation can all be tested with FH and dragon derived spacecraft.

* large scale energy production on Mars
No this won't happen until enough people get there (>1MW) to layout and maintain solar farm, while it could be done with automated craft, it is no more difficult to get to this level from several 13,000kg craft than several 25,000kg craft)
* water production on Mars
* methane/oxygen production on Mars
as above
* landing, retanking and MCT (precursor) return to Earth
Probably not retanking, though it isn't impossible, just seems too cumbersome, but certainly a 13,000kg lander can have a sample return as part of it (or several can put samples in Mars orbit to be collected by a single return craft that was the SEP testbed).
* flight operations and trajectory execution
* communications
* high bandwidth, high latency internet access on Mars
Already done with the above steps, I expect one of the first SpaceX payloads to Mars from a single FH launch will be the local network for Mars with low latency 150kg satellites in a constellation with one or two larger high latency Earth link satellites. This network needs to be in place to facilitate the automated precursor flights including the first few MCT's.
* booster launch and recovery (using Raptor)
plenty of time to do this to launch and fuel the first MCT. That is 8 flights right there. I am betting on 4 MCT's being launched in the two synods before the first manned flight

* second stage recovery (if any)
As above, but if we made an alternate FH upper stage that was raptor powered maybe it would make sense to work out the major kinks. Note that going from an intermediate MCT re-entering to a full sized one is probably as big a step of development as going from Dragon 2 to the intermediate. Certainly it is not just scaling and will not require significantly less expense because you went through an intermediate step that cost you more than half as much as the last step. I am even afraid that MCT and tanker version upper stages might have enough differences to involve considerable unique costs.

* re-tanking in LEO
This could justify some work on a reusable FH upper stage right there. I think it needs to be done. However, it really can be done with just the planned FH.

* first human on Mars and survivability
* first habitat on Mars

As I mentioned above I think we will see several MCT's sent to Mars once FH based survey efforts have short listed the first settlement sites. The way to start with human presence is permanent, not spend nearly as much on flags and foot prints only to go back with something that costs only a little more to establish a settlement.

IF you are going to do the BFR/MCT and that is your plan for colonization, then that needs to be where you start sending people, not waste nearly as much as the human components for that would cost developing the human components for the intermediate sized vehicles.

* first plant growth on Mars using Mars soil
* first sustainable food growth on Mars


I think that can be done and tested with autonomous 13,000kg landers.

And that are just the biggies. All this needs to be ready for colonization. And all this is easier with a smaller version of BFR/MCT than the ultimate goal noted by Musk.
Once these technologies are in place and tested and ready, a full size MCT makes sense. I would not be surprised that after the logistical hassles are overcome with the first missions, a bigger version of MCT are produced, one that is closer or even capable of 100 humans to Mars. Even though this particular capability would not be used.
4. I dont think that SpaceX will have the funds to do it alone. They will need the help of governments, NASA might not even be enough. When in cooperation with space agencies, pork needs to be provided. That is far easier with a precursor MCTs that focus on technology development and science rather than direct colonization of a naked planet.

While I would suggest that it could be done step wise with an intermediate vehicle, that vehicle would need to have a business case like the F9/FH does right now. If it does not (and it does not right now) then it makes more sense to spend the money once going straight to your Mars vehicles which are as likely to find an alternate business case as the intermediate step vehicle would.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/04/2015 02:03 am
I've done a mass breakdown of my proposed MCT vehicle.

Thermal Protection Airoshell:  5 to 10 kg/m^2 metallic fully reusable, 650 m^2                    5 Mt

Tanks and plumbing:  5% of 300 Mt propellant load                                                            15 Mt

Landing Gear:    10% of landed mass based on F9-R ratio with F9 expendable                   18 Mt

Raptor Engines:    1.5 Mt each based on 150:1 T/W ratio and 2300 KN force x4                   6 Mt

Vernier Engines:    Hover 175 Mt on Mars with 100:1 T/W ratio                                             1 Mt

Miscellaneous:    Transit solar panels, thermal radiators, avionics, cargo handling                5 Mt

Structural Frame:      11% of Entry mass, carbon-fiber skeleton                                           25 Mt

Total  Dry Mass                                                                                                                      75 Mt

Cargo                                                                                                                                   100 Mt

Landing Propellant:   Provide 800 m/s Terminal decent DeltaV                                              40 Mt

Total Entry mass                                                                                                                  215 Mt
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 09/04/2015 05:48 am
Needed space per Astronaut. NASA calculates 10mł per person as small. Well, 40mł for 4 Astronauts is small. But there is economy of scale. 1000mł for 100 people is not small IMO.

SpaceX did do evolutionary steps from Falcon 1 and Merlin 1A up to the full thrust version of Merlin 1D and Falcon 9 1.2. That was part of a necessary learning curve. I strongly doubt that there will be a Raptor 1A. It may evolve from a Raptor 1D to a Raptor 1D full thrust and initial payload may go up from 70t to 100t over time. But I don't see them to repeat the whole learning curve on BFR/MCT and Raptor.

I can see them launching BFR from LC-39A with not all Raptor firing or even installed because they can do a lot of testing that way before they need their own full capacity launch pad. But it would be the full BFR/MCT design. They don't have the money and time to do it in smaller steps.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 09/04/2015 06:12 am
I've done a mass breakdown of my proposed MCT vehicle.

Thermal Protection Airoshell:  5 to 10 kg/m^2 metallic fully reusable, 650 m^2                    5 Mt

Tanks and plumbing:  5% of 300 Mt propellant load                                                            15 Mt

Landing Gear:    10% of landed mass based on F9-R ratio with F9 expendable                   18 Mt

Raptor Engines:    1.5 Mt each based on 150:1 T/W ratio and 2300 KN force x4                   6 Mt

Vernier Engines:    Hover 175 Mt on Mars with 100:1 T/W ratio                                             1 Mt

Miscellaneous:    Transit solar panels, thermal radiators, avionics, cargo handling                5 Mt

Structural Frame:      11% of Entry mass, carbon-fiber skeleton                                           25 Mt

Total  Dry Mass                                                                                                                      75 Mt

Cargo                                                                                                                                   100 Mt

Landing Propellant:   Provide 800 m/s Terminal decent DeltaV                                              40 Mt

Total Entry mass                                                                                                                  215 Mt

Here's a fully fueled 180mT MCT outbound from LEO (100mT cargo) compared with the launch back from Mars' surface with "only" 25 mT cargo

MCT Dry Wt & Cargo   180   mT
S2 Mass w/MCT   1025   mT  LEO departure.  Mars Return is 75 mT less
S2 Mass w/MCT   2.3   Million LBS
Stage 2 Km/sec    6.48   Km/sec Rocket Equation  LEO
S2 Mars Return 25mT Cargo  8.5Km/sec Rocket Equation

Exponentials help when you reduce the mass.  Just refuel with less propellant to reduce "excess" Km/sec.
The technical challenge is a lightweight MCT vehicle able to withstand Earth re-entry if that is the goal rather than return to some high Earth/moon orbit.

We have a cap of 180-210T on the permanently attached components of the MCT, due to initial Earth launch considerations, what Gwynne Shotwell said about the launch vehicle they were designing.

A BA-2100 should be approximately the right size for 100 people in terms of pressurized volume, and is supposed to weigh 70-100T at launch without consumables or non-essential internal outfitting.  That's a vacuum-only design.  Skylab managed only 1/7th that pressurized volume by using a dry lab, at 77 tons, plus some functions fielded out to the visiting Apollo CSM.

It's hard to extrapolate, but based on that I wouldn't expect a structural aluminum hab with 2000-2500m3 pressurized volume and long-run ECLSS, with thermal isolation from the fuel tanks and heat shields all around, to be below 100 tons, before any 'useful cargo', ISRU gear, surface deployables, rocket stage, or propellant is considered.

I think you need to start much bigger.  Even non-reusable, prelanded-hab/MAV-dependent DRA 5 gives 28 tons for an inflatable transit hab for just 6 crew, plus 13 tons food and a 10 ton return vehicle.

I think we'll probably end up closer to 600 tons at Mars atmospheric interface than 200 tons.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/04/2015 04:48 pm
Launch Vehicles beyond 200 Mt capacity are hitting all kinds of practical limits such as being transportable by ANY method, having more thrust then any launch pad can handle, being a potentially catastrophic explosion on the pad requiring huge stand-off distances.  Lastly their is the problem of complete impracticality for any use other then launching to Mars, aka the SLS problem but multiplied about 100 fold.

If anything the 225 Mt number for BFR launch mass I'm speculating is aggressive.  I'm concerned about what the 2nd stage recovery cost will be and if this will kill the performance and lower the % of launch mass reaching orbit as philw1776 thought his own analysis looked high in this regard.

Attempts to derived the volume of MCT by calculating the long-duration habitation volume of 100 people is in my opinion flawed, the MCT will hold 100 persons only for brief periods of 3 days or less in something like a train-sleeper-car arrangement which will put it within the range of a 400 m^3 pressurized module placed inside a 500 m^3 cargo bay.  Some kind of large transit vehicle habitat (like BA 2100) will be employed.


As for Vehicle Evolution

I agree with most that the BFR rocket will not evolve significantly, it may see some thrust and performance ingresses, even a bit of a stretch but it will be basically the same vehicle all the way through.  The main focus will be improving the turn-around time to support a rising launch volume and reducing the penalties associated with re-use or the 2nd stage.

The landing vehicle I'm proposing is intended to be used through the whole course of Mars colonization, from the initial human landing all the way to huge volume transport of cargo and people because it is designed to be a rapid-cycling surface to orbit ferry and this actually makes the vehicle easier to design and build then a direct return vehicle.  Avoiding a redesign of the EDL portion of the mission will reduce risk and the delay of re-validating a new system.

I see all the the important system evolution occurring in the interplanetary transit vehicles.  These with be SEP which is a technology advancing by leaps-and-bounds in contrast with chemical propulsion so it makes the most sense to both allow and encourage radical improvement in the mission phase most likely to have the opportunity.  Early transit vehicles would be tugs that move a single lander, later the pace is accelerated by leaving the lander at Mars and using the tugs to haul naked cargo containers or inflatable habitats, finally a large freighter/liner could be created with specialization for cargo or passenger transport as larger vehicles invariably end up being more cost effective.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 09/04/2015 05:37 pm
If anything the 225 Mt number for BFR launch mass I'm speculating is aggressive.  I'm concerned about what the 2nd stage recovery cost will be and if this will kill the performance and lower the % of launch mass reaching orbit as philw1776 thought his own analysis looked high in this regard.

I think you might have misunderstood me here.  My suggestion is that ~200 tons launched from Earth to LEO seems like the limit, but that limit only has to cover spending on structure & permanently-attached habitat; One adds to that with supplemental launches and reaches ~600 tons at Mars entry, with the extra spent on food, people, ECLSS, ISRU gear, surface equipment, and descent propellent.  Then you factor in propellant for Earth Departure and reach 2000-3000 tons IMLEO (4.5 to 6km/s).

And that buys you a conjunction-class colony-in-a-can mission, for 25 people at least;  And maybe 100 people with prelanded assets.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/04/2015 08:50 pm
If anything the 225 Mt number for BFR launch mass I'm speculating is aggressive.  I'm concerned about what the 2nd stage recovery cost will be and if this will kill the performance and lower the % of launch mass reaching orbit as philw1776 thought his own analysis looked high in this regard.

I think you might have misunderstood me here.  My suggestion is that ~200 tons launched from Earth to LEO seems like the limit, but that limit only has to cover spending on structure & permanently-attached habitat; One adds to that with supplemental launches and reaches ~600 tons at Mars entry, with the extra spent on food, people, ECLSS, ISRU gear, surface equipment, and descent propellent.  Then you factor in propellant for Earth Departure and reach 2000-3000 tons IMLEO (4.5 to 6km/s).

And that buys you a conjunction-class colony-in-a-can mission, for 25 people at least;  And maybe 100 people with prelanded assets.

I'm having trouble following you, is that 2-3K IMLEO for just a single vehicle landing which carries 100 Mt cargo or it's equivalent in passengers/habs?  Either your describing the total mass needing to be delivered across several vehicles or your singular vehicle is YUUGE!

I've just been talking about a single landing vehicle with mass at mars entry of ~200 Mt and delivering a payload of 100 Mt.  IMLEO for one round trip of said vehicle would be near 1000 Mt even when utilizing SEP.

P.S.  I've always assumed that the landing vehicle will launch with cargo loaded from Earths surface so the landers dry mass is limited to the under 100 Mt as half of the launch mass is cargo.  If your willing to launch the lander and cargo separately then this restriction wouldn't apply.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Hop_David on 09/07/2015 05:58 am
Humm, if I am launching from Mars surface and I want to enter an elliptical hohoman transfer around the sun I need to decrease my heliocentric velocity aka I need to be going slower then Mars itself after having left it's sphere of influence.  Thus gravity loss incurred during escape may actually be beneficial IF it results in the loss in heliocentric velocity that one needs to reach Earth.

This is completely wrong.

For trans earth injection you need to to go slower with regard to the sun. Gravity loss during Mars escape make you go slower wrt Mars.

Mars is moving about 24.16 km/s wrt sun and the aphelion of a mars to earth Hohmann is moving about  21.52 wrt sun. So we need to lose about about 2.64 km/s to drop to a 1 A.U. perihelion. This 2.64 km/s is referred to as Vinf.

To escape from Mars and inject to trans earth orbit you need sqrt(Vescape2 + Vinf2). Someone's already noted Mars escape at surface is about 5 km/s. sqrt(52+2.642) is about 5.7. Without gravity loss we would need about 5.7 km/s to achieve trans earth injection. This is 5.7 km/s with regard to Mars.

Does gravity loss during ascent help us achieve 5.7 km/s? No it does not. It adds to the 5.7.

According to https://en.wikipedia.org/wiki/File%3aDelta-Vs_for_inner_Solar_System.svg you need 5.5 km/s DeltaV to reach escape

Wrong again. The delta V map shows 4.1 from Mars to LMO, another .9 to Phobos transfer, .3 to Deimos transfer and another .2 to reach C3=0. So 5.5 to escape if you make three stops along the way.

From Mars surface, escape is 5.023 km/s (without gravity loss).









Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/07/2015 07:15 am
I was thinking of something more akin to a gravitational slingshot in which the vehicle is ahead of mars in it's orbit and mars pulls it back, the vehicle loses velocity relative to the sun and mars gains it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: cdleonard on 09/25/2015 02:46 pm
I just had a wild idea about the MCT design. What if it was inflatable by itself, without a separate habitat?

Bigelow habitats generally have a solid cylindrical core surrounded by an inflatable shell. But is there any particular reason why a conical shape wouldn't work just as well? Imagine a scaled-up SuperDragon enclosed in a layer of inflatable material which is puffed-up in vacuum.

The capsule would be launched deflated and only inflate once safely out of the atmosphere. When it's time to enter the atmosphere of Mars you can repack all the furniture back into the solid core and deflate the exterior. This pull brings the inflatable portion back behind the heat shield. On the surface of mars you can inflate it again and will end up with a sort of mushroom-shaped habitat. You can mount light-weight flooring inside the inflated region when on the surface..

The "inflatable" portion doesn't have to touch actually the heat shield. You will have side-mounted engines surrounding the heatshield, similar to the current Dragon.

Such a design requires that the skin material have some thermal resistance, similar to the sides of a normal capsule. It would likely need a fairing for flying upwards through the earth's atmosphere. The habitat also needs to support inflation/deflation while people are inside the core. Deflation seems particularly difficult. The simplest way would be to make core itself mostly airtight and pump out the air from the exterior portion.

This design only makes sense for shipping large numbers of people. You give them plenty of space during the transit period and on the surface but pack them closely together for takeoff and landing. It solves the "habitable volume" problem without increasing payload diameter too much.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jimmy Murdok on 09/25/2015 03:13 pm
I just had a wild idea about the MCT design. What if it was inflatable by itself, without a separate habitat?

Bigelow habitats generally have a solid cylindrical core surrounded by an inflatable shell. But is there any particular reason why a conical shape wouldn't work just as well? Imagine a scaled-up SuperDragon enclosed in a layer of inflatable material which is puffed-up in vacuum.

The capsule would be launched deflated and only inflate once safely out of the atmosphere. When it's time to enter the atmosphere of Mars you can repack all the furniture back into the solid core and deflate the exterior. This pull brings the inflatable portion back behind the heat shield. On the surface of mars you can inflate it again and will end up with a sort of mushroom-shaped habitat. You can mount light-weight flooring inside the inflated region when on the surface..

The "inflatable" portion doesn't have to touch actually the heat shield. You will have side-mounted engines surrounding the heatshield, similar to the current Dragon.

Such a design requires that the skin material have some thermal resistance, similar to the sides of a normal capsule. It would likely need a fairing for flying upwards through the earth's atmosphere. The habitat also needs to support inflation/deflation while people are inside the core. Deflation seems particularly difficult. The simplest way would be to make core itself mostly airtight and pump out the air from the exterior portion.

This design only makes sense for shipping large numbers of people. You give them plenty of space during the transit period and on the surface but pack them closely together for takeoff and landing. It solves the "habitable volume" problem without increasing payload diameter too much.
Too complicated, this system is designed to break all current limitations. You want to keep it as simple as possible. If there is an inflatable easier to be a docked module until Mars, but I don't think is the case.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 09/25/2015 03:50 pm
I was thinking of something more akin to a gravitational slingshot in which the vehicle is ahead of mars in it's orbit and mars pulls it back, the vehicle loses velocity relative to the sun and mars gains it.

... and when you are behind mars, the gravity pulls you towards mars. No net gain. This is all calculated into the escape velocity.

You cannot slingshot with the gravity source you are leaving from.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 09/30/2015 07:10 am
I ran across this MCT speculation/article, from the French chapter of the Mars Society: (my apologies if this has already been discussed)

ANALYSIS OF A CONCEPT IN MARCH COLONIZATION TRANSPORTATION (MCT) LAUNCHES TWO [google translation]
http://planete-mars.com/analyse-dun-concept-mars-colonization-transport-mct-a-deux-lancements/

If you have the chrome browser, it will automatically translate the site for you.

Here are some interesting images from the MCT architecture of this article:
Image 1: Two MCT's docking in LMO for propellant transfer
Image 2: Launch abort module interior
Image 3: Launch abort module from behind
Image 4: MCT landed horizontally on Mars
Image 5: MCT interior
Image 6: BFR base
Image 7: BFR/MCT stack

In is an interesting concept, but I'm not sure that horizontal landing is practical. And their MCT seems to be lacking any kind of engines for propulsion. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 09/30/2015 07:27 am
BTW, here is a link to the author's (Richard Heidmann) previous articles on the subject: http://planete-mars.com/author/heidmann/

He has really gone all in on the horizontal landing idea... Anything else doesn't seem to enter his mind as a possibility.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Patchouli on 09/30/2015 07:43 am
I think MCT might resemble the Pegasus VTOL in shape and operation though the denser propellant might eliminate most or all of the drop tanks.
http://www.astronautix.com/lvs/pegvtovl.htm
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 09/30/2015 08:51 pm
Nice concept. But quite frankly, I like the concept developed in L2 better. Hyperion et al. seem to have a better handle on the subject. Its very interesting to the development though and only good things can come from independent groups tackle the same problem.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/01/2015 04:12 am
In a previous article, the same author, Richard Heidmann, seems to have fixed on the idea that BFR is an SSTO, that MCT has no main engine, just belly thrusters for landing. That's led to some weird conclusions, and hence the current article.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/01/2015 07:58 am
How could anyone think that, it would be non-reusable which is by far the point Musk is most Emphatic on.  If someone showed me a pair of roller-skates and told me that was Musk's MCT design it would be more credible as the vehicle Musk is designing then anything expendable simple because it would fulfill the reusable criteria.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 10/01/2015 08:11 am
In a previous article, the same author, Richard Heidmann, seems to have fixed on the idea that BFR is an SSTO, that MCT has no main engine, just belly thrusters for landing. That's led to some weird conclusions, and hence the current article.

Simply not true.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Rocket Surgeon on 10/02/2015 01:34 am
Nice concept. But quite frankly, I like the concept developed in L2 better. Hyperion et al. seem to have a better handle on the subject. Its very interesting to the development though and only good things can come from independent groups tackle the same problem.

I definitely agree, though it is reassuring to see two independent designs that seem to be converging. Really the difference at this point seems to be changes made to base assumptions and what the designers consider to be 'more efficient'
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Rocket Surgeon on 10/02/2015 01:55 am
I've got a question about the general biconic MCT (both integrated and non-integrated). It looks like the abort rockets are designed to save pretty much everything north of the fuel tank, but would it be better to have a small, dedicated abort section? Essentially just cram everyone into the nose and pop it off if something goes wrong. Something like the recent planete-mars biconic design, and maybe double it as a solar storm shelter. That way the abort engines could be small and even use a storable propellants (like hypergolics or solids) or (my personal favorite) use methalox that is temporarily charged when they are likely to be needed (ie during launch or possibly entry).

Given that the abort rockets aren't being used for landing, and you're only focusing on saving the people, it could save a fair bit on weight.

http://planete-mars.com/analyse-dun-concept-mars-colonization-transport-mct-a-deux-lancements/4/
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/02/2015 04:20 am
Or how about this radical idea. Drop the abort capsule altogether. I've argued this before, but the idea seems to be very ingrained in people, almost like the idea of landing a shuttle with wings "horizontally" on Mars. Both ideas make just as much sense, IMO.  (In other words, not much sense)

There is no place to abort to when landing on or taking off from Mars. If you find launch abort essential for Earth departure, shuttle people up while the MCT is in LEO being refueled.

At some point you've got to put "big boy pants" on if you want to go to Mars. Or roll a hard six. Or name your own analogy. :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/02/2015 07:13 am
What does it take to keep Raptor ready for ignition from takeoff? Let the full MCT be the escape capsule. It may not cover every catastrophic event but should be able to get MCT away from a first stage for anything short of an explosion without any advance warning time.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/02/2015 07:33 am
Or how about this radical idea. Drop the abort capsule altogether. I've argued this before, but the idea seems to be very ingrained in people, almost like the idea of landing a shuttle with wings "horizontally" on Mars. Both ideas make just as much sense, IMO.  (In other words, not much sense)

There is no place to abort to when landing on or taking off from Mars. If you find launch abort essential for Earth departure, shuttle people up while the MCT is in LEO being refueled.

We know that most flights will be for cargo - they don't need an abort system.

It is likely, in my opinion, that crew and cargo MCT will be identical (at least at first). What makes them different would be the cargo for the crew MCT would be the hab.

First crew sizes are likely to be quite small - under 15. So will fit into a couple of Dragon 2.

We've been told that payload back is ~ 25% of payload there, so ~ 25 tonnes. It is really hard to fit an abort system (capsule?) + hab for 100 (or even 15) into 25 tonnes - even if they return dry and empty.

Later flights might use an optimised crew MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/02/2015 07:47 am
Sending a passenger MCT back should not be a problem with 25t cargo. Sending passengers and consumables may  become a problem even if way less than 100.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/02/2015 07:57 am
That approach doesn't really work to maximize the rest of the vehicle.

EITHER:
The MCT launches full of fuel and has lots of delta V, which maximizes the payload mass fraction to orbit, but has a TWR too low to use for launch abort
OR:
The MCT launches empty of fuel and has high TWR, but with low enough delta V that part or all of the BFR has to come close to, or reach, orbit.  This lowers payload mass fraction by a large amount, or for a fixed payload makes the BFR required substantially larger.
OR:
The MCT launches with an order of magnitude more engine power than it will require for the rest of the mission, which is retained as waste mass throughout the rest of the mission, reducing space for other payload, or increasing launch requirements, by a large factor.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 10/02/2015 09:20 am
That approach doesn't really work to maximize the rest of the vehicle.

EITHER:
The MCT launches full of fuel and has lots of delta V, which maximizes the payload mass fraction to orbit, but has a TWR too low to use for launch abort
OR:
[The MCT launches empty of fuel and has high TWR, but with low enough delta V that part or all of the BFR has to come close to, or reach, orbit.  This lowers payload mass fraction by a large amount, or for a fixed payload makes the BFR required substantially larger.
OR:
The MCT launches with an order of magnitude more engine power than it will require for the rest of the mission, which is retained as waste mass throughout the rest of the mission, reducing space for other payload, or increasing launch requirements, by a large factor.

Musk has already said MCT will refuel in orbit. It seems reasonable that this could happen at both ends, if needed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/02/2015 09:25 am
That approach doesn't really work to maximize the rest of the vehicle.

I don't see it that way. I already stated that it will not be able to speed away from an explosion without warning. But it can separate from a failing first stage with shut down engines. Being heavy it would have to burn a lot of fuel before it can land. There is that one point that it will not have enough time to go through a lengthy precooling period. That's why I asked if Raptor can be kept in a state ready for ingnition throughout launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/02/2015 06:33 pm
I ran across this MCT speculation/article, from the French chapter of the Mars Society: (my apologies if this has already been discussed)

ANALYSIS OF A CONCEPT IN MARCH COLONIZATION TRANSPORTATION (MCT) LAUNCHES TWO [google translation]
http://planete-mars.com/analyse-dun-concept-mars-colonization-transport-mct-a-deux-lancements/

If you have the chrome browser, it will automatically translate the site for you.

Here are some interesting images from the MCT architecture of this article:
Image 1: Two MCT's docking in LMO for propellant transfer
Image 2: Launch abort module interior
Image 3: Launch abort module from behind
Image 4: MCT landed horizontally on Mars
Image 5: MCT interior
Image 6: BFR base
Image 7: BFR/MCT stack

In is an interesting concept, but I'm not sure that horizontal landing is practical. And their MCT seems to be lacking any kind of engines for propulsion.

Hmmm...this seems so familiar, where have I seen this before?

Oh yea...from me...earlier in this thread....  :-)

(except with vertical landing rather than horizontal).

http://forum.nasaspaceflight.com/index.php?topic=37808.msg1401739#msg1401739

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/02/2015 06:41 pm
BTW, here is a link to the author's (Richard Heidmann) previous articles on the subject: http://planete-mars.com/author/heidmann/

He has really gone all in on the horizontal landing idea... Anything else doesn't seem to enter his mind as a possibility.

Looks like Heidmann evolved some from his space plane looking concept to a more cylindrical bionic concept...like mine.  :-)

He does like that horizontal landing and take off thing though.  And not quite sure how HCT gets itself from booster staging to LEO without aft engines.  It just pitches horizontal after staging be enigne ignition?

I still like the vertical style with aft engines myself.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/02/2015 07:23 pm
That approach doesn't really work to maximize the rest of the vehicle.

I don't see it that way. I already stated that it will not be able to speed away from an explosion without warning. But it can separate from a failing first stage with shut down engines. Being heavy it would have to burn a lot of fuel before it can land. There is that one point that it will not have enough time to go through a lengthy precooling period. That's why I asked if Raptor can be kept in a state ready for ingnition throughout launch.

Or how about this radical idea. Drop the abort capsule altogether. I've argued this before, but the idea seems to be very ingrained in people, almost like the idea of landing a shuttle with wings "horizontally" on Mars. Both ideas make just as much sense, IMO.  (In other words, not much sense)

There is no place to abort to when landing on or taking off from Mars. If you find launch abort essential for Earth departure, shuttle people up while the MCT is in LEO being refueled.

At some point you've got to put "big boy pants" on if you want to go to Mars. Or roll a hard six. Or name your own analogy. :)


First crew sizes are likely to be quite small - under 15. So will fit into a couple of Dragon 2.

We've been told that payload back is ~ 25% of payload there, so ~ 25 tonnes. It is really hard to fit an abort system (capsule?) + hab for 100 (or even 15) into 25 tonnes - even if they return dry and empty.

Later flights might use an optimised crew MCT.

The team (for fun team...on our own time) I've been working with and Hyperion has posted some on over on L2 have preferred an LAS system. however, this was my original preference too.

Putting an extra Raptor on the integrated MCT.  AS well as on the booster.  That way if there's an engine out on the booster, it can compensate and get MCT to proper staging point.  If there's an engine out on MCT, then it can get nominally to Orbit, and then can abort the mission and come home.

This cannot get away from an exploding booster, as Burninate points out:

That approach doesn't really work to maximize the rest of the vehicle.

EITHER:
The MCT launches full of fuel and has lots of delta V, which maximizes the payload mass fraction to orbit, but has a TWR too low to use for launch abort
OR:
The MCT launches empty of fuel and has high TWR, but with low enough delta V that part or all of the BFR has to come close to, or reach, orbit.  This lowers payload mass fraction by a large amount, or for a fixed payload makes the BFR required substantially larger.
OR:
The MCT launches with an order of magnitude more engine power than it will require for the rest of the mission, which is retained as waste mass throughout the rest of the mission, reducing space for other payload, or increasing launch requirements, by a large factor.

But it can handle the most common failure, and engine problem. 
It could do an emergency separation from the booster early, but the engines would need to be brought on line, so there's a window from launch to that point where some multi-engine booster failure would result in no abort scenario. 

But yes, early missions will probably have 4-6 crew, and a single D2 can take them up to MCT in orbit, no LAS needed.  Missions will grow and two D2's would still be feasible.  The problem is later when you have 100 people.  That's a lot of D2's to fill it up.  At that point it would probably be desirable to launch them on MCT.  So either you need an LAS, or just take a more "Space Shuttle" or "Airliner" approach.  Lots of redundant system, but if something goes boom, there's not contingency for that.  By that time there'd probably literally be dozens of MCT launches, so hopefully you'd know then if it was reliable or not.
That was my original thought.

However, there are some LAS options with some benefits.

The first is a separable crew/hab section, like Heidmann has.  The crew is in their launch seats and that aborts off from an exploding booster.  Then it propulsively lands.  A lifeboat LAS.
Another is launching MCT dry on a 2nd stage rather than the integrated design, with just enough propellant to power it's LAS engines.  So the whole dry MCT is aborted and lands.  For a nominal launch, it docks with the depot, and the 2nd stage does it's own EDL and returns to launch site.
The 3rd option Burninate mentions, just to have a very overpowered integrated MCT is problematic because Raptors will need time to come up to ignition.  That's why pressure fed fast reacting engines like Superdracos would be necessary.  Even if Raptor could do it, then you have a lot more Raptors that you need for the rest of the mission.

So as I like my pet integrated biconic MCT concept from earlier in this thread, I go back to that at a separable crew section.  This some additional potention advantages other than just LAS.

1)  Once separated, it's a traditional biconic vehicle (see below).  It could be separated when in-bound to Mars or Earth if there's a problem with the rest of the vehicle.  As it will have the TPS system, it can do it's own EDL. 

2)  It could be used for launch abort when lifting off of Mars.  Although there would have to be some infrastructure on Mars for the crew to then be able to access.  Or they'd be marooned wherever the lifeboat landed.

3)  Additionally, it can be used to land MCT on Earth.  Raptor will be a vacuum nozzle, which could very well not work at sea level if it's too over expanded.   You'd need some sort of retractable nozzle, jettisonable nozzle, or something else.  But, the propulsive dV requirement for landing on Earth is pretty low.  Terminal velocity will be about 120MPH.  So the LAS system...if it were external like Dragon 2's, could be used to land MCT on Earth without Raptor needed.
The propulsive dV on Mars is much greater, but it's near vacuum so Raptor can be used to supply that efficiently on Mars, with the LAS thrusters being used for hover and landing assist. 
A top mounted thruster system like this would be inherrently stable, unlike landing on a tail engine (F9 booster)....like a helicopter is stable with it's thrust up on top and it's mass hanging below it.
Like super versions of the cold gas thrusters F9 booster uses.  And they'd be pressure fed, deeply throttleable, and fast reacting.  Very good for hovering and landing.

So, for reason #3, I do now favor having them.  This gets around actually having to hover and land on Raptor...which may be hard to design to react and throttle to that degree.  The ones positioned on the ventral (chin) side would need to be desinged in a way so they are protected during EDL.  But the Space shuttle has RCS/OMS thrusters in the nose that are protected during EDL, so I would think that could be done. 

Now...how -much- do you abort?  Everything north of the tanks?  Or just a lifeboat crew section?
I favor the lifeboat crew section, and make that the biconic nose of the vehicle.  The nose aborts away from the cylinder. 
Or the nose plus whatever part of the cylinder is hab only, leaving a cargo deck with the tanks.  The reason being is if you have an exploration mission with say a crew of 7, you might have 50mt of cargo below the hab to support them on the surface.  How big does the LAS needs to be to take all of that cargo with it?
If you do want to land with the LAS system, it will have to be at least large enough to somewhat slow and hover about 125mt on Earth and 200 X 0.38g = 76mt equivalent on Mars.  A system that can do that might be able to quickly abort away about 35mt from an exploding booster, but not 70mt with cargo.

So there'd need to be some trades done to see how large it needs to be to double as a landing system, and then seem how much abort mass it can handle.  And figure a sweet spot from there.  Obviously the abort requirements are much greater than the hover and landing requirements.
 
(The bottom pic is the full integrated biconic MCT doing atmospheric entry.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/03/2015 12:11 am
Nice concept. But quite frankly, I like the concept developed in L2 better. Hyperion et al. seem to have a better handle on the subject. Its very interesting to the development though and only good things can come from independent groups tackle the same problem.

It's actually evolved quite a lot towards the Integrated Biconic MCT I talked about here a few months ago, and the team has been fleshing out and posting on L2.  Heinmann's first concept was sort of a booster assisted SSTO space plane.  I like this better, but I don't really like the horizontal landing.  Seems like it'd be hard to keep the engines balancing the CoG if propellant is sloshing around.  And it'd have to have a side feed system, rather than a traditional bottom feed for a vertical configuration.  Not to mention you need engine doors in your TPS...which seems like it would be better if it can be avoided.
I think the difficulties of getting cargo and crew to the surface for a taller vertical lander are less than the difficulties of side/ventral side propulsion like this.

So I like ours better too.  :-)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/03/2015 12:57 am
A top mounted thruster system like this would be inherrently stable, unlike landing on a tail engine (F9 booster)....like a helicopter is stable with it's thrust up on top and it's mass hanging below it.

I'm rather surprised that you aren't aware of the Pendulum Fallacy: https://en.wikipedia.org/wiki/Pendulum_rocket_fallacy
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/03/2015 12:58 am
Nice concept. But quite frankly, I like the concept developed in L2 better.

If you aren't willing to show/share it, don't bring it up here. This kind of information sand boxing is why I'm not joining L2 anytime soon. Just my personal opinion...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 10/03/2015 01:08 am
I'd like to offer a completely different MCT LAS for consideration:

Considering that the MCT will certainly have high efficiency Methalox engine(s) for its main thrust (and perhaps landing?) the issue seems to be the delay time required to 'spin up' the turbines in the case of a mid flight abort.  So this means that the MCT really only needs a short burst (<4-5 seconds?) of high thrust  (5gs?) to pull it safely away from a disintegrating 1st stage.  Correct?

So, how about placing an LAS set of engines, with associated fuel, in the interstage between the booster and the MCT?  Under normal conditions, the MCT would stage, leaving the interstage attached to the booster, and  the booster plus interstage/LAS would RTLS and be completely reused.  Under abort conditions, the LAS engines would fire and the interstage/LAS would separate from the booster and propel the MCT a distance away.  The MCT main engine(s) (Raptors?) would spin up during this LAS firing period, then the MCT would detach from the interstage and proceed to do an abort landing.

The LAS could be fast acting, high thrust (poor ISP) hypergols, or even (gulp) solids.  This system wouldn't need to be very massive, given its short firing duration, but it would admittedly still be considerable parasitic mass hurting the RTLS effort.

I like this idea because (1) no parasitic mass going to orbit and beyond, penalizing the whole system, (2) entire system is reusable, and (3) unlike 'puller' LAS systems, you don't require that the LAS system cleanly separate from the manned portion as an additional staging event, lest you have LOM.

Thoughts?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/03/2015 04:01 am
Lobo:  Is that L2 vehicle concept posted anywhere where us plebs can read it?

As I'm sure you remember I favor the 2nd of your scenarios, "Another is launching MCT dry on a 2nd stage rather than the integrated design, with just enough propellant to power it's LAS engines.  So the whole dry MCT is aborted and lands.  For a nominal launch, it docks with the depot, and the 2nd stage does it's own EDL and returns to launch site."

I'm looking at a MCT vehicle that at launch has 175 mT total dry mass and a modest 20 mT of propellents for launch abort and landing.  That means a launch mass of 200 mT that needs to be pushed away from the rest of the vehicle in an emergency.  4 Raptor engines at their 2,300 KN each would provide sufficient thrust to accelerate the MCT away at about 5 g's which is comparable to a Dragon capsule.

Note that if abort occurs at anything other then during the early phases of the first stage burn then the MCT vehicle would certainly land in the ocean and as the location is unplanned a platform won't be available so it will be a touchdown into water (much like the early F9 first stage tests).  The empty tanks should make the vehicle buoyant but it would float quite low in the water such that cargo and passenger compartments would be well underwater.  Needless to say the salt-water contact would necessitate a considerable disassembling and rebuilding of the whole vehicle and it's engines, but I can't see any abort scenario that doesn't put the vehicle in the water if were launching from typical launch sites like Canaveral.  I think we should just be happy everyone is OK in such a situation.

In addition I've been thinking about a set a smaller faster operating vernier engines operating on Metho-Lox with the thrust equivalent to ~10 Super Dracos used primarily during touchdown on Mars and Earth.  I like your idea of placing these on the upper flanks of the vehicle as this solves a head-ache I've had with finding the space for them on the bottom of the vehicle and provides better leverage over the vehicle, and it will eliminate entirely any rocket plume impinging on the ground on Mars an important safety concern.  Cosine loses shouldn't be a problem as they fire for such time.  On Mars the bulk of supersonic retro-propulsion would be via Raptor at the highest efficiency.  Using these engines during abort should add an additional 8% more thrust so why not use it, besides they should start faster then the Raptors which is out main concern when using them for abort.

BTW Lobo, you may be interested in an idea I've had for assisting a biconic vehicle in landing on Mars by use of a mechanically deployed and reusable decelerator.  The rear of the vehicle consists of body flaps much like the two steering flaps you've show on your concept, but they extend around the entire vehicle.  These extend right after the peak deceleration heating to widen the vehicle and steer it.  Once in the supersonic range the second expansion occurs in which telescoping spare extend from the back side of the flaps and deploy a cloth sail of nomex of some other comparable material between each spar.  This should slow the vehicle considerable while still allowing steering and because it's deployed after peak heating the fabric is not chard/ablated and is fully reusable while being thin and light.  It would still necessitate propulsive landing but it might save considerably on entry mass as the mass of a decelerator is generally less then the mass of propellant it replaces.





Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/03/2015 04:03 am
GORDAP - I like it! If abort is only practical for Earth launch, it is an elegant solution.

The MCT will somehow need to be able to use Methalox for its thrusters - not sure how that will work. Would there be smaller LOX and Methane containers that are pressurized at high pressure (continuously refilled from the main tanks) that feed the maneuvering thrusters? One could also imagine such a system could be scaled up for abort/landing thrusters.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/03/2015 05:29 am
Agreed, a pushing fast-start 1 second abort motor located in the interstate is a very clever solution.

I think the solid booster solution is viable (though SpaceX seems to dislike all pyrotechnics).  Also it doesn't need to really be the whole of the inter-stage, all you really need is a naked thrust-structure that connects the abort motor to the bottom of the MCT which can generate and transmit the ~9 million N of thrust.  As that is a lot of force I would recommend just sticking cones into the nozzles of the Raptors and pushing on them directly (a bit like the new center-pusher stage separator) so your reusing the thrust structure of the vehicle itself as if the engines were running without having to create new hard-points that bypass the engines.  As the Raptors start up they will simply push out the abort motors as they are burning out.

Based on the total impulse of the Shuttle boosters and their total mass I would estimate that to deliver 9 million N-s of total impulse would require 15 mT of solid rocket motors, quite heavy.  But total take off mass might be lessened by the fact that your putting less abort propellents in the MCT itself.  Still it is a hit to take on returning the stage it is on.  If that is a first stage it should be do able without much problem, but if it's a 2nd stage as I've proposed it looks like it could be problematic.


So I propose to do the Dragon abort trick, use the abort engine to land the 2nd stage in the event that no abort happens.  That means if their is an abort the 2nd stage is sacrificed even if the fault is in the first, but your probably fleeing an explosion that was going to destroy it anyway so no big loss.  Now the abort system isn't as parasitic because we MUST have smaller vernier engines to land a second stage, the main propulsion system of Vacuum Raptor engines is not going to cut it as their are too few engines and they can't throttle low enough or safely at Sea Level.  Though certainly the amount that we need for abort is over kill over what we would for just landing.

If a Super-Draco like liquid engine in used you would need A LOT of them, like 120 to get the same thrust, around a 10 m core you should just manage to get that on the vehicle in a giant ring of engines packed side by side.  In reality I think we will see some new engine several times more powerful then Super Draco (SuperDuber Dracos??) and the number will be more reasonable.  Still a large number of engines will make touch-down very easy, no only can you come to halt really fast but with such a large depth of throttle it should be possible to put the stage down on very delicate tooth-pick landing gear which should save considerable mass.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 10/03/2015 12:52 pm
Well, Lars.. I don't want to persuade anyone of joining L2. If you want to support the exististances of this Web page, join. If you think it's not worth it then don't. Your money, your choice.
We are not allowed in L2 to discuss public links and here we are not allowed to discuss content from within L2. My comment was unspecific because I don't have an other choice.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 10/03/2015 01:02 pm
I am not sure an interstage abort system would work. The mechanical loads on the MCT would be 10 or more times stronger during an abort than during normal operation. The MCT including fuel would need an acceleration of 5+gs as opposed to less than 1. Plus the force to overcome atmospheric pressure at max Q. The parasitic mass would be within the metal structure of MCT instead of fuel and abort angines. I am not sure that is lighter than a crew abort capsule. Also you can't abort from an exploding MCT during first ascend on earth or ascent on Mars. An ascent abort on Mars might be required when a colony is already established and an infrastructure for rescue on Mars is available.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 10/03/2015 01:07 pm
GORDAP - I like it! If abort is only practical for Earth launch, it is an elegant solution.

The MCT will somehow need to be able to use Methalox for its thrusters - not sure how that will work. Would there be smaller LOX and Methane containers that are pressurized at high pressure (continuously refilled from the main tanks) that feed the maneuvering thrusters? One could also imagine such a system could be scaled up for abort/landing thrusters.

Lars, glad you like the idea, but I'm not clear how it affects the thrusters and/or landing engine choice for the MCT itself.  Though I kinda expect, given the very long duration of end-to-end mission for the MCT, that you'd want to use the same storable, ISRU producible fuel combination (Methalox) for these things as you would for the main propulsion in any case.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 10/03/2015 01:25 pm
Agreed, a pushing fast-start 1 second abort motor located in the interstate is a very clever solution.

I think the solid booster solution is viable (though SpaceX seems to dislike all pyrotechnics).  Also it doesn't need to really be the whole of the inter-stage, all you really need is a naked thrust-structure that connects the abort motor to the bottom of the MCT which can generate and transmit the ~9 million N of thrust.  As that is a lot of force I would recommend just sticking cones into the nozzles of the Raptors and pushing on them directly (a bit like the new center-pusher stage separator) so your reusing the thrust structure of the vehicle itself as if the engines were running without having to create new hard-points that bypass the engines.  As the Raptors start up they will simply push out the abort motors as they are burning out.

Based on the total impulse of the Shuttle boosters and their total mass I would estimate that to deliver 9 million N-s of total impulse would require 15 mT of solid rocket motors, quite heavy.  But total take off mass might be lessened by the fact that your putting less abort propellents in the MCT itself.  Still it is a hit to take on returning the stage it is on.  If that is a first stage it should be do able without much problem, but if it's a 2nd stage as I've proposed it looks like it could be problematic.


So I propose to do the Dragon abort trick, use the abort engine to land the 2nd stage in the event that no abort happens.  That means if their is an abort the 2nd stage is sacrificed even if the fault is in the first, but your probably fleeing an explosion that was going to destroy it anyway so no big loss.  Now the abort system isn't as parasitic because we MUST have smaller vernier engines to land a second stage, the main propulsion system of Vacuum Raptor engines is not going to cut it as their are too few engines and they can't throttle low enough or safely at Sea Level.  Though certainly the amount that we need for abort is over kill over what we would for just landing.

If a Super-Draco like liquid engine in used you would need A LOT of them, like 120 to get the same thrust, around a 10 m core you should just manage to get that on the vehicle in a giant ring of engines packed side by side.  In reality I think we will see some new engine several times more powerful then Super Draco (SuperDuber Dracos??) and the number will be more reasonable.  Still a large number of engines will make touch-down very easy, no only can you come to halt really fast but with such a large depth of throttle it should be possible to put the stage down on very delicate tooth-pick landing gear which should save considerable mass.

Impaler, love the idea of using these abort engines as landing engines.  That way, their fuel is not parasitic at all!  There may be more engines than are needed for landing (so I guess the unused ones are 'parasitic'), but these can also just serve as redundant backups, as they are on the Dragon 2.

I'm in the camp that's expecting the BFR to be a single stage booster, with the MCT serving as its own embedded second stage.  If this is the case, then the LAS engines could be used on the BFR stage 1 to assist landing, and I'll bet their not much oversized for that mission.  Hmm, I think the  BFR would still use a center Raptor to do the big initial 'boostback' burn though.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 10/03/2015 01:37 pm
I am not sure an interstage abort system would work. The mechanical loads on the MCT would be 10 or more times stronger during an abort than during normal operation. The MCT including fuel would need an acceleration of 5+gs as opposed to less than 1. Plus the force to overcome atmospheric pressure at max Q. The parasitic mass would be within the metal structure of MCT instead of fuel and abort angines. I am not sure that is lighter than a crew abort capsule. Also you can't abort from an exploding MCT during first ascend on earth or ascent on Mars. An ascent abort on Mars might be required when a colony is already established and an infrastructure for rescue on Mars is available.

Semmel, not sure I'm following your arithmetic re loads.  Whether the BFR is one stage or two, I'd expect the MCT to see in the neighborhood of 3g's at burnout before separation.  In fact, I'd think the BFR will need to throttle down to stay under this limit to protect people and payloads.  That is the force that will be seen at the interstage/MCT interface.  If the LAS is in the interstage, and it gives a short burst of 5g's during an abort, that's all this interface will see, which is 67% more, not 10X.  What am I missing?

Agree that the LAS in my proposal would have to be significantly larger to abort the entire MCT, with it's payload and fuel, as opposed to just jettisoning a smallish crew cabin.  But the upside of course is that you don't lose the MCT and payload.  I have no idea if that will be worth it to the designers of this system.

I agree that this leaves no LAS for the launch from Mars phase of the MCT.  But as others have pointed out, it's debatable whether or not an LAS is needed/useful for an SSTO vehicle (which the MCT is at this point).

[All - sorry for my 3 posts in a row, but I haven't posted in a while and I need to get it out of my system  ;) ]
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 10/03/2015 03:15 pm
The difference is, that in an abort, the MCT (assuming it is its own second stage) has to be abortet including its entire mass of fuel. I  think I remember that the dry mass of the MCT is about 20 % of its wett mass. So the 3g in normal operation would be reached near dry mass. The 5 g abort would be reached at wett mass. The force on the metal structure is F=m*a, mass times acceleration. Wett mass is 5 times dry mass, acceleration is higher, and air resistance is higher. So during about, the structure of MCT must take I would guess more than 10 times the force of normal operation. The metal structure must be sized accordingly.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/03/2015 03:45 pm
[LAS lifeboat]

Essentially you've added the cost of developing a 100-person Super-Dragon capsule, with the added cost of integrating it into MCT like a matryoshka doll. (And you rarely actually use it. Most of the time, all of its independent systems are just dead weight. And it won't have the develop-use-update-use pattern that SpaceX prefers.)

If you're going to the expense of developing an extra vehicle, why not just use the 100-person "lifeboat" as a shuttle to ferry passengers to LEO when the MCTs are fuelled and ready to go? It doesn't need to go to Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/03/2015 09:12 pm
I'd like to offer a completely different MCT LAS for consideration:

Considering that the MCT will certainly have high efficiency Methalox engine(s) for its main thrust (and perhaps landing?) the issue seems to be the delay time required to 'spin up' the turbines in the case of a mid flight abort.  So this means that the MCT really only needs a short burst (<4-5 seconds?) of high thrust  (5gs?) to pull it safely away from a disintegrating 1st stage.  Correct?

So, how about placing an LAS set of engines, with associated fuel, in the interstage between the booster and the MCT?  Under normal conditions, the MCT would stage, leaving the interstage attached to the booster, and  the booster plus interstage/LAS would RTLS and be completely reused.  Under abort conditions, the LAS engines would fire and the interstage/LAS would separate from the booster and propel the MCT a distance away.  The MCT main engine(s) (Raptors?) would spin up during this LAS firing period, then the MCT would detach from the interstage and proceed to do an abort landing.

The LAS could be fast acting, high thrust (poor ISP) hypergols, or even (gulp) solids.  This system wouldn't need to be very massive, given its short firing duration, but it would admittedly still be considerable parasitic mass hurting the RTLS effort.

I like this idea because (1) no parasitic mass going to orbit and beyond, penalizing the whole system, (2) entire system is reusable, and (3) unlike 'puller' LAS systems, you don't require that the LAS system cleanly separate from the manned portion as an additional staging event, lest you have LOM.

Thoughts?
The question is implicitly about the power to weight ratio of rocket engines.

Ejecting an MCT at somewhere between 500 and 5000 tons at 5-10 G's, even for a second or two, is nontrivial.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/03/2015 09:20 pm

Impaler, love the idea of using these abort engines as landing engines.  That way, their fuel is not parasitic at all!  There may be more engines than are needed for landing (so I guess the unused ones are 'parasitic'), but these can also just serve as redundant backups, as they are on the Dragon 2.

I'm in the camp that's expecting the BFR to be a single stage booster, with the MCT serving as its own embedded second stage.  If this is the case, then the LAS engines could be used on the BFR stage 1 to assist landing, and I'll bet their not much oversized for that mission.  Hmm, I think the  BFR would still use a center Raptor to do the big initial 'boostback' burn though.

Glad you approve, as you've given me a major solution form the configuration I'm pursuing it seems the least I could do.  And as you say the same principle applies if your BFR is one stage or two, most or all of the propellents will actually cause no parasitic loss, though the engine hardware would the expellent T:W ratio of SpaceX engine technology minimizes this.

In the one stage BFR your looking at the combo 2nd stage MCT vehicle is going to be considerably more massive then the smaller and un-fueled one I'm looking at, that will mean probably 3x more thrust needed for separation.  Rather then the 9 million N I'm estimating for a 200 mT MCT your looking at 27 million N, the thrust of 12 raptor engines.  I see a problem with rapidly initiating that much thrust INSIDE the interstate when the vehicle is still assembled, it would be like setting off a bomb.  So the thrust must be vented laterally with Dragon like canted rocket nozzles along the perimeter of the inter-stage.  With the cosine loss were looking at something like 400 Super Draco equivalent rockets.  Do able probably by having multiple bands of nozzles such that the entire outer surface of the inter-stage is nozzles.  But we should be aware that were increasing the number of parasitic engines, though they parasatizing the first stage rather then the 2nd which means they count for only 1/10th as much in final payload.

The decisive factor I think is that in a 2 stage BFR with the abort engines atop the 2nd stage and below a smaller MCT is that you can abort during both first AND second stage burn.  You only give up the abort motor once full Earth orbit has been achieved.  Where as with a one stage BFR your in a black zone after first stage separation and yet your still attached to a potential bomb which has 6-7 raptor engines which might set the thing off.

Also with regard to g-forces on the structure of the MCT, I've described a ~5 g abort acceleration which is comparable to Dragon, this would certainly put a lot of stress of the structure but because the MCT has cargo and only minimal propellant it's mass is half of what it would be at Mars takeoff.  The arrangement of propellent over cargo that I'm assuming means that the thrust structure that supports the propellant is under comparable load and won't collapse onto the cargo.   Likewise when ascending on Mars the rising acceleration is balanced by the falling propellant mass to keep forces under control.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/03/2015 09:23 pm
[LAS lifeboat]

Essentially you've added the cost of developing a 100-person Super-Dragon capsule, with the added cost of integrating it into MCT like a matryoshka doll. (And you rarely actually use it. Most of the time, all of its independent systems are just dead weight. And it won't have the develop-use-update-use pattern that SpaceX prefers.)

If you're going to the expense of developing an extra vehicle, why not just use the 100-person "lifeboat" as a shuttle to ferry passengers to LEO when the MCTs are fuelled and ready to go? It doesn't need to go to Mars.
You come perilously close to one of my ideas: using said Super-Dragon for Earth Abort, Earth Return, as MAV, and as Mars landing propulsion, then returning the main habitat & cargo section of MCT a year later.  I am not yet decided on incorporating that element: It becomes favored if the ISRU equipment has a low propellant mass production ratio, and I don't have firm numbers for that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/04/2015 08:22 am
I agree that this leaves no LAS for the launch from Mars phase of the MCT.  But as others have pointed out, it's debatable whether or not an LAS is needed/useful for an SSTO vehicle (which the MCT is at this point).
Remembering that the point of the MCT is that there IS a colony on Mars, one would assume that there will be a support and rescue service of some form. One of the side effects of "wild west" multi-company independent and only semi-regulated growth in a colony is that it will create a risk level for some colonists that NASA would never accept (and the implications of that will be important in many ways, but not for this thread). I actually suspect that the rescue service will be a private venture too, that's pretty well the point of this colonisation model.

So rescue from an abort capsule will be possible on Mars.

But I agree that the LAS on Mars is not a necessity. There are practical constraints that limit what can actually be achieved and there are some hefty goals here that we don't want thrown out (including affordable settlement generally). SpaceX intends for only small numbers of people to return, so numbers launching back should be low, and I suspect that the risk on the surface of Mars will be far higher than the risk of a launch failure anyway.

If it can be done they'll try though, and it'll be made more possible if it can easily share the same system used for the Earth LAS or an in-transit lifeboat or whatever.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 10/04/2015 07:46 pm
The topic of a Mars ascend LAS is of course highly debatable. If there is no infrastructure to rescue people after an ascend abort, there is no point in aborting in the first place. But if there is already an established colony, that might be a different topic.

If we learned anything from the first shuttle failure, it is that we need to have an abort mechanism. It is not possible to have a system "secure by design" it doesn't work that way. How often do you suppose a return MCT can fail before people think that the Mars Colony is a death trap? I dont know how to come to a conclusion on that topic. Given how strong the influence of that topic is on the design of any MCT, it would be extremely helpful to settle the topic, one way or the other.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/04/2015 09:29 pm
In a previous article, the same author, Richard Heidmann, seems to have fixed on the idea that BFR is an SSTO, that MCT has no main engine, just belly thrusters for landing. That's led to some weird conclusions, and hence the current article.
Of course once you get to 50km or so, you could flip around and use those belly thrusters to achieve Earth Orbit or use them for Mars injection. I mean, a little dumb, but still possible.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/05/2015 04:05 am
We can all agree that MCT is SSTO on MARS, and that means the only means of abort would be disassembly of the vehicle via something like a nose-cone escape crew capsule.

This should be avoided because we shouldn't even HAVE an integrated crew cabin, if the MCT simply has a large cargo hold in which cargo or crew modules are interchangeably placed then it becomes possible to make a powered escape module and place this into the vehicle when ever crew are on board.

This won't weigh down the vehicle when it is serving in a cargo only flight (which will be probably x10 more numerous then crewed flights) and it allows us to change and modify the crew carrying modules for evolving needs and numbers, from small crews which will initially live inside the MCT to future high volume passenger counts which will immediately disembark.

Also note that when aborting to the Mars surface your possible landing sights are very nearly a great circle around Mars as your point of landing varies becomes a track of the landing point of a sub-orbital flight, if it is late in the MCT assent phase and thrust is lost then your looking at a landing sight possibly on the opposite side of the planet from where you launched.  Not a feasible distance from a base for rescue to pick up survivors even if they were landed without a scratch, an extremely difficult matter when your basically performing full EDL which is a process which requires considerable heat-shields and retro-propulsion.

Basically you want to stay WITH the MCT as long as possible as it by necessity is capable of EDL and should be loaded for more then enough propellant to do a landing until very near the point when orbit is achieved, so you may be able to transition directly from a once-around the planet controlled landing abort to an abort to orbit.  If the MCT blows up your just SOL, but the next most likely problem with be Engine-out so I recommend the MCT have abundant surplus engines such that it can sustain one or more engines being lost and still achieve either orbit OR a once-around abort.

A MCT with a 400 mT gross take of mass has a weight of ~1,500 kN which would allow it to ascend on just one Raptor engine, but a single central engine would make the failure of the single engine would leave you with no propulsion.  So I'm looking at two pairs of engines with nominal flight being to ascend on one member of each pair in a diagonal line, in the event of a failure the opposite diagonal  pair engages.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/05/2015 08:14 am
The 4 engine setup makes sense as a failsafe.

I think trying to model how an aircraft handles issues is worthwhile in a SSTO rocket ... expanding from methods for aborting before take off to the options they have if something goes wrong in the first minute of flight and so on (i.e. planes don't need a way of ejecting 100 passengers if something goes wrong). Have options which include aborting to preset locations around Mars, or a full orbit abort, abort to LMO (with a plan to land soon after?), even dropping power 5 seconds after take off to slow down and land (if feasible)... the point being a new set of options that increase safety.

This won't weigh down the vehicle when it is serving in a cargo only flight (which will be probably x10 more numerous then crewed flights) and it allows us to change and modify the crew carrying modules for evolving needs and numbers, from small crews which will initially live inside the MCT to future high volume passenger counts which will immediately disembark.

Does cargo really have the same mass-volume relationship as human "cargo"?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/05/2015 09:38 am

Does cargo really have the same mass-volume relationship as human "cargo"?

So long as the cargo-hold volume is sufficient for the lowest density thing you want to transport then there's no problem, the denser items will just leave some volume unoccupied.  I'm looking at a volume of 500 m^3 for the cargo hold so minimum allowable density is 200 kg/m^3 or about 12.5 lb/ft^3 a number I selected specifically to match the average density of airfreight cargo.

Now lets look at a reasonable habitat analog the ISS Destiny module which masses 14 mT and has a volume of 100 m^3, fill the cargo hold with something that density and your mass if 72 mT which is ball park what we can carry and I'm sure pushing the density up a bit is feasible particularly when a lot of it will be consumables like food and water and we don't need such a big corridor down the middle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/05/2015 10:48 pm
So long as the cargo-hold volume is sufficient for the lowest density thing you want to transport then there's no problem, the denser items will just leave some volume unoccupied.

If the ECLSS for 30 people is twice as big as the ECLSS for 15 people... which I'm not sure is true at all... then splitting the people between 2 MCTs allows the unoccupied volume to be used for personal space for the passengers.

That unoccupied space is very valuable for people, just not valuable for cargo. (I would say for initial missions there is value in pre-assembled Mars-Cars, but otherwise not).

(My question still ties back to the value of 9 cargo MCTs and 1 passenger MCT, vs 10 passenger+cargo MCTs)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/06/2015 12:58 am
That's like asking why do we have airplanes that are full of only people and ones that are full of only air-freight.  That's the nature of every mature transportation system to make a very sharp distinction of between a cargo carrying trip and a passenger trip, it makes the logistics simpler and maximizes passenger comfort.

In spacecraft going to mars we have a huge savings in propellants if we go slow but this is deleterious to human health so we send them fast and freight slow, this is all the incentive we need to segregate passengers and freight trips.  And their is almost certainly a reduction in marginal mass needed as passenger counts grow due to the redundancy needed for probabilistic equipment failure and the ability to time-share public space and amenities, that's why the service is better on a 747 then on a piper-cub.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mme on 10/06/2015 01:40 am
That's like asking why do we have airplanes that are full of only people and ones that are full of only air-freight.  That's the nature of every mature transportation system to make a very sharp distinction of between a cargo carrying trip and a passenger trip, it makes the logistics simpler and maximizes passenger comfort.
...
Virtually all large passenger aircraft also carry cargo because it's nice source of income.  The logistics are not difficult.  Passengers are not inconvenienced by ULD (http://vrr-aviation.com/uld-intro)s that contain cargo.  There are financial advantages to being a "cargo only" airline, dealing with humans is a hassle.  You need to provide food, flight attendants, etc.  But there is no financial advantage to being "passenger only" and the airline business is not one that can afford to leave money on the table.

There may be all sorts of reasons to separate cargo and humans when colonizing Mars, but the airline industry is not a model for doing so.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 10/06/2015 01:52 am
The topic of a Mars ascend LAS is of course highly debatable. If there is no infrastructure to rescue people after an ascend abort, there is no point in aborting in the first place. But if there is already an established colony, that might be a different topic.

If we learned anything from the first shuttle failure, it is that we need to have an abort mechanism. It is not possible to have a system "secure by design" it doesn't work that way.

Well, airliners don't have a LAS, and they carry lots of passengers.

I don't think the shuttle lesson means all manned space systems, forever, must have an LAS.

(and I'd heard that it's questionable whether a practical LAS could have saved the crew in that case due to the speed ... could be wrong though.)


(EDIT for my illiteracy: "feel" and "speed" are different words.... :( )
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 10/06/2015 06:32 am
Cargo MCTs don't need life support.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 10/06/2015 07:03 am
Cargo MCTs don't need life support.

Yes they do. Unless you going to unload and maintained the cargo MCT in pressure suits while on the Martian surface. Also that will excluded the cargo MCT as backup crew deep space habs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/06/2015 08:17 am
No one is going to be unloading cargo by HAND, your going to be using forklifts, scissor-lifts movers and other wheeled equipment to take out large containers which would then be taken into garages or coupled to pressurized areas, this is what we do already on ISS for Christ sake.  The lack of basic knowledge of logistical functions here is maddening sometimes.

MCT doesn't need life-support because their is only a need for ONE vehicle variant which is a universal carrying shell, you put pressurized habitat modules (which has all the life-support equipment in it) in when you want to carry passengers and you put cargo containers in it when you want to carry cargo.  Why is this so hard to understand?  It is infinity more flexible and efficient then any other configuration.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/06/2015 09:18 am
10 or 100 people per flight.

10 people means 10 times the number of manned flights. Which means 10 times the likelihood of a flight with crew loss. Will people say, oh well, it is only 10 people, not 100, that's OK? I doubt it.

Plus that many facilities don't scale linearly so a flight with 100 people will be a lot more efficient.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/06/2015 09:40 am
That's like asking why do we have airplanes that are full of only people and ones that are full of only air-freight.  That's the nature of every mature transportation system to make a very sharp distinction of between a cargo carrying trip and a passenger trip, it makes the logistics simpler and maximizes passenger comfort.

In spacecraft going to mars we have a huge savings in propellants if we go slow but this is deleterious to human health so we send them fast and freight slow, this is all the incentive we need to segregate passengers and freight trips.  And their is almost certainly a reduction in marginal mass needed as passenger counts grow due to the redundancy needed for probabilistic equipment failure and the ability to time-share public space and amenities, that's why the service is better on a 747 then on a piper-cub.
I think that's a fair analogy but raises my reasoning because it doesn't respond to that.

My comment stemmed originally from the intense debate about there not being enough space per person in an MCT, so the concept of unused space on a separate ship is worth exploring. I imagine that there is lots of open space on cargo planes also that your average person would happily use instead of being crammed in economy... but there are far more passenger flights than cargo and not enough money in offering that space in that case.

Then there was a comparison made about having an ECLSS 12 times larger than ISS to handle 12 times the people. (I thought you were saying that actually). Hence my question about whether that's true or whether there are useable efficiencies of scale. meekGee's thread on taking Oxygen and CO2 chemical scrubber certainly implies 10 times the oxygen and scrubbers for 10 times the people, but there's more to it.

I do agree that if the cargo MCTs can be sent on a slow run that's great, provided they can still launch as often. And yes as you and guck fan say you get better facility usage etc if you've got a larger number - and that means you don't need as many spare toilets etc.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/06/2015 07:06 pm
A top mounted thruster system like this would be inherrently stable, unlike landing on a tail engine (F9 booster)....like a helicopter is stable with it's thrust up on top and it's mass hanging below it.

I'm rather surprised that you aren't aware of the Pendulum Fallacy: https://en.wikipedia.org/wiki/Pendulum_rocket_fallacy

Don't be surpised...I never claimed to be a rocket engineer.  ;-)
Although I am a mechanical engineer...but work in liquid and fluids.  Been a long time since my Dynamics class in college.  heheheh.

But thanks for sharing.  Always good to become more educated.

But I don't know that my stated bit about inherent stability is incorrect.  Just not exactly as I stated.

Down farther in the article it talks about "Solution" and the Apollo LAS system.  That's more like what this would be.  The LAS thrusters would be on top of a fairly tall cylinder (not nearly as bad as F9 booster, but still), and would be pressure fed fast reacting powerful engines.  The engines would be canted outwards and downwards.  And can react to keep the stack upright during hover and landing.  In that, would it not be similar to a helicopter?  Why is a helicopter more stable than something like the LLRV? Why does a bamboo-copter work with the shaft haning down, but not with it pointed up? (with reversed blade pitch)
And in this way I think they'd act more like the F9 core grid fins, which are placed up high to provide force (via air resistance rather than a jet of thrust) to help stabilize the core for landing.
I don't know that Goddard's rocket concept is quite the same thing?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/06/2015 07:30 pm
Nice concept. But quite frankly, I like the concept developed in L2 better.

If you aren't willing to show/share it, don't bring it up here. This kind of information sand boxing is why I'm not joining L2 anytime soon. Just my personal opinion...

Lobo:  Is that L2 vehicle concept posted anywhere where us plebs can read it?

As I'm sure you remember I favor the 2nd of your scenarios, "Another is launching MCT dry on a 2nd stage rather than the integrated design, with just enough propellant to power it's LAS engines.  So the whole dry MCT is aborted and lands.  For a nominal launch, it docks with the depot, and the 2nd stage does it's own EDL and returns to launch site."


Lars, Impaler,

There's nothing really L2-ish about the concepts the "team" I'm a part of has been posting on L2.  I think mainly the other members preferred the smaller L2 viewership than the public forum as the feed back is usually a little more focused.  Things can get more tangential on the public forum.
Plus there's some SpaceX employees and other who'll comment on L2, but don't on the public forum.
Hyperion5 is really the guy who usually is the "spokesman".

But I can answer questions and comment on it, just from my working with the team.  I guess technically the L2 discussions by others need to stay there...but again, this is just some of our work for fun.  There's nothing "secret" about it or anything.  So ask if you have a question.  :-)   

Impaler,

In a nut shell, we've been looking at 3 concepts.
A SuperDragon type large capsule was the initial favorite of the rest of the Team.  Very much like you described.  It's big advantage is that is has a conservative reentry profile like a capsule.  The main draw back is you need to have engine doors in your heat shield.  Not for landing, that's done with a combination LAS/landing thruster system very much like Dragon 2.  But for taking off again, and in-space burns.
Also, a biconic which essentially does the same thing as the Capsule, but with a biconic EDL profile, which is more complex than a Capsule.  But it has better L/D ratio and you don't need doors in your heat shield for your engines.

But the integrated biconic design that you and I discussed/debated back thread seems to be the one coming out on top for many of the reasons I suspected it would.  But the design is more refined as we've investigated it.  It has the best efficiency to LEO (as it's just one stage instead of two, so no mass is duplicated like a dedicated 2nd stage).  We've added an LAS to the top, as I've discussed here.  My original Integrated biconic concept didn't have an LAS.  But the difficulties of landing on a vacuum Raptor on Earth meant some means of landing would need to be added.  Vacuum Raptor can land on Mars, but would need a retractable nozzle or separate landing thrusters or something to land on Earth.  So we've been looking at having the nose lifeboat abort engines also double as landing engines on Earth, and landing assist on Mars.
Looks like it will mass around that of the Super Capsule concept, but a little more than the Non Integrated Biconic with the dedicated S2.   It also is the most simple, with just 2 pieces to develop rather than 3.  It can do duty as a tanker, depot, and satellite launcher too...with variants of the Mars vehicle.

But the Super Capsule is the most mature concept.  The two biconics are still being played with.


As far as visualization.  For the SuperDragon MCT and Non integrated biconic MCT, just picture a 12m wide Raptor powered reusable booster, with some sort of 2nd stage with 3 vacuum Raptors in a tripod configuration with a cental [new] methalox landing engine to land it.  It 's still in the works, but it will probably look similar to the Falcon 9 reusable upper stage concept of SpaceX's..just with a central landing engine.
Then on top, you have a really big Dragon 2, or a biconic.

For the Integrated biconic, it'd look like this, but on top of that 12m booster, when sitting on the pad.
 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/06/2015 07:46 pm
I'd like to offer a completely different MCT LAS for consideration:

Considering that the MCT will certainly have high efficiency Methalox engine(s) for its main thrust (and perhaps landing?) the issue seems to be the delay time required to 'spin up' the turbines in the case of a mid flight abort.  So this means that the MCT really only needs a short burst (<4-5 seconds?) of high thrust  (5gs?) to pull it safely away from a disintegrating 1st stage.  Correct?

So, how about placing an LAS set of engines, with associated fuel, in the interstage between the booster and the MCT?  Under normal conditions, the MCT would stage, leaving the interstage attached to the booster, and  the booster plus interstage/LAS would RTLS and be completely reused.  Under abort conditions, the LAS engines would fire and the interstage/LAS would separate from the booster and propel the MCT a distance away.  The MCT main engine(s) (Raptors?) would spin up during this LAS firing period, then the MCT would detach from the interstage and proceed to do an abort landing.

The LAS could be fast acting, high thrust (poor ISP) hypergols, or even (gulp) solids.  This system wouldn't need to be very massive, given its short firing duration, but it would admittedly still be considerable parasitic mass hurting the RTLS effort.

I like this idea because (1) no parasitic mass going to orbit and beyond, penalizing the whole system, (2) entire system is reusable, and (3) unlike 'puller' LAS systems, you don't require that the LAS system cleanly separate from the manned portion as an additional staging event, lest you have LOM.

Thoughts?

Originally I thought of this for the lifeboat LAS on the IBMCT.  One issue with it is over pressure, you probably need blow out panels or something otherwise you could get an overpressure in the interstage and damage the bottom of the lifeboat.  I think the CST-100 LAS has something like that.

But I think we're moving them outside to eliminate that concept, and then so they can be used for landing assistance.
A large Capsule design could have the LAS outside like Dragon 2 for abort and for landing.  It has the disadvantage if having these inefficient engines have to slow down the MCT during MArs EDL.  It's not an issue of Earth because of the much slower terminal velocity, but on MArs, you are still supersonic at terminal velocity.  The large Capsule LAS/landing engines have cosine losses, and cannot have very large nozzles due to size constrains in their mounting...like Superdracos can't.
With the biconics, they can actually use the much more efficient Raptor to provide all that dV, and then actually land on Raptor, and/or cut in the LAS thrusters for hover and landing. 

GORDAP - I like it! If abort is only practical for Earth launch, it is an elegant solution.

The MCT will somehow need to be able to use Methalox for its thrusters - not sure how that will work. Would there be smaller LOX and Methane containers that are pressurized at high pressure (continuously refilled from the main tanks) that feed the maneuvering thrusters? One could also imagine such a system could be scaled up for abort/landing thrusters.

Separate pressurized tanks for the LAS/landing engines.  So they will be fast acting and responsive.  They would be filled on the pad on Earth, and then filled from the main tanks on Mars prior to ascent. 
They could be drained to the main tanks for the cruise to Mars, and then refilled  before Mars EDL.  Ditto for the return trip.  That way the cryo's don't need to be stored in the separate tanks for very long.  That would be figured out in development.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/06/2015 07:55 pm
[LAS lifeboat]

Essentially you've added the cost of developing a 100-person Super-Dragon capsule, with the added cost of integrating it into MCT like a matryoshka doll. (And you rarely actually use it. Most of the time, all of its independent systems are just dead weight. And it won't have the develop-use-update-use pattern that SpaceX prefers.)

If you're going to the expense of developing an extra vehicle, why not just use the 100-person "lifeboat" as a shuttle to ferry passengers to LEO when the MCTs are fuelled and ready to go? It doesn't need to go to Mars.

That was actually my original thought.   Not to have an LAS on the Integrated Biconic MCT.  Others thought it needed it, as later during colonization they'd want to launch all 100 people on the MCT rather than have a separate ferry.
For early exploration missions Dragon 2 would be sufficient, no separate system needed as crews will only be maybe 6-7.

But again, others felt it should have one.  And I see their logic.

Also, without one, MCT will need a way to land on Earth.  It can land on Mars on vacuum Raptor, but not at sea level.  You may need separate landing thrusters -anyway-, this is a way to get double duty out of them. 

The lifeboat would be similar to Heidmann's concept Lars posted a page or two back.  A flight deck in the nose with a bulkhead and hatch between it and the rest of the hab.  Not much more to it that that.  Not quite like a separate spacecraft.  It'd just have a traditional biconic EDL profile if separated. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/06/2015 07:58 pm
The difference is, that in an abort, the MCT (assuming it is its own second stage) has to be abortet including its entire mass of fuel. I  think I remember that the dry mass of the MCT is about 20 % of its wett mass. So the 3g in normal operation would be reached near dry mass. The 5 g abort would be reached at wett mass. The force on the metal structure is F=m*a, mass times acceleration. Wett mass is 5 times dry mass, acceleration is higher, and air resistance is higher. So during about, the structure of MCT must take I would guess more than 10 times the force of normal operation. The metal structure must be sized accordingly.

Semmel,

Not, not exactly.  An integrated biconic MCT would be impractical to abort the entire thing as it's main tanks may be loaded with propellant.  Rather it would have a separable noze section with more reasonably sized LAS thrusters, which would double as landing engines if there's no abort, as the whole integrated biconic MCT would be landed pretty much empty.  So they can abort the lifeboat, or land the whole craft on Earth, and on Mars with Raptor doing most of the desceleration from terminal velocity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/06/2015 08:11 pm

In the one stage BFR your looking at the combo 2nd stage MCT vehicle is going to be considerably more massive then the smaller and un-fueled one I'm looking at, that will mean probably 3x more thrust needed for separation.  Rather then the 9 million N I'm estimating for a 200 mT MCT your looking at 27 million N, the thrust of 12 raptor engines.  I see a problem with rapidly initiating that much thrust INSIDE the interstate when the vehicle is still assembled, it would be like setting off a bomb.  So the thrust must be vented laterally with Dragon like canted rocket nozzles along the perimeter of the inter-stage.  With the cosine loss were looking at something like 400 Super Draco equivalent rockets.  Do able probably by having multiple bands of nozzles such that the entire outer surface of the inter-stage is nozzles.  But we should be aware that were increasing the number of parasitic engines, though they parasatizing the first stage rather then the 2nd which means they count for only 1/10th as much in final payload.

No, a separable lifeboat with externally mounted engines.  Which will do double duty to land.  Aborting a fully fueled integrated MCT would be impractical.  A separate LEO taxi would be a much better solution if you didn't want a separable lifeboat.

Also, looks like dry mass of the Integrated biconic won't be much too more than that of the non integrated biconic.   It's a little longer, but the extra tank alloy and additional TPS to cover it doesn't add a lot of mass.  And it's much more efficient to LEO.  It's less efficient after that because it is a little heavier, but that's not too big of an issue because you have fuel in LEO, and fuel on the Mars surface.  So you just need to put a little more in orbit, and make a little more on the surface.  Where this an Apollo type mission where you had to bring all of your return propellant with you, then every kg of mass is critical.  Then multiple stages give a definate advantage.

The decisive factor I think is that in a 2 stage BFR with the abort engines atop the 2nd stage and below a smaller MCT is that you can abort during both first AND second stage burn.  You only give up the abort motor once full Earth orbit has been achieved.  Where as with a one stage BFR your in a black zone after first stage separation and yet your still attached to a potential bomb which has 6-7 raptor engines which might set the thing off.

can do that with the separable lifeboat nose.
Also, can do an abort on approach to Mars or Earth if there was a problem with the whole MCT.  The nose could do it's own EDL.  Obviously there'd have to be some resources available on Mars or aborting to the surface just means a slow death marooned on the surface.  But if it has 100 people, that means there will be a whole colony already there.  If it had just an exploration crew, the lifeboat would be large enough to support a small crew for at least some time.  Hopefully there'd be like a backup MCT already placed there, like MArs Direct and Semi-Direct.  Abort options are dependent on that. 

The main advantages of the 3-piece MCT's is that then aborting the entire MCT becomes an option, because you launch it dry other than the abort propellant.  You don't need a separable design.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/06/2015 08:25 pm
6 posts in a row? Is there some obscure forum record you are trying to break, Lobo? ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/06/2015 09:35 pm
Ok let me just touch base on terminology and what looks to be a set of acronyms that will describe them.

Super Dragon Mars Colonial Transport (SDMCT):  A dragon shaped vehicle which lands with a bottom side heat-shield and is powered by either side-wall engines or a heat-shield penetrating central engine.  It launches on a 2 stage rocket which is essentially an enormous F9 colloquially known as the BFR.  Least imaginative design, initially popular with many but now falling out of favor.  Would abort as Dragon dose by pushing away the whole vehicle from the 2nd stage.

Separate Bi-conic Mars Colonial Transport (SBMCT): A obviously bi-conic vehicle with bottom mounted engines and a horizontal high lift entry orientation that keeps engines and other systems in the rear.  Propellant would be in the nose of the vehicle and cargo in the base just above engines.  Launches on top of a conventional 2 stage rocket comparable to the SDMCT.  Would abort similar to SDMCT by pushing the whole vehicle away from the 2nd stage.  Designed around single stage to Low Mars orbit and a 'semi-direct' like architecture.  My currently preferred solution.

Integrated Bi-conic Mars Colonial Transport (IBMCT) A modification of the SBMCT which 'integrates' it with the 2nd stage of the rocket it would launch on such that their is a bi-conic nose and a cylindrical aft body, the tip of the nose is an abort capsule, the next section down is cargo and propellant fills the cylinder.  Launches on a single stage rocket which is similar to the first stages of the alternative configurations.  Designed specifically for Single stage Direct Earth return.  Lobo and others currently preferred solution.

Dose that look like an accurate depiction of the current positions?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/06/2015 10:27 pm
6 posts in a row? Is there some obscure forum record you are trying to break, Lobo? ;)

Sorry, I hadn't caught up in the last few days so was trying to catch up today.  :-)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/06/2015 10:50 pm
Ok let me just touch base on terminology and what looks to be a set of acronyms that will describe them.

Super Dragon Mars Colonial Transport (SDMCT):  A dragon shaped vehicle which lands with a bottom side heat-shield and is powered by either side-wall engines or a heat-shield penetrating central engine.  It launches on a 2 stage rocket which is essentially an enormous F9 colloquially known as the BFR.  Least imaginative design, initially popular with many but now falling out of favor.  Would abort as Dragon dose by pushing away the whole vehicle from the 2nd stage.

Separate Bi-conic Mars Colonial Transport (SBMCT): A obviously bi-conic vehicle with bottom mounted engines and a horizontal high lift entry orientation that keeps engines and other systems in the rear.  Propellant would be in the nose of the vehicle and cargo in the base just above engines.  Launches on top of a conventional 2 stage rocket comparable to the SDMCT.  Would abort similar to SDMCT by pushing the whole vehicle away from the 2nd stage.  Designed around single stage to Low Mars orbit and a 'semi-direct' like architecture.  My currently preferred solution.

Integrated Bi-conic Mars Colonial Transport (IBMCT) A modification of the SBMCT which 'integrates' it with the 2nd stage of the rocket it would launch on such that their is a bi-conic nose and a cylindrical aft body, the tip of the nose is an abort capsule, the next section down is cargo and propellant fills the cylinder.  Launches on a single stage rocket which is similar to the first stages of the alternative configurations.  Designed specifically for Single stage Direct Earth return.  Lobo and others currently preferred solution.

Dose that look like an accurate depiction of the current positions?

Yup, pretty close.  Except we've been referring to #2 as a "Non-Integrated Biconic MCT" or "NIBMCT", just for clarity between the two biconics.  And at least so far we've assumed crew and cargo on top of the tanks, not below.  This could actually be a full biconic...essentailly a capsule shape but nose/side entry (see McDonnell-Douglas X-33 biconic concept below)  Or it could be a cylinder with a biconic nose like the IBMCT...just shorter due to the smaller tanks, and with two Raptors rather than 3.
It could have a full vehicle LAS like the Super Dragon with LAS engines located in the MPS around the Raptors, or actually have a separable upper section too.  The biconics can do that because they take the TPS with them.  If you separate a capsule you leave the TPS behind and so you need to have another...which adds more mass...although it's certainly possible.

Super Dragon is the most mature, followed by IBMCT and then NIBMCT. 

There's still some debate about how much of the top of IBMCT (or NIBMCT) to take off with the LAS.  Just a "flight deck" in the nose?  Which could hold just 100 people (see Heidmann's concept Lars posted), or a crew of 7 plus a fair amount of hab space for exploration crews?  Or the flight deck plus the cylindrical hab volume below it?  So all the hab/ECLSS/etc stays with the lifeboat rather than being split apart?  As it probably wouldn't add too much mass?
Or everything north of the tanks, including cargo deck?  This seems unlikely because in exploration missions, the cargo would be mainly surface equipment and unneeded to keep with the abort for Earth ascent, and it would be left on the Mars surface for a Mars ascent abort anyway....and could add maybe 50mt of added mass that the LAS needs to pull away.
The argument for it is that could be millions of dollars of equipment, and SpaceX may want to keep it in case of abort to use for another mission.

I suppose it really depends on how big the LAS system needs to be to land the whole vehicle on Earth.  At that size, how much can it abort?  Just the nose?  The nose + hab cylinder?  The nose + hab cylinder + cargo deck?  If it's already big enough to land on Earth that it can abort everything north of the tanks, then why not?  But kinda doubt it will be.  Landing is much less dV than for a fast abort away from an exploding booster I think.
But we've not investigated it that far yet.

The Full vehicle aborts of SDMCT and NIBMCT-option, of course do keep all the cargo along with the whole vehicle.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/06/2015 11:03 pm
We can all agree that MCT is SSTO on MARS, and that means the only means of abort would be disassembly of the vehicle via something like a nose-cone escape crew capsule.

This should be avoided because we shouldn't even HAVE an integrated crew cabin, if the MCT simply has a large cargo hold in which cargo or crew modules are interchangeably placed then it becomes possible to make a powered escape module and place this into the vehicle when ever crew are on board.

This won't weigh down the vehicle when it is serving in a cargo only flight (which will be probably x10 more numerous then crewed flights) and it allows us to change and modify the crew carrying modules for evolving needs and numbers, from small crews which will initially live inside the MCT to future high volume passenger counts which will immediately disembark.

Also note that when aborting to the Mars surface your possible landing sights are very nearly a great circle around Mars as your point of landing varies becomes a track of the landing point of a sub-orbital flight, if it is late in the MCT assent phase and thrust is lost then your looking at a landing sight possibly on the opposite side of the planet from where you launched.  Not a feasible distance from a base for rescue to pick up survivors even if they were landed without a scratch, an extremely difficult matter when your basically performing full EDL which is a process which requires considerable heat-shields and retro-propulsion.


That last is where a separable lifeboat LAS has an advantage.  Since MCT is a SSTO for Mars ascent, if there's an explosive problem with the main propulsion system, the crew is lost.  That'd be the case for full vehicle abort of the SDMCT and NIBMCT.  The LAS lifeboat can get away and then "fly" down range to a landing spot within it's ascent trajectory.  What they do when they land safely is another story.

If in the early exploration phase, the returning crew is small.  If the lifeboat is of sufficient size to support them until they can get to a backup vehicle somewhere else on the surface, then that would be good.  If later in colonization phase, there'd be a full colony with presumably long range rovers that could be dispatched for rescue.  The returning MCT should only have a small crew though, as most would be colonists left there.  So you really shouldnt' have to rescue 100 people, unless there's some abort from orbit and the lifeboat lands somewhere far away form the intended LZ 

The IBMCT would have 3 Raptors, but only two are needed for Mars ascent (maybe only one).  It has 3 because 3 are needed to get it from booster staging to LEO.  So it has engine-out backup for Mars EDL (with LAS assist) and it has engine out backup for Mars ascent.  And if the MPS exploded, it's LAS can abort the lifeboat away.

The SDMCT and NIBMCT have only two engines, as they don't do Earth ascent.  If there's an engine out at Mars ascent, there's some issue of how to handle it.  One engine thrusting at full throttle should keep it aloft long enough to burn off enough propellant so the LAS system can land it again for an emergency landing.  It might not be able to get to orbit, but it should be able to do a controlled emergency landing.  And it depends when the engine were to fail, far enough up just one engine should still get it home.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/06/2015 11:26 pm
No one is going to be unloading cargo by HAND, your going to be using forklifts, scissor-lifts movers and other wheeled equipment to take out large containers which would then be taken into garages or coupled to pressurized areas, this is what we do already on ISS for Christ sake.  The lack of basic knowledge of logistical functions here is maddening sometimes.

MCT doesn't need life-support because their is only a need for ONE vehicle variant which is a universal carrying shell, you put pressurized habitat modules (which has all the life-support equipment in it) in when you want to carry passengers and you put cargo containers in it when you want to carry cargo.  Why is this so hard to understand?  It is infinity more flexible and efficient then any other configuration.

And you have nothing in it to be a tanker (perhaps stretched tanks within the same Outer Mold Lines).  Just a big empty volume.

And you have some cryo-refrigeration equipment in it as a depot.

And you put a payload bay behind the nose to deploy FH and D4H class satellites to GTO.  The vehicle then comes back around on the GTO eliptical orbit to Earth, where it does a small deorbit burn and does Earth EDL.  Not expendable PLF required.

The working idea is that all concepts would have a Dragon 2 like nose hatch (maybe about 5m wide or so) under which could be a docking collar.  Tanker and depot dock in LEO and proceed to do a slow spin to settle propellants in the bottom of the tanks where it can then be pumped from the tanker to the depot, and later from the depot to MCT.  Propellant lines would run from the nose to the tanks.  (unless there's a way to pump liquids in zero g without using centrifugal forces?  That's a bit of a gray area.)
The crew MCT would also have an access tunnel for access to the flight deck and on through to the hab area below it.
The Sat launcher would have a payload bay under the nose cap instead of a docking collar or access tunnel.  Something like Rocketplane Kistler K-1 (below).  The sat launcher has no need to refuel, so no need for a docking collar installed.
OML's are the same.

This is where I prefer the IBMCT.  Just one vehicle, rather than than two including the dedicated SII.  It's not an expendable "dumb" stage, it has to be it's own LEO reusable spacecraft in it's own right.  And may or may not share much with the booster and MCT.  There's extra cost in that.
The IBMCT would have the same tank tooling, bulkheads, etc as the booster.  So just 2 pieces with a lot of commonality.  That wouldn't be the case for the Super Capsule.  And may or may not be for NIBMCT depending on it's design.  If a full biconic, then it won't share much with anything else.  If a cylinder/biconic then it might, but it will run into issues that using booster sized tank tooling and domes will make the LOX tanks too big using 12m domes, because the tanks are smaller than IBMCT.  So you might need custom tankage anyway.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/06/2015 11:38 pm
I still think it makes little sense to have a LAS on a Mars SSTO such as "MCT". And in that case, it really makes no sense to put the crew (and cargo?) on top. It produces significant operational difficulties during when ground handling the vehicle on Mars.

One significant factor that needs to be taken into account for a biconic vehicle (which I advocate) is a the mass distribution. It needs to be have the proper balance when almost empty (normal atmospheric entry & landing), and it needs to be able to also have the proper balance for a near full propellant load. (Earth or Mars abort) Also, when near empty of propellant the vehicle must also be properly balanced for a full cargo load vs empty.

To handle this range, the layout that makes most sense (IMO) is to put the cargo/crew in the middle of the vehicle - with the LOX tank above, and Methane tank below. This would allow a balanced biconic sideways reentry with ANY cargo load, and ANY propellant load.

EDIT: See image below for how that might look, in this DC-Y(?) drawing:
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 10/06/2015 11:55 pm
The first generation MCT is only going to carry a small crew, not the 100 passengers needed for colonization. So, instead of a separate LAS, the crew can ride up on a Dragon to meet the MCT in orbit.

Once the BFR and MCT stack is shown to be reliable, the crew can launch with the MCT.

Economics and insurance might demand a LAS even if the engineers don't think it is needed. Since we're talking about private spaceflight instead of the government, I'm sure they will need a LAS for the crew. Look at how much it costs the airlines when they are sued after a fatal crash. It might also be hard to find more colonists after 100 die in a BFR explosion.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/07/2015 12:09 am
The returning MCT should only have a small crew though, as most would be colonists left there.

Is there any reason to assume there is a "crew" vs "colonists"?
I think of them all as passengers.... does "crew" imply active employees of the SpaceX Transport?

We believe that the system will be mostly (all?) automated, and we know that the radiation maximums will prevent someone making several Earth-Mars trips (or even one!). So while some people will go back, I'm not sure there's a crew.

The working idea is that all concepts would have a Dragon 2 like nose hatch (maybe about 5m wide or so) under which could be a docking collar.  Tanker and depot dock in LEO and proceed to do a slow spin to settle propellants in the bottom of the tanks where it can then be pumped from the tanker to the depot, and later from the depot to MCT. 

Elon said at one stage that the MCT would go up first and then have tankers top it up. An interim depot adds complexity but reduces wait-time for passengers - and I can see it'd be safer for passengers to have a single depot fill-up.

Would you mind sharing the thought processes here?
(and thanks for all the thought sharing you've done here, L2 as well as the work itself!)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/07/2015 12:34 am
Isn't LOX heavier than Liquid methane? Also it will take twice the lox to burn the methane.  So shouldn't the Lox tank be on bottom with the Methane on top?   I also like the idea of a plug nozzle engine as depicted in the sketch.  It is not only a good engine all the way from ground to vacuum, but it can also become the heat shield when coming through the atmosphere from space.  Yes debris can flash back when landing on Mars, however, one could just have longer landing legs, that can retract after landing to lower the spacecraft.  Then raise the craft back up for take off. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/07/2015 02:33 am

That last is where a separable lifeboat LAS has an advantage.  Since MCT is a SSTO for Mars ascent, if there's an explosive problem with the main propulsion system, the crew is lost.  That'd be the case for full vehicle abort of the SDMCT and NIBMCT.  The LAS lifeboat can get away and then "fly" down range to a landing spot within it's ascent trajectory.  What they do when they land safely is another story.

If in the early exploration phase, the returning crew is small.  If the lifeboat is of sufficient size to support them until they can get to a backup vehicle somewhere else on the surface, then that would be good.  If later in colonization phase, there'd be a full colony with presumably long range rovers that could be dispatched for rescue.  The returning MCT should only have a small crew though, as most would be colonists left there.  So you really shouldnt' have to rescue 100 people, unless there's some abort from orbit and the lifeboat lands somewhere far away form the intended LZ 

The IBMCT would have 3 Raptors, but only two are needed for Mars ascent (maybe only one).  It has 3 because 3 are needed to get it from booster staging to LEO.  So it has engine-out backup for Mars EDL (with LAS assist) and it has engine out backup for Mars ascent.  And if the MPS exploded, it's LAS can abort the lifeboat away.

The SDMCT and NIBMCT have only two engines, as they don't do Earth ascent.  If there's an engine out at Mars ascent, there's some issue of how to handle it.  One engine thrusting at full throttle should keep it aloft long enough to burn off enough propellant so the LAS system can land it again for an emergency landing.  It might not be able to get to orbit, but it should be able to do a controlled emergency landing.  And it depends when the engine were to fail, far enough up just one engine should still get it home.

In Early exploration any abort to surface is fatal because their is zero rescue infrastructure on the surface and no conceivable capsule could carry sufficient supplies to see them through more then a few days.  So I consider this a pointless abort.  By the time you have an infrastructure to do surface rescue your passenger count is much too high for the small capsule your proposing, it would need to be a large vehicle comprising a significant portion of the whole mass of the vehicle and would present great difficulty in landing as you going to be falling on a ballistic trajectory from a high altitude and need massive retro-propulsion to not impact the surface, it in no way resembles the kind of un-powered capsule landing that can be done on Earth.

IF your using a semi-direct architecture and their is a waiting transit vehicle in mars orbit then abort to orbit may be viable, in a direct earth return architecture anything greater then mars escape velocity but short of the target trajectory is a heliocentric orbit that misses the Earth giving you a long slow death in space.

Also note that in my Separate Bi-conic concept their are 4 raptor engines with mars assent being possible with either diagonal pair so engine out capability is their during mars assent.  The same 4 raptor engines give you whole vehicle abort on launch from Earth because your intentionally not filling propellant tanks to full to keep mass low enough for fast full abort after a brief 1 second burn from the inter-stage pusher system described earlier by GORDAP.



And you have nothing in it to be a tanker (perhaps stretched tanks within the same Outer Mold Lines).  Just a big empty volume.

And you have some cryo-refrigeration equipment in it as a depot.

And you put a payload bay behind the nose to deploy FH and D4H class satellites to GTO.  The vehicle then comes back around on the GTO eliptical orbit to Earth, where it does a small deorbit burn and does Earth EDL.  Not expendable PLF required.

The working idea is that all concepts would have a Dragon 2 like nose hatch (maybe about 5m wide or so) under which could be a docking collar.  Tanker and depot dock in LEO and proceed to do a slow spin to settle propellants in the bottom of the tanks where it can then be pumped from the tanker to the depot, and later from the depot to MCT.  Propellant lines would run from the nose to the tanks.  (unless there's a way to pump liquids in zero g without using centrifugal forces?  That's a bit of a gray area.)
The crew MCT would also have an access tunnel for access to the flight deck and on through to the hab area below it.
The Sat launcher would have a payload bay under the nose cap instead of a docking collar or access tunnel.  Something like Rocketplane Kistler K-1 (below).  The sat launcher has no need to refuel, so no need for a docking collar installed.
OML's are the same.

This is where I prefer the IBMCT.  Just one vehicle, rather than than two including the dedicated SII.  It's not an expendable "dumb" stage, it has to be it's own LEO reusable spacecraft in it's own right.  And may or may not share much with the booster and MCT.  There's extra cost in that.
The IBMCT would have the same tank tooling, bulkheads, etc as the booster.  So just 2 pieces with a lot of commonality.  That wouldn't be the case for the Super Capsule.  And may or may not be for NIBMCT depending on it's design.  If a full biconic, then it won't share much with anything else.  If a cylinder/biconic then it might, but it will run into issues that using booster sized tank tooling and domes will make the LOX tanks too big using 12m domes, because the tanks are smaller than IBMCT.  So you might need custom tankage anyway.



I've said all along that an elongated 2nd stage would do tanker duty, and depots are in my opinion unnecessary, the MCT will act as it's own depot taking on propellants from visiting 2nd stages until it is full.  As MCT must depart Earth with some propellant for EDL at mars and must then hold significant amounts while on the martian surface (which while cold is still warmer then cryogenic LOX), so the MCT will have to have significant long-term cryo-storage capabilities likely through a combination of insulation and cryo-coolers, thus it makes an excellent depot. 

These cryo-systems along with radiators and solar arrays are the only systems that I would integrated into the vehicle.  Human habitats placed into the MCT are simply plugged into these utilities much like an RV.

As for the BFR I am looking at a 10 m core and 2nd stage, 19 Raptors on the core and 7 on the 2nd stage.  Gross take off mass of ~5,000 mT which would put 100 mT payload into LEO after reuse penalty which I'm estimating at 50% (first stage RTLS, 2nd once around the Earth to land at launch site).  This configuration would be used for conventional payload at the top in a fairing com-sat launches (3 at a time 10 mT each to GTO) as well as the any other high payload missions NASA can find and SpaceX's own LEO satellite swarms and finally with the stretched 2nd stage as the tanker delivery configuration with 100 mT of residual propellants to transfer.  Ideally we someday use this configuration to launch containerized cargo which will be loaded into the MCT in space so no longer have to launch the cargo and vehicle together.  This configuration is designed to maximize speed of turn around by minimizing waiting time to reassemble the vehicle and allows payloads to be readied separately and then mated to the 2nd stage just prior to launch.

A second higher power configuration is needed to launch the MCT when loaded with cargo but these are so infrequent (even if we were doing nothing but mars related launches propellant launches would be 3-4 times greater then MCT launches) it doesn't make sense to design the whole vehicle to do this one thing at the expense of smaller launches, rather is is a like today's modular rockets in which we boost the performance on only the edge cases with boosters.  In this case we use the F9H side booster and give it 4 Raptor engines making is very much resemble a Zenit booster, 6 of these raise the gross take off mass to ~7,200 mT and more then double the thrust, the boosters do a RTLS but the core will now be doing downrange landing.  With all the stops pulled out the payload should be over 200 mT to LEO which puts the MCT into orbit.


I don't know if you saw it earlier but I did a mass brake down of my MCT concept.  I'd like to see what the IBMCT comes out at.


Thermal protection at 5 kg/ m^2 over an area of 650 m^2:  5 mT

Tanks and Plumbing 5% of 300 mT propellant mass:  15 mT

Landing legs, 10% of touch down mass: 18 mT

4 Raptor Engines at 150:1 T:W ratio:  6 mT

Vernier Engines that can hover on landing at 100:1 T:W ratio:  1 mT

Solar, Radiator and computer systems:  5 mT

Structural skeleton, 1/3rd of dry mass: 25 mT

Total 75 mT dry mass
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/07/2015 04:40 am
In Early exploration any abort to surface is fatal because their is zero rescue infrastructure on the surface and no conceivable capsule could carry sufficient supplies to see them through more then a few days.  So I consider this a pointless abort. By the time you have an infrastructure to do surface rescue your passenger count is much too high for the small capsule your proposing, it would need to be a large vehicle comprising a significant portion of the whole mass of the vehicle and would present great difficulty in landing as you going to be falling on a ballistic trajectory from a high altitude and need massive retro-propulsion to not impact the surface, it in no way resembles the kind of un-powered capsule landing that can be done on Earth.

This. You put it better than I could have. This is why IMO the way to increase safety for the MCT is to make he whole thing abort capable, through added redundancies in propulsion and systems.

If a MCT has to abort during a Mars ascent and land far down-range, the crew can survive for an *extended* period in the MCT. Not in a small capsule where everyone is squeezed into. Designing in a pointless separable abort capsule leads you down the path of terrible engineering trade-offs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 10/07/2015 05:35 am
I don't know if you saw it earlier but I did a mass brake down of my MCT concept.  I'd like to see what the IBMCT comes out at.


Thermal protection at 5 kg/ m^2 over an area of 650 m^2:  5 mT

Tanks and Plumbing 5% of 300 mT propellant mass:  15 mT

Landing legs, 10% of touch down mass: 18 mT

4 Raptor Engines at 150:1 T:W ratio:  6 mT

Vernier Engines that can hover on landing at 100:1 T:W ratio:  1 mT

Solar, Radiator and computer systems:  5 mT

Structural skeleton, 1/3rd of dry mass: 25 mT

Total 75 mT dry mass

How do you intend to return to Earth with that?

In fact, how do you get 100t payload to Mars with it?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/07/2015 05:54 am
A SEP transit vehicle that takes you to high earth orbit followed by a perigee burn near Earth to send you to Mars, the SEP vehicle flies independently to mars and you rendevoue with it on low mars orbit to return to a high Earth orbit where crew disembark on a Dragon capsule.  The bi-conic just dose mars assent with a 25 mT habitat inside pluss a modest landing propellent reserve. The intent is to ultimatly be able to do a rapid cycle between mars surface and low orbit, loading cargo and orbit and unloading on the surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/07/2015 04:26 pm
In Early exploration any abort to surface is fatal because their is zero rescue infrastructure on the surface and no conceivable capsule could carry sufficient supplies to see them through more then a few days.  So I consider this a pointless abort. By the time you have an infrastructure to do surface rescue your passenger count is much too high for the small capsule your proposing, it would need to be a large vehicle comprising a significant portion of the whole mass of the vehicle and would present great difficulty in landing as you going to be falling on a ballistic trajectory from a high altitude and need massive retro-propulsion to not impact the surface, it in no way resembles the kind of un-powered capsule landing that can be done on Earth.

This. You put it better than I could have. This is why IMO the way to increase safety for the MCT is to make he whole thing abort capable, through added redundancies in propulsion and systems.

If a MCT has to abort during a Mars ascent and land far down-range, the crew can survive for an *extended* period in the MCT. Not in a small capsule where everyone is squeezed into. Designing in a pointless separable abort capsule leads you down the path of terrible engineering trade-offs.

I'm not sure I agree with that.

Ok, so let's say you have a 12.5m wide IBMCT (our working diameter for it and the booster).  A separable nose would be 12.5m wide at the base, tapering down.  So you'd have quite a lot of volume there for a small crew returning from Mars if they had to abort and land down range.  For 100 people, yea, it's not going to keep them for very long, but for a crew of 5-7?  Should be just fine.  In fact, that may be the only hab space they need/have for exploration missions, with everything below for surface cargo.  That's a volume twice as wide as Skylab op the base, and probably about the same height as the Skylab pressurized volume.  There's no squeezing involved.
They would have provisions and supplies sufficient for the 4-6 month transit back to Earth, so they should be ok for quite awhile.

Then you have the question of what sort of contingency plan do you want to have in place to deal with them at that point.  That's really a separate discussion.  Maybe a remote operated large pressurized rover that could drive itself over to the lifeboat, to give them transportation to a supply cache somewhere pre-positioned for such a contingency?

In a situation where they are transporting 100 people to Mars, obviously 100 people won't be coming back home, so there will be far fewer people on it.  Probably just some SpaceX employees or NASA personnel returning home after a tour of serving at the colony, and a few people who have either become more ill than can be treated on Mars, or have changed their minds and want to go home.   But even if it were more people, with a colony on Mars, rescue could be dispatched anywhere on the globe, it's just a matter of how long it would take to get there, so the lifeboat would need to be set up to support X number of people of Y length of time needed to get rescue there.

As far as whole vehicle abort goes, there really is no such thing for Mars ascent.  If the MCT MPS explodes, a separable lifeboat can save the crew.  Whole vehicle abort would only work for Earth ascent. 
If there's a non explosive failure, like an engine out, that's when having a redundant engine comes in. 
So it's really all or nothing if you don't have a separable design.  And that's ok, the LAS lifeboat is mainly for Earth ascent so the crew can get away from an exploding booster where you cannot abort the whole fueled stage.  But with that comes the ability to abort on Mars if necessary.  But there would need to be contingency plans to for the marooned crew obviously.

In Early exploration any abort to surface is fatal because their is zero rescue infrastructure on the surface and no conceivable capsule could carry sufficient supplies to see them through more then a few days.  So I consider this a pointless abort. By the time you have an infrastructure to do surface rescue your passenger count is much too high for the small capsule your proposing, it would need to be a large vehicle comprising a significant portion of the whole mass of the vehicle and would present great difficulty in landing as you going to be falling on a ballistic trajectory from a high altitude and need massive retro-propulsion to not impact the surface, it in no way resembles the kind of un-powered capsule landing that can be done on Earth.

Not necessarily.  It would only be a smaller portion of the whole weight of the vehicle (Maybe 1/3 total dry mass or so?...but more importantly is it leaves all the propellant mass behind with just the LAS/landing propellant on board).  It would leave behind the main tanks, engines, most of the TPS covering, etc.  It wouldn't be insignificant, but it would be certainly less than the whole vehicle.  The LAS engines and tanks would need to be sized not only for abort, but for propulsive landing.
Also it would be a biconic shape.  So it can do a biconic EDL rather than ballistic.  It would still need a large retro propulsion as any vehicle would, but again, that would have to be designed into the LAS system if you wanted it.

Again, this a concept in reaction to some who feel strongly the LAS is necessary.  (I argued against an LAS, but was out voted, heh)  It could very easily be left off, with no Mars ascent abort option (for an explosive event, you can abort to orbit with just an engine out), and a separate LEO-taxi with LAS for Earth ascent.  For those that favor that, I think that's viable too.
It would probably still need landing thrusters of some sort to land on Earth, which would likely be pressure fed for fast reaction control and reliability.  Otherwise a means of landing on Earth with a vacuum Raptor nozzle would need to be figured out.  Something like a retractable nozzle extension, or a jettisonable nozzle extension, so that the Raptor thrust isn't too over expanded for sea level.  I'm not an engine expert, but have been told by several that vacuum engines with large vacuum nozzles like M1D-Vac and RL-10B cannot operate at sea level due to their large high efficiency nozzles.
But Raptor would still have to be capable of quickly responsive throttle in order to be able to land, which it may not be being a big pump fed staged combustion main propulsion engine.  Otherwise you are back to landing thrusters.




Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/07/2015 04:41 pm
Isn't LOX heavier than Liquid methane? Also it will take twice the lox to burn the methane.  So shouldn't the Lox tank be on bottom with the Methane on top?   

That was discussed.  I can't remember the exact discussion but it was determined the LOX would be better placed on top.  But weight isn't always the reason for tank placement.  LOX tanks are on top of LH2 in the Shuttle ET and D4 booster.   And the mass of the LOX in the Shuttle ET was about 6X that of the mass of LH2.  D4 is probably a similar mass ratio.
The guy who did the renderings originally placed the LCH4 on top, but then after discussion, changed it so the LOX was on top.

Volumetrically, I think the LOX and LCH4 tanks will be similar in size.  At least more similar than kerolox and hydrolox tanks.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/07/2015 04:52 pm

I've said all along that an elongated 2nd stage would do tanker duty, and depots are in my opinion unnecessary, the MCT will act as it's own depot taking on propellants from visiting 2nd stages until it is full.  As MCT must depart Earth with some propellant for EDL at mars and must then hold significant amounts while on the martian surface (which while cold is still warmer then cryogenic LOX), so the MCT will have to have significant long-term cryo-storage capabilities likely through a combination of insulation and cryo-coolers, thus it makes an excellent depot. 

These cryo-systems along with radiators and solar arrays are the only systems that I would integrated into the vehicle.  Human habitats placed into the MCT are simply plugged into these utilities much like an RV.


That'd be personal preference.  That was my original thought too.  Except, what do you want loitering in LEO while it's being filled up?  A reusable unmanned depot, or your crewed MCT?  I think the preference would be to not have MCT floating around up there any longer than necessary.  Even if you sent the crew up later once it was tanked up, it's just that much more time in LEO to get struck by MMOD.  Just that many more miles on the odometer before the mission even really starts.  Plus you have multiple docking events from the tankers rather than just one from a depot.

And the depot would just be an MCT without the hab section in it.  It's not really -another- vehicle.  Once it's filled up an MCT bound for Mars it can come back down, be refitted, and go back up for the next mission.

As for an active cryo system, MCT with a depot probably wouldn't need one.  It wouldn't be loitering in LEO, and it would burn most of it's propellant shorter after debarking from the depot for the TMI burn.  And it could carry enough residuals to account for boiloff...which shouldn't be too bad with medium cryos like LOX and LCH4. 

Again, it's personal preference.  Neither is right or wrong.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/07/2015 04:58 pm

One significant factor that needs to be taken into account for a biconic vehicle (which I advocate) is a the mass distribution. It needs to be have the proper balance when almost empty (normal atmospheric entry & landing), and it needs to be able to also have the proper balance for a near full propellant load. (Earth or Mars abort) Also, when near empty of propellant the vehicle must also be properly balanced for a full cargo load vs empty.

To handle this range, the layout that makes most sense (IMO) is to put the cargo/crew in the middle of the vehicle - with the LOX tank above, and Methane tank below. This would allow a balanced biconic sideways reentry with ANY cargo load, and ANY propellant load.

EDIT: See image below for how that might look, in this DC-Y(?) drawing:

The IBMCT would have most of the dry mass in the nose and MPS as the aft (Engines, thrust structure, etc).  Between the two would empty main propellant tanks, a cargo deck, and volumous, but relatively light Hab area.   The cargo deck would be between the hab volume and the tanks, and may have a fairly heavy mass when loaded with surface cargo.  So for Mars EDL, that would be about in the middle.  So you have your greatest mass areas in the nose, in the tail, and [roughly] in the middle.  So it shouldn't be too bad.  There will be some residuals in the tanks to power Raptor from terminal velocity to hover.

I don't know you need two separate tanks top and bottom like in this concept.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 10/07/2015 05:05 pm
Again, this a concept in reaction to some who feel strongly the LAS is necessary.  (I argued against an LAS, but was out voted, heh)  It could very easily be left off, with no Mars ascent abort option (for an explosive event, you can abort to orbit with just an engine out), and a separate LEO-taxi with LAS for Earth ascent.  For those that favor that, I think that's viable too.

I think SpaceX will be forced to have a LAS on MCT or a LEO-taxi with LAS because of liability issues.

The LEO-taxi also means the 100 passengers won't have to wait in orbit for refueling or any other delays, but it would add extra cost using another vehicle design.

Guys, keep up the great work. There are a lot of interesting MCT concepts in this thread.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/07/2015 05:45 pm

One significant factor that needs to be taken into account for a biconic vehicle (which I advocate) is a the mass distribution. It needs to be have the proper balance when almost empty (normal atmospheric entry & landing), and it needs to be able to also have the proper balance for a near full propellant load. (Earth or Mars abort) Also, when near empty of propellant the vehicle must also be properly balanced for a full cargo load vs empty.

To handle this range, the layout that makes most sense (IMO) is to put the cargo/crew in the middle of the vehicle - with the LOX tank above, and Methane tank below. This would allow a balanced biconic sideways reentry with ANY cargo load, and ANY propellant load. Or to balance cargo above and below propellant tanks.

EDIT: See image below for how that might look, in this DC-Y(?) drawing:

The IBMCT would have most of the dry mass in the nose and MPS as the aft (Engines, thrust structure, etc).  Between the two would empty main propellant tanks, a cargo deck, and volumous, but relatively light Hab area.   The cargo deck would be between the hab volume and the tanks, and may have a fairly heavy mass when loaded with surface cargo.  So for Mars EDL, that would be about in the middle.  So you have your greatest mass areas in the nose, in the tail, and [roughly] in the middle.  So it shouldn't be too bad.  There will be some residuals in the tanks to power Raptor from terminal velocity to hover.

I don't know you need two separate tanks top and bottom like in this concept.

No. If you are truly scaling this to be able to deliver 100t of cargo, you really need to have it in the middle. Not up front with the hab volume. When you do atmospheric entry, the propellant tanks will be mostly empty, so then by placing the cargo up top you are now forcing yourself to have to have a substantial minimum cargo load or the thing won't fly right.

Think about it. 100t. And it could be there, or it could be empty. If you do a sideways re-entry, that DOES constrain you to a center placement of cargo. OR you need to split the cargo into two balanced areas, one below and one above propellant tanks.

Think of MCT as a cargo aircraft. The cargo AND propellant must be balanced properly. So you either have to put the cargo in the middle of two propellant tanks, or the propellant in the middle of two cargo bays.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/07/2015 05:52 pm
Except, what do you want loitering in LEO while it's being filled up?  A reusable unmanned depot, or your crewed MCT?  I think the preference would be to not have MCT floating around up there any longer than necessary.  Even if you sent the crew up later once it was tanked up, it's just that much more time in LEO to get struck by MMOD.

There will have to be plenty of loiter time in LEO for MCTs. Why? Because of launch windows to Mars. You will likely want to launch a fleet of them in very close succession, and this will require lots of loitering to place, refuel, & prepare the MCT's in orbit. Having a couple of weeks system checkouts in the relative safety of LEO is also advantageous.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RocketmanUS on 10/07/2015 07:03 pm
Except, what do you want loitering in LEO while it's being filled up?  A reusable unmanned depot, or your crewed MCT?  I think the preference would be to not have MCT floating around up there any longer than necessary.  Even if you sent the crew up later once it was tanked up, it's just that much more time in LEO to get struck by MMOD.

There will have to be plenty of loiter time in LEO for MCTs. Why? Because of launch windows to Mars. You will likely want to launch a fleet of them in very close succession, and this will require lots of loitering to place, refuel, & prepare the MCT's in orbit. Having a couple of weeks system checkouts in the relative safety of LEO is also advantageous.
And above the weather for TMI burn.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/07/2015 07:05 pm


No. If you are truly scaling this to be able to deliver 100t of cargo, you really need to have it in the middle. Not up front with the hab volume. When you do atmospheric entry, the propellant tanks will be mostly empty, so then by placing the cargo up top you are now forcing yourself to have to have a substantial minimum cargo load or the thing won't fly right.

Think about it. 100t. And it could be there, or it could be empty. If you do a sideways re-entry, that DOES constrain you to a center placement of cargo. OR you need to split the cargo into two balanced areas, one below and one above propellant tanks.

It's 100mt of payload.   That may be 100mt of pure cargo down the road at some point, but for quite some time it will be mixed cargo and crew/hab. 

So you have your IBMCT.  It has it's fairly heavy MPS on the bottom.  Above that you have two stacked cylindrical tanks that go up to about the center of the overall vehicle (when measured from tip to tail)...up a little over half way up the cylindrical portion.  Above that you'll have a cargo deck for mixed flights that is maybe 3 meters tall.  As the cargo will have to be lowered to the surface, none of it can be -too- large in one piece, but it will be heavy overall.  Above that you will have a pressurized hab volume filling the rest of the cylinder, and then another tapered pressurized hab volume in the nose.  If an LAS is required, the nose will have LAS/landing engines it it as well, along with small pressurized tanks to fuel them.   Overall, it will have a fair amount of mass in it.
So again, you'll have a mass area in the tail, amidships, and in the nose. 

With 100mt of pure cargo, and no hab area at all, that may be a little more tricky if all that 100mt is between the nose and the tanks.  They'd probably stow the heaviest pieces just above the tanks, with lighter and lighter pieces above that to help with weight distribution.

But, it's obviously something that'd have to be looked at in more detail by actual SpaceX engineers during the actual design process to see how the real weight distribution will interact with the EDL profile.

This divided concept would have the problem of being nose-light.  The mass will be concentrated in the middle, and at the aft in the MPS.  But given it's tapered overall OML, maybe that still makes for a feasible distribution for EDL?  It's a little above my area.  :-)

With the SDMCT, obviously that's not a problem because it's always vertical.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/07/2015 07:28 pm
You are still not getting what I'm trying to say. Let me try again.

The MCT must be able to launch, fly, and land with full cargo/crew. But ALSO when no cargo/crew is present.
The MCT must be able to launch, fly, and land with full propellant load. But ALSO with tanks nearly empty.

That places severe constraints on the placement of these elements on a biconic entry vehicle, and you can't just hand-wave that away by a "100t payload vs 100t cargo" semantic discussion. It doesn't matter.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 10/07/2015 07:33 pm
A SEP transit vehicle that takes you to high earth orbit followed by a perigee burn near Earth to send you to Mars, the SEP vehicle flies independently to mars and you rendevoue with it on low mars orbit to return to a high Earth orbit where crew disembark on a Dragon capsule.  The bi-conic just dose mars assent with a 25 mT habitat inside pluss a modest landing propellent reserve. The intent is to ultimatly be able to do a rapid cycle between mars surface and low orbit, loading cargo and orbit and unloading on the surface.

I think SEP from LEO to HEO is no-go if you want to fly MCT every synod. How much time do you think will be left after returning to Earth? (looking at all opportunities).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/07/2015 08:05 pm
I'm rather surprised that you aren't aware of the Pendulum Fallacy (https://en.wikipedia.org/wiki/Pendulum_rocket_fallacy)
But I don't know that my stated bit about inherent stability is incorrect.  Just not exactly as I stated.
In that, would it not be similar to a helicopter?  Why is a helicopter more stable

Helicopters aren't gravitationally stabilised. If you roll to one side and then let go of the controls, helicopters do not come back to level. They are perfectly happy to roll over and fly straight into the ground.

than something like the LLRV?

Remember that the Flying Bedstead was not being fully controlled by the pilot. Instead the jet engine was to simulate partial gravity for a system intended for 1/6th g (which had never actually been flown and was being controlled by flight systems that were one step above clockwork.) Once it tilted too far off centre, the jet was no longer reducing gravity, it was driving you to one side while you fell to the ground. And none of the "lunar" thrusters were powerful enough to actually offset a full-gravity without that jet. Give the designers another five years and a half-dozen version, and I'm sure they would have come up with something safer... But, of course, that wasn't its purpose.

By contrast, the LEM also had its engines underneath, but was much more stable. By your argument, it should have been as twitchy as the LLRV, but it wasn't.

And in this way I think they'd act more like the F9 core grid fins, which are placed up high to provide force (via air resistance rather than a jet of thrust) to help stabilize the core for landing.

The grid fins are at the top for the opposite reason. The rocket is descending engines-first, hence the grid-fins are at the "back" of the rocket during that phase of flight, essentially playing the role of a "tail" on a conventional aircraft. However, like a tail on a plane, the grid-fins don't result in the rocket having any preferred "neutral" orientation. Ie, it won't "hang down" from the grid-fins, you have to actively control it to keep the rocket vertical.

The lifeboat would be [....] A flight deck in the nose with a bulkhead and hatch between it and the rest of the hab.  Not much more to it that that.  Not quite like a separate spacecraft.

It has to be a separate spacecraft, or it can't operate as a escape vehicle. Such a double-vehicle would become hideously complex. Particularly if you are trying the use the escape vehicle's engines as landing engines for the entire MCT. The forces on the connectors, which must be instantly separable during launch-abort, would be ridiculous.

For early exploration missions Dragon 2 would be sufficient, no separate system needed as crews will only be maybe 6-7.

I assume you mean that the early crews would ferry up to an MCT in LEO using D2? (Since D2 can't launch back off the surface of Mars. It will never be used for human missions to Mars.)

In which case, you are proposing an entirely different kind of MCT just for the first few missions. Your escape vehicle can't be retro-fitted to an existing MCT design. You can't just cut through a few joins connecting the flight-deck to the rest of the MCT and add some pyro-bolts. You have the design the entire MCT around the separation mechanism. That's not going to be an afterthought or upgrade.

Others thought it needed it, as later during colonization they'd want to launch all 100 people on the MCT rather than have a separate ferry.
I argued against an LAS, but was out voted, heh

Sounds like there's some group-think going on. Alternative suggestions are shouted down by a few dominant voices and their followers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/07/2015 08:12 pm
10 or 100 people per flight.
10 people means 10 times the number of manned flights. Which means 10 times the likelihood of a flight with crew loss. Will people say, oh well, it is only 10 people, not 100, that's OK? I doubt it.

However, with extra crew ships on the same route, if there is a failure of a major system on one of the ships, those 10 people can be spread amongst the remaining 9 ships. Additionally, during the emergency, they'd have nearby external help operating out of safe, fully functional ships, rather than trying to save themselves from within the failing ship using failing systems (with the nearest advice operating behind several minutes comms lag.)

With a single crew, no chance of rescue, any major failure means LOM/LOC.

The advantage of that 9-fold backup, IMO, is worth its weight in diamonds.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/07/2015 08:18 pm
10 or 100 people per flight.
10 people means 10 times the number of manned flights. Which means 10 times the likelihood of a flight with crew loss. Will people say, oh well, it is only 10 people, not 100, that's OK? I doubt it.

However, with extra crew ships on the same route, if there is a failure of a major system on one of the ships, those 10 people can be spread amongst the remaining 9 ships. Additionally, during the emergency, they'd have nearby external help operating out of safe, fully functional ships, rather than trying to save themselves from within the failing ship using failing systems (with the nearest advice operating behind several minutes comms lag.)

With a single crew, no chance of rescue, any major failure means LOM/LOC.

The advantage of that 9-fold backup, IMO, is worth its weight in diamonds.

You are assuming the major risk is in the cruise phase. I assume it is during launch, TMI and landing,
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/08/2015 12:20 am

I assume you mean that the early crews would ferry up to an MCT in LEO using D2? (Since D2 can't launch back off the surface of Mars. It will never be used for human missions to Mars.)

In which case, you are proposing an entirely different kind of MCT just for the first few missions. Your escape vehicle can't be retro-fitted to an existing MCT design. You can't just cut through a few joins connecting the flight-deck to the rest of the MCT and add some pyro-bolts. You have the design the entire MCT around the separation mechanism. That's not going to be an afterthought or upgrade.


First, it won't be just a few missions.  Probably all the missions for the first couple decades.  There will be many exploration missions with just a small crew before they can possibly think about actual colonization with large numbers of colonists.  You have to explore various potential location looking for a promising site with favorable conditions for a colony.  Then you have to test out the new systems which the colony will use, and test out resource collection, etc.  Not to mention I think it highly likely NASA would jump in bed with them as soon as it were to look likley they could land people on Mars.  They'll provide fund which will be beneficial for SpaceX, but they'll have their own agenda of places they want to go too. 

And you can only fly out every 2 years.  So, after maybe 20 years of Mars mission, you are ready to put 100 colonists on an MCT, what do you do then?
That's the question.

And I think you are viewing this like the Space Shuttle.  There are just a handful ever built.  Any change would require it to be broken apart and remodeled.  But I think there would be more than that built for MCT.  So it's certainly possible to have a "Block 2" MCT which would have the LAS systems installed and some design changes to facilitate it. 
SpaceX isn't modifying D1's to make them D2's, they are building new D2's with the new systems in them.  SpaceX is no more tied to their first MCT design than they are to their first Dragon design.

So an LAS doesn't have to be in the exploration-class design, if deemed unwanted.  It could be added to a Block 2 Colony Transport.  Old Block 1 MCT's could continue to be used for Cargo service.

Or a separate LEO-Taxi version could be developed specifically around an Earth launch abort system, so an LAS wouldn't need to be added to MCT. 
Or maybe after 20 years of operation, the booster is just deemed reliable enough that with 1 redundant engine for an engine out contingency, it's just deemed an LAS system is not critical enough to account for.
My original preference was for the IBMCT was one extra engine on the booster, and an additional engine on the IBMCT, so that you are covered for an engine out on the booster and/or on the IBMCT after staging.  Along with other redundant systems, the crew can safely get to orbit in most failure modes other than explosive failure.  And deem this "safe enough" as by then, there will be some 20 years of flight history to get it reliable.

Options abound.  Again, it was a way to address concerns of those who feel strongly that MCT must have an LAS system on an integrated MCT design.  If you don't like it, then you can favor the SDMCT or NIBMCT which launch empty on a dedicated S2 and abort the whole vehicle...or something else entirely.  That means you have two spacecraft to design from the start rather than one, but that's certainly an option.  And an option originally favored by the team.  My IBMCT kinda grew on them over time.  :-)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: UberNobody on 10/08/2015 12:31 am
Just as a reminder, we have a thread full of direct quotes about MCT.  Most everything recent is there. 

http://forum.nasaspaceflight.com/index.php?topic=37839.0
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/08/2015 01:00 am
You are still not getting what I'm trying to say. Let me try again.

The MCT must be able to launch, fly, and land with full cargo/crew. But ALSO when no cargo/crew is present.
The MCT must be able to launch, fly, and land with full propellant load. But ALSO with tanks nearly empty.

That places severe constraints on the placement of these elements on a biconic entry vehicle, and you can't just hand-wave that away by a "100t payload vs 100t cargo" semantic discussion. It doesn't matter.

I've given some though to mass distribution in my design.  First off my some what naive understanding of a bi-conic (or any entry vehicle) is that you want the center of mass forward of the center of aerodynamic lift or drag.  In essence we have a shuttlecock and we drag is primarily in the rear and the mass in the front so it remains pointed properly into the wind and doesn't disastrous tumble over.  This was one of the biggest dangers in Shuttle re-entry because it was heavy in the rear and often had nothing in the cargo bay making it unstable.

First thing is that I did was give the vehicle a considerable cylindrical hollow 'skirt' below the two conic frustums, these would be a perimeter of hinged body flaps which allow a lot of drag to be generated far in the rear of the vehicle and most importantly allow the amount of drag to be adjusted in flight based on mass distribution, atmospheric conditions and as a general decelerator the the lower martian atmosphere.

Second propellant tankage is divided between a forward tank  set in the first frustum and saddle tanks in the second lower frustum of the vehicle which flank the cargo hold.   All tanks are full only for the assent from mars when the vehicle is a standard assent rocket, during any entry the propellant loads will be small enough for significant mass shifting of mass probably preferably placing it towards the tip of the vehicle.



I'm not sure I agree with that.

Ok, so let's say you have a 12.5m wide IBMCT (our working diameter for it and the booster).  A separable nose would be 12.5m wide at the base, tapering down.  So you'd have quite a lot of volume there for a small crew returning from Mars if they had to abort and land down range.  For 100 people, yea, it's not going to keep them for very long, but for a crew of 5-7?  Should be just fine.  In fact, that may be the only hab space they need/have for exploration missions, with everything below for surface cargo.  That's a volume twice as wide as Skylab op the base, and probably about the same height as the Skylab pressurized volume.  There's no squeezing involved.
They would have provisions and supplies sufficient for the 4-6 month transit back to Earth, so they should be ok for quite awhile.

Then you have the question of what sort of contingency plan do you want to have in place to deal with them at that point.  That's really a separate discussion.  Maybe a remote operated large pressurized rover that could drive itself over to the lifeboat, to give them transportation to a supply cache somewhere pre-positioned for such a contingency?

In a situation where they are transporting 100 people to Mars, obviously 100 people won't be coming back home, so there will be far fewer people on it.  Probably just some SpaceX employees or NASA personnel returning home after a tour of serving at the colony, and a few people who have either become more ill than can be treated on Mars, or have changed their minds and want to go home.   But even if it were more people, with a colony on Mars, rescue could be dispatched anywhere on the globe, it's just a matter of how long it would take to get there, so the lifeboat would need to be set up to support X number of people of Y length of time needed to get rescue there.

As far as whole vehicle abort goes, there really is no such thing for Mars ascent.  If the MCT MPS explodes, a separable lifeboat can save the crew.  Whole vehicle abort would only work for Earth ascent. 
If there's a non explosive failure, like an engine out, that's when having a redundant engine comes in. 
So it's really all or nothing if you don't have a separable design.  And that's ok, the LAS lifeboat is mainly for Earth ascent so the crew can get away from an exploding booster where you cannot abort the whole fueled stage.  But with that comes the ability to abort on Mars if necessary.  But there would need to be contingency plans to for the marooned crew obviously.

In Early exploration any abort to surface is fatal because their is zero rescue infrastructure on the surface and no conceivable capsule could carry sufficient supplies to see them through more then a few days.  So I consider this a pointless abort. By the time you have an infrastructure to do surface rescue your passenger count is much too high for the small capsule your proposing, it would need to be a large vehicle comprising a significant portion of the whole mass of the vehicle and would present great difficulty in landing as you going to be falling on a ballistic trajectory from a high altitude and need massive retro-propulsion to not impact the surface, it in no way resembles the kind of un-powered capsule landing that can be done on Earth.

Not necessarily.  It would only be a smaller portion of the whole weight of the vehicle (Maybe 1/3 total dry mass or so?...but more importantly is it leaves all the propellant mass behind with just the LAS/landing propellant on board).  It would leave behind the main tanks, engines, most of the TPS covering, etc.  It wouldn't be insignificant, but it would be certainly less than the whole vehicle.  The LAS engines and tanks would need to be sized not only for abort, but for propulsive landing.
Also it would be a biconic shape.  So it can do a biconic EDL rather than ballistic.  It would still need a large retro propulsion as any vehicle would, but again, that would have to be designed into the LAS system if you wanted it.

Again, this a concept in reaction to some who feel strongly the LAS is necessary.  (I argued against an LAS, but was out voted, heh)  It could very easily be left off, with no Mars ascent abort option (for an explosive event, you can abort to orbit with just an engine out), and a separate LEO-taxi with LAS for Earth ascent.  For those that favor that, I think that's viable too.
It would probably still need landing thrusters of some sort to land on Earth, which would likely be pressure fed for fast reaction control and reliability.  Otherwise a means of landing on Earth with a vacuum Raptor nozzle would need to be figured out.  Something like a retractable nozzle extension, or a jettisonable nozzle extension, so that the Raptor thrust isn't too over expanded for sea level.  I'm not an engine expert, but have been told by several that vacuum engines with large vacuum nozzles like M1D-Vac and RL-10B cannot operate at sea level due to their large high efficiency nozzles.
But Raptor would still have to be capable of quickly responsive throttle in order to be able to land, which it may not be being a big pump fed staged combustion main propulsion engine.  Otherwise you are back to landing thrusters.


It seems to me that this abort capsule is nearly the size of the entire Separate Bi-conic vehicle I'm imagining.  In essence the split is right along the lines of the 2nd stage and the Bi-conic where I'd just have two separate vehicles.

One of the main issues I see with mars abort capsules is that they need to have basically full mars EDL capability, it needs thermal protection, it needs flight control, it needs lots of retro-propulsion, it needs landing legs and radar to acquire the ground and soft-land.  In fact because the abort capsule is on and unplanned trajectory it's angle of entry into the atmosphere is uncontrolled and atmospheric entry angle is critical to making the process survivable. 

This is a KEY consideration when comparing a direct Earth return vehicle to one ascending to LMO.  The direct return vehicle doesn't arc over, it just goes strait up trying to achieve mars escape.  If you abort from that before escape velocity your now just falling strait down on mars and that is an un-survivable entry due to g-forces alone, the lift provided by a bi-conic shape is perpendicular the the surface and just shifts your point of impact on the surface, it's only useful if your coming in basically horizontal to the surface and the lift is countering gravity and allowing you to bleed speed horizontally.  A vertical entry isn't survivable on Earth either, only by going on a mostly horizontal trajectory intended for orbit do we manage to survive aborts in capsules as we re-enter at a glancing angle. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jcc on 10/08/2015 01:09 am
Why wouldn't a Mars escape trajectory arc over some? Do you wait until Mars rotates exactly towards Earth and then launch? I'm being a little facetious, but you get the idea, you need to turn anyway, so why not reduce gravity losses while you are doing it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: M_Puckett on 10/08/2015 01:18 am
http://www.iflscience.com/space/huge-spacex-announcement-coming-soon-could-be-mars-mission

Ok Chris, you knew we were going to get ahold of this eventually. ;D

First question:  Bigger than a Breadbox?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/08/2015 01:25 am
[separate launch "taxi"]
That means you have two spacecraft to design from the start rather than one, but that's certainly an option.

But you propose two spacecraft in one. The LAS you propose is a separate spacecraft, according to you capable of full EDL. But it must also be integrated back into the MCT in a way that doesn't just allow it to break away as a LAS, doesn't just require it to be integrated tightly enough to handle re-entry while acting as the nose of the MCT (while still being able to break-away instantly), but its engines must also be able to serve as the landing engines for the whole MCT, both on Mars and on Earth.

(Plus you want another non-LAS "explorer" MCT for smaller crews. Plus yet another MCT design for cargo. So four spacecraft.)

I can't fathom how you think that is going to be somehow easier to nest two spacecraft inside each other like matryoshka dolls than to build them independently.

To use an analogy, do you think is would be cheaper/easier to design a car whose drivers-side wheels, seat and side panels split off to become a motorbike, or to just design a normal car and a separate normal motorbike?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/08/2015 01:42 am

First, it won't be just a few missions.  Probably all the missions for the first couple decades.  There will be many exploration missions with just a small crew before they can possibly think about actual colonization with large numbers of colonists.  You have to explore various potential location looking for a promising site with favorable conditions for a colony.  Then you have to test out the new systems which the colony will use, and test out resource collection, etc.  Not to mention I think it highly likely NASA would jump in bed with them as soon as it were to look likley they could land people on Mars.  They'll provide fund which will be beneficial for SpaceX, but they'll have their own agenda of places they want to go too. 

And you can only fly out every 2 years.  So, after maybe 20 years of Mars mission, you are ready to put 100 colonists on an MCT, what do you do then?
That's the question.


I'd like to second this emotion, Gradualism is the way things actually happen.  Far too much of the speculation about MCT assumes the usage will be immediately at some kind of designed maximum threshold and permanent settlements will be put down at the first spot on mars where mankind puts it's first footprints.  Initially mobility should be maximized to the point that I would recommend putting a single large rover/hab vehicle in each MCT to go completely nomad without a base of any kind other then having to return to the MCT for Earth return.    For example I might see a typical mission progression something like...

1 MCT with a crew of 6 + 1 cargo MCT
2 MCT with a crew of 12 each + 2 cargo MCT
4 MCT with a crew of 25 each + 12 cargo MCT
8 MCT with a crew of 50 each + 20 cargo MCT
20 MCT with crew of 100 each + 50 cargo MCT

In each stage your expanding crew while reducing mobility hardware for surface use and doing increasing amounts of base construction and consolidation.  Each of these 5 phases might take a decade which is hardly any time when we consider that's only 4 1/2 launch opportunities, less then the number of Apollo landings.

I've been developing a number of schemes for how to increase the tonnage sent to mars using the same basic bi-conic vehicle by leveraging it with auxiliary vehicles, mostly SEP spacecraft which would improve the efficiency and scale of the whole transport infrastructure over time while eliminating the need to constantly integrate new features into MCT.  The base vehicle alone would do a bare-bones mission and only the whole vehicle portfolio dose the huge volumes but they do them far more efficiently then simply having fleets of MCT's.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/08/2015 01:58 am
Why wouldn't a Mars escape trajectory arc over some? Do you wait until Mars rotates exactly towards Earth and then launch? I'm being a little facetious, but you get the idea, you need to turn anyway, so why not reduce gravity losses while you are doing it.

No, by my understanding the gravity loss is minimized by moving away from the planet as fast as possible, that's why you go strait up and out and your launch window would be during the time of day when the line on which you want to escape mars on is as close to your local zenith as possible.  Their might be some deflection of your assent trajectory because the latitude your at means the ground normal is not actually point in that direction (planetary tilt matters here too) but your not arcing over to do 90% of your thrusting parallel to the ground as in an assent to orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/08/2015 03:45 am
Hans Koenigsmann .... "but at least 100 times is our goal."
Should have asked earlier - assume it's BFR here due to thread. Is that right? (MCT can only launch every 18 months, so 100 uses is over 50 years)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: colbourne on 10/08/2015 06:03 am
http://www.iflscience.com/space/huge-spacex-announcement-coming-soon-could-be-mars-mission

Ok Chris, you knew we were going to get ahold of this eventually. ;D

First question:  Bigger than a Breadbox?

They are also planning a Moon mission

http://phys.org/news/2015-10-israeli-team-advances-contest-spacecraft.html?utm_source=nwletter&utm_medium=email&utm_content=ctgr-item&utm_campaign=daily-nwletter
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/08/2015 07:25 am
That's just SpaceX selling a rocket to any who can plunk the money down, once the payload is released SpaceX's job is done.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: rpapo on 10/08/2015 11:21 am
Hans Koenigsmann .... "but at least 100 times is our goal."
Should have asked earlier - assume it's BFR here due to thread. Is that right? (MCT can only launch every 18 months, so 100 uses is over 50 years)
Whoever said they would only make one MCT?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/08/2015 11:27 am
Not sure that relates to how many times each MCT is reused... ?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/08/2015 12:22 pm
Hans Koenigsmann .... "but at least 100 times is our goal."
Should have asked earlier - assume it's BFR here due to thread. Is that right? (MCT can only launch every 18 months, so 100 uses is over 50 years)

One MCT launch to Mars requires a minimum of 3-4 launches. Each synod needs at least 2 MCT to maintain a station, more to expand it, say at least 3. That's 9-12 launches every synod of 26 months. That's a bare minimum. I am quite sure there will be more.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: symbios on 10/08/2015 01:22 pm
Hans Koenigsmann .... "but at least 100 times is our goal."
Should have asked earlier - assume it's BFR here due to thread. Is that right? (MCT can only launch every 18 months, so 100 uses is over 50 years)

One MCT launch to Mars requires a minimum of 3-4 launches. Each synod needs at least 2 MCT to maintain a station, more to expand it, say at least 3. That's 9-12 launches every synod of 26 months. That's a bare minimum. I am quite sure there will be more.

I think Mr Musk was quite clear that he would do all possible for the MCT to return to Earth during the same synod. This would enable the same MCT to be serviced and reused during the next synod. Possible or not that is the goal.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/08/2015 01:33 pm
Hans Koenigsmann .... "but at least 100 times is our goal."
Should have asked earlier - assume it's BFR here due to thread. Is that right? (MCT can only launch every 18 months, so 100 uses is over 50 years)

One MCT launch to Mars requires a minimum of 3-4 launches. Each synod needs at least 2 MCT to maintain a station, more to expand it, say at least 3. That's 9-12 launches every synod of 26 months. That's a bare minimum. I am quite sure there will be more.

Not that it matters I guess, but ... my question doesn't matter. It MUST be the BFR.

(Your answer generalises it to the Mars Colonial Transport system. Which means BFR and tankers etc)

If the goal is for the MCT component that goes to Mars to be reused 100 times, and that component launches once every synod, but Koenigsmann doesn't think it'll last 30 years, then obviously he's talking about something else. If 2 or 10 MCTs launch that's not the same as a single MCT being reused 2 or 10 times.... but it would reuse the BFR.

Anyway, think we're just splitting hairs over it. I fully expect a single BFR (first stage) to launch a couple of MCTs, a bunch of tankers etc each synod.

(I'll have a listen to the speech and see if there was something else)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/08/2015 02:21 pm
Not that it matters I guess, but ... my question doesn't matter. It MUST be the BFR.

(Your answer generalises it to the Mars Colonial Transport system. Which means BFR and tankers etc)

I did not generalize to the MCT. Or at least it was not my intention. When I wrote it I had it in the back of my mind that other uses are possible too.  ;)

If the goal is for the MCT component that goes to Mars to be reused 100 times, and that component launches once every synod, but Koenigsmann doesn't think it'll last 30 years, then obviously he's talking about something else. If 2 or 10 MCTs launch that's not the same as a single MCT being reused 2 or 10 times.... but it would reuse the BFR.

My take on the statement was that he meant it will not fly daily for 30 years which would be over 10,000 uses.

(I'll have a listen to the speech and see if there was something else)

It is in german and there was not much else in it for us space fans. It was an interview in a general news magazine.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/08/2015 08:57 pm
My take on the statement was that he meant it will not fly daily for 30 years which would be over 10,000 uses.
Ahh, so in a sense he was recontextualising reuse, almost to say that the MCT's version of reuse is still much less than a plane.

I think that makes more sense to me... thanks guckyfan.

It is in german and there was not much else in it for us space fans. It was an interview in a general news magazine.

I'd only understand 70% probably and it would take my full attention.... but may be good to keep my ear active.

Then again your report on the useful bit is already better probably!.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/08/2015 09:37 pm
I think Mr Musk was quite clear that he would do all possible for the MCT to return to Earth during the same synod. This would enable the same MCT to be serviced and reused during the next synod. Possible or not that is the goal.

A one synod cycle require opposition trajectory and a short (1 month) stay on Mars.  This will not be the initial flight mode simply because their is not enough time to produce return propellants.  Only one propellant infrastructure is built up can that become the norm so I don't expect that for many years.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/08/2015 11:03 pm
You are still not getting what I'm trying to say.

Actually I do.  I just don't think it'll be a deal-breaker in the design like you do.  As in, I think if SpaceX were to go with something like this, they'll address the issue of balancing out the mass for atmospheric entry.

I don't think the current arrangement is particularly out of balance.  When the Space Shuttle was doing atmospheric entry after delivering a cargo, most of it's mass was in the tail and nose too, I believe?

But, if actual engineers working on it do deem that it would be out of balance enough, then they'll work out a way to balance it better.  Could even be as simple as extra propellants left in the tank as ballast.  That option seems particularly flexible actually, as especially for cargo-only missions, the mass distribution can vary form mission to mission depending on what cargo is packed into the cargo area between the top of the tanks and the nosecone. 

If moving one of the tanks to the nose is the -only- possible solution, then they can do that.  But it would eliminate pretty much any possibility of an LAS system for an integrated design.  It would be ok for a non integrated biconic doing a whole vehicle abort.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/08/2015 11:13 pm

It has to be a separate spacecraft, or it can't operate as a escape vehicle. Such a double-vehicle would become hideously complex.


Yes.  That's probably why such a cylinder-cone vehicle with a separable nose cone with a crew hab has never been thought of before.

;-)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/08/2015 11:25 pm
[separate launch "taxi"]
That means you have two spacecraft to design from the start rather than one, but that's certainly an option.

But you propose two spacecraft in one. The LAS you propose is a separate spacecraft, according to you capable of full EDL. But it must also be integrated back into the MCT in a way that doesn't just allow it to break away as a LAS, doesn't just require it to be integrated tightly enough to handle re-entry while acting as the nose of the MCT (while still being able to break-away instantly), but its engines must also be able to serve as the landing engines for the whole MCT, both on Mars and on Earth.

(Plus you want another non-LAS "explorer" MCT for smaller crews. Plus yet another MCT design for cargo. So four spacecraft.)

I can't fathom how you think that is going to be somehow easier to nest two spacecraft inside each other like matryoshka dolls than to build them independently.

To use an analogy, do you think is would be cheaper/easier to design a car whose drivers-side wheels, seat and side panels split off to become a motorbike, or to just design a normal car and a separate normal motorbike?

It's not really two spacecraft in one, like MCT+ S2 would be two completely separate spacecraft.  It's more a spacecraft, with an additional section.  Since everything below the lifeboat cannot function on it's own as it own spacecraft.
So unlike your analogy, it's more like a semi tractor and trailer.  They can be one combined vehicle, or the tractor can operate on it's own.   Hence the term "Integrated Biconic MCT".  Where a main propulsion stage is "integrated" with habitat, rather than two separate main propulsion stages on two vehicles.

Or I suppose, like a Command Module and Service Module. 

It's something we are looking into to address concerns of an LAS...and of landing on Earth.  Please let that be the last time I have to repeat that.  I'm wholly unqualified (and unpaid) to design an entire MCT all by myself, and I never claimed otherwise.
Yes, of course there are design challenges in this, just as there are in any design. 

Input is welcome, and if it's actually constructive I will take it back to the team and we can kick it around as see about concept modifications.  :-)




Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 10/08/2015 11:52 pm
You are assuming the major risk is in the cruise phase. I assume it is during launch, TMI and landing

STS's major failures were during launch and landing, but those failures had to do with flawed design. The only serious in-flight failure Apollo ever had certainly was during cruise phase.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/08/2015 11:53 pm

Particularly if you are trying the use the escape vehicle's engines as landing engines for the entire MCT. The forces on the connectors, which must be instantly separable during launch-abort, would be ridiculous.


yes, a fair point about the tension forces of having the lift on top could be a problem.  It'd have to be designed for tension as well as compression.  Which may prove impractical during the actual design process.  When landing on Earth it would be relieved of all of it's cargo mass and all of it's main propellant mass, so the underslung weight would at least be at it's minimum. 

The alternative is bottom mounted landing thrusters, or figuring out a way to land on Vacuum Raptor at sea level.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 10/09/2015 12:21 am

It has to be a separate spacecraft, or it can't operate as a escape vehicle. Such a double-vehicle would become hideously complex.


Yes.  That's probably why such a cylinder-cone vehicle with a separable nose cone with a crew hab has never been thought of before.

;-)

Doesn't even need to be cylinder/cone:

(http://i.stack.imgur.com/GmW0i.jpg)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/09/2015 12:30 am

It has to be a separate spacecraft, or it can't operate as a escape vehicle. Such a double-vehicle would become hideously complex.


Yes.  That's probably why such a cylinder-cone vehicle with a separable nose cone with a crew hab has never been thought of before.

;-)

Doesn't even need to be cylinder/cone:



:-)

Well said.

Now obviously I'm being a little facetious with Paul.  Those vehicles don't do a side entry into an atmosphere as a stack and that will add a level of complexity.  (The the cylinder-cone geometry might be a bit easier to cover with a TPS than the Soyuz geometry.  Heh.)

But the point being, to say the the pieces being joined where they can separate in an emergency is "hideously complex" may be a tad over stated.  ;-)


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/09/2015 03:08 am
[images of Apollo CM+SM and Dragon+trunk]

Apollo didn't and Dragon doesn't do EDL with those modules attached. The level of integration your require is an order of magnitude more complex.

It's not really two spacecraft in one, like MCT+ S2 would be two completely separate spacecraft. It's more a spacecraft, with an additional section.  Since everything below the lifeboat cannot function on it's own as it own spacecraft. So unlike your analogy, it's more like a semi tractor and trailer.

The back portion is not being "towed" like a trailer, it must be joined as a single continuous vehicle.

What I'm reacting to is that you responded to the idea of an MCT being launched to LEO unmanned, with a smaller shuttle bringing up the 100 passengers, by saying (paraphrasing) "But that means designing two spacecraft", as if you aren't required to design two (much more complex) spacecraft with your lifeboat/MCT concept. Which you continue to maintain; "it's not really two spacecraft in one".

But the point being, to say the the pieces being joined where they can separate in an emergency is "hideously complex" may be a tad over stated.

Do you not understand that a vessel that must function independently and as a deeply integrated functional part of a larger vessel (your lifeboat) is going to be much more complex than a vessel that only has to function independently (a LEO taxi)? And that a larger vessel that must be designed around a major piece that separates is going to be much more complex than a similar sized vessel that doesn't come apart?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/09/2015 05:09 am
A very rough way to estimate the cost of a vehicle development is looking at it's mass and multiplying by a factor weighted by the type of vehicle it is, for example a City buss costs less to develop them a rocket.

I think the Separate Bi-conic is attractive in this regard because rocket stages are cheaper to develop per unit of dry weight then manned capsules which are very nearly the most expensive things in aerospace development, we need only look at the relative budgets of SLS and Orion to see that Orion costs more per pound to develop.  Likewise SpaceX needed considerable NASA funding to develop Dragon and to make the 2nd version which is still short of the sophistication level likely to be employed in MCT.  We have every reason to belive the ratio in development costs in large, possibly in excess of 10:1.

I estimate a bi-conic would have a mass of around 75 mT, and the 2nd stage would be 72 mT.  I expect the Integrated version would have a mass greater then 75 but probably less the the raw additive 150 of the two separate vehicles due to some savings on redundancies, but it will probably have a development cost that is per pound equal to the smaller bi-conic I'm looking at.  This will wipe out the advantage of not developing a 2nd stage and makes the total cost greater unless the integrated vehicle has an exceedingly low mass or the cost ratio between stages/capsules is extremely low perhaps due to the difficulty of 2nd stage reuse engineering.

I would really like to hear some exact mass number from Lobo about the whole vehicle stack, dry masses for the first stage, the integrated bi-conic dry mass (without abort systems if that's your preference) and propellant loads in each so I can plug them into the launch vehicle performance calculator I've been using http://www.silverbirdastronautics.com/LVperform.html and do an apples to apples comparison to see how gross take off weight differs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/09/2015 05:43 am
I think the Separate Bi-conic is attractive in this regard because rocket stages are cheaper to develop per unit of dry weight then manned capsules

Not sure I'm seeing how you use the development cost of a conventional rocket stage to compare the development cost of MCT and a manned capsule.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/09/2015 07:15 am
But the point being, to say the the pieces being joined where they can separate in an emergency is "hideously complex" may be a tad over stated.

Do you not understand that a vessel that must function independently and as a deeply integrated functional part of a larger vessel (your lifeboat) is going to be much more complex than a vessel that only has to function independently (a LEO taxi)? And that a larger vessel that must be designed around a major piece that separates is going to be much more complex than a similar sized vessel that doesn't come apart?

The MCT is already very complex, just think of the requirements:

1. it needs to act as its own stage (IBMCT and variants)
2. it needs to be refuelled in LEO (perhaps multiple dockings).
3. it needs to have significant loiter time in LEO
4. it needs to do the TMI
5. it needs to act as a hab, with full multiply redundant life support
6. it needs to have interplanetary comms
7. it needs a large power supply and radiators - which need to be deployed, then stowed before EDL
8. it needs to do EDL on Mars
9. it needs to land on an unprepared (or only modestly prepared) site
10. it needs a way of unloading crew and cargo - and possibly loading cargo and crew before return to Earth
11. it needs to survive on Mars for about 550 days - longer if it does not return the next synod
12. it needs to be refuelled
13. it needs to do Mars ascent and TEI - all with components that have sat at Mars for 550 days.
14. it needs to do Earth EDL (with a heat shield that has already been used for Mars EDL)
15. ideally it needs to be refurbish-able for later use.
16. it needs to do all this with a low probability of LOM and lower probability of LOC
17. the same basic design needs to be usable for cargo, crew (and as a tanker?)
18. it needs to meet cost and schedule goals during development as otherwise SpaceX won't be able to afford it.

[obviously different mission plans would lead to different requirements - these are just a sample]

These are only the top level requirements, there are many second level requirements that also have to be met (life support, fire suppression, radiation tolerance, etc.)

Each of these top level requirements add to the complexity of the MCT, so much so that the biggest argument against an IBMCT is that it has too many requirements and that they cannot all be met in one vehicle at reasonable cost and with near term technology.

My point is that MCT is already horrendously difficult to design, adding a lifeboat makes it far more difficult.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/09/2015 07:48 am
Quote
11. it needs to survive on Mars for about 550 days - longer if it does not return the next synod

They can waive that requirement if they have to. I always anticipated that the first few MCT which have long surface times on Mars may never return. That would include the first passenger MCT that serves as habitat for at least one synod on Mars.

Those first ~3 MCT will serve as a monument for many generations of martians. :)

Later MCT will be unloaded, refuelled, checked then fly back to earth after a short stay. They will land on better prepared landing sites too.

The really hard requirements are 5) 7) 8) 9) 13) 14) But that is already plenty I agree.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/09/2015 07:57 am
My point is that MCT is already horrendously difficult to design, adding a lifeboat makes it far more difficult.

And its not just a lifeboat. That would be one thing. In the system Lobo proposes, the "lifeboat" is a major section of the re-entry system for the MCT and the primary propulsion for landing.

I struggle to find an analogy that Lobo understands. It's worse than the flight-deck of the Shuttle orbiter (just that top bit) being able to jettison during launch. It's that the entire front portion of the orbiter, including heat shield, RCS, front landing gear, must be able to serve as launch abort system, and be a space-plane in its own right to do a full EDL, and still function in its original role as a significant functional part of the Orbiter.

But to then not only argue that these two spacecraft (nose-LAS and orbiter + nose-LAS) are easier to design than two equivalent separate vehicles, but actually arguing that they aren't two spacecraft, just one and a "module".

Those first ~3 MCT will serve as a monument for many generations of martians.

Early settlers tend to be less sentimental than "future generations" would wish. So expect those MCTs to be quickly stripped for parts.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/09/2015 08:01 am
Quote
11. it needs to survive on Mars for about 550 days - longer if it does not return the next synod

They can waive that requirement if they have to. I always anticipated that the first few MCT which have long surface times on Mars may never return. That would include the first passenger MCT that serves as habitat for at least one synod on Mars.

Those first ~3 MCT will serve as a monument for many generations of martians. :)

Later MCT will be unloaded, refuelled, checked then fly back to earth after a short stay. They will land on better prepared landing sites too.

The really hard requirements are 5) 7) 8) 9) 13) 14) But that is already plenty I agree.

Waive a requirement to last for 550 days on Mars, replace with requirement to last indefinitely ?!?!

And the crew needs to get back somehow - first few missions won't have colonists.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/09/2015 09:11 am
Waive a requirement to last for 550 days on Mars, replace with requirement to last indefinitely ?!?!

And the crew needs to get back somehow - first few missions won't have colonists.

Waive the requirement to fly back after that time. The ISS shows that a habitat can be maintained for decades. That would be more valid for a habitat that can at some point be connected to an external ECLSS specifically designed for Mars and an expanding local power supply.

Part of the crew will go back with the passenger MCT that brings the crew that will man the station for the next synod and flies back after a few weeks. There will likely not be a life boat MCT. What would it be good for? It cannot go before the return window opens and that will be when the next MCT has arrived.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/09/2015 10:00 am
Waive a requirement to last for 550 days on Mars, replace with requirement to last indefinitely ?!?!

And the crew needs to get back somehow - first few missions won't have colonists.

Waive the requirement to fly back after that time. The ISS shows that a habitat can be maintained for decades. That would be more valid for a habitat that can at some point be connected to an external ECLSS specifically designed for Mars and an expanding local power supply.

Part of the crew will go back with the passenger MCT that brings the crew that will man the station for the next synod and flies back after a few weeks. There will likely not be a life boat MCT. What would it be good for? It cannot go before the return window opens and that will be when the next MCT has arrived.

So it is still a requirement to fly back one synod later. Not much of a gain there, at the cost of adding extra requirements about long duration surface stays and connection to external ECLSS.

Also I don't think short stays are possible without adding more requirements. They usually need a long duration return leg which expose the crew to higher radiation levels and adds requirements onto the MCT for long duration transits.

http://nssdc.gsfc.nasa.gov/planetary/mars/marsprof.html
Quote
The Short-Stay Mission - often referred to as an opposition-class mission, this mission profile provides Mars stay times of 30 to 90 days with a round trip total time of 400 to 650 days. This mission class requires a large amount of energy to be expended in transit, even after taking advantage of either a Venus swingby (on either the inbound or outbound leg) or a deep space propulsive maneuver in order to limit Mars and Earth entry speeds.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/09/2015 10:14 am
So it is still a requirement to fly back one synod later. Not much of a gain there, at the cost of adding extra requirements about long duration surface stays and connection to external ECLSS.


Sounds almost like you are deliberately misunderstanding me.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/09/2015 11:13 am
So it is still a requirement to fly back one synod later. Not much of a gain there, at the cost of adding extra requirements about long duration surface stays and connection to external ECLSS.


Sounds almost like you are deliberately misunderstanding me.

Let me restate it again, then.

There are two types of Mars mission classes, conjunction (long-stay) and opposition (short-stay). Opposition class missions spend over a year in space (often about 500 days on the return leg) and come closer to the Sun than the Earth (e.g. Venus swing-by). The short duration transits are conjunction class missions.

Let us assume that the initial crew come on a conjunction class mission, if they return on an opposition class mission then they will spend excessive time in space (zero-g and radiation), this adds requirements for more supplies, better ECLSS, Venus distance thermal control, etc.

Opposition class missions might be used for cargo at total duration is generally enough less than 2 years that they may be reused again at the next synod. I see no way of using Opposition class missions for crew transport without adding extra requirements to the MCT and increasing LOC probability.

So there is always a requirement for conjunction class missions for crew, which is what I meant by fly back one synod later. Any stay of the MCT (actively being used) on Mars longer than one synod adds extra requirements, as does connection to an external ECLSS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/09/2015 12:06 pm
As far as we know all MCT, both cargo and passenger, will go on trajectories that allow them to return after a short stay on Mars and return in the same synod. At least that is what Elon Musk has set as a goal for his transport system to reuse them every synod instead of every second synod.
That means the return leg will be significantly longer than the leg earth-mars. You are introducing a new requirement for shorter return flights that would mean that manned MCT could not be reused every synod. That may or may not be the case. IMO it is just a reason to reduce the number of people who return to earth to a minimum, maybe have more water as shielding for at least a part of the crew space for the return leg. But that is problematic as the mass budget available for return is much smaller.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Chris Bergin on 10/09/2015 12:29 pm
I think that's a good point about the difference between NASA Mars and SpaceX Mars. NASA Mars is very much focused on rotation. SpaceX Mars is to create a colony.

I doubt they would be short of customers who would be willing to spend some cash (probably affordable to a lot of people via selling their home) and up sticks and become a resident of Mars.....and not return (the element of increasing the population, as opposed to several years stays and coming back).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BroncoBill on 10/09/2015 12:38 pm
With you having been given advanced sight of the SpaceX MCT architecture, every word you post on this "speculation" thread from now onwards will be scrutinised with a fine tooth coombe until the grand reveal ! not that I'm suggesting in anyway that you should refrain from posting on this thread until the reveal, PLEASE keep on posting  :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 10/09/2015 01:03 pm
With you having been given advanced sight of the SpaceX MCT architecture, every word you post on this "speculation" thread from now onwards will be scrutinised with a fine tooth coombe until the grand reveal ! not that I'm suggesting in anyway that you should refrain from posting on this thread until the reveal, PLEASE keep on posting  :)

Did CB say anything about MCT? Not sure his tweet did....

I repeat.

"DEATH STAR"
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/09/2015 01:18 pm
As far as we know all MCT, both cargo and passenger, will go on trajectories that allow them to return after a short stay on Mars and return in the same synod. At least that is what Elon Musk has set as a goal for his transport system to reuse them every synod instead of every second synod.
That means the return leg will be significantly longer than the leg earth-mars. You are introducing a new requirement for shorter return flights that would mean that manned MCT could not be reused every synod. That may or may not be the case. IMO it is just a reason to reduce the number of people who return to earth to a minimum, maybe have more water as shielding for at least a part of the crew space for the return leg. But that is problematic as the mass budget available for return is much smaller.

A short return trip adds few extra requirements onto the MCT as there already are requirements for a short trip to Mars. However a long return trip which goes into the orbit of Venus adds requirements that are not needed on other phases of the mission. For cargo it adds a few extra requirements, but for crew it adds far more, especially as the MCT will be limited to 25% payload on the return trip.

It is helpful to make a distinction between mission requirements and MCT requirements. Using a short duration return is a mission requirement, as is returning N crew at a time. Handling the heat at the distance of Venus from the Sun and keeping a crew (of size N) healthy for a 500 days in space are MCT requirements.

I think Elon will be satisfied if the 90% cargo missions can be reflown in 1 synod while the 10% crew missions are reflown in 2 synods. Crew MCT probably need far more refurbishment than cargo MCT so it would be a push to get them reflown the next synod anyway.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/09/2015 01:37 pm
I think that's a good point about the difference between NASA Mars and SpaceX Mars. NASA Mars is very much focused on rotation. SpaceX Mars is to create a colony.

I doubt they would be short of customers who would be willing to spend some cash (probably affordable to a lot of people via selling their home) and up sticks and become a resident of Mars.....and not return (the element of increasing the population, as opposed to several years stays and coming back).

I think most people commenting on this thread realise that.

We see a distinction between early MCT missions which will likely have small crew sizes of professional astronauts, having an emphasis on exploration, basic engineering research on how to use ISRU especially for fuel and life support, and setting up an initial base. ISS style economy - crew do not pay for the resources they use. Most of these astronauts are likely to return home after one or more synods on Mars.

Later synods where the emphasis in on building the base(s) and modest scale mining, where the cost per person is still high. These people are likely to be sponsored (i.e. hired on Earth to do specific jobs), when their contracts are over they may return, and I think many will (think mines in the outback),  with a few very wealthy individuals. Company town economy. MCT and BFR are likely to have been updated.

Then finally 20+ years after the first landing mass colonisation at $500k per trip. Mixed economy. Economic migrants, going to make a better life for themselves (in terms of challenge and contributing to a frontier). Large colonial fleets.

Recent discussion on this thread has been on the first stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 10/09/2015 02:40 pm
I think MCT will be a system, not a single vehicle. Elon said as much. I also think that when Elon said "land the whole thing" he meant landing on Mars, not Mars and Earth.

1. The MCT would be launched into LEO by the BFR. It would be loaded with supplies, but not crew. No LAS is needed. It could be lifted by a second stage or act as its own second stage.
2. Additional BFR launches would refuel the MCT using a second stage as a tanker.
3. A maximum crew of seven would ride uphill to the MCT on a Dragon 2. The Dragon 2 returns empty.
4. MCT conducts mission to Mars and back as we have been discussing. Maximum crew of seven makes ECLSS issues simpler. Plenty of cargo capacity available for supplies if the ECLSS isn't closed loop.
5. On return, MCT does not land on Earth, but goes to LEO.
6. Dragon 2 picks up crew and samples. Depending on what the crew brings back, it might take multiple flights.
7. Another MCT is launched and both MCTs are prepared for the next synod.
8. Third mission opportunity can have three MCTs and add one each opportunity.

Reloading a returned MCT with cargo is an issue. If modular, cargo could be transferred by BFR and a tug.

A benefit is Earth planetary protection since MCTs never land on Earth.

Landing on Earth is not required for maintenance. With a launch every two years or so, a MCT will probably make no more than ten round trip flights. Even the heat shield can be designed to handle that. If engine replacement is needed, a modular engine mount system can make on orbit repairs possible.

The MCTs could be staged somewhere in cis-lunar space instead of LEO to reduce outgoing and return delta V requirements. Makes it more difficult to stage, but could be worth the effort.

Removing the requirement to land on Earth makes designing the MCT far simpler. No need for a LAS, the structure and landing legs do not have to be as strong, and less wear on the heat shield. It does require more effort to stage for the mission, but Elon mentioned orbital refueling and SpaceX will already have Dragon 2.

Sending 100 passengers and $500,000 each can wait for a later vehicle when there is a colony on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/09/2015 03:04 pm
Why doesn't SpaceX just build the MCT with a metholox plug nozzle engine and strap 8 Falcon 9's around it to launch it off earth?  They already have the Falcon 9's.  8 would give about 12 million lbs thrust.  A plug nozzle engine would allow landing in Earth's or Mar's atmosphere.  Like the Rombus or Ithacus designs or Phillip Bono in the 1960's.  Fuel in the MCT could be stored in cylinders that are concentric circles, one inside the other and go the length of the MCT in the center.  Cargo, passengers, solar panels or whatever could be stored around the sides with bay doors and easily unloaded low.  Supporting ribs along the sides would hold the Falcon 9's and landing legs.  It would be probably 12m in diameter and slightly higher than the Falcon 9 booster.   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 10/09/2015 03:20 pm
Reloading a returned MCT with cargo is an issue. If modular, cargo could be transferred by BFR and a tug.

Landing on Earth is not required for maintenance.

The MCTs could be staged somewhere in cis-lunar space instead of LEO to reduce outgoing and return delta V requirements. Makes it more difficult to stage, but could be worth the effort.

Why bring back the MCT to cis-lunar space or LEO if you do not land on Earth? Just keep it at Mars. Use it to shuttle cargo/personnel from Mars orbit to the surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 10/09/2015 03:27 pm
Reloading a returned MCT with cargo is an issue. If modular, cargo could be transferred by BFR and a tug.

Landing on Earth is not required for maintenance.

The MCTs could be staged somewhere in cis-lunar space instead of LEO to reduce outgoing and return delta V requirements. Makes it more difficult to stage, but could be worth the effort.

Why bring back the MCT to cis-lunar space or LEO if you do not land on Earth? Just keep it at Mars. Use it to shuttle cargo/personnel from Mars orbit to the surface.

I'm assuming a reusable interplanetary vehicle would be useful. Also direct entry to Mars instead of going into Mars orbit. I believe that is what Elon has in mind. Of course, other options are possible.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/09/2015 04:14 pm
Why doesn't SpaceX just build the MCT with a metholox plug nozzle engine and strap 8 Falcon 9's around it to launch it off earth?  They already have the Falcon 9's.

Because plug nozzles / aerospikes are not as easy to make - nor as effective - as we would all like. If they were, everyone would be doing it.

And I'm sorry, but strapping 8 F9 around a "MCT" is a terrible idea, both from launch pad complexity and engine count. 72 Merlins!!!!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 10/09/2015 04:40 pm
But the point being, to say the the pieces being joined where they can separate in an emergency is "hideously complex" may be a tad over stated.  ;-)

(https://upload.wikimedia.org/wikipedia/en/thumb/1/17/CEV_Lockheed_Martin.jpg/220px-CEV_Lockheed_Martin.jpg)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/09/2015 05:02 pm
But the point being, to say the the pieces being joined where they can separate in an emergency is "hideously complex" may be a tad over stated.  ;-)

(https://upload.wikimedia.org/wikipedia/en/thumb/1/17/CEV_Lockheed_Martin.jpg/220px-CEV_Lockheed_Martin.jpg)

And your point with this image is...?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RocketmanUS on 10/09/2015 05:12 pm
I think that's a good point about the difference between NASA Mars and SpaceX Mars. NASA Mars is very much focused on rotation. SpaceX Mars is to create a colony.

I doubt they would be short of customers who would be willing to spend some cash (probably affordable to a lot of people via selling their home) and up sticks and become a resident of Mars.....and not return (the element of increasing the population, as opposed to several years stays and coming back).
By the time people have payed off their home or have enough equity in their home to pay for the couple to move to Mars they would have already raised their kids. Not good to start a colony with people who have already raised their kids. More likely the first colonist will be sent there by sponsors.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/09/2015 05:48 pm
By the time people have payed off their home or have enough equity in their home to pay for the couple to move to Mars they would have already raised their kids. Not good to start a colony with people who have already raised their kids. More likely the first colonist will be sent there by sponsors.

I fully agree. This always seemed a fatal flaw in Elon Musks reasoning to me.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/09/2015 08:19 pm
I think the Separate Bi-conic is attractive in this regard because rocket stages are cheaper to develop per unit of dry weight then manned capsules which are very nearly the most expensive things in aerospace development,

That could be.  I don't know how expensive a manned reusable spacecraft is vs. an unmanned reusable spacecraft.  Either way, they'll both be independent spacecraft. 
However, they -could- possibly be made to have some commonality.  unlike with the Super Capsule design.  It may be possible for them both to share essentially the same OML  one has more "tankage" inside the OML, and the other has less tankage, but additional open space for crew hab and/or cargo.  Then the two could have the same...or at least similar EDL profiles, MPS's, landing gear, landing thruster systems, TPS shapes and types, tank tooling, etc. Like two Space Shuttles with different payloads in the payload bay...kind of.  Would need an interstage adaptor to house the conical nose of the S2 though.

I estimate a bi-conic would have a mass of around 75 mT, and the 2nd stage would be 72 mT.  I expect the Integrated version would have a mass greater then 75 but probably less the the raw additive 150 of the two separate vehicles due to some savings on redundancies, but it will probably have a development cost that is per pound equal to the smaller bi-conic I'm looking at.  This will wipe out the advantage of not developing a 2nd stage and makes the total cost greater unless the integrated vehicle has an exceedingly low mass or the cost ratio between stages/capsules is extremely low perhaps due to the difficulty of 2nd stage reuse engineering.

I would really like to hear some exact mass number from Lobo about the whole vehicle stack, dry masses for the first stage, the integrated bi-conic dry mass (without abort systems if that's your preference) and propellant loads in each so I can plug them into the launch vehicle performance calculator I've been using http://www.silverbirdastronautics.com/LVperform.html and do an apples to apples comparison to see how gross take off weight differs.

I'd have to go look up the working numbers for the booster.  I think the IBMCT was around 86mt...about the same as the SDMCT.  And the NIBMCT was a little lighter, as it's a little shorter, with only 2 engines where the S2 and IBMCT had 3.  I think the dedicated S2 was around 70mt.  (running off memory here).
These are still in flux, as they depend on assumptions we're still undecided on.  The working method of landing the S2 would be a fair amount lighter than the LAS/landing pressure fed systems, since reliability isn't as important.  That' part of the lesser mass.

But yes, one of the hooks of the IBMCT, is that you aren't duplicating your main propulsion, landing systems, tankage and TPS.  So it's more mass efficient to LEO, although a little heavier than the NIBMCT...but much lighter than NIBMCT + Dedicated S2.

Now, if you were to assume the IBMCT had no LAS system, as I originally entertained myself, and just essentially focused on making it as simple/common/standard as possible, it may be closer in mass or even light than the NIBMCT with the whole vehicle abort engines.  Then that gets around all the issues of having it quickly separable, while designing it for compressive, tensile, and side loads.
If an LAS for Earth ascent is not deemed as absolutely necessary, but engine-out and redundant systems are deemed "safe enough", and simplicity is the focus, or just that there'd be some alternative method of getting people to LEO than riding on MCT, then IBMCT may be the favored design for that person.

If you deem an LAS for Earth Ascent as absolutely necessary, then the NIBMCT may be the favored design for that person.

If one wants to be as conservative as possible overall, then the Super Capsule concept may be favored for that person.  As it has the more simple blunt body EDL profile unlike a biconic.   No real mass balance issues like a biconic as it's always vertical, and no side loads.  But it would really have nothing in common with the S2 or the booster.  It would be 3 very unique pieces.  The S2 and booster could share the same tank tooling...but that's about it.

Those were the reasons we had 3 different concepts.  After some discussion the IBMCT with LAS concept came about as kind of a way to try to have your cake and eat it too.  The LEO efficiency of IBMCT with a means to still abort the crew.  The best of both.  It could be implausible at the end of the day...it is a stab at it only..




Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/09/2015 08:36 pm
But the point being, to say the the pieces being joined where they can separate in an emergency is "hideously complex" may be a tad over stated.  ;-)

(https://upload.wikimedia.org/wikipedia/en/thumb/1/17/CEV_Lockheed_Martin.jpg/220px-CEV_Lockheed_Martin.jpg)

And your point with this image is...?

Lars,

Your own post here may be more appropriate, which kicked off this whole new discussion.  :-)
The 2nd and 3rd image in particular.

https://forum.nasaspaceflight.com/index.php?topic=37808.msg1431160#msg1431160


And its not just a lifeboat. That would be one thing. In the system Lobo proposes, the "lifeboat" is a major section of the re-entry system for the MCT and the primary propulsion for landing.

See Lars's post too.  It may be impractical, but I'm not the only one to propose it.  Heidmann's is more "CST-100" than "Dragon 2".  Which was our first thought on it too.  But we need a method to land on Earth which cannot be done one Vacuum Raptor as it sits.  So the idea of moving them external and landing on Earth on them as double duty was considered, vs. another set of landing engines at the base.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/09/2015 09:21 pm
A short return trip adds few extra requirements onto the MCT as there already are requirements for a short trip to Mars. However a long return trip which goes into the orbit of Venus adds requirements that are not needed on other phases of the mission. For cargo it adds a few extra requirements, but for crew it adds far more, especially as the MCT will be limited to 25% payload on the return trip.
....
I think Elon will be satisfied if the 90% cargo missions can be reflown in 1 synod while the 10% crew missions are reflown in 2 synods. Crew MCT probably need far more refurbishment than cargo MCT so it would be a push to get them reflown the next synod anyway.

If you can do a short trip to Mars with a longer return trip, to fit into 1 synod, I would assume you could do a long trip to Mars with a short return trip.

From an Earth perspective a human-return MCT would return from Mars just a few months after the main fleet leaves for Mars. The people would offload, and it would be refurbed and leave with cargo only (having missed the short trip window) for a 1 year trip to Mars.
 
From the Martian perspective you'd have that cargo MCT arriving a year after the passenger MCTs (which have been sent back with cargo on a slow return already). Offload the cargo, load with passengers, and launch back on a quick trajectory again.

It allows each MCT to be used once per synod - but I apologise in advance that I don't have a good enough grasp of the orbital mechanics involved. Is there any reason we hear more about a short trip to Mars, 1 month stay, with long return - and not the opposite long trip to Mars, 1 month stay, with short return?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RocketmanUS on 10/09/2015 10:07 pm
A short return trip adds few extra requirements onto the MCT as there already are requirements for a short trip to Mars. However a long return trip which goes into the orbit of Venus adds requirements that are not needed on other phases of the mission. For cargo it adds a few extra requirements, but for crew it adds far more, especially as the MCT will be limited to 25% payload on the return trip.
....
I think Elon will be satisfied if the 90% cargo missions can be reflown in 1 synod while the 10% crew missions are reflown in 2 synods. Crew MCT probably need far more refurbishment than cargo MCT so it would be a push to get them reflown the next synod anyway.

If you can do a short trip to Mars with a longer return trip, to fit into 1 synod, I would assume you could do a long trip to Mars with a short return trip.

From an Earth perspective a human-return MCT would return from Mars just a few months after the main fleet leaves for Mars. The people would offload, and it would be refurbed and leave with cargo only (having missed the short trip window) for a 1 year trip to Mars.
 
From the Martian perspective you'd have that cargo MCT arriving a year after the passenger MCTs (which have been sent back with cargo on a slow return already). Offload the cargo, load with passengers, and launch back on a quick trajectory again.

It allows each MCT to be used once per synod - but I apologise in advance that I don't have a good enough grasp of the orbital mechanics involved. Is there any reason we hear more about a short trip to Mars, 1 month stay, with long return - and not the opposite long trip to Mars, 1 month stay, with short return?
An emplty MCT would have a greater delta v capability than one that is carring cargo or crew. This could reduce the travel time back to Earth and or have more return windows.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/09/2015 10:08 pm
As far as we know all MCT, both cargo and passenger, will go on trajectories that allow them to return after a short stay on Mars and return in the same synod. At least that is what Elon Musk has set as a goal for his transport system to reuse them every synod instead of every second synod.
That means the return leg will be significantly longer than the leg earth-mars. You are introducing a new requirement for shorter return flights that would mean that manned MCT could not be reused every synod. That may or may not be the case. IMO it is just a reason to reduce the number of people who return to earth to a minimum, maybe have more water as shielding for at least a part of the crew space for the return leg. But that is problematic as the mass budget available for return is much smaller.
I do not believe we have shown whether this is possible or not, in terms of how much delta V is required for what overall mission duration & entry velocities.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 10/09/2015 10:48 pm
Reloading a returned MCT with cargo is an issue. If modular, cargo could be transferred by BFR and a tug.

Landing on Earth is not required for maintenance.

The MCTs could be staged somewhere in cis-lunar space instead of LEO to reduce outgoing and return delta V requirements. Makes it more difficult to stage, but could be worth the effort.

Why bring back the MCT to cis-lunar space or LEO if you do not land on Earth? Just keep it at Mars. Use it to shuttle cargo/personnel from Mars orbit to the surface.

I'm assuming a reusable interplanetary vehicle would be useful. Also direct entry to Mars instead of going into Mars orbit. I believe that is what Elon has in mind. Of course, other options are possible.

A number of reasons why I think SEP/NEP is better suited for interplanetary transfer than chemical + aerocapture:

- I imagine that after aerocapture at both Mars and Earth the heatshield would need a complete overhaul, respectively be replaced. Something you probably have to do on Earth. Entry from Mars orbit is benign in comparison.
- No volume constraints. A hab providing space and supplies for dozens of people is going to be huge (bigger than BA2100). You also need solar arrays and radiators. In the future you might even want stuff like artificial gravity.
- In order to arrive back at Earth within one synod you must refuel MCTs in Mars orbit, meaning some MCTs must fly refueling missions from Mars.
- Significantly lower IMLEO, less refueling operations. It will matter for cost.
- You need to develop a powerful SEP tug, but your Mars lander is going to be simpler. In general with a high-ISP system things are not so mass-sensitive.
- Technological progress favors SEP.
- If you want to go to Jupiter one day, good old chemicals won't do it  ;)

Anyway, old arguments.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/10/2015 03:14 am
I'm strongly in favor of SEP and see considerable use for it making VERY FAST transit possible.

How is this possible?  Wouldn't the system need to be huge and have magical power sources and such (insert anything Zubrin has ever said).  NO, you can get a Fast transit on the order of 100 days to Mars with a slow, low power SEP system.

The trick is you use your SEP to move your Mars bound vehicle with propellants up to high Earth orbit and then then drop by the Earth for a huge Oberth assisted burn.  For 2 km/s you should leave Earth with huge escape velocity and reach mars in 100 days (average). 

Now the problem is capturing at mars, the answer is Magneto-Plasma Aerocapture, this lets us avoid expensive propulsive capture and is then followed by about a week of Plasma assisted aerobraking which lets the eventual EDL be from a gentle 4 km/s.  So we get to have both fast transit and easy low speed EDL.

The SEP system has not even left Earth yet in this scenario, so you can do either one of two things, bring it back down to LEO for refueling and do it again (basically making it a Cis-lunar tug), or send it to mars by the conventional slow method of spiraling out from the Earths SOI (the SEP is too delicate to take the high thrust of the Oberth maneuver).  In the latter case your going to arrive much later then the manned capsule but if this is a conjunction mission the crew will be spending around 600 days on mars so their is plenty of time for the SEP to arrive before it is needed for departure which is what I favor.

The MCT would only need to reach low Mars orbit and would then rendezvous with the SEP and head for Earth, this return transit is made reasonably short by the fact the MCT is a completely dry shell now of only 100 mT (75 vehicle mass + 25 return cargo) and the SEP is nearly dry too so power to weight ratios are increased, also were not aiming to match Earth's orbit and capture gently, were going to simply intersect it on an elliptical orbit around the sun, that cuts the DeltaV needed.  At Earth we used the Magneto to capture again and bring both SEP and the MCT down to LEO (they probably need to separate to do this as the SEP is more delicate and would slow the process down for the MCT).  The crew can be retrieved via a Dragon capsule now, and we need to send another tanker to LEO to put landing propellants into the MCT, if we use enough the MCT can do a lot of retro-propulsion on entry and bring it's entry speed down from the 7.7 km/s of orbit down to the range of 4 km/s which matches it's mars entry speed, so all the thermal protection systems can be designed for this low performance point.

IMLEO is estimated at 570 mT of which 100 mT is the cargo load, 75 mT is the MCT dry mass, 200 mT is chemical propellant in the MCT (2 tanker loads of 100 mT each), 155 is SEP propellant, 15 mT is the SEP tank and 22 mT is the SEP hardware which has a power output of 4.5 MW which corresponds to an alpha value of 5 kg/kw.

BTW Using a braking system like Magneto Plasma is the only way I can see an Integrated Bi-conic and direct Earth return being viable, without it the entry conditions are too extreme to meet the low dry mass fractions that it's advocates are proposing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 10/10/2015 03:59 am
I'm strongly in favor of SEP and see considerable use for it making VERY FAST transit possible.

How is this possible?  Wouldn't the system need to be huge and have magical power sources and such (insert anything Zubrin has ever said).  NO, you can get a Fast transit on the order of 100 days to Mars with a slow, low power SEP system.

The trick is you use your SEP to move your Mars bound vehicle with propellants up to high Earth orbit and then then drop by the Earth for a huge Oberth assisted burn.  For 2 km/s you should leave Earth with huge escape velocity and reach mars in 100 days (average). 

Now the problem is capturing at mars, the answer is Magneto-Plasma Aerocapture, this lets us avoid expensive propulsive capture and is then followed by about a week of Plasma assisted aerobraking which lets the eventual EDL be from a gentle 4 km/s.  So we get to have both fast transit and easy low speed EDL.

The SEP system has not even left Earth yet in this scenario, so you can do either one of two things, bring it back down to LEO for refueling and do it again (basically making it a Cis-lunar tug), or send it to mars by the conventional slow method of spiraling out from the Earths SOI (the SEP is too delicate to take the high thrust of the Oberth maneuver).  In the latter case your going to arrive much later then the manned capsule but if this is a conjunction mission the crew will be spending around 600 days on mars so their is plenty of time for the SEP to arrive before it is needed for departure which is what I favor.

The MCT would only need to reach low Mars orbit and would then rendezvous with the SEP and head for Earth, this return transit is made reasonably short by the fact the MCT is a completely dry shell now of only 100 mT (75 vehicle mass + 25 return cargo) and the SEP is nearly dry too so power to weight ratios are increased, also were not aiming to match Earth's orbit and capture gently, were going to simply intersect it on an elliptical orbit around the sun, that cuts the DeltaV needed.  At Earth we used the Magneto to capture again and bring both SEP and the MCT down to LEO (they probably need to separate to do this as the SEP is more delicate and would slow the process down for the MCT).  The crew can be retrieved via a Dragon capsule now, and we need to send another tanker to LEO to put landing propellants into the MCT, if we use enough the MCT can do a lot of retro-propulsion on entry and bring it's entry speed down from the 7.7 km/s of orbit down to the range of 4 km/s which matches it's mars entry speed, so all the thermal protection systems can be designed for this low performance point.

IMLEO is estimated at 570 mT of which 100 mT is the cargo load, 75 mT is the MCT dry mass, 200 mT is chemical propellant in the MCT (2 tanker loads of 100 mT each), 155 is SEP propellant, 15 mT is the SEP tank and 22 mT is the SEP hardware which has a power output of 4.5 MW which corresponds to an alpha value of 5 kg/kw.

BTW Using a braking system like Magneto Plasma is the only way I can see an Integrated Bi-conic and direct Earth return being viable, without it the entry conditions are too extreme to meet the low dry mass fractions that it's advocates are proposing.

That sounds far too ambitious. First of all, why VERY FAST transit? What's the point? Not worth the effort IMO, not in any near future.

You probably want some chemical propulsion on your SEP stage, at least for the crew transfer, but not anything on the scale of MCT.

Magneto-Plasma Aerocapture? Are you sure that's not only for aerobraking? Either way, probably far from ready.

Why take the Lander back to LEO if you do not need it for aerocapturing? If they can't "refurbish" it on Mars at the beginning, you might as well expend it.

4.5MW is huge and 5kg/kw is far below the numbers I've seen.

The SEPs can cycle between LEO/HEO and HEO/Mars, that way they are back a lot faster and you need less power.

375t is a freaking huge payload for SEP. You can divide that into cargo/hab/lander and get 100t+ pieces. Again, less power.

My 2 cents.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/10/2015 06:51 am
That sounds far too ambitious. First of all, why VERY FAST transit? What's the point? Not worth the effort IMO, not in any near future.

Musk has had time of flight goals that are very aggressive as he seems to want to basically outrun the radiation danger and have a transit time that most people would find acceptable when crammed in small spaces.  The main point is that can get such transit times using SEP in an indirect way but getting to HEO followed by a TMI on Earth swingbuy, if we find transit times don't need to be so short we can subtract chem propellants from the lander and have it make a lesser burn on Earth swing buy and we would get something as low as the traditional Hohomann transfer. 

You probably want some chemical propulsion on your SEP stage, at least for the crew transfer, but not anything on the scale of MCT.

I don't believe it is necessary to make a hybrid drive SEP stage, the thrust level of chemical propulsion would require the SEP to have far higher rigidity they it otherwise would and it's mass would essentially be parasitic when doing the chemical burn as we intend to leave Earth with all the escape velocity needed to reach mars.  The SEP can fly slowly and efficiently to mars on it's own and brake their via the same Magneto brake tech the lander is using so separation of the two at high Earth orbit is the most efficient solution.

Magneto-Plasma Aerocapture? Are you sure that's not only for aerobraking? Either way, probably far from ready.

It is low TRL now but it is in active development, a demonstration cube sat will be launched soon by NASA.  And yes it is very much capable of Aerocapture as well as Aerobraking.  Were dealing with new technology all over the place with MCT such as an engine that is still in development and a launch vehicle that hasn't even been designed yet so I don't see why we can't use some tech that needs some development especially when it offers IMLEO reductions of near 50%.  See this paper
https://www.nasa.gov/sites/default/files/files/Kirtley_2012_PhI_PlasmaAerocapture.pdf

Why take the Lander back to LEO if you do not need it for aerocapturing? If they can't "refurbish" it on Mars at the beginning, you might as well expend it.

Nothing in the SpaceX mars transport system will be expendable, I though that was the one universal rule we could all agree on.  And it is needed here to carry the return habitat from mars surface to orbit and it carries the primary Magneto system to brake with upon return to Earth.  The SEP would have a brake too but much smaller as it's more delicate and doesn't have the urgency because it doesn't carry the crew.

4.5MW is huge and 5kg/kw is far below the numbers I've seen.

It's a conservative value consistent with Hall thrusters with power conversion units and solar at 300 W/kg.  Perhaps you misread it as kw/kg, it is the other way.

The SEPs can cycle between LEO/HEO and HEO/Mars, that way they are back a lot faster and you need less power.

That is an attractive architecture and would fit in this plan with a slight variation as a kind of triangle route, LEO->HEO, HEO->Mars, Mars->LEO.  As we need to pick up SEP at LEO it makes sense to have the returning SEP's from Mars brake fully on Earth return rather then having the ones at HEO expend propellants to spiral down.  Much depends on how much transfer of cargo/propellants are being done at HEO or at LMO, I'm assuming none initially but that it would grow as the system matures and stations (perhaps entirely robotic) are created to handle this activity as I assume you will need robotic arms for this.

375t is a freaking huge payload for SEP. You can divide that into cargo/hab/lander and get 100t+ pieces. Again, less power.

I'm avoiding any in-space loading/unloading of landers for initial missions, the habs are inside the landers at launch and all the way to mars to be unloaded only on the surface.  If you take these things out of the landers then they don't have any chemical thrust to do TMI and would have to be pushed by the SEP, which is slow and fine for cargo but not the crew, the description I've provided is just for the crew lander. 

But you are spot on when it comes to the propellants for the TMI, they could easily be separately conveyed to HEO which would split the total payload very nearly in half.  I will need to examine what this dose for Earth return transit time though as a larger SEP speeds that up considerably.  Two identical but smaller SEP's certainly reduce development costs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/10/2015 04:01 pm
Fast transit makes a lot of sense if you have refueling by cheap reusable launch vehicles. It cuts microgavity exposure, it cuts transit radiation dose in half, it cuts food needed in half, it cuts the needed habitat volume (thus reducing dry mass and thus cost and also partly off-setting the IMLEO increase from greater delta-v), and allows you to reuse your hardware twice as often (which means you need half as much of it).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 10/10/2015 04:34 pm
Refueling on both end is key to scaling up the delivered mass, too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/10/2015 05:24 pm
The trick is you use your SEP to move your Mars bound vehicle with propellants up to high Earth orbit and then then drop by the Earth for a huge Oberth assisted burn.
You probably want some chemical propulsion on your SEP stage, at least for the crew transfer, but not anything on the scale of MCT.
the thrust level of chemical propulsion would require the SEP to have far higher rigidity they it otherwise would and it's mass would essentially be parasitic when doing the chemical burn as we intend to leave Earth with all the escape velocity needed to reach mars.

Doing a drop'n'go Oberth manoeuvre means that your SEP is a high thrust type. (You can't spend days doing a HEO-LEO-MTO Oberth burn.)

That implies that your SEP-ship is already quite rigid. (Doing aerobraking into Mars orbit also implies that your ship is pretty rigid.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/10/2015 05:43 pm
Yep. SEP is a non-starter for a Mars transit. At a minimum it needs to be augmented by significant chemical propulsion for most of the effective delta-V. So why bother?

And if you treat the ship as essentially a cycler (in high orbits on both ends), then you are dealing with the same problem that cycler-advocates keep forgetting... In order to reach your SEP "battlestar galactica", you have to use chemical propulsion to accelerate all the crew, supplies, cargo, AND lander propellant to that high (almost escape) orbit for rendezvous. This last element is what SEP and cycler advocates seem to always forget about.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/10/2015 07:09 pm
The trick is you use your SEP to move your Mars bound vehicle with propellants up to high Earth orbit and then then drop by the Earth for a huge Oberth assisted burn.
You probably want some chemical propulsion on your SEP stage, at least for the crew transfer, but not anything on the scale of MCT.
the thrust level of chemical propulsion would require the SEP to have far higher rigidity they it otherwise would and it's mass would essentially be parasitic when doing the chemical burn as we intend to leave Earth with all the escape velocity needed to reach mars.

Doing a drop'n'go Oberth manoeuvre means that your SEP is a high thrust type. (You can't spend days doing a HEO-LEO-MTO Oberth burn.)

That implies that your SEP-ship is already quite rigid. (Doing aerobraking into Mars orbit also implies that your ship is pretty rigid.)

No you misunderstand, the SEP pushes the lander up to HEO first, then the Lander and SEP SEPARATE at HEO, only the lander with it's chemical propulsion system and inherent ability to tolerate high acceleration goes through the Oberth maneuver.

The SEP spirals away from the Earth on low thrust without any Oberth benefits, but it isn't carrying ANY cargo and isn't needed at mars for nearly 2 years so it can travel slowly and at high efficiency.



Yep. SEP is a non-starter for a Mars transit. At a minimum it needs to be augmented by significant chemical propulsion for most of the effective delta-V. So why bother?

And if you treat the ship as essentially a cycler (in high orbits on both ends), then you are dealing with the same problem that cycler-advocates keep forgetting... In order to reach your SEP "battlestar galactica", you have to use chemical propulsion to accelerate all the crew, supplies, cargo, AND lander propellant to that high (almost escape) orbit for rendezvous. This last element is what SEP and cycler advocates seem to always forget about.


No most of the effective acceleration is still coming from the SEP, to simply have the Lander perform depart form LEO with this much Escape velocity would require nearly 5.8 km/s DeltaV which would mean an IMLEO of 1000 mT for the same TMI mass.

A SEP transit vehicle is not at all like a cycler, it is making a controlled propulsive orbital insertion or braking maneuver at each planet, that means your not blasting off at escape velocity to catch the thing as it flies by on a hyperbolic trajectory each time.

No one who favors SEP for heliocentric HEO->Mars transfer would neglect using it for going between LEO->HEO as each of these is about equal in DeltaV for a low thrust system.  Only the crew in a small capsule needs to be sent via chemical propulsion for radiation avoidance, but all cargo, all consumables, all propellants and the vehicle hardware would obviously be a positioned in HEO by SEP leaving <1% of the mass to be moved by Chem. 


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/10/2015 08:08 pm
No you misunderstand, the SEP pushes the lander up to HEO first, then the Lander and SEP SEPARATE at HEO, only the lander with it's chemical propulsion system and inherent ability to tolerate high acceleration goes through the Oberth maneuver.
The SEP spirals away from the Earth on low thrust without any Oberth benefits, but it isn't carrying ANY cargo and isn't needed at mars for nearly 2 years so it can travel slowly and at high efficiency.

Ah, missed that in your original post. I take it the SEP brings them back home?

No one who favors SEP for heliocentric HEO->Mars transfer would neglect using it for going between LEO->HEO

They might. The radiation during a slow LEO-HEO spiral is apparently hell on solar panels. That means your efficiency is already degraded by the time you do the long Mars flight.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 10/10/2015 08:21 pm

No one who favors SEP for heliocentric HEO->Mars transfer would neglect using it for going between LEO->HEO

They might. The radiation during a slow LEO-HEO spiral is apparently hell on solar panels. That means your efficiency is already degraded by the time you do the long Mars flight.

Actually I favour using high acceleration chemical or NTR for LEO to high energy TMI and using SEP for the remainder of the trip matching to Mars velocity allowing for a faster than Hohmann transit and a low energy capture at Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 10/10/2015 11:17 pm
Musk has had time of flight goals that are very aggressive as he seems to want to basically outrun the radiation danger and have a transit time that most people would find acceptable when crammed in small spaces.

Well if they're going to Mars I suppose they must get used to it anyway. And 100 days or so is still a lot of time so you're not getting away with less habitable space.

I don't believe it is necessary to make a hybrid drive SEP stage, the thrust level of chemical propulsion would require the SEP to have far higher rigidity they it otherwise would...

Not really, a thrust of 1/10 of the stage's mass is sufficient, and ISP can be low. Just look at NASA's designs.

It is low TRL now but it is in active development, a demonstration cube sat will be launched soon by NASA.

I haven't seen it being used in any of NASA's designs, not even mentioned.

But if it works, I agree it would be a big deal for any architecture. I think it could drastically reduce the transfer time for SEP only, for starters. Or capture habitats without aeroshell. Or, in the case of MCT, drastically reduce heat shield requirements.

And it is needed here to carry the return habitat from mars surface to orbit and it carries the primary Magneto system to brake with upon return to Earth.  The SEP would have a brake too but much smaller as it's more delicate and doesn't have the urgency because it doesn't carry the crew.

I thought the "Magneto system" needs a lot of power...?

I imagine the SEP would have to create a bigger field in order to reduce max Q.

It's a conservative value consistent with Hall thrusters with power conversion units and solar at 300 W/kg.  Perhaps you misread it as kw/kg, it is the other way.

Values I've come across are for example:

Power system alpha: 20kg/kw
Tank mass: 4% of propellant.
Structure mass: 27% of (tank mass + power system mass).

I think 5kg/kw is more of a long term goal.

I quote from a paper called "Fast Transits to Mars Using Electric Propulsion" (2010).

Quote
The potential does exist to use solar
power for exploration within the inner solar
system. Solar array technology continues
to improve in cell efficiencies and in
system alpha. The expanded use of electric
prolusion, and the synergistic benefit of
electric propulsion and increasing power
availability is driving commercial and
government towards higher power systems.
The SOA solar arrays are currently 15 - 20
kg/kW. The DARPA Fast Access
Spacecraft Testbed (FAST) program has
progressed the SOA has with near-term
projected goals of 8 kg/kW at 1 AU.19
NASA studies have far-term predictions
approaching 3.3 kg/kW including the array,
based on Stretched Lens Array Square
Rigger (SLASR) technology with advanced
cells, gimbals, booms, power cabling, etc.20
A point design for a 232kW system had a current best estimate (CBE) system mass of 781 kg.21 Using an advanced
cell, a 100 kW End-of-Life, after 10 years at GEO, stretched lens array design has a predicted mass performance of
1.85 kg/kW


Yep. SEP is a non-starter for a Mars transit. At a minimum it needs to be augmented by significant chemical propulsion for most of the effective delta-V. So why bother?

Actually the chemical propulsion would only provide little delta-v, around 600m/s. That allows for pressure-fed storable propulsion.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/10/2015 11:34 pm
Yep. SEP is a non-starter for a Mars transit. At a minimum it needs to be augmented by significant chemical propulsion for most of the effective delta-V. So why bother?...
"Non-starter"?? That clearly doesn't mean what you think it means. SEP is baselined for Mars transit in NASA's current Mars exploration plan, and SpaceX has mentioned it's being traded for MCT.

That makes SEP pretty much the opposite of "non-starter."
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/11/2015 04:24 am
Yep. SEP is a non-starter for a Mars transit. At a minimum it needs to be augmented by significant chemical propulsion for most of the effective delta-V. So why bother?...
"Non-starter"?? That clearly doesn't mean what you think it means. SEP is baselined for Mars transit in NASA's current Mars exploration plan, and SpaceX has mentioned it's being traded for MCT.

That makes SEP pretty much the opposite of "non-starter."

Let me clarify. Anything that relies *primarily* on SEP for Mars transit propulsion is IMO a non-starter.

I've seen reasonable arguments for SEP during the long transit, but for Mars I don't think this helps a whole lot. (Going to the outer planets? Yes, essential, but not for the inner planets)

Especially in an MCT type architecture where "you land the whole thing" being a baseline assumption. With SEP you fall back into just another "Battlestar Galactica" mission mold (massive mother ships). If that is your thing... Sure, but there are more suitable threads for reviving those ideas.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 10/11/2015 04:28 am
With SEP you fall back into just another "Battlestar Galactica" mission mold (massive mother ships).

Which is evidently wrong, because SEP vehicles tend to be a lot more lightweight. What makes them appear massive are the big solar arrays.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/11/2015 04:40 am
In order to reach your SEP "battlestar galactica", you have to use chemical propulsion to accelerate all the crew, supplies, cargo, AND lander propellant to that high (almost escape) orbit for rendezvous. This last element is what SEP and cycler advocates seem to always forget about.

No most of the effective acceleration is still coming from the SEP, to simply have the Lander perform depart form LEO with this much Escape velocity would require nearly 5.8 km/s DeltaV which would mean an IMLEO of 1000 mT for the same TMI mass.

A SEP transit vehicle is not at all like a cycler, it is making a controlled propulsive orbital insertion or braking maneuver at each planet, that means your not blasting off at escape velocity to catch the thing as it flies by on a hyperbolic trajectory each time.

No one who favors SEP for heliocentric HEO->Mars transfer would neglect using it for going between LEO->HEO as each of these is about equal in DeltaV for a low thrust system.  Only the crew in a small capsule needs to be sent via chemical propulsion for radiation avoidance, but all cargo, all consumables, all propellants and the vehicle hardware would obviously be a positioned in HEO by SEP leaving <1% of the mass to be moved by Chem.

HEO (or even worse, a highly elliptical LEO-HEO transfer orbit) is a terrible assembly/rendezvous point, for a variety of reasons. Some that immediately come to mind:
 - Time to get there for SEP cargo runs - you need a LOT of SEP transfer vehicles to preposition cargo for a flotilla of your Mars transfer vehicles.
 - The number of runs you need to take through the Van Allen belts with a crew is significant, even if you dock and depart ASAP. It's not great for all the cargo spirals either.

So Im curious, what exactly do you mean by "HEO"?

Again what you propose does not have much left in common with what we know of the MCT architecture, so the discussion should probably move.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/11/2015 04:43 am
With SEP you fall back into just another "Battlestar Galactica" mission mold (massive mother ships).

Which is evidently wrong, because SEP vehicles tend to be a lot more lightweight. What makes them appear massive are the big solar arrays.

Wrong in the strict sense of mass (not size)... But nothing that is designed to push around 100s of tons of mass is going to be flyweight. A SEP system trades mass for many other problematic tradeoffs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/11/2015 06:58 am

HEO (or even worse, a highly elliptical LEO-HEO transfer orbit) is a terrible assembly/rendezvous point, for a variety of reasons. Some that immediately come to mind:
 - Time to get there for SEP cargo runs - you need a LOT of SEP transfer vehicles to preposition cargo for a flotilla of your Mars transfer vehicles.
 - The number of runs you need to take through the Van Allen belts with a crew is significant, even if you dock and depart ASAP. It's not great for all the cargo spirals either.

So Im curious, what exactly do you mean by "HEO"?

Again what you propose does not have much left in common with what we know of the MCT architecture, so the discussion should probably move.



Our SEP tug is reusable and we expect to be launching continually from Earth to build up a

High  Earth Orbit, aka something near escape velocity, could be Lagrange point, Lunar Distant Retrograde, highly elliptical orbits etc etc, basically something out at the very edge of Earth's Sphere of influence, the DeltaV is similar for them all.

-  High Earth orbit is FAR better then LEO in every way, it is free of dangerous orbital junk, it is colder meaning propellant boil-off is minimized, the SEP won't be shaded as it would be in LEO meaning it can depart at full power, their is no appreciable drag which would require constantly re-boosting stuff.

- Time to conduct the raising of cargo is inconsequential because we expect a continual non-stop launch campaign on Earth putting cargo into a stream going to the assembly point, the SEP tugs and their propellants will be less massive then the equivalent propellants needed to move cargo to HEO and do TMI from their then doing it from LEO on chem even at the slowest transfer.

- Why do I have to keep shooting down this straw-man, I have told you on several occasions that crew are sent up to the assembly point by a capsule on chemical propulsion, they do not make multiple passes through the Belt and I have never heard any evidence that the belt will be harmful to cargo.  Amorphous silicon solar collectors are basically immune to radiation degradation and can make plenty of passes through the belt as well.

Your INTERPRETATION of Musk's comments is different then my own, your interpretation is common, even dominant I grant that but it basically amounts to a single stage from LEO being then going all the way to mars surface and then back to Earth surface with refueling at LEO and mars surface.  I've rejected this as physically impossible as it makes a SSTO vehicle on Earth look easy in comparison.  I interpret his landing comment to refer to just the lander, aka the lander dose not shed any parts during EDL, a transit vehicle in mars orbit will be necessary to return to Earth.  I interpret any ambiguous comments from Musk in the most conservative manor possible and expect that system will be more complex then even Musk's original plans call for as he aims for the simplest solution first and has to compromise once he gets flight experience.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/11/2015 08:56 am
I'm strongly in favor of SEP and see considerable use for it making VERY FAST transit possible.

How is this possible?  Wouldn't the system need to be huge and have magical power sources and such (insert anything Zubrin has ever said).  NO, you can get a Fast transit on the order of 100 days to Mars with a slow, low power SEP system.

The trick is you use your SEP to move your Mars bound vehicle with propellants up to high Earth orbit and then then drop by the Earth for a huge Oberth assisted burn.  For 2 km/s you should leave Earth with huge escape velocity and reach mars in 100 days (average). 

Now the problem is capturing at mars, the answer is Magneto-Plasma Aerocapture, this lets us avoid expensive propulsive capture and is then followed by about a week of Plasma assisted aerobraking which lets the eventual EDL be from a gentle 4 km/s.  So we get to have both fast transit and easy low speed EDL.

The SEP system has not even left Earth yet in this scenario, so you can do either one of two things, bring it back down to LEO for refueling and do it again (basically making it a Cis-lunar tug), or send it to mars by the conventional slow method of spiraling out from the Earths SOI (the SEP is too delicate to take the high thrust of the Oberth maneuver).  In the latter case your going to arrive much later then the manned capsule but if this is a conjunction mission the crew will be spending around 600 days on mars so their is plenty of time for the SEP to arrive before it is needed for departure which is what I favor.

The MCT would only need to reach low Mars orbit and would then rendezvous with the SEP and head for Earth, this return transit is made reasonably short by the fact the MCT is a completely dry shell now of only 100 mT (75 vehicle mass + 25 return cargo) and the SEP is nearly dry too so power to weight ratios are increased, also were not aiming to match Earth's orbit and capture gently, were going to simply intersect it on an elliptical orbit around the sun, that cuts the DeltaV needed.  At Earth we used the Magneto to capture again and bring both SEP and the MCT down to LEO (they probably need to separate to do this as the SEP is more delicate and would slow the process down for the MCT).  The crew can be retrieved via a Dragon capsule now, and we need to send another tanker to LEO to put landing propellants into the MCT, if we use enough the MCT can do a lot of retro-propulsion on entry and bring it's entry speed down from the 7.7 km/s of orbit down to the range of 4 km/s which matches it's mars entry speed, so all the thermal protection systems can be designed for this low performance point.

IMLEO is estimated at 570 mT of which 100 mT is the cargo load, 75 mT is the MCT dry mass, 200 mT is chemical propellant in the MCT (2 tanker loads of 100 mT each), 155 is SEP propellant, 15 mT is the SEP tank and 22 mT is the SEP hardware which has a power output of 4.5 MW which corresponds to an alpha value of 5 kg/kw.

BTW Using a braking system like Magneto Plasma is the only way I can see an Integrated Bi-conic and direct Earth return being viable, without it the entry conditions are too extreme to meet the low dry mass fractions that it's advocates are proposing.
Do you have math to back this mission plan up?

Edit: For the case of the highly simplified circular Mars / circular Earth orbit rendezvous, based on:
http://forum.nasaspaceflight.com/index.php?topic=37536.msg1371984#msg1371984

If you start at high Earth orbit and descend to perigee, then you can burn for 2241m/s to raise aphelion to 3.31AU, which drops time of flight to 100.03 days.  Then you come in to the Mars approach at 12880m/s, and have to burn off 9275m/s in order to capture into a highly elliptical orbit.  This is fairly difficult (capture intensity goes up faster than linearly because you have a shorter chord of atmosphere to cut through, not just less time in that atmosphere), and exceeds the capabilities of any chemical propulsion capacity in this planning exercise by a large measure.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/11/2015 11:26 pm
Yes that is the escape manuver as I had calculated it, but I'm proposing Magneto-Plasma aerocapture which doesn't consume any propellant.  I'm not entirely sure that the MP system can provide enough drag to do such a capture primarily because it dose not look to be able to create lift, only drag so the atmospheric cord is quite small.

Withing this propellent-less braking system the trajectory clearly dose not work as it's beyond any feasible propulsive capture or any reasonable sized aeroshell.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/12/2015 06:11 am

HEO (or even worse, a highly elliptical LEO-HEO transfer orbit) is a terrible assembly/rendezvous point, for a variety of reasons. Some that immediately come to mind:
 - Time to get there for SEP cargo runs - you need a LOT of SEP transfer vehicles to preposition cargo for a flotilla of your Mars transfer vehicles.
 - The number of runs you need to take through the Van Allen belts with a crew is significant, even if you dock and depart ASAP. It's not great for all the cargo spirals either.

So Im curious, what exactly do you mean by "HEO"?

Again what you propose does not have much left in common with what we know of the MCT architecture, so the discussion should probably move.

Our SEP tug is reusable and we expect to be launching continually from Earth to build up a High  Earth Orbit, aka something near escape velocity, could be Lagrange point, Lunar Distant Retrograde, highly elliptical orbits etc etc, basically something out at the very edge of Earth's Sphere of influence, the DeltaV is similar for them all.

Not all of them are the same - nor stable. The moon will influence many of them. But eccentricity matters a lot. Make it too high and you WILL make lots of passes through the Van Allen belts. And no, Delta-V is NOT similar for them all.

-  High Earth orbit is FAR better then LEO in every way, it is free of dangerous orbital junk, it is colder meaning propellant boil-off is minimized, the SEP won't be shaded as it would be in LEO meaning it can depart at full power, their is no appreciable drag which would require constantly re-boosting stuff.

In every way?  ::) Oh boy. Not for accessibility, that's for sure. Nor travel time for supplies. Nor for solar flare protection. There are good some valid trade-offs to be made by staging there, but pretending to that there are no down sides just makes your argument look silly and it taints the rest of your arguments.

- Time to conduct the raising of cargo is inconsequential because we expect a continual non-stop launch campaign on Earth putting cargo into a stream going to the assembly point, the SEP tugs and their propellants will be less massive then the equivalent propellants needed to move cargo to HEO and do TMI from their then doing it from LEO on chem even at the slowest transfer.

Inconsequential?  ;D As said by everyone when real world practicality gets in the way. But I suppose being so generic allows you to hand-wave away all concerns. And the number of SEP tugs that would be needed. You haven't even settled on a HEO staging point, so how can we challenge your math assumptions for a SEP tug and how many you will need, and how large such SEP tugs would be?

But since you say you have made some basic calculations, please offer some information about these tugs. 1. Name a HEO staging orbit. 2. Settle on a SEP spiraling transit time. (weeks? months?) 3. Settle on how much cargo per SEP tug. (if you don't have a suggestion, lets make it 100t) Now can your show how large/massive/complex a SEP tug would have to be to accomplish the transfer of said amount cargo in said amount time to the defined staging point?

- Why do I have to keep shooting down this straw-man, I have told you on several occasions that crew are sent up to the assembly point by a capsule on chemical propulsion, they do not make multiple passes through the Belt and I have never heard any evidence that the belt will be harmful to cargo.  Amorphous silicon solar collectors are basically immune to radiation degradation and can make plenty of passes through the belt as well.

I only mentioned it to make you define your HEO staging orbit. And since you have not - above you wrote that "highly elliptical orbits" were a possible staging place, and those could certainly intersect with Van Allen belts. (again, specificity about a staging orbit would help avoid us bringing up these "straw-men" arguments) As for the effect on computers, arrays, and other equipment, I'm not sure what the point would be to bring it up to you, since you have already hand-waved away such concerns.

Your INTERPRETATION of Musk's comments is different then my own, your interpretation is common, even dominant I grant that but it basically amounts to a single stage from LEO being then going all the way to mars surface and then back to Earth surface with refueling at LEO and mars surface. I've rejected this as physically impossible as it makes a SSTO vehicle on Earth look easy in comparison.  I interpret his landing comment to refer to just the lander, aka the lander dose not shed any parts during EDL, a transit vehicle in mars orbit will be necessary to return to Earth.  I interpret any ambiguous comments from Musk in the most conservative manor possible and expect that system will be more complex then even Musk's original plans call for as he aims for the simplest solution first and has to compromise once he gets flight experience.

Well, now that *you* have rejected it...  ;) So you admit that you are basically using this thread now as a soap box for your own Mars architecture, now that you have rejected the aspects of it that are unique? And are there any more exotic (theoretical with no actual work done on them) technologies like Magneto Plasma Aerocapture that you want to throw in? NEP?

Whatever shape SpaceX's Mars plans actually solidify into will likely follow their current paradigm. Better, more practical use of existing technologies instead of chasing the very cutting edge of performance. It will be something that is more affordable rather than exotic. Taking something like a Mars SSTO lander and realizing that with some added performance and propellant transfer it can be used for Mars transit. And it could boost itself into LEO. Who would have thunk? Your ideas are almost the opposite of the SpaceX approach. Multiple staging points. Multiple kinds of vehicles. Are you *trying* to make this as expensive as possible by mutating it into a NASA-ish Mars program?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/12/2015 07:00 am
I agree @LarsJ, Impaler is not discussing a SpaceX MCT based on what we know. His ideas may work (I don't know) but they need a thread in the Mars forum instead of here.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/12/2015 07:16 am
Magnetic capture/deceleration may be included in the plan sooner than we think. It sounds like it is real and has very major advantages. We can assume though that it is not part of the plan now. There is much to do, lets wait it out.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/12/2015 07:27 am
Magnetic capture/deceleration may be included in the plan sooner than we think. It sounds like it is real and has very major advantages. We can assume though that it is not part of the plan now. There is much to do, lets wait it out.

How is it "real" in any way? Some theoretical papers aside, nothing much has been done on it, am I wrong here? And you could say the same about ANY technology on the horizon. EM drive?  ;D At some point the discussion needs to be based on what we actually know instead of what we would like it to be.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/12/2015 07:45 am
In every way?  ::) Oh boy. Not for accessibility, that's for sure. Nor travel time for supplies. Nor for solar flare protection. There are good some valid trade-offs to be made by staging there, but pretending to that there are no down sides just makes your argument look silly and it taints the rest of your arguments.

No where did I say they were better in every way, please stop putting words in my mouth.

Inconsequential?  ;D As said by everyone when real world practicality gets in the way. But I suppose being so generic allows you to hand-wave away all concerns. And the number of SEP tugs that would be needed. You haven't even settled on a HEO staging point, so how can we challenge your math assumptions for a SEP tug and how many you will need, and how large such SEP tugs would be?

My preferred staging point would be EML1, are you happy now?  The number, power level and transit time for SEP tugs would all involve trade offs between the size of the launch vehicle, the propellant tankers used, and ISP.  The MCT will likely be the largest payload and how much that can be reduced or subdivided will be key to sizing them.  I expect around a year for transit.

I only mentioned it to make you define your HEO staging orbit. And since you have not - above you wrote that "highly elliptical orbits" were a possible staging place, and those could certainly intersect with Van Allen belts. (again, specificity about a staging orbit would help avoid us bringing up these "straw-men" arguments) As for the effect on computers, arrays, and other equipment, I'm not sure what the point would be to bring it up to you, since you have already hand-waved away such concerns.

You really seem to hate the idea that anyone might have any flexibility when developing an idea and want to use that as a mean of attack rather then as a basis for rational discussion.  I find your straw-manning to be quite intentional and disrespectful, you repeatedly forget explanations from a few pages ago and bring up repeatedly debunked criticisms.

Well, now that *you* have rejected it...  ;) So you admit that you are basically using this thread now as a soap box for your own Mars architecture, now that you have rejected the aspects of it that are unique? And are there any more exotic (theoretical with no actual work done on them) technologies like Magneto Plasma Aerocapture that you want to throw in? NEP?

Whatever shape SpaceX's Mars plans actually solidify into will likely follow their current paradigm. Better, more practical use of existing technologies instead of chasing the very cutting edge of performance. It will be something that is more affordable rather than exotic. Taking something like a Mars SSTO lander and realizing that with some added performance and propellant transfer it can be used for Mars transit. And it could boost itself into LEO. Who would have thunk? Your ideas are almost the opposite of the SpaceX approach. Multiple staging points. Multiple kinds of vehicles. Are you *trying* to make this as expensive as possible by mutating it into a NASA-ish Mars program?

Everyone's ideas here are their own architectures or else no one but Elon Musk could post in this thread.  My ideas are perfectly consistent with the few crumbs of information we actually have and I fully expect to be predictive of the eventual mission architecture.

We know for a FACT that SpaceX is considering SEP (which btw is a 40 year old technology) from quotes by Shotwell herself, and Musk has said that HALL thrusters are easy to manufacture (and solar panels are simpler then drywall).  The Magneto Plasma Aerocapture is the most ambitious tech but it is well worth the development efforts and something SpaceX could easily do if they tried.

Your comments about adding performance to a SSTO vehicle reveal the kind of 'DeltaV-only' thinking that I find misleads most speculators here.  I rejected direct Earth return not because of insufficient velocity (which is is just barely achievable) it is the re-entry at 12-14 km/s at Earth which is not survivable for anything other then a small capsule like vehicle with high structural mass fraction.  I pay attention to entry velocities and g-forces as significant factors in the vehicles performance envelop and try to minimize them as much as possible.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Rocket Surgeon on 10/12/2015 07:50 am
The biggest problem with using SEP in cislunar space is the Van Allen radiation belt. This makes it an issue as you'll be forced to dwell in this high radiation zone for a long time as you raise up. Bad idea for people, but not for inert material. So you either need to boost past the belt quickly, or have A LOT of heavy shielding.

So here's a fun idea. If we go with the idea that the MCT will need several refuelings before leaving the earth-moon system, could we make the tankers also SEP powered? Deploy them to LEO then SEP all the way to above the Van Allen radiation belt, lets say L1. Then launch the MCT either with enough fuel to reach fueling point or refuel in LEO, boost out of the Van Allen radiation belt, then refuel at L1 and Launch to Mars for a fast transfer. Once done, the SEP-tankers come back down and reenter for servicing.

Of course, this would only be worth while if it saved a significant amount of mass, if you're only saving a hand full of tons, it wouldn't be worth it as a fully reusable Super Heavy Lift Rocket would probably drop $/kg to orbit down a fair bit. If Elon seriously wants to hit the '$500,000 a Mars Ticket' goal, we're talking ~$50/kg.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/12/2015 02:35 pm
SEP tugs themselves could be refueled in LEO. 

A refueling assembly station at L1.  This would be a fuel depot and cargo storage facility. 

SEP tugs would refuel and pick up cargo and fuel and transfer this to L1 on a continuous basis. 

MCT would launch, refuel at a LEO station, go to L1, refuel and load cargo containers, then go to Mars.

Or

Another set of SEP tugs would take cargo to Mars orbit.

A reusable lander would be stationed at Mars.  RL for short

RL's would make their fuel on Mars and bring up from Mars Argon of the SEP tugs.

RL's would refuel the SEP tugs and load cargo container and land this container on Mars. 

RL would refuel itself and refuel argon tank for re-launch later.  Cargo could be as little as 20 ton units. 

So you would have a continuous running of SEP tugs between L1 and Mars.  A continuous running of SEP tugs between LEO and L1.  And a continuous running of small reusable landers taking smaller cargo loads between Mars orbit and Mars and back. 

All of this can be done with existing rockets.  This would keep everyone happy, including foreign suppliers who want to get in on the Mars colonization.

MCT might not have to be as large if refueling is done in LEO, L1 and at Mars.  With SEP just carrying fuel to L1 from LEO, then they might not even be necessary between L1 and Mars, or build a huge SEP tug to carry 100 tons of cargo to Mars with enough argon to fly from L1 to Mars and Back. 

SEP allows for lots of flexibility. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/12/2015 07:14 pm
Using FH to launch SEP tugs.  At the very least, they could install a Martian communication satellite system around Mars and the moon.  We need communication before we go to Mars.  Also when Mars is on the far side of the sun away from Earth, some type of system would need to be in place to communicate around the sun.  Also, if we ever get an L2 station, communication on the back side of the moon will be necessary.  SEP tugs could put all these satellites and backup satellites in place.  GPS systems for the moon and Mars are eventually going to be needed also.  So in the near future, Falcon 9, and Falcon heavy will be busy installing not only Wi-Fi systems around earth, but systems around the moon and Mars.  LEO MCT refueling stations could be built with FH or they could wait for BFR.  50 ton SEP tugs can probably carry a lot of satellites or cargo payloads before BFR and MCT are built. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/12/2015 09:29 pm
SEP tugs themselves could be refueled in LEO. 

A refueling assembly station at L1.  This would be a fuel depot and cargo storage facility. 

SEP tugs would refuel and pick up cargo and fuel and transfer this to L1 on a continuous basis. 

MCT would launch, refuel at a LEO station, go to L1, refuel and load cargo containers, then go to Mars.

I like the picture you paint. It does have complexity but regularity to it. Including the low-speed cargo runs to Mars.

But when thinking SpaceX I try to judge by scalability and price. A few years down the track, if this is the plan, how many launches does it take to send 20 MCTs to Mars and back? Does it scale down significantly in price as the launch numbers increase to this and beyond?

I'm trying to envision this by that standard and I feel like there are too many launches and rendezvous. How do you feel it scales?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/12/2015 10:00 pm
Yep. SEP is a non-starter for a Mars transit. At a minimum it needs to be augmented by significant chemical propulsion for most of the effective delta-V. So why bother?

And if you treat the ship as essentially a cycler (in high orbits on both ends), then you are dealing with the same problem that cycler-advocates keep forgetting... In order to reach your SEP "battlestar galactica", you have to use chemical propulsion to accelerate all the crew, supplies, cargo, AND lander propellant to that high (almost escape) orbit for rendezvous. This last element is what SEP and cycler advocates seem to always forget about.
I think you're misunderstanding the concept, which seems sound to me, other than the notion that a technology as immature as MAC could be in the critical path of the plan without SpaceX having already purchased MSNW.  I think you guys are talking past each other because you may not understand the concept.

I understand why the crew will require chemical propulsion to reach high orbit rendezvous, but what about everything else?  Why can't they use SEP tugs to climb in and out of the gravity well?

What's your alternative that you are implying exists?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/12/2015 10:34 pm
Yep. SEP is a non-starter for a Mars transit. At a minimum it needs to be augmented by significant chemical propulsion for most of the effective delta-V. So why bother?

And if you treat the ship as essentially a cycler (in high orbits on both ends), then you are dealing with the same problem that cycler-advocates keep forgetting... In order to reach your SEP "battlestar galactica", you have to use chemical propulsion to accelerate all the crew, supplies, cargo, AND lander propellant to that high (almost escape) orbit for rendezvous. This last element is what SEP and cycler advocates seem to always forget about.
I think you're misunderstanding the concept, which seems sound to me, other than the notion that a technology as immature as MAC could be in the critical path of the plan without SpaceX having already purchased MSNW.  I think you guys are talking past each other because you may not understand the concept.

I understand why the crew will require chemical propulsion to reach high orbit rendezvous, but what about everything else?  Why can't they use SEP tugs to climb in and out of the gravity well?

What's your alternative that you are implying exists?

Why are you quoting a days old post? Some of my misunderstandings have been corrected, but not my conviction that this scheme solves some problems but introduces/ignores others. (complexity, cost, unproven tech.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/12/2015 11:36 pm
You seem to be taking a Zubrinist position, that no new technology is needed and simple 'brute force' can achieve all of SpaceX's mars goals.  Cost was no object to Zubrin he didn't bat an eyelash at 100 Billion to perform a single mission to mars which would have been flags and footprints.  The price points Musk wants to achieve are so radically low in comparison that they are in almost another universe.  And we know that Zubrin was dead wrong about even being able to archive his Direct missions without new technology or at his estimated costs. 

So it stands to reason that we need a LOT of new tech to do what Musk wants.  With any transportation system the higher the upfront development cost the lower the per trip cost.  The trick is to leave plenty of margin and look at technologies that offer big payoffs.


That's quite fascinating... Because from my point of view, "DeltaV-only thinking" seems to be what *you* are doing, making you turn to SEP, interesting trajectories, and Magneto Plasma Aerocapture. Again, pursuing performance at any cost is not what SpaceX is known for doing. They prefer a more brute force but cost effective approach.

No, you might accuse a SEP advocate of being ISP focused or propellant fraction focused but it is not a focus on ONLY DeltaV.  I'm looking to save propulsive DeltaV where possible but I am more then willing to incur greater DeltaV if it lowers thermal and g-force problems.  DeltaV only thinking is when people just look at the longest 'pole' of DeltaV in the mission, declare the vehicle has that capability and is X many tons of propellant at Y propellant fraction and think they are done without even examining other constraints.

I'm looking at all constraints, even trying to see what kind of limits Magneto Plasma Aerocapture has as at some point the necessary braking force is too high in g-forces for the vehicle to survive no matter how large of an effective diameter the plasma has.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: meekGee on 10/13/2015 01:00 am
Yep. SEP is a non-starter for a Mars transit. At a minimum it needs to be augmented by significant chemical propulsion for most of the effective delta-V. So why bother?...
"Non-starter"?? That clearly doesn't mean what you think it means. SEP is baselined for Mars transit in NASA's current Mars exploration plan, and SpaceX has mentioned it's being traded for MCT.

That makes SEP pretty much the opposite of "non-starter."

I don't know if "non-starter" is the right term, but the numbers don't look very good for SEP on a 100 day trip.

Why did NASA baseline it?  I didn't read said plan (I try to stick to non-fiction) but NASA makes a lot technological decisions that are not ideal.

Why is NASA still sticking with H2 and solids?  Why parachutes? 

NASA is a) not a singular body but rather made up of many "selfish" bodies, b) is influence by many irrelevant and political factors, and ) sometimes makes honest to goodness mistakes.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/13/2015 02:07 am
Yep. SEP is a non-starter for a Mars transit. At a minimum it needs to be augmented by significant chemical propulsion for most of the effective delta-V. So why bother?...
"Non-starter"?? That clearly doesn't mean what you think it means. SEP is baselined for Mars transit in NASA's current Mars exploration plan, and SpaceX has mentioned it's being traded for MCT.

That makes SEP pretty much the opposite of "non-starter."

I don't know if "non-starter" is the right term, but the numbers don't look very good for SEP on a 100 day trip.

Why did NASA baseline it?  I didn't read said plan (I try to stick to non-fiction) but NASA makes a lot technological decisions that are not ideal.

Why is NASA still sticking with H2 and solids?  Why parachutes? 

NASA is a) not a singular body but rather made up of many "selfish" bodies, b) is influence by many irrelevant and political factors, and ) sometimes makes honest to goodness mistakes.

NASA isn't looking at 100 day transits much. SpaceX is. And SEP does reduce IMLEO dramatically for a typical 6-7 month trajectory that NASA likes to look at. And NASA is planning surface rendezvous, so most flights to Mars will carry cargo (which doesn't benefit much from fast transit).

SEP actually trades quite well, and technology improvements allow Isp improvements, not being limited in Isp like chemical and NTR by needing to keep your combustion chamber from melting.

SEP allows you to reduce transit time (versus an equivalent-IMLEO chemical-only system) if you have good enough solar array and thruster technology, but its chief benefit is usually a dramatic reduction in IMLEO. And SpaceX could leverage that just for hauling propellant from LEO to HEO if they so desired. Remember, SpaceX's LEO Constellation will use SEP tech, so SpaceX will be quite capable technically of building SEP tugs (and will be producing Megawatts' worth of SEP arrays/thrusters anyway just for the constellation).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: meekGee on 10/13/2015 05:07 am
Yep. SEP is a non-starter for a Mars transit. At a minimum it needs to be augmented by significant chemical propulsion for most of the effective delta-V. So why bother?...
"Non-starter"?? That clearly doesn't mean what you think it means. SEP is baselined for Mars transit in NASA's current Mars exploration plan, and SpaceX has mentioned it's being traded for MCT.

That makes SEP pretty much the opposite of "non-starter."

I don't know if "non-starter" is the right term, but the numbers don't look very good for SEP on a 100 day trip.

Why did NASA baseline it?  I didn't read said plan (I try to stick to non-fiction) but NASA makes a lot technological decisions that are not ideal.

Why is NASA still sticking with H2 and solids?  Why parachutes? 

NASA is a) not a singular body but rather made up of many "selfish" bodies, b) is influence by many irrelevant and political factors, and ) sometimes makes honest to goodness mistakes.

NASA isn't looking at 100 day transits much. SpaceX is. And SEP does reduce IMLEO dramatically for a typical 6-7 month trajectory that NASA likes to look at. And NASA is planning surface rendezvous, so most flights to Mars will carry cargo (which doesn't benefit much from fast transit).

SEP actually trades quite well, and technology improvements allow Isp improvements, not being limited in Isp like chemical and NTR by needing to keep your combustion chamber from melting.

SEP allows you to reduce transit time (versus an equivalent-IMLEO chemical-only system) if you have good enough solar array and thruster technology, but its chief benefit is usually a dramatic reduction in IMLEO. And SpaceX could leverage that just for hauling propellant from LEO to HEO if they so desired. Remember, SpaceX's LEO Constellation will use SEP tech, so SpaceX will be quite capable technically of building SEP tugs (and will be producing Megawatts' worth of SEP arrays/thrusters anyway just for the constellation).

Clearly, the longer the transit, the more time you have to benefit from it, but we're talking about MCT here.
You asked "so why does NASA use it" when someone challenged SEP in this context...  So here's your answer.

I'll also add that in addition to the trip duration, there's the "land the whole thing" mentality.   If you're talking about ISS-esque solar array and radiator array, the idea of stowing them before EDL is not practical.

If instead you have a "Hermes"-type orbit-to-orbit ship in mind, then now SEP starts making sense.

But again, this is about MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/13/2015 05:25 am
SEP has exponentially larger benefits the faster you want to get to Mars.

To do a slow Hohmann transfer you need about 3.5 km/s in LEO.  But to try to do 100 days from LEO takes even more on the order of 5.5 km/s which is around 80% propellant fraction and very likely multiple booster stages as the weight of a tank has some minimum fraction leaving something like 10% payload.  Worse your arrival velocity on Mars is high and must be shed via either propulsion or aerocapture which is still in it's infancy using an aeroshell.

With SEP you can basically get the first ~3 km/s of your LEO departure speed done outside of the vehicle actually being sent TMI which is achieving the remaining ~2 km/s vastly easier if your doing it via chemical propulsion because your propellant is now less massive then the payload.

While doing SEP directly to Mars is estimated to reduce the IMLEO by half, using it to set up a periapsis burn is going to reduce your required mass by something like a factor of 4 because the move from LEO to high orbit is going to only require a propellant fraction of 13% to 19% depending on ISP range of 5k to 3k.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/13/2015 05:35 am

I'll also add that in addition to the trip duration, there's the "land the whole thing" mentality.   If you're talking about ISS-esque solar array and radiator array, the idea of stowing them before EDL is not practical.

If instead you have a "Hermes"-type orbit-to-orbit ship in mind, then now SEP starts making sense.

But again, this is about MCT.

We KNOW SpaceX is considering SEP for Mars, and as it is impossible to land a SEP, that mean IPSO FACTO that they are have ALSO considered a Semi-Direct architecture of a transit-vehicle and a separate landing vehicle.  And that such a vehicle trades very well against a single massive direct vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/13/2015 06:09 am
With SEP you can basically get the first ~3 km/s of your LEO departure speed done outside of the vehicle actually being sent TMI which is achieving the remaining ~2 km/s vastly easier if your doing it via chemical propulsion because your propellant is now less massive then the payload.

Again you completely hand-wave away complexity of a massive SEP booster stage. The fully loaded and fueled Mars transit vehicle/lander would mass what? 200t? 400t? More?  What delta-V of departure burn from the assembly point (EML1) is necessary? How large would your super-duper-mega SEP need to be to accelerate the assembled Mars craft to a 3 km/s boost at perigee? How long would it take to build that up the 3 km/s? Please... Some specifics. I dare you. (as a bonus, estimate the cost of establishing such an infrastructure of smaller SEP tugs and massive SEP boosters - one needed for every MCT!)

Congratulations on the thread hijack, BTW. Mission accomplished. Can we rename this thread to "MCT using SEP", so another thread can be created without this religious fervor?

We KNOW SpaceX is considering SEP for Mars, and as it is impossible to land a SEP, that mean IPSO FACTO that they are have ALSO considered a Semi-Direct architecture of a transit-vehicle and a separate landing vehicle.  And that such a vehicle trades very well against a single massive direct vehicle.

This is the scene I picture when Impaler reads something vaguely connecting SpaceX and SEP: (original movie scene transcript here:  http://www.imdb.com/title/tt0109686/quotes?item=qt0383410 )

SEP: What do you think the chances are of a guy like you and a girl like me... ending up together?
SpaceX: Well, SEP, that's difficult to say. I mean, we don't really...
SEP: Hit me with it! Just give it to me straight! I came a long way just to see you, SpaceX. The least you can do is level with me. What are my chances?
SpaceX: Not good.
SEP: You mean, not good like one out of a hundred?
SpaceX: I'd say more like one out of a million.
[pause]
SEP: So you're telling me there's a chance... YEAH!

 :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/13/2015 06:24 am
Please list some new technologies/systems you actually support developing other then huge boosters.

I'm still shocked that anyone can consider HALL thrusters EXOTIC propulsion in this day and age, they have existed for decades, are on hundreds of com-sats.  The bloody Ruskies have had them as baseline propulsion systems for their Mars mission plans for decades (first nuclear powered now solar powered), and they are kind of know for using 'brute force' technologies.  Just because NASA and American Aerospace only 'discovered' them 10 years ago dosn't mean they are some finniky bleeding edge tech.

The only remotely cutting edge tech I'm advocating is Magneto-Plasma Aerocapture and it has excellent effects on the IMLEO, even more then in NASA DRM plans because the MCT needs to soft land on Earth which means we can use it twice on each mission.  Frankly all-chem advocates like yourself SHOULD be jumping on this as a means to catch up with Electric propulsion architectures as the savings for chem of not having to do propulsive braking are far higher then for electric propulsion which can brake for a few scant additional percentages of propellant fraction.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Rocket Surgeon on 10/13/2015 06:44 am


No. If you are truly scaling this to be able to deliver 100t of cargo, you really need to have it in the middle. Not up front with the hab volume. When you do atmospheric entry, the propellant tanks will be mostly empty, so then by placing the cargo up top you are now forcing yourself to have to have a substantial minimum cargo load or the thing won't fly right.

Think about it. 100t. And it could be there, or it could be empty. If you do a sideways re-entry, that DOES constrain you to a center placement of cargo. OR you need to split the cargo into two balanced areas, one below and one above propellant tanks.

It's 100mt of payload.   That may be 100mt of pure cargo down the road at some point, but for quite some time it will be mixed cargo and crew/hab. 

So you have your IBMCT.  It has it's fairly heavy MPS on the bottom.  Above that you have two stacked cylindrical tanks that go up to about the center of the overall vehicle (when measured from tip to tail)...up a little over half way up the cylindrical portion.  Above that you'll have a cargo deck for mixed flights that is maybe 3 meters tall.  As the cargo will have to be lowered to the surface, none of it can be -too- large in one piece, but it will be heavy overall.  Above that you will have a pressurized hab volume filling the rest of the cylinder, and then another tapered pressurized hab volume in the nose.  If an LAS is required, the nose will have LAS/landing engines it it as well, along with small pressurized tanks to fuel them.   Overall, it will have a fair amount of mass in it.
So again, you'll have a mass area in the tail, amidships, and in the nose. 

With 100mt of pure cargo, and no hab area at all, that may be a little more tricky if all that 100mt is between the nose and the tanks.  They'd probably stow the heaviest pieces just above the tanks, with lighter and lighter pieces above that to help with weight distribution.

But, it's obviously something that'd have to be looked at in more detail by actual SpaceX engineers during the actual design process to see how the real weight distribution will interact with the EDL profile.

This divided concept would have the problem of being nose-light.  The mass will be concentrated in the middle, and at the aft in the MPS.  But given it's tapered overall OML, maybe that still makes for a feasible distribution for EDL?  It's a little above my area.  :-)

With the SDMCT, obviously that's not a problem because it's always vertical.

To go back to balancing the Biconic for a bit, would it be possible to have a configuration similar to the Phoenix (see attached), except applied to a Biconic and with some sort of escape system in the nose (sorry, really like the idea of the nose section being a dedicated 'lifeboat'. I just see it as a way to solve so many problems) It would still have the central column, as a way to move down to the main pressurized area.
Not sure what this would do to the mass in total, but wouldn't it allow for a more evenly distributed mass during EDL?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/13/2015 07:00 am
To go back to balancing the Biconic for a bit, would it be possible to have a configuration similar to the Phoenix (see attached), except applied to a Biconic and with some sort of escape system in the nose (sorry, really like the idea of the nose section being a dedicated 'lifeboat'. I just see it as a way to solve so many problems) It would still have the central column, as a way to move down to the main pressurized area.
Not sure what this would do to the mass in total, but wouldn't it allow for a more evenly distributed mass during EDL?

I do like that image, it is close to what I have in mind for an MCT. But I think a lengthy tunnel through a cryogenic tank might have issues.

If you insist on have a nose-mounted LAS, another way around it might be to have just a giant central tank (split between oxidizer and fuel), and then have a lower cargo bay (just above engines), and an upper cargo bay in the nose. It would force some level of cargo balance, but that would allow you to put all the pressurized volume up top. And as a bonus the unpressurized/heavy cargo would be easily offloaded near the surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/13/2015 08:19 am
To go back to balancing the Biconic for a bit, would it be possible to have a configuration similar to the Phoenix (see attached), except applied to a Biconic and with some sort of escape system in the nose (sorry, really like the idea of the nose section being a dedicated 'lifeboat'. I just see it as a way to solve so many problems) It would still have the central column, as a way to move down to the main pressurized area.
Not sure what this would do to the mass in total, but wouldn't it allow for a more evenly distributed mass during EDL?

I do like that image, it is close to what I have in mind for an MCT. But I think a lengthy tunnel through a cryogenic tank might have issues.

If you insist on have a nose-mounted LAS, another way around it might be to have just a giant central tank (split between oxidizer and fuel), and then have a lower cargo bay (just above engines), and an upper cargo bay in the nose. It would force some level of cargo balance, but that would allow you to put all the pressurized volume up top. And as a bonus the unpressurized/heavy cargo would be easily offloaded near the surface.
One additional benefit to a tunnel through a fuel tank: It makes the best solar storm shelter you can buy on the mass required for the tunnel segment and some electric blankets.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 10/13/2015 09:06 am
Please list some new technologies/systems you actually support developing other then huge boosters.

I'm still shocked that anyone can consider HALL thrusters EXOTIC propulsion in this day and age, they have existed for decades, are on hundreds of com-sats.  The bloody Ruskies have had them as baseline propulsion systems for their Mars mission plans for decades (first nuclear powered now solar powered), and they are kind of know for using 'brute force' technologies.  Just because NASA and American Aerospace only 'discovered' them 10 years ago dosn't mean they are some finniky bleeding edge tech.

station-keeping thruster with millinewtons thrust is totally different thing than electric engine that can give multiple km/s delta-v in reasonable short time for a big spacecraft.

The energy source for big SEV spacecraft is the exotic part, not the thruster itself.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/13/2015 09:53 am
With SEP you can basically get the first ~3 km/s of your LEO departure speed done outside of the vehicle actually being sent TMI which is achieving the remaining ~2 km/s vastly easier if your doing it via chemical propulsion because your propellant is now less massive then the payload.

Again you completely hand-wave away complexity of a massive SEP booster stage. The fully loaded and fueled Mars transit vehicle/lander would mass what? 200t? 400t? More?  What delta-V of departure burn from the assembly point (EML1) is necessary? How large would your super-duper-mega SEP need to be to accelerate the assembled Mars craft to a 3 km/s boost at perigee? How long would it take to build that up the 3 km/s? Please... Some specifics. I dare you. (as a bonus, estimate the cost of establishing such an infrastructure of smaller SEP tugs and massive SEP boosters - one needed for every MCT!)

Small-thruster SEP is now routine on commsats for stationkeeping.  Hall Effect Thrusters have recently solved the erosion problems that limited their lifetime.  Large arrays of small thrusters are trivially easy.  The design of large arrays of solar panels require only moderate scaleup efforts relative to the monetary outlays discussed in Mars mission planning;  The only reason we don't have them yet seems to be that we're not pushing much money into those efforts.  The current generation of commsat builders are all selling SEP orbit-raising solutions for GTO -> GSO, the "all-electric propulsion satellite";  The business model seems to be "Two satellites for the launch price of one" rather than "A satellite twice as big" for now.

With SEP you can basically get the first ~3 km/s of your LEO departure speed done outside of the vehicle actually being sent TMI which is achieving the remaining ~2 km/s vastly easier if your doing it via chemical propulsion because your propellant is now less massive then the payload.

Again you completely hand-wave away complexity of a massive SEP booster stage. The fully loaded and fueled Mars transit vehicle/lander would mass what? 200t? 400t? More?  What delta-V of departure burn from the assembly point (EML1) is necessary? How large would your super-duper-mega SEP need to be to accelerate the assembled Mars craft to a 3 km/s boost at perigee? How long would it take to build that up the 3 km/s? Please... Some specifics. I dare you. (as a bonus, estimate the cost of establishing such an infrastructure of smaller SEP tugs and massive SEP boosters - one needed for every MCT!)
Let's work with this.  Let's say that after the BFR+MCT unknown is answered, we can get 100 tons of large-diameter freight to the high end of LEO in a completely reusable manner, with nothing left in orbit.

Our cargo staging point is some undecided orbit in the general vicinity of the Moon (DRO, EML1, EML2), with geocentric semimajor axis about 384,400km, orbital velocity about 1018m/s.

Our cargo will launch into a 1500x1500km Low Earth Orbit, high enough that it doesn't contribute to the debris problem and (not coincidentally) right in the middle of a high radiation zone.  Orbital velocity at this altitude is about 7117m/s.

Delta V for a low-thrust transfer between circular orbits on the same plane, seems to approximate the difference in orbital velocities.  Delta V required to reach cargo staging point on SEP: 6099m/s.

Let's arbitrarily add another 901m/s for plane change and whatever costs are associated with Lunar capture.  That gives us 7000m/s dV.  We're going to add another 1000m/s dV for the terminal staging, which I'll get to later.

The NEXT thruster has been tested to 5.5 years of burn;  Earth-Mars synodic cycles are more like 2.135 years.  We'll give the tug 4 years after launch to get on target, and give it NEXT thrusters for propulsion, with 4190s Isp.  At 4190s Isp, a vehicle that weighs 100 tons wet reaches 8km/s after depleting enough propellant that it weighs 82.3 tons dry.

The tug requires an average acceleration over this time of 8000m/s / 4 years, or 5.55*10^-5 m/s.  The vehicle mass averages about 91.15 tons during its burn, so average acceleration needs to be about 5.78N.  This is a lot relative to current designs.  A  NEXT thruster gives us only about 236mN of thrust.  We would need 25 of them per tug to do the mission in 4 years.  Let's arbitrarily bring it up to 40 - there's going to be some time when the vehicle is shadowed by Earth, after all.  40 NEXT thrusters consume 6.9kW apiece for 276kW total;  Let's bring that up to 300kW since there will be some degradation over time.  I'm going to assume with enough work we can achieve a 300kW array that weighs 2000kg (150W/kg).  40 NEXT thrusters weighs around 2000kg as well.  Give 1000kg to structural support for these things.  Assume that the chemical tank and solar shield the SEP tug is carrying as cargo can be done for 7300kg.

That leaves 70 tons of cargo chemical propellant in our Lunar staging orbit with 1000m/s left, for every BFR launch.

Next stage: We define the _Deep Elliptical Orbit_, a name chosen because of how much ambiguity "H" and "E" have, as an orbit with one leg on the Moon and one leg on Earth.  The propellant tugs reach Lunar staging orbit and start to burn retrograde, lowering periapsis back to Earth.  This is wasteful relative to the chemical manner of achieving elliptical orbits, but they can afford it, because 4190s Isp.  They burn for about 1000m/s and drop perigee down to 300km.

You now have 70 tons of chemical propellant where you need it for the Impaler Short Transit.

---

This proposal is external to the issue of how you would send the vehicle up, whether the lander would reach Lunar staging orbit or whether it would go with the crew capsule or what.  Use my math to deduce the answers to those questions.

If you can indeed MAC away all your excess velocity at Mars, and you still need chemical propulsion for descent, then you can send the lander up to DEO, running out of propellant at ~3.1km/s, then refuel from the propellant depot already in DEO, and you'll have the 2241m/s (plus some small number, that was based on "descent from high orbit") that you need to go from DEO to the Impaler Short Transit.  Then, assuming 4.5km/s total vehicle capability (you need that to get from the Mars surface to LMO), you'll have another 2259m/s to work with for descent and course corrections.  For a 400 ton loaded-but-dry-weight lander, that 4.5km/s wet mass is 1338 tons, or 938 tons of propellant.  The vehicle in DEO won't be truly empty, though - it will still have another ((4.5 - 3.1 = 1.4km/s) run through the delta V equation = 183 tons) in it, useful for abort-to-Earth-landing contingencies.  In the face of that propellant delivery need, (938 - 183) = 755 tons, you'll want to have 11 BFR launches of SEP propellant tugs to DEO, on top of the prop required in LEO to get the BFR itself to DEO (or however you wanna do that, with SEP perhaps if you have a separate nested manned capsule).

The tradeoff is: you can keep the BFR as a 4.5km/s vehicle instead of making it a (3.2km/s earth escape) + (2.4km/s Impaler Short Transit injection) + (~2km/s or whatever you need for EDL) ~= a 7.6km/s vehicle. 

You're also going to need comparable efforts to get the thing home on a fast transit, though.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RotoSequence on 10/13/2015 09:56 am
Has anyone suggested the possibility of SpaceX's announcement including "a reusable, nuclear (fission, fusion, either or) upper stage for the BFR" yet?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/13/2015 09:14 pm
Re: "Non-starter"

That really is one of the most obnoxious terms commonly used on this site. I wish the mods would add it to the unacceptable-language list.

You seem to be taking a Zubrinist position, that no new technology is needed and simple 'brute force' can achieve all of SpaceX's mars goals.  Cost was no object to Zubrin he didn't bat an eyelash at 100 Billion to perform a single mission to mars which would have been flags and footprints.

While Zubrin is prone to exaggerate problems in rival proposals, and underplay issues with his own, we have to be fair and remember he came into the game trying to suggest a realistic alternative to a late '80s/early '90s NASA proposal that was priced somewhere around $500 billion.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/13/2015 09:36 pm
Has anyone suggested the possibility of SpaceX's announcement including "a reusable, nuclear (fission, fusion, either or) upper stage for the BFR" yet?

As far as I know their are few advocates for Nuclear propulsion left on these forums and none have advanced it for use by SpaceX, it is hard to imagine that a company which finds Hydrogen 'not worth the effort' would go Nuclear.  I've read some old threads in which the Nuclear camp got schooled badly by a guy named Sorenson, even NASA has basically been downplaying the idea compared to decades past.

As for the technology itself, Nuclear Thermal rockets are not reusable, in fact they are difficult to even fire more then once because the core will want to melt-down from decay heat after propellant flow stops.  Nothing Fusion based is anywhere near to even getting off a chalk board right now.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/13/2015 09:51 pm
I think a nuclear fusion engine using magnetic control of the plasma and having one end expel the plasma for propulsion with the other end feeding liquid hydrogen in and continuously making plasma for propulsion would work.  It would still require a lot of power just to use lasers to create the fusion at one end.

However if you are going to use some other type of power source to create the fusion for the engine, one still needs a lot of power, and you have to have heavy hydrogen to operate.  How much I don't know? 

So it seems SEP with very large arrays and a cluster of a lot of ion engines and a large tank of propellant could also make a very large in space, higher speed cargo or even human run to Mars. 

A small NEP reactor, sealed, use for several years, and throw away, by shooting it to the Sun.  It might be somewhat smaller and could make several Mars runs before depleting its fuel.  Technology for small sealed reactors should be improved first. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/13/2015 10:00 pm
I think the biconic shape is the way to go.  I do think concentric fuel/oxygen tanks running the entire length of the MCT in the center would allow for more balance.  Say with liquid methane in the center tube and the lox in a donut tube around the methane.    Cargo, solar panels, landing legs, thrusters and thruster fuel, etc could be around this central tanking system.  The picture on post 733 is what I like except with concentric center fuel/lox tanking.  One can still dock on the nose, as tank dome could stop short of the nose.  Heavy cargo could be stored near the bottom for easier unloading.  Instead of the plug nozzle engine as shown, standard Raptors vacuum engines could be on the bottom.  The interstage could double as heat protection flaps when coming back through the atmosphere. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/13/2015 11:17 pm
Has anyone suggested the possibility of SpaceX's announcement including "a reusable, nuclear (fission, fusion, either or) upper stage for the BFR" yet?

I think a nuclear fusion engine using magnetic control of the plasma and having one end expel the plasma for propulsion with the other end feeding liquid hydrogen in and continuously making plasma for propulsion would work.  It would still require a lot of power just to use lasers to create the fusion at one end.

However if you are going to use some other type of power source to create the fusion for the engine, one still needs a lot of power, and you have to have heavy hydrogen to operate.  How much I don't know? 

So it seems SEP with very large arrays and a cluster of a lot of ion engines and a large tank of propellant could also make a very large in space, higher speed cargo or even human run to Mars. 

A small NEP reactor, sealed, use for several years, and throw away, by shooting it to the Sun.  It might be somewhat smaller and could make several Mars runs before depleting its fuel.  Technology for small sealed reactors should be improved first.
Yeah...  these are tangents that really don't belong in this thread.  Fusion engineering is comparable in scope to the most expensive Mars programs proposed.  Fusion propulsion is way, way out there, quite possibly postdating practical fusion power;  Not that it shouldn't be explored, but this is a thing that Elon Musk wants to fly in a decade, not in half a century.

Here's what we *thought* when we started work on fusion, and what actually happened:

(http://i.imgur.com/sjH5r.jpg)

ITER won't start even experimental work on the easiest D-T reaction for another 12 years, and it weighs 23,000 tons and isn't even designed for the extraction of useful electrical power.  Newer IEC fusion approaches are optimistic, but tiny in the amount of effort being expended; see the "actual funding" line for the tokomak work that's ended up monopolizing most of our efforts.

Fission Nuclear Thermal Rockets have seen plenty of speculation, starting with Von Braun if not earlier, but they're questionable from a performance perspective, a fairly immature technology (vacuum restart is much less plausible than for turbopumped chemical rockets) , the very worst thing you can get permission to fly through the air, and do not scale down to convenient test units.  NTR still looks interesting to NASA because it permits less complex missions with fewer launches, but the progress in SEP has been vast since the last time it looked like they were actually going to develop something, under Reagan's Star Wars projects.  The best use case seems to be a fairly small engine (but they only get so small) pushing a large load through interplanetary burns (where TWR isn't such an issue);  But that delves into the difficult problem of long-term storage of hydrogen, the most efficient propellant for NTRs.  I've seen a proposal to do it using water (http://spirit.as.utexas.edu/~fiso/telecon/Adamo_7-23-14/), or ammonia, but not sure how serious that is, and it further damages the numbers relative to SEP.

I think the biconic shape is the way to go.  I do think concentric fuel/oxygen tanks running the entire length of the MCT in the center would allow for more balance.  Say with liquid methane in the center tube and the lox in a donut tube around the methane.    Cargo, solar panels, landing legs, thrusters and thruster fuel, etc could be around this central tanking system.  The picture on post 733 is what I like except with concentric center fuel/lox tanking.  One can still dock on the nose, as tank dome could stop short of the nose.  Heavy cargo could be stored near the bottom for easier unloading.  Instead of the plug nozzle engine as shown, standard Raptors vacuum engines could be on the bottom.  The interstage could double as heat protection flaps when coming back through the atmosphere.

Remember: The methalox propellant has to be stored at about 100K.  The humans have to be stored at about 295K.  The black-body temperature of Solar radiation is around 255K.  Increasing the surface area where the propellant and the human habitat come together, and increasing the variety of angles that the sun can strike the propellant tank, increases the amount of thermal load you have to deal with.  You're describing a worst-case-scenario thermally.  It may well be a best-case-scenario for solar & galactic cosmic ray protection, but the steady flow of GCRs are only slightly affected by any practical amount of mass (they penetrate better, being higher energy), and the solar ones only occur in short-timespan events, solar storms.  This is why there's a degree of elegance to preserving a spot at ~100K inside the propellant tank, and only heating it up for human habitation (incurring lots of boil-off) during the solar storms that should happen for around 12 hours every fifth mission or so (IIRC?).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/14/2015 01:41 am

I'll also add that in addition to the trip duration, there's the "land the whole thing" mentality.   If you're talking about ISS-esque solar array and radiator array, the idea of stowing them before EDL is not practical.

If instead you have a "Hermes"-type orbit-to-orbit ship in mind, then now SEP starts making sense.

But again, this is about MCT.

We KNOW SpaceX is considering SEP for Mars, and as it is impossible to land a SEP, that mean IPSO FACTO that they are have ALSO considered a Semi-Direct architecture of a transit-vehicle and a separate landing vehicle.  And that such a vehicle trades very well against a single massive direct vehicle.
It's not, in fact, impossible to land an SEP on Mars. Just kind of odd and mass inefficient. But with a sufficiently good solar array, you could do it. I should point out that an "ISS-esque" solar array is, in fact, retractable!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 10/14/2015 01:47 am
Has anyone suggested the possibility of SpaceX's announcement including "a reusable, nuclear (fission, fusion, either or) upper stage for the BFR" yet?

I think many of us have considered it, but it'd actually be rather disappointing since it'd stack additional (legal) impediments against the possibility of a SpaceX mars mission. It's also unnecessary when you have something as big as the BFR.

Seeing a gigantic nuclear interplanetary colony ship descending through Earth's atmosphere bound back from Mars would truly be an incredible experience to have in one's lifetime though.

Edit:
It's not, in fact, impossible to land an SEP on Mars. Just kind of odd and mass inefficient. But with a sufficiently good solar array, you could do it. I should point out that an "ISS-esque" solar array is, in fact, retractable!

I agree that it's possible and would be great on the fuel extraction/colonial front if you can extend them again on the surface, but it's horribly terrifying. If at any point they don't retract/extend properly, you have a problem. If whatever protective cover you have over them whilst stowed doesn't lock properly, you have a problem. Whilst it would solve radiator and power issues, the concept is still pretty frightening.

Edit edit: As the ISS has proved to an extent, big, movable solar panels in space can be rather unreliable, although there's probably ways to engineer that issue into the floor.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Rocket Surgeon on 10/14/2015 03:02 am
To go back to balancing the Biconic for a bit, would it be possible to have a configuration similar to the Phoenix (see attached), except applied to a Biconic and with some sort of escape system in the nose (sorry, really like the idea of the nose section being a dedicated 'lifeboat'. I just see it as a way to solve so many problems) It would still have the central column, as a way to move down to the main pressurized area.
Not sure what this would do to the mass in total, but wouldn't it allow for a more evenly distributed mass during EDL?

I do like that image, it is close to what I have in mind for an MCT. But I think a lengthy tunnel through a cryogenic tank might have issues.

If you insist on have a nose-mounted LAS, another way around it might be to have just a giant central tank (split between oxidizer and fuel), and then have a lower cargo bay (just above engines), and an upper cargo bay in the nose. It would force some level of cargo balance, but that would allow you to put all the pressurized volume up top. And as a bonus the unpressurized/heavy cargo would be easily offloaded near the surface.

I do like this idea, it seems elegant. It helps solve the problem of mass distribution, allows for the nose mounted Lifeboat, and allows you easily access, once landed, to large payloads that don't need to be pressurized during the flight (earth moving equipment possibly?)

Just on the Lifeboat idea, I know it was mentioned back-thread that it would be making things a lot more complex, but I think it would be worth it. Why? Not only can you Abort during Launch and EDL both at Earth AND Mars anywhere through the flight, but it allows for something I've been worried about, Abort during transit.
If we assume these things are traveling in a fleet (say 10 MCT's for 1000 colonists to Mars?), if one suffers a mishap during flight, then the colonists can load up and punch out from the failing MCT and rendezvous with another nearby one. Granted, depending on the mishap, the 'other' MCT could just come to them anyway, but there may be issues necessitating a quick departure, for example during Mars approach and entry...I'm pretty sure you can't keep 100 people alive on an MCT for 2 years waiting for free-return to Earth if you miss.
The other MCT would have to put up with 200 people for a short time, while they can be distributed amongst the rest of the fleet, giving you 9 MCT's with 110 people each for the rest of the trip.
And while the Lifeboat would be expensive, it wouldn't be as bad as the MCT, give it the capability to cram in 100 people as tightly as possible and keep them alive for say, 10 hours, long enough for rescue. Like current lifeboats are used for.
It may be expensive both in terms of mass and money, but it is terrible engineering to hope that 'it won't fail'... Especially when 'failure' includes the loss of 100 lives. Most risk assessments I've seen would still have that as an 'extreme risk', no matter how small the likelihood.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/14/2015 05:39 am
It's not, in fact, impossible to land an SEP on Mars. Just kind of odd and mass inefficient. But with a sufficiently good solar array, you could do it. I should point out that an "ISS-esque" solar array is, in fact, retractable!

Yes, they have run into their share of problems. Solar arrays for an MCT lander would need to be a lot more mechanically reliable to allow multiple open and close events during a round trip. And you'd want arrays that could function in space as well on the Martian surface.

It's a tricky engineering problem to solve, even for a relatively small set of Arrays. And if you to also provide a SEP cruise boost, you need to make them even larger. Easier said than done, even for smaller arrays.

EDIT: Here's an old animation showing the complexity of the ISS array deployment:
https://www.youtube.com/watch?v=JC_CSuQzjq8
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/14/2015 05:50 am
Just on the Lifeboat idea, I know it was mentioned back-thread that it would be making things a lot more complex, but I think it would be worth it. Why? Not only can you Abort during Launch and EDL both at Earth AND Mars anywhere through the flight,

Don't make the mistake of thinking that all an abort capsule needs to do is taking passengers away from an imminent explosion, to just survive the imminent danger. That works on Earth, because rescue is nearby, and the environment is survivable.

But that is NOT enough for Mars. An abort capsule is USELESS if it just dooms you to death a couple of hours later. To be a proper abort/rescue vehicle it basically needs to be a fully independent spacecraft/lander, built into another spacecraft/lander. By adding enough rescue/survival capability, you get into a dark spiral that eventually leads you to conclude that your escape capsule needs another escape capsule.

But there is another way. Build safety margins and redundancy into your MCT/lander and forego an abort system that is effectively useless.

but it allows for something I've been worried about, Abort during transit.
If we assume these things are traveling in a fleet (say 10 MCT's for 1000 colonists to Mars?), if one suffers a mishap during flight, then the colonists can load up and punch out from the failing MCT and rendezvous with another nearby one. Granted, depending on the mishap, the 'other' MCT could just come to them anyway, but there may be issues necessitating a quick departure, for example during Mars approach and entry...I'm pretty sure you can't keep 100 people alive on an MCT for 2 years waiting for free-return to Earth if you miss.
The other MCT would have to put up with 200 people for a short time, while they can be distributed amongst the rest of the fleet, giving you 9 MCT's with 110 people each for the rest of the trip.

Being able to abort/rescue during transit is a completely separate aspect from whether or not you have a launch abort capsule. Any reasonable MCT proposal would have a fleet of them going during a launch window, so that rescue would be available even without abort capsules.

And no, I don't think you need to have a rapid way to escape your MCT during transit. At some point you just have to accept that there will be riskier times during a trip. Those who cannot accept risks can stay behind.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Rocket Surgeon on 10/14/2015 06:22 am
Just on the Lifeboat idea, I know it was mentioned back-thread that it would be making things a lot more complex, but I think it would be worth it. Why? Not only can you Abort during Launch and EDL both at Earth AND Mars anywhere through the flight,

Don't make the mistake of thinking that all an abort capsule needs to do is taking passengers away from an imminent explosion, to just survive the imminent danger. That works on Earth, because rescue is nearby, and the environment is survivable.

But that is NOT enough for Mars. An abort capsule is USELESS if it just dooms you to death a couple of hours later. To be a proper abort/rescue vehicle it basically needs to be a fully independent spacecraft/lander, built into another spacecraft/lander. By adding enough rescue/survival capability, you get into a dark spiral that eventually leads you to conclude that your escape capsule needs another escape capsule.

But surely if we're assuming a mostly developed Mars Colony ready to accept 1000 new immigrants, then it is reasonable to assume that they could mount a quick rescue of an abort capsule? Something like a dedicated MCT with enough fuel to do a sub orbital hop, on station and ready to go could make it to the capsules landing site in a few hours, and if the capsule was close enough, you could even go over land. That's why it would only need to sustain the colonists for a few hours, not days or weeks. That keeps the capsule more simplistic. Simple CO2 scrubbers, maybe a dedicated radiator if the base hull rejection rates are naturally too low and batteries for power. Add some pressure fed hypergolic rockets, or methalox ones that are made so the tanks can be 'charged' from the main tanks when they are likely to be needed (for those who don't like hypergols) and a parachute or two to help slow down. Again, I'm not saying it'll be 'cheap' either in terms of mass or money, I'm saying that it is worth it. It would have to cost more than $1.5 billion to save 100 lives for it to be considered 'Grossly improportional' and for SpaceX to have a reasonable argument that is was too expensive.

Being able to abort/rescue during transit is a completely separate aspect from whether or not you have a launch abort capsule. Any reasonable MCT proposal would have a fleet of them going during a launch window, so that rescue would be available even without abort capsules.

And no, I don't think you need to have a rapid way to escape your MCT during transit. At some point you just have to accept that there will be riskier times during a trip. Those who cannot accept risks can stay behind.

I agree, but if you could have a system that does double duty, why not? and as I stated in my original post, it is unlikely that you'll need to rapidly escape a MCT in flight, but what about during Mars approach? if the engines/OMS fail or if a flaw is found in the heat shield and you cannot enter Mars orbit, you've condemned a ship of 100 people to slowly starve to death in deep space. Unless there is a way to keep them alive for several years on a free-return trajectory. Another possible option there, though would be to have cycling 'rescue' stations that could rendezvous with any MCT that 'misses' Mars. Could pull double duty as a deep space research station, or ship....but that's getting dangerously 'Star Trek' :P
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Krevsin on 10/14/2015 06:52 am

I'll also add that in addition to the trip duration, there's the "land the whole thing" mentality.   If you're talking about ISS-esque solar array and radiator array, the idea of stowing them before EDL is not practical.

If instead you have a "Hermes"-type orbit-to-orbit ship in mind, then now SEP starts making sense.

But again, this is about MCT.

We KNOW SpaceX is considering SEP for Mars, and as it is impossible to land a SEP, that mean IPSO FACTO that they are have ALSO considered a Semi-Direct architecture of a transit-vehicle and a separate landing vehicle.  And that such a vehicle trades very well against a single massive direct vehicle.
urm, that is quite a logic leap.

The fact that SpaceX were looking into SEP could mean they were looking at an all-in-one vehicle with both SEP and chemical propulsion.

The fact is that we don't know what kind of SEP approach they were considering (though it is probably safe to assume "all of them") and that unless we get a definitive statement on MCT architecture from SpaceX, all we have to go on is fragments.

So unless Elon or Gwynne or someone else from SpaceX says otherwise, MCT will remain a "land the entire thing" architecture, no matter how disagreeable you find the prospect of it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/14/2015 08:18 am
The fact that SpaceX were looking into SEP could mean they were looking at an all-in-one vehicle with both SEP and chemical propulsion.

As was already mentioned in the thread, that would require the large solar arrays not only somehow be retracted into the MCT itself but also be deployed again after re-launch from Mars, and thus be so reliably shielded from re-entry (and issues on the surface like dust) that you can guarantee they will redeploy for the return trip to Earth. There's simply no advantage to justify that complexity.

MCT will remain a "land the entire thing" architecture, no matter how disagreeable you find the prospect of it.

The original land-the-entire-thing comment was made in the context of the typical multi-stage launch/landing architectures. It doesn't mean that Musk has ruled out having a SEP stage that remains in orbit.

And given that he's happy to do EOR refuelling, to avoid the restrictions of monolithic launches that are typical of Mars architectures, I can't see why anyone would think he'd arbitrarily rule out such an option just to satisfy one interpretation of a throw away quote.

We might find out in a month or so. Until then, these options are on the table... "No matter how disagreeable you find the prospect."
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/14/2015 01:15 pm
My idea of the fuel tanks would be tall cylinders concentric.  Inside about 5m diameter would be methane.  Next outer ring would be lox at say 7m.  Then insulation.  Then human/cargo area.  Then outer walls and insulation.  All concentric circles so that you maintain balance.   On the ground our large liquid natural gas tanks were double hulled with a vacuum pulled in between.  That could be done also.  Doesn't have to be super thick, just enough to hold a vacuum.  Since liquid methane and lox are only about 20 degrees C apart, one inside the other vertically would eliminate any balance problems landing and taking off vertically.  Humans could be at the top.  Cargo can be around the sides, since most cargo shouldn't have a freezing problem.  I'll try to sketch it and put it in a reply. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/14/2015 01:27 pm
My question is, why not send the crew up in traditional capsules to dock and load into the MCT.  If the MCT has to refuel in LEO.  The refueling station could be where the crew transfers in.   No need to put launch escape system on MCT.  It will only be landing on Mars and on Earth.  One take off on Mars with its lower gravity shouldn't be a problem.  If the MCT explodes on take off on Mars, you are not getting home anyway.  Even if you did have, you would be stranded on Mars unless there was room in another MCT to get back. 

Also, the first wave of MCTs are going to build and establish the colony living quarters, power production equipment, fuel production equipment, greenhouse equipment, among other things.  This will take some time so why not minimal crew of say 12, leaving 10, returning two to earth on each trip.  The ones who stay will be busy getting everything up and running, building, exploring, etc.  This will take some time.  They could stay for say 2 years with replacement crews eventually coming and going with more staying each time and staying longer.  This would be like military duty except longer.  Volunteers can stay longer or return.  At least a hospital would need to be built for a more permanent colony.  There might be childbirth at some point.  How would these children fare if they return to earth with heavier gravity? 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 10/14/2015 01:39 pm
My question is, why not send the crew up in traditional capsules to dock and load into the MCT. 

Because that'd be way expensive cumulatively than launching the MCT itself, and cost is a factor.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/14/2015 01:56 pm
How would these children fare if they return to earth with heavier gravity?

We can only speculate. However they are genetically still humans. I am quite sure they can adapt though it might be hard to start with. It is only 2.6 times what they are used to. We do see people move around with 2.6 time the weight they are supposed to have and we are not genetically designed for that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 10/14/2015 02:52 pm
My question is, why not send the crew up in traditional capsules to dock and load into the MCT. 

Because that'd be way expensive cumulatively than launching the MCT itself, and cost is a factor.

Depends on the capsule size. Two or three capsules, 30-50 people each. Small compared with the MCT itself. Fully reusable, cost is approx. the cost of the fuel. So as long as the cost of the fuel for 2 or three flights is less than the cost to launch the whole MCT, it won't be more expensive.

Given the size requirements of the MCT, it's going to weigh more than 2-3 times that of a 30-50 person capsule. So capsules would probably be cheaper.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/14/2015 03:48 pm
I was thinking in terms of the beginning of colonization, 100, 50 even 30 people will not be going initially.  6 in two capsules to load would only require 2 launches of Falcon 9.  MCT then would not have to have LAS.  Later after the MCT has proven itself taking cargo to Mars with no crashes, then passenger flights could begin.  They have already said, it would take 10 cargo flights per one passenger flight to set up a colony.  So... why not take along 12 crew per MCT flight and say 90 tons of cargo.  Smaller requirements for human habitation in transit, thus more room for cargo.  Even one crew of 6 per MCT would only require one docking other than refueling. One BFR refueling tanker, one MCT launch, and one Falcon 9 launch with a crew of 6 per MCT trip to Mars. 

Four people could stay on Mars till the next synod, while two return with the MCT.  10 MCT landings per synod to begin with, would have 40 colonists.  Next Synod, with production, fuel depots, more MCTs could come to Mars, and reusable boosters, reusable MCT's, and more in production, say 80 people next synod, then 120.  As production of BFR's and MCT's increase, so would colonization.  No real need to send 100 at a time until a large living, production, greenhouses, etc have been established on Mars.  Also. Martian manufacturing of living, life support, and various other manufacturing production would have to be in full swing for construction of cities for mass migrations of 100 people at a time.  I think it will start with a trickle, then grow exponentially over time.  Over 50 years after the first landing, there might be 50-100,000 colonists, especially if some other companies or governments, build reusable MCT's to match SpaceX.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/14/2015 05:04 pm
But surely if we're assuming a mostly developed Mars Colony ready to accept 1000 new immigrants, then it is reasonable to assume that they could mount a quick rescue of an abort capsule? Something like a dedicated MCT with enough fuel to do a sub orbital hop, on station and ready to go could make it to the capsules landing site in a few hours, and if the capsule was close enough, you could even go over land. That's why it would only need to sustain the colonists for a few hours, not days or weeks. That keeps the capsule more simplistic. Simple CO2 scrubbers, maybe a dedicated radiator if the base hull rejection rates are naturally too low and batteries for power. Add some pressure fed hypergolic rockets, or methalox ones that are made so the tanks can be 'charged' from the main tanks when they are likely to be needed (for those who don't like hypergols) and a parachute or two to help slow down. Again, I'm not saying it'll be 'cheap' either in terms of mass or money, I'm saying that it is worth it. It would have to cost more than $1.5 billion to save 100 lives for it to be considered 'Grossly improportional' and for SpaceX to have a reasonable argument that is was too expensive.

It is 'grossly improportional' if it also cripples your architecture. And I still don't think you are understanding how capable your abort capsule would have to be to avoid black zones on Mars. And parachutes won't help much for something this size. (they don't scale up well, and Mars atmosphere is thin to begin with) Consider this... Delta-V to reach low Mars orbit is over 3 km/s. So if you have a problem when you are *almost* in orbit, you now have ~2(?) km/s of propulsive capability that this capsule needs to have in order to land softly - and you will land far over the horizon, on the other side of the planet. Any capsule capable of 2+ km/s that is large enough to hold 100(!) people is going to be massive. MASSIVE. Your simple capsule just won't cut it. 

Sometimes abort capability is impractical, and you mitigate risks other ways. You make your vehicle capable of abort, by having engine out capabilities and redundant systems. But you cannot remove all risks. Airliners still sometimes fall out of the sky, yet we don't have escape pods or parachutes.

But I'm tired of arguing these points over and over. For some, launch abort seems to be an essential that they just cannot comprehend going without.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Krevsin on 10/14/2015 05:09 pm
The fact that SpaceX were looking into SEP could mean they were looking at an all-in-one vehicle with both SEP and chemical propulsion.

As was already mentioned in the thread, that would require the large solar arrays not only somehow be retracted into the MCT itself but also be deployed again after re-launch from Mars, and thus be so reliably shielded from re-entry (and issues on the surface like dust) that you can guarantee they will redeploy for the return trip to Earth. There's simply no advantage to justify that complexity.
I was making an example of how the statement that they were "looking into SEP" could be understood in a different manner, not an actual plan.

MCT will remain a "land the entire thing" architecture, no matter how disagreeable you find the prospect of it.

The original land-the-entire-thing comment was made in the context of the typical multi-stage launch/landing architectures. It doesn't mean that Musk has ruled out having a SEP stage that remains in orbit.

And given that he's happy to do EOR refuelling, to avoid the restrictions of monolithic launches that are typical of Mars architectures, I can't see why anyone would think he'd arbitrarily rule out such an option just to satisfy one interpretation of a throw away quote.

We might find out in a month or so. Until then, these options are on the table... "No matter how disagreeable you find the prospect."
He wasn't comparing traditional mars architectures to MCT, he was saying that he was not intending on starting off with a cycler or using Dragons adapted for landing. When asked what vehicle he would use, he replied that "you should just land the entire thing."

Quote
Musk’s architecture for this human Mars exploration effort does not employ cyclers, reusable spacecraft that would travel back and forth constantly between the Red Planet and Earth — at least not at first.

"Probably not a Mars cycler; the thing with the cyclers is, you need a lot of them," Musk told SPACE.com. "You have to have propellant to keep things aligned as [Mars and Earth’s] orbits aren’t [always] in the same plane. In the beginning you won’t have cyclers."

Musk also ruled out SpaceX's Dragon capsule, which the company is developing to ferry astronauts to and from low-Earth orbit, as the spacecraft that would land colonists on the Red Planet. When asked by SPACE.com what vehicle would be used, he said, "I think you just land the entire thing."

Asked if the "entire thing" is the huge new reusable rocket — which is rumored to bear the acronymic name MCT, short for Mass Cargo Transport or Mars Colony Transport — Musk said, "Maybe."
source (http://www.space.com/18596-mars-colony-spacex-elon-musk.html)

I do not know how to interpret "land the entire thing" other than what they have in mind for MCT is an approach with no dedicated in-space hardware.

Also worthy of note, during his reddit AMA, he twice called the MCT a "spaceship and booster" system  and said they'd both be using raptor engine (and also, but not in the reddit AMA "We’re looking at our Mars transporter being around 15 million pounds of thrust" source (http://www.askmen.com/entertainment/right-stuff/elon-musk-interview.html))

Now, in there I managed to find a couple of sources that said SpaceX was looking into SEP, most notably Gwynne Shotwell's quote from the interview with her (https://youtu.be/EoCDLUHb0y4)
Quote
around 4:25 "So we're looking at solar-electric propulsion. I think we're gonna umm, look at some other interesting IN-space propulsion technologies..."

and at AIAA 2011, Elon Musk said they were looking into using SEP as an "accelerator" for the trip to Mars.
(source (https://youtu.be/gYJyw8RGWyY), he starts talking about it around 24:00)

But nowhere did I find any indication that they are stepping away from a monolithic MCT and looking into having dedicated in-space elements, which means the original statement by Elon that their design goal for the MCT is "land the whole thing" remains a valid criterion in ascertaining whether or not a marsbound architecture can be considered an MCT architecture or not.

Now, you may argue that this is me reading too deeply into quotes and that any design posted in this thread is, as it were, cut from whole cloth. While that is all true (Especially the former, as I love reading too deeply into things), the purpose of this thread is to design a vehicle and accompanying architecture based entirely on criteria extracted from the fragments of information we are able to scrounge up.

I like Impaler's proposed architecture. However, I disagree on it being a viable MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 10/14/2015 08:00 pm
Whatever gets discussed here, I'd put money on it being a lot more radical that people are currently thinking! SEP, chemical, something else, Battlestar Galactica, Death Star, Dark Star. Going to be fun whatever comes out!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/14/2015 08:07 pm
The fact that SpaceX were looking into SEP could mean they were looking at an all-in-one vehicle with both SEP and chemical propulsion.

As was already mentioned in the thread, that would require the large solar arrays not only somehow be retracted into the MCT itself but also be deployed again after re-launch from Mars, and thus be so reliably shielded from re-entry (and issues on the surface like dust) that you can guarantee they will redeploy for the return trip to Earth. There's simply no advantage to justify that complexity.

MCT will remain a "land the entire thing" architecture, no matter how disagreeable you find the prospect of it.

The original land-the-entire-thing comment was made in the context of the typical multi-stage launch/landing architectures. It doesn't mean that Musk has ruled out having a SEP stage that remains in orbit.

And given that he's happy to do EOR refuelling, to avoid the restrictions of monolithic launches that are typical of Mars architectures, I can't see why anyone would think he'd arbitrarily rule out such an option just to satisfy one interpretation of a throw away quote.

We might find out in a month or so. Until then, these options are on the table... "No matter how disagreeable you find the prospect."

His original understanding based on the interview he gave was that they would try to eliminate all complexity by doing a mission without any orbital rendezvous: Take off from Earth, go directly to Mars (in 3-4 months), come directly back.

The delta V requirements for that are enormous, however you slice it.  It's not a workable plan: The math does not permit a savvy businessman to do this.  He backpedalled in his next interview by saying something about LEO refueling, which is the first of a number of interventions they're going to have to do to cut the maximum stage delta V requirement (ISRU was the zeroeth).  The requirements for an MCT vehicle which does perfect massless aerocapture and refuels only in LEO and on the Martian surface with ~100d transfers are still over 10km/s in that one stage. are still 7.6km/s in that one stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/14/2015 08:21 pm

His original understanding based on the interview he gave was that they would try to eliminate all complexity by doing a mission without any orbital rendezvous: Take off from Earth, go directly to Mars (in 3-4 months), come directly back.

I disagree with that interpretation. He never said they go without refuelling in orbit. He just did not mention it, probably thinking it is obvious. So he did not backpedal from such a statement. He just clarified that there would be refuelling.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/14/2015 08:23 pm
The requirements for an MCT vehicle which does perfect massless aerocapture and refuels only in LEO and on the Martian surface with ~100d transfers are still over 10km/s in that one stage.

Are you sure you are adding up the right numbers? Because with the most efficient (not fastest) Hohmann transfer, i get ~9.5 km/s from LEO to the Martian surface, but that is with NO aerobraking at Mars. With aerobraking that should come down to less than 8km/s, right?

Yes, a lot of the ideas that Musk have thrown out for "MCT" seem almost impossible (or actually impossible) if one assumes they are all true, at once. Many of them I interpret as "nice to have" for future versions, and one of them I see that way is the "fast transit". I don't expect that to happen until a propellant depot is established in LMO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/14/2015 09:27 pm
The requirements for an MCT vehicle which does perfect massless aerocapture and refuels only in LEO and on the Martian surface with ~100d transfers are still over 10km/s in that one stage. are still 7.6km/s in that one stage.

Are you sure you are adding up the right numbers? Because with the most efficient (not fastest) Hohmann transfer, i get ~9.5 km/s from LEO to the Martian surface, but that is with NO aerobraking at Mars. With aerobraking that should come down to less than 8km/s, right?

Yes, a lot of the ideas that Musk have thrown out for "MCT" seem almost impossible (or actually impossible) if one assumes they are all true, at once. Many of them I interpret as "nice to have" for future versions, and one of them I see that way is the "fast transit". I don't expect that to happen until a propellant depot is established in LMO.

I'm strongly in favor of SEP and see considerable use for it making VERY FAST transit possible.

How is this possible?  Wouldn't the system need to be huge and have magical power sources and such (insert anything Zubrin has ever said).  NO, you can get a Fast transit on the order of 100 days to Mars with a slow, low power SEP system.

The trick is you use your SEP to move your Mars bound vehicle with propellants up to high Earth orbit and then then drop by the Earth for a huge Oberth assisted burn.  For 2 km/s you should leave Earth with huge escape velocity and reach mars in 100 days (average). 

Now the problem is capturing at mars, the answer is Magneto-Plasma Aerocapture, this lets us avoid expensive propulsive capture and is then followed by about a week of Plasma assisted aerobraking which lets the eventual EDL be from a gentle 4 km/s.  So we get to have both fast transit and easy low speed EDL.

The SEP system has not even left Earth yet in this scenario, so you can do either one of two things, bring it back down to LEO for refueling and do it again (basically making it a Cis-lunar tug), or send it to mars by the conventional slow method of spiraling out from the Earths SOI (the SEP is too delicate to take the high thrust of the Oberth maneuver).  In the latter case your going to arrive much later then the manned capsule but if this is a conjunction mission the crew will be spending around 600 days on mars so their is plenty of time for the SEP to arrive before it is needed for departure which is what I favor.

The MCT would only need to reach low Mars orbit and would then rendezvous with the SEP and head for Earth, this return transit is made reasonably short by the fact the MCT is a completely dry shell now of only 100 mT (75 vehicle mass + 25 return cargo) and the SEP is nearly dry too so power to weight ratios are increased, also were not aiming to match Earth's orbit and capture gently, were going to simply intersect it on an elliptical orbit around the sun, that cuts the DeltaV needed.  At Earth we used the Magneto to capture again and bring both SEP and the MCT down to LEO (they probably need to separate to do this as the SEP is more delicate and would slow the process down for the MCT).  The crew can be retrieved via a Dragon capsule now, and we need to send another tanker to LEO to put landing propellants into the MCT, if we use enough the MCT can do a lot of retro-propulsion on entry and bring it's entry speed down from the 7.7 km/s of orbit down to the range of 4 km/s which matches it's mars entry speed, so all the thermal protection systems can be designed for this low performance point.

IMLEO is estimated at 570 mT of which 100 mT is the cargo load, 75 mT is the MCT dry mass, 200 mT is chemical propellant in the MCT (2 tanker loads of 100 mT each), 155 is SEP propellant, 15 mT is the SEP tank and 22 mT is the SEP hardware which has a power output of 4.5 MW which corresponds to an alpha value of 5 kg/kw.

BTW Using a braking system like Magneto Plasma is the only way I can see an Integrated Bi-conic and direct Earth return being viable, without it the entry conditions are too extreme to meet the low dry mass fractions that it's advocates are proposing.
Do you have math to back this mission plan up?

Edit: For the case of the highly simplified circular Mars / circular Earth orbit rendezvous, based on:
http://forum.nasaspaceflight.com/index.php?topic=37536.msg1371984#msg1371984

If you start at high Earth orbit and descend to perigee, then you can burn for 2241m/s to raise aphelion to 3.31AU, which drops time of flight to 100.03 days.  Then you come in to the Mars approach at 12880m/s, and have to burn off 9275m/s in order to capture into a highly elliptical orbit.  This is fairly difficult (capture intensity goes up faster than linearly because you have a shorter chord of atmosphere to cut through, not just less time in that atmosphere), and exceeds the capabilities of any chemical propulsion capacity in this planning exercise by a large measure.

  -snip-  (see original post)  -snip-

The tradeoff is: you can keep the BFR as a 4.5km/s vehicle instead of making it a (3.2km/s earth escape) + (2.4km/s Impaler Short Transit injection) + (~2km/s or whatever you need for EDL) ~= a 7.6km/s vehicle. 

You're also going to need comparable efforts to get the thing home on a fast transit, though.
Yeah, I made an error there (I added escape velocity twice).  7.6km/s to get to Mars from LEO in 100 days assuming that perfect aerobraking accepts all excess velocity for free.  But you go too far on the other point: Without aerobraking you'rs looking at 9.3km/s just for capture, making the total stage capability more like 16.9km/s.  If you assume a direct descent to a Vacuum Mars Analog, the figure is 12.9km/s plus gravity losses, making for a total stage capability of 20.5km/s.

These numbers are so high because 100 day transfers require lots of extra energy that 200 day transfers do not. 

If you're content with 200 day transfers...

-numbers to come, WIP-
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/14/2015 09:57 pm
My question is, why not send the crew up in traditional capsules to dock and load into the MCT.  If the MCT has to refuel in LEO.  The refueling station could be where the crew transfers in. No need to put launch escape system on MCT.

Yes. Not a literal "capsule" necessarily, but if you are building an escape vehicle into the nose... as the nose... of the MCT, you have already developed a suitably sized "LEO taxi" which can instead launch your passengers separately. By only using it separately, you eliminate the cost and complexity of trying to integrate it into the already complex MCT.

It also provides SpaceX with another second income stream, ferrying commercial passengers in and out of LEO (and perhaps to cis-Lunar activities) in addition to the Mars colonists, like an upsized version of commercial crew.

It also provides them with a stepping stone for development. I mean the gap between Dragon and MCT is... substantial.

My question is, why not send the crew up in traditional capsules to dock and load into the MCT.
Because that'd be way expensive cumulatively than launching the MCT itself, and cost is a factor.

Whereas the cost of trying to build a LAS capsule into the the MCT which also somehow functions as part of the MCT during normal landing...

Complexity doesn't just have increased development costs, it also inevitably increases ongoing operational costs.

Now, you may argue that this is me reading too deeply into quotes

Way too deeply. Especially as we are talking about a single throw away line from someone who we know will change his plans in response to reality, rather than chase the nominal "goal" at the expense of the original reason for pursuing that goal. (As often happens in spaceflight. See the Shuttle development, X-33, Ares, Orion, Altair, SLS, JWST...)

Musk dropped the idea of a reusable F9 second stage as soon as re-entry for stages proved more difficult than expected. He dropped or delayed cross-feed on FH when uprating Merlin proved more effective at improving payload. He's changed fuel. He's changed engine size for Raptor. He's dropped the idea of multi-core from BFR in response to the issues that must have arisen during FH development.

If they are doing trades on SEP, then clearly everything is on the table. As Lars-J said, Musk clearly has a wishlist of desirable features, and IMO he'll pursue whichever turn out to be viable, abandon whichever don't, and spin on a dime when required.

I think there's been a tendency for a group-mind to form around specific interpretations: A small group interprets Musk's comments as having one meaning, and suddenly that interpretation is the only one allowed and anyone who dares to talk about an alternative path is "hijacking the thread" to "pursue their own personal agenda". It's not exactly conducive to an open discussion.

MCT "Speculation", it's right there in the thread name.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/14/2015 09:58 pm

But nowhere did I find any indication that they are stepping away from a monolithic MCT and looking into having dedicated in-space elements, which means the original statement by Elon that their design goal for the MCT is "land the whole thing" remains a valid criterion in ascertaining whether or not a marsbound architecture can be considered an MCT architecture or not.

Now, you may argue that this is me reading too deeply into quotes and that any design posted in this thread is, as it were, cut from whole cloth. While that is all true (Especially the former, as I love reading too deeply into things), the purpose of this thread is to design a vehicle and accompanying architecture based entirely on criteria extracted from the fragments of information we are able to scrounge up.

I like Impaler's proposed architecture. However, I disagree on it being a viable MCT.

I'm perplexed, you clearly quote Musk saying SEP is under consideration, yet it is not a viable as a speculative prediction of their design?

I've never said Musk statements rule out super-direct all chemical architectures, I've said physics, engineering and cost and other merit based evaluations rule them out.  And that Musk will arrive at that conclusion after trying his hardest to get it to work on paper because it looks like the simplest solution on the surface.

The Musk design space is/was huge, he clearly wanted to leave no stone unturned in the search for an efficient architecture and that space included everything from SEP to single massive integrated 2nd stages like others are championing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/14/2015 10:12 pm

It is 'grossly improportional' if it also cripples your architecture. And I still don't think you are understanding how capable your abort capsule would have to be to avoid black zones on Mars. And parachutes won't help much for something this size. (they don't scale up well, and Mars atmosphere is thin to begin with) Consider this... Delta-V to reach low Mars orbit is over 3 km/s. So if you have a problem when you are *almost* in orbit, you now have ~2(?) km/s of propulsive capability that this capsule needs to have in order to land softly - and you will land far over the horizon, on the other side of the planet. Any capsule capable of 2+ km/s that is large enough to hold 100(!) people is going to be massive. MASSIVE. Your simple capsule just won't cut it. 

Sometimes abort capability is impractical, and you mitigate risks other ways. You make your vehicle capable of abort, by having engine out capabilities and redundant systems. But you cannot remove all risks. Airliners still sometimes fall out of the sky, yet we don't have escape pods or parachutes.

But I'm tired of arguing these points over and over. For some, launch abort seems to be an essential that they just cannot comprehend going without.

While we may disagree on propulsion technology, I strongly agree with this sentiment on abort capsules for use during mars assent.  They are simply pointless because they needs to be very nearly as functional as the assent vehicle they are aborting from, they need to carry away the majority of the assent cargo mass 25 mT which we should be assuming is all passenger compartments, need very nearly the full DeltaV of a lander, the same or even greater thermal protection, it needs terminal thrust, landing gear radars etc etc.

The impossibility of any rescue on the martian surface is almost moot when you can't cross even separate and land this hypothetical abort vehicle.

The only place where abort makes any sense is on Earth where I favor launching the whole MCT off the top of the launch rocket via a pusher abort system comprised mainly of the MCT's own integral engines.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/14/2015 10:38 pm
The requirements for an MCT vehicle which does perfect massless aerocapture and refuels only in LEO and on the Martian surface with ~100d transfers are still over 10km/s in that one stage. are still 7.6km/s in that one stage.

Are you sure you are adding up the right numbers? Because with the most efficient (not fastest) Hohmann transfer, i get ~9.5 km/s from LEO to the Martian surface, but that is with NO aerobraking at Mars. With aerobraking that should come down to less than 8km/s, right?

Yes, a lot of the ideas that Musk have thrown out for "MCT" seem almost impossible (or actually impossible) if one assumes they are all true, at once. Many of them I interpret as "nice to have" for future versions, and one of them I see that way is the "fast transit". I don't expect that to happen until a propellant depot is established in LMO.

I'm strongly in favor of SEP and see considerable use for it making VERY FAST transit possible.

How is this possible?  Wouldn't the system need to be huge and have magical power sources and such (insert anything Zubrin has ever said).  NO, you can get a Fast transit on the order of 100 days to Mars with a slow, low power SEP system.

The trick is you use your SEP to move your Mars bound vehicle with propellants up to high Earth orbit and then then drop by the Earth for a huge Oberth assisted burn.  For 2 km/s you should leave Earth with huge escape velocity and reach mars in 100 days (average). 

Now the problem is capturing at mars, the answer is Magneto-Plasma Aerocapture, this lets us avoid expensive propulsive capture and is then followed by about a week of Plasma assisted aerobraking which lets the eventual EDL be from a gentle 4 km/s.  So we get to have both fast transit and easy low speed EDL.

The SEP system has not even left Earth yet in this scenario, so you can do either one of two things, bring it back down to LEO for refueling and do it again (basically making it a Cis-lunar tug), or send it to mars by the conventional slow method of spiraling out from the Earths SOI (the SEP is too delicate to take the high thrust of the Oberth maneuver).  In the latter case your going to arrive much later then the manned capsule but if this is a conjunction mission the crew will be spending around 600 days on mars so their is plenty of time for the SEP to arrive before it is needed for departure which is what I favor.

The MCT would only need to reach low Mars orbit and would then rendezvous with the SEP and head for Earth, this return transit is made reasonably short by the fact the MCT is a completely dry shell now of only 100 mT (75 vehicle mass + 25 return cargo) and the SEP is nearly dry too so power to weight ratios are increased, also were not aiming to match Earth's orbit and capture gently, were going to simply intersect it on an elliptical orbit around the sun, that cuts the DeltaV needed.  At Earth we used the Magneto to capture again and bring both SEP and the MCT down to LEO (they probably need to separate to do this as the SEP is more delicate and would slow the process down for the MCT).  The crew can be retrieved via a Dragon capsule now, and we need to send another tanker to LEO to put landing propellants into the MCT, if we use enough the MCT can do a lot of retro-propulsion on entry and bring it's entry speed down from the 7.7 km/s of orbit down to the range of 4 km/s which matches it's mars entry speed, so all the thermal protection systems can be designed for this low performance point.

IMLEO is estimated at 570 mT of which 100 mT is the cargo load, 75 mT is the MCT dry mass, 200 mT is chemical propellant in the MCT (2 tanker loads of 100 mT each), 155 is SEP propellant, 15 mT is the SEP tank and 22 mT is the SEP hardware which has a power output of 4.5 MW which corresponds to an alpha value of 5 kg/kw.

BTW Using a braking system like Magneto Plasma is the only way I can see an Integrated Bi-conic and direct Earth return being viable, without it the entry conditions are too extreme to meet the low dry mass fractions that it's advocates are proposing.
Do you have math to back this mission plan up?

Edit: For the case of the highly simplified circular Mars / circular Earth orbit rendezvous, based on:
http://forum.nasaspaceflight.com/index.php?topic=37536.msg1371984#msg1371984

If you start at high Earth orbit and descend to perigee, then you can burn for 2241m/s to raise aphelion to 3.31AU, which drops time of flight to 100.03 days.  Then you come in to the Mars approach at 12880m/s, and have to burn off 9275m/s in order to capture into a highly elliptical orbit.  This is fairly difficult (capture intensity goes up faster than linearly because you have a shorter chord of atmosphere to cut through, not just less time in that atmosphere), and exceeds the capabilities of any chemical propulsion capacity in this planning exercise by a large measure.

  -snip-  (see original post)  -snip-

The tradeoff is: you can keep the BFR as a 4.5km/s vehicle instead of making it a (3.2km/s earth escape) + (2.4km/s Impaler Short Transit injection) + (~2km/s or whatever you need for EDL) ~= a 7.6km/s vehicle. 

You're also going to need comparable efforts to get the thing home on a fast transit, though.
Yeah, I made an error there (I added escape velocity twice).  7.6km/s to get to Mars from LEO in 100 days assuming that perfect aerobraking accepts all excess velocity for free.  But you go too far on the other point: Without aerobraking you'rs looking at 9.3km/s just for capture, making the total stage capability more like 16.9km/s.  If you assume a direct descent to a Vacuum Mars Analog, the figure is 12.9km/s plus gravity losses, making for a total stage capability of 20.5km/s.

These numbers are so high because 100 day transfers require lots of extra energy that 200 day transfers do not. 

If you're content with 200 day transfers...

-numbers to come, WIP-

From Hop_David's spreadsheet (http://forum.nasaspaceflight.com/index.php?topic=37536.msg1371984#msg1371984), I offer five cases:

Straight Hohmann with propulsive capture - 259 days
A straight-up Hohmann burn from a {1AUx1AU heliocentric, 300km x 300km altitude geocentric} orbit to a {1.524AUx1.524AU heliocentric, 3697x23459km semimajor axis aereocentric} coplanar orbit using a {1AUx1.5240001AU heliocentric} transfer costs 510m/s plus change on Earth departure, over and above the 3220m/s escape velocity burn.  Then to propulsively capture into a highly elliptical Mars orbit it costs 1021m/s.  Conservative aerobraking can reduce that ellipse down to LMO for another 668m/s that we don't need to pay, where standard EDL penalties apply (I'll assume them to be 2km/s for purposes of this discussion).

Total: 3220 + 510 + 1021 + 2000 = 6751m/s
Wet to drymass ratio at 380s Isp: 6.12 to 1

The spreadsheet author's suggested non-Hohmann trajectory with propulsive capture - 102 days
The author would reduce perihelion in order to balance the perigee and periaerion burn into something sensible, assuming that propulsive capture is necessary.  He uses non-prograde burns or a suboptimal burn time in Earth orbit, which is highly inefficient, to balance out the Earth and Mars sides for minimal total dV.  From a {1AUx1AU heliocentric, 300km x 300km altitude geocentric} orbit to a {1.524AUx1.524AU heliocentric, 3697x23459km semimajor axis aereocentric} coplanar orbit using a {0.87AUx1.8AU heliocentric} transfer orbit costs 3146m/s plus change on Earth departure, over and above the 3220m/s escape velocity burn.  Then to propulsively capture into a highly elliptical Mars orbit it costs 4668m/s.  Conservative aerobraking can reduce that ellipse down to LMO for another 668m/s that we don't need to pay, where standard EDL penalties apply (I'll assume them to be 2km/s for purposes of this discussion).

Total: 3220 + 3146 + 4668 + 2000 = 13034m/s
Wet to drymass ratio at 380s Isp: 33.1 to 1

A 100 day semi-Hohmann transit given perfect free aerocapture - 100 days
From a {1AUx1AU heliocentric, 300km x 300km altitude geocentric} orbit to a {1.524AUx1.524AU heliocentric, 3697x23459km semimajor axis aereocentric} coplanar orbit using a {1AUx3.31AU heliocentric} transfer orbit costs 2241m/s plus change on Earth departure, over and above the 3220m/s escape velocity burn.  Then to propulsively capture into a highly elliptical Mars orbit it costs 9276m/s, but we're not going to do that: Instead, magnetoshell or some other aerocapture technology is going to do that all in one go;  Then it's going to, in the same step, further reduce the elliptical orbit down to LMO  for another 668m/s that we don't need to pay, then go directly into EDL, where standard EDL penalties apply (I'll assume them to be 2km/s for purposes of this discussion).

Total: 3220 + 2241 + 2000 = 7461m/s
Wet to drymass ratio at 380s Isp: 7.41 to 1

A 100 day semi-Hohmann transit given propulsive capture - 100 days
Examining the previous proposition without the non-prograde burns that the spreadsheet author makes.  From a {1AUx1AU heliocentric, 300km x 300km altitude geocentric} orbit to a {1.524AUx1.524AU heliocentric, 3697x23459km semimajor axis aereocentric} coplanar orbit using a {1AUx3.31AU heliocentric} transfer orbit costs 2241m/s plus change on Earth departure, over and above the 3220m/s escape velocity burn.  Then to propulsively capture into a highly elliptical Mars orbit it costs 9276m/s.    Conservative aerobraking can reduce that ellipse down to LMO for another 668m/s that we don't need to pay, where standard EDL penalties apply (I'll assume them to be 2km/s for purposes of this discussion).

Total: 3220 + 2241 + 9276 + 2000 = 16737m/s
Wet to drymass ratio at 380s Isp: 89.3 to 1

A reasonable 180 day near-Hohmann transfer with mild aerocapture - 180 days
From a {1AUx1AU heliocentric, 300km x 300km altitude geocentric} orbit to a {1.524AUx1.524AU heliocentric, 3697x23459km semimajor axis aereocentric} coplanar orbit using a {1AUx1.652AU heliocentric} transfer orbit costs 655m/s plus change on Earth departure, over and above the 3220m/s escape velocity burn.  Then to propulsively capture into a highly elliptical Mars orbit it costs 2443m/s, but we're not going to do that: Instead, magnetoshell or some other aerocapture technology is going to do that.  Conservative aerobraking can reduce that ellipse down to LMO for another 668m/s that we don't need to pay, where standard EDL penalties apply (I'll assume them to be 2km/s for purposes of this discussion).

Total: 3220 + 655 + 2000 = 5875m/s
Wet to drymass ratio at 380s Isp: 4.84 to 1
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/14/2015 10:58 pm
Burninate,
Thanks for those numbers. The wet to dry mass numbers are fascinating as well.

I certainly favor the slower, more delta-V conservative approaches. And I think it is the best hope of making an "MCT" work, without a LMO propellant depot.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/14/2015 11:04 pm
Burninate,
Thanks for those numbers. The wet to dry mass numbers are fascinating as well.

I certainly favor the slower, more delta-V conservative approaches. And I think it is the best hope of making an "MCT" work, without a LMO propellant depot.

Oh, I think there's still room for an LMO prop depot even in the most conservative case.  There's still a question of whether slow-transit, LEO depot, plus LMO depot is *enough* for a vehicle with integrated ISRU capacity on Mars to do a first mission to a new site reusably.  A lot of it falls on what the mass return ratio for the ISRU system ends up being.  ISRU gear mass is some fraction of landed mass, and as ISRU gets less and less productive that fraction goes up, perhaps even eclipsing useful cargo.  That uncertainty is part of why I end up with bigger MCT landed mass figures than most of you.  The ISRU productivity is extremely important because when it goes down

If it's not high enough, you either *have* to resort to a nested MAV in a 1&2 synod split mission (and return the big'un after 26 more months), plan on a 2-synod human mission, or you just have to throw away a whole MCT for every site you land at, as a permanently landed asset.

Also keep in mind that the above figures are based on the simplifying assumption of circular coplanar orbits for Mars and Earth.  The real numbers are probably a bit worse.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/14/2015 11:14 pm
Would anyone like to do the work of reversing that spreadsheet so we could look at more refined estimates of return delta V?  I might try it at some point, but not today.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/14/2015 11:15 pm
Burninate,
Thanks for those numbers. The wet to dry mass numbers are fascinating as well.

I certainly favor the slower, more delta-V conservative approaches. And I think it is the best hope of making an "MCT" work, without a LMO propellant depot.

Oh, I think there's still room for an LMO prop depot even in the most conservative case.  There's still a question of whether slow-transit, LEO depot, plus LMO depot is *enough* for a vehicle with integrated ISRU capacity on Mars to do a first mission to a new site reusably.  A lot of it falls on what the mass return ratio for the ISRU system ends up being.

If it's not high enough, you either *have* to resort to a nested MAV (and return the big'un next synod), or you just have to throw away a whole MCT for every site you land at, as a permanently landed asset.

That has always been my assumption - that every new site would have not just one, but several unmanned MCT land to set up ISRU and other equipment. Most of those initial unmanned "pathfinder" MCT would not be returned, I would expect - They would instead become the first outpost habitats, storage sheds, and MCT spare part depots. ;)

This is not flags and footprints that are planned here. The goal is to create a permanent manned outpost. But the first crews would not be launched until the next launch window after ISRU production is well underway.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/14/2015 11:21 pm
Burninate,
Thanks for those numbers. The wet to dry mass numbers are fascinating as well.

I certainly favor the slower, more delta-V conservative approaches. And I think it is the best hope of making an "MCT" work, without a LMO propellant depot.

Oh, I think there's still room for an LMO prop depot even in the most conservative case.  There's still a question of whether slow-transit, LEO depot, plus LMO depot is *enough* for a vehicle with integrated ISRU capacity on Mars to do a first mission to a new site reusably.  A lot of it falls on what the mass return ratio for the ISRU system ends up being.

If it's not high enough, you either *have* to resort to a nested MAV (and return the big'un next synod), or you just have to throw away a whole MCT for every site you land at, as a permanently landed asset.

That has always been my assumption - that every new site would have not just one, but several unmanned MCT land to set up ISRU and other equipment. Most of those initial unmanned "pathfinder" MCT would not be returned, I would expect - They would instead become the first outpost habitats, storage sheds, and MCT spare part depots. ;)

This is not flags and footprints that are planned here. The goal is to create a permanent manned outpost. But the first crews would not be launched until the next launch window after ISRU production is well underway.

The threshold you have to pass, then, is being able to set up and run an ISRU water-mining workflow without any human assistance, perhaps without any realtime telerobotics, if we don't go for a landing.

You also need it to last a decade.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/14/2015 11:29 pm
That has always been my assumption - that every new site would have not just one, but several unmanned MCT land to set up ISRU and other equipment. Most of those initial unmanned "pathfinder" MCT would not be returned, I would expect - They would instead become the first outpost habitats, storage sheds, and MCT spare part depots. ;)

This is not flags and footprints that are planned here. The goal is to create a permanent manned outpost. But the first crews would not be launched until the next launch window after ISRU production is well underway.

The threshold you have to pass, then, is being able to set up and run an ISRU water-mining workflow without any human assistance, perhaps without any realtime telerobotics, if we don't go for a landing.

Yes, certainly. How else would you return crews? They would be stuck until they got it going. The MCT model, as I interpret it, is dependent on being able to "fill up" on Mars surface. Otherwise you have to add another ~4 km/s capability to the lander, so it can reach MLO again. 

Sending unmanned MCTs with ISRU in advance also allows you to reduce risk by testing/verifying the most risky part of the mission. (EDL)

You also need it to last a decade.

Yes. But that is less of a problem, as I would expect a permanent population after that, so they can maintain it and replace it. Every synod/launch window would bring additional crew, supplies, and spare parts.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 10/14/2015 11:31 pm
Burninate, I still see a potential for SEP instead of the magneto hydrodynamic breaking in what you describe.

Imagine going with say a 120 day transfer to a point where Mars would have been about 20 days before the craft gets there, but for the full length of the 150 day flight SEP is running at 0.4 mm/s2 to alter the orbit so that it actually arrives at Mars later, a little further along on Mars orbit, but at almost the same speed for a relatively low energy capture (say around 1km/s for capture).

and yes that is just roughed out, I don't have Andy Weir's continuous thrust orbit model software. So really it is a matter of optimizing for the mass of the SEP system including solar arrays against how much faster than a standard half ellipse Hohmann you want to fly.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/15/2015 12:09 am
Burninate, I still see a potential for SEP instead of the magneto hydrodynamic breaking in what you describe.

Imagine going with say a 120 day transfer to a point where Mars would have been about 20 days before the craft gets there, but for the full length of the 150 day flight SEP is running at 0.4 mm/s2 to alter the orbit so that it actually arrives at Mars later, a little further along on Mars orbit, but at almost the same speed for a relatively low energy capture (say around 1km/s for capture).

and yes that is just roughed out, I don't have Andy Weir's continuous thrust orbit model software. So really it is a matter of optimizing for the mass of the SEP system including solar arrays against how much faster than a standard half ellipse Hohmann you want to fly.

This is my preference as well.  Absent a good characterization of MAC, let's keep its use at a manageably small level.  We have a good characterization of SEP, on the other hand, and SEP can be used for much of capture.  The simplified case that's most conservative on MAC would be to go with the 180-day version I calculated above, but plan on burning for about 2 months while approaching aphelion.  There are other benefits to using modest amounts of SEP;  It makes things like Mars-orbit habs and propellant much easier to deal with.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/15/2015 01:06 am
That has always been my assumption - that every new site would have not just one, but several unmanned MCT land to set up ISRU and other equipment. Most of those initial unmanned "pathfinder" MCT would not be returned, I would expect - They would instead become the first outpost habitats, storage sheds, and MCT spare part depots.

Hmmm, in theory, only the first site or two would need that. Once you have the initial 3-6 MCTs left at those 1-2 sites, they could be used as suborbital hoppers for ferrying equipment (even people) to secondary sites to prep them for the incoming (fully reusable) MCTs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: meekGee on 10/15/2015 01:26 am

I'll also add that in addition to the trip duration, there's the "land the whole thing" mentality.   If you're talking about ISS-esque solar array and radiator array, the idea of stowing them before EDL is not practical.

If instead you have a "Hermes"-type orbit-to-orbit ship in mind, then now SEP starts making sense.

But again, this is about MCT.

We KNOW SpaceX is considering SEP for Mars, and as it is impossible to land a SEP, that mean IPSO FACTO that they are have ALSO considered a Semi-Direct architecture of a transit-vehicle and a separate landing vehicle.  And that such a vehicle trades very well against a single massive direct vehicle.
It's not, in fact, impossible to land an SEP on Mars. Just kind of odd and mass inefficient. But with a sufficiently good solar array, you could do it. I should point out that an "ISS-esque" solar array is, in fact, retractable!

RB.  You just used the word "in fact" along with stating you can build an engine with a T/W of 0.25, and an ISP in the thousands.

Forget Mars...  With your engine you can roam the solar system at will!   

You need a sanity check sometimes.   You can't just add brochure numbers for this and that (solar panels, thruster) and arrive at meaningful numbers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/15/2015 01:37 am

This is my preference as well.  Absent a good characterization of MAC, let's keep its use at a manageably small level.  We have a good characterization of SEP, on the other hand, and SEP can be used for much of capture.  The simplified case that's most conservative on MAC would be to go with the 180-day version I calculated above, but plan on burning for about 2 months while approaching aphelion.  There are other benefits to using modest amounts of SEP;  It makes things like Mars-orbit habs and propellant much easier to deal with.

From what I have read their is really no practical upper limit to how large of a effective drag radius that can be generated and the total drag force generated on the vehicle.  The limits are all how much g-force the vehicle and crew can tolerate.  As the ratio of ring diameter to drag radius looks to be nearly 20:1, aka papers describing 2.5 meter diameter magneto rings massing under a ton would generate an effective drag radius of 40 meter diameter.

Given the bi-conic configurations that are popular it may be possible to put a ring nearly as large as the vehicle tucked under the outer edge of vehicles bottom frustum.  If dragged by a number of cables along it's perimeter a ring this size would generate an enormous drag area.  By adjusting the tension on these cables in flight the ring could be tilted relative to the main craft, this may allow the bi-conic to generate more lift and further control the process as my current understanding is that the lack of lift generation from the Magneto will cap the amount of deceleration for a given g-limit.  With high lift you can 'skim' the planets atmosphere in a lift-down configuration and do a long low g arc through the atmosphere.

So to be conservative I'm limiting the Capture DeltaV to around 3 km/s.  That would mean having a velocity at mars periapsis of <8 km/s initially to bring one down to just under escape at 5 km/s or less.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/15/2015 02:12 am

I'll also add that in addition to the trip duration, there's the "land the whole thing" mentality.   If you're talking about ISS-esque solar array and radiator array, the idea of stowing them before EDL is not practical.

If instead you have a "Hermes"-type orbit-to-orbit ship in mind, then now SEP starts making sense.

But again, this is about MCT.

We KNOW SpaceX is considering SEP for Mars, and as it is impossible to land a SEP, that mean IPSO FACTO that they are have ALSO considered a Semi-Direct architecture of a transit-vehicle and a separate landing vehicle.  And that such a vehicle trades very well against a single massive direct vehicle.
It's not, in fact, impossible to land an SEP on Mars. Just kind of odd and mass inefficient. But with a sufficiently good solar array, you could do it. I should point out that an "ISS-esque" solar array is, in fact, retractable!

RB.  You just used the word "in fact" along with stating you can build an engine with a T/W of 0.25, and an ISP in the thousands.

Forget Mars...  With your engine you can roam the solar system at will!   

You need a sanity check sometimes.   You can't just add brochure numbers for this and that (solar panels, thruster) and arrive at meaningful numbers.

...Um, what the heck are you talking about? You don't land using the electric thrusters, you land with chemical rockets. The only time you wouldn't use chemical rockets is on very low-gravity bodies. I said "land on SEP on Mars," not "land using electric thrusters."

But it is possible to fold in a solar array and protect it during reentry. X-37B does this, and I believe the original crewed Dragon concept did this (folded into the nose). It's awkward and heavy (less so with extremely high performance solar arrays), but it is possible. (And if MCT is supposed to have a big payload bay for cargo, then they could fold the solar array into that with plenty of room to spare.) If there's a problem retracting it, just blow some explosive bolts and separate it before reentry. If there's problem deploying it, you can either take a slower route or you can dock with another MCT. Either way, it's something that can be engineered around, and is an easier problem to solve than, say, their first stage recovery and reuse for Falcon 9.

I doubt this is what SpaceX is planning, so if they are considering SEP, they are most likely considering it as a separate craft which does not land along with the MCT. Either it is a propulsion stage that stays attached to the MCT to throw it to Mars (and then back to Earth) or perhaps it's to be used to shuttle propellant around. The latter would be a fairly easy "add-on" that need not be there for initial trips.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/15/2015 02:17 am
Would anyone like to do the work of reversing that spreadsheet so we could look at more refined estimates of return delta V?  I might try it at some point, but not today.

Orbits are time reversible so don't we just need to look at the 'Vinf at mars' and calculate the DeltaV needed to archive that escape velocity from mars surface, then we would (if we pointed ourselves in the right direction) be headed back down the equivalent half of the outbound orbit and we should reach Earth in the specified time and with the specified Vinf so we know what we need to do to aerocapture at Earth as well.

It would be nice to have this done for us on the spreadsheet though.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/15/2015 02:25 am
There is an example of a reusable spacecraft that contains an unfolding solar array that can be stowed for thruster firings and reentry:

https://www.newscientist.com/blogs/shortsharpscience/2011/03/solar-stowaways-give-us-spacep.html

In fact, it's in orbit right now, and it's the fourth flight (two flights each for two vehicles).

Here is the patent:
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&co1=AND&d=PTXT&s1=6,581,883.PN.&OS=PN/6,581,883&RS=PN/6,581,883
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/15/2015 02:45 am
Stowable solar arrays of around that size will certainly need to be part of MCT even it is an all chemical vehicle (you don't survived months in transit on batteries). 

My own design for solar arrays on a biconic is to have body flaps along the bottom of the vehicle (for aerodynamic control and braking), these can hinge out to almost perpendicular in orbit and the solar arrays which are stowed in boxes just behind the flaps and extend out on scissor type extensions much like ISS radiators past the flaps to point at the sun which is over the nose of the vehicle.  Giwires an retract the arrays and on the surface of mars they can extend again with the wires taking the load and the angle just a bit below horizontal so they touch the surface and rest on a boot which protects them when folded by being a cap.

But the difference between this and the scale needed to power meaningful SEP is huge.  Were talking about MW solar arrays here and while we have the technology to do that none of the current solar arrays of the size needed to do the job can fold up and making them do so would very likely cripple their energy density.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/15/2015 04:03 am

That has always been my assumption - that every new site would have not just one, but several unmanned MCT land to set up ISRU and other equipment. Most of those initial unmanned "pathfinder" MCT would not be returned, I would expect - They would instead become the first outpost habitats, storage sheds, and MCT spare part depots.

Hmmm, in theory, only the first site or two would need that. Once you have the initial 3-6 MCTs left at those 1-2 sites, they could be used as suborbital hoppers for ferrying equipment (even people) to secondary sites to prep them for the incoming (fully reusable) MCTs.

Yes, good point.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/15/2015 05:37 am
If these MCT are in good enough shape to do suborbital hops they are probably in good enough shape to go back to earth. That's assuming the heatshield is not the limiting factor.

I expect two scenarios:

1) The new site is close enough that equipment can be sent on the ground to prepare for MCT landing.

2) They do it with new MCT. Hopefully there will be enough experience that they have to expend only one or maybe none.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/15/2015 07:12 pm
[images of Apollo CM+SM and Dragon+trunk]

Apollo didn't and Dragon doesn't do EDL with those modules attached. The level of integration your require is an order of magnitude more complex.


That is correct, but note that Dragon 2 will abort with it's trunk still attached (which presumably would have at least some cargo in it.).  If the joint can survive being aborted off an exploding booster in tension, then there's no reason it couldn't propulsively land that way too, as the tensile loads would be much less for landing than abort.

So you have a joint there that can handle compression, and rapid tension as well.  It is 2/3 of the way to a lifeboat on a biconic MCT.  Designing that joint to additionally handle lateral loading during atmospheric entry would be an engineering hurdle to overcome, certainly.

It's mainly a question of if you think SpaceX could design that in or not, as to if this would be feasible or not.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/15/2015 07:43 pm
Just on the Lifeboat idea, I know it was mentioned back-thread that it would be making things a lot more complex, but I think it would be worth it. Why? Not only can you Abort during Launch and EDL both at Earth AND Mars anywhere through the flight,

Don't make the mistake of thinking that all an abort capsule needs to do is taking passengers away from an imminent explosion, to just survive the imminent danger. That works on Earth, because rescue is nearby, and the environment is survivable.

But that is NOT enough for Mars. An abort capsule is USELESS if it just dooms you to death a couple of hours later. To be a proper abort/rescue vehicle it basically needs to be a fully independent spacecraft/lander, built into another spacecraft/lander. By adding enough rescue/survival capability, you get into a dark spiral that eventually leads you to conclude that your escape capsule needs another escape capsule.

But there is another way. Build safety margins and redundancy into your MCT/lander and forego an abort system that is effectively useless.


Lars,

You make some good points here.

My initial thought on the IBMCT is just that, to not have an LAS at all.  To use Dragon 2 as a LEO taxi for exploration crews for the first couple of decades until MCT builds up a track record of reliability.  Then go with the Space Shuttle or Airliner model when it's time to put a full 100 passengers on board.  MCT should have dozens of launches under it's belt by then.
It'd have full booster engine out capability, as well as full IBMCT engine out capability.  So an engine out during ascent on either stage would still result in a nominal LEO insertion.
It doesn't protect against one failure mode, an exploding booster.  It's popular to look at the booster explosions on the N-1 tests and take that to mean you must protect against that, but what really needs to be looked at is how often to American liquid boosters actually explode once they are out of test phase and in to actual production?  I don't know the answer to that exactly, but I don't think it's very often.  Especially in modern times.  The Challenger flight is one of the most famous examples, but that really wasn't a liquid booster failure.  It was an o-ring joint failure from a segmented SRB than then caused a failure of the liquid booster.  Had the O-ring failed on the outboard side so it didn't burn into the side of the ET, the stack likely wouldn't have exploded.  Once detected they probably would have done an emergency orbiter abort and glided to a contingency landing site.  Or the booster may have lasted to SRB staging.

There was a Delta II that failed spectacularly not so long ago, but I think that was an SRB failure as well, not of the liquid core.  I don't think there was a booster failure of the a production Saturn 1B or Saturn V, or Atlas II, III, or V, or Delta IV, III, or II outside of the SRB failure.
And I think most of the Titan IV failures were SRB issues, and not the core (which wasn't really a booster, but a 2nd stage that ignited after SRB sep.)

So, how often have liquid boosters went "boom" in the US?
How important is it to protect against that one failure mode?

Those are the questiona to ask and debate.

As you say Lars, aborting on Mars has different issues than on Earth.  If you are dooming the crew to a slow death marooned on the surface, that means an LAS system is -really- only good for Earth ascent...and won't really be a benefit for the 99% of the mission after Earth ascent.  And is arguably a lot of extra cost and complexity and performance hit for just protection in that first even of a 2+ year long mission.

Later, once there is a colony, an LAS system would be more plausible as there's a plausible chance of rescue coming from the colony.   Until then, it can be "problematic".

Now, that said, there are still LAS lifeboat scenarios on  Mars even early on.
Exploration crews of 6-7 could have sufficient hab volume, life support, and provisions on the lifeboat to survive for some time marooned on the surface.  For at least the projected cruise back of say 6 months.  They'll need that amount of provisions to get home, so they can life on the surface in that same hab with those same provisions for the same amount of time.
But...they will die after that if there's no rescue.  Can a rescue come from Earth in time?
Can there be another unmanned MCT on the suface somewhere accessible by the crew?  Can there be a pressurized rover that can drive autonomously from the landing location they just took off from that could drive to their emergency landing location, that could pick them up and take them to an unmanned backup MCT?
Can there be a surface hab with a cache of provisions the rover could take them too which could sustain them until a rescue can come from Earth?

So it's not automatically a death sentence to Abort a lifeboat on Mars Ascent.  But contingencies would NEED to be in place before it's not a death sentence.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/15/2015 08:05 pm
[Dragon's trunk] It is 2/3 of the way to a lifeboat on a biconic MCT.

It really, really isn't.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 10/15/2015 08:12 pm
So, how often have liquid boosters went "boom" in the US?
How important is it to protect against that one failure mode?

Antares, October 28, 2014.

Falcon 9, June 28, 2015.

That's two in the past 12 months.

At least launching from Earth, it's pretty important. As you mentioned, for early MCT missions with a small crew, send the crew up on a Dragon 2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/15/2015 10:37 pm
Would anyone like to do the work of reversing that spreadsheet so we could look at more refined estimates of return delta V?  I might try it at some point, but not today.

Orbits are time reversible so don't we just need to look at the 'Vinf at mars' and calculate the DeltaV needed to archive that escape velocity from mars surface, then we would (if we pointed ourselves in the right direction) be headed back down the equivalent half of the outbound orbit and we should reach Earth in the specified time and with the specified Vinf so we know what we need to do to aerocapture at Earth as well.

It would be nice to have this done for us on the spreadsheet though.
They're reversible, but you're forgetting the Oberth effect: because on the way from Earth to Mars, you can dump your exhaust in a deeper gravity well than Mars to Earth, it takes less delta-v.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/15/2015 10:43 pm
So, how often have liquid boosters went "boom" in the US?
How important is it to protect against that one failure mode?

Antares, October 28, 2014.

Falcon 9, June 28, 2015.

That's two in the past 12 months.

At least launching from Earth, it's pretty important. As you mentioned, for early MCT missions with a small crew, send the crew up on a Dragon 2.

Sort of.  I was referring to exploding boosters.
As I understand, F9's was the 2nd stage which blew up causing the booster to then fail, which is different than the booster itself exploding, and trying to abort away form it.  Which is usually what your LAS is trying to do.  If that were an Integrated MCT, then the LAS lifeboat would be within a few meters of the exploding tank.  Could an LAS could save it with such close proximity...especially if it exploded...rather than more "ruptured" as it appeared the F9US did.  (Which was one of the problems with putting Orion on a side mounted SDHLV if I recall correctly.  Orion would be right next to the ET, so even with an LAS system, it's unlikely the crew could get away from a sudden ET explosion). Maybe...
Again, I said that would be the question that would have to be asked and answered.   If answered "no", then that IBMCT with no LAS is a fairly slick option overall for simplicity and economics.  If answered "yes"...then either a lifeboat top to the IBMCT, or go with a non integrated biconic MCT launching unfueled on top of a dedicated 2nd stage, so that the whole vehicle aborts and you don't have to break apart the spacecraft.  Or a separate LEO Taxi with LAS to take large crews up to LEO for transfer to MCT.  (All are plausible solutions IMO, if an LAS is deemed absolutely necessary for Earth ascent.)

The F9 v1.1 booster failure from a few years ago was an engine out, which as I said, would be accounted for.

Antares was also an engine out.  But with just 2 engines, there was no engine out redundancy so they terminated the LV, as I understand.  Had Antares had engine out redundancy, there's not reason to think it wouldn't have made staging nominally.

But, yes, for that first several dozen flights of MCT, the crew can just go up on a simple F9/D2.  There will be 4 active Falcon pads in operation after one, 3 on the East Coast.  One of those launched per Mars mission seems pretty reasonable.
By the time you'd be looking at putting 100 people on it, there'll be many exploration missions over decades.  You'll probably have a pretty good idea of that point if it's reasonable to put people on MCT for launch, or go another route like a "Big Dragon" on a FH or something that can hold 100 people, and have a Earth LAS system.  Or some other route.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 10/15/2015 11:03 pm
So, how often have liquid boosters went "boom" in the US?
How important is it to protect against that one failure mode?

Antares, October 28, 2014.

Falcon 9, June 28, 2015.

That's two in the past 12 months.

At least launching from Earth, it's pretty important. As you mentioned, for early MCT missions with a small crew, send the crew up on a Dragon 2.

Not quite.  I was referring to exploding boosters.
As I understand, F9's was the 2nd stage which blew up causing the booster to then fail, which is different than the booster itself exploding, and trying to abort away form it.   If that were an Integrated MCT, then the LAS lifeboat would be within a few meters of the exploding tank.  Could an LAS could save it with such close proximity? (Which was one of the problems with putting Orion on a side mounted SDHLV if I recall correctly.  Orion would be right next to the ET, so even with an LAS system, it's unlikely the crew could get away from a sudden ET explosion).
The F9 v1.1 booster failure from a few years ago was an engine out, which as I said, would be accounted for.

Antares was also an engine out.  But with just 2 engines, there was no engine out redundancy so they terminated the LV, as I understand.  Had Antares had engine out redundancy, there's not reason to think it wouldn't have made staging nominally.

It doesn't matter whether it is an engine out or a tank rupture or first stage or second stage. In both cases, if there was a manned capsule, a LAS would have saved the crew. Without a LAS the crew would have been lost.

You can't design the perfect launcher to survive any possible contingency. No one imagined a F9 second stage coming apart while the first stage was still burning.

But, yes, for that first several dozen flights of MCT, the crew can just go up on a simple F9/D2.  There will be 4 active Falcon pads in operation after one, 3 on the East Coast.  One of those launched per Mars mission seems pretty reasonable.
By the time you'd be looking at putting 100 people on it, there'll be many exploration missions over decades.  You'll probably have a pretty good idea of that point if it's reasonable to put people on MCT for launch, or go another route like a "Big Dragon" on a FH or something that can hold 100 people, and have a Earth LAS system.  Or some other route.

That's reasonable. As I've posted before, I expect insurance and liability concerns will require a LAS of some sort on all Earth to orbit launches.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sheltonjr on 10/15/2015 11:12 pm
So, how often have liquid boosters went "boom" in the US?
How important is it to protect against that one failure mode?

Antares, October 28, 2014.

Falcon 9, June 28, 2015.

That's two in the past 12 months.

At least launching from Earth, it's pretty important. As you mentioned, for early MCT missions with a small crew, send the crew up on a Dragon 2.

Falcon 9 turned out to be a mechanical failure.

Antares does not have, engine out capability,  so no real advantage to shutting down,

With advanced current and near future engine monitoring, a engine can be shut down before a RUD can occur.

I really like the choice configuration that they chose for Raptor. Great performance, but can still have a lower pressure pump and chamber for long life and reliability and no worry about a fuel/air interseal in the turbopump.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Rocket Surgeon on 10/16/2015 01:46 am
Just on the Lifeboat idea, I know it was mentioned back-thread that it would be making things a lot more complex, but I think it would be worth it. Why? Not only can you Abort during Launch and EDL both at Earth AND Mars anywhere through the flight,

Don't make the mistake of thinking that all an abort capsule needs to do is taking passengers away from an imminent explosion, to just survive the imminent danger. That works on Earth, because rescue is nearby, and the environment is survivable.

But that is NOT enough for Mars. An abort capsule is USELESS if it just dooms you to death a couple of hours later. To be a proper abort/rescue vehicle it basically needs to be a fully independent spacecraft/lander, built into another spacecraft/lander. By adding enough rescue/survival capability, you get into a dark spiral that eventually leads you to conclude that your escape capsule needs another escape capsule.

But there is another way. Build safety margins and redundancy into your MCT/lander and forego an abort system that is effectively useless.


Lars,

You make some good points here.

My initial thought on the IBMCT is just that, to not have an LAS at all.  To use Dragon 2 as a LEO taxi for exploration crews for the first couple of decades until MCT builds up a track record of reliability.  Then go with the Space Shuttle or Airliner model when it's time to put a full 100 passengers on board.  MCT should have dozens of launches under it's belt by then.
It'd have full booster engine out capability, as well as full IBMCT engine out capability.  So an engine out during ascent on either stage would still result in a nominal LEO insertion.
It doesn't protect against one failure mode, an exploding booster.  It's popular to look at the booster explosions on the N-1 tests and take that to mean you must protect against that, but what really needs to be looked at is how often to American liquid boosters actually explode once they are out of test phase and in to actual production?  I don't know the answer to that exactly, but I don't think it's very often.  Especially in modern times.  The Challenger flight is one of the most famous examples, but that really wasn't a liquid booster failure.  It was an o-ring joint failure from a segmented SRB than then caused a failure of the liquid booster.  Had the O-ring failed on the outboard side so it didn't burn into the side of the ET, the stack likely wouldn't have exploded.  Once detected they probably would have done an emergency orbiter abort and glided to a contingency landing site.  Or the booster may have lasted to SRB staging.

There was a Delta II that failed spectacularly not so long ago, but I think that was an SRB failure as well, not of the liquid core.  I don't think there was a booster failure of the a production Saturn 1B or Saturn V, or Atlas II, III, or V, or Delta IV, III, or II outside of the SRB failure.
And I think most of the Titan IV failures were SRB issues, and not the core (which wasn't really a booster, but a 2nd stage that ignited after SRB sep.)

So, how often have liquid boosters went "boom" in the US?
How important is it to protect against that one failure mode?

There is a potentially good compromise here. If there is still a lack of confidence in the BFR/MCT system to LEO, then could you launch the MCT empty, then man it and refuel it at the same time? If the MCT is being refueled in LEO, then you could make the tankers hybrid tankers/LEO transports, ferrying up, say XX people at a time and that could have an abort capability. It would take more flights, but if you're lowing the mass that is need to get to LEO but upping the flights, it may make things more operationally attractive (no need for an ASDS).
I'll admit I'm being convinced that a LAS is not necessary, but I'll point out that a Plane doesn't drop out of the sky if it loses all it's engines, and doesn't carry the liquid chemical equivalent of a nuclear bomb. The potential energy stored there cannot be ignored.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/16/2015 01:54 am
Would anyone like to do the work of reversing that spreadsheet so we could look at more refined estimates of return delta V?  I might try it at some point, but not today.

Orbits are time reversible so don't we just need to look at the 'Vinf at mars' and calculate the DeltaV needed to archive that escape velocity from mars surface, then we would (if we pointed ourselves in the right direction) be headed back down the equivalent half of the outbound orbit and we should reach Earth in the specified time and with the specified Vinf so we know what we need to do to aerocapture at Earth as well.

It would be nice to have this done for us on the spreadsheet though.
They're reversible, but you're forgetting the Oberth effect: because on the way from Earth to Mars, you can dump your exhaust in a deeper gravity well than Mars to Earth, it takes less delta-v.

I was just referring to the heliocentric portion of the transit being reversible, we would obviously need to take mars's smaller gravity well into account, that's why I said the Vinf at mars is needs to be looked at.  Here let me take some of Burnate's example and reverse them into mars-Earth transits and show how I would do it.

Straight Hohmann with propulsive capture - 259 days
Vinf at mars is 2.652818827 km/s that is our velocity at this point in the heliocentric orbit before we enter the mars gravity well, naturally we accelerate when falling into that gravity well but we would just come out again with the same speed aka were hyperbolic.  To get back to Earth we need that same heliocentric speed (pointed back in now) when leaving mars to return to Earth in 259 days.  To determine this we just take the escape velocity at mars surface 5 km/s, square it along with the needed Vinf add them together and get the square root which is 5.660 km/s.

Likewise we can use the previously 'escape' burn from Earth to know how much deceleration we need to shed to go into that high orbit at Earth after which we will aerobrake down to LEO, I'll assume that we can be refueled by tanker at this point in order to do our Earth landing as that will avoid having to blast off from mars with propellant we wont need until now in LEO where we know their is a continuous refueling process in place.

Earth return reversal
Total: 5660 + 510 = 6170m/s
Wet to drymass ratio at 380s Isp:  5.24 to 1


The spreadsheet author's suggested non-Hohmann trajectory with propulsive capture - 102 days

Earth return reversal
Total 9241 + 3145 = 12386 m/s
Wet to drymass ratio at 380s Isp:  27.82 to 1


A 100 day semi-Hohmann transit given perfect free aerocapture - 100 days

Earth return reversal
Total 13816 m/s
Wet to drymass ratio at 380s Isp:  40.85 to 1

This can be improved over simply reversing the outbound orbit which was {1AUx3.31AU heliocentric}, I've found  {.76AUx1.67AU heliocentric} with the same travel time which can decrease the mars escape burn substantially but at the cost of raising Earth side capture needs.

Earth return reversal
Total 8792 m/s
Wet to drymass ratio at 380s Isp: 10.6  to 1


A 100 day semi-Hohmann transit given propulsive capture - 100 days

Earth return reversal
Total 13816 + 2241 = 16057 m/s
Wet to drymass ratio at 380s Isp:  74.57 to 1

Using my alternative trajectory
Total 8792 + 4597 m/s = 13389
Wet to drymass ratio at 380s Isp: 36.42  to 1


A reasonable 180 day near-Hohmann transfer with mild aerocapture - 180 days

Earth return reversal
Total 7047 m/s
Wet to drymass ratio at 380s Isp: 6.63 to 1


Conclusions:  There seems to be no viable fast (100 day) returns from mars, unlike on the outbound even with perfect free aerocapture doesn't allow it at any kind of propellant fraction and DeltaV which would be believable.  The problem is that were starting from mars surface unlike LEO in the the outbound assumptions, that's putting us around 3600 m/s behind where we would be.  If we had propellant depots in mars orbit fast return would be a reasonable number if we also had free aerocapture as the wet/dry ratio would be 4:1, which would require something around 300 mT of propellant in mars orbit a huge amount.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/16/2015 02:38 am
Great work, but could you please break out your math a bit more rather than listing totals?  For example, what dV do you assume for Mars Ascent leg?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/16/2015 02:42 am
Also: 300 tons of propellant in Mars orbit is not a very high amount, given that you can use SEP all the way and the gear ratio is excellent on that;  If you want a short transit you have to send more launches worth of propellant to deep elliptical earth orbit for the outbound leg than to LMO for the inbound leg (using your SEP propellant tug idea), which in turn is far fewer than if you avoided DEO rendezvous altogether and stuck to LEO rendezvous only.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/16/2015 03:31 am
Impaler: I don't think Musk mentioned 100 day trajectory on the return trip, just on the way there. Also, exactly 100 is a little bit of, um, spurious precision. 102 days is essentially the same thing. (I know you know this, just want to point it out.)

Not sure SpaceX would start at LEO. A high orbit seems more realistic, as it allows you to leverage SEP without actually including SEP on MCT directly. SEP would be just used to haul up propellant from LEO. This helps reduce IMLEO a LOT.

But yeah, I still think MCT will start on the surface of Mars and go straight to Earth, with a much-longer-than-100-day trajectory.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/16/2015 04:14 am
Impaler: I don't think Musk mentioned 100 day trajectory on the return trip, just on the way there. Also, exactly 100 is a little bit of, um, spurious precision. 102 days is essentially the same thing. (I know you know this, just want to point it out.)

Not sure SpaceX would start at LEO. A high orbit seems more realistic, as it allows you to leverage SEP without actually including SEP on MCT directly. SEP would be just used to haul up propellant from LEO. This helps reduce IMLEO a LOT.

But yeah, I still think MCT will start on the surface of Mars and go straight to Earth, with a much-longer-than-100-day trajectory.
The 102 day transfer above is very different from the 100 day transfer.  I included it because it's the author's default values on the spreadsheet;  The decision is made to go with a perihelion below 1AU in an attempt to balance propulsive capture with propulsive transfer injection, unlike in the 100 day transfer.

-

I don't see the point of selling the benefits of a 100 day transfer so hard unless you can have it in both directions. 

You say that a six month transfer to Mars is intolerable for passengers, so you guys are proposing that we go to these great lengths to avoid it.  And the identical six month transfer back from Mars is...  more tolerable?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 10/16/2015 04:20 am
So, how often have liquid boosters went "boom" in the US?
How important is it to protect against that one failure mode?

Antares, October 28, 2014.

Falcon 9, June 28, 2015.

That's two in the past 12 months.

At least launching from Earth, it's pretty important. As you mentioned, for early MCT missions with a small crew, send the crew up on a Dragon 2.

Dragon survived the Falcon 9 second stage failure, that was not a "boom".

If there had been humans onboard the craft, and the software would have sent the command to open the parachutes, they would have survived even without LAS.

And now they've added the command to open the parachutes to their software ;)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/16/2015 07:15 am
You say that a six month transfer to Mars is intolerable for passengers, so you guys are proposing that we go to these great lengths to avoid it.  And the identical six month transfer back from Mars is...  more tolerable?

100 people out, mostly colonists, 15-20 back, mostly crew. Different rules.

Dragon survived the Falcon 9 second stage failure, that was not a "boom".

All RUDs are "booms", eventually.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/16/2015 07:43 am
You say that a six month transfer to Mars is intolerable for passengers, so you guys are proposing that we go to these great lengths to avoid it.  And the identical six month transfer back from Mars is...  more tolerable?

100 people out, mostly colonists, 15-20 back, mostly crew. Different rules.

The 100 day transfer was not about making it acceptable for people. The sole reason is doing a return flight during one launch window so MCT would be able to launch again in the next window. Elon Musk was very clear on this. In that sense any flight duration would be acceptable as long as it allows the reuse goal. That is why it applies to cargo as well as crew - economy. That would mean though if fast transfer doubles the cost or halves the payload it is no longer economic and it would be better to use slow transfers. But assuming that it mostly needs fuel to LEO and launching is cheap he has come to the conclusion that fast transfer is the economic way. If it serves to make the flight more bearable to the colonists that's an added bonus.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/16/2015 08:58 am
Great work, but could you please break out your math a bit more rather than listing totals?  For example, what dV do you assume for Mars Ascent leg?

I described the math in the first section, for each of these I took the apihelion, perihelion values you provide, then took the mars Vinf squared it added mars escape velocity at surface squared and then take the root.  That would give you the needed escape velocity on a direct escape burn without stopping in orbit.  I did not account for any drag or gravity loss in this calculation but both should be much less then on Earth.


Also: 300 tons of propellant in Mars orbit is not a very high amount, given that you can use SEP all the way and the gear ratio is excellent on that;  If you want a short transit you have to send more launches worth of propellant to deep elliptical earth orbit for the outbound leg than to LMO for the inbound leg (using your SEP propellant tug idea), which in turn is far fewer than if you avoided DEO rendezvous altogether and stuck to LEO rendezvous only.

Using SEP it is a possibility, I should have prefaced that statement that it was a lot if it had to be brought up from mars surface in multiple loads by a tanker vehicle such as a second MCT.  I will run some numbers on delivering propellant to LMO by SEP with rendezvous their.

Impaler: I don't think Musk mentioned 100 day trajectory on the return trip, just on the way there. Also, exactly 100 is a little bit of, um, spurious precision. 102 days is essentially the same thing. (I know you know this, just want to point it out.)

Not sure SpaceX would start at LEO. A high orbit seems more realistic, as it allows you to leverage SEP without actually including SEP on MCT directly. SEP would be just used to haul up propellant from LEO. This helps reduce IMLEO a LOT.

But yeah, I still think MCT will start on the surface of Mars and go straight to Earth, with a much-longer-than-100-day trajectory.

I don't think we will actually see 100 day transits mainly do to capture g-force limitations, Musk may have wanted that for archiving a 1 synod mission but I'm not really seeing a viable means to that particularly early in the exploration.  I'm focusing on what I think may be a sweet spot at 150 days, a month faster then the previous 'best' of 180 days in mainstream studies but not the blazing 100 day transit.

The use of SEP as a leveraging tool on a MCT vehicle which is itself fully chem powered is what I've tried to demonstrate and I think it's clear that a small MCT with modest DeltaV when combined with SEP can do just about any conceivable outbound trajectory and transit time that the really large IBMCT concepts could achieve from LEO if not faster ones.

The ability to do direct earth return from mars surface on a slow hohmann comes in at just over 6 km/s, as I've said this is just within possible propellant fractions.  But unless the advocate of such a trajectory also embraces some form of radical propellant less aerocapture for Earth then your not going to survive re-entry their.


You say that a six month transfer to Mars is intolerable for passengers, so you guys are proposing that we go to these great lengths to avoid it.  And the identical six month transfer back from Mars is...  more tolerable?

Agreed, and I do not think this issue can be brushed away by claiming that their are few (or no) return passengers.  All trips to mars will come with FREE return according to Musk, and I fully expect all personnel to rotate in and out at a rate that is so close to 1:1 that it might as well be that.

Remember out whole REASON for fast transit is health and cumulative radiation exposure so inbound/outbound time are completely equal in harm and concern.  And if we are worried about physiological issues due to confinement/stress etc etc, these are likely to actually be worse on the return because of accumulated stress of being on mission for some 3 years by this point.


Some further calculations

5022 m/s escape velocity on mars surface
4880 m/s escape velocity from 200 km mars
3451 m/s orbital velocity 200 km circular mars

Rough analysis looks like to do the ~150 day return will require a 2.5 to 1 wet/dry ratio from Mars orbit.  As my MCT concept is for a vehicle which would have dry mass of 100 mT at this point we need 150 mT of propellants which I think might be deliverable by SEP.  This would provide a mission with 3 SEP tugs, one to move the MCT to EML1, one to move the outbound propellants to EML1 and a third to move another propellant load to low mars orbit.  The mission would have two refueling rendezvouses, one at EML1 and one in low mars orbit with only the later one really being critical, aka failure would result in LOC.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 10/16/2015 04:59 pm
Why is it that for every other Mars mission architecture, people want to be risk-averse and say stuff such as (http://forum.nasaspaceflight.com/index.php?topic=36768) "landing crew in heavy payloads (dozens of tons) is too hard and risky, a 'showstopper'; we must land the crew separately and with a small, fully propulsive, dedicated lander" or (http://forum.nasaspaceflight.com/index.php?topic=22056.msg619858#msg619858) "the mission must be divided into 10 or 20-ton chunks on Mars as a not-too-ambitious extension of current EDL capabilities"

and yet people here easily accept that MCT will be capable of landing dozens of people in the same vehicle that was used for the interplanetary transfer, or up to 100 tons of cargo?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jim Davis on 10/16/2015 05:11 pm
and yet people here easily accept that MCT is going to land dozens of people and/or dozens of tons of cargo?

Because of his successes, Musk's statements, even his off the cuff remarks, receive far more credibility than they might otherwise.

If Interorbital Systems were proposing the MCT it would be greeted with snorts of derision. But Musk has succeeded so often in the past, and is saying something we all fervently want to be so, that we sometimes forget that Musk is only human after all.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 10/16/2015 05:18 pm
and yet people here easily accept that MCT is going to land dozens of people and/or dozens of tons of cargo?
Because of his successes, Musk's statements, even his off the cuff remarks, receive far more credibility than they might otherwise.

If Interorbital Systems were proposing the MCT it would be greeted with snorts of derision. But Musk has succeeded so often in the past, and is saying something we all fervently want to be so, that we sometimes forget that Musk is only human after all.
SpaceX having succeeded in launching resupply missions to the ISS as well as satellites to LEO and GTO doesn't make statements about "Mars colonization plans" (which are vastly more ambitious and difficult) any more credible.

(That doesn't mean I don't want them to succeed, however)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/16/2015 05:25 pm
and yet people here easily accept that MCT is going to land dozens of people and/or dozens of tons of cargo?
Because of his successes, Musk's statements, even his off the cuff remarks, receive far more credibility than they might otherwise.

If Interorbital Systems were proposing the MCT it would be greeted with snorts of derision. But Musk has succeeded so often in the past, and is saying something we all fervently want to be so, that we sometimes forget that Musk is only human after all.
SpaceX having succeeded in launching resupply missions to the ISS as well as satellites to LEO and GTO doesn't make statements about "Mars colonization plans" (which are vastly more ambitious and difficult) any more credible.

SpaceX succeeded in going from the Earth's surface to launching resupply missions to the ISS at a development cost of about one tenth NASA estimates and a fraction of a single Shuttle launch, has become highly competitive with the world's commercial launch providers, is shortly going to totally outcompete all of their designs for medium-large launch vehicles, and is a privately held company whose explicit purpose is achieving the dream of multiplanetary civilization.

All these discussions are part of a design exercise: We don't know exactly what cards Musk is holding, but we're trying to figure out what could possibly work to achieve the admittedly extreme ends he aims for.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: symbios on 10/16/2015 05:33 pm
and yet people here easily accept that MCT is going to land dozens of people and/or dozens of tons of cargo?
Because of his successes, Musk's statements, even his off the cuff remarks, receive far more credibility than they might otherwise.

If Interorbital Systems were proposing the MCT it would be greeted with snorts of derision. But Musk has succeeded so often in the past, and is saying something we all fervently want to be so, that we sometimes forget that Musk is only human after all.
SpaceX having succeeded in launching resupply missions to the ISS as well as satellites to LEO and GTO doesn't make statements about "Mars colonization plans" (which are vastly more ambitious and difficult) any more credible.

You must study Mr. Musk more. He is a genius. If he says 100 tons by 2020, maybe it will be 75 tons by 2025, but by 2030 it will be 125 tons. He does not throw unfounded speculations out there, maybe optimistic but always grounded in sound basic principles/calculations.

But this is still way so much further than anyone else is aiming at. And this is where his cred is coming in.

Everyone has always in the past told him that he is crazy, he is lying, it is impossible, etc. But he has so far always delivered, maybe late, maybe not 100% but he does, and then he evolves it to surpass what he previously said. That is Mr Musk.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 10/16/2015 05:39 pm
NASA has already landed several rovers on Mars, so they have at least some experience with Mars missions. SpaceX still hasn't even landed their own demonstration payload there yet.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 10/16/2015 05:45 pm

SpaceX having succeeded in launching resupply missions to the ISS as well as satellites to LEO and GTO doesn't make statements about "Mars colonization plans" (which are vastly more ambitious and difficult) any more credible.


Actually it does.

Both of those you have mentioned SpaceX was the first none-govermental agency to do so. It was also the first none-govermental spaceflight agency to get to orbit with a liquid fueled rocket. They are the first space agency in the world to try stage recovery from orbital launches, and have nearly made the tech work. They are going to be one of the two leaders in the commercial crew program. They are designing the first reentry capsules that have the capacity to land on a planetary body without the intervention of parachutes. They have proven that they are remarkably failure resilient and have an exceptionally rapid rate of Research and Development.

In short, they have a record of impressive firsts that they keep aspiring to top every time they succeed. Colonising Mars is just another impressive first, and just another item on the list. Viewed from that perspective, it's entirely rational to believe SpaceX has at least mildly good odds of getting to Mars, instead of overwhelmingly negative odds.

Edit: I strongly recommend you get L2 if you haven't already for reasons such as this one - it's one of the few paywalls on the internet that is entirely worth the money.  :-X
Title: Re: MCT Speculation and Discussion Thread 4
Post by: symbios on 10/16/2015 05:54 pm
NASA has already landed several rovers on Mars. SpaceX still hasn't even landed their own demonstration payload there yet.

And this has what to do with anything? They have already done so many things that none other than goverment agencies has done them... so why is that going to stop them now? If anything is going to stop them, it will be economics not technical, but that is years away. If they have come far enough by then, maybe NASA will step in and "help" (order something  :P).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/16/2015 06:57 pm
[Dragon's trunk] It is 2/3 of the way to a lifeboat on a biconic MCT.

It really, really isn't.

Yes, you are correct.  I see no similarities.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oiorionsbelt on 10/16/2015 07:37 pm
NASA has already landed several rovers on Mars, so they have at least some experience with Mars missions. SpaceX still hasn't even landed their own demonstration payload there yet.
To add to what others have said, they are also the first and only entity so far to do supersonic retro propulsion. In fact NASA learning from SpaceX with respect to this aspect of a Mars landing.

Quote
An innovative partnership between NASA and SpaceX is giving the U.S. space agency an early look at what it would take to land multi-ton habitats and supply caches on Mars for human explorers, while providing sophisticated infrared (IR) imagery to help the spacecraft company develop a reusable launch vehicle

http://gcd.larc.nasa.gov/2014/10/nasa-spacex-share-data-on-supersonic-retropropulsion/#.ViFQlup-yrU
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 10/16/2015 09:08 pm
Oh yeah, you're right about that.

Still, imagine if that risk-averse mentality (e.g. we must have smaller payloads because EDL for larger ones is a "showstopper"; we must have separate, all-propulsive, dedicated crew landers; etc.) was applied to MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/16/2015 11:06 pm
I find the whole 'NASA risk aversion' myth so annoying and dumb.  People seem to forget all the failed NASA missions and development efforts that were so crazy ambitious.  Dose anyone remember the X-33 which was in all likelihood a less ambitious vehicle/mission profile then MCT?  NASA isn't caviler with astronaut lives and neither is SpaceX nor will they ever be if they want to actually sell tickets to normal people.

I get this sense form folks who repeat this 'risk-averse' meme that this allows them to resolve the cognitive dissidence of why we don't live in the Buck-rogers Sci-fi future they feel was promised.  It's like something out of post WWI Germany that says they WERE wining until the 'stab in the back', with the culprit being some combination of government funding inadequacy or some kind of self-loathing on the part of NASA itself. 

I do not want to get into why we are not on mars, or how much actual money or time it will actually take to do by SpaceX or anyone else.  These things are nearly impossible to figure out for the top experts in aerospace, we are groping in the dark pointlessly.  We can at best examine our speculations and assign them rank order difficulty as we try to identify better solutions then the ones we have available now.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/16/2015 11:17 pm
...

Agreed, and I do not think this issue can be brushed away by claiming that their are few (or no) return passengers.  All trips to mars will come with FREE return according to Musk, and I fully expect all personnel to rotate in and out at a rate that is so close to 1:1 that it might as well be that....
...then you aren't describing a real colonization effort. A colony isn't just a "bigger base." Either there's a much larger net flux toward Mars than away /or/ MCT won't be needing to carry 100 passengers anyway because not enough people will be going. And then you shouldn't call it MCT.

In an emergency situation, people going back to Earth in a full MCT will just have to tolerate the longer trip. But other than that, and assuming MCT is actually used to transport colonists, there will be much more space per passenger.

This thread is about MCT, not about what Impaler thinks a Mars architecture should be. As such, we need to assume the same assumptions about MCT as have been mentioned by SpaceX in the past.

You have to link the assumptions together, or the architecture doesn't close. You can't drop the "much greater influx than outflux" assumption without then changing the "~100 day transfer to Mars" (but not necessarily the other way around) assumption. And if you drop both those assumptions, then you're no longer talking about MCT in a meaningful way. No problem with that, but you should use a different thread.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/16/2015 11:27 pm
...
I don't think we will actually see 100 day transits mainly do to capture g-force limitations...
What, exactly, are you talking about? Humans can withstand 6 gees for at least 10 minutes, which is 36km/s of delta-v, usually while still doing simple tasks (unnecessary in this case, since capture/entry/reentry would be automated). Such a long period of fairly constant deceleration is possible using a lifting (re)entry, actually including negative lift. Once captured, your next trip through the atmosphere can be for landing (possibly with a skip). So you just need to get rid of your hyperbolic velocity on the first pass because the next pass will take care of actual (re)entry.

I don't think this is any more radical than anything else SpaceX is doing. And isn't more radical than Shuttle's reentry. Sure, we need a good estimate of Mars' atmospheric state, but that is also a solvable problem.

36km/s of hyperbolic velocity is much more than enough for a 100 day transfer.


...lifting (re)entry is well within the state-of-the-art for both Mars and Earth. SpaceX already does this fairly regularly with Dragon. SpaceX also has a very good heatshield material (PICA-X) that they're very familiar with. I don't have any clue why they would shoot themselves in the foot by not leveraging these things to their full potential.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/17/2015 12:02 am
I find the whole 'NASA risk aversion' myth so annoying and dumb.  People seem to forget all the failed NASA missions and development efforts that were so crazy ambitious.  Dose anyone remember the X-33 which was in all likelihood a less ambitious vehicle/mission profile then MCT?  NASA isn't caviler with astronaut lives and neither is SpaceX nor will they ever be if they want to actually sell tickets to normal people.

NASA is not monolithic. Nor is NASA unchanging through time. Some elements of current NASA are not risk averse, but other elements are. But risk aversion is not bad by itself, unless it is taken to the extreme. (Human spaceflight being part of that - Witness Orion/SLS, the "Apollo revived with Shuttle parts" mixture, designed to be as conservative as possible)

A side note: Your X-33 example would carry more weight if it actually flew.  ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 10/17/2015 12:39 am

NASA is not monolithic. Nor is NASA unchanging through time. Some elements of current NASA are not risk averse, but other elements are. But risk aversion is not bad by itself, unless it is taken to the extreme. (Human spaceflight being part of that - Witness Orion/SLS, the "Apollo revived with Shuttle parts" mixture, designed to be as conservative as possible)

A side note: Your X-33 example would carry more weight if it actually flew.  ;)

NASA's risk-aversion historically depends on what it's asked to do (and how firmly it is asked to do it) by the government. Mercury, Gemini, Apollo and the Space Transportation System are all reflective of their time of conception. Dreams that did not become realities usually happened due to the governmental sense of risk aversion, be it technical, fiscal or regarding the value of human life, didn't equate to the requirements of the program. This is not an objectively bad thing, and whilst it (may) have kept us off the moon and away from Mars, it's also saved billions of dollars, the lives of a good few people, and the careers of many, many more. This applies by extension to every government funded agency in every democratic nation. The NASA with the greatest funding and the most impressive mandate took the widest steps - Apollo - and Apollo was a gratuitously nutty program. It's a testament to the team geniuses they had there that the moon landings occurred without greater contingencies than did actually occur.

SpaceX doesn't have as many factors to add up (they still have a ridiculous number, but not an equivalent number), so they have greater freedom in how risk-averse they can choose to be, and the answer is: very. There's a different between making extremely well educated chances and taking leaps of faith with dubious expertise, capabilities and data to support those leaps. F1 and F9 were such leaps; much of what has come after, has come on the back of greater awareness, consciousness and conscientiousness.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/17/2015 05:37 am
...
I don't think we will actually see 100 day transits mainly do to capture g-force limitations...
What, exactly, are you talking about? Humans can withstand 6 gees for at least 10 minutes, which is 36km/s of delta-v, usually while still doing simple tasks (unnecessary in this case, since capture/entry/reentry would be automated). Such a long period of fairly constant deceleration is possible using a lifting (re)entry, actually including negative lift. Once captured, your next trip through the atmosphere can be for landing (possibly with a skip). So you just need to get rid of your hyperbolic velocity on the first pass because the next pass will take care of actual (re)entry.

I don't think this is any more radical than anything else SpaceX is doing. And isn't more radical than Shuttle's reentry. Sure, we need a good estimate of Mars' atmospheric state, but that is also a solvable problem.

36km/s of hyperbolic velocity is much more than enough for a 100 day transfer.


...lifting (re)entry is well within the state-of-the-art for both Mars and Earth. SpaceX already does this fairly regularly with Dragon. SpaceX also has a very good heatshield material (PICA-X) that they're very familiar with. I don't have any clue why they would shoot themselves in the foot by not leveraging these things to their full potential.

I never said crew was the limit.  The limits are mostly on the vehicle and it's structure, remember that our aerocapture g's in a bi-conic vehicle are negative, aka nose bleed g's so they represent a 2nd direction that the vehicle needs to tolerate, and the more lift their is the more lateral g you get.

Aerocapture of a large mass at mars from a hohmann trajectory (low incoming speed and low DeltaV needed) would be possible with a bi-conic shape, but 100 day transits result in MUCH larger deceleration needs which means you simply need more surface area then the vehicle itself can provide.  So some kind of 'expander' is needed, either an inflatable device (which is disposable) or the magneto which looks to be fully reusable.  The limitation I see with the magneto is that it doesn't produce lift.  That makes the g-forces much higher because your doing a single short burst of drag.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/17/2015 05:45 am
[Dragon's trunk] It is 2/3 of the way to a lifeboat on a biconic MCT.

This is 2/3rds of the way to MCT?


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/17/2015 05:49 am
and yet people here easily accept that MCT will be capable of landing dozens of people in the same vehicle that was used for the interplanetary transfer, or up to 100 tons of cargo?

There are at least 4 threads on just this topic, in just this section, of people not merely accepting that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/17/2015 06:20 am
The limitation I see with the magneto is that it doesn't produce lift.  That makes the g-forces much higher because your doing a single short burst of drag.

I recall from the relevant thread that the possibility was mentioned that producing lift by making the magnetic braking device unsymmetric should be possible. In that case it even might be able to do a lot of steering and adjusting to different conditions of the local atmosphere.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/17/2015 07:55 am
The limitation I see with the magneto is that it doesn't produce lift.  That makes the g-forces much higher because your doing a single short burst of drag.

I recall from the relevant thread that the possibility was mentioned that producing lift by making the magnetic braking device unsymmetric should be possible. In that case it even might be able to do a lot of steering and adjusting to different conditions of the local atmosphere.

The same thought had occurred to me, but I realized that the combined vehicle would simply pivot to bring the center of mass on the end of the tether into line with the center of drag.  The effect is analogous to deploying two different sized round non-lift producing parachutes at the same time, they would create different amounts of drag but your line angles would simply be skewed such that the load is directly under the center of drag and you would descend vertically.  Or at least this is my mental picture of what would happen when the plasma is not deflecting any air laterally which by definition this can't do because it's drag is entirely from ion collisions which scatter in all directions and end with the incoming gas just being swallowed into the existing plasma vortex, without deflection you can't have lift because you would be violating conservation of angular momentum.

The only means I can see to get lift is the use the primary vehicle air frame as a kind of canard, angling it strongly off the axis of motion and using it's normal lift properties but perhaps at an angle and lift beyond what would be possible if were also the center of drag.  But this is all really counter to the magneto concept which is all about braking at such a high altitude that the vehicle feels almost no heat or dynamic pressure, once your in dense enough air to get lift your also getting all the nasty effects of near re-renty conditions and the vehicle will not be saving as much mass as it could by being built to lower entry profile margins.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/17/2015 08:06 am
and yet people here easily accept that MCT will be capable of landing dozens of people in the same vehicle that was used for the interplanetary transfer, or up to 100 tons of cargo?

There are at least 4 threads on just this topic, in just this section, of people not merely accepting that.

I would like to point out that my own involvement in these threads should not be taken as an acceptance of any of Musk or SpaceX goals being attainable (particularly in 'Musk-time').  I simply lay out what I think would be the most LIKELY means of succeeding at them given the resources they have available.  I use numerous means to try to reduce the required vehicle performance metrics as much as possible as I believe one of the biggest dangers in the design phase of a vehicle is boxing yourself into a design that needs more performance then the underlying technologies and physics allow.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MP99 on 10/17/2015 08:35 am


The limitation I see with the magneto is that it doesn't produce lift.  That makes the g-forces much higher because your doing a single short burst of drag.

I recall from the relevant thread that the possibility was mentioned that producing lift by making the magnetic braking device unsymmetric should be possible. In that case it even might be able to do a lot of steering and adjusting to different conditions of the local atmosphere.

The same thought had occurred to me, but I realized that the combined vehicle would simply pivot to bring the center of mass on the end of the tether into line with the center of drag.  The effect is analogous to deploying two different sized round non-lift producing parachutes at the same time, they would create different amounts of drag but your line angles would simply be skewed such that the load is directly under the center of drag and you would descend vertically.  Or at least this is my mental picture of what would happen when the plasma is not deflecting any air laterally which by definition this can't do because it's drag is entirely from ion collisions which scatter in all directions and end with the incoming gas just being swallowed into the existing plasma vortex, without deflection you can't have lift because you would be violating conservation of angular momentum.

Yes, that was my takeaway from that thread, also.

Cheers, Martin
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 10/17/2015 11:38 am
and yet people here easily accept that MCT will be capable of landing dozens of people in the same vehicle that was used for the interplanetary transfer, or up to 100 tons of cargo?

There are at least 4 threads on just this topic, in just this section, of people not merely accepting that.
I'm sorry, but where exactly would those be? All I seem to see are people speculating on how MCT/BFR would work, and taking such a system for granted (i.e. they don't seem to acknowledge that EDL for heavy payloads is very hard, unlike every other discussion on Mars mission architectures)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/17/2015 01:59 pm
...
I don't think we will actually see 100 day transits mainly do to capture g-force limitations...
What, exactly, are you talking about? Humans can withstand 6 gees for at least 10 minutes, which is 36km/s of delta-v, usually while still doing simple tasks (unnecessary in this case, since capture/entry/reentry would be automated). Such a long period of fairly constant deceleration is possible using a lifting (re)entry, actually including negative lift. Once captured, your next trip through the atmosphere can be for landing (possibly with a skip). So you just need to get rid of your hyperbolic velocity on the first pass because the next pass will take care of actual (re)entry.

I don't think this is any more radical than anything else SpaceX is doing. And isn't more radical than Shuttle's reentry. Sure, we need a good estimate of Mars' atmospheric state, but that is also a solvable problem.

36km/s of hyperbolic velocity is much more than enough for a 100 day transfer.


...lifting (re)entry is well within the state-of-the-art for both Mars and Earth. SpaceX already does this fairly regularly with Dragon. SpaceX also has a very good heatshield material (PICA-X) that they're very familiar with. I don't have any clue why they would shoot themselves in the foot by not leveraging these things to their full potential.

I never said crew was the limit.  The limits are mostly on the vehicle and it's structure, remember that our aerocapture g's in a bi-conic vehicle are negative, aka nose bleed g's so they represent a 2nd direction that the vehicle needs to tolerate, and the more lift their is the more lateral g you get.

Aerocapture of a large mass at mars from a hohmann trajectory (low incoming speed and low DeltaV needed) would be possible with a bi-conic shape, but 100 day transits result in MUCH larger deceleration needs which means you simply need more surface area then the vehicle itself can provide.  So some kind of 'expander' is needed, either an inflatable device (which is disposable) or the magneto which looks to be fully reusable.  The limitation I see with the magneto is that it doesn't produce lift.  That makes the g-forces much higher because your doing a single short burst of drag.
You're still speaking entirely in generalities. What sort of g-load do you believe is a limit? You can't make a claim like you're making (that g-loads are prohibitively high for 100 day transits) without giving some numbers.

As a side note, a Falcon 9 first stage already has 8 deployed aerosurfaces that generate drag. You think SpaceX will not be able to have ANY deployed aerosurfaces for MCT?

SpaceX, on the other hand, has never mentioned magnetohydrodynamic drag devices. You are basically handicapping them by disallowing any of their current ways of solving the problem so you can introduce your own pet solution.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/17/2015 03:21 pm
If magnetic deceleration can be used it would help a lot with reusability. If a first pass can achieve capture then a second or third pass can achieve landing. Replacing the heatshield after every flight will cost time and money. I don't see magnetic as a requirement but i hope for it. A metallic heatshield will not do especially for EDL back on earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/17/2015 04:43 pm
If magnetic deceleration can be used it would help a lot with reusability. If a first pass can achieve capture then a second or third pass can achieve landing. Replacing the heatshield after every flight will cost time and money. I don't see magnetic as a requirement but i hope for it. A metallic heatshield will not do especially for EDL back on earth.
Even a PICA-X shield can take multiple entries (Musk said 100, which is an overstatement but is a lot more than MCT will need). And yes, a metallic shield would work, you just have to do it gently enough. But I suspect SpaceX is looking at PICA-X. A tanker going to LEO, most certainly, could use a metallic TPS without any hard limits on numbers of reuses (thousands are possible).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/17/2015 06:06 pm
If magnetic deceleration can be used it would help a lot with reusability. If a first pass can achieve capture then a second or third pass can achieve landing. Replacing the heatshield after every flight will cost time and money. I don't see magnetic as a requirement but i hope for it. A metallic heatshield will not do especially for EDL back on earth.
Even a PICA-X shield can take multiple entries (Musk said 100, which is an overstatement but is a lot more than MCT will need). And yes, a metallic shield would work, you just have to do it gently enough. But I suspect SpaceX is looking at PICA-X. A tanker going to LEO, most certainly, could use a metallic TPS without any hard limits on numbers of reuses (thousands are possible).

A metallic heatshield for reentry from interplanetary speeds? I doubt it. PicaX reusable yes. But from interplanetary speeds? To Mars and back, yes, thats two uses, the second very heavy. But again? Maybe two return flights, maybe not.

Edit: I hope I am wrong.

Metallic heatshield for the tankers, that would help a lot, I agree. Many tank flights without refurbishing the heatshield. But it would mean a completely different design for the tanker. The tanker coming back from LEO can probably make a significant number of flights before refurbishing with PicaX.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/17/2015 10:49 pm
You're still speaking entirely in generalities. What sort of g-load do you believe is a limit? You can't make a claim like you're making (that g-loads are prohibitively high for 100 day transits) without giving some numbers.

As a side note, a Falcon 9 first stage already has 8 deployed aerosurfaces that generate drag. You think SpaceX will not be able to have ANY deployed aerosurfaces for MCT?

SpaceX, on the other hand, has never mentioned magnetohydrodynamic drag devices. You are basically handicapping them by disallowing any of their current ways of solving the problem so you can introduce your own pet solution.

Partly because I'm still doing research on high speed aerocapture, but I'm looking at 2 g's as a limit for both the aerocapture and the EDL to keep the structural masses under control, the terminal landing burn might go up to 4 because this is in the launch orientation and the vehicle must be able to survive that to abort.

Also my design in fact uses considerable deployed aerosurfaces around the base of a bi-conic which form a kind of shuttlecock effect and act as both control flaps during entry and as a decelerator prior to retro-propulsion being applied.  I believe they will be very useful in shifting the center of drag forward (by retracting the flaps) and allowing a flip over maneuver to bring the engines forward to fire. These flaps might prove useful in aerocapture as well but I do not think that even with this technique the vehicle can create enough surface area to do the very high speed aerocapture your looking for.

My preferred trajectory of 150 days still requires shedding 2.786 km/s in aerocapture and has a velocity at mars perigee of 7.3 km/s which nearly that of Earth re-entry.  With 2 minutes in the atmosphere the force would be 2.3 g's.  The Earth return is even worse in terms of velocity, 11.9 km/s a speed I think is only survivable with the magneto taking virtually all the forces so the vehicles metallic skin isn't experiencing significant heating as around 7 km/s looks to be the limit of entry speed for metallic thermal protection systems, any higher and they just get too hot and melt.  The larger radius of the Earth means we should have an easier time making a longer cord through the atmosphere and that should give more time to shed the relatively low 1160 m/s to achieve capture though we may wish to shed more to keep our apogee below the inner Van Allen belt.

By comparison a 100 day transit has a velocity at mars perigee of 13.7 km/s and must shed 9.27 km/s.  Even if I had unlimited size and unlimited thermal protection at that speed the time in the martian atmosphere is on the order of ~1 minute and you would experience 15 g's for that time to get the necessary deceleration.  So not only is the crew a red smear on the back of the spacecraft, the front of the spacecraft is likewise a smear on the back of the spacecraft.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/18/2015 12:12 am
2 gees is way too low. You're essentially sand-bagging aerocapture and (re)entry. Apollo did over 6 gees (Apollo 16 did 7.19).

You could do both an aerocapture and then a(n) (re)entry on both ends, giving you the ability to stretch your deceleration over many minutes and control your peak deceleration. You're going to need to bring a heatshield along with anyway, it would be stupid not to take full advantage of it.

15 gees is not realistic for a lifting aerocapture followed by a lifting entry. In both cases, lift allows you to spread the deceleration over several minutes. Again, you're sand-bagging it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/18/2015 02:38 am
I am already assuming separate aerocapture and entry at both ends and the DeltaV I stated were the minimum to capture, aka you go into a big elliptical orbit.

Given the size of the MCT and the mass it has to work with I think 2 gs's is the best that can be reasonably hopped for and it will still in fact be hard to make the vehicle that strong.  Your not taking into account the square-cube law that makes a large object proportionally weaker then a small one.


Apollo was a tiny capsule just a 3.3 m tall and with a mass of 5.5 mT, at 6 g's that would be a compression force of 323400 N.  Now lets just approximate the vehicles structural mass as a cylindrical rod of aluminum (600 MPa strength, 2.8 g/cm^3) running along the axis of compression.  It would need a rod with a mass of just 5 kg, but in reality the capsule had a structural mass of 1,560 kg (28%) because the real limits tend to be the buckling strengths of the much larger structure along with loads from other directions but it gives us a basis for comparison.

Now lets look at a MCT, it will likely have an entry mass of 200 mT when full of cargo, and will be some 20 m long minimum.  The force at 6 g's is 11760000 N.  The abstracted rod of aluminum to support this force over this distance is now 1100 kg!!!  A factor of 220x over Apollo and if it were subject to the same multiplier as in Apollo to get the real structural mass we would be 50% over the whole entry mass just for structure.  Switching to carbon composites (1500 MPa strength, 1.75 g/cm^3) cuts the abstract rod mass down to 274 kg a big improvement but it would still translate to a total structural mass of 85 mT with the 313x multiplier from the Apollo example. 

If the g-forces are reduced to 2 g's the mass comes down proportionally to 28 mT, very close to my vehicle estimated structural mass of 25 mT which would be 33% of the vehicles dry mass and 16% of the entry mass.  So you see that using our best materials can just barely get a vehicle of this size to survive a very modest g loads and why I consider forces as great at 6 g's impossible as they would cause such growth in structural mass that the vehicle expand beyond any possibility of launching it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/18/2015 07:23 am
NASA did studies for Inspiration Mars. They came to the conclusion that direct reentry from Mars at earth return would be the way to go assuming PicaX as a heatshield material. A skip reentry would increase heatshield stress.

I was considering using high pressure to stabilize MCT during reentry. Maybe 40 to 50 PSI or 3 times earth atomospheric pressure. This pressure during the minutes of reentry will not cause problems to crew given what we know from diving.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MP99 on 10/18/2015 12:32 pm


I am already assuming separate aerocapture and entry at both ends and the DeltaV I stated were the minimum to capture, aka you go into a big elliptical orbit.

Given the size of the MCT and the mass it has to work with I think 2 gs's is the best that can be reasonably hopped for and it will still in fact be hard to make the vehicle that strong.  Your not taking into account the square-cube law that makes a large object proportionally weaker then a small one.

MCT will surely undergo greater g forces during launch to LEO.

Cheers, Martin
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Dante2121 on 10/18/2015 01:01 pm
NASA did studies for Inspiration Mars. They came to the conclusion that direct reentry from Mars at earth return would be the way to go assuming PicaX as a heatshield material. A skip reentry would increase heatshield stress.

I was considering using high pressure to stabilize MCT during reentry. Maybe 40 to 50 PSI or 3 times earth atomospheric pressure. This pressure during the minutes of reentry will not cause problems to crew given what we know from diving.

Is there any concept of a reverse gravity slingshot?- e.g. Use the gravity of the moon to slow down before re-entering earth's atmosphere. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 10/18/2015 02:19 pm


Is there any concept of a reverse gravity slingshot?- e.g. Use the gravity of the moon to slow down before re-entering earth's atmosphere.

First the moon's orbit is both slow & long and worse yet inclined off plane so the chance of the moon being where you need it to be is tine.

But given that the moon's mass (1/80th Earth) is too small to shed any meaningful velocity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/18/2015 03:07 pm
NASA did studies for Inspiration Mars. They came to the conclusion that direct reentry from Mars at earth return would be the way to go assuming PicaX as a heatshield material. A skip reentry would increase heatshield stress.
Yes, it's true that if you're just trying to minimize heatshield mass using an ablative heatshield, you often just want to go hot and fast. But in our discussion, it's peak acceleration that we're attempting to minimize, not heatshield mass. 6 gees is a pretty good peak acceleration to use. 5 gees has also been used. Nobody that I'm aware of has used 2 gees in any serious analysis. Heck, a /regular/ reentry uses more than 2 gees. So I find that disingenuous.

Quote
...I was considering using high pressure to stabilize MCT during reentry. Maybe 40 to 50 PSI or 3 times earth atomospheric pressure. This pressure during the minutes of reentry will not cause problems to crew given what we know from diving.
Clever idea. I like it. This gives an important point: there is room for innovation in improving structural mass for a given load. Better materials and better manufacturing techniques are developed regularly. I don't think it's wise to sand-bag peak acceleration to something ridiculously low like 2 gees.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: meekGee on 10/18/2015 05:26 pm


Is there any concept of a reverse gravity slingshot?- e.g. Use the gravity of the moon to slow down before re-entering earth's atmosphere.

First the moon's orbit is both slow & long and worse yet inclined off plane so the chance of the moon being where you need it to be is tine.

But given that the moon's mass (1/80th Earth) is too small to shed any meaningful velocity.

I think for gravity assists, the assisting body is essentially infinite in mass, so it doesn't matter.

What matters is the speed of that body, and in the case of a reverse slingshot, a slow moon is a good thing - except you'll be using it "retrograde" so a fast moon would be even better.  However, it is what it is, and I think the answer is "good enough".

Since the vehicle is coming from Mars, you can aim anywhere you want in the Moon-Earth system, and so the vehicle-Moon-Earth system can form a single plane - so that's not a problem either.

Timing is an issue as you state, but you'll know all about that during departure from Mars.

Not saying that's it's possible or beneficial - but those specific objections I think are solvable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bob Shaw on 10/18/2015 05:48 pm
I'd be very wary of overly-complex orbital dynamics being used on manned missions, but for supplies - especially items where you don't mind a slower transit time (to choose some extreme examples, corrugated iron, bags of cement or water) then any amount of silly stuff would be acceptable. I think the benefits are greater on the way out than the way in, and would tend to revolve around loosely captured vehicles in halo and other orbits rather than classical fast flybys of our Moon. Coming back, you might use clever trajectories to minimise the fuel needed to get into super-high Earth orbit, saving the need for extra mass being lifted into space.

Cargo first, though!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/18/2015 09:06 pm
NASA did studies for Inspiration Mars. They came to the conclusion that direct reentry from Mars at earth return would be the way to go assuming PicaX as a heatshield material. A skip reentry would increase heatshield stress.
Yes, it's true that if you're just trying to minimize heatshield mass using an ablative heatshield, you often just want to go hot and fast. But in our discussion, it's peak acceleration that we're attempting to minimize, not heatshield mass. 6 gees is a pretty good peak acceleration to use. 5 gees has also been used. Nobody that I'm aware of has used 2 gees in any serious analysis. Heck, a /regular/ reentry uses more than 2 gees. So I find that disingenuous.


Bigger spacecraft can tolerate less g forces, that is a clear pattern.  If I tried to say a small sample return capsule of under 1 m couldn't tolerate more then 6 g's then THAT would be sandbagging as such capsules and missiles routinely tolerate >20 g's.

The Shuttle was the largest re-entry vehicle ever flown and it maxed out at 3 g's for launch and 2 for landing while being half the likely entry mass of a MCT.  When I say 2 g's I am making accommodation for the vehicles size rather then just hand-waving away a WELL understood engineering relationship between size and strength and substituting the g-forces experienced by a craft of a completely different scale and claiming it as a legitimate basis for comparison.

Launch g's are experienced in one orientation, and I specified that I'm worried about the 'nose bleed' negative g's that a bi-conic would experience.  If your a fan of a 'Super Dragon' type MCT they you can claim the launch g's and aerocapture g's are oriented the same way and the same structures resist both forces and that could get you up to ~4 g's without any additional structure over what's needed for launch.  But I would then point out that your a low lift configuration with high ballistic coefficient which would increase g-forces during entry well beyond 4 g's.

This is a key point, flipping the whole vehicle over and applying forces from the opposite direction is huge.  It's the difference between designing a normal skyscraper and one that still stands when upside down.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/19/2015 01:58 am
NASA did studies for Inspiration Mars. They came to the conclusion that direct reentry from Mars at earth return would be the way to go assuming PicaX as a heatshield material. A skip reentry would increase heatshield stress.
Yes, it's true that if you're just trying to minimize heatshield mass using an ablative heatshield, you often just want to go hot and fast. But in our discussion, it's peak acceleration that we're attempting to minimize, not heatshield mass. 6 gees is a pretty good peak acceleration to use. 5 gees has also been used. Nobody that I'm aware of has used 2 gees in any serious analysis. Heck, a /regular/ reentry uses more than 2 gees. So I find that disingenuous.


Bigger spacecraft can tolerate less g forces, that is a clear pattern.  If I tried to say a small sample return capsule of under 1 m couldn't tolerate more then 6 g's then THAT would be sandbagging as such capsules and missiles routinely tolerate >20 g's.

The Shuttle was the largest re-entry vehicle ever flown and it maxed out at 3 g's for launch and 2 for landing while being half the likely entry mass of a MCT.  When I say 2 g's I am making accommodation for the vehicles size rather then just hand-waving away a WELL understood engineering relationship between size and strength and substituting the g-forces experienced by a craft of a completely different scale and claiming it as a legitimate basis for comparison.

Launch g's are experienced in one orientation, and I specified that I'm worried about the 'nose bleed' negative g's that a bi-conic would experience.  If your a fan of a 'Super Dragon' type MCT they you can claim the launch g's and aerocapture g's are oriented the same way and the same structures resist both forces and that could get you up to ~4 g's without any additional structure over what's needed for launch.  But I would then point out that your a low lift configuration with high ballistic coefficient which would increase g-forces during entry well beyond 4 g's.

This is a key point, flipping the whole vehicle over and applying forces from the opposite direction is huge.  It's the difference between designing a normal skyscraper and one that still stands when upside down.
The shuttle orbiter is about the same mass as I expect a dry MCT will be, but is in a shape that I don't expect MCT to be. Those wings are very heavy structurally. If it's the side of a pressure vessel, and the whole thing is pressurized to some extent or another, then MCT could be far more structurally efficient than Shuttle was. Additionally, MCT will have access to superior materials and manufacturing techniques.

You are substituting hand-waving for actual analysis. I maintain that you are sandbagging aerocapture/entry with unrealistically pessimistic numbers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/19/2015 03:16 am
The shuttle dry mass was 75 mT which yes is the same dry mass as I estimate as well , but for a vehicle with STAGGERINGLY lower performance requirements then your demanding of it. 

But Shuttle did not perform entry with 100 mT of cargo plus terminal landing propellants.  So it's entry mass would be less then half of what MCT would experience, THAT eats up all the improved materials and manufacturing techniques of today as well as savings from not having wings.

No one has produced any speculative MCT that doesn't have at least 200 mT entry mass, if you have such a vehicle then present it or stop making dishonest complaints about entry mass.

You have not provided one shred of analysis here only reasoning by grasping at the performance values of other vehicles without though to scale or mass, while I just provided you with one which is admittedly incredibly simple but still demonstrates the difficulties of getting a huge heavy vehicle to withstand high g forces due to cube-square scaling.  I expect you to at least ACKNOWLEDGE THIS http://forum.nasaspaceflight.com/index.php?topic=37808.msg1437142#msg1437142 (http://forum.nasaspaceflight.com/index.php?topic=37808.msg1437142#msg1437142) analysis and give a rebuttal before you respond again and rethink who is the one doing the hand-waving.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/19/2015 03:47 am
If you're limited to just 2 gees on reentry, that's a good argument for base-first entry, same load-path.

But there are other ways to carry a buckling load. Consider, for example, if the load of 9MN (150 tons times 6 gees) was distributed over the surface of a biconic with dimensions of roughly 15m by 15m (or 10m by 22m or whatever). That is the equivalent to less than 6psi. That's less than the internal pressure of the vehicle (and likely you'd pressurize the tanks for reentry, since you'll need to do a landing burn anyway). In other words, you don't have to deal with a buckling force (like with shuttle which was mostly unpressurized) but the tensile force of a pressure vessel which you already need anyway.

It's a minimal analysis, but still far better than your hand-waving about square-cube-law making things so much worse for MCT, so impossibly worse that you'll throw out either significant aerocapture or 100 day transits.


...and heck, even at your sand-bagged 2 gees, that still doesn't rule out 100 day transfers with multi-pass aerocapture/entry at the end. With a lifting entry, you can spread out that acceleration over a long time.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/19/2015 04:09 am
...and heck, even at your sand-bagged 2 gees, that still doesn't rule out 100 day transfers with multi-pass aerocapture/entry at the end. With a lifting entry, you can spread out that acceleration over a long time.

Aerocapture is hard precisely because it must come all at once, lest the craft shoot out on a modified heliocentric orbit;  Consequences for unpredictable failure usually involve loss of crew.  'Lifting entry' is primarily useful after capture has occurred, when you have plenty of time-in-atmosphere to work with.

100 day transfers don't just involve high amounts of velocity to dissipate, more and more of that velocity has to be dissipated on the first pass.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/19/2015 04:39 am
...and heck, even at your sand-bagged 2 gees, that still doesn't rule out 100 day transfers with multi-pass aerocapture/entry at the end. With a lifting entry, you can spread out that acceleration over a long time.

Aerocapture is hard precisely because it must come all at once, lest the craft shoot out on a modified heliocentric orbit;  Consequences for unpredictable failure usually involve loss of crew.
That was also true for each and every Shuttle and Apollo reentry. The reentry corridor was narrow. But if one MCT out of 500 ships did skip out on a heliocentric trajectory, you'd just have to devote one or two stripped-down MCTs in orbit or on the surface of Mars to be ready to mount a rescue mission (or wouldn't even have to be devoted to that purpose, just ready to be fueled up when the MCTs are arriving). In the grand scheme of things, that would be fairly cheap insurance.
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'Lifting entry' is primarily useful after capture has occurred, when you have plenty of time-in-atmosphere to work with.
No, it's also useful during aerocapture because you can adjust for uncertainties in the atmosphere's density. And you can utilize negative lift to give you more time-in-atmosphere.

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100 day transfers don't just involve high amounts of velocity to dissipate, more and more of that velocity has to be dissipated on the first pass.
Sure. But not more than needs to be dissipated for lunar reentry.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/19/2015 08:02 am
If you're limited to just 2 gees on reentry, that's a good argument for base-first entry, same load-path.

Yes it is, and if you want to advocate for base-first entry, though you would have other series trade-offs to justify.


That was also true for each and every Shuttle and Apollo reentry. The reentry corridor was narrow. But if one MCT out of 500 ships did skip out on a heliocentric trajectory, you'd just have to devote one or two stripped-down MCTs in orbit or on the surface of Mars to be ready to mount a rescue mission (or wouldn't even have to be devoted to that purpose, just ready to be fueled up when the MCTs are arriving). In the grand scheme of things, that would be fairly cheap insurance.

No, Shuttle did not do Aerocapture because it was not going anywhere near escape velocity on atmospheric entry and could not leave the Earth if it over-shot, it did controlled skips and banked turns along the atmosphere to dissipate energy but that is not the same as aerocapture.  When you under-shoot aerocapture you end up back on a Heliocentric orbit leaving the planet entirely.

The rescue idea is ridiculous, the lost vehicle would be heading for a aphelion well into the asteroid belt and even if another MCT on mars had the DeltaV to rendezvous with it they would have not have the DeltaV to return to mars or likely any other planet on a time scale of less then years.

No, it's also useful during aerocapture because you can adjust for uncertainties in the atmosphere's density. And you can utilize negative lift to give you more time-in-atmosphere.

Yes this is correct, the more lift you can generate the wider your aerocapture corridor is and the more adjustment can be made in real time due to atmospheric conditions.  It is an argument in favor of the bi-conic shape when doing aerocapture.

Quote
Quote
100 day transfers don't just involve high amounts of velocity to dissipate, more and more of that velocity has to be dissipated on the first pass.
Sure. But not more than needs to be dissipated for lunar reentry.

Apollo entry was at 10.77 km/s, contrary to popular belief they could not skip off the atmosphere and be lost in space forever, they would simply have re-entered later after a large elliptical orbit during which they would run out of oxygen because they were below escape velocity.

Burnate already did the numbers, on the 102 day transit your perigee at mars is 9.17 km/s and you need to shed 4.7 km/s.  That's about half your velocity, and about 50% of the energy of the Apollo return.

The 100 day transit is even worse (it saves Earth Escape DeltaV by raising velocity at mars), cause your velocity is 13.77 km/s of which you must shed 9.2 km/s, which is 88% of your total energy.  In fact you need to shed more energy then the entire Apollo lunar return, about 60% more.

I'm very skeptical that the cord through the martian atmosphere can be long enough to provide this much deceleration within even your g limits.  The faster your going to less time you spend in the atmosphere and your deceleration force needs to increase exponentially.   And as entry velocities increase the corridor gets narrower and narrower, according to http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930003532.pdf even with 5 g limit the entry velocity had to kept to under 9 km/s to keep the corridor to 1 degree wide with a 0.3 L/D vehicle like a capsule.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/19/2015 11:27 pm
If magnetic deceleration can be used it would help a lot with reusability. If a first pass can achieve capture then a second or third pass can achieve landing. Replacing the heatshield after every flight will cost time and money. I don't see magnetic as a requirement but i hope for it. A metallic heatshield will not do especially for EDL back on earth.
Even a PICA-X shield can take multiple entries (Musk said 100, which is an overstatement but is a lot more than MCT will need). And yes, a metallic shield would work, you just have to do it gently enough. But I suspect SpaceX is looking at PICA-X. A tanker going to LEO, most certainly, could use a metallic TPS without any hard limits on numbers of reuses (thousands are possible).

A metallic heatshield for reentry from interplanetary speeds? I doubt it. PicaX reusable yes. But from interplanetary speeds? To Mars and back, yes, thats two uses, the second very heavy. But again? Maybe two return flights, maybe not.

Edit: I hope I am wrong.

Metallic heatshield for the tankers, that would help a lot, I agree. Many tank flights without refurbishing the heatshield. But it would mean a completely different design for the tanker. The tanker coming back from LEO can probably make a significant number of flights before refurbishing with PicaX.

That would be my thought too.  Especially if the MCT was an integrated design.  Do they wan to have two different heat shields for the tanker version and the Mars version?  Or just use Pica-X on both for commonality, and just replace it after may one round trip from Mars, or like 10 [for example] trips to LEO?  Probably need to thoroughly go through a tanker after 10 round trips anyway and look for other wear items.

Now, if MCT rides empty on a dedicated S2 so that it were to have whole vehicle abort capability, then the S2 may be very different from MCT in OML and EDL profile...so there may be little commonality between them even if they both use Pica-X.   SO going with two different TPS types in that case may not be an issue.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/20/2015 04:15 am
Do they wan to have two different heat shields for the tanker version and the Mars version?  Or just use Pica-X on both for commonality, and just replace it after may one round trip from Mars, or like 10 [for example] trips to LEO?  Probably need to thoroughly go through a tanker after 10 round trips anyway and look for other wear items.

Again like in other discussions we run into the situation that we need to differentiate between different phases. I would assume that initially the tanker too would have PicaX for ease of development. If and when the number of flights really takes off it can be worth it to redesign the tanker to be more reusable without changing the heatshield. Then metallic or even better magnetic would look quite attractive.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 10/20/2015 05:31 am
Again like in other discussions we run into the situation that we need to differentiate between different phases. I would assume that initially the tanker too would have PicaX for ease of development. If and when the number of flights really takes off it can be worth it to redesign the tanker to be more reusable without changing the heatshield. Then metallic or even better magnetic would look quite attractive.

Is a metallic heat shield lighter than PicaX?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/20/2015 05:53 am
While SpaceX clearly has experience with PICA and their own formulations of such, I don't think they would be afraid of pursuing metallic if they felt it made good engineering and cost sense.  The biggest factor in favor of metallic TPS is that is it the only way you get to a true 'gas-and-go' vehicle and we know that's ultimately what they want.  The hypothetical Tanker-2-LEO vehicle is clearly going to have a rapid launch cadence, much more so then the vehicle which actually transits to and from mars so it's the logical the first place something like metallic TPS would be useful.

The question is given all the other things that will be needed to turn a vehicle around if the process actually takes a week or two (still a huge improvement over Shuttle) dose the replacement of an ablative heat-shield really impact your turn around time significantly, especially if it is replaced only infrequently.  I suspect this will be the case, that the best vehicle that can presently be built won't really need metallic TPS for it's turn around time so it won't initially have it.  But if the turn around process is improved, perhaps after several years of doing it to the point that heat-shield replacement becomes a bottleneck then I can see this being a desirable upgrade.

Now if on the other hand metallic systems can manage to beat PICAX on weight then they have a clear path to being in the design right from the start.  It is very hard to say if this would be the case because metallics haven't been used before (but they have been well developed during the X-33 project) and we don't know how much PICA is actually used on Dragon or how much would be needed on a hypothetical Tanker.  My own analysis shows metallics being at about parity with PICA for a relatively low temperature range consistent with lifting entry vehicles, but this is based on only a speculation of the PICAX thickness and doesn't factor in any potential SpaceX improvement to the metallic system either so I can't say anything other then that it might be possible.

Metallics might be inappropriate because of stagnation point temperatures in excess of what they handle such as on a low lift blunt vehicle like Dragon and thouse temperatures depend hugely on the actual entry characteristics of the vehicle which are entirely speculative right now.  Perhaps even a combination of ablatives at the stagnation point/s and metalics on the flanks and leeward sides of the vehicle could work.  I am very sure that we will not see PICAX directly applied to propellant tankage though as some have speculated, the bonding of a brittle material to a tank wall that will become cryogenic strikes me as unfeasible as ablatives are attached with adhesives which are notoriously bad when cold, nor dose it offer any means of repair or replacement as ablation takes place.  You need a structural frame that holds the ablative and allows it to be removed, this would also be the default means of using metallic TPS in large panels, though I can conceive of a monocoque design in which the a multi-layer sandwiching of metals creates the tank wall, the insulation layer and the outer skin.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: aceshigh on 10/20/2015 01:44 pm
why is MCT always considered a single vehicle launched from Earth? Has Musk in any way indicated that?

isn´t there any possibility MCT could be a space only craft in permanent transit between Mars and Earth, picking people on Earth and dropping them on Mars?

that way, MCT could be faster and bigger. Because you wouldn´t need to accelerate an habitat for 100 people to live for 6 months (or less if possible) EVERY trip.

Just accelerate (to catch up with MCT and transfer people) a "small" capsule where you have 100 people crammed in a tight space with their luggage.


The idea of a big transport to Mars for people to live in for 6 months being launched EVERY trip sounds to me somewhat like launching half the space station into space every time a new astronaut goes to it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 10/20/2015 01:54 pm
why is MCT always considered a single vehicle launched from Earth? Has Musk in any way indicated that?

isn´t there any possibility MCT could be a space only craft in permanent transit between Mars and Earth, picking people on Earth and dropping them on Mars?

that way, MCT could be faster and bigger. Because you wouldn´t need to accelerate an habitat for 100 people to live for 6 months (or less if possible) EVERY trip.

Just accelerate (to catch up with MCT and transfer people) a "small" capsule where you have 100 people crammed in a tight space with their luggage.


The idea of a big transport to Mars for people to live in for 6 months being launched EVERY trip sounds to me somewhat like launching half the space station into space every time a new astronaut goes to it.

Elon wants a shorter transit time and you can't do that with a cycler.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: aceshigh on 10/20/2015 03:51 pm
how shorter does he want the transit times?

from here https://en.wikipedia.org/wiki/Mars_cycler it seems plenty of them are under 3 months?


but anyway, isn´t there a middle term? Cyclers hardly use any fuel at all. What about a cycler which also has fuel assist BUT still would use much less fuel (for it´s size) than launching from Earth?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/20/2015 04:08 pm
why is MCT always considered a single vehicle launched from Earth? Has Musk in any way indicated that?


Musk made some comments about "landing the whole thing" and "using MCT as the surface habitat initially."   This has lead to people assuming there won't be multiple vehicle that land, launch, and transit separately like Mars Semi-direct or something. 

It's not much to go on, and SpaceX's eventual actual MCT concept could have completely changed since those comments.  But it's all we've had to go on so far.  :-)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 10/20/2015 04:20 pm
how shorter does he want the transit times?

from here https://en.wikipedia.org/wiki/Mars_cycler it seems plenty of them are under 3 months?


but anyway, isn´t there a middle term? Cyclers hardly use any fuel at all. What about a cycler which also has fuel assist BUT still would use much less fuel (for it´s size) than launching from Earth?

Note the long return to Earth time. Elon also want MCT to get back to Earth quickly so it can be prepped for its next flight the next synod.

SpaceX has mentioned looking into SEP. A hybrid system would allow a quick TMI using chemical rockets and then SEP would allow a slow continuous acceleration to reduce flight time.

why is MCT always considered a single vehicle launched from Earth? Has Musk in any way indicated that?


Musk made some comments about "landing the whole thing" and "using MCT as the surface habitat initially."   This has lead to people assuming there won't be multiple vehicle that land, launch, and transit separately like Mars Semi-direct or something. 

It's not much to go on, and SpaceX's eventual actual MCT concept could have completely changed since those comments.  But it's all we've had to go on so far.  :-)

Personally, I think it means landing on Mars and returning to Earth orbit (or cis-lunar), but yeah, we only got old quotes to work with.

I'm sure we will be amazed at the MCT architecture when SpaceX releases it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/20/2015 05:01 pm
While SpaceX clearly has experience with PICA and their own formulations of such, I don't think they would be afraid of pursuing metallic if they felt it made good engineering and cost sense.  The biggest factor in favor of metallic TPS is that is it the only way you get to a true 'gas-and-go' vehicle and we know that's ultimately what they want.  The hypothetical Tanker-2-LEO vehicle is clearly going to have a rapid launch cadence, much more so then the vehicle which actually transits to and from mars so it's the logical the first place something like metallic TPS would be useful.

The question is given all the other things that will be needed to turn a vehicle around if the process actually takes a week or two (still a huge improvement over Shuttle) dose the replacement of an ablative heat-shield really impact your turn around time significantly, especially if it is replaced only infrequently.  I suspect this will be the case, that the best vehicle that can presently be built won't really need metallic TPS for it's turn around time so it won't initially have it.  But if the turn around process is improved, perhaps after several years of doing it to the point that heat-shield replacement becomes a bottleneck then I can see this being a desirable upgrade.


Agreed.  The MCT that goes to Mars will probably get quite a refurbishment between missions as it will have been gone a long time, habitated for a long time, and loitered in space and on the dusty surface of MArs for a long time, that it will probably go into a processing building for an extensive inspection and refurb when it gets back.
But the tanker will have a goal of launch, dock with depot, return, repeat.  That makes it a good candidate for metallic as it offers that potential without burning a little away each return like Pica-X.

But, there will probably be a certain limited service live for safety where it will get say 10 mission (for example) and then go into a processing facility and get thoroughly inspected and refurbished where necessary.  At that point while it's off line for a while anyway, replacing the large PICA-X tiles wouldn't be too difficult.  Especially if a nice smooth biconic shape that doesn't have a lot of complex surface area like the Shuttle.  Even if a tanker had had a metallic TPS, it'll still likely need to go into the processing facility at regular intervals to make sure it stay reliable.  So a metallic TPS probably won't prevent that.  PICA would need to be of sufficient thickness to last that service life between refurbishments.  How heavy would that be vs. the metallic?  That'd probably be a major factor in evaluation of both.

I am very sure that we will not see PICAX directly applied to propellant tankage though as some have speculated, the bonding of a brittle material to a tank wall that will become cryogenic strikes me as unfeasible as ablatives are attached with adhesives which are notoriously bad when cold, nor dose it offer any means of repair or replacement as ablation takes place.  You need a structural frame that holds the ablative and allows it to be removed, this would also be the default means of using metallic TPS in large panels, though I can conceive of a monocoque design in which the a multi-layer sandwiching of metals creates the tank wall, the insulation layer and the outer skin.

Agreed.  My thoughts too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/20/2015 07:33 pm
why is MCT always considered a single vehicle launched from Earth? Has Musk in any way indicated that?

isn´t there any possibility MCT could be a space only craft in permanent transit between Mars and Earth, picking people on Earth and dropping them on Mars?

that way, MCT could be faster and bigger. Because you wouldn´t need to accelerate an habitat for 100 people to live for 6 months (or less if possible) EVERY trip.

Just accelerate (to catch up with MCT and transfer people) a "small" capsule where you have 100 people crammed in a tight space with their luggage.


The idea of a big transport to Mars for people to live in for 6 months being launched EVERY trip sounds to me somewhat like launching half the space station into space every time a new astronaut goes to it.

Not, always, I'm one of a few voices in the wilderness that still see semi-direct like architectures as most likely and fully compatible with Musk's goals and statements so far.  And we should NOT be taking even clear statements of intent as evidence that alternatives have been taken off the table as their are FAR too many instances of early statements of intent in the engineering minutia by SpaceX that fall through.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 10/20/2015 07:34 pm
Presumably they will use something that can withstand a year in transit (I'm thinking micrometeorite impacts) then still be usable for a shield. Which is best suited, PicaX or metallic?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 10/20/2015 07:36 pm
why is MCT always considered a single vehicle launched from Earth? Has Musk in any way indicated that?

isn´t there any possibility MCT could be a space only craft in permanent transit between Mars and Earth, picking people on Earth and dropping them on Mars?

that way, MCT could be faster and bigger. Because you wouldn´t need to accelerate an habitat for 100 people to live for 6 months (or less if possible) EVERY trip.

Just accelerate (to catch up with MCT and transfer people) a "small" capsule where you have 100 people crammed in a tight space with their luggage.


The idea of a big transport to Mars for people to live in for 6 months being launched EVERY trip sounds to me somewhat like launching half the space station into space every time a new astronaut goes to it.

Not, always, I'm one of a few voices in the wilderness that still see semi-direct like architectures as most likely and fully compatible with Musk's goals and statements so far.  And we should NOT be taking even clear statements of intent as evidence that alternatives have been taken off the table as their are FAR too many instances of early statements of intent in the engineering minutia by SpaceX that fall through.
I'm wilderness bound. MUsk's statement was a while ago, and things definitely change. I think its going to be a lot more radical than people have been speculating so far.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/20/2015 08:15 pm
I'm wilderness bound. MUsk's statement was a while ago, and things definitely change. I think its going to be a lot more radical than people have been speculating so far.

Things do change and I can't wait for the great reveal. I like MCT going all the way and back for a simple reason, not only because Elon Musk said so. It is operationally simple, straightforward and elegant. Making MCT ready for the next flight is a lot simpler down on earth than in space. Getting the weight back up into orbit is not an expensive problem given the capability of BFR.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/20/2015 08:54 pm
Things do change and I can't wait for the great reveal. I like MCT going all the way and back for a simple reason, not only because Elon Musk said so. It is operationally simple, straightforward and elegant. Making MCT ready for the next flight is a lot simpler down on earth than in space. Getting the weight back up into orbit is not an expensive problem given the capability of BFR.

I agree, with a proviso:

As you add more and more little things to make it work, a straightforward plan can have terrible complexities. Many refueling dockings, transferring people from several Dragons to the MCT, etc... there will be a point where making an easy system work isn't easy.

But otherwise yes... if they can make it work in the simple way envisaged it will make the trip cheaper (which is ultimately the SpaceX goal). And 20 Synods later they'll have a different vision for higher numbers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/20/2015 11:50 pm
Sorry it took me a while to respond. I apologize in advance for my abrasive tone, but I'm a little annoyed at the lack of an attempt to understand what I wrote and instead go with an obviously absurd interpretation (at least for the first part).

...


That was also true for each and every Shuttle and Apollo reentry. The reentry corridor was narrow. But if one MCT out of 500 ships did skip out on a heliocentric trajectory, you'd just have to devote one or two stripped-down MCTs in orbit or on the surface of Mars to be ready to mount a rescue mission (or wouldn't even have to be devoted to that purpose, just ready to be fueled up when the MCTs are arriving). In the grand scheme of things, that would be fairly cheap insurance.

No, Shuttle did not do Aerocapture because it was not going anywhere near escape velocity on atmospheric entry and could not leave the Earth if it over-shot
Thank you Captain Obvious.
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it did controlled skips and banked turns along the atmosphere to dissipate energy but that is not the same as aerocapture.
Nope, but the reentry corridor is quite narrow in order to keep the reusable and fragile TPS intact, which was my point: narrow reentry corridor.
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When you under-shoot aerocapture you end up back on a Heliocentric orbit leaving the planet entirely.
Of course. If you screw up the Shuttle reentry corridor, you don't just end up on a heliocentric orbit, you end up completely dead. I'd rather be on a heliocentric trajectory, waiting on a rescue mission, than completely dead. But the narrow reentry corridor didn't kill anyone on either Shuttle or Apollo, and we have more sophisticated guidance and navigation than we did then.

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The rescue idea is ridiculous, the lost vehicle would be heading for a aphelion well into the asteroid belt and even if another MCT on mars had the DeltaV to rendezvous with it they would have not have the DeltaV to return to mars or likely any other planet on a time scale of less then years.
Um, yes it would. A stripped down MCT in elliptical Mars orbit could have capability for FAR more C3 than the MCT that didn't quite aerocapture enough. It could launch almost immediately after the failed aerocapture, easily catching up to the MCT in question. You aren't stuck waiting for orbits to come back around because you would have plenty of delta-v to work with. On the scale that SpaceX is dealing with, this sort of capability would be cheap. It's not "ridiculous" if this is the only reason keeping you from attempting aerocapture.

Additionally, the MCT that missed the full aerocapture still has 0.5-1km/s of propellant on board for landing that it could use (while still deep in Mars' gravity well, so getting an Oberth Multiplier of up to 4) to put itself into an elliptical orbit if it only undershot the aerocapture a little bit. So you would have to be REALLY far off (not just slightly off) in order to be automatically on a heliocentric trajectory. Even during a regular, low-speed entry, being significantly off can easily kill you, so it's something you'll have to get pretty good at regardless of whether or not you do aerocapture.

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No, it's also useful during aerocapture because you can adjust for uncertainties in the atmosphere's density. And you can utilize negative lift to give you more time-in-atmosphere.

Yes this is correct, the more lift you can generate the wider your aerocapture corridor is and the more adjustment can be made in real time due to atmospheric conditions.  It is an argument in favor of the bi-conic shape when doing aerocapture.
Sure, but even a typical capsule shape can generate significant lift. And with greater entry precision, that amount of lift may be all you really need (more later).
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100 day transfers don't just involve high amounts of velocity to dissipate, more and more of that velocity has to be dissipated on the first pass.
Sure. But not more than needs to be dissipated for lunar reentry.

Apollo entry was at 10.77 km/s, contrary to popular belief they could not skip off the atmosphere and be lost in space forever, they would simply have re-entered later after a large elliptical orbit during which they would run out of oxygen because they were below escape velocity.

Burnate already did the numbers, on the 102 day transit your perigee at mars is 9.17 km/s and you need to shed 4.7 km/s.  That's about half your velocity, and about 50% of the energy of the Apollo return.

The 100 day transit is even worse (it saves Earth Escape DeltaV by raising velocity at mars), cause your velocity is 13.77 km/s of which you must shed 9.2 km/s, which is 88% of your total energy.  In fact you need to shed more energy then the entire Apollo lunar return, about 60% more.
I pretty clearly was talking about velocity difference (i.e. acceleration times time), not energy.

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I'm very skeptical that the cord through the martian atmosphere can be long enough to provide this much deceleration within even your g limits.  The faster your going to less time you spend in the atmosphere and your deceleration force needs to increase exponentially.   And as entry velocities increase the corridor gets narrower and narrower, according to http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930003532.pdf even with 5 g limit the entry velocity had to kept to under 9 km/s to keep the corridor to 1 degree wide with a 0.3 L/D vehicle like a capsule.
So we'll have to get within less than a degree wide. I don't see the problem; we're much better at Mars entry precision than we were when that document was written (1992), particularly with the Curiosity rover's entry, and clearly some sort of areospatial positioning system could be deployed to enhance the precision to within a tiny fraction of a degree (on Earth, you can get within centimeters). But even with purely optical aids, you can do much better than a single degree: "Other investigators have shown that with the use of onboard optical sightings of the Martian moons, the error in the atmospheric entry angle could be reduced to +/-0.25 degrees without the need for secondary spacecraft to serve as navigational aides (Ref. 45)." (In fact, we already have spacecraft around Mars that could be used for this purpose.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/21/2015 12:03 am
why is MCT always considered a single vehicle launched from Earth? Has Musk in any way indicated that?

isn´t there any possibility MCT could be a space only craft in permanent transit between Mars and Earth, picking people on Earth and dropping them on Mars?

that way, MCT could be faster and bigger. Because you wouldn´t need to accelerate an habitat for 100 people to live for 6 months (or less if possible) EVERY trip.

Just accelerate (to catch up with MCT and transfer people) a "small" capsule where you have 100 people crammed in a tight space with their luggage.


The idea of a big transport to Mars for people to live in for 6 months being launched EVERY trip sounds to me somewhat like launching half the space station into space every time a new astronaut goes to it.

Because cyclers are inherently a ... dumb idea. IMO. You've got to accelerate all the crew, crew consumables, cargo, and propellant for the lander to a Mars transfer orbit anyway. Just to catch up to the cycler. All while stuck in VERY cramped conditions. This has some very serious failure modes - what if you cannot rendezvous with the cycler?

Do the math, look at the size of the "capsule" you need to transport all that to the cycler, and you'll realize that your small transfer vessel is almost at the size you need for normal transit, so you might as well just scale up the crew area and skip the cycler altogether. (And that larger crew area will be needed on Mars as well)

And that doesn't even beging to deal with the limited and few launch windows a cycler offers. And how you deal with a fleet of ships going in the same launch window.

No, I maintain that "cyclers" make no sense. And I'm dumbfounded why otherwise brilliant people such as Aldrin keep advocating for them.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Space Ghost 1962 on 10/21/2015 12:59 am
why is MCT always considered a single vehicle launched from Earth? Has Musk in any way indicated that?

isn´t there any possibility MCT could be a space only craft in permanent transit between Mars and Earth, picking people on Earth and dropping them on Mars?

that way, MCT could be faster and bigger. Because you wouldn´t need to accelerate an habitat for 100 people to live for 6 months (or less if possible) EVERY trip.

Just accelerate (to catch up with MCT and transfer people) a "small" capsule where you have 100 people crammed in a tight space with their luggage.


The idea of a big transport to Mars for people to live in for 6 months being launched EVERY trip sounds to me somewhat like launching half the space station into space every time a new astronaut goes to it.

Because cyclers are inherently a ... dumb idea. IMO. You've got to accelerate all the crew, crew consumables, cargo, and propellant for the lander to a Mars transfer orbit anyway. Just to catch up to the cycler. All while stuck in VERY cramped conditions. This has some very serious failure modes - what if you cannot rendezvous with the cycler?

Do the math, look at the size of the "capsule" you need to transport all that to the cycler, and you'll realize that your small transfer vessel is almost at the size you need for normal transit, so you might as well just scale up the crew area and skip the cycler altogether. (And that larger crew area will be needed on Mars as well)

And that doesn't even beging to deal with the limited and few launch windows a cycler offers. And how you deal with a fleet of ships going in the same launch window.

No, I maintain that "cyclers" make no sense. And I'm dumbfounded why otherwise brilliant people such as Aldrin keep advocating for them.
Google "The MCV: A Mars Colonization Vehicle". Two kids at the Mars Society (Musk was there too!). Slightly different concept, but enough like Aldrin's cycler in ways that he was verbally jousting with them.

They were doing accelerated orbits with both Mars and Earth assists for high velocity exchanges of small craft carrying scalable numbers of crew mostly.

To a captured and repurposed asteriod. They got the idea from Rusty Schwieckart and Robert Farquhar - the orbital mechanics is of a chaotic orbit with chosen encounters. Using asteroid deflection to drive asteroids to accurate closest possible encounters as a means of high velocity propulsion.

They were after the GCR radiation protection of the asteroid, and the ability to accumulate resources successively, with ISRU and food cultivation reducing the need for supply mass. A later version added the ability to use SEP in the relaxation period of the chaotic orbit (when unusable for transport given Earth Mars orientation) for high mass additions, where a low velocity encounter on a long period orbit occurs.

So yes, a related concept does work, but it solves the dilemmas differently then Aldrin's cycler. Oh, and the safety for a missed rendezvous is to bleed off delta-v with a close pass to Earth or Mars, recapturing the small transfer craft. The supplies needed are an issue for initial capture and orbital insertion/management, but in operation only a few days consumables (for safety) beyond transfer needs are used. Rendezvous is well before encounters.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/21/2015 02:37 am
Has anyone considered the possibility that the upcoming reveal will just be the Rocket, aka BFR, and not in fact the whole system?  I really suspect that SpaceX will be doing just BFR development over the next decade while the actual vehicle to mars will continue to be studied and refined without a firm mission architecture until they actually have to cross that bridge.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oiorionsbelt on 10/21/2015 02:53 am
Has anyone considered the possibility that the upcoming reveal will just be the Rocket, aka BFR, and not in fact the whole system?  I really suspect that SpaceX will be doing just BFR development over the next decade while the actual vehicle to mars will continue to be studied and refined without a firm mission architecture until they actually have to cross that bridge.
Possibly but it's also possible that reusable second stage and Mars ambitions combine to make BFR/MCT the next step.
 SpaceX has always been a builder of spacecraft as well as a builder of launch vehicles.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 10/21/2015 03:06 am

 SpaceX has always been a builder of spacecraft as well as a builder of launch vehicles.

That's true. We knew about F9 and Dragon pretty much at the same time when both were in development. Actually, didn't dragon development start before F9 did?

I don't imagine this will be prescient. BFR will either come at the same time as the MTC or slightly before. One prescient I do believe in: there won't be a BFR Falcon V analogue, they'll go full monty, and just iteratively upgrade the full size rocket/space craft over time like they're oft to do with F9.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oiorionsbelt on 10/21/2015 03:14 am

 SpaceX has always been a builder of spacecraft as well as a builder of launch vehicles.

That's true. We knew about F9 and Dragon pretty much at the same time when both were in development. Actually, didn't dragon development start before F9 did?

I don't imagine this will be prescient. BFR will either come at the same time as the MTC or slightly before. One prescient I do believe in: there won't be a BFR Falcon V analogue, they'll go full monty, and just iteratively upgrade the full size rocket/space craft over time like they're oft to do with F9.
I have a hard time picturing a payload other than MCT for the first BFR test flight.
Especially if the the MCT is the second stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 10/21/2015 03:25 am
Has anyone considered the possibility that the upcoming reveal will just be the Rocket, aka BFR, and not in fact the whole system?  I really suspect that SpaceX will be doing just BFR development over the next decade while the actual vehicle to mars will continue to be studied and refined without a firm mission architecture until they actually have to cross that bridge.

No the clues from several sources (like Peter Nasa's post (http://forum.nasaspaceflight.com/index.php?topic=38677.msg1437710#msg1437710) earlier today) suggest that there will be a planned sequence of steps presented that include definite plans with several Mars activities, a more intricate timeline,  further refined definition of the systems that will be used, and finally more clarity on some of the resources being brought to bear to pay for it all.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sghill on 10/21/2015 01:18 pm
I think the announcement of a SpaceX teaming agreement/partnership/knowledge sharing agreement/ stock swap with a submarine manufacturer will be the trigger that SpaceX is moving forward in earnest with designing the MCT and associated surface pieces. 

General Dynamics would be the natural partner.  A partnership arrangement gets GD back into launching rockets (it's been out of the launcher business since 1998 and the satellite business since 2010).  For SpaceX, it gets large, mobile, long-duration, and potentially nuclear-powered,  habitat systems design and engineering capabilities into their hands. 

It also gets one of the "big three" U.S. defense contractors on its team- something that shouldn't be ignored long term for SpaceX.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 10/21/2015 01:23 pm
Has anyone considered the possibility that the upcoming reveal will just be the Rocket, aka BFR, and not in fact the whole system?  I really suspect that SpaceX will be doing just BFR development over the next decade while the actual vehicle to mars will continue to be studied and refined without a firm mission architecture until they actually have to cross that bridge.

That is precisely my thinking.
The BFR is congruent with SX's core competency and is a necessary precursor. Even it will undergo changes after hopefully SX succeeds in recovering and re-flying F9 cores. 

I think Musk will speak to the MCT issue, but still in vague terms.  Even were he somewhat specific I don't think many observers here would expect the details to hold true during what I expect would be a longer than a decade gestation for the Block One MCT, which I expect to be quite different from its folllow-on.
There are too many outside SX technology developments ongoing* to fixate and spend R&D $ on a MCT in this decade, and probably for the early part of the next.

*SEP panels & engines, plasma propulsion, magneto aero capture, life support systems tech, etc. 
Never mind extreme wildcards like one of the myriad small fusion projects actually working.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/21/2015 07:01 pm

Because cyclers are inherently a ... dumb idea. IMO. You've got to accelerate all the crew, crew consumables, cargo, and propellant for the lander to a Mars transfer orbit anyway. Just to catch up to the cycler. All while stuck in VERY cramped conditions. This has some very serious failure modes - what if you cannot rendezvous with the cycler?

Do the math, look at the size of the "capsule" you need to transport all that to the cycler, and you'll realize that your small transfer vessel is almost at the size you need for normal transit, so you might as well just scale up the crew area and skip the cycler altogether. (And that larger crew area will be needed on Mars as well)

And that doesn't even beging to deal with the limited and few launch windows a cycler offers. And how you deal with a fleet of ships going in the same launch window.

No, I maintain that "cyclers" make no sense. And I'm dumbfounded why otherwise brilliant people such as Aldrin keep advocating for them.

Yea I think they are ideas that seem better in theory than in practice...for reasons you mention.

They make a little more sense for expensive expendable systems where you perhaps aren't refueling on Mars and every gram is important....like Apollo (and several Mars mission concepts).  So if you can shed a little bit of mass by not having to loft the hab, then there can be advantage.

But, if we are assuming here fully reusable components, with on-surface fueling and a LEO depot that will be cheap [relatively] to launch cheap propellant to...then even gram isn't so precious.  You can sacrifice some mass efficiency for economic efficiency or for additional simplicity/safety.  And just launch one more tanker to the depot for a mission that you might otherwise...and make a little more propellant on the surface prior to coming back.
(That is a reason that SEP may not really be necessary either.)

Additionally, pure hab space isn't all that heavy.  And if we're talking what the initial several exploration missions will need, we're talking smaller crew of maybe 6 or 7ish, so the hab volume isn't all that much anyway....there won't be 100 people coming at once for a long time.   But they'll need a lot of surface equipment and provisions and supplies for their stay as there won't be anything/much already there.  The cycler doesn't help with that, that needs to be launched from Earth every time.
Then once they get to Mars, they leave that nice cycler hab in space...but will still need one on Mars.  If MArs was habitable, then a cycler could make more sense.  Like a bus.  You ride it there...and get off and stay at your destination.  Then you catch it back, and can travel light.
But people need a place to stay there.  So it's more like an R/V.  They have a place for the trip there, for the stay there, and for the trip back.  IF you need to bring an R/V with you anyway, it doesn't make much sense to tow it where you are going and stay in hotels while traveling, just drive it and live in it along the way. 

Now...down the road when they are moving 100 people at a time, you get into the "bus" model rather than the R/V.  It might make more sense there.  But  your spacecraft is already designed to be large enough to eventually carry and support 100 people to Mars with additional life support and hab volume where the equipment storage was for the exploration missions, so I'm not sure it would serve much purpose even then.  Plus you don't have to worry about missing your cycler rendezvous if your hab is in your spacecraft, or hitting that narrow launch window.  Which I think adds a lot of safety margin.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/21/2015 07:15 pm
Has anyone considered the possibility that the upcoming reveal will just be the Rocket, aka BFR, and not in fact the whole system?  I really suspect that SpaceX will be doing just BFR development over the next decade while the actual vehicle to mars will continue to be studied and refined without a firm mission architecture until they actually have to cross that bridge.
Possibly but it's also possible that reusable second stage and Mars ambitions combine to make BFR/MCT the next step.
 SpaceX has always been a builder of spacecraft as well as a builder of launch vehicles.

Anything is possible.  We won't know until they see. 

But, "BFR" is a term I think only we've used here on the forums.  I don't think SpaceX or Musk has ever differentiated a HLV and MCT as separate items.  It's always been 'MCT' as I recall seeing.

So I see it as being more like "STS" than "Saturn V" and "Apollo" or "Falcon" and "Dragon" or even "Energia" and "Buran"...as separate systems.

The orbiter was integral to STS, not optional.  You couldn't really unveil the launch vehicle without the orbiter too.

As always, I might be completely misreading EM's intent.  heh.  ;-)



Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 10/21/2015 07:31 pm
Has anyone considered the possibility that the upcoming reveal will just be the Rocket, aka BFR, and not in fact the whole system?  I really suspect that SpaceX will be doing just BFR development over the next decade while the actual vehicle to mars will continue to be studied and refined without a firm mission architecture until they actually have to cross that bridge.
Possibly but it's also possible that reusable second stage and Mars ambitions combine to make BFR/MCT the next step.
 SpaceX has always been a builder of spacecraft as well as a builder of launch vehicles.

Anything is possible.  We won't know until they see. 

But, "BFR" is a term I think only we've used here on the forums.  I don't think SpaceX or Musk has ever differentiated a HLV and MCT as separate items.  It's always been 'MCT' as I recall seeing.

So I see it as being more like "STS" than "Saturn V" and "Apollo" or "Falcon" and "Dragon" or even "Energia" and "Buran"...as separate systems.

The orbiter was integral to STS, not optional.  You couldn't really unveil the launch vehicle without the orbiter too.

As always, I might be completely misreading EM's intent.  heh.  ;-)

EM did say MCT would be a system, so I think you are correct. Booster, shuttle, tanker, etc. could be generic names for the components of MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oiorionsbelt on 10/21/2015 07:35 pm
I'm pretty sure the term BFR has at least, been used by SpaceX if they didn't coin the term.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/21/2015 08:18 pm
I'm pretty sure the term BFR has at least, been used by SpaceX if they didn't coin the term.

Yes EM's said it. I think it was something like "you need a really big f'ing rocket, a BFR". But if that memory is correct, then he wasn't really calling it a BFR at the time... just describing it.

Since then some publications have called it a "Big Falcon Rocket". Maybe BFR will stick.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/21/2015 10:15 pm
I'm pretty sure the term BFR has at least, been used by SpaceX if they didn't coin the term.

Yes EM's said it. I think it was something like "you need a really big f'ing rocket, a BFR". But if that memory is correct, then he wasn't really calling it a BFR at the time... just describing it.

Since then some publications have called it a "Big Falcon Rocket". Maybe BFR will stick.

If that was the only mention of it, then the context still doesn't seem to indicate differentiation between a launch vehicle and a spacecraft  f he was saying to land 100mt on Mars, you need a really big f'ing rocket...for example...there's nothing in that to indicate a stand alone rocket, and a separate spacecraft. 

I'm more saying, was there a reference to "BFR" and "MCT" being referred to separately in the same comment, like how "Dragon" and "Falcon" are referred to differently in the same comment.  If so, then there could be a reasonable chance EM will just be announcing the LV.  Although even then, it's main purpose would be to loft MCT to space, just like the main purpose of the Saturn V was to loft the Apollo CSM and LEM through TLI.  The spacecraft were in the "unveilings" from the beginning.  Even when it was originally Direct Ascent instead of LOR. 
So I would expect something like that for this unveiling.  At least a working concept for the spacecraft, even if there is a stand alone LV.

But good to know that EM actually did use the term.  I'd not been aware of that.  :-)

 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/21/2015 10:23 pm
I really suspect that SpaceX will be doing just BFR development over the next decade while the actual vehicle to mars will continue to be studied and refined without a firm mission architecture until they actually have to cross that bridge.

Even if there is a separate BFR and MCT vehicle, and they aren't integrated like STS, I think they'll need to have some degree of working concept of the MCT vehicle, because it's requirements are what will drive BFR's design.  It will need to be big enough to get MCT to LEO, it can't be any smaller, and it probably won't be any bigger.  So they'd need at least a certain amount of design on the MCT vehicle before they could finalize a BFR design.  But as you say, the BFR could fly first while they are still refining MCT, where the oribiter had to pretty much be finalized before STS could ever fly it's first launch as they were integrated.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/21/2015 10:48 pm
Things do change and I can't wait for the great reveal. I like MCT going all the way and back for a simple reason, not only because Elon Musk said so. It is operationally simple, straightforward and elegant. Making MCT ready for the next flight is a lot simpler down on earth than in space. Getting the weight back up into orbit is not an expensive problem given the capability of BFR.

I agree, with a proviso:

As you add more and more little things to make it work, a straightforward plan can have terrible complexities. Many refueling dockings, transferring people from several Dragons to the MCT, etc... there will be a point where making an easy system work isn't easy.

But otherwise yes... if they can make it work in the simple way envisaged it will make the trip cheaper (which is ultimately the SpaceX goal). And 20 Synods later they'll have a different vision for higher numbers.

That is true, and the MCT vehicle will be complex obviously.  But I don't think it's quite as daunting to have those various roles as many think...if they are related and not opposing.

So, lets start first with the basic MCT vehicle.  What does it need to do at a minimum, from what we know/can plausibly speculate from EM's comments.

1)  It will need to get itself from some sort of Earth orbit to Mars, or else there'd need to be an expendable stage, which wouldn't be reusable, so unlikely I think.
2)  It will need to be capable of atmospheric EDL on Mars...in order to take off against from Mare (unless we are assuming a lander is left like Mars Direct, but then it wouldn't be reusable...so that seems unlikely).
3)   It will need to be a SSTO vehicle for taking off from Mars. 

I think most here agree mostly with those basic functions.

So what what else would we perhaps like it to do?

1)  EDL on Earth, so the whole vehicle comes home.  That's advantageous for many reasons, including refurbishment on the surface rather than in space.  MCT will already be capable of EDL on Mars, and Earth is not too different.  The atmosphere supplies much more dV to decelerate than Mars atmosphere, so no main engine retro propulsion needed.  The atmosphere will slow it down to around 120 MPH.  Only a small amount of retro propulsion needed.  However, the TPS will take more heat, so essentially, to make it capable of Earth EDL, you just need to make sure the TPS can withstand EArth EDL after doing a Mars EDL.  A little thicker layer of PICA-X tiles, for example.  I don't think too difficult....check.

2)  TEI without Mars orbit refueling.  Since MCT already needs to be capable of TMI, TEI is no more difficult.  It a matter of getting it to Mars orbit with enough propellant for TEI.  So mainly a matter of making sure the propellant tanks and propulsion system is of size enough to get that extra propellant off the surface and to Mars orbit, so it can do TEI.  I don't think too difficult.  Larger tanks and thrust...Check.

3)  In the case of an integrated design, MCT gets itself from booster staging to LEO.  But MCT will alrady be a SSTO vehicle to get off Mars.  It's really not different on Earth, but the dV is larger because of Earth's deeper gravity well.  So we put a reusable booster under it to supply that extra dV...I don't think anyone assumed any different anyway...Check.

4)  Using one common MCT hab for transit both ways and on the surface.  Well, if the rest of the above is true, MCT will get itself to Mars, land itself, stay on Mars, then get itself back off MArs, and get itself back to Earth.  So no need for a second hab, the primary hab will service the crew for the entire trip.  It needs to be designed for zero-g operation and Mars gravity operation.  That's not a given, but I don't think it too hard either.  Especially for a smaller crew of 6-7 for the early exploration missions.  Once there's a colony, then the colonists will use the facilities already on the surface when they get there and not need to habitate in MCT.
So, a hab designed to support 6-7 astronauts in gravity as well as in zero-g...shouldn't be a big issue...so check.

People like to look at the compromise design of the shuttle as an example of trying not to do too much.   But remember, those were competing design criteria it had to deal with, not complementing design criteria like MCT. 

Where with the shuttle, as I understand...NASA, USAF, and politicians all had some quite different requirements that STS had to do if it was going to get joint support and funding.  Many of which didn't really have anything to do with what NASA needed STS to do.    MCT won't really have that problem, as it can focus only on what EM wants it to do without anything competing with that.
It's not going to have big companies like LM and ATK causing political pressure for certain hardware to be used, they won't have USAF requiring things like on-pad payload change out and a excessive cross range to to enable single polar orbit spy satellite deployment/capture in there pressuring the design to vary from it's primary goals.  It won't need features and hardware just so a politician can bring political pork back do their district.

So, most of these things are just a little in addition to a primary function MCT will need to do already, rather than competing with a primary function.  So I don't think it necessarily will had huge amounts of complexity to MCT, and it can add a lot of mass and economic efficiency to it by reducing the number of different vehicles and systems required to develop and maintain overall.

IMHO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/21/2015 11:18 pm
Has anyone considered the possibility that the upcoming reveal will just be the Rocket, aka BFR, and not in fact the whole system?  I really suspect that SpaceX will be doing just BFR development over the next decade while the actual vehicle to mars will continue to be studied and refined without a firm mission architecture until they actually have to cross that bridge.

That is precisely my thinking.
The BFR is congruent with SX's core competency and is a necessary precursor. Even it will undergo changes after hopefully SX succeeds in recovering and re-flying F9 cores. 

I think Musk will speak to the MCT issue, but still in vague terms.  Even were he somewhat specific I don't think many observers here would expect the details to hold true during what I expect would be a longer than a decade gestation for the Block One MCT, which I expect to be quite different from its folllow-on.
There are too many outside SX technology developments ongoing* to fixate and spend R&D $ on a MCT in this decade, and probably for the early part of the next.

*SEP panels & engines, plasma propulsion, magneto aero capture, life support systems tech, etc. 
Never mind extreme wildcards like one of the myriad small fusion projects actually working.

I sure we will get some nice video of a giant rocket taking off.  It might just have some totally ambiguous payload-fairing on it leaving everything beyond the launch unspecified much the way Vulcan was introduced, this would be a clear sign that they are shopping BFR around to commercial customers, but even I would find that a bit conservative given the hype that has been built up.

More likely were shown some kind of large mars vehicle reaching LEO on top of the BFR.  But then the video might just cut to said vehicle landing on mars with all the details of refueling, trajectory, aerocapture, entry etc etc left out.  Or on the opposite end of the spectrum we could see a nearly full 'architecture' which covers all these steps and Musk will be open with the numbers.

But even the most minimal video will give some ideas as to what the present preferred architecture is and one of the three camps of 'Super Dragon', 'Integrated Bi-conic' and 'Separate Bi-conic' will likely get to crow, despite the fact that the shown architecture is still in flux, given the kind of 'Holy writ' that people ascribe to offhand statements of Musk their will be no point arguing with a video. 

The speculation would then narrow down to other operational details of how the vehicle actually dose the mission and what the ultimate cost will be, how fast if at all SpaceX can put the vehicle into service, if SLS is doomed and when first landing on mars might happen.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/21/2015 11:36 pm
Has anyone considered the possibility that the upcoming reveal will just be the Rocket, aka BFR, and not in fact the whole system?  I really suspect that SpaceX will be doing just BFR development over the next decade while the actual vehicle to mars will continue to be studied and refined without a firm mission architecture until they actually have to cross that bridge.

That is precisely my thinking.
The BFR is congruent with SX's core competency and is a necessary precursor. ...
You seem to forget that Dragon is clearly also SpaceX's core competency. Dragon is at least as impressive as F9 is. And what will the second stage of BFR be? MCT and BFR's second stage are solving almost all the same problems. The ones that are left are ones that Dragon is helping to solve.
Quote
...
There are too many outside SX technology developments ongoing* to fixate and spend R&D $ on a MCT in this decade, and probably for the early part of the next.

*SEP panels & engines, plasma propulsion, magneto aero capture, life support systems tech, etc. 
Never mind extreme wildcards like one of the myriad small fusion projects actually working.
Um, SpaceX is absolutely working SEP panels/engines/plasmapropulsion and life support systems tech right now. Magneto aerocapture is a totally unproven idea that is only really being pursued by one company (with nearly no funding), and it will remain to be seen if it's either practical or worthwhile. Regardless, evangelists for the tech (mainly Jon Goff here ;) ) seem to emphasize its ability to allow /existing/ tech to utilize it, so SpaceX need not put off developing MCT even if it's a totally real thing. And I would put even less faith in the small fusion projects.


...and anyway, developing BFR first doesn't make ANY sense. There's nothing for them to launch with it! And then they have to pay for the upkeep of that expensive infrastructure. That's exactly the sort of senseless thing that NASA would do (ahem), not SpaceX.

And I guarantee you that whenever Elon gets around to announcing this, it's not going to merely be BFR. SpaceX has a much more solid grasp on this stuff than folks like you and Impaler, who insist on handicapping the architecture in weird ways.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/21/2015 11:37 pm
Developing BFR first wouldn't make any sense. It'd be a total waste of resources.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/21/2015 11:38 pm
MCT need not be more "complex" than a combination of what we've seen for SpaceX's reusable F9 upper stage (now obsolete) and crew Dragon. Just bigger and using Methane. Don't overthink it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/21/2015 11:50 pm
Has anyone considered the possibility that the upcoming reveal will just be the Rocket, aka BFR, and not in fact the whole system?  I really suspect that SpaceX will be doing just BFR development over the next decade while the actual vehicle to mars will continue to be studied and refined without a firm mission architecture until they actually have to cross that bridge.

That is precisely my thinking.
The BFR is congruent with SX's core competency and is a necessary precursor. Even it will undergo changes after hopefully SX succeeds in recovering and re-flying F9 cores. 

I think Musk will speak to the MCT issue, but still in vague terms.  Even were he somewhat specific I don't think many observers here would expect the details to hold true during what I expect would be a longer than a decade gestation for the Block One MCT, which I expect to be quite different from its folllow-on.
There are too many outside SX technology developments ongoing* to fixate and spend R&D $ on a MCT in this decade, and probably for the early part of the next.

*SEP panels & engines, plasma propulsion, magneto aero capture, life support systems tech, etc. 
Never mind extreme wildcards like one of the myriad small fusion projects actually working.

I sure we will get some nice video of a giant rocket taking off.  It might just have some totally ambiguous payload-fairing on it leaving everything beyond the launch unspecified much the way Vulcan was introduced, this would be a clear sign that they are shopping BFR around to commercial customers, but even I would find that a bit conservative given the hype that has been built up.

More likely were shown some kind of large mars vehicle reaching LEO on top of the BFR.  But then the video might just cut to said vehicle landing on mars with all the details of refueling, trajectory, aerocapture, entry etc etc left out.  Or on the opposite end of the spectrum we could see a nearly full 'architecture' which covers all these steps and Musk will be open with the numbers.

But even the most minimal video will give some ideas as to what the present preferred architecture is and one of the three camps of 'Super Dragon', 'Integrated Bi-conic' and 'Separate Bi-conic' will likely get to crow, despite the fact that the shown architecture is still in flux, given the kind of 'Holy writ' that people ascribe to offhand statements of Musk their will be no point arguing with a video. 

The speculation would then narrow down to other operational details of how the vehicle actually dose the mission and what the ultimate cost will be, how fast if at all SpaceX can put the vehicle into service, if SLS is doomed and when first landing on mars might happen.
What Musk says isn't "holy writ." You don't have to like it, but if you're going to discuss MCT, you have to actually discuss /MCT/ (which means what little we have to go on), not make up your favorite architecture in its place. You can do that in the Mars subsection of the more general forum.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/22/2015 12:52 am
Yes EM's said it. I think it was something like "you need a really big f'ing rocket, a BFR". But if that memory is correct, then he wasn't really calling it a BFR at the time... just describing it.

If that was the only mention of it, then the context still doesn't seem to indicate differentiation between a launch vehicle and a spacecraft  f he was saying to land 100mt on Mars, you need a really big f'ing rocket...for example...there's nothing in that to indicate a stand alone rocket, and a separate spacecraft. 

I'm more saying, was there a reference to "BFR" and "MCT" being referred to separately in the same comment, like how "Dragon" and "Falcon" are referred to differently in the same comment.  If so, then there could be a reasonable chance EM will just be announcing the LV.  Although even then, it's main purpose would be to loft MCT to space, just like the main purpose of the Saturn V was to loft the Apollo CSM and LEM through TLI.  The spacecraft were in the "unveilings" from the beginning.  Even when it was originally Direct Ascent instead of LOR. 
So I would expect something like that for this unveiling.  At least a working concept for the spacecraft, even if there is a stand alone LV.

But good to know that EM actually did use the term.  I'd not been aware of that.  :-)

He has used the term BFR several times I'm sure, but the whole area has been vague and I think his early comments were of a generic sense (a big rocket) - slowly converting to his own code name (given his naming of the barges, "Insane" mode on Tesla's and volume going up to 11, I think the name might stick - especially if it has a legitimate interpretation too).

I don't think I've heard him use the terms MCT and BFR when spelling it out but someone here must remember better. He has spoken about "landing the whole thing" which I've interpreted as MCT, as well as needing a BFR to get to orbit, so I think it's a fairly safe assumption that we've made.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/22/2015 12:55 am
This might be useful Lobo

[Question about getting to Mars.] I don't think the Moon is a necessary step, but I think if you've got a rocket and spacecraft capable of going to Mars, you might as well go to the Moon as well - it's along the way. That's like crossing the English Channel, relative to Mars. So, it's like, if you have these ships that could cross the Atlantic, would you cross the English Channel? Probably. It's definitely not necessary, but you'd probably end up having a Moon base just because, like, why not, ya know. It terms of the key technologies, obviously it would be great to have some sort of fundamental new thing that's never existed before and pushes the boundaries of physics, that'd be great, but as far as the physics that we know today, I actually think we've got the basic ingredients - they're there. I mean, if you do a densified liquid methalox rocket with on-orbit refueling, so like you load the spacecraft into orbit and then you send a whole bunch of refueling missions to fill up the tanks and you have the Mars colonial fleet - essentially - that gets built up during the time between Earth-Mars synchronizations, which occur every 26 months, then the fleet all departs at the optimal transfer point. I think we have - we don't need any sort of thing that people don't already know about, I believe. I believe we've got the building blocks, but the mass efficiency is extremely important. So, having better heat shields, that obviously are reusable.

http://shitelonsays.com/transcript/elon-musk-at-mits-aeroastro-centennial-part-2-of-6-2014-10-24

and this from 2005:

In past talks Musk has hinted at the development of something called the “BFR” (where B stands for “big” and R for “rocket”), a heavy-lift vehicle far larger than the Falcon family of vehicles. At SpaceVision2005 Musk disclosed that the BFR, in its current iteration, would use “multiple” Merlin 2 engines. The BFR would be able to place 100 tons in low Earth orbit, putting it in competition with NASA’s planned shuttle-derived heavy-lift launcher. The BFR is so big, Musk said, that it’s too large for the BFTS at their Texas test site...

http://www.thespacereview.com/article/497/1
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/22/2015 03:08 am
This might be useful Lobo

[Question about getting to Mars.] I don't think the Moon is a necessary step, but I think if you've got a rocket and spacecraft capable of going to Mars, you might as well go to the Moon as well - it's along the way. That's like crossing the English Channel, relative to Mars. So, it's like, if you have these ships that could cross the Atlantic, would you cross the English Channel? Probably. It's definitely not necessary, but you'd probably end up having a Moon base just because, like, why not, ya know. It terms of the key technologies, obviously it would be great to have some sort of fundamental new thing that's never existed before and pushes the boundaries of physics, that'd be great, but as far as the physics that we know today, I actually think we've got the basic ingredients - they're there. I mean, if you do a densified liquid methalox rocket with on-orbit refueling, so like you load the spacecraft into orbit and then you send a whole bunch of refueling missions to fill up the tanks and you have the Mars colonial fleet - essentially - that gets built up during the time between Earth-Mars synchronizations, which occur every 26 months, then the fleet all departs at the optimal transfer point. I think we have - we don't need any sort of thing that people don't already know about, I believe. I believe we've got the building blocks, but the mass efficiency is extremely important. So, having better heat shields, that obviously are reusable.

http://shitelonsays.com/transcript/elon-musk-at-mits-aeroastro-centennial-part-2-of-6-2014-10-24

and this from 2005:

In past talks Musk has hinted at the development of something called the “BFR” (where B stands for “big” and R for “rocket”), a heavy-lift vehicle far larger than the Falcon family of vehicles. At SpaceVision2005 Musk disclosed that the BFR, in its current iteration, would use “multiple” Merlin 2 engines. The BFR would be able to place 100 tons in low Earth orbit, putting it in competition with NASA’s planned shuttle-derived heavy-lift launcher. The BFR is so big, Musk said, that it’s too large for the BFTS at their Texas test site...

http://www.thespacereview.com/article/497/1
We have a thread that is just for information like this, where you'll find more information. Please put that in here if it isn't already: http://forum.nasaspaceflight.com/index.php?topic=37839.0
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/22/2015 09:05 am
Has anyone considered the possibility that the upcoming reveal will just be the Rocket, aka BFR, and not in fact the whole system?  I really suspect that SpaceX will be doing just BFR development over the next decade while the actual vehicle to mars will continue to be studied and refined without a firm mission architecture until they actually have to cross that bridge.

SpaceX are in a unique position where they can design several things in parallel:

1. Rocket engines - Raptor
2. Booster - BFR
3. Spacecraft - MCT (crew/cargo + tankers)
4. Mission architecture(s) - Mars (+perhaps Moon and others)
5. Ground infrastructure (factories, test and launch facilities)

This is a big advantage in both time and money. It is almost the exact opposite to SLS/Orion used for Mars where the engines, rocket and spacecraft are already designed (and based on earlier versions) and the mission architecture has to adapt to those.

At some point things have to be nailed down: e.g. rocket thrust and Isp, booster size and payload - and this then allows more detailed design of the other elements. It is not necessary, and probably not a good idea, for the final architecture and supporting mission elements to be created initially, just a reasonable stab at it and the flexibility to change things in reaction to changing circumstances.

But I see no reason for SpaceX to give up one of their big advantages - the ability to design and evolve all elements in parallel. The idea that they will create a BFR over the next decade and only then firm up the MCT and mission architecture is silly. NASA have done this with SLS/Orion and we've seen how it limits them as the cost of maintaining the capability is so high. SpaceX can probably maintain BFR capability much cheaper than NASA with SLS, but SpaceX have far more limited resources and so creating a BFR with no near-term missions is just as unaffordable.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 10/22/2015 10:45 am
Lobo is on the right track here. Before jumping to design solutions, we need to find the requirements for BFR and MCT first. Thats like engineering 101. That hasn't been happening to the extend needed to define an MCT or BFR. Lobo just started that process and I am very glad he did it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: symbios on 10/22/2015 01:05 pm
Lobo is on the right track here. Before jumping to design solutions, we need to find the requirements for BFR and MCT first. Thats like engineering 101. That hasn't been happening to the extend needed to define an MCT or BFR. Lobo just started that process and I am very glad he did it.

This discussion has been ongoing on and of since the first post of the first thread of the MCT. the problem is that there is as many version of the requirements as there is people posting. Especially since not one can even agree what the MCT should be able to do.

So if you can nail that down I would recommend you for the Nobel peace price.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/22/2015 01:06 pm
Lobo is on the right track here. Before jumping to design solutions, we need to find the requirements for BFR and MCT first. Thats like engineering 101. That hasn't been happening to the extend needed to define an MCT or BFR. Lobo just started that process and I am very glad he did it.
Agree that's necessary - but I believe he and a few others with the appropriate knowledge have been getting into those requirements for quite some time - and from that trying to ascertain what could work that still fits within what EM has said.

(Or did I miss some new approach?)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/22/2015 05:02 pm
Lobo is on the right track here. Before jumping to design solutions, we need to find the requirements for BFR and MCT first. Thats like engineering 101. That hasn't been happening to the extend needed to define an MCT or BFR. Lobo just started that process and I am very glad he did it.
Agree that's necessary - but I believe he and a few others with the appropriate knowledge have been getting into those requirements for quite some time - and from that trying to ascertain what could work that still fits within what EM has said.

(Or did I miss some new approach?)

That's mainly what I've been trying to do anyway.  :-)
Ironically, SpaceX's actual concept may not have much to do with EM's previous comments if the design work leads them in other directions.  But for us, it's all we have to go on.  heh.

I think the booster (whether that is one stage or two stages) will be wholly dictated by the needs of MCT and it's design.  If it's an integrated design, the booster will be just one piece.  If it's a non integrated design, then the booster will need to be two pieces.  That's pretty important to know for booster design.
Then depending on what MCT's payload really needs to be (100mt assumed at this point), the dry mass of MCT will be dictated by what's needed to get that to Mars in a reusable vehicle, pluswhatever other features you want to have.  After you have a reasonable idea of all of that, only then can you really start designing the booster. 
So I have a hard time seeing the booster design first, and then MCT's design to be just whatever the booster ends up being able to lift.  I don't think they'd want to risk that the booster ended up being too small...or overly large (which can mean more expensive and complex and difficult than necessary). 

Whatever system -that- ends up being, then may have an unmanned payload delivery capability of X tonnes, which will probably be quite a bit more than any current systems next to SLS.  So it could readily compete for payload that would otherwise need a D4H or a fully expendable FH (or SLS).  But that will be more a secondary objective that will be a result rather than a design criteria.  Just as the Apollo Program's requirements drove the Saturn V's design, the resultant design would have then been a pretty capable LV for launching unmanned payloads...like whole space stations.  :-)
I would think similar for MCT.  Having a non integrated MCT might be better for that purpose, but again, I think that will be a resultant, rather than a design driver.  They'll design MCT and the booster for the most efficient way to send cargo and crew to Mars.  And whatever else it can do, is just bonus.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 10/23/2015 02:13 pm
Musk has worked out just enough about potential "MCT" approaches that he has a generic requirement for his BFR launcher.  I am certain that he has explored the solution space for Mars transport and wants a launch capability that can support solutions from all chemical solution to SEP/chemical hybrid transport and other possible more exotic solutions.  Technology over a >10 year timeframe does not stay still.  The 1st and  2nd stage need only be able to get the 100mT cargo plus MCT dry weight into appropriate LEO.  If all his broad brush Mars transport solution space fits within these parameters and their evolutionary improvements (e.g.Merlin to Merlin FT), he's good to go.

Assuming that this time he really does give us more insight into his plans as promised for later this year, I am certain that the MCT portion of the architecture vs what actually flies a decade or more from now will have substantial differences.  SX has yet to fly a single crewed Dragon mission and yet to learn the lessons necessary to demonstrate a core competence in this area.  So, the Block One MCT will likely again be different from the MCT that lands the first crew on Mars June 2033 following the un-crewed MCT bringing the ISRU equipment May 2031.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TrevorMonty on 10/23/2015 06:28 pm
Sleeping your way to mars.

http://www.parabolicarc.com/2015/10/23/snooze-mars/
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 10/23/2015 07:30 pm
Sleeping your way to mars.

http://www.parabolicarc.com/2015/10/23/snooze-mars/

Yeah, only problem I'd have is that I snore.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/23/2015 11:37 pm
Musk has worked out just enough about potential "MCT" approaches that he has a generic requirement for his BFR launcher.  I am certain that he has explored the solution space for Mars transport and wants a launch capability that can support solutions from all chemical solution to SEP/chemical hybrid transport and other possible more exotic solutions.  Technology over a >10 year timeframe does not stay still.  The 1st and  2nd stage need only be able to get the 100mT cargo plus MCT dry weight into appropriate LEO.  If all his broad brush Mars transport solution space fits within these parameters and their evolutionary improvements (e.g.Merlin to Merlin FT), he's good to go.
But why build BFR first? BFR has the most infrastructure requirements. Additionally, you're making the implicit assumption that MCT isn't essentially BFR's second stage. I really, REALLY don't expect SpaceX to make the same mistake NASA is currently making by building a super-expensive-to-develop-and-maintain launch vehicle without really anything to launch.


Quote
... So, the Block One MCT will likely again be different from the MCT that lands the first crew on Mars June 2033 following the un-crewed MCT bringing the ISRU equipment May 2031.
I have no doubt MCT will evolve, but your timeline is not the same as SpaceX's timeline. They expect crewed missions much earlier. Which makes sense, as it doesn't make sense to develop a capability and then essentially just let it languish, sucking up money while nothing is accomplished (another mistake NASA is making, though this is mostly Congress's fault).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 10/24/2015 01:43 am
Musk has worked out just enough about potential "MCT" approaches that he has a generic requirement for his BFR launcher.  I am certain that he has explored the solution space for Mars transport and wants a launch capability that can support solutions from all chemical solution to SEP/chemical hybrid transport and other possible more exotic solutions.  Technology over a >10 year timeframe does not stay still.  The 1st and  2nd stage need only be able to get the 100mT cargo plus MCT dry weight into appropriate LEO.  If all his broad brush Mars transport solution space fits within these parameters and their evolutionary improvements (e.g.Merlin to Merlin FT), he's good to go.
But why build BFR first? BFR has the most infrastructure requirements. Additionally, you're making the implicit assumption that MCT isn't essentially BFR's second stage. I really, REALLY don't expect SpaceX to make the same mistake NASA is currently making by building a super-expensive-to-develop-and-maintain launch vehicle without really anything to launch.

philw1776:  No, I see the MCT as the BFR stage 2.  Just its specifics beyond engines & tankage at TBD.  I see several cargo refueler MCTs as does Musk to fuel up the transit MCT.

Quote
... So, the Block One MCT will likely again be different from the MCT that lands the first crew on Mars June 2033 following the un-crewed MCT bringing the ISRU equipment May 2031.
I have no doubt MCT will evolve, but your timeline is not the same as SpaceX's timeline. They expect crewed missions much earlier. Which makes sense, as it doesn't make sense to develop a capability and then essentially just let it languish, sucking up money while nothing is accomplished (another mistake NASA is making, though this is mostly Congress's fault).

Musk NEVER meets schedule, hence my timeline.  I see him as cash flow limited for R&D for BFR and MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/24/2015 05:50 am
Musk has worked out just enough about potential "MCT" approaches that he has a generic requirement for his BFR launcher.  I am certain that he has explored the solution space for Mars transport and wants a launch capability that can support solutions from all chemical solution to SEP/chemical hybrid transport and other possible more exotic solutions.  Technology over a >10 year timeframe does not stay still.  The 1st and  2nd stage need only be able to get the 100mT cargo plus MCT dry weight into appropriate LEO.  If all his broad brush Mars transport solution space fits within these parameters and their evolutionary improvements (e.g.Merlin to Merlin FT), he's good to go.
But why build BFR first? BFR has the most infrastructure requirements. Additionally, you're making the implicit assumption that MCT isn't essentially BFR's second stage. I really, REALLY don't expect SpaceX to make the same mistake NASA is currently making by building a super-expensive-to-develop-and-maintain launch vehicle without really anything to launch.

You can't have it both ways, either SpaceX is a lean and efficient vertically integrated company that's vastly more efficient then 'Old-Space' capable of making a rocket without a huge standing army or they aren't.  If BFR takes huge infrastructure to build and maintain like SLS dose then the prospect of getting to mars is already busted.

I've said a dozen times I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars, that will build precious flight history before people fly on it.  Two or three large com satellites at a time, Bigelow type space stations, the LEO satellite swarms, and any NASA missions that would have flown on SLS are all potential things to fill the rocket with.  And because these things require a normal 2nd stage that is the configuration that makes sense, it allows a product that can fend for itself in the marketplace and pay for it's own infrastructure without putting that whole cost onto the back of the mars ticket.  Also it doesn't risk completely bankrupting the company in getting to mars turns out to be harder then expected to develop or customers are not ready to buy when the ride is offered. 

As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.  But NASA will need a decade or more to develop and ready the ground systems.  But to fund that SLS needs to be canceled first and that not going to come until a proven alternative has been fully demonstrated to be reliable.

Were already seeing spiral development from SpaceX when they layed down considerable time and money for Raptor development which was clearly started without the full mars architecture in place, and probably no more then a vague sense of how large BFR would be either.  They just set out to the make the best engine possible and then build the best launch vehicle with and around it.  At each point they are just building the best device they can come up with while utilizing their existing parts, this is how I see the mars bound spacecraft being done as well.


Quote
... So, the Block One MCT will likely again be different from the MCT that lands the first crew on Mars June 2033 following the un-crewed MCT bringing the ISRU equipment May 2031.
I have no doubt MCT will evolve, but your timeline is not the same as SpaceX's timeline. They expect crewed missions much earlier. Which makes sense, as it doesn't make sense to develop a capability and then essentially just let it languish, sucking up money while nothing is accomplished (another mistake NASA is making, though this is mostly Congress's fault).

Which is exactly why an integrated 2nd stage is a bad idea, it makes the launcher too narrow and unable to serve any other role efficiently.  It is also unfeasible on technical grounds but no one seems willing to admit this.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sublimemarsupial on 10/24/2015 07:07 am

... It is also unfeasible on technical grounds but no one seems willing to admit this.

Can you show us the math that proves this or are you just blowing smoke and speculating like everyone else in this thread?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/24/2015 07:46 am
You can't have it both ways, either SpaceX is a lean and efficient vertically integrated company that's vastly more efficient then 'Old-Space' capable of making a rocket without a huge standing army or they aren't.  If BFR takes huge infrastructure to build and maintain like SLS dose then the prospect of getting to mars is already busted.

Disagree. Even with much smaller fixed cost it would be a lot for SpaceX. It would also introduce massive slips of the timeline.

I've said a dozen times I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars, that will build precious flight history before people fly on it.  Two or three large com satellites at a time, Bigelow type space stations, the LEO satellite swarms, and any NASA missions that would have flown on SLS are all potential things to fill the rocket with.  And because these things require a normal 2nd stage that is the configuration that makes sense, it allows a product that can fend for itself in the marketplace and pay for it's own infrastructure without putting that whole cost onto the back of the mars ticket.  Also it doesn't risk completely bankrupting the company in getting to mars turns out to be harder then expected to develop or customers are not ready to buy when the ride is offered. 

Anything that makes design compromises for cisluar space would be less than perfect for Mars. MCT will be designed for Mars and Mars alone. So much was clearly said by Elon Musk and is not some design detail that can be changed when appropriate. It is a part of the basic development philosophy. Which does not say it cannot be used for anything else. Cargo MCT will have large payload doors, similar to the SpaceShuttle. It can deploy satellites and space station modules. Not mass efficient but operationally efficient.

As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.  But NASA will need a decade or more to develop and ready the ground systems.  But to fund that SLS needs to be canceled first and that not going to come until a proven alternative has been fully demonstrated to be reliable.

If NASA is to be the first customer the concept is dead in the waterspace. It would introduce decades of delay as you yourself state. It is not going to happen.

Were already seeing spiral development from SpaceX when they layed down considerable time and money for Raptor development which was clearly started without the full mars architecture in place, and probably no more then a vague sense of how large BFR would be either.  They just set out to the make the best engine possible and then build the best launch vehicle with and around it. 

Not at all. They see how the best suited engine turns out and then design BFR for it. But the capabilities of BFR do not change by that. Just the number of engines changes. The capabilities of BFR are fixed by what MCT needs.

Which is exactly why an integrated 2nd stage is a bad idea, it makes the launcher too narrow and unable to serve any other role efficiently.

See above. BFR/MCT will not be designed for anything else but Mars.


It is also unfeasible on technical grounds but no one seems willing to admit this.

How do you come to that conclusion?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 10/24/2015 04:53 pm

Which is exactly why an integrated 2nd stage is a bad idea, it makes the launcher too narrow and unable to serve any other role efficiently.  It is also unfeasible on technical grounds but no one seems willing to admit this.

Do you think SpaceX, Musk or anybody would bank their reputation and solvency on something which is technically unfeasible? If the BFR/MCT architecture wasn't practical, wouldn't they instead have figured that out by now, especially before they got to the phase of developing the craft's propulsion?

Edit: People have been collectively running math here for years and there's nothing theoretically showstopping about it. Yes, it's tricky engineering, but it's not physics violating engineering. This isn't so much of a quantum leap as the R7 was from the V2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/24/2015 05:37 pm
People have been collectively running math here for years and there's nothing theoretically showstopping about it. Yes, it's tricky engineering, but it's not physics violating engineering. This isn't so much of a quantum leap as the R7 was from the V2.

Designing MCT for Mars EDL will be tricky and in the end they may fail on that. Success is not guaranteed. But I am optimistic about it. As you said, there are years of engineering behind it by top designers. It is not like Elon Musk was on it alone and it is all pipe dreams.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/24/2015 08:32 pm
People have been collectively running math here for years and there's nothing theoretically showstopping about it. Yes, it's tricky engineering, but it's not physics violating engineering. This isn't so much of a quantum leap as the R7 was from the V2.

Designing MCT for Mars EDL will be tricky and in the end they may fail on that. Success is not guaranteed. But I am optimistic about it. As you said, there are years of engineering behind it by top designers. It is not like Elon Musk was on it alone and it is all pipe dreams.

The biggest questionmark for making a large vehicle like that do Mars EDL was supersonic retropropulsion, which SpaceX has already demonstrated. The rest is stuff that you'd basically already need for a reusable upper stage for an Earth TSTO RLV (vertical landing, heatshield, etc).

I don't think people quite understand here how much these requirements for different segments actually overlap. Going with VTVL and a very good mass fraction for your RLV instead of parachutes or wings for everything means an operationally simpler design that is scalable and applicable to other celestial bodies.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/24/2015 10:45 pm
Yes, one of the misunderstood reasons that Elon is a genius is simply an ability to take existing known quantities and technologies and put them together in ways that other people can't see. In this case he's said from the beginning he believes that travelling to Mars and living on Mars can be done without having to invent something entirely new.

That doesn't mean the solutions are ready to go, just that if you have the vision and the money you can put together something that will work. It's actually not a leap of faith in the technology (though it requires societal support).

There's 2 reasons other people can't do this
1) it's hard to see anything on a huge scale, even for the best people
2) not many people can control the funds to put behind the solution

Because we as humans have difficulties with huge scales we see it as taking a risk. (That doesn't mean there aren't risks in the vision, or in other similar scales, just that it's a type of risk we aren't able to intuitively understand).

He is pushing the limits here though. Supersonic retropropulsion is not a trusted 'known'. And he's pushing the edge in developing the MCT and so on.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 10/24/2015 10:50 pm
Musk has worked out just enough about potential "MCT" approaches that he has a generic requirement for his BFR launcher.  I am certain that he has explored the solution space for Mars transport and wants a launch capability that can support solutions from all chemical solution to SEP/chemical hybrid transport and other possible more exotic solutions.  Technology over a >10 year timeframe does not stay still.  The 1st and  2nd stage need only be able to get the 100mT cargo plus MCT dry weight into appropriate LEO.  If all his broad brush Mars transport solution space fits within these parameters and their evolutionary improvements (e.g.Merlin to Merlin FT), he's good to go.
But why build BFR first? BFR has the most infrastructure requirements. Additionally, you're making the implicit assumption that MCT isn't essentially BFR's second stage. I really, REALLY don't expect SpaceX to make the same mistake NASA is currently making by building a super-expensive-to-develop-and-maintain launch vehicle without really anything to launch.

You can't have it both ways, either SpaceX is a lean and efficient vertically integrated company that's vastly more efficient then 'Old-Space' capable of making a rocket without a huge standing army or they aren't.  If BFR takes huge infrastructure to build and maintain like SLS dose then the prospect of getting to mars is already busted.

Very confusing. Just where was this said that you're rebutting?  Looks like a strawman arguement to me.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/25/2015 02:05 am
First the idea of a high maintenance cost is inconsistent with SpaceX operations, they shown the ability to build and launch with much less manpower.  It also ignores the intended re-usable nature of BFR, they do not need to manufacture them at a rate of one a month like Falcon, though they will likely make Raptor engines at a few a week with a comparable labor input and assembly-line like production like Merlin manufacturing.

RB is arguing that the whole top to bottom mars transportation system has to come into being simultaneously.  But his argument of 'high maintenance cost' is actually made worse by trying to make the whole system, you would incur both the cost of BFR maintenance along with the cost of the mars transit vehicle aka MCT, claiming that the launcher and transit vehicle are designed to be incapable of operating independently dose not lower the cost.  Your just raising costs while pushing revenue collection further into the future and narrowing it's customer base.  The safe strategy is to do the rocket first, which is the most conventional part of the system and the only part that might be monetized independently of the rest, then push on to the more challenging parts.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 10/25/2015 06:42 pm
Appreciate the clarification.  I was confused, but I agree.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/25/2015 07:11 pm
I think they will get the engine built and tested first.  Then design the BFR around the engine or engines.  They also have to determine how big the BFR will be to either use existing infrastructure or to build new infrastructure for the first stage.  Remember existing inland waterway barges are only a certain size.  Falcon was designed to the maximum size of existing road transportation equipment.  Then they will design a reusable 2nd stage.  I think the MCT will be an evolution of the second stage.  I also think it will be designed modular so it could be a second stage for launching large payloads.  The MCT cargo version, and later an MCT human transporter.  I think they will know more when they get the exact specifications for the Raptor engine, power, thrust to weight ration, etc.   Of course this is a speculation thread. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/25/2015 09:15 pm
This is my guess at a MCT plan. Note I've separated out the tanker, cargo and crew variants of MCT although they are all based on the same design.

YearElementPhaseNotes
2014Raptorinitial investigations
Q4 2015Architecturerelease
Q1 2016RaptorPDR
2016-7BFR+MCTinitial designsseveral iterations towards a PDR in 2018
Q4 2017RaptorCDR
Q1 2018BFRPDRdepends on Raptor PDR
2018Red dragonsite surveysurface element demos
2019MCTPDRdepends on Raptor PDR
2020BFRCDR
2020Red dragon(s)site survey(s)surface element demos & subsequent synods
2022MCTCDRtanker and cargo versions
2023MCTCDRcrew versions
2023BFRFirst flight1st stage only
2024MCTDemo flightbare bones tanker version
2025BFRDemo flight(s)cargo version & refueling
2026BFRDemo flight(s)crew version - LEO (unmanned)
2027-31BFRDemo flight(s)crew version - LEO long duration (manned)
2028BFRDemo flight(s)cargo version - Mars + crew version - cis-lunar
2031BFRCargo flight(s)cargo version - Mars
2033BFRCrew flight(s)crew+cargo versions - Mars

It would be difficult to meet the 2031 launch window for the first crew flight and just about impossible to meet a Nov 2028 launch window. To meet a Oct 2026 launch window would require Apollo-like resources devoted to it and a fair bit of luck.

Lack of resources or problematic development would delay this schedule by one or more synods.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/25/2015 10:48 pm
First the idea of a high maintenance cost is inconsistent with SpaceX operations, they shown the ability to build and launch with much less manpower.  It also ignores the intended re-usable nature of BFR, they do not need to manufacture them at a rate of one a month like Falcon, though they will likely make Raptor engines at a few a week with a comparable labor input and assembly-line like production like Merlin manufacturing.
SpaceX will lose a huge advantage in per-launch labor efficiency if they only build, say, 1 BFR a year. That is exactly why SLS is ridiculously expensive. SpaceX may beat the industry-standard labor efficiency for rocket manufacture and development by 2-3x, MAYBE, but their main advantage is picking reasonable solutions, i.e. not building a ridiculously expensive rocket using technology half a century old and that will only launch a couple times per year at most.

Also, you're missing a really important point: There isn't actually a market for HLV launch. Nobody* wants more than about EELV Heavy capability (except for exploration, but even then it's not required). There aren't even commercial or military processing facilities for payloads over 5 meters in diameter. There isn't a commercial launch need for BFR, and NASA doesn't even have any payloads that need an HLV. F9 and Falcon Heavy are MORE than enough for all the commercial, civil, and military payloads. I've held this viewpoint for years, I've been vocal about it, and I haven't actually changed my mind on it. The only thing that might make sense for an HLV is if you had some good rationale for flying enough payloads per year that you could take FULL advantage of a full manufacturing line (multiple shifts) /and/ full advantage of full reuse (both first and second stages). To keep a production line busy, you probably need at least 10 flights per year. To do that with multiple shifts, probably about 40 first stage cores per year (and more upper stages). To make first stage reuse make sense, you need to reuse the stage at least ten times. To make full reuse make sense, you need to reuse the first stage at least 100 times and the upper stage 10-30 times. That's roughly a thousand launches per year at a minimum. Partial reuse can get by with maybe 100 launches per year, 40 per year if some are expendable. Otherwise, it's not really the economic optimum. Unless you get to 1000 launches per year, though, you probably aren't launching enough to gain anything by using an HLV. (In fact, you'd reduce your economic efficiency since you wouldn't be reusing as much.)

Only something like large-scale colonization ticks those boxes. Otherwise, put your money into full reuse, not making a mega-rocket.

But let's just pretend that you're right about there being some big market for HLVs out there.

Quote
RB is arguing that the whole top to bottom mars transportation system has to come into being simultaneously.
Ignoring for the moment that you're putting words in my mouth: You mean with Mars transfer vehicle, a lander/ascent vehicle, SEP propulsion, depots and everything? Am I arguing that? No. I'm arguing that a Mars transport system of BFR and MCT as the second stage is basically the same thing as a TSTO RLV BFR.

The requirements between a very large TSTO RLV's second stage capable of higher energy orbits (which is where the real money is), an integrated reusable fairing, and long-loiter capability (essential for cislunar, direct GSO, and multi-plane constellation deployments) is almost entirely overlapping with what an initial cargo MCT would likely do. The only thing different is ability to refuel bidirectionally (this is a thing ULA is working on, so they think it's worth it even though they don't care about Mars much) and long-range comms (both would be very valuable for cislunar). Long-range comms is actually a very easy requirement if you operate at a low data rate.


Quote
...The safe strategy ...
Yeah, no, there's nothing safe about BFR or MCT or SpaceX's Mars plans. If they were merely playing safe, they would still be at Falcon 1 or maybe a Falcon 5. BFR/MCT is not at all a safe strategy.


*I don't take Bigelow's grandiose plans very seriously, and besides, a couple LEO payloads doesn't justify a whole HLV. Bigelow can't carry the cost of a BFR. And if you wanted to put his stations in lunar orbit or on the lunar surface, you'd want something with long-loiter capability like MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/25/2015 10:51 pm
SpaceX may beat the industry average labor cost efficiency, but they aren't magic. Building a huge rocket and a huge factory for it well before they plan on actually using it doesn't make sense. If they build it then mothball it, they will have to relearn it when they want to start it up again. If they build it then keep it operating at a low level, then it will suck up a lot of funds and certainly won't be cheaper than F9 or Falcon Heavy.

No, they will be working on BFR/MCT at the same time. They would be super foolish to do what NASA is doing and building a rocket without anything to launch on it. NASA and SpaceX would both be better served by saving up that money until they're ready to do both. (Though NASA can't really save money from year to year like that, SpaceX can and does... they bought some Solar City bonds when they got a big cash infusion a while back.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/25/2015 11:40 pm
The only thing that might make sense for an HLV is if you had some good rationale for flying enough payloads per year that you could take FULL advantage of a full manufacturing line (multiple shifts) /and/ full advantage of full reuse (both first and second stages). To keep a production line busy, you probably need at least 10 flights per year. To do that with multiple shifts, probably about 40 first stage cores per year (and more upper stages). To make first stage reuse make sense, you need to reuse the stage at least ten times. To make full reuse make sense, you need to reuse the first stage at least 100 times and the upper stage 10-30 times. That's roughly a thousand launches per year at a minimum. Partial reuse can get by with maybe 100 launches per year, 40 per year if some are expendable. Otherwise, it's not really the economic optimum. Unless you get to 1000 launches per year, though, you probably aren't launching enough to gain anything by using an HLV. (In fact, you'd reduce your economic efficiency since you wouldn't be reusing as much.)

We do keep hearing high numbers from SpaceX. Fleets, scouting the globe for launch locations to move a lot of people. But I don't think we think in the right scale yet.

SpaceX release of plans will help us get the right ball park. Obviously if you're moving 10,000 people a year to Mars ( in 50 years, based on having a million people there in 100 years), that's launching 100 MCTs a year. Add fuel launches and cargo launches and you move up to your 1000 BFR launches a year (in 50 years).

Then one question is how fast they ramp up to that number. I'm not sure how accurate your estimates of cost efficiency are (not saying they are or aren't, I'm just not sure). Elon has previously run factories on single shifts then moved to multiple shifts so that's likely. And they may find making they're making many upper stage fuel tanks etc and less BFRs - or that the number of reuses is lower initially so they have a higher number of new BFRs to start with.

This is my guess at a MCT plan. Note I've separated out the tanker, cargo and crew variants of MCT although they are all based on the same design.

Obviously vastly different scales of approaches.

But in either case - I think an early launch of surface scanning satellites and scouting RD missions in the early 2020s could be added.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/25/2015 11:50 pm
Musk mentioned like 80,000 people per year. He didn't specify synod. So that's almost another whole order of magnitude. But my figures are not meant to be taken literally... They are rough +/- order of magnitude only. Main thing to take from them is that you shouldn't build an HLV unless you're doing something on the order of colonization. Nothing else really makes sense.

In many ways, though, MCT is more critical than BFR. MCT serves more roles, as a reusable upper stage that can refuel and loiter and land or do orbital insertion of large payloads just about anywhere in the inner solar system, including Earth orbit/cislunar.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/25/2015 11:58 pm
Musk mentioned like 80,000 people per year. He didn't specify synod. So that's almost another whole order of magnitude.
Really? When was that?

The goal thrown out is 1 million people right? But the timeframe isn't clear.
80,000 a year gets to a million very quickly, unless it's 80,000 a year once the colony is up at the million mark, which makes more sense.

Even with fewer people, the huge scale like you describe will allow them to build large farms, big factories, and start mining - while also dropping the interim resources required in doing that.

I do think it might be the only way to resolve the chicken and egg problem. As long as a few of the world's biggest mining and manufacturing companies decide it's worthwhile.


(ps. yes I've been trying to be careful on years vs synods)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/26/2015 12:06 am
https://twitter.com/elonmusk/status/273483420468932608

Quote from: @elonmusk
Millions of people needed for Mars colony, so 80k+ would just be the number moving to Mars per year
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/26/2015 05:01 am

Also, you're missing a really important point: There isn't actually a market for HLV launch. Nobody* wants more than about EELV Heavy capability (except for exploration, but even then it's not required). There aren't even commercial or military processing facilities for payloads over 5 meters in diameter. There isn't a commercial launch need for BFR, and NASA doesn't even have any payloads that need an HLV. F9 and Falcon Heavy are MORE than enough for all the commercial, civil, and military payloads. I've held this viewpoint for years, I've been vocal about it, and I haven't actually changed my mind on it. The only thing that might make sense for an HLV is if you had some good rationale for flying enough payloads per year that you could take FULL advantage of a full manufacturing line (multiple shifts) /and/ full advantage of full reuse (both first and second stages). To keep a production line busy, you probably need at least 10 flights per year. To do that with multiple shifts, probably about 40 first stage cores per year (and more upper stages). To make first stage reuse make sense, you need to reuse the stage at least ten times. To make full reuse make sense, you need to reuse the first stage at least 100 times and the upper stage 10-30 times. That's roughly a thousand launches per year at a minimum. Partial reuse can get by with maybe 100 launches per year, 40 per year if some are expendable. Otherwise, it's not really the economic optimum. Unless you get to 1000 launches per year, though, you probably aren't launching enough to gain anything by using an HLV. (In fact, you'd reduce your economic efficiency since you wouldn't be reusing as much.)


Customers don't care how big the rocket is they care how much it costs.  In order to get anywhere near the cost structure Musk desires the cost to launch the BFR would need to be well in the range where it would be a cost effective commercial launcher.  While it may cost more then one sat customer would be willing to pay for we already have a NORMAL practice in the industry of launching multiple satellites simultaneously so it is not at all hard to see a viable commercial sat launch market for BFR if it achieved the full reusability which is it's main goal.

The manufacturing of BFR consists of two parts, engines and the tanks, we know the engines will be made in an assembly line like manor similar to Merlin.  If we estimate 36 engines total and a week to make each one then a whole rocket in made under a year with a manufacturing base comparable to that which exists for Merlin now, it would run steadily at full utilization but hardly be huge compared to what's already being done.  The tanks would likely be made at Michoud and if made on a pace to match the engines your looking at a steady state production line as well.

This will not cost billions per year to maintain like SLS which is looking at 2 Billion for maintaining it's work force and half a billion in marginal production costs (giving us a likely 2.5 Billion per year cost for 1 yearly launch).  SpaceX is likely going to do it for 1/10th that much in maintenance (200 million), and one quarter as much to manufacture (125 million).  If the production time is 36 weeks and their are 10 uses out of each rocket initially then you end up with just 14 launches per year and overhead costs are absorbed at around 25 million per launch.  Now of course refurbishment is going to be an unknown factor plus all the non-manufacturing related costs of launch such as pad operations, payload integration etc etc.

Your argument that thousands of launches per year are necessary dose not hold water.  Lots of folks have done lots of speculating on reuse and none of it shows much benefit past 10 uses, if the rocket isn't profitable with 10 uses going to 100 isn't going to change it.  Second their is no way you can find a customers base to purchase thousands of launches per year to immediately soak up this absurd supply suddenly being put onto the market all at once.  That's the kind of volume that would be necessary to achieve the 80K immigrants per year goal.  The system must be viable at a lower initial volume so it can survive to ramp up over decades.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/26/2015 05:23 am
https://twitter.com/elonmusk/status/273483420468932608

Quote from: @elonmusk
Millions of people needed for Mars colony, so 80k+ would just be the number moving to Mars per year
Thanks for that.

It seems to stem from a misunderstanding though. Musk estimates $36 billion to set up a colony, and calculates it as part of the US GDP.  "Some money has to be spent on establishing a base on Mars. It’s about getting the basic fundamentals in place". The article then talks about $500,000 a colonist, and divides that into $40billion to get the "80,000 colonist" number.

The article uses that in the opening. But it doesn't make sense to have colonists paying the $40 billion if the government is paying it. It also wasn't saying 80,000 total.

So Musk's tweet then clarifies that a bit. He talks about a million people, not 80,000. His throwaway about "80,000 a year" is more likely just trying to emphasise how low that number is.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/26/2015 05:27 am

If NASA is to be the first customer the concept is dead in the waterspace. It would introduce decades of delay as you yourself state. It is not going to happen.

First customer for mars bound flights, private colonists are not going to be the first humans on mars.  Astronauts from NASA along with possible international partners are the only foreseeable first mission personnel which means selling them transport services similar to how NASA buys commercial crew trips to ISS.  Their would be a decade of earlier commercial customers using BFR in cis-lunar space so SpaceX has an initial customer base without relying on NASA as the sole purchaser.

It is also unfeasible on technical grounds but no one seems willing to admit this.

How do you come to that conclusion?

Propellant mass fractions that are on par with SSTO vehicles combined with re-entry conditions that make lunar return look mild.  It's really not that hard to figure out, the proposed super-direct mission requires performance from the vehicle which is beyond that required of several different vehicles.  Higher entry speed then Apollo capsules, 4x the payload of Shuttle at the same mass or less, carrying more propellant mass then the Shuttle external tank, all able to land and take off from rough terrain without servicing.

It's the engineering equivalent of asking for a flying submarine monster-truck.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sublimemarsupial on 10/26/2015 05:29 am
The system must be viable at a lower initial volume so it can survive to ramp up over decades.

This is where your core assumption is incorrect. The system does not have to be viable on its own at all - only SpaceX as a company does. Listen to what Elon has been saying, and look at how they have operated - they will operate on a overall cash flow basis for the foreseeable future, with the revenues from their commercial Falcon launches and their internet satellite constellation funding the development and operation of the MCT fleet until it can get the marginal cost down to where the ticket price for a trip to Mars covers the operational costs of the vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/26/2015 05:48 am
No that is not at all reasonable, they will put money generated in other areas into development but they would not RUN the whole system at a loss for decades waiting for volume to grow.  That would  suck up all their surplus from other activities leaving nothing for continued development and upgrading the system, you make a profitable system and then make it more profitable with your profits. This is completely counter to the entire history of careful and financially cautious development done by SpaceX up till now.

Like the old adage "Every complex program that has ever worked has evolved from a simple program that worked, not a complex program that didn't work".

Title: Re: MCT Speculation and Discussion Thread 4
Post by: sublimemarsupial on 10/26/2015 06:08 am
No that is not at all reasonable, they will put money generated in other areas into development but they would not RUN the whole system at a loss for decades waiting for volume to grow.  That would  suck up all their surplus from other activities leaving nothing for continued development and upgrading the system, you make a profitable system and then make it more profitable with your profits. This is completely counter to the entire history of careful and financially cautious development done by SpaceX up till now.

Like the old adage "Every complex program that has ever worked has evolved from a simple program that worked, not a complex program that didn't work".

You have a seriously flawed view of how SpaceX has operated. They have pretty much been exactly the opposite of  careful and financially cautious - a careful company wouldn't completely abandon it its only money making product (Falcon 1) in favor of an unproven and much more difficult development project (F9 v1.0), and then do that again (F9v1.0 to F9v1.1) and again (F9v1.1 to F9 Full Thrust), each time betting the farm that the new rocket will work. Nor would they have come within several days of bankruptcy in 2008. Furthermore, THE MARS COLONY IS THE ENTIRE REASON THE COMPANY EXISTS, Elon has said it over and over. Its the mission statement of the company - make life multiplanetary. Everything they have done up until now has been almost singularly focused on that objective, to the point where they have abandoned projects they have felt don't help them learn anything that would help them with Mars (Stratolaunch) and dropped projects cold as soon as they no longer have benefit for Mars (Falcon 1).

They will budget sufficiently to operate and improve Falcon and do their satellites, but all revenue on top of that will go to the Mars program and BFR+MCT, and those programs will run at a loss, 100% guaranteed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/26/2015 07:50 am
Can we move the financing talk to the financing thread (or elsewhere?)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oiorionsbelt on 10/26/2015 02:47 pm
Will BFR/MCT do a full mission - to Mars - refuel - back to Earth unmanned before the first crew? Elon has mentioned Droids and automation as being essential elements.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/26/2015 04:13 pm
Will BFR/MCT do a full mission - to Mars - refuel - back to Earth unmanned before the first crew? Elon has mentioned Droids and automation as being essential elements.

It is not part of NASA's plans. Let's see what is the plan for SpaceX. They could do a test flight of MCT to the moon. Land it there and get it back to earth. If they feel they need to test two entries of the heatshield they can land the same MCT twice. Going to Mars and back would delay a manned landing at least by two years.

BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/26/2015 04:26 pm
BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/26/2015 04:58 pm
BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.

Not doom. They would not be colonists but they will IMO likely stay for a full synod until a replacement crew arrives. Probably a few stay on to extend their experience to the next crew. Worst case something goes wrong and they stay two synods. On the next synod they would receive spare parts to get fuel ISRU going.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/26/2015 10:42 pm
BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.

Not doom. They would not be colonists but they will IMO likely stay for a full synod until a replacement crew arrives. Probably a few stay on to extend their experience to the next crew. Worst case something goes wrong and they stay two synods. On the next synod they would receive spare parts to get fuel ISRU going.
Musk is borrowing somewhat from Mars Direct (or is it Semi-Direct?) where an already-fueled ascent vehicle is fueled up on the surface. I don't see a good reason not to have a fueled up vehicle ready when they arrive.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/27/2015 01:32 am

BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.

Not doom. They would not be colonists but they will IMO likely stay for a full synod until a replacement crew arrives. Probably a few stay on to extend their experience to the next crew. Worst case something goes wrong and they stay two synods. On the next synod they would receive spare parts to get fuel ISRU going.

Mostly Irrelevant, because they are not going to risk crews on the first mission and landing anyway. And the first unmanned missions need to provide a proof of concept that the ISRU equipment functions. So since they will already have hardware on the ground, making it an all-up test that produces propellant makes the most sense.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/27/2015 02:24 am

BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.

Not doom. They would not be colonists but they will IMO likely stay for a full synod until a replacement crew arrives. Probably a few stay on to extend their experience to the next crew. Worst case something goes wrong and they stay two synods. On the next synod they would receive spare parts to get fuel ISRU going.

Mostly Irrelevant, because they are not going to risk crews on the first mission and landing anyway. And the first unmanned missions need to provide a proof of concept that the ISRU equipment functions. So since they will already have hardware on the ground, making it an all-up test that produces propellant makes the most sense.

Agreed, the two things that will retire the most risk are.  1) Testing the landing system and ISRU process at full scale and 2) Doing a mission to mars orbit/moons and back of the full duration of the intended surface mission.  Once these are completed (which could be simultaneously) the next logical step is the crewed surface landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 10/27/2015 03:43 am
Propellant mass fractions that are on par with SSTO vehicles

Not really, there's a huge difference between what's needed for 6.5-8 km/s vs. 9.5 km/s. (I get a mass ratio of about 5.75 for 6.5 km/s, 8.6 for 8 km/s, 12.8 for 9.5 km/s).

Quote
combined with re-entry conditions that make lunar return look mild.

Yeah but they also have a better heat shield material than Apollo. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/27/2015 04:35 am
Propellant mass fractions that are on par with SSTO vehicles

Not really, there's a huge difference between what's needed for 6.5-8 km/s vs. 9.5 km/s. (I get a mass ratio of about 5.75 for 6.5 km/s, 8.6 for 8 km/s, 12.8 for 9.5 km/s).

Did you remember to factor in the ISP differences, all thouse SSTO vehicles were going to use Hydro-Lox at 450 ISP.  When you use use that kind of ISP the 9.5 km/s DeltaV requires an 8.62 ratio.  So yes they are quite equivalent.

Quote
combined with re-entry conditions that make lunar return look mild.

Yeah but they also have a better heat shield material than Apollo.

Their are g-forces, entry corridor width and landing accuracy to consider as well as heating, all of which come from the underlying driver, entry velocity.  And I've never gotten any firm numbers on how massive the Dragon heat-shield is to give a quantification of how much shielding mass has dropped by or if it has dropped enough to not completely consume the entire vehicle mass on it's own.  Also my understanding is that our better ability to model super-sonic heating and greatly reduce unnecessary margins are the main drivers of today's thinner shields, not the materials.

And remember it is not any ONE performance metric that's unfeasible it is having them all together in one package.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/27/2015 05:45 pm
The only thing that might make sense for an HLV is if you had some good rationale for flying enough payloads per year that you could take FULL advantage of a full manufacturing line (multiple shifts) /and/ full advantage of full reuse (both first and second stages). To keep a production line busy, you probably need at least 10 flights per year. To do that with multiple shifts, probably about 40 first stage cores per year (and more upper stages). To make first stage reuse make sense, you need to reuse the stage at least ten times. To make full reuse make sense, you need to reuse the first stage at least 100 times and the upper stage 10-30 times. That's roughly a thousand launches per year at a minimum. Partial reuse can get by with maybe 100 launches per year, 40 per year if some are expendable. Otherwise, it's not really the economic optimum. Unless you get to 1000 launches per year, though, you probably aren't launching enough to gain anything by using an HLV. (In fact, you'd reduce your economic efficiency since you wouldn't be reusing as much.)

We do keep hearing high numbers from SpaceX. Fleets, scouting the globe for launch locations to move a lot of people. But I don't think we think in the right scale yet.


"Fleet" is a relative term.  The Space shuttle orbiters built were regularly referred to as the "fleet", but there were never more than 4 operational at any one time. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/27/2015 06:49 pm

Also, you're missing a really important point: There isn't actually a market for HLV launch. Nobody* wants more than about EELV Heavy capability (except for exploration, but even then it's not required). There aren't even commercial or military processing facilities for payloads over 5 meters in diameter. There isn't a commercial launch need for BFR, and NASA doesn't even have any payloads that need an HLV. F9 and Falcon Heavy are MORE than enough for all the commercial, civil, and military payloads. I've held this viewpoint for years, I've been vocal about it, and I haven't actually changed my mind on it. The only thing that might make sense for an HLV is if you had some good rationale for flying enough payloads per year that you could take FULL advantage of a full manufacturing line (multiple shifts) /and/ full advantage of full reuse (both first and second stages). To keep a production line busy, you probably need at least 10 flights per year. To do that with multiple shifts, probably about 40 first stage cores per year (and more upper stages). To make first stage reuse make sense, you need to reuse the stage at least ten times. To make full reuse make sense, you need to reuse the first stage at least 100 times and the upper stage 10-30 times. That's roughly a thousand launches per year at a minimum. Partial reuse can get by with maybe 100 launches per year, 40 per year if some are expendable. Otherwise, it's not really the economic optimum. Unless you get to 1000 launches per year, though, you probably aren't launching enough to gain anything by using an HLV. (In fact, you'd reduce your economic efficiency since you wouldn't be reusing as much.)


Customers don't care how big the rocket is they care how much it costs.  In order to get anywhere near the cost structure Musk desires the cost to launch the BFR would need to be well in the range where it would be a cost effective commercial launcher.  While it may cost more then one sat customer would be willing to pay for we already have a NORMAL practice in the industry of launching multiple satellites simultaneously so it is not at all hard to see a viable commercial sat launch market for BFR if it achieved the full reusability which is it's main goal.


Keep in mind that most likely Falcon won't be going anywhere even once BFR flies.  SpaceX is investing if 4 pads for it.  Even if they were to turn 39A into a BFR pad at some point, that's still 3 pads.  It's sized good for comsats, and you aren't putting a 4mt comsat going to GTO on something the size of Saturn V or bigger.  Multiple payloads are a possibility, but ArianeSpace is moving away from that, not doubling down on it with Ariane 6.  Otherwise, why not make an Ariane 6 that's larger than Ariane 5 and can launch 5 or 6 sats at once?  Becuase it's a bit of a challenge to get just two sats going to close enough of the same orbits that can launch together...much less more.
So I don't see comsats being launched in big clusters by BFR.  That's what F9 is for and it'll do a nice job of that.
Bigger than F9 would be an FH with 3 reusable boosters.

So what -could- BFR/MCT launch besides crewed, propellant, cargo, or depot versions of MCT?  Even a fully reusable BFR/MCT which requires only nominal processing between flights (unlike STS) will have a fair cost...but could be less than say a D4H, or an FH-E or A5-551 or whatever the heavy Vulcan variant is.   So it could be the most affordable launcher for those big government birds.
It could also do planetary probes with an expendable kick stage.
It could do a Bigelow module or large space telescope or something too, but those would be pretty rare, more one time events.  Big telescopes are expensive and you only need so many big Bigelow modules in orbit.  Cargo service to a big Bigelow station is a possible routine job for BFR though. 

So those are some potential markets for BFR, I'm pretty sure it's not going to take over F9R/FHR's markets.

Quote
... So, the Block One MCT will likely again be different from the MCT that lands the first crew on Mars June 2033 following the un-crewed MCT bringing the ISRU equipment May 2031.
I have no doubt MCT will evolve, but your timeline is not the same as SpaceX's timeline. They expect crewed missions much earlier. Which makes sense, as it doesn't make sense to develop a capability and then essentially just let it languish, sucking up money while nothing is accomplished (another mistake NASA is making, though this is mostly Congress's fault).

Which is exactly why an integrated 2nd stage is a bad idea, it makes the launcher too narrow and unable to serve any other role efficiently.  It is also unfeasible on technical grounds but no one seems willing to admit this.

Unfeasible?  I don't know about that.  How so?  Because keep in mind, even if you have a dedicated reusable 2nd stage, and MCT sits on top, that 2nd stage will still almost certainly be some sort of biconic.  It might get away with a more blunted nose and ballistic reentry like the reusable Falcon 9 upper stage, but it will still have to come in nose first...just like MCT.   And since it's likely to come back from GTO trajectories if it's to deploy sats where most customers want them deployed, it'll be coming in faster than from just LEO. 
Which an integrated MCT platform would already be designed to do.  But would a dedicated S2 be designed for that?  It'd only ever need to go to LEO for purposes of launching MCT, and taking propellant to a LEO depot.  It'd need to have HEO return capability built into it's TPS...again, like the integrated stage already will have.

Which is what RobotBeat has hit on in a few posts.  These are complementary tasks, not competing tasks.  Where there is overlap anyway, why not go with it?  Why have a separate 2nd stage that will have to be designed to do basically the same thing as the MCT basic platform?

And how will it be easier to launch unmanned payloads from a biconic 2nd stage that cannot carry people (in any version) than it is from a biconic 2nd stage that can carry people when configured in a certain way?
I'm not seeing the advantage...or how the later is technically unfeasible.  If you can do one, you should be able to do the other.  Either way, you need some sort of payload carrier that can be built in behind the nosecone cap (which would be used for docking and propellant transfer in either the integrated or non integrated concepts), or have some sort of expendable payload fairly that would mount on the nose.

The only real advantage of a dedicated 2nd stage, as best I can see, is to allow an MCT to launch unfueled with fast reaction whole-vehicle abort capability.  Something that cannot be done with the integrated design.  But that's immaterial for the purpose of launching unmanned payloads to space.




 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/27/2015 07:12 pm
BTW I was surprised that Elon Musk mentioned they would land humans only when the return fuel is waiting for them. I would have expected to land the equipment but set it up for fuel production only after the human landing.

It makes perfect sense, otherwise you could literally doom/maroon the first crew. Remember that the MCT architecture (as we know it) is completely dependent on manufacturing ALL propellant for the journey home.

The first people to land are not going to be permanent colonist.

Not doom. They would not be colonists but they will IMO likely stay for a full synod until a replacement crew arrives. Probably a few stay on to extend their experience to the next crew. Worst case something goes wrong and they stay two synods. On the next synod they would receive spare parts to get fuel ISRU going.
Musk is borrowing somewhat from Mars Direct (or is it Semi-Direct?) where an already-fueled ascent vehicle is fueled up on the surface. I don't see a good reason not to have a fueled up vehicle ready when they arrive.

This would be safest.  However, I've always been skeptical about the ability for the MCT to produce enough propellant to refuel itself unmanned before the first crew arrives.  It'd need a lot of power, which means a lot of solar panels runrolled on the surface.  And that assumes mining moisture out of the air or bringing LH2 feedstock with it. 

Once there's a crew on the surface, they can set up large arrays of solar film all over the ground until they have enough, just unsure how that gets done prior to the first crew.

An alternative would be to send an unmanned MCT first with all of that propellant hardware, and lots of spare parts and extra provisions.  It'll sit and wait for the first crew.  Then when the first crew arrives, they can use that propellant hardware to set up shop and start production.  Their own MCT will have rovers and other manned surface equipment for exploration.   If there's a problem with their own MCT, then could fuel up the unmanned MCT and return on that.  So they'd always have a backup. 
Additionally, if another ship and crew are coming in the next launch window anyway, they will have help coming if something's going really wrong.  They'll need to get by until it arrives...but that's not quite being Marooned.  Wouldn't they be marooned until the next return window comes once they land anyway?  I don't think they can just go home whenever they want to (I'm not expert on Mars trajectories though)

If everything goes well, they'll return the next return window, while the next ship is inbound, and they'll leave a spare ship and propellant production equipment for the next crew to use.

This may be the more practical alternative, as I'm not sure how difficult it will be to fuel up a whole MCT unammned on Mars and just having it sitting there waiting for the crew when they get there.



 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mvpel on 10/27/2015 09:44 pm
It could do a Bigelow module or large space telescope or something too, but those would be pretty rare, more one time events.  Big telescopes are expensive and you only need so many big Bigelow modules in orbit.

Personally, I suspect they'll be launching as many Bigelow modules as they can as fast as they can much sooner than anyone expects. A dozen nations will have their own space stations with daisy chains of Bigelow modules, International Hotels Group will become Interplanetary Hotels Group, and if the price of oil goes back up Saudi princes will vacation in private gold-plated BA-2100's. The BFR will probably be chucking BA-330's and supporting hardware to the libration points and the moon too. We used to have Raytheon Polar Services, so I reckon we'll eventually have to design a Raytheon Lunar Services logo too.

There's a reason they're working diligently towards RTLS and "gas-and-go" operations for the Falcon - if Skylon can't keep up, they'll be launching crewed and cargo Dragons one after the other all week long. You won't have to plan months in advance to see a Falcon launch, you'll just stop by Playalinda some afternoon when it's convenient for you and watch the 2:30.

This whole thread is about speculation about the technology required for building a new branch of human civilization on Mars, and absolutely nothing above is any more implausible than that. Indeed, I see it as a natural outgrowth of such a venture. The kind of technology needed to travel to and settle on Mars will enable and empower the blossoming of a spacefaring society with thousands of people in various orbits and on the lunar surface pursuing their own goals, be it profit or something else. I think that the launch of the first 100-person MCT trip to Mars will be watched by people on at least two celestial bodies.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/28/2015 01:04 am
An interesting all be it old study on fast transit trajectories to and FROM mars.

http://www.dtic.mil/dtic/tr/fulltext/u2/a272591.pdf

Many folks have speculated about a trajectory that would allow a one synod mission cadence rather then the traditional every other synod cadence.  Most folks are familiar with 'Opposition' type trajectories which can get you back in one synod but at the cost of spending nearly the entire synod in deep space. 

The return leg is what makes this trajectory so long and the reason is the phase angle between Earth and Mars, essentially which planet would be ahead of the other when viewed from the perspective of the sun.  Normally we depart Earth when Mars is ahead of the Earth, the vehicle leaves Earth and falls behind the Earth and meets Mars well after the Earth is past mars. 

The optimum return from mars starts with the same configuration, Earth is behind and catching up with mars, the vehicle leaves mars and move ahead of mars meeting Earth well after Earth has past Mars.  This means we can't do BOTH of these things back to back and have to wait on Mars for years in the conventional 'Conjunction' trajectory.

But if you go SO FAST that your vehicle is from a phase perspective racing ahead of Earth on the outbound flight, has a week long stop over on mars right when Earth is passing mars and then can catch-up with with Earth on the return flight it becomes possible to do.  The velocities are very near solar-escape though and the transit time is a mind blowing 76 days each way.

The DeltaV from LEO for the outbound leg is around 8 km/s but the mars return is 16 km/s and that's from mars orbit not the surface.  Entry velocities are also off the charts, 18.8 km/s at mars, 15.4 km/s at Earth.  These are far beyond what even the most optimistic people could believe in.

It is interesting to note that at Hohmann transfer speeds the departure DeltaV and Entry velocity are higher at Earth then corresponding departure DeltaV and entry velocities at Mars.  As speed increases the DeltaV and entry velocities go up at both Earth and Mars, but they go up FASTER at Mars and entry velocities reach parity at 12.9 km/s for 106 day transfer, note that this requires much more velocity to be shed at mars so dose not represent equal difficulty in Aerocapture.  The DeltaV crossover point between LEO and mars orbit looks to be around 125 days at 5 km/s, and may not cross-over at all if your coming from mars surface at Hohmann bottoms out at around 4 km/s which is what you need just reach mars orbit. 

Finally for Earth return of >100 days the lower deltaV is obtained with Aphelion at Mars, where as <100 days it is with Perihelion at Earth.  For Earth departure Perihelion should always be at Earth.  So for a most discussions a simple symmetrical in/out trajectory is not the optimum.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: ThereIWas3 on 10/28/2015 01:52 am
The big safety reason to send the unmanned ISRU equipment first is so that if it breaks down, all the humans are still back on Earth.  You don't even launch the crew until you know that the ISRU worked and the fuel (and other stuff, like water and oxygen) is in storage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/28/2015 02:52 am

Keep in mind that most likely Falcon won't be going anywhere even once BFR flies.  SpaceX is investing if 4 pads for it.  Even if they were to turn 39A into a BFR pad at some point, that's still 3 pads.  It's sized good for comsats, and you aren't putting a 4mt comsat going to GTO on something the size of Saturn V or bigger.  Multiple payloads are a possibility, but ArianeSpace is moving away from that, not doubling down on it with Ariane 6.  Otherwise, why not make an Ariane 6 that's larger than Ariane 5 and can launch 5 or 6 sats at once?  Becuase it's a bit of a challenge to get just two sats going to close enough of the same orbits that can launch together...much less more.
So I don't see comsats being launched in big clusters by BFR.  That's what F9 is for and it'll do a nice job of that.
Bigger than F9 would be an FH with 3 reusable boosters.

So what -could- BFR/MCT launch besides crewed, propellant, cargo, or depot versions of MCT?  Even a fully reusable BFR/MCT which requires only nominal processing between flights (unlike STS) will have a fair cost...but could be less than say a D4H, or an FH-E or A5-551 or whatever the heavy Vulcan variant is.   So it could be the most affordable launcher for those big government birds.
It could also do planetary probes with an expendable kick stage.
It could do a Bigelow module or large space telescope or something too, but those would be pretty rare, more one time events.  Big telescopes are expensive and you only need so many big Bigelow modules in orbit.  Cargo service to a big Bigelow station is a possible routine job for BFR though. 

So those are some potential markets for BFR, I'm pretty sure it's not going to take over F9R/FHR's markets.

How Falcon and BFR split the launch manifest is certainly something to look at but if SpaceX is operating a full portfolio of reusable rockets the trading of launches between them becomes much less of an issue because your operating a fleet at that point.

All the non-satellite launch missions for BFR I have stated already as well, and these would not actually require much modification if the vehicle is a conventional 2 stage rocket, though the Earth Escape probe would definitely need an escape stage I see something like Centaur just being put under the probe and treated as part of the payload and not something SpaceX provides.

Finally their are potential savings by 'Raptorizing' the Falcon vehicles and retiring Merlin production, 4 Raptor engines should substitute for the 9 first stage Merline engines if a small landing engine/s is used either in the center or around the periphery.  So far SpaceX has saved money by only making one turbo-pump fed engines, once Raptor is available the incentive is clearly their to get rid of the old engine and propellant mix, though I am not sure what would be done in the upper stage of Falcon, possibly a low thrust variant can be made.

Unfeasible?  I don't know about that.  How so?  Because keep in mind, even if you have a dedicated reusable 2nd stage, and MCT sits on top, that 2nd stage will still almost certainly be some sort of biconic.  It might get away with a more blunted nose and ballistic reentry like the reusable Falcon 9 upper stage, but it will still have to come in nose first...just like MCT.   And since it's likely to come back from GTO trajectories if it's to deploy sats where most customers want them deployed, it'll be coming in faster than from just LEO. 
Which an integrated MCT platform would already be designed to do.  But would a dedicated S2 be designed for that?  It'd only ever need to go to LEO for purposes of launching MCT, and taking propellant to a LEO depot.  It'd need to have HEO return capability built into it's TPS...again, like the integrated stage already will have.

Which is what RobotBeat has hit on in a few posts.  These are complementary tasks, not competing tasks.  Where there is overlap anyway, why not go with it?  Why have a separate 2nd stage that will have to be designed to do basically the same thing as the MCT basic platform?

And how will it be easier to launch unmanned payloads from a biconic 2nd stage that cannot carry people (in any version) than it is from a biconic 2nd stage that can carry people when configured in a certain way?
I'm not seeing the advantage...or how the later is technically unfeasible.  If you can do one, you should be able to do the other.  Either way, you need some sort of payload carrier that can be built in behind the nosecone cap (which would be used for docking and propellant transfer in either the integrated or non integrated concepts), or have some sort of expendable payload fairly that would mount on the nose.

The only real advantage of a dedicated 2nd stage, as best I can see, is to allow an MCT to launch unfueled with fast reaction whole-vehicle abort capability.  Something that cannot be done with the integrated design.  But that's immaterial for the purpose of launching unmanned payloads to space.

That is not what I think a reusable 2nd stage would look like, this equivalency has been your core argument from the beginning, that a reusable 2nd stage and the MCT are so equal in performance that they might as well be the same vehicle but I couldn't disagree more.

Lets look at all the ways they differ

Active time of flight:  R2S (Reusable 2nd Stage):  Hours   MCT:  Months

Entry Velocity:    R2S: 7.7 km/s    MCT:  >12 km/s

Aerocapture necessary:   R2S:  NO    MCT: YES

Landing Site:  R2S:  Spaceport concrete pad + support facilities    MCT:  Unprepared martian regolith surface

Landed Payload Mass:  R2S:  Self dry mass     MCT:  Self dry mass + 100 mT cargo (mars) 25 mT (Earth)

Payload Carrying System:  R2S:  Payload adapter at top of tank     MCT:  Internal cargo bay with doors

Payload Separation Conditions:  R2S:  Axial decoupling in zero-g    MCT:  Horizontal removal on mars surface

Single use disposable Landing systems allowed (parachutes, airbags etc):   R2S:  YES    MCT:  NO

Abort system necessary:  R2S:  NO    MCT: YES

Take off Site:  R2S:  Upper atmosphere after stage separation    MCT:  Unprepared martian regolith surface



The differences are almost endless and I foresee a very different 2nd stage that is a fairly normal cylindrical shape about 20 m tall and 10 m diameter holding around 1200 mT of propellants and equipped with 7 Raptor engines.  It would be recovered by using a petal segment heat-shield covering the engines (rather then the unstable head-first entry depicted in the old F9 reuse video).  The petals would then open and act as landing legs, the heat shield material can be a single use ablative (PICAX) that is attached to the structural leg/rib.  The tank sides would likely have a metallic sandwich TPS system to protect them as well.  The top of the vehicle would deploy parachutes, decelerators and other disposable systems from underneath the payload adapter.  Grid-fins and vernier engines for touchdown would likewise be positioned at the top.  Dry mass fraction of 6% would yield a 75 mT dry mass.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/28/2015 07:29 am
Lets look at all the ways they differ

Active time of flight:  R2S (Reusable 2nd Stage):  Hours   MCT:  Months

Entry Velocity:    R2S: 7.7 km/s    MCT:  >12 km/s

Aerocapture necessary:   R2S:  NO    MCT: YES

Landing Site:  R2S:  Spaceport concrete pad + support facilities    MCT:  Unprepared martian regolith surface

Landed Payload Mass:  R2S:  Self dry mass     MCT:  Self dry mass + 100 mT cargo (mars) 25 mT (Earth)

Payload Carrying System:  R2S:  Payload adapter at top of tank     MCT:  Internal cargo bay with doors

Payload Separation Conditions:  R2S:  Axial decoupling in zero-g    MCT:  Horizontal removal on mars surface

Single use disposable Landing systems allowed (parachutes, airbags etc):   R2S:  YES    MCT:  NO

Abort system necessary:  R2S:  NO    MCT: YES

Take off Site:  R2S:  Upper atmosphere after stage separation    MCT:  Unprepared martian regolith surface

So effectively MCT has a superset of the R2S requirements. Anything the R2S can do the MCT can do as well, so there is no need for the R2S.

For GEO satellite deployment MCT could be refuelled in LEO, transfer to GEO, drop off the satellites and return. Only one MCT per year is necessary for all the commercially competed GEO satellites, plus 1-3 tanker flights.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/28/2015 07:35 am
The differences are almost endless and I foresee a very different 2nd stage that is a fairly normal cylindrical shape about 20 m tall and 10 m diameter holding around 1200 mT of propellants and equipped with 7 Raptor engines.  It would be recovered by using a petal segment heat-shield covering the engines (rather then the unstable head-first entry depicted in the old F9 reuse video).  The petals would then open and act as landing legs, the heat shield material can be a single use ablative (PICAX) that is attached to the structural leg/rib.  The tank sides would likely have a metallic sandwich TPS system to protect them as well.  The top of the vehicle would deploy parachutes, decelerators and other disposable systems from underneath the payload adapter.  Grid-fins and vernier engines for touchdown would likewise be positioned at the top.  Dry mass fraction of 6% would yield a 75 mT dry mass.

A 2nd stage would have similar terminal velocity to Dragon, if SpaceX can do fully propulsive landings with Dragon 2, they should be able to do do propulsive for a 2nd stage. Petals which open as landing legs may even give a lower terminal velocity than Dragon 2.

Although I like the petal idea I can't quite see how they are configured during launch when they obviously cannot cover the engines.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/28/2015 02:11 pm
(From a couple of pages back.)

The 1st and  2nd stage need only be able to get the 100mT cargo plus MCT dry weight into appropriate LEO.

Hmmm, this seems to be another point that people should clarify when they debate options.

Musk said, paraphrasing, that BFR is intended to get approximately 100 tonnes to LEO.

Interpretation 1: 100 tonnes including MCT dry-mass.
Interpretation 2: 100 tonnes in addition to MCT dry-mass.

These are vastly different requirements.

(And that's in addition to discussing whether the MCT is the second stage.)

[ Edit: 100t to LEO is pulled from a comment on the MCT Source Info thread (http://forum.nasaspaceflight.com/index.php?topic=37839.msg1392607#msg1392607) ]

--

Re: Commercial MCT use.

(Interpreted as MCT as second stage, with 100t + drymass to LEO.)

Musk mentioned ten cargo MCTs per passenger MCT, so 11 MCT's per 100 colonists.

However, orbital refuelling means multiple launches in addition to the main launch. So if you need, say, three launches of fuel per MCT-to-Mars, then you've 44 launches per 100 colonists.

If the price per colonist is $500,000, that puts the price of a single launch at $1.14m (less for the launch itself, since the total price includes all the extra orbital handling for refuelling, the ECLSS for 100day flights, etc.)

At a bit over a million per launch, BFR/MCT combination will be profitable as a commercial launcher if they carry a single 1 tonne satellite for $2m.

Even if these numbers are out by an order of magnitude (especially at the beginning), that's still 100 tonnes to LEO for a mere $10-20m. At that price BFR/MCT will quickly eat up the entire FH and F9R's launch market, just as F9 ate F1's market. (Better to fly as a secondary or multiple payload and use a bit of extra fuel to shuffle into your target orbit than buy the full capacity of F9R.)

That allows SpaceX to shut down F9/FH and Merlin production and focus on a single production line. And it allows them to incrementally test and improve BFR at someone else's expense. And to develop the simplest possible MCT as the first iteration (as a reusable BFR upper stage), before adding the complexity of orbital refuelling, 100-day ECLSS, Mars EDL/refuel/re-launch... etc.

Sounds like a plan to me.

When you think about how expensive BFR would have to get before it's not a viable commercial launcher, it's a lot higher than the point where it's no longer a viable Mars colony vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/28/2015 02:42 pm
Musk said, paraphrasing, that BFR is intended to get approximately 100 tonnes to LEO.

Interpretation 1: 100 tonnes including MCT dry-mass.
Interpretation 2: 100 tonnes in addition to MCT dry-mass.

That is not at all what was said and there is no ambiguity whatsoever. The number was 100t net payload landed on Mars.

Which does not exclude the possibility that this capability will be reached only with the second or third iteration of MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/28/2015 02:53 pm
An interesting all be it old study on fast transit trajectories to and FROM mars.

http://www.dtic.mil/dtic/tr/fulltext/u2/a272591.pdf



I'll take a look at that document when I get a chance.  Thanks for the info Impaler.  I've not really taken the time to work up my knowledge in the area of orbital mechanics like this.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/28/2015 03:00 pm
(From a couple of pages back.)

The 1st and  2nd stage need only be able to get the 100mT cargo plus MCT dry weight into appropriate LEO.

Hmmm, this seems to be another point that people should clarify when they debate options.

Musk said, paraphrasing, that BFR is intended to get approximately 100 tonnes to LEO.

Interpretation 1: 100 tonnes including MCT dry-mass.
Interpretation 2: 100 tonnes in addition to MCT dry-mass.

These are vastly different requirements.

(And that's in addition to discussing whether the MCT is the second stage.)

On the contrary.  He said that MCT would get "100 tons useful cargo to the surface of Mars".  Meaning if I want to ship 100 tons of candy bars to the surface of Mars for Halloween, that is doable.

BFR is something Shotwell rather than Musk has been talking about;  A launch vehicle that can loft 180-210 tons IIRC.  It doesn't really make much sense to launch MCT 'full' of small cargo, because MCT can be substantially heavier given a finite-sized launch vehicle if it's not packed with, eg, food, during ascent to LEO.

The questions are further down the road:
Interpretation 3A: 100 tonnes to the surface of Mars not including the ISRU equipment necessary to return (and reuse) the MCT, which will be additional mass
Interpretation 3B: 100 tonnes to the surface of Mars including the ISRU equipment necessary to return (and reuse) the MCT
Interpretation 3C: 100 tonnes to the surface of Mars with no ISRU equipment onboard;  MCT will only be used with prelanded ISRU assets on a 1-synod cycle
Interpretation 4A: 100 tonnes to the surface of Mars not including the ISRU equipment necessary to return (and reuse) the MCT, plus return 100 tonnes of cargo
et cetera, et cetera

Musk has also said things about "100 passengers".  This necessitates quite a large mass of food, and they need a very high-volume hab besides.  Maybe this is a *subjective guess* as to the terminal capacity that fits into "100 tons", but only if everything goes right and a functioning colony is first established.  Maybe it's one-way, Mars One style.  Maybe it refers (in the worst-case) to a first mission, and we need to return 100 passengers using onboard ISRU.  Maybe not everything gets landed.  We can't be sure.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/28/2015 03:04 pm
Musk said, paraphrasing, that BFR is intended to get approximately 100 tonnes to LEO.

Interpretation 1: 100 tonnes including MCT dry-mass.
Interpretation 2: 100 tonnes in addition to MCT dry-mass.

That is not at all what was said and there is no ambiguity whatsoever. The number was 100t net payload landed on Mars.

Which does not exclude the possibility that this capability will be reached only with the second or third iteration of MCT.

If I recall correctly, I think the term was 100 tons of "useful payload".

But yea, that pretty much indicates that number doesn't include the dry mass of the vehicle.


Edit:  Burninate beat me to it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/28/2015 04:11 pm

How Falcon and BFR split the launch manifest is certainly something to look at but if SpaceX is operating a full portfolio of reusable rockets the trading of launches between them becomes much less of an issue because your operating a fleet at that point.

All the non-satellite launch missions for BFR I have stated already as well, and these would not actually require much modification if the vehicle is a conventional 2 stage rocket, though the Earth Escape probe would definitely need an escape stage I see something like Centaur just being put under the probe and treated as part of the payload and not something SpaceX provides.

Finally their are potential savings by 'Raptorizing' the Falcon vehicles and retiring Merlin production, 4 Raptor engines should substitute for the 9 first stage Merline engines if a small landing engine/s is used either in the center or around the periphery.  So far SpaceX has saved money by only making one turbo-pump fed engines, once Raptor is available the incentive is clearly their to get rid of the old engine and propellant mix, though I am not sure what would be done in the upper stage of Falcon, possibly a low thrust variant can be made.


Yes, they may upgrade Falcon in the future.  If their past is any indication, that's probably pretty likely. 
Will they go to methane or even Raptor?  Maybe.  Although the two issues with Raptor are too few and too powerful of engines on the booster (as you said) which would likely necessitate some other means to land it.  And that a single vacuum Raptor on the upper stage would probably be way over powered for F9US.  Whereas the Merlins are sized correctly. 

But that's somewhat immaterial, as the point is SpaceX has mad a lot of investment into Falcon, and it most likely won't be going anywhere once BFR/MCT is flying.  It will cost effectively service payloads from EELV-medium class on down with booster reusability, and cheap upper stage mass production.  (Economics of scale can reduce costs as well as reusability).  It may be a Falcon v1.5, or v2.0, but it will still be Falcon in some form, because that's the butter size.  And it's affordable to launch single sats to their specific orbits rather than run into an Ariane 5 issue on steroids with a BFR.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 10/28/2015 04:50 pm
So effectively MCT has a superset of the R2S requirements. Anything the R2S can do the MCT can do as well, so there is no need for the R2S.

What Impaler was trying to refute was the idea that anything MCT is supposed to do is as easy and simple as having a reusable second stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/28/2015 04:55 pm

That is not what I think a reusable 2nd stage would look like, this equivalency has been your core argument from the beginning, that a reusable 2nd stage and the MCT are so equal in performance that they might as well be the same vehicle but I couldn't disagree more.

Lets look at all the ways they differ

Active time of flight:  R2S (Reusable 2nd Stage):  Hours   MCT:  Months

Entry Velocity:    R2S: 7.7 km/s    MCT:  >12 km/s

Aerocapture necessary:   R2S:  NO    MCT: YES

Landing Site:  R2S:  Spaceport concrete pad + support facilities    MCT:  Unprepared martian regolith surface

Landed Payload Mass:  R2S:  Self dry mass     MCT:  Self dry mass + 100 mT cargo (mars) 25 mT (Earth)

Payload Carrying System:  R2S:  Payload adapter at top of tank     MCT:  Internal cargo bay with doors

Payload Separation Conditions:  R2S:  Axial decoupling in zero-g    MCT:  Horizontal removal on mars surface

Single use disposable Landing systems allowed (parachutes, airbags etc):   R2S:  YES    MCT:  NO

Abort system necessary:  R2S:  NO    MCT: YES

Take off Site:  R2S:  Upper atmosphere after stage separation    MCT:  Unprepared martian regolith surface

I'm not saying a dedicated 2nd stage couldn't be made cheaper and easier than an integrated MCT basic platform stage.  It's criteria aren't as harsh as for MCT. 
But, that doesn't speak to your original comment about an integrated design being technically unfeasible.  There may be other reasons to go with a dedicated 2nd stage, but I don't think those are reasons because the integrated design is some sort of impossible or implausible concept.

Now, if the integrated design is feasible, that just leaves the question of if it's the better way to go or not?
Mike speaks well to that here:


So effectively MCT has a superset of the R2S requirements. Anything the R2S can do the MCT can do as well, so there is no need for the R2S.

For GEO satellite deployment MCT could be refuelled in LEO, transfer to GEO, drop off the satellites and return. Only one MCT per year is necessary for all the commercially competed GEO satellites, plus 1-3 tanker flights.

That's always been my point.  You have to have MCT anyway.  It already can do everything a cheaper/easier S2 can do anyway.  Why not just make it be the S2 then?

Will it be a little heavier than the dedicated S2?  Probably.  It probably won't have quote the payload capability of the integrated MCT platform.  But will that be a problem?  Probably not.  It's only going to be an issue for two potential MCT/BFR missions.

1)  Unmanned payload launching to space.
2)  Tanker service to depot.

The first shouldn't be much issue, because there's already nothing that needs 100mt of throw capacity (although it would likely be even more than that, because it would be stripped down to just the tanks, engines, and OML)  To my knowledge there's no current or near term future need for more capacity than D4H or FHE will have to LEO or to GTO.  And such an integrated BFR would have much more capacity than those.  So if you have 100mt to LEO instead of say 120mt to LEO for a dedicated lighter/cheaper S2, it doesn't hurt you from the commercial or government payload launching market.

As for a tanker, it probably wouldn't be able to get quite as much propellant to a depot per launch.  But then again, you have a reusable launch system.  So if it takes 5 BFR launches to fill up a depot prior to a Mars mission instead of 4, is that really a detriment? 
And again, when comparing the dedicated S2 to the basic integrated MCT platform...stripped of everything but the bare shell, tanks, engines, and landing gear, I doubt the difference would be all that much.

Also, as a satellite launcher, it wouldn't really need it's big MCT solar arrays.  And it would have large residuals of propellants.  So a little methalox fuel cell or IVF engine could generate the short term loiter power it needs, so it wouldn't even need to have the solar arrays.  A dedicated S2 would need something like that too....or a lot of batteries.  Either way that would be needed.


Payload Carrying System:  R2S:  Payload adapter at top of tank     MCT:  Internal cargo bay with doors

You could either have an internal cargo bay for MCT...as there will be an empty volume between the nose and tanks, or have a payload adapter on the nose like you say for the S2.  Either set up will have a TPS on the nose, so there's not much difference in have a payload adapter on one vs. the other. 


The differences are almost endless and I foresee a very different 2nd stage that is a fairly normal cylindrical shape about 20 m tall and 10 m diameter holding around 1200 mT of propellants and equipped with 7 Raptor engines.  It would be recovered by using a petal segment heat-shield covering the engines (rather then the unstable head-first entry depicted in the old F9 reuse video).  The petals would then open and act as landing legs, the heat shield material can be a single use ablative (PICAX) that is attached to the structural leg/rib.  The tank sides would likely have a metallic sandwich TPS system to protect them as well.  The top of the vehicle would deploy parachutes, decelerators and other disposable systems from underneath the payload adapter.  Grid-fins and vernier engines for touchdown would likewise be positioned at the top.  Dry mass fraction of 6% would yield a 75 mT dry mass.


Yes, there can be differences, but it doesn't change that MCT would do everything S2 would do, and much more.  So the advantage of going that way is you only need to develop one spaceship, and all of them have the same basic common platform.  Where as the two spacecraft you've described appear to have different landing legs, different TPS systems, and different methods of landing...a lot of different duplicated systems that cost more to develop and support, and add extra mass to the stack when launching MCT.
 I think there's a plausible argument than the economic and logistic advantage...as well as mass advantage to LEO of have the one common integrated system outweigh loosing a little mass efficiency as a tanker or satellite launcher...especially when it could still be very capable at both.
which gets to the larger point, I think as others have pointed out, MCT/BFR will be designed to do specifically one thing primarily...serve as a Mars vehicle.  It'll be able to do other things of course, (which can generate money to help fund the Mars goals...definately a good thing for SpaceX) but the hardware won't be designed around those things primarily, it'll be designed around going to Mars as safely and economically and efficiently as possible. 
An integrated design also has better throw capacity to LEO when launching MCT...which would be it's primary designed function.  Whereas with the dedicated S2, it would have more throw capacity to LEO when launching payloads other than MCT...which isn't it's primary designed function.
So (IMHO) a dedicated S2 will probably only be part of the system if there's a Mars-centric reason for it.  Like a whole vehicle fast abort option for MCT or maybe they want the most efficient tanker possible, which would be a dedicated S2-tanker.  Or some other Mars related reason.




Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/28/2015 05:25 pm

For GEO satellite deployment MCT could be refuelled in LEO, transfer to GEO, drop off the satellites and return. Only one MCT per year is necessary for all the commercially competed GEO satellites, plus 1-3 tanker flights.


I think it better to just have it go to a GTO, and then do what's typically done today, which is drop it off there and have the payload place itself in the GEO orbit.  I think the propulsive hit becomes large when entering a GEO orbit to directly deploy the sat, and then have to deorbit from there.
A GTO will bring it right back to Earth, where it can do a small deorbit burn and come right home. 
(I think there are transfer orbits which go to near escape before coming back, just like a GTO.  So possibly it could launch a planetary probe with a kick stage to such an orbit, deploy it, and return while the kick stage does the rest of the dV to escape. If it could get itself and enough propellant to LEO to do it anyway.)

If you have an expendable stage, then it really doesn't matter if you drop off it GTO, or take all the way to GEO, the stage doesn't have to get home.  But for a reusable stage, getting home needs to be factored in.

There's never been a sat to GTO that D4H couldn't carry (to my knowledge), at 11.4mt to GTO (1500 m/s to GEO) or 13.4mt to GTO (1800 m/s to GEO).  An MCT-sat launcher could take such a 11-13mt Sat plus around 90mt or more of propellant to LEO.  Someone would have to run the numbers to make sure that's sufficient to get it's own dry mass plus the payload to a GTO 1800 m/s to GEO orbit, with enough left to do a little deorbit burn and land.  Probably only need one central Raptor to do the GTO burn and the deorbit burn.   If there's a DoD requirement that the LV put the sat directly into GEO (which I think they have with EELV, although I don't think it's done that way often) then SpaceX always has FH to use, as the upper stage isn't coming back.

Note:  MCT-sat launcher would be the basic integrated MCT platform, less anything not needed to launch sats, to maximize payload mass.  Essentially a shell with tanks, engines, and landing legs...with a short term power source like a methalox fuel cell or IVF generator.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/28/2015 05:31 pm
I think you are right Lobo.  SpaceX has the same diameter S2 on Falcon 9, and the same engine optimized for vacuum.  It makes sense to have the same Raptor engine second stage optimized for vacuum, same fuel as first stage, even the same landing legs.  Either a clamshell heat shield for the S2 engines that doubles as interstage, or the conical one side coated heat shield on the second stage/MCT for atmospheric entry.  Like you said, a dedicated S2 might through 20 more tons into orbit, but then you have three things going on.  S1, S2, MCT.  Cheaper would be S1, S2/MCT combo.  Both build robustly and reusable for cost reusability cost effectiveness.  Same with airlines.  Same planes are for either passengers or cargo.  Only the guppy versions for large diameter items are different.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Space Ghost 1962 on 10/28/2015 05:49 pm
Briefly butting in here. Consider gaining flight history on Raptor ahead of any BFR concept.

And consider that FH's US is limiting factor in certain mission profiles.

Only way I can factor in a non-BFR use of Raptor is as a oversized diameter US, flown on only FH. For a limited scope of missions. Which is against the SX economics as a whole I'll grant.

Things that argue for this:
  * Raptor originally was a hydrolox US engine - clearly they earlier saw the need
  * Raptor was scaled up in size, then scaled down in size - launch architecture clearly being "tuned" around US and Mars ascent requirements
  * Environment to prove this would be in high/no atmosphere, not test stand
  * You'd also want long duration in space operations, not unlike what ACES/IVF is aimed for
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/28/2015 06:55 pm
A 2nd stage would have similar terminal velocity to Dragon, if SpaceX can do fully propulsive landings with Dragon 2, they should be able to do do propulsive for a 2nd stage. Petals which open as landing legs may even give a lower terminal velocity than Dragon 2.

Although I like the petal idea I can't quite see how they are configured during launch when they obviously cannot cover the engines.

I see the petals staying closed on re-entry until the last kilometer, much as the legs on F9 only deploy just before touch-down.  The primary engines don't fire within the atmosphere and the actual landing engines are outside the petals.  As for how you configure for launch, the petals are closed and inside the inter-stage space, the top of the first stage would be concave and the stage separation pushes directly on the closed petals and they spring open once clear of the first stage and then the second stage engines ignite.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/28/2015 06:59 pm
Methalox will have a higher ISP than kerolox on Falcon 9.  I/we are assuming BFR will use a minimum of 9 Raptors, probably about 24.  Therefore upperstage/MCT will use a minimum of 5 raptors if scaled like Falcon9.  5 may be needed to blast off Mars but probably only one will be needed to land the upperstage/MCT.   Once you get 100 tons to LEO, this much payload is not limited in scope.  Refueling you go to Mars or the Moon.  Or you off load multiple satellites to be sent to GSO.  Metholox would be easier to keep cold in long term space than hydrolox.  Less power required to keep liquid. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/28/2015 07:12 pm

For GEO satellite deployment MCT could be refuelled in LEO, transfer to GEO, drop off the satellites and return. Only one MCT per year is necessary for all the commercially competed GEO satellites, plus 1-3 tanker flights.


I think it better to just have it go to a GTO, and then do what's typically done today, which is drop it off there and have the payload place itself in the GEO orbit.  I think the propulsive hit becomes large when entering a GEO orbit to directly deploy the sat, and then have to deorbit from there.
A GTO will bring it right back to Earth, where it can do a small deorbit burn and come right home. 

Up to now I thought the same. But given the capabilities of a refuelled MCT GSO may well be the better option. No need to give com sats the capability to reach GSO on their own. GTO was so far the better option because the launch vehicle could be smaller and the upper stage can easily deorbit after placing the payload in GTO. None of the restrictions would be applicable for MCT, especially when refuelled but with few sats maybe even without refuelling.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/28/2015 07:20 pm
Briefly butting in here. Consider gaining flight history on Raptor ahead of any BFR concept.

And consider that FH's US is limiting factor in certain mission profiles.

Only way I can factor in a non-BFR use of Raptor is as a oversized diameter US, flown on only FH. For a limited scope of missions. Which is against the SX economics as a whole I'll grant.

Things that argue for this:
  * Raptor originally was a hydrolox US engine - clearly they earlier saw the need
  * Raptor was scaled up in size, then scaled down in size - launch architecture clearly being "tuned" around US and Mars ascent requirements
  * Environment to prove this would be in high/no atmosphere, not test stand
  * You'd also want long duration in space operations, not unlike what ACES/IVF is aimed for

Why are FH and F9 upgrades being discussed in this thread? Seems a bit off-topic.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MP99 on 10/28/2015 07:33 pm
Quote from: Impaler link=topic=37808.msg1439383#msg1439383 So what -could- BFR/MCT launch besides crewed, propellant, cargo, or depot versions of MCT? 
[/quote

Is there a chance to have a depot in a GTO orbit? Maybe an 80,000 km apogee.

Deliver satellite, adjust orbit to meet up with depot, deliver prop load, then return to Earth.

Once the depot is full, I believe it could make its way to EML with quite a low dV boost.

Cheers, Martin
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/28/2015 07:49 pm
With metholox having a higher ISP, has anyone figured if the MCT could make GTO as also a second stage?  Would a depot there be better? 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/28/2015 08:46 pm

For GEO satellite deployment MCT could be refuelled in LEO, transfer to GEO, drop off the satellites and return. Only one MCT per year is necessary for all the commercially competed GEO satellites, plus 1-3 tanker flights.


I think it better to just have it go to a GTO, and then do what's typically done today, which is drop it off there and have the payload place itself in the GEO orbit.  I think the propulsive hit becomes large when entering a GEO orbit to directly deploy the sat, and then have to deorbit from there.
A GTO will bring it right back to Earth, where it can do a small deorbit burn and come right home. 

Up to now I thought the same. But given the capabilities of a refuelled MCT GSO may well be the better option. No need to give com sats the capability to reach GSO on their own. GTO was so far the better option because the launch vehicle could be smaller and the upper stage can easily deorbit after placing the payload in GTO. None of the restrictions would be applicable for MCT, especially when refuelled but with few sats maybe even without refuelling.

Hmmm...interesting.

How difficult is it to put enough propellant on a sat for it to do it's own GEO insertion?  I assumed it was pretty easy/common, as that's usually how it's done now, isn't it?

The thing I'd think they'd want to stay away from is refueling, because that means another BFR/MCT launch is required to put the propellant in the depot so the MCT-sat launcher can tank up.  So that's two giant BFR launches for a sat that could otherwise go on an expendable FH.  I get it's fully reusable, but that just seems like a lot of overkill for a D4H/FH class payload.  There's something about the optics there that seems like it would make using BFR/MCT less economic than even an expendable FH.

Maybe that's an incorrect perception though.

But if it's typical/common/inexpensive to add propellant tanks to a sat so it can do it's own GEO insertion, it's probably a moot point.  Most GEO sats have a propulsion system anyway, don't they?  For orbital corrections and such?  And to deorbit at the end of their service life?  (I thought that was some new thing for sats to help cut down on the space clutter of dead sats).  So it's it just a matter of enlarging the tanks on the system the sat would have anyway?  That doesn't seem like a bid deal.  But it's not something I'm well versed in, so I may have an incorrect perception of it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/28/2015 08:46 pm
Interpretation 2: 100 tonnes in addition to MCT dry-mass.

This is the correct interpretation, this is one of the few clear goal statements we have from Musk and while I think many folks over interpret many statements this one isn't being embellished.  At a minimum a vehicle holding 100 mT of cargo will land on mars, and most of us assume that it will be launched with the cargo inside, but most agree that significant amount of additional support launches will be necessary to get one lander onto mars.


Musk mentioned ten cargo MCTs per passenger MCT, so 11 MCT's per 100 colonists.

However, orbital refuelling means multiple launches in addition to the main launch. So if you need, say, three launches of fuel per MCT-to-Mars, then you've 44 launches per 100 colonists.

If the price per colonist is $500,000, that puts the price of a single launch at $1.14m (less for the launch itself, since the total price includes all the extra orbital handling for refuelling, the ECLSS for 100day flights, etc.
Sounds like a plan to me.

When you think about how expensive BFR would have to get before it's not a viable commercial launcher, it's a lot higher than the point where it's no longer a viable Mars colony vehicle.

I think your in error assuming that a passenger ticket comes with 10 mT of luggage at no additional cost.  SpaceX will likely be charging money for 'freight' flights in proportion to their cost and the passenger flight represents the cost of moving just a person with a suitcase to mars.  I anticipate a cost of around 200-300 million per launch of a BFR initially when it is in early deployment and reuses are limited (and occasionally cut short due to recovery failures), this would still be more then enough to push SLS completely to the side as NASA could afford 4-5 launches a year for what they are going to pay for 1 SLS launch.  Prices would gradually drop as scale increases, refurbishment is streamlined, reuse lifetime maximized and launch facility throughput is improved.

The efficiency of LEO->Mars surface mass transfer needs to improve too which is one of the major reasons to go SEP, if pushed to the extreme that ratio could be near 80%, with an all chemical propulsion system it won't get past 10% meaning you will always need large numbers of propellant launches per cargo or passenger launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/28/2015 09:00 pm
I think you are right Lobo.  SpaceX has the same diameter S2 on Falcon 9, and the same engine optimized for vacuum.  It makes sense to have the same Raptor engine second stage optimized for vacuum, same fuel as first stage, even the same landing legs.  Either a clamshell heat shield for the S2 engines that doubles as interstage, or the conical one side coated heat shield on the second stage/MCT for atmospheric entry.  Like you said, a dedicated S2 might through 20 more tons into orbit, but then you have three things going on.  S1, S2, MCT.  Cheaper would be S1, S2/MCT combo.  Both build robustly and reusable for cost reusability cost effectiveness.  Same with airlines.  Same planes are for either passengers or cargo.  Only the guppy versions for large diameter items are different.

That's the thought anyway.  The synergy between the F9 booster and S2 is one example, although a dedicated S2 can share the same tank tooling as the booster and a separate biconic MCT.   The Rocketplane Kistler K-1 is another, although that has different diameter stages.  It's be like if SpaceX mounted a Dragon 2 less the heat shield on an F9US, and then coat the nose and one side with your TPS.  Much thinner TPS tiles as it would have a much better L/D ratio.  And now you have a reusable crew capsule as well as a reusable upper stage, and the whole integrated assembly would weigh less than a separate reusable Dragon 2 and reusable F9US.
But this of course then runs into the issue of fast abort and pad abort options, just like it does for the integrated Biconic MCT concept. 

Putting a clamshell type heat shield on the bottom of a dedicated S2 means you have to launch it with the doors open, so they need to have a way to not interfere with the interstage until booster sep.  Then they need to close up again air tight or else you risk loosing the stage.   Which is why I prefer biconic concepts rather than Super Capsule concepts for MCT...you aren't trying to open and close large doors in your heat shield.  And for a dedicated S2 as well.  Biconic is probably the best bet. 

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/28/2015 10:22 pm
I'm not saying a dedicated 2nd stage couldn't be made cheaper and easier than an integrated MCT basic platform stage.  It's criteria aren't as harsh as for MCT. 
But, that doesn't speak to your original comment about an integrated design being technically unfeasible.  There may be other reasons to go with a dedicated 2nd stage, but I don't think those are reasons because the integrated design is some sort of impossible or implausible concept.

Now, if the integrated design is feasible, that just leaves the question of if it's the better way to go or not?
Mike speaks well to that here:



So effectively MCT has a superset of the R2S requirements. Anything the R2S can do the MCT can do as well, so there is no need for the R2S.

For GEO satellite deployment MCT could be refuelled in LEO, transfer to GEO, drop off the satellites and return. Only one MCT per year is necessary for all the commercially competed GEO satellites, plus 1-3 tanker flights.

That's always been my point.  You have to have MCT anyway.  It already can do everything a cheaper/easier S2 can do anyway.  Why not just make it be the S2 then?

Will it be a little heavier than the dedicated S2?  Probably.  It probably won't have quote the payload capability of the integrated MCT platform.  But will that be a problem?  Probably not.  It's only going to be an issue for two potential MCT/BFR missions.

1)  Unmanned payload launching to space.
2)  Tanker service to depot.

The first shouldn't be much issue, because there's already nothing that needs 100mt of throw capacity (although it would likely be even more than that, because it would be stripped down to just the tanks, engines, and OML)  To my knowledge there's no current or near term future need for more capacity than D4H or FHE will have to LEO or to GTO.  And such an integrated BFR would have much more capacity than those.  So if you have 100mt to LEO instead of say 120mt to LEO for a dedicated lighter/cheaper S2, it doesn't hurt you from the commercial or government payload launching market.

As for a tanker, it probably wouldn't be able to get quite as much propellant to a depot per launch.  But then again, you have a reusable launch system.  So if it takes 5 BFR launches to fill up a depot prior to a Mars mission instead of 4, is that really a detriment? 
And again, when comparing the dedicated S2 to the basic integrated MCT platform...stripped of everything but the bare shell, tanks, engines, and landing gear, I doubt the difference would be all that much.

Also, as a satellite launcher, it wouldn't really need it's big MCT solar arrays.  And it would have large residuals of propellants.  So a little methalox fuel cell or IVF engine could generate the short term loiter power it needs, so it wouldn't even need to have the solar arrays.  A dedicated S2 would need something like that too....or a lot of batteries.  Either way that would be needed.

First off, NO it is not a simple super-set, it is clearly harsher in totality, but not all in the same ways.  Many avenues would be available for easing the design of one that aren't available to the other or to the composite.  Second your MCT hurdles are only that high when you DON'T have a 2nd stage.

I need to see some better figures from you on the total mass and thrust of your BFR concept and the actual mass of this integrated 2nd stage to even get an idea what your LEO performance is and what it's likely to cost, you really can't throw around generic statements like 'lighter' when I have SPECIFIC mass estimates and DeltaV goals.  You need to do more homework to demonstrate this (or show the homework from L2 as I suspect this is where it all is).  The launch vehicle performance calculator http://www.silverbirdastronautics.com/LVperform.html should be the basis for comparison as I've used it for my calculations (median performance estimates only).



Payload Carrying System:  R2S:  Payload adapter at top of tank     MCT:  Internal cargo bay with doors

You could either have an internal cargo bay for MCT...as there will be an empty volume between the nose and tanks, or have a payload adapter on the nose like you say for the S2.  Either set up will have a TPS on the nose, so there's not much difference in have a payload adapter on one vs. the other. 

Wait a sec, we are both in favor of Bi-conic entry vehicles for MCT (you convinced me of that), and you can't put anything on top of a bi-conic that is where the heat-shield is, you can't have exposed attachment point for payload, they would melt and I can't see retracting them into doors as being practical either.  The picture we were shown of a F9 reusable upper stage was fatally flawed when it depicted a heat shield on the top of the stage, it is both unstable as an entry vehicle and it provides no attachment, that's why I came up with the petal heat-shield/legs and bottom first entry.




The differences are almost endless and I foresee a very different 2nd stage that is a fairly normal cylindrical shape about 20 m tall and 10 m diameter holding around 1200 mT of propellants and equipped with 7 Raptor engines.  It would be recovered by using a petal segment heat-shield covering the engines (rather then the unstable head-first entry depicted in the old F9 reuse video).  The petals would then open and act as landing legs, the heat shield material can be a single use ablative (PICAX) that is attached to the structural leg/rib.  The tank sides would likely have a metallic sandwich TPS system to protect them as well.  The top of the vehicle would deploy parachutes, decelerators and other disposable systems from underneath the payload adapter.  Grid-fins and vernier engines for touchdown would likewise be positioned at the top.  Dry mass fraction of 6% would yield a 75 mT dry mass.


Yes, there can be differences, but it doesn't change that MCT would do everything S2 would do, and much more.  So the advantage of going that way is you only need to develop one spaceship, and all of them have the same basic common platform.  Where as the two spacecraft you've described appear to have different landing legs, different TPS systems, and different methods of landing...a lot of different duplicated systems that cost more to develop and support, and add extra mass to the stack when launching MCT.
 I think there's a plausible argument than the economic and logistic advantage...as well as mass advantage to LEO of have the one common integrated system outweigh loosing a little mass efficiency as a tanker or satellite launcher...especially when it could still be very capable at both.
which gets to the larger point, I think as others have pointed out, MCT/BFR will be designed to do specifically one thing primarily...serve as a Mars vehicle.  It'll be able to do other things of course, (which can generate money to help fund the Mars goals...definately a good thing for SpaceX) but the hardware won't be designed around those things primarily, it'll be designed around going to Mars as safely and economically and efficiently as possible. 
An integrated design also has better throw capacity to LEO when launching MCT...which would be it's primary designed function.  Whereas with the dedicated S2, it would have more throw capacity to LEO when launching payloads other than MCT...which isn't it's primary designed function.
So (IMHO) a dedicated S2 will probably only be part of the system if there's a Mars-centric reason for it.  Like a whole vehicle fast abort option for MCT or maybe they want the most efficient tanker possible, which would be a dedicated S2-tanker.  Or some other Mars related reason.

Your ignoring the fact that I'm calling for a MCT with STAGGERINGLY lower performance requirements then you are, your trying to pretend this a comparison between an RV towing a boat, vs your proposed RV only (cheap by 1 boat), but what you have is more like a hovercraft with a house on it which would be much harder to make and may not even be possible.  Two or more vehicles that split the missions performance hurdles between them are infinity easier to develop (and less risky) then one which shoulders all the burden.  Making vehicles reusable costs a considerable performance margin as well.

The differences between our MCT vehicle concepts is huge, your looking at 8 km/s DeltaV and (I think) full speed aerocapture at >12 km/s (I'm still not clear on your preferred trajectory and how aggressive your transit times are).  I've been trying to use every tool available to to lower the performance specs of the MCT lander down to 4 km/s DeltaV and EDL from just 4 km/s to make the 'long-pole' of the whole operation as short as possible.

A simpler lander is made possible BECAUSE of the 2nd stage and the use of SEP tugs as well.  And your even admitting that the 2nd stage makes a better LEO tanker, which will be launched 6-12 times more often then the lander so it is quite important. 

Your logic that the whole system will be designed with zero consideration for uses other then mars is deeply flawed, this will not lower the price, it will raise it because the history of vehicles of every kind is that lowest prices are achieved with highest volume.  If MCT can be used for a wider set of missions then volume goes up and price goes down.  And this is particularly important when laying down a big investment on a new vehicle it needs to cover as much market space as possible to ensure that it survives, the rocket that's a flop financially and becomes a millstone around your neck is infinity more damaging to Mars colonization then one that might be a little lower in performance but actually flies.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/28/2015 11:11 pm
....
Lets look at all the ways they differ

Active time of flight:  R2S (Reusable 2nd Stage):  Hours   MCT:  Months
So basically you're saying SpaceX wouldn't want their 2nd stage to be capable of cislunar flights like Vulcan's 2nd stage will be capable of?

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Entry Velocity:    R2S: 7.7 km/s    MCT:  >12 km/s
So basically you're saying BFR wouldn't be useful for anything beyond LEO? Interesting, as beyond-LEO is where the vast majority of the commercial and military launch market is (and commercial/military launch is basically the whole argument for why you'd want to release BFR before MCT). Anyway, SpaceX is probably going to use PICA-X, which works in both cases. A big reason why RLVs are normally considered for LEO is that they're either single stage (does not apply here) or use a low-temperature TPS (also does not apply).
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Aerocapture necessary:   R2S:  NO    MCT: YES
This is basically a subset of the above. Either could work with aerocapture.

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Landing Site:  R2S:  Spaceport concrete pad + support facilities    MCT:  Unprepared martian regolith surface
Citation needed. There's a pretty good chance SpaceX could be sending Dragons with equipment ahead of time. In either case, this would be irrelevant after the first MCT landing. You cannot say that the MCT will be landing on unprepared regolith.

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Landed Payload Mass:  R2S:  Self dry mass     MCT:  Self dry mass + 100 mT cargo (mars) 25 mT (Earth)
The first valid point!

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Payload Carrying System:  R2S:  Payload adapter at top of tank     MCT:  Internal cargo bay with doors
Yet another argument to skip straight to MCT, so they don't have to develop a payload adapter at the top of the tank.

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Payload Separation Conditions:  R2S:  Axial decoupling in zero-g    MCT:  Horizontal removal on mars surface
Meh. Horizontal removal works, we've done it before. And using MCT means you ALSO can recover payloads from orbit or potentially save expensive payloads in case of a first stage mishap. Additionally, if the payload bay is at the top, they still can do axial decoupling in zero-g just fine.

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Single use disposable Landing systems allowed (parachutes, airbags etc):   R2S:  YES    MCT:  NO
Not from what we saw from SpaceX's Falcon 9 upper stage reuse video. Additionally, SpaceX is moving /away/ from this sort of expensive disposable system. Why would they decide to reverse course and invest millions on a technology that for them is a dead-end?

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Abort system necessary:  R2S:  NO    MCT: YES
Only needed for crewed MCT flights. There are other ways to do abort for crewed flights, like the Delta Clipper concept.

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Take off Site:  R2S:  Upper atmosphere after stage separation    MCT:  Unprepared martian regolith surface
Again, you have NO citation for that, and there are very good arguments that MCT will be neither landing on nor taking off from unprepared Martian regolith.



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The differences are almost endless and I foresee a very different 2nd stage that is a fairly normal cylindrical shape about 20 m tall and 10 m diameter holding around 1200 mT of propellants and equipped with 7 Raptor engines.  It would be recovered by using a petal segment heat-shield covering the engines (rather then the unstable head-first entry depicted in the old F9 reuse video).  The petals would then open and act as landing legs, the heat shield material can be a single use ablative (PICAX) that is attached to the structural leg/rib.  The tank sides would likely have a metallic sandwich TPS system to protect them as well.  The top of the vehicle would deploy parachutes, decelerators and other disposable systems from underneath the payload adapter.  Grid-fins and vernier engines for touchdown would likewise be positioned at the top.  Dry mass fraction of 6% would yield a 75 mT dry mass.
So in other words, MCT doesn't fit with what your ENTIRELY made-up reusable 2nd stage would look like, even though it probably fits pretty well with what SpaceX /has/ released so far with respect to a reusable 2nd stage, so obviously they're totally different. Uh huh.

The only real point you've got there is the requirements for landing a dry stage and landing a significant payload on Mars are different, so you'd probably need somewhat beefier legs on MCT than what would be absolutely essential for an empty upper stage. That's true, but not a good enough reason to develop a completely different vehicle. Heck, even if BFR/MCT DOES have 3 effective stages (big booster, reusable 2nd stage, and MCT), you'd still probably want to keep the 2nd stage and MCT /very/ similar in order to avoid having to pay for development of a completely different vehicle, totally different TPS, etc. (as well as the loss of safety since you aren't also testing MCT every time you launch another payload)

And things like an abort system or beefier legs could be developed at a later time. Sure as heck beats the cost of developing an /entirely/ different spacecraft from the 2nd stage, as you propose.

Money matters.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/28/2015 11:47 pm
Let me clarify.

Impaler, I don't think your ideas of how to build a reusable upper stage are technically bad, I'm just not at all convinced that that is what SpaceX has in mind, based on their F9 reusable upper stage, their work with Dragon, and their various statements about MCT/BFR. A more integrated system fits very well with statements like this from Musk:
"We’re looking at our Mars transporter being around 15 million pounds of thrust"
(from here: http://forum.nasaspaceflight.com/index.php?topic=37839.msg1391925#msg1391925 )
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 10/28/2015 11:57 pm
I still don't get it, why is integration of systems not acceptable for this:

However, many viewed [the Mars Direct plan] as too technologically ambitious to be credible – citing a myriad of issues, such as hopelessly optimistic technology assumptions, and lack of adequate mass margin.

The Mars Semi-Direct architecture proposal that followed (also 1991) might be interpreted as a partial rebuttal to some of these concerns. Instead of specifying such a wildly ambitious “do it all” ERV vehicle, the function of ferrying the crew from Mars surface back to Earth was split up into two parts, to be performed by two separate vehicles: A Mars ascent vehicle (MAV), which needed only to generate enough fuel for the crew to ascend to Mars’ orbit, and the Earth return vehicle (ERV) which was pre-placed in Mars’ orbit – and which would perform the propulsive maneuver needed to send the crew back to Earth.

but is acceptable for MCT?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/29/2015 12:40 am
Because:
1) SpaceX has demonstrated supersonic retropropulsion. That alone is HUGELY enabling for large payloads on Mars. Since you need rockets to land anyway, it also greatly simplifies the whole EDL process.

2) MCT assumes lots of equipment on the ground, not least of which extensive water/CO2 to Methane/O2 ISRU.

3) MCT assumes orbital refueling, at least in Earth orbit but that also leaves open the possibility of orbital refueling in Mars orbit which would allow propellant to be loaded on to MCT for Trans-Earth-injection and also for landing (on Earth or Mars). So if you think all those various roles means that SpaceX isn't able to get MCT up to 6.5-8km/s or so delta-v, they can use orbital refueling (on both sides) to fill that gap, at least until they're able to refine MCT.

4) Related to this is that MCT will likely experience refinement. If at first you end up with F9 v1.0, you can double the performance to LEO (and more to higher energy orbits) with some evolutionary refinement by the time you get to v1.1 full thrust. The /platform/ just has to allow the stated performance goals (which in the case of MCT are listed in terms of round numbers with low implied precision, like "100 tons useful payload" or "up to ~100 passengers" or "~100 day transit to Mars"), /eventually/.

These various factors are self-reinforcing: ballistic coefficient too low? Use more propellant. Supersonic retropropulsion is nicely scalable that way. Not good enough mass fraction so far? Refuel more often. After all, you're launching the propellant to Earth orbit using a large RLV, and you're producing the propellant on Mars with an expanding infrastructure (and also using the same large RLV). If you want better IMLEO, you can maneuver the propellant using SEP.

Because MCT is much bigger than the Mars Direct vehicle, it makes the other roles much easier and less marginal.

But just because people were skeptical about Mars Direct doesn't mean it wouldn't have worked. For all the skepticism it generated, its influence is largely mainstream now in NASA, and all subsequent DRMs bear the mark of Mars Direct.

 (BTW, refueling in general is incredibly important: it allows "staging" without needing to reconfigure your vehicle, thus cutting down on the analysis that needs to be done. Also, it means you don't need to design, build, test, and launch a new stage. Mars Direct goes partway by doing surface fueling, but by refueling multiple times in each mission cycle, you can hugely improve the mission cost. And it doesn't even have to require a lot of delta-v in your vehicle---maybe 5km/s--as you can add more delta-v just by refueling.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 10/29/2015 12:55 am
Did you remember to factor in the ISP differences, all thouse SSTO vehicles were going to use Hydro-Lox at 450 ISP.  When you use use that kind of ISP the 9.5 km/s DeltaV requires an 8.62 ratio.  So yes they are quite equivalent.

Oh I think you'd use methane or propane for a pure-rocket (not Skylon) reusable SSTO in real life, liquid hydrogen just isn't worth it, especially since the greater losses on ascent (IIRC) and the huge bulky tankage largely wipe out the advantages.

Their are g-forces, entry corridor width and landing accuracy to consider as well as heating,

MCT is doing propulsive landing not parachute, so it should get a landing accuracy advantage for that.


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if it has dropped enough to not completely consume the entire vehicle mass on it's own. 

Wait, what? Mars re-entry velocities aren't nearly THAT high! The Galileo probe did an entry at over 40 km/s and even it wasn't 100% heat-shield (about 50% IIRC) and that's like x10 the kinetic energy. So how could MCT possibly have to be all heat-shield?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/29/2015 01:07 am
Let me clarify.

Impaler, I don't think your ideas of how to build a reusable upper stage are technically bad, I'm just not at all convinced that that is what SpaceX has in mind, based on their F9 reusable upper stage, their work with Dragon, and their various statements about MCT/BFR. A more integrated system fits very well with statements like this from Musk:
"We’re looking at our Mars transporter being around 15 million pounds of thrust"
(from here: http://forum.nasaspaceflight.com/index.php?topic=37839.msg1391925#msg1391925 )

This is an odd figure for you to bring up because it's not really very relevant to the Integrated vs non Integrated 2nd stage argument.  The thrust is clearly referring to the First stage boosters thrust which would not be all that different.  Lobo seems to be operating under the assumption that the first stage booster is identical in both cases (but I really want to see his numbers on the booster size).

I see a BFR with 12 million pounds of thrust in the core which can be augmented with pairs of raptorized FH boosters with each pair adding 3 million pounds.  That gives a 12, 15, 18 and 21 million pounds of thrust as options.  The no booster configuration would do all the propellant milk-runs, commercial launches etc etc, with the maxed out configurations being used for MCT.  LEO performance (28 degree inclination 200 km circular orbit) would be 110, 140, 168, 193 mT respectively as you add boosters (with full recovery of everything).  To GTO I estimate you would get around 30 after accounting for the boost back to LEO for the stage to be recovered. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/29/2015 01:24 am
Did you remember to factor in the ISP differences, all thouse SSTO vehicles were going to use Hydro-Lox at 450 ISP.  When you use use that kind of ISP the 9.5 km/s DeltaV requires an 8.62 ratio.  So yes they are quite equivalent.

Oh I think you'd use methane or propane for a pure-rocket (not Skylon) reusable SSTO in real life, liquid hydrogen just isn't worth it, especially since the greater losses on ascent (IIRC) and the huge bulky tankage largely wipe out the advantages.

Their are g-forces, entry corridor width and landing accuracy to consider as well as heating,

MCT is doing propulsive landing not parachute, so it should get a landing accuracy advantage for that.


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if it has dropped enough to not completely consume the entire vehicle mass on it's own. 

Wait, what? Mars re-entry velocities aren't nearly THAT high! The Galileo probe did an entry at over 40 km/s and even it wasn't 100% heat-shield (about 50% IIRC) and that's like x10 the kinetic energy. So how could MCT possibly have to be all heat-shield?

I get the sense that I am the only person who dose any research on EDL around here.  Super-sonic-retro-propulsion is not a magic wand that eliminates all your problems and make landing on mars like landing on the moon (aka a purely propulsive operation that you just throw propellant at).

SRP happens AFTER peak drag and heating after >90% of your speed has been dissipated, it basically substitutes for a parachute or SIAD.  It doesn't save you any heat-shield mass or structural mass, it just lets you break out of the parachute size constraint and makes landing safer because your using one system (rocket) for both supersonic and terminal landing rather then having two systems with must operate flawlessly to not crash.

All the thermal, and g-force problems are still present and the systems to mitigate them would be dangerously close to consuming everything that is not the payload and propellants which we need to carry for the later SRP and landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/29/2015 01:28 am
Hypersonic retropropulsion is also possible.

Also, you seem to think that PICA sucks. It is, in fact, one of the highest performing TPSes that exist, used on the highest speed entries, used on Mars Curiosity Rover's hyperbolic entry, and a serious candidate for Orion's heatshield before they went to Avcoat (because they thought they could just do the Apollo-era solution, though now they're going with a tile-based solution anyway). It is very lightweight (I have a sample of it on my desk) and an excellent insulator. You could put it all around your vehicle if you wanted to (though that is not necessary, as even a metallic coating on the Apollo capsule's backshell survived). And SpaceX has made some improvements on it after flying it several times on its own Dragon.

You bring up entry accuracy as if it's still a problem. You read a paper from 1992 and then continue to rehash old problems that have already been solved for probes like MSL Curiosity. Modern tracking means we can get VERY high precision entry accuracy, and adding some spatial positioning satellites (as well as atmospheric monitoring) at Mars can enhance this even more. A huge amount of MSL's dispersion in landing position is due to its use of parachutes, by the way. And in principle, there's no reason a vertical landing rocket can't get within a meter or two of a landing spot (heck, even tens of centimeters is possible and has been demonstrated via GPS). And if SpaceX needs to do a burn before they aerocapture, or if the early missions need to be 120-180 day transits, then so be it. None of these things are the showstoppers you seem to think they are.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/29/2015 02:03 am
I'm well aware that PICA is the best ablative we currently have but neither you nor anyone else who insists it will be used can give me a heat-shield mass for a prospective vehicle and entry profile.  And for the millionth time structural mass counts too and are of a greater concern then the thermal protection systems.

At entry the vehicle will have nearly 50% payload mass, just SRP will require ~20% propellant fraction.  That leaves something like 30% for all the structure, all the TPS, all the engines and tank mass, landing gear, systems used only in space like solar arrays and radiators that have been stowed etc etc.  This is not remotely easy even when you do as I've suggested and enter from mars orbit at just 4 km/s rather then twice as fast or more coming in on direct entry.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/29/2015 02:51 am
I'm well aware that PICA is the best ablative we currently have but neither you nor anyone else who insists it will be used can give me a heat-shield mass for a prospective vehicle and entry profile.
And? Can you give me a heatshield mass estimate? I don't see your estimate. Previous times we estimated the math, we came up with something like:
Dragon has 8cm thick of PICA-X, and when it reentered, barely any of it had burned away. PICA-X is about .27grams/cc. So each square meter would weigh about 20kg. 15 meters by 20 meters of surface is about 6.5 tons of PICA-X. Dragon has a ballistic coefficient of about 1000kg/m^2 (let's arbitrarily set drag coefficient to 1 to allow easier comparison), but if MCT weighs 150-200 tons with payload, then MCT should have a superior ballistic cofficient, almost half as much as Dragon. Of course, there's structure underneath the heatshield to interface the heatshield to the rest of the structure, but I doubt it weighs more than the mass of the PICA-X itself. And if it does, it's a good target for mass optimization, so I'll say 50% of the PICA-X mass. So, about 10 tons for the TPS, another 2 tons for some SPAM on the backshell (if it needs more than just a nice reflective coating) for 12 tons total with an entry mass of 150-200 tons. And by the way, that's for the max 100 ton payload. Nowhere did Musk say 100 day transits for 100 ton payloads! So those are separate things. You'd have slow transits with high payload or fast transits with low payload.

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And for the millionth time structural mass counts too and are of a greater concern then the thermal protection systems.
For the millionth time, pressure stabilization will be used and can be used for the compressive loads. Additionally, tensile structures inside can be made out of high performance materials like Spectra (or certain types of carbon fiber), with a strength-to-weight ratio ten times that of high performance aluminum alloys as well as very high toughness.

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At entry the vehicle will have nearly 50% payload mass, just SRP will require ~20% propellant fraction.  That leaves something like 30% for all the structure, all the TPS, all the engines and tank mass, landing gear, systems used only in space like solar arrays and radiators that have been stowed etc etc.  This is not remotely easy even when you do as I've suggested and enter from mars orbit at just 4 km/s rather then twice as fast or more coming in on direct entry.
3.5km/s, actually, not 4km/s (actually, at the equator, it's more like 3.25km/s). Easy, no, but mars luckily has places with much lower terminal velocity. Valles Marineris is 5km below datum, and Hellas Basin can be 8km below datum. Terminal velocity is proportional to: e^(h/(2*10.8km)) since the scale height of Mars is 10.8km, so at -5km in Valles Marineris, you have a terminal velocity 79% of that at the datum.


Additionally, there's an important thing you have neglected to mention: If MCT has a very large delta-v capability, like 7km/s with a low payload, then you could do a fully propulsive landing with a HUGE payload from low Mars orbit, provided you use strong legs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/29/2015 04:20 am
My whole mass breakdown was pages ago for every part of the vehicle with the justification for each value.

http://forum.nasaspaceflight.com/index.php?topic=37808.msg1433370#msg1433370

This is actually the second time I posted them too.

My mass for metallic TPS that only need to handle the low heating rates of a LMO entry is just 5 kg/m^2 and the area is 650 m^2 (the entire surface excluding the bottom), which would be 3250 kg which I then padded to 5 mT even.  The skin is applied directly over the structural frame and doesn't have an additional backing requirements.


I'm not clear on the shape of your vehicle, is it a circular blunt body Dragon like capsule, why not express the area as a diameter then rather then an arbitrary rectangle.  A 15 m diameter Dragon (the Super Dragon concept) is only an area of 176 m^2 about half the area your specifying.


Pressure stabilization only keeps the propellant tanks from crumpling and their is zero evidence that technique can tolerate that much force and what it will cost in extra tank masses to withstand the pressure, the portion of the vehicle that carries cargo (actually ever portion of the vehicle) also needs to withstand high g-forces.

The altitude to which we need to land cargo has never been specified by Musk, I do not think the vehicle will be restricted to only landing at low altitudes.  Though it may have to lower the payload mass to achieve high altitude landings.  I think the most neutral interpretation is land 100 mT at the Datum but until Musk clarifies we can't say for sure.  Terminal velocity is rather meaningless on Mars as it is super-sonic and quite lethal and you never reach terminal velocity, you switch to propulsion long before you get close to terminal velocity and while still several km from the surface.  Past missions cared a lot about landing altitude because it was so important to parachutes, if we aren't using thouse it matters a lot less.

The last statement really makes no sense, how is MCT full of propellants at entry when you used them all to to depart Earth?  Or are you in favor of SEP tugs bringing it to LMO, a solution I'm considering for Earth return?  You can't bring propellants from the surface of mars, even after establishing a base because your landing solution involves burning ten times more to land then could possibly be delivered to orbit by the MCT's.  At most I could see a MCT bringing enough propellant to orbit to be able to land again say 800 m/s DeltaV which is still a considerable 40 mT by my estimate, which I'm aiming for in my design but we certainly can not do an all propulsive or even mostly propulsive landing.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/29/2015 09:52 pm
We don't know the exact shape of MCT, so I used a ballpark figure. I don't expect it to be better than +100%/-50% accurate, so sure, your 15m-diameter Dragon could work, too. It'd have about the same ballistic coefficient as regular Dragon (with largely-empty tanks).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/29/2015 10:16 pm
...
The last statement really makes no sense, how is MCT full of propellants at entry when you used them all to to depart Earth?  Or are you in favor of SEP tugs bringing it to LMO, a solution I'm considering for Earth return?  You can't bring propellants from the surface of mars...
How does it make no sense when you yourself thought of an acceptable solution? :)

Also, who says you have to use all the propellants to depart Earth? A 100mT uncrewed payload doesn't need to have an especially fast transit.

But yes, I had in mind that you would probably launch the propellant from Mars (especially as a colony is established, this will become increasingly more attractive versus launching it from the surface of Earth). From the surface of Mars to LMO is about 4.1km/s (you could do slightly better, let's leave it at that). To land would take, worst case, about 4.1km/s again (although realistically, about 1km/s less because aerodynamics is helping you, even without a need for significant TPS) for a total of 8.2km/s even with no significant TPS. A Raptor-based booster with a mass ratio of 21 (it would be ~30 for a Falcon Heavy booster, but I give 23.75 given the lower bulk density of methane/LOx, and 21 mass ratio to take into account the mass of the legs and stuff, though that can be less massive on Mars) can give you 11.3km/s, so you have plenty of margin to deliver lots and lots of propellant on the first 4.1km/s leg. I calculate that you can put about 20-25% of your lift-off mass to Mars orbit. But that's with basically zero TPS, so an ideal vehicle with TPS should be able to improve on that. With MCT's TPS (and everything else stripped off to save weight, and using lighter weight legs than regular MCT and maybe a couple less Raptors), you can probably do about that 20-25% figure.


...but you could also get that fuel from Earth. A slow-boat trajectory from Earth to Mars with modest aerocapture and then multi-pass aerobraking would allow a huge amount of propellant to be brought from Earth without needing to send a SEP tug to Mars (although you could have a cislunar SEP tug to improve the efficiency of LEO-to-Earth-Escape if you wanted to).

There's a lot of ways to skin that cat. We don't need to pick a favorite one here, just point out at least one that is acceptable. Relying on a heavily-propulsive-landing is one possible way to allow the occasional 100mT payload to the surface of Mars without that requirement unduly burdening the rest of the MCT requirements. Yet again, the power and versatility of refueling.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/29/2015 10:57 pm
The only real point you've got there is the requirements for landing a dry stage and landing a significant payload on Mars are different, so you'd probably need somewhat beefier legs on MCT than what would be absolutely essential for an empty upper stage. That's true, but not a good enough reason to develop a completely different vehicle

@this.  But I would think that'd be immaterial.  MCT would be landing with 100mt payload on Mars on unprepared regolith.
That would be in the 0.38g of Mars gravity...where the MCT plus payload will still weight less than a dry MCT back on Earth.  Probably weigh less than a dedicated dry S2 back on Earth. 

So the landing gear may not really have to be much different (or different at all).    Dragon 2 is being designed to land on a prepared pad on Earth.  Yet SpaceX seems to be thinking about trying to drop one on the unprepared regolith on Mars.  So the two may not really be different.  Maybe MCT would have larger foot pads and a means of auto-leveling the legs for the uneven surface where they won't need those on a prepared level pad.  But that's not too much difference.

Heck, even if BFR/MCT DOES have 3 effective stages (big booster, reusable 2nd stage, and MCT), you'd still probably want to keep the 2nd stage and MCT /very/ similar in order to avoid having to pay for development of a completely different vehicle, totally different TPS, etc. (as well as the loss of safety since you aren't also testing MCT every time you launch another payload)

Agreed.  I've mentioned this before.  If MCT were a non integrated biconic vehicle on an S2...so it could do full vehicle abort for example, then there's not much reason the S2 couldn't share as many systems with MCT as possible.  Same TPS panels, same landing gear, same landing systems (landing thrusters or a central Raptor capable of operating at sea level) and maybe even the same outer mold line.  If MCT is riding on top of an S2, then it's tanks will be smaller, although it will have volume inside for cargo and hab.  The S2 would have longer tanks, but no need of internal volume.  So they could have similar or the same OML, so that they still are only developing one spaceship, which will have just one EDL profile.  One "flight" trajectory during reentry, one system of landing, etc.  It would look a bit like two MCT's stacked on each other on the booster, with an interstage adaptor which would house the biconic nose of the S2.

Hard to say if that's what SpaceX would do...but it's seems like a way that could help to minimize development and maximize commonality.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 10/29/2015 11:24 pm

I need to see some better figures from you on the total mass and thrust of your BFR concept and the actual mass of this integrated 2nd stage to even get an idea what your LEO performance is and what it's likely to cost, you really can't throw around generic statements like 'lighter' when I have SPECIFIC mass estimates and DeltaV goals.  You need to do more homework to demonstrate this (or show the homework from L2 as I suspect this is where it all is).  The launch vehicle performance calculator http://www.silverbirdastronautics.com/LVperform.html should be the basis for comparison as I've used it for my calculations (median performance estimates only).

Well, that's kind of the problem.  I was told by Chris specifically that I cannot post any pictures or details of the project, since it's been posted to, and discussed on L2.  I checked with him after discussing it in general here, to see how much I could share or say.  Since other members of their group posted our work on L2, it's all pretty much sandboxed in there is what I was told (in no uncertain terms).  So What I do say is more my personal impressions of what we've worked on.  The Integrated biconic MCT was sort of my baby, but fleshed out a lot by the rest of the group, including a lot of performance the mass estimates by guys more knowledgible than me about it.   I'm more of a "concept" guy.  ;-)

I do apologize if I allude to anything I can't expand on.  I'm trying to stay away from doing that because it's poor form. 

But, in general, when I say that the IBMCT will mass less than an MCT + S2, and thus will have more gross LEO capability, that's simple logic.  You aren't duplicating your hardware and systems, like you are with a S2R + MCT.  You have one TPS, not two.  You have two tanks, with one common bulkhead and two domes instead of four tanks with 2 common bulkheads and 4 domes.  You have one set of Raptors rather than two.  You have no interstage adapter between MCT and the S2R.  One have one set of landings legs, rather than two.  So the mass sitting on top of the booster will be less with the IBMCT, just by logic.  So if you assume the same booster for either, then the LEO dry mass to LEO will be less for the integrated vs. non integrated.  You'd need to enlarge the booster for the non integrated design to get the two on par with each other.
IF you were doing a 3 stage to LEO, that might be different.  But you are talking TSTO either way, the only difference is how much total mass is sitting above the booster.  And that will be more with a non integrated system by necessity.


Wait a sec, we are both in favor of Bi-conic entry vehicles for MCT (you convinced me of that), and you can't put anything on top of a bi-conic that is where the heat-shield is, you can't have exposed attachment point for payload, they would melt and I can't see retracting them into doors as being practical either.  The picture we were shown of a F9 reusable upper stage was fatally flawed when it depicted a heat shield on the top of the stage, it is both unstable as an entry vehicle and it provides no attachment, that's why I came up with the petal heat-shield/legs and bottom first entry.

Oh, I think you can put something above a biconic nose.  But I'm not a rocket engineer, so it's above my pay grade to say -how- exactly it would be done.  But SpaceX seemed to think they could do it for their more blunted F9USR.  As far as attachment points in the TPS, didn't the Space Shuttle have 3 attachement points in it's TPS where the ET and propellant lines were attached?  What if you have had some sort of payload adaptor that used 4 such type attachments on the biconic nose?  Maybe something like the Apollo LAS attachment?  (Just with a payload carrier rather than solid LAS).
Dunno...it's just a guess.  But I think it's plausible that real rocket engineers could get it to work, as they got it to work in the 70's for the Space Shuttle.

I don't know about stability for reentry, but both SpaceX and Rocketplane Kistler thought that blunt nosed cylinder would work for reentry.  So I assume there's plausible ways to make that design work.

I'll address you last point when I get more time.  I gotta run now, sorry!


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/30/2015 01:36 am
And remember DC-X demonstrated the Swan Dive maneuver, a transition from slightly angled down nose-first entry to vertical landing. A small aerosurface or two might help if you wanted to go at an even greater angle, but I see nothing that suggests the transition is impossible.

https://www.youtube.com/watch?v=wv9n9Casp1o

BTW, I guess that conceptually, I think of MCT as a less-ambitious version of DC-Y/DeltaClipper/DC-I. Less ambitious because: It wouldn't need to be SSTO (6-8km/s is all that's needed, which makes a HUGE difference vs 9.5km/s... basically it means you can afford TWICE the dry mass including payload!), it uses methane (which in spite of the Isp hit probably would make SSTO easier due to the FAR higher bulk density) instead of hydrogen, and it'd basically always operate in vacuum except for final landing at Earth, thus making an aerospike nozzle unnecessary. But like DC-Y/DC-I, you would have very high delta-V, ability to land on just about any solid, flat surface (especially if prepared... and you can do the preparing via a rover), an option for a cargo bay, and ability to carry crew WITH any-altitude abort capability. If we can figure out how to put abort capability on DC-I's design, then we can put it on MCT (though Mars abort would require Soyuz-style or MER-style rockets for terminal landing of the abort pod, this actually could be done fairly compactly).


Things like a prepared surface or a crane to remove payloads, etc, should be secondary or tertiary concerns. They can be addressed without impacting the main MCT design itself. MCT will necessarily have to rely on some preplaced ground infrastructure. It will be incredibly foolish to hobble the fundamental design just because of the very first mission. If it is a problem, SpaceX can use Dragon to pre-land a rover or a crane, or some one-shot modifications made to MCT to allow it to land on an unprepared surface.

http://www.astronautix.com/lvs/dcy.htm



BTW, if you want an argument why methane (and higher hydrocarbons, like ethylene, which can be made exothermally from methane using the right catalyst) is better than hydrogen for a SSTO vehicle, see here:
http://web.archive.org/web/20130826050557/http://dunnspace.com/alternate_ssto_propellants.htm
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/30/2015 03:52 am
MCT will necessarily have to rely on some preplaced ground infrastructure. It will be incredibly foolish to hobble the fundamental design just because of the very first mission. If it is a problem, SpaceX can use Dragon to pre-land a rover or a crane, or some one-shot modifications made to MCT to allow it to land on an unprepared surface.

No, I *strongly* disagree with this. MCT will need to be capable of landing on unprepared Martian ground. There is no question about it, if you think about it.
1. Otherwise it has no abort capability, and it has no ability to handle off-nominal EDL that put it outside the expected landing area.
2. The heavy equipment necessary for doing the preparing a solid landing pad could not be delivered by a "Red Dragon". It just isn't possible. A tiny rover (MSL size or smaller) cannot do it, other than *maybe* push some small boulders out of the way, and that's not going to help much. The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover.

So while a prepared landing pad for MCT will be of great value to increase the life expectancy of the MCT hardware (engines and landing gear) down the road, you cannot demand it to be there. And any equipment that is able to build MCT pads will by necessity be large enough to need delivery by MCT.

But since (IMO) the first few landed MCTs will likely just one way pathfinder cargo delivery vehicles for ISRU equipment, it also makes sense to at the same time also deliver heavy equipment for soil movement and landing pad preparation. This will allow the next MCTs (that actually are planned to fly again) to land on better "pads".

This is of course challenging for the leg design. It will likely require them to be much shorter and sturdier than F9R legs. Maybe even fixed legs that are integral to the thrust structure with a small spring/dampener element. Imagine the DC-X (below), but slightly shorter legs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/30/2015 04:12 am
I'm not sure you get to have short, stubby legs and rear engine hoverslam landings at the same time on unprepared soil.  Excavation by the plume is a problem.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/30/2015 04:15 am
I'm not sure you get to have short, stubby legs and rear engine hoverslam landings at the same time on unprepared soil.  Excavation by the plume is a problem.

Nobody said it would be easy.  :) There will have to be a engineering trades, but I certainly believe a MCT gear must be very strong - and to save mass, short. Remember that it also needs to be capable of supporting a full propellant load before takeoff.

The legs will need to be more like Dragons legs than F9R.

EDIT: It could certainly end up being the case that no reuse/takeoff from Mars will be practical without having landed on a properly prepared surface, which also needs to be able to support the launch propellant mass. But this goes with my earlier assertions that a Mars outpost will need to be "seeded" with a few not-reused MCTs to deliver initial equipment.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/30/2015 04:29 am
I'm not sure you get to have short, stubby legs and rear engine hoverslam landings at the same time on unprepared soil.  Excavation by the plume is a problem.

Nobody said it would be easy.  :) There will have to be a engineering trades, but I certainly believe a MCT gear must be very strong - and to save mass, short. Remember that it also needs to be capable of supporting a full propellant load before takeoff.

The legs will need to be more like Dragons legs than F9R.
It's not about strength, it's about center of mass and stability;  Excavation by those engines is going to fragment the landing surface erratically, and even a small slope will tip the thing over in a static case, to say nothing of the levering action of actually colliding with the surface.

{Unprepared soil, all thrust from rear engines, small legs}: Pick two if you're lucky, one if you're unlucky in the engineering trade study.  Of the couplets, Unprepared soil / small legs  (but higher engines) seems the hardest, unprepared soil / all thrust from rear engines (but massive wide legs) the middle, and all thrust from rear engines / small legs  (but prepared levelled hard pad) the easiest eventually, but impossible to start with.

IMO we should conservatively assume big legs / unprepared soil / mix of canard and rear engines, because landing at an unprepared site is how the project will start out regardless.  I think the legs have to be *more capable* than F9R's legs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/30/2015 06:52 am
Mostly unprepared underground yes. Maybe some boulders removed. However I watched that NASA workshop about selecting landing sites for manned missions to Mars. For each of the proposed sites it was mentioned that there are flat hard surfaces available to land on. The NASA landers would not be as big as MCT though.

I believe the landing legs won't need to be like the Falcon 9 first stage legs. F9 is long and slender. MCT will be short and stubby in comparison. I believe also that the legs will not need to support MCT fully fuelled for launch. They could add supports for that purpose before tanking takes place.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 10/30/2015 09:37 am
There are a few flat areas of exposed rock on Mars, with limited covering of dust and few stones and boulders.

See e.g. 1057pdf in http://www.nasa.gov/sites/default/files/atoms/files/mars-c-abstracts_in_order_of_presentation10242015_0.pdf (http://www.nasa.gov/sites/default/files/atoms/files/mars-c-abstracts_in_order_of_presentation10242015_0.pdf)

There is probably no need for special preparation of the initial landing site.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 10/30/2015 09:57 am
I'm not sure you get to have short, stubby legs and rear engine hoverslam landings at the same time on unprepared soil.  Excavation by the plume is a problem.

Is the hoverslam an assumption?

They may plan earlier, lower thrusts (requiring good control and variability).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/30/2015 10:03 am
I believe the landing legs won't need to be like the Falcon 9 first stage legs. F9 is long and slender. MCT will be short and stubby in comparison.

However, F9R lands with minimal fuel and lots of engines, making it bottom heavy and therefore more stable. The MCT, at least the biconic version, must be more balanced through its length. Swings'n'roundabouts.

(MCT would be more stable in a belly landing, if you can tolerate the extra mass of dedicated landing engines. Plus tilted (unprepared) ground would put less strain on the legs.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 10/30/2015 12:51 pm
But, in general, when I say that the IBMCT will mass less than an MCT + S2, and thus will have more gross LEO capability, that's simple logic.  You aren't duplicating your hardware and systems, like you are with a S2R + MCT.  You have one TPS, not two. [...]

C'mon, you know you can't linearly sum non-linear systems like that. The systems on two vehicles will be individually lighter (and designed for a lighter vehicle) than the systems on a larger integrated vehicle. For example, the TPS on the second stage will not need to cope with Mars direct-return velocity. Ie, 7km/s instead of 11, or just 40% of the energy and at a lower g-load. Same with all the flow-on effects of requiring larger systems, higher mass, then sturdier structures to deal with the higher mass, increasing the mass further...

So if you assume the same booster for either [...]
IF you were doing a 3 stage to LEO, that might be different.  But you are talking TSTO either way [...]

The MCT has tanks and engines. Why wouldn't you take advantage of that and use it as a third stage to increase payload?

However, for me the clincher is that the if we assume SpaceX take the same incremental approach they did with the development of F9R and Dragon, then the development path goes through the lower requirements of a reusable second stage. Incrementally developing that stage will provide them with key insights in developing the MCT. For example, in theory, a larger stage will be easier to re-enter due to its lower density; but in practice, structural strength has been an issue. Which one dominates in the MCT design?

A less demanding second stage should help them learn as they go. If you can more easily solve the structural issues, you go big - Integrated stage MCT. If structural issues dominate, you split the vehicles - MCT with separate second stage. Developing directly to MCT will invariably involve making decisions early that cause problems later, since you don't know in advance which systems are going to work better than expected and which are going to be harder, more expensive, or higher maintenance.

[Example, SpaceX has apparently found for FH that increasing the performance of the Merlin engines is easier than cross-feed. And for BFR, that more engines on a single core is easier to manage than more cores; which goes against previous industry assumptions.]

The issue isn't "what is the optimum Mars vehicle that I, and my chums on L2, can design", instead it's "what is the likely lowest-cost development path for SpaceX for the whole system". That path goes through a second stage. Where it leads after that... depends on how that second stage performs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/31/2015 12:33 am

No, I *strongly* disagree with this. MCT will need to be capable of landing on unprepared Martian ground. There is no question about it, if you think about it.

In addition to your two points I would add that with the ability to land on unprepared surfaces the MCT would be usable for sub-orbital hops of perhaps several thousand miles and thus serve as a means of rapid transit between base locations and the hinterlands, effectively the same role that helicopters and bush-planes would serve on Earth and we see heavy use of such vehicle in wilderness/pioneering areas.


I do apologize if I allude to anything I can't expand on.  I'm trying to stay away from doing that because it's poor form. 

Understandable but still highly annoying, if you can't show L2 figures here can you take my figures and post them into the L2 discussion and report back the substance of the comparison and reaction to them without actually getting into specifics.  If you need a concise write up I can do that to make the job easier.




And remember DC-X demonstrated the Swan Dive maneuver, a transition from slightly angled down nose-first entry to vertical landing. A small aerosurface or two might help if you wanted to go at an even greater angle, but I see nothing that suggests the transition is impossible.

If this is in reference to a 2nd stage doing nose first re-entry it is misplaced.  My concern is not that the vehicle can not turn in the lower atmosphere once under thrust, that is clearly achievable even if we would prefer to avoid it.  My concern is that the vehicle will tumble during the peak dynamic pressure of entry when it is without thrust and control surfaces are at minimum effectiveness.  A cylindrical body with rounded ends is not stable unless the heavy end is forward, and on a rocket stage the engines are the heavy end so bottom first entry is the preferred method, this is already the method used for the first stage and it experiences a far more mild entry then a 2nd stage would.  DC-X is a conical vehicle and somewhat stable in tip forward configuration when the center of mass is in the rear.  For the MCT itself which I see as being a bi-conic it would have considerable flaps at the bottom/rear of the vehicle to bring the center of drag back closer to the center of mass, also I'm looking at a vehicle much less slender like then the DC-X.



BTW, I guess that conceptually, I think of MCT as a less-ambitious version of DC-Y/DeltaClipper/DC-I. Less ambitious because: It wouldn't need to be SSTO (6-8km/s is all that's needed, which makes a HUGE difference vs 9.5km/s... basically it means you can afford TWICE the dry mass including payload!), it uses methane (which in spite of the Isp hit probably would make SSTO easier due to the FAR higher bulk density) instead of hydrogen, and it'd basically always operate in vacuum except for final landing at Earth, thus making an aerospike nozzle unnecessary.

In general shape yes but you greatly exaggerate the effect propellant density on the vehicles performance.  Propellant density helps in three main ways, thrust density, drag reduction and reduced gravity loss.  All these factors make dense propellants great at launch (even to the point that horrible solid boosters look good), but by the time you get the the altitude of staging (which should be about the same for either the integrated MCT or the separate 2nd stage) these factors are no longer significant and high ISP clearly out-performs.

And as I have said repeatedly, getting 8 km/s DeltaV from Metho-Lox rockets requires the same dry mass fraction as 9.5 km/s requires from a Hydro-Lox vehicle 12% for all vehicle structure and payload.  So this is not significantly easier.

I am favorable to use of Ethane or methyl-acetylene as these would improve bulk density and require less hydrogen/water collection on mars, so long as it dose not foul the engine of course.  Hopefully the Raptor will be able to run on both these propellants and LNG.


I'm not sure you get to have short, stubby legs and rear engine hoverslam landings at the same time on unprepared soil.  Excavation by the plume is a problem.

My solution would be to place around a dozen small vernier engines up on the side about 3/4ths of the way up the vehicle canted outwards where they would not impinge on the ground or the landing gear.  These have just enough thrust to hover the vehicle at landing so the primary propulsion system 'slams' at a height of a 100 m shuts down (after successful start of the verniers is verified) and allows these vernier engines to do the final touchdown at lower speed.  On Earth the Raptor may not be able to fire due to instability and the Verniers may have to fire over a longer period though the lower terminal velocity should help.

These engines also act as orbital maneuvering thrusters and assist in flipping the vehicle from it's nose first entry into landing orientation, the larger number and angle give good leverage and throttle control during touchdown.  Lastly they may be able to fire during assent and reduce or eliminate the need to gimbal the primary Raptor engines which could save some mass and eliminate a point of failure in the hydraulic system.  They do not offer a solution to Raptor plumes impinging on the ground at launch, this will need to be mitigated by site alteration prior to launch, likely via some kind of protective material being placed on the ground.




I believe the landing legs won't need to be like the Falcon 9 first stage legs. F9 is long and slender. MCT will be short and stubby in comparison. I believe also that the legs will not need to support MCT fully fuelled for launch. They could add supports for that purpose before tanking takes place.

I don't think this is likely, the landing mass will be close to 200 mT and take off mass around 400 mT (for my mars orbital rendezvous mission design).  This is a modest enough difference that holding static weight of twice the touchdown should not be a problem as it would easily fall with the necessary structural margin of a rougher landing.

The leg types I see are telescoping pneumatic Shock absorber arrayed around the vehicles outer edges and sloping at an angle matching the outer mold line of the vehicle.  This spreads the legs (6 of them btw) as widely as possible and allows for up to 1 leg to fail.  Being along the outer surface the legs can be very long and extend nearly half the length of the vehicle which will keep the large engine bells from hitting the surface.  The tops of the legs structures will connect to some kind of structural disk/floor in the mid vehicle (where their is either cargo or a structure to support a propellant tank/s in the nose) so the lower portion of the vehicle is clear of intrusions.  In my design the cargo is in the lowest portion of the vehicle making it as bottom heavy as possible during landing.


But, in general, when I say that the IBMCT will mass less than an MCT + S2, and thus will have more gross LEO capability, that's simple logic.  You aren't duplicating your hardware and systems, like you are with a S2R + MCT.  You have one TPS, not two. [...]

C'mon, you know you can't linearly sum non-linear systems like that. The systems on two vehicles will be individually lighter (and designed for a lighter vehicle) than the systems on a larger integrated vehicle. For example, the TPS on the second stage will not need to cope with Mars direct-return velocity. Ie, 7km/s instead of 11, or just 40% of the energy and at a lower g-load. Same with all the flow-on effects of requiring larger systems, higher mass, then sturdier structures to deal with the higher mass, increasing the mass further...

Well said

So if you assume the same booster for either [...]
IF you were doing a 3 stage to LEO, that might be different.  But you are talking TSTO either way [...]

The MCT has tanks and engines. Why wouldn't you take advantage of that and use it as a third stage to increase payload?

However, for me the clincher is that the if we assume SpaceX take the same incremental approach they did with the development of F9R and Dragon, then the development path goes through the lower requirements of a reusable second stage. Incrementally developing that stage will provide them with key insights in developing the MCT. For example, in theory, a larger stage will be easier to re-enter due to its lower density; but in practice, structural strength has been an issue. Which one dominates in the MCT design?

A less demanding second stage should help them learn as they go. If you can more easily solve the structural issues, you go big - Integrated stage MCT. If structural issues dominate, you split the vehicles - MCT with separate second stage. Developing directly to MCT will invariably involve making decisions early that cause problems later, since you don't know in advance which systems are going to work better than expected and which are going to be harder, more expensive, or higher maintenance.

[Example, SpaceX has apparently found for FH that increasing the performance of the Merlin engines is easier than cross-feed. And for BFR, that more engines on a single core is easier to manage than more cores; which goes against previous industry assumptions.]

The issue isn't "what is the optimum Mars vehicle that I, and my chums on L2, can design", instead it's "what is the likely lowest-cost development path for SpaceX for the whole system". That path goes through a second stage. Where it leads after that... depends on how that second stage performs.

I've considered using MCT tanks for 3rd stage benefits, it might be worth 2-3 km/s if full at launch.  But in manned launches I believe it would make MCT too massive for rapid abort.  Some propellant would be needed for that abort, around 20-40 mT I estimate and this is allowed for in sizing the whole launch vehicle.  In a cargo launch it is an option and provides some margin in case of a premature 2nd stage shutdown, or it may be of assistance in raising a ~200 km orbit up to ~400 km where rendezvous with SEP would need to take place due to drag on such vehicles being dangerous below this level.

The rest of your post I strongly agree with, SpaceX needs a spiral development path not a single miracle vehicle that springs from our foreheads like Athena.  I've been thinking about what comes before and after the primary lander (aka MCT), the stuff before it should help retire risk and make money, and the things after it should act as force multipliers to get more cargo and people to mars at lower cost then could be done with just a single vehicle type.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 10/31/2015 01:04 am
My take is if the second stage can come back through the thicker earth's atmosphere, and land in the heavier gravity than Mars, then it should be easy to modify for the MCT, thus serving two purposes.  Bottom half could be the same.  Top half would either be empty for a payload, or the modular MCT cargo, human habitation, and solar panels for power along with the metholox production equipment. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bob Shaw on 10/31/2015 01:21 am

The issue isn't "what is the optimum Mars vehicle that I, and my chums on L2, can design", instead it's "what is the likely lowest-cost development path for SpaceX for the whole system". That path goes through a second stage. Where it leads after that... depends on how that second stage performs.

This is exactly the way that SpaceX operates - they have learned the Soviet incremental approach to goals, but with vertically integrated manufacturing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/31/2015 01:24 am
My take is if the second stage can come back through the thicker earth's atmosphere, and land in the heavier gravity than Mars, then it should be easy to modify for the MCT, thus serving two purposes.  Bottom half could be the same.  Top half would either be empty for a payload, or the modular MCT cargo, human habitation, and solar panels for power along with the metholox production equipment.
Right, we are in violent agreement. :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/31/2015 01:35 am
Impaler:

My analysis comes from Dunn's work comparing SSTO propellants. I am not exaggerating the improvement in mass ratio you get for using methane/LOx over hydrolox. For the same dry mass and tank size, you can get 2.25 times the propellant using methane (plus you don't need thick insulation), thus more than doubling your mass ratio. Sure, you get 15-20% higher Isp with hydrolox, but the 2.25x mass ratio of methane/LOx can overcome that advantage, even with the logarithm. See here: http://web.archive.org/web/20130826050557/http://dunnspace.com/alternate_ssto_propellants.htm

Another advantage over hydrogen is that to produce a certain mass of methane/LOx takes much less water and power than does producing the same mass hydrolox propellant.

And instead of ethane or propyne (shorter name for methylacetylene), propylene would be a better propellant because it can be fairly easily made on Mars and gets nearly the same performance as propyne. Propylene and ethylene (often coproduced when synthesizing from Methane) also can be easily polymerized to make structures on Mars. Of course, with these higher hydrocarbons you lose some of the advantage methane has in being highly resistant to coking.


Additionally, 8km/s is a lot easier to achieve in vacuum (higher Isp) when you don't need an T/W ratio greater than 1 (means you also don't need to throttle down as much). But 8km/s is at the VERY high end that I think MCT would be capable of. More likely 6-7.5km/s (6km/s is /just/ enough to do a direct return to Earth from Mars surface on a slow trajectory using an equatorial launch site).



...and for the record, building an SSTO RLV isn't impossible, just difficult. Especially at sea level.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/31/2015 02:02 am
...
The issue isn't "what is the optimum Mars vehicle that I, and my chums on L2, can design", instead it's "what is the likely lowest-cost development path for SpaceX for the whole system". That path goes through a second stage. Where it leads after that... depends on how that second stage performs.

Put some cargo doors on that second stage, and we're in violent agreement.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 10/31/2015 03:18 am
In addition to your two points I would add that with the ability to land on unprepared surfaces the MCT would be usable for sub-orbital hops of perhaps several thousand miles and thus serve as a means of rapid transit between base locations and the hinterlands, effectively the same role that helicopters and bush-planes would serve on Earth and we see heavy use of such vehicle in wilderness/pioneering areas.

No an expensive massive spacecraft like MCT would not be used in such a way. Regardless of whether or not it can land on an unprepared surface, landing pads will be built after the first one lands if it can't be done by equipment delivered by Dragons.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/31/2015 03:23 am

The issue isn't "what is the optimum Mars vehicle that I, and my chums on L2, can design", instead it's "what is the likely lowest-cost development path for SpaceX for the whole system". That path goes through a second stage. Where it leads after that... depends on how that second stage performs.

This is exactly the way that SpaceX operates - they have learned the Soviet incremental approach to goals, but with vertically integrated manufacturing.

Soviet's were/are vertically integrated too, I think the key difference is SpaceX has brought much higher quality control then they ever had in their heyday (and it has now got to crap).  Also SpaceX brought in the standard American light tanks that the Soviets never had or needed because their engines were/are so superior.  By combining the two SpaceX can actually contemplate reusable rocket that still have a payload.

But yes basically the SpaceX philosophy is WWKD "What Would Korolev Do", where as the rest of the industry takes after Wernher von Braun who in typical German fashion goes for maximum performance at any price.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 10/31/2015 05:04 am
For the same dry mass and tank size

That's the major flaw in the work your siting, at equal volume the difference in propellant density means a huge difference in gross take off weight and gross vehicle weight would follow that relationship not remain static.  And costs scale with dry vehicle weight not volume so it is simply not a fair comparison.

If your backing off to a hohmann transfer speed direct from mars that would indeed be ~6 km/s and comes in at a dry mass fraction of 20%, considerably more reasonable and well below the mass fraction of SSTO vehicles of any propellant, if you were to include an efficient aerocapture system like magneto-plasma I could even see this vehicle being possible all be it optimistic.  But the transit time is now no good for passengers, only cargo.

But this dose give me an idea, if you were to take my concept which targets LMO 4 km/s when carrying the Musk specified 25 mT cargo and instead carry no cargo it should be right at that 6 km/s DeltaV.  As I've always assumed the 25 mT return is for passenger and no geological samples or martian wine exports it means that very few MCT will actually have this return cargo burden thus allowing them to do direct return to Earth all be it bone-dry and needing refueling in LEO to be able to land.



I see a nominal mission working something like this.  MCT with cargo is placed in LEO, 2 SEP tugs are placed in LEO, both are loaded with Xenon themselves and one is loaded with chemical propellants as a tanker, the other carries the MCT.  Both tugs to to EML1, propellant transferred to MCT, crew is launched on cis-lunar Dragon and sent to rendezvous and transfer to MCT.  MCT dose Earth swing-by burn to a 150 day transfer trajectory.

Tugs return to LEO and are refilled this time with both of them carrying chemical propellant loads, both spiral out and do fully electric powered transfer to mars arriving long after the MCT but just prior to Earth-Mars alignment.  MCT having produced/loaded propellant at mars launches to LMO 4 km/s, take on propellants from both tugs to reach full propellant load again and performs burn of another 4 km/s for another 150 day transfer to Earth.  SEP tugs return to Earth under electric power in time for next conjunction.

Cargo flights start in a similar manor but at EML1 each propellant carrying tug can service 2 cargo carrying MCTs.  At mars the MCTs do direct return empty of cargo so no SEP tugs need to transit to mars. 

For both manned and cargo flights the cadence is once every other synod for initial missions, later as infrastructure allows a more rapid cadence may be possible using an opposition return trajectory for the unmanned cargo MCT's if a propellant depot can be employed at mars and some MCT's tasked with running propellant too it.  In many years (looks like 40% of the time) it would still not be possible to get the vehicle back in time for the next launch window as opposition return is always slow.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/31/2015 12:51 pm
For the same dry mass and tank size

That's the major flaw in the work your siting, at equal volume the difference in propellant density means a huge difference in gross take off weight and gross vehicle weight would follow that relationship not remain static.  And costs scale with dry vehicle weight not volume so it is simply not a fair comparison....
Dry vehicle weight, to first order, scales with volume (look at the pressure vessel equation), so it is a fair comparison. Did you read my link?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MP99 on 10/31/2015 01:21 pm
Quick thought that I haven't seen anyone mention.

When ISS visiting vehicles are opened up, the crew wear masks to avoid floating debris - and this is after the loading crews make efforts to avoid contamination.

For a crew that are living out of MCT on the surface, or even just making occasional visits, ISTM they will trek in a lot more debris than the CRS vehicles suffer.

How would this be mitigated? Crew wear masks and the ventilation turned to max to filter the air as quickly as possible?

Cheers, Martin
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 10/31/2015 02:03 pm
Quick thought that I haven't seen anyone mention.

When ISS visiting vehicles are opened up, the crew wear masks to avoid floating debris - and this is after the loading crews make efforts to avoid contamination.

For a crew that are living out of MCT on the surface, or even just making occasional visits, ISTM they will trek in a lot more debris than the CRS vehicles suffer.

How would this be mitigated? Crew wear masks and the ventilation turned to max to filter the air as quickly as possible?

Cheers, Martin

Checkout the thread where NASA is looking into this:

Mars Surface Tunnel Element Concept

http://forum.nasaspaceflight.com/index.php?topic=38733.0 (http://forum.nasaspaceflight.com/index.php?topic=38733.0)

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150019637.pdf (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150019637.pdf)

One possibility for MCT would be to use suit port spacesuits in a suit lock airlock. Instead of the suit ports being directly exposed to the outside, they are located in an airlock. This also protects the suits from reentry and takeoff. Nothing from the surface is ever brought into the crew areas. The only exception would be a little dust getting in if an incapacitated astronaut had to be carried in from the suit lock. As long as astronauts can pull themselves out of their suits no one ever has to enter the contaminated suit lock.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MP99 on 10/31/2015 04:27 pm
Thanks - I had seen that, and it helps.

But I am assuming that so much habitable volume may be used throughout its stay on the surface, and humans generate a lot of debris just in day to day living and eating.

Of course, they will do the same during transit in zero g, but the transition from surface to orbit could release debris created throughout the surface stay.

I guess this is an issue that Apollo had to deal with.

Cheers, Martin
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/31/2015 04:59 pm
The reason they wear facemasks when opening CRS vehicles is because in zero-gee, stuff floats around and you could inhale it (also, there's a worry of stale air or some sort of outgasing). Even very slight gravity would mitigate those effects (there'd be natural convection and debris would pretty much just fall to the ground) such that facemasks would not be required.


...of course, if you have a lot of dust tracked in to your airlock, that would probably make some sort of simple mask a good idea even with Earth gravity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MP99 on 10/31/2015 05:04 pm


The reason they wear facemasks when opening CRS vehicles is because in zero-gee, stuff floats around and you could inhale it...

Yup, that was exactly what I was discussing. Human occupation of the MCT on Mars' surface will create a debris problem once it's launched back to LMO.

Cheers, Martin
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/31/2015 05:08 pm


The reason they wear facemasks when opening CRS vehicles is because in zero-gee, stuff floats around and you could inhale it...

Yup, that was exactly what I was discussing. Human occupation of the MCT on Mars' surface will create a debris problem once it's launched back to LMO.

Cheers, Martin
Oh, right. Once a base is set up with separate habs, you'd probably have a time when you'd clean out the MCT before launch. Swab the deck, etc. Before that, with small crews and such, you'd probably wear dust masks when you got in orbit.

Anyway, we have a VERY good historical analogue: what did Apollo do? They tracked a bunch of dust inside, since they had a one-room lander.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/31/2015 05:25 pm
...The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover....

Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.

But anyway, it doesn't have to take a large rover. Something the size of a Bobcat can do a LOT of work, and that could be landed on Mars using Red Dragon. From Ames' Red Dragon research, Dragon would be capable of landing at least 2 tons. Bobcats weigh about 1-2 tons, and the vast majority of their mass is steel. Aerospace alloys and composites can have a strength-to-weight ratio about 20 times as great as steel, thus allowing your 2 ton mass budget to land a MUCH more capable vehicle than a typical bobcat. And like a bobcat, you'd use ballast boxes filled with Mars regolith to increase your traction. This could give you the equivalent of, say, a 10-20 ton bulldozer. Of course, you'd also need to land a solar array set to recharge from and you'd want to use lithium-sulfur batteries (500Wh/kg) or something like that.

I don't think you've actually thought through exactly how big of something you could land on Mars using Red Dragon. Given Dragon's fairly large internal volume and 1-2 ton payload capability, it could be quite significant indeed, enough to do some serious civil engineering.


And I know as a matter of fact that research is being done to see how to build a prepared landing pad using a rover and in-situ rocks. Even if we're limited to something like a Bobcat, there's a LOT that can be done, especially with the right landing site.

EDIT: See this tweet:
https://twitter.com/DrPhiltill/status/659882680943775744
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Hauerg on 10/31/2015 05:28 pm
15 years ago I had a bobcat working around my house. I fail to see how you get that into the and out of the Dragon 2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 10/31/2015 07:03 pm
15 years ago I had a bobcat working around my house. I fail to see how you get that into the and out of the Dragon 2.

Yeah, Red Dragon is a good idea for getting some experiments to Mars without having to design a custom lander, but something like a small robotic bulldozer will need a custom lander.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: cro-magnon gramps on 10/31/2015 07:42 pm
15 years ago I had a bobcat working around my house. I fail to see how you get that into the and out of the Dragon 2.

Yeah, Red Dragon is a good idea for getting some experiments to Mars without having to design a custom lander, but something like a small robotic bulldozer will need a custom lander.

Give it to a guy from CREME; the Creme' de la Creme' and he'll find a way... anyway, whatever is happening with Red Dragon is happening behind "THE CURTAINS" at SpaceX and as we have been told, we'd think them crazy for what they are working on.. a Bobcat in a Dragon may be one of the lessor crazy stunts they want to work on... my Samhain Celebration opinion  :o in other words, you give Engineers too little credit for their ingenuity / ability to improvise a successful outcome...

Cheers and a Merry Samhain to all and sundry...

Gramps
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/31/2015 09:26 pm
...The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover....

Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.


1) MRO can resolve objects of "about a meter across", but not in good enough detail to build a DEM with them;  That can only work with much larger surfaces, or with a big program of shadow inference at dawn/dusk.  Nevertheless, MRO is not the last imaging satellite we will send to Mars.  Let's dismiss that point.
2) MRO cannot resolve objects that are belowground before MCT's landing engines expose them.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 10/31/2015 09:37 pm
It seems like SpaceX went to some pain to eliminate hydrazine RCS from Falcon 9, replacing it with compressed nitrogen at a much poorer performance level.

What exactly would be used for high-frequency, low-latency thrust in an MCT?  One of the ideas I'm tossing around is supplementing the massive methalox tanks & Raptor engines with a moderate amount of hydrazine + NTO, and using SuperDracos.  This fulfills the need for RCS (which I don't think raptors are suited for), does not introduce any new engines (which SpaceX have specified: they're only working on one) and gives some thermal benefits relative to methalox alternatives.

An alternative might be one of the upcoming green propellant blends.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 10/31/2015 09:47 pm
I am quite sure they will use pressure fed methalox thrusters for RCS. The pressurized tanks can be small and get refilled from the main tanks when needed. The morpheus moon lander testbed has not only the main engine but methalox thrusters too. I would not see this as a contradiction to working on one engine only. Thrusters are not engines in that sense.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 10/31/2015 09:50 pm
It seems like SpaceX went to some pain to eliminate hydrazine RCS from Falcon 9, replacing it with compressed nitrogen at a much poorer performance level.

What exactly would be used for high-frequency, low-latency thrust in an MCT?  One of the ideas I'm tossing around is supplementing the massive methalox tanks & Raptor engines with a moderate amount of hydrazine + NTO, and using SuperDracos.  This fulfills the need for RCS (which I don't think raptors are suited for), does not introduce any new engines (which SpaceX have specified: they're only working on one) and gives some thermal benefits relative to methalox alternatives.

An alternative might be one of the upcoming green propellant blends.

The obvious answer seems to be pressurized MethaLOX, if is it practical. A smaller set of tanks pressurized at a igh pressure. But whatever is chosen, it would have to be something that could be made from ISRU at Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/31/2015 10:57 pm
15 years ago I had a bobcat working around my house. I fail to see how you get that into the and out of the Dragon 2.
Red Dragon would necessarily have modifications to allow egress of equipment.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 10/31/2015 10:59 pm
...The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover....

Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.


1) MRO can resolve objects of "about a meter across"...
MRO has a resolution of ~30cm per pixel. Multiple exposures of the same site from different angles and ESPECIALLY with the Sun at high angles (thus casting long shadows) can identify hazards.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/01/2015 12:01 am
I am quite sure they will use pressure fed methalox thrusters for RCS. The pressurized tanks can be small and get refilled from the main tanks when needed. The morpheus moon lander testbed has not only the main engine but methalox thrusters too. I would not see this as a contradiction to working on one engine only. Thrusters are not engines in that sense.

Agreed, drawing off the common propellant supply and using a small pressurization vessel sounds good, but do the pumps have to do the pressurizing or would you rely on a pressurant gas obtainable on mars such as CO2, or perhaps generate gaseous O2 and Methane to pressurize each tank respectively?  The piston-pump system XCOR developed looks like it might be an interesting way to go.

I'd place these thrusters around the vehicles nose/flanks so they can perform the final touch-down without cratering the ground.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 11/01/2015 01:35 am
If your backing off to a hohmann transfer speed direct from mars that would indeed be ~6 km/s and comes in at a dry mass fraction of 20%, considerably more reasonable and well below the mass fraction of SSTO vehicles of any propellant, if you were to include an efficient aerocapture system like magneto-plasma I could even see this vehicle being possible all be it optimistic.  But the transit time is now no good for passengers, only cargo.

I dunno, 8-9 months in zero-g isn't THAT bad, the Russians have done 14 months and that guy (Valeri Polyakov)  was able to walk out of the capsule afterwards.

Radiation would be an issue of what regulations they have to deal with, probably not a "real" concern - those cancers develop so slow that you're talking 2050-60 medical tech ... so modern estimates of death risk from them are meaningless.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 11/01/2015 03:47 am
...The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover....

Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.


1) MRO can resolve objects of "about a meter across"...
MRO has a resolution of ~30cm per pixel. Multiple exposures of the same site from different angles and ESPECIALLY with the Sun at high angles (thus casting long shadows) can identify hazards.

Perhaps, but that kind of coverage does not exist. Yes. And even when it does, it tells you nothing about the relative strength of the surface. It could be the Martian equivalent of quicksand for all we know.

But it is still irrelevant. MCT will need to be able to land on unprepared terrain, it will be necessary to allow of off-nominal EDL and abort scenarios. So it will need a sturdy gear, and you seem reluctant for some reason to admit that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/01/2015 04:16 am
Probably because it's another nail in the idea that MCT will have single digit dry mass percentage.

Lets look at what landing gear will likely mass.  The primary driver is touchdown mass which would be 100 mT + vehicle dry mass + reserves from the landing propellants.  I'd call that all 200 mT, and no we do not get to deduct because of mars gravity, the vehicle has kinetic energy at touchdown which is independent of gravity.  If you expect a hover-slam landing like F9 the vehicle would experience comparable stress.

The landing legs on F9R are said to be 10% of the empty stage mass (and that's with use of carbon-fiber) so I take this as my basis for MCT legs structure.  Around 20 mT, though I expect them to telescope inside the vehicle rather then be on the surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 11/01/2015 07:57 am
Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.


1) MRO can resolve objects of "about a meter across"...
MRO has a resolution of ~30cm per pixel. Multiple exposures of the same site from different angles and ESPECIALLY with the Sun at high angles (thus casting long shadows) can identify hazards.

Perhaps, but that kind of coverage does not exist. Yes. And even when it does, it tells you nothing about the relative strength of the surface. It could be the Martian equivalent of quicksand for all we know.

But it is still irrelevant. MCT will need to be able to land on unprepared terrain, it will be necessary to allow of off-nominal EDL and abort scenarios. So it will need a sturdy gear, and you seem reluctant for some reason to admit that.

You should have watched the NASA workshop for selecting Mars landing sites. They do know a lot. They have identified landing spots with a hard surface that allow for safe landing. They do have a lot of coverage for different kinds of observation already and the teams can request more observations for each of the proposed 40 landing sites. They can do very thorough orbital survey for multiple data once they have narrowed down to few potential sites.

MCT will certainly not need to be designed for landing on any not suitable off target landing sites so don't try to include such requirements into your mass budget.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/01/2015 08:19 am
How much mass would we need for a canard-engine landing, like a 'Sky Crane' but without separation?

Let's take a SuperDraco.  A dry mass of 300 tons delivered to ~1km above the surface at zero velocity, needs maybe 1G capability to land on Mars after main engine cutoff.  I've seen the SuperDraco compared to a pair of AJ-10 thrusters at 100kg each, but "probably lighter, given modern construction methods".  If SuperDraco masses 100kg total and produces 73kN, a TWR of 73, then 1G hoverslam requires 41 engines plus some propellant.  Round that up to 48 engines given that they need to carry their own mass, so 300 + 48 = 348T;  I'm inclined to say terminal landing dV needs are going to be somewhere in the 30m/s to 300m/s range - adding between 1.1% and 11.5% propellant load to the dry mass assuming ~280s Isp (a blind guess as to soft vacuum performance of optimized SD).  Take the higher of those estimates and we arrive at 388 tons for a terminal retrorocket burn from canard engines, a 29.3% increase in dry mass.

Speculating further:  An object delivered to ~1km above the surface at zero velocity, and capable of 1G acceleration, is easy to model (or at least approximate, without doing more abstract math) for minimum delta V to land under the Martian 3.7m/s^2 gravity using a suicide burn.  Absent intervention it will impact the ground at 23.25 seconds at a velocity of 86m/s by the equations governing freefall acceleration.  If the vehicle is capable of 9.8m/s^2 acceleration, that's 8.77 seconds of thrust to cancel out that velocity, adding an additional 32.5m/s of gravity loss, which takes an additional 3.3 seconds of thrust, adding an additional 12.2m/s of gravity loss, which takes an additional 1.2 seconds of thrust, adding an additional 4.4m/s of gravity loss, which takes an additional 0.45 seconds of thrust, adding an additional 1.7m/s of gravity loss, at which point you're close enough with a sum of 136.8m/s and a thrust time of 13.7 seconds.

At 280s Isp and 348t dry mass, 136.8m/s can be accomplished with a wet mass of 367.1t;  That means you can achieve canard engine landing for ~22.3% extra mass.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/01/2015 08:46 am
Oy, I seem to have forgotten to account for cosine losses.  I expect I could accomplish that by simply canting all the canard engines 30 degrees off vertical, and assuming they produce (3^0.5)/2 times as much thrust, or 86.6%, with 86.6% as much Isp as well.

Maintaining the 1G acceleration capability, that corrects to ~56 engines & ~243s Isp, a dry mass of 356 tons and a wet mass of 377 tons.  25.7% mass premium over a full rear engine landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/01/2015 09:29 am
Wooo, your landing mass is more like 200 mT, not 300 and your going to use Raptor engines for all your deceleration and bring yourself to a hover at 100 m from the surface.  The touchdown engines are not slamming your into the surface they are just countering the gravity on mars and giving you fine control to maneuver around any boulders.

The thrust total your projecting is more then an entire Raptor engine would produce, if we needed or wanted that much we wouldn't bother with these vernier engines so I think you've mixed up some where (several some wheres?), for example you make each engine weight 1 mT when you were adding them to the vehicles mass.

A 200 mT lander on mars has a weight of 744 kN meaning you need just 10 Super Draco engine equivalents which means 1 mT and no significant impact to the landers dry mass.  Their would be some cosine loss too but I actually expect an improved engine running on Methane to be employed improving the thrust as well as a touchdown mass of just 175 mT.  The propellant for a few seconds of touchdown (20 seconds at mars gravity would be 75 m/s) is not going to be significant propellant fraction, though obviously a significant portion was burned prior to this by the Raptor engine, that is a separate calculation unaffected by our choice of touchdown systems.

On Earth were going to be lighter by 75 mT and we would be landing on a concrete pad so we can have a little higher speed at touch down and we might very briefly throttle up right at touchdown too.  I've doubtful that Raptor can safely fire in atmosphere but if I'm wrong then it would certainly be used here when their is no danger of debris from the surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/01/2015 09:57 am
Wooo, your landing mass is more like 200 mT, not 300 and your going to use Raptor engines for all your deceleration and bring yourself to a hover at 100 m from the surface.  The touchdown engines are not slamming your into the surface they are just countering the gravity on mars and giving you fine control to maneuver around any boulders.

The thrust total your projecting is more then an entire Raptor engine would produce, if we needed or wanted that much we wouldn't bother with these vernier engines so I think you've mixed up some where (several some wheres?), for example you make each engine weight 1 mT when you were adding them to the vehicles mass.

A 200 mT lander on mars has a weight of 744 kN meaning you need just 10 Super Draco engine equivalents which means 1 mT and no significant impact to the landers dry mass.  Their would be some cosine loss too but I actually expect an improved engine running on Methane to be employed improving the thrust as well as a touchdown mass of just 175 mT.  The propellant for a few seconds of touchdown (20 seconds at mars gravity would be 75 m/s) is not going to be significant propellant fraction, though obviously a significant portion was burned prior to this by the Raptor engine, that is a separate calculation unaffected by our choice of touchdown systems.

On Earth were going to be lighter by 75 mT and we would be landing on a concrete pad so we can have a little higher speed at touch down and we might very briefly throttle up right at touchdown too.  I've doubtful that Raptor can safely fire in atmosphere but if I'm wrong then it would certainly be used here when their is no danger of debris from the surface.
Ahh, I knew that sounded like a lot.  Thanks for spotting the error - 10 times too much mass allocated to engines.  That should bring the extra mass margin down below +10%.

If you're trying to avoid unprepared landing site excavation issues, you need space for the exhaust plume to spread out a bit.  I picked ~1km for a very rough & arbitrary figure.  At 100m, the exhaust plume is barely larger than the vehicle fairing diameter.  Shut the main engines down at 1km AGL after doing the full job of entry & descent, and they won't destroy the landing pad.  Then drop for a bit (now's a nice time to correct to vertical and unfurl the legs), & start controlled thrusting on the sideways-canted canard engines;  Any terrain damage they do will be well away from the place the legs impact the ground.  They still need plenty of thrust, however.  If they were only capable of precisely Mars gravity acceleration, they could hover at this 1km point, but not descend (because they could never correct for that additional velocity);  Pure gravity loss.  To minimize gravity loss they need substantially larger thrust in order to accomplish an efficient suicide burn.

EDIT: To clear up your confusion, a supplementary set of engines towards the top of the vehicle ("Canard engines") are intended to solve the problems raised in posts like this http://forum.nasaspaceflight.com/index.php?topic=37466.msg1372150#msg1372150 .  As a secondary point, they might be used if a nested MAV design turns out to be needed because of low ISRU mass payoffs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 11/01/2015 12:03 pm
The set of eight superdracos on Dragon 2 could land 100mT on Mars with margin to spare, once velocity is reduced to near zero by the Raptor engines.  Scaling these engines up and fueling them with methlox should provide the fine control needed for landing.  Could be used to lift-off the surface, too, before the large, centerline engine(s) are started.  This technology/approach could be useful for a reusable lander that explores undeveloped sites.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/01/2015 12:13 pm
The set of eight superdracos on Dragon 2 could land 100mT on Mars with margin to spare, once velocity is reduced to near zero by the Raptor engines.  Scaling these engines up and fueling them with methlox should provide the fine control needed for landing.  Could be used to lift-off the surface, too, before the large, centerline engine(s) are started.  This technology/approach could be useful for a reusable lander that explores undeveloped sites.

I would *really like* to employ them in an integrated single-vehicle system for liftoff, but that would also mean a hell of a lot more of them.  Liftoff thrust requirements are a large multiple of landing thrust requirements.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 11/01/2015 12:25 pm
The set of eight superdracos on Dragon 2 could land 100mT on Mars with margin to spare, once velocity is reduced to near zero by the Raptor engines.  Scaling these engines up and fueling them with methlox should provide the fine control needed for landing.  Could be used to lift-off the surface, too, before the large, centerline engine(s) are started.  This technology/approach could be useful for a reusable lander that explores undeveloped sites.

I would *really like* to employ them in an integrated single-vehicle system for liftoff, but that would also mean a hell of a lot more of them.  Liftoff thrust requirements are a large multiple of landing thrust requirements.

If you've off-loaded 100mT of cargo and taken on equivalent fuel, the lift-off problem is same as landing.  Why are lift-off thrust requirements 'a large multiple' of landing?  You only need to clear the ground by 100m (and maybe move laterally a bit)...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 11/01/2015 01:42 pm
Could be used to lift-off the surface, too, before the large, centerline engine(s) are started.
I would *really like* to employ them in an integrated single-vehicle system for liftoff, but that would also mean a hell of a lot more of them.  Liftoff thrust requirements are a large multiple of landing thrust requirements.
If you've off-loaded 100mT of cargo and taken on equivalent fuel, the lift-off problem is same as landing.

To reach TEI from Mars surface, you're looking at around 400 tonnes of fuel (depending on dry-mass). Additionally, launch needs to be at 2-3 g to reduce gravity losses. So minimum 2*9.8*500 = 9.3MN. So over 130 Super-Dracos just to reach 100m. (Hell, 25 just to hover.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/01/2015 01:49 pm
The set of eight superdracos on Dragon 2 could land 100mT on Mars with margin to spare, once velocity is reduced to near zero by the Raptor engines.  Scaling these engines up and fueling them with methlox should provide the fine control needed for landing.  Could be used to lift-off the surface, too, before the large, centerline engine(s) are started.  This technology/approach could be useful for a reusable lander that explores undeveloped sites.

I would *really like* to employ them in an integrated single-vehicle system for liftoff, but that would also mean a hell of a lot more of them.  Liftoff thrust requirements are a large multiple of landing thrust requirements.

If you've off-loaded 100mT of cargo and taken on equivalent fuel, the lift-off problem is same as landing.  Why are lift-off thrust requirements 'a large multiple' of landing?  You only need to clear the ground by 100m (and maybe move laterally a bit)...

Because of all that methalox!  At landing the vehicle is near the penultimate dry mass.  At liftoff it's at around 3.35x the dry mass (in the case of 380s Isp & LMO refueling at ~4.5km/s dV), or 6.55x the dry mass (in the case of 380s Isp & no LMO refueling with Hohmann transfer home at ~7km/s dV) or more (in fast transit cases without LMO refueling).

This translates directly into proportionately higher thrust.  This higher thrust figure is achievable, but the sheer weight of the engines required adds quite a bit to the vehicle.

Admittedly, you need lower acceleration at liftoff than at landing;  I need to do further math on this.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 11/01/2015 02:26 pm
The set of eight superdracos on Dragon 2 could land 100mT on Mars with margin to spare, once velocity is reduced to near zero by the Raptor engines.  Scaling these engines up and fueling them with methlox should provide the fine control needed for landing.  Could be used to lift-off the surface, too, before the large, centerline engine(s) are started.  This technology/approach could be useful for a reusable lander that explores undeveloped sites.

I would *really like* to employ them in an integrated single-vehicle system for liftoff, but that would also mean a hell of a lot more of them.  Liftoff thrust requirements are a large multiple of landing thrust requirements.

If you've off-loaded 100mT of cargo and taken on equivalent fuel, the lift-off problem is same as landing.  Why are lift-off thrust requirements 'a large multiple' of landing?  You only need to clear the ground by 100m (and maybe move laterally a bit)...

Because of all that methalox!  At landing the vehicle is near the penultimate dry mass.  At liftoff it's at around 3.35x the dry mass (in the case of 380s Isp & LMO refueling at ~4.5km/s dV), or 6.55x the dry mass (in the case of 380s Isp & no LMO refueling with Hohmann transfer home at ~7km/s dV) or more (in fast transit cases without LMO refueling).

This translates directly into proportionately higher thrust.  This higher thrust figure is achievable, but the sheer weight of the engines required adds quite a bit to the vehicle.

Admittedly, you need lower acceleration at liftoff than at landing;  I need to do further math on this.

Not true... a 100mT payload plus the vehicle dry weight (~25mT?) at landing -- at lift-off, 25mT plus 4x propellant gives same mass as at landing. (Sorry for the gross approximations.)  This gets you back to LMO where you fuel-n-go for Hohmann transfer home.  If vehicle is a lander, it refuels in LMO and prepares for another descent to the surface.

The 'sheer weight' of a set of 8 superdracos is less than 1mT if I recall correctly.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 11/01/2015 02:39 pm
Could be used to lift-off the surface, too, before the large, centerline engine(s) are started.
I would *really like* to employ them in an integrated single-vehicle system for liftoff, but that would also mean a hell of a lot more of them.  Liftoff thrust requirements are a large multiple of landing thrust requirements.
If you've off-loaded 100mT of cargo and taken on equivalent fuel, the lift-off problem is same as landing.

To reach TEI from Mars surface, you're looking at around 400 tonnes of fuel (depending on dry-mass). Additionally, launch needs to be at 2-3 g to reduce gravity losses. So minimum 2*9.8*500 = 9.3MN. So over 130 Super-Dracos just to reach 100m. (Hell, 25 just to hover.)

Isn't 'g' equal to 9.8*0.38 on Mars?  And why does launch have to be at 2-3 Martian gs -- only 1.2g is typical from Earth's surface?

You need to lift the craft off the ground to 100m or so (at an increment above 0.38g) before the Raptor firing to return to LMO (scenario we are discussing).  Even if the 25 to hover is accepted, which I don't, this is just a 3x increase in superdraco power... not a show-stopper (superdracos were a 200x scale-up from dracos).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 11/01/2015 03:05 pm
But it is still irrelevant. MCT will need to be able to land on unprepared terrain, it will be necessary to allow of off-nominal EDL and abort scenarios. So it will need a sturdy gear, and you seem reluctant for some reason to admit that.

It might be needed for the first MCT. It's not required to get people or cargo to Mars after that. It's an optional safety feature not a requirement.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 11/01/2015 03:58 pm
Musk is borrowing somewhat from Mars Direct (or is it Semi-Direct?) where an already-fueled ascent vehicle is fueled up on the surface. I don't see a good reason not to have a fueled up vehicle ready when they arrive.

I see no reason why to land the fuel production equipment at all.
It can do the same job on orbit.

you have said it yourself:
 http://forum.nasaspaceflight.com/index.php?topic=17984.msg620589#msg620589
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 11/01/2015 06:02 pm
Perhaps, but that kind of coverage does not exist. Yes. And even when it does, it tells you nothing about the relative strength of the surface. It could be the Martian equivalent of quicksand for all we know.

But it is still irrelevant. MCT will need to be able to land on unprepared terrain, it will be necessary to allow of off-nominal EDL and abort scenarios. So it will need a sturdy gear, and you seem reluctant for some reason to admit that.

You should have watched the NASA workshop for selecting Mars landing sites. They do know a lot. They have identified landing spots with a hard surface that allow for safe landing. They do have a lot of coverage for different kinds of observation already and the teams can request more observations for each of the proposed 40 landing sites. They can do very thorough orbital survey for multiple data once they have narrowed down to few potential sites.

I did watch many of those workshops. And I also know that observations from the above is not as comprehensive as one might think, unless one also has ground observations to validate them. And if you have any reference of how they can judge the hardness of a surface (brittle and compressible vs hard as granite), then please link to the presentation where they show that.

MCT will certainly not need to be designed for landing on any not suitable off target landing sites so don't try to include such requirements into your mass budget.

If you are willing to claim that no off-nominal landing will ever happen, nor be planned for, then go ahead. I'm not part of the crowd that cries for a useless abort system, but I do think a sturdier landing gear with some extra margin is mass well spent. Extra margin to allow landing on marginal sites during an emergency/off-nominal, NOT any site on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 11/01/2015 06:12 pm
I did watch many of those workshops. And I also know that observations from the above is not as comprehensive as one might think, unless one also has ground observations to validate them. And if you have any reference of how they can judge the hardness of a surface (brittle and compressible vs hard as granite), then please link to the presentation where they show that.

Available hard surfaces for landing were mentioned in many presentations. And emphasized in general discussion. Of course you can chose not to believe them.


If you are willing to claim that no off-nominal landing will ever happen, nor be planned for, then go ahead. I'm not part of the crowd that cries for a useless abort system, but I do think a sturdier landing gear with some extra margin is mass well spent. Extra margin to allow landing on marginal sites during an emergency/off-nominal, NOT any site on Mars.


Of course off-nominal landing can and will happen. It is not to be expected that MCT will survive those undamaged. It is enough that the passengers have a chance to survive. When landing off-nominal that MCT will never fly again. Landing gear will always have margin, no need to add anything.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/01/2015 07:03 pm
The set of eight superdracos on Dragon 2 could land 100mT on Mars with margin to spare, once velocity is reduced to near zero by the Raptor engines.  Scaling these engines up and fueling them with methlox should provide the fine control needed for landing.  Could be used to lift-off the surface, too, before the large, centerline engine(s) are started.  This technology/approach could be useful for a reusable lander that explores undeveloped sites.

I would *really like* to employ them in an integrated single-vehicle system for liftoff, but that would also mean a hell of a lot more of them.  Liftoff thrust requirements are a large multiple of landing thrust requirements.

If you've off-loaded 100mT of cargo and taken on equivalent fuel, the lift-off problem is same as landing.  Why are lift-off thrust requirements 'a large multiple' of landing?  You only need to clear the ground by 100m (and maybe move laterally a bit)...

Because of all that methalox!  At landing the vehicle is near the penultimate dry mass.  At liftoff it's at around 3.35x the dry mass (in the case of 380s Isp & LMO refueling at ~4.5km/s dV), or 6.55x the dry mass (in the case of 380s Isp & no LMO refueling with Hohmann transfer home at ~7km/s dV) or more (in fast transit cases without LMO refueling).

This translates directly into proportionately higher thrust.  This higher thrust figure is achievable, but the sheer weight of the engines required adds quite a bit to the vehicle.

Admittedly, you need lower acceleration at liftoff than at landing;  I need to do further math on this.

Not true... a 100mT payload plus the vehicle dry weight (~25mT?) at landing -- at lift-off, 25mT plus 4x propellant gives same mass as at landing. (Sorry for the gross approximations.)  This gets you back to LMO where you fuel-n-go for Hohmann transfer home.  If vehicle is a lander, it refuels in LMO and prepares for another descent to the surface.

The 'sheer weight' of a set of 8 superdracos is less than 1mT if I recall correctly.

Vehicle structural dry weight of 25mT is, in my judgement, about an order of magnitude too low for a reusable lander with integrated habitat that brings 100mT payload to the surface.  Yes, there's a question about whether ISRU gear is inside or outside the '100mT useful cargo' box, but the weight of the vehicle alone is at 100mT-200mT in most other people's scenarios, I just favor raising it to 300mT-500mT with my own special sauce.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/01/2015 08:32 pm

Ahh, I knew that sounded like a lot.  Thanks for spotting the error - 10 times too much mass allocated to engines.  That should bring the extra mass margin down below +10%.

If you're trying to avoid unprepared landing site excavation issues, you need space for the exhaust plume to spread out a bit.  I picked ~1km for a very rough & arbitrary figure.  At 100m, the exhaust plume is barely larger than the vehicle fairing diameter.  Shut the main engines down at 1km AGL after doing the full job of entry & descent, and they won't destroy the landing pad.  Then drop for a bit (now's a nice time to correct to vertical and unfurl the legs), & start controlled thrusting on the sideways-canted canard engines;  Any terrain damage they do will be well away from the place the legs impact the ground.  They still need plenty of thrust, however.  If they were only capable of precisely Mars gravity acceleration, they could hover at this 1km point, but not descend (because they could never correct for that additional velocity);  Pure gravity loss.  To minimize gravity loss they need substantially larger thrust in order to accomplish an efficient suicide burn.

EDIT: To clear up your confusion, a supplementary set of engines towards the top of the vehicle ("Canard engines") are intended to solve the problems raised in posts like this http://forum.nasaspaceflight.com/index.php?topic=37466.msg1372150#msg1372150 .  As a secondary point, they might be used if a nested MAV design turns out to be needed because of low ISRU mass payoffs.

I think 1 km is far too high an elevation to start worrying about plumes impinging the ground.  A large rocket lifting off the ground is not still bathing the launch pad in flames when it is 1 km up, rather it looks to be mostly over within 1-2 times the height of the launch tower. 

Remember our goal as you point out is to avoid making craters in the ground and making dangerous ejecta which might impact the vehicle, at 100 m height their should be no danger to the vehicle even if some sand and dust are being swept up on the surface.  Under the near vacuum conditions of mars the plume will also spread MUCH wider then the vehicles base, just as the plume of a rocket expands markedly as it rises, it will never resemble the 'welding torch' look of a rocket at liftoff on Earth.

Your right that we would need slightly more then 1 G so that we can actually reach a true zero speed or something close too it.  Apollo lander was designed for 3 m/s vertical touch-down speed.  If started at that speed when Raptors cut out then we used propulsion exactly equaling mars gravity we would descend for 30 seconds at 3 m/s.


Also it occurs to me that one of the most significant differences between a landing system designed for hard landing pads and regolith is going to be the foot-pad area necessary.  On soft soil much larger pads will be needed to avoid penetrating to deeply into the ground.  We need to know (or estimate) the bearing strength of the surface which is something we really need to know for any effective ground vehicle design.  In addition you need to be able to handle a modest amount of slope or to accommodate differential soil strength which results in uneven amounts of leg penetration.

Here is a paper looking at the landing system for a hopper vehicle which would have some harsh un-improved landing site goals.  http://solarsystem.nasa.gov/docs/Gullotta_Resettable%20Landing%20Gear%20for%20Mars%20Hopper.pdf

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/01/2015 09:31 pm
Well that's hilariously awful.  Per your link, current leg design for all landers to date actually crushes the footpads to absorb impact energy.

The leg actuation & damper is an interesting question;  Pneumatics are out in a vacuum, per the link.  I have seen assertions that we would just operate with a consummable pneumatic/hydraulic reserve, but they are not quantified and I'm skeptical about the ability to hold leg position for an 18 month deployment.  In my (completely unresearched) musings on the subject I resorted to mechanical linkages strung with actuated wire winches.  Those electric winches perform damping in convenient radial motion rather than the linear solenoid depicted.  As a bonus, you can use a gearbox for leverage against constant stresses, and still have shock absorption (even shock absorption in a large range of spring constants) from a tensioning spring (https://en.wikipedia.org/wiki/Tensioner) wheel.  All solid, vacuum-safe, microgravity-safe materials, all usable without consumables.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: meekGee on 11/01/2015 09:32 pm

...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


I'm catching up on this thread so apologies for necro-quoting, but is this a widely shared opinion?  Basically that by the time SpaceX is ready with BFR, they will not be ready with a mission for it?

Or did you mean that NASA is the only conceivable customer other than SpaceX itself?

I can't be 100% sure that the first BFR mission will head to Mars, but I'm pretty sure there won't be a "good long time" (years?) in which BFR is used commercially before it used for MCTs to Mars.   I can see how maybe during off-season they are used for commercial purposes since why not, but they are built for a purpose, and I expect the Mars program to be pretty efficient in that things will mature by the time they are needed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/01/2015 09:38 pm

Ahh, I knew that sounded like a lot.  Thanks for spotting the error - 10 times too much mass allocated to engines.  That should bring the extra mass margin down below +10%.

If you're trying to avoid unprepared landing site excavation issues, you need space for the exhaust plume to spread out a bit.  I picked ~1km for a very rough & arbitrary figure.  At 100m, the exhaust plume is barely larger than the vehicle fairing diameter.  Shut the main engines down at 1km AGL after doing the full job of entry & descent, and they won't destroy the landing pad.  Then drop for a bit (now's a nice time to correct to vertical and unfurl the legs), & start controlled thrusting on the sideways-canted canard engines;  Any terrain damage they do will be well away from the place the legs impact the ground.  They still need plenty of thrust, however.  If they were only capable of precisely Mars gravity acceleration, they could hover at this 1km point, but not descend (because they could never correct for that additional velocity);  Pure gravity loss.  To minimize gravity loss they need substantially larger thrust in order to accomplish an efficient suicide burn.

EDIT: To clear up your confusion, a supplementary set of engines towards the top of the vehicle ("Canard engines") are intended to solve the problems raised in posts like this http://forum.nasaspaceflight.com/index.php?topic=37466.msg1372150#msg1372150 .  As a secondary point, they might be used if a nested MAV design turns out to be needed because of low ISRU mass payoffs.

I think 1 km is far too high an elevation to start worrying about plumes impinging the ground.  A large rocket lifting off the ground is not still bathing the launch pad in flames when it is 1 km up, rather it looks to be mostly over within 1-2 times the height of the launch tower. 

Remember our goal as you point out is to avoid making craters in the ground and making dangerous ejecta which might impact the vehicle, at 100 m height their should be no danger to the vehicle even if some sand and dust are being swept up on the surface.  Under the near vacuum conditions of mars the plume will also spread MUCH wider then the vehicles base, just as the plume of a rocket expands markedly as it rises, it will never resemble the 'welding torch' look of a rocket at liftoff on Earth.

Ahh, but you have to remember: "Bathed in flames" is not the standard.  You can only see flames where the exhaust gasses exist as a hot plasma, but they do not cease to exist farther down the plume as they cool down.  Massflow per unit surface area is the standard.  You could dig a big ditch with an 8400kN cold gas thruster too.

Either way: 1km is not prohibitive, so lesser figures are also achievable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 11/01/2015 09:50 pm

...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


I'm catching up on this thread so apologies for necro-quoting, but is this a widely shared opinion?  Basically that by the time SpaceX is ready with BFR, they will not be ready with a mission for it?

Or did you mean that NASA is the only conceivable customer other than SpaceX itself?

I can't be 100% sure that the first BFR mission will head to Mars, but I'm pretty sure there won't be a "good long time" (years?) in which BFR is used commercially before it used for MCTs to Mars.   I can see how maybe during off-season they are used for commercial purposes since why not, but they are built for a purpose, and I expect the Mars program to be pretty efficient in that things will mature by the time they are needed.

I, for one, don't expect SpaceX to sell any purely commercial flights (comm sats, for instance) on BFR before heading to Mars.  Exceptions could be flights that advance the technology toward Mars such as large Bigelow habs, or Lunar technology demos, fuel depots, etc.  I think they will schedule (maybe quietly) trips at a sequence of Mars conjunctions, including the BFR when it is ready, and NASA will (maybe not so quietly) climb aboard.

If SpaceX advances the timeline by a large factor and scales up the scope of the expeditions, NASA will not pass up the opportunity to be aboard -- they won't wait until 32 SLS launches are funded (if ever) and 2039 rolls around.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/01/2015 09:52 pm

...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


I'm catching up on this thread so apologies for necro-quoting, but is this a widely shared opinion?  Basically that by the time SpaceX is ready with BFR, they will not be ready with a mission for it?

Or did you mean that NASA is the only conceivable customer other than SpaceX itself?

I can't be 100% sure that the first BFR mission will head to Mars, but I'm pretty sure there won't be a "good long time" (years?) in which BFR is used commercially before it used for MCTs to Mars.   I can see how maybe during off-season they are used for commercial purposes since why not, but they are built for a purpose, and I expect the Mars program to be pretty efficient in that things will mature by the time they are needed.

The business case and usage schedule is far more up in the air than than even the technical details of BFR & MCT.  We don't have high-quality speculation to offer.  All we know is that BFR launches will be cheaper with high launch rate than with low launch rate.  On this basis and on the expectation that only a long record of successful unmanned launches proves safety of a manned launch vehicle to *my satisfaction*, I expect them to seek out whatever customers they can.  It's arguably a prerequisite that they find these customers, before scaling up the Mars project;  For that matter, the business viability of the Mars project as a private passenger delivery system without Apollo-grade Congressional outlays is... questionable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 11/01/2015 10:12 pm

Vehicle structural dry weight of 25mT is, in my judgement, about an order of magnitude too low for a reusable lander with integrated habitat that brings 100mT payload to the surface.  Yes, there's a question about whether ISRU gear is inside or outside the '100mT useful cargo' box, but the weight of the vehicle alone is at 100mT-200mT in most other people's scenarios, I just favor raising it to 300mT-500mT with my own special sauce.

The point is that a set of eight superdracos such as is installed on the (existing) Dragon 2 can land 125mT of payload on Mars, given that the Raptor engines have slowed the vehicle to near zero at a nominal distance above the ground.  If the vehicle itself is somewhere between 100 and 200mT (say 150) and the delivered payload is 100mT, then double the Dragon 2 complement will do the job nicely.  Doubling the complement, four quads instead of four pairs, or doubling the thrust of a pair seems to be an easy step technically.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MP99 on 11/01/2015 11:10 pm



Vehicle structural dry weight of 25mT is, in my judgement, about an order of magnitude too low for a reusable lander with integrated habitat that brings 100mT payload to the surface.  Yes, there's a question about whether ISRU gear is inside or outside the '100mT useful cargo' box, but the weight of the vehicle alone is at 100mT-200mT in most other people's scenarios, I just favor raising it to 300mT-500mT with my own special sauce.

The point is that a set of eight superdracos such as is installed on the (existing) Dragon 2 can land 125mT of payload on Mars, given that the Raptor engines have slowed the vehicle to near zero at a nominal distance above the ground.  If the vehicle itself is somewhere between 100 and 200mT (say 150) and the delivered payload is 100mT, then double the Dragon 2 complement will do the job nicely.  Doubling the complement, four quads instead of four pairs, or doubling the thrust of a pair seems to be an easy step technically.

ISTM the SDs could have a vacuum nozzle for Mars, with associated Isp & thrust benefits.

Cheers, Martin
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/02/2015 12:20 am

...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


I'm catching up on this thread so apologies for necro-quoting, but is this a widely shared opinion?  Basically that by the time SpaceX is ready with BFR, they will not be ready with a mission for it?

Or did you mean that NASA is the only conceivable customer other than SpaceX itself?

I can't be 100% sure that the first BFR mission will head to Mars, but I'm pretty sure there won't be a "good long time" (years?) in which BFR is used commercially before it used for MCTs to Mars.   I can see how maybe during off-season they are used for commercial purposes since why not, but they are built for a purpose, and I expect the Mars program to be pretty efficient in that things will mature by the time they are needed.

The business case and usage schedule is far more up in the air than than even the technical details of BFR & MCT.  We don't have high-quality speculation to offer.  All we know is that BFR launches will be cheaper with high launch rate than with low launch rate.  On this basis and on the expectation that only a long record of successful unmanned launches proves safety of a manned launch vehicle to *my satisfaction*, I expect them to seek out whatever customers they can.  It's arguably a prerequisite that they find these customers, before scaling up the Mars project;  For that matter, the business viability of the Mars project as a private passenger delivery system without Apollo-grade Congressional outlays is... questionable.

Burninate you put your finger on the reasons the system needs to find some non-mars bound commercial business, basically cost amortization and flight history build up.  I would also add that splitting development up over time, having experience with large reusable vehicles that survive high speed entry at Earth before trying it on Mars, and finally having a the launchers lift capacity fully characterized and upgraded to it's maximum potential so you know your ceiling mass for the MCT.

To clarify my prior post, I think NASA (in the course of a large Congressionaly funded mars mission) is the only conceivable first customer for a mars transport system.  That transport system will be both the rocket and a mars lander and possibly other transport elements provided by SpaceX (such as SEP tugs, Propellant production equipment).   Think of it like Mars-COTS, SpaceX schleps people & cargo for NASA under contract. 

This is the only way SpaceX can actually make any revenue from mars, they might be able to direct their satellite launch profits into vehicle development but actually run the system they need huge payments at low volume and government is the only possible customer during that start up period even if you want to sell to private interest later, just as we are under no illusions that Dragon capsule would have been developed without the COTS program.

SpaceX will control the whole payload interface of the BFR and mars bound vehicle and design it for their goals, and these will probably not resemble any current interfaces, so NASA will design all of the cargo it wants sent to mars around the SpaceX vehicles cargo capacity both in terms of mass and volume.  That is going to take time and money and training, billions of dollars and perhaps a decade.

But NASA can't actually do anything like that when it is saddled with the Orion/SLS millstone which basically sucks up all it's money.  The BFR can lift this off NASA's shoulders IF it can match all the SLS capabilities, is drastically cheaper, safer AND SpaceX is manufacturing in enough states to get support or at least defuse opposition in the senate to the cancellation of these programs.  SLS won't go away until BFR has a solid launch history, the political forces will always be able to justify keeping it going if SpaceX isn't superior in every metric.

So the first priority is to get SLS retired, everyone knows that SLS and BFR would be in direct competition and the universe is not big enough for them both.  If SpaceX get BFR up and running quickly I could see SLS being canceled in about a decade after a few flights, probably ARM as a face-saving last mission.  That opens up $3 billion a year for actual mars systems.  Meanwhile SpaceX will be well into designing the mars bound vehicle/s and a it will be both politically and economically easy to slip into a parallel development course in which SpaceX finishes the mars vehicle while NASA gives out contracts for surface system development as consolation prizes to the folks who lose out when SLS/Orion ended.  In another 10 years both are done and your ready to land on mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: meekGee on 11/02/2015 02:41 am
But we know that SpaceX, even in the fast build-up scenario, needs to send multiple unmanned payloads to Mars first.

BFR is an Earth-to-orbit vehicle, and so you're not risking a two-year delay when you first launch it.  Yes, the first launch may not carry an MCT, but by the same token, it won't carry any other one-of-a-kind payload.  Being reusable, it's a complete non-brainer to fly a dummy payload.  If it works, you you relaunch.  It it doesn't, good thing you didn't.

Actually, once you're shifted to a reusable rocket, test flights are cheap enough that you could do multiple dummy payloads before you put an MCT on top - and it's not like you wasted multiple rockets doing it.

So I think the "build up flight history" argument doesn't apply.


...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


I'm catching up on this thread so apologies for necro-quoting, but is this a widely shared opinion?  Basically that by the time SpaceX is ready with BFR, they will not be ready with a mission for it?

Or did you mean that NASA is the only conceivable customer other than SpaceX itself?

I can't be 100% sure that the first BFR mission will head to Mars, but I'm pretty sure there won't be a "good long time" (years?) in which BFR is used commercially before it used for MCTs to Mars.   I can see how maybe during off-season they are used for commercial purposes since why not, but they are built for a purpose, and I expect the Mars program to be pretty efficient in that things will mature by the time they are needed.

The business case and usage schedule is far more up in the air than than even the technical details of BFR & MCT.  We don't have high-quality speculation to offer.  All we know is that BFR launches will be cheaper with high launch rate than with low launch rate.  On this basis and on the expectation that only a long record of successful unmanned launches proves safety of a manned launch vehicle to *my satisfaction*, I expect them to seek out whatever customers they can.  It's arguably a prerequisite that they find these customers, before scaling up the Mars project;  For that matter, the business viability of the Mars project as a private passenger delivery system without Apollo-grade Congressional outlays is... questionable.

Burninate you put your finger on the reasons the system needs to find some non-mars bound commercial business, basically cost amortization and flight history build up.  I would also add that splitting development up over time, having experience with large reusable vehicles that survive high speed entry at Earth before trying it on Mars, and finally having a the launchers lift capacity fully characterized and upgraded to it's maximum potential so you know your ceiling mass for the MCT.

To clarify my prior post, I think NASA (in the course of a large Congressionaly funded mars mission) is the only conceivable first customer for a mars transport system.  That transport system will be both the rocket and a mars lander and possibly other transport elements provided by SpaceX (such as SEP tugs, Propellant production equipment).   Think of it like Mars-COTS, SpaceX schleps people & cargo for NASA under contract. 

This is the only way SpaceX can actually make any revenue from mars, they might be able to direct their satellite launch profits into vehicle development but actually run the system they need huge payments at low volume and government is the only possible customer during that start up period even if you want to sell to private interest later, just as we are under no illusions that Dragon capsule would have been developed without the COTS program.

SpaceX will control the whole payload interface of the BFR and mars bound vehicle and design it for their goals, and these will probably not resemble any current interfaces, so NASA will design all of the cargo it wants sent to mars around the SpaceX vehicles cargo capacity both in terms of mass and volume.  That is going to take time and money and training, billions of dollars and perhaps a decade.

But NASA can't actually do anything like that when it is saddled with the Orion/SLS millstone which basically sucks up all it's money.  The BFR can lift this off NASA's shoulders IF it can match all the SLS capabilities, is drastically cheaper, safer AND SpaceX is manufacturing in enough states to get support or at least defuse opposition in the senate to the cancellation of these programs.  SLS won't go away until BFR has a solid launch history, the political forces will always be able to justify keeping it going if SpaceX isn't superior in every metric.

So the first priority is to get SLS retired, everyone knows that SLS and BFR would be in direct competition and the universe is not big enough for them both.  If SpaceX get BFR up and running quickly I could see SLS being canceled in about a decade after a few flights, probably ARM as a face-saving last mission.  That opens up $3 billion a year for actual mars systems.  Meanwhile SpaceX will be well into designing the mars bound vehicle/s and a it will be both politically and economically easy to slip into a parallel development course in which SpaceX finishes the mars vehicle while NASA gives out contracts for surface system development as consolation prizes to the folks who lose out when SLS/Orion ended.  In another 10 years both are done and your ready to land on mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/02/2015 03:53 am
But we know that SpaceX, even in the fast build-up scenario, needs to send multiple unmanned payloads to Mars first.

BFR is an Earth-to-orbit vehicle, and so you're not risking a two-year delay when you first launch it.  Yes, the first launch may not carry an MCT, but by the same token, it won't carry any other one-of-a-kind payload.  Being reusable, it's a complete non-brainer to fly a dummy payload.  If it works, you you relaunch.  It it doesn't, good thing you didn't.

Actually, once you're shifted to a reusable rocket, test flights are cheap enough that you could do multiple dummy payloads before you put an MCT on top - and it's not like you wasted multiple rockets doing it.

So I think the "build up flight history" argument doesn't apply.

It will be cheaper per kg to LEO, but it is by no means going to be cheap enough to build an adequate flight history (~12 launches) with nothing but dummy payloads all at SpaceX's own expense.  A rocket is typically tested only once with a dummy payload with subsequent launches being with paid customers who have satellites.  I expect prices of ~200 million per launch even with recovery (about $1000 per kg, Musk's optimistic goal) so it would cost Billions to do these launches without customers.

I expect that 1st stage recovered will be attempted on every single BFR flight with very likely full success from the start.  If first stage recovery works on the dummy flight and is declared a solved problem then the price point will likely be set such that SpaceX is fully covering the cost of the 2nd stage in case it is lost as I expect 2nd stage recover to require a long campaign of attempts with lots of failures and redesigns as we have seen with F9, the customer will not care any more about the success or failure of these recovery attempts any more then they care about 1st stage recovery attempts now. 

By the time you have your 12 flight history your close to getting the 2nd stage to recover reliably and can drop the price to perhaps 100 million and try to get more volume.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 11/02/2015 07:36 am

...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


Is this a widely shared opinion? 

Developing BFR and MCT is a huge investment by SpaceX. I dont think they can make it without picking up money in some fashion along the way. Even the internet satellite constellation cant do that much on the time scales that are envisioned. Hell, BFR might even be used to get it to orbit.

My expectation is, that the first version of BFR will be a vehicle, purely used for commercial satellites. BFRv1 would be shorter than the one used for Mars and less capable of course. I expect it to have an early version of the Raptor engine, maybe even less engines in total. I also expect that a cargo version of MCT will ride BFR as an integrated second stage. It would have no pressurized volume, but large cargo doors to release satellites in orbit, up to GTO. It would be re-usable, test reentry and landing systems and would be a precursor to MCT in general.

I dont think SpaceX will be able to fund BFR to Mars from the get go. Not even if NASA hitches a ride. Development and production of BFR is way too expensive. They need tons of tests before cargo can be send to Mars for real. Better use BFR commercially as early as possible and refine designes on the way. Thats how SpaceX operated in the past and I assume will continue to operate in the future. Look at the development of Falcon 9 and Dragon. Its the same story, I expect history to repeate it self.

I voiced that view in before and from experience, most users here on the forum disagree with that view.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 11/02/2015 10:12 am
But we know that SpaceX, even in the fast build-up scenario, needs to send multiple unmanned payloads to Mars first.

BFR is an Earth-to-orbit vehicle, and so you're not risking a two-year delay when you first launch it.  Yes, the first launch may not carry an MCT, but by the same token, it won't carry any other one-of-a-kind payload.  Being reusable, it's a complete non-brainer to fly a dummy payload.  If it works, you you relaunch.  It it doesn't, good thing you didn't.

Actually, once you're shifted to a reusable rocket, test flights are cheap enough that you could do multiple dummy payloads before you put an MCT on top - and it's not like you wasted multiple rockets doing it.

So I think the "build up flight history" argument doesn't apply.

<snip>

Maybe not a MCT. But using the BFR tooling SpaceX can make an austere BFR upper stage with one Raptor Vac and an adopter for the current fairing. An interim upper stage suitable for most interplanetary missions.

Hmm a 300 to 400 mT restartable upper stage should have some kick.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 11/02/2015 11:27 am
NASA is planning to fly crew on SLS flight #2... where is the 12 flight requirement originating?

If twelve flights are needed, hundreds (thousands) of tons of fuel and precursor hardware/infrastructure can and probably will be positioned in advance of first crewed expeditions to Mars. NASA will be aboard the entire way, but the timeline and scale will be SpaceX's.

This is not your father's flags and footprints 'mission.'
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 11/02/2015 12:09 pm

...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


I'm catching up on this thread so apologies for necro-quoting, but is this a widely shared opinion?  Basically that by the time SpaceX is ready with BFR, they will not be ready with a mission for it?

Speaking for myself, I don't think that.

There are several people talking about BFR being for other missions first. I personally suspect most don't agree that would happen, but since we know we're about to learn a whole lot soon it's not hugely valuable to argue it. And absolutely I could be wrong.

However, I should qualify what I think a little.

I think the plan for Mars has no room for 10 years of BFR side missions, the plan has no room for distracting from the prime goal of Mars colonisation. But I think the plan has many big asterisks in it with the note "insert huge investment here". Musk is likely playing several angles on where that investment comes from, and no doubt space based commercial activity is part of it (since it already is...).

Musk's comment to the Royal Astronautical Society was headlined as 80,000 people on Mars, which he clarified was wrong and changed to a million... "more like 80,000 a year". But reading the calculations he was talking about a portion of GDP,  $36billion a year, and he wasn't saying for 1 year. He also spoke about charging $500,000 for the trip (which people misunderstood and put together, dividing 500,000 into $40billion to get 80,000 people.) 

That's best argued in the financing thread of course! but I read it as $36billion a year in addition to ongoing individual trip costs.

So there's a huge amount of money he wants to make this happen. It's not going to come easy.  At some stage he will be making commercial deals using his developed technology. But I just don't see that as being part of "the plan" per se. I would possibly concede that the argument made by Semmel and others may be a way of raising funds, but it's not an MCT design speculation, it's a MCT or colony funding speculation.

And on that financing note... I don't think he'll make even a small portion of $36billion a year from BFR launches ... so he has a bigger challenge for funding, and adding this kind of implementation distraction could have some significant negatives.

edit: I should note that Semmel, Burminate and others do relate it back to the funding issues too. But I believe their argument falls into the trap that Musk is trying to avoid... and that's shifting the focus from Mars. The focus needs to be Mars in order for the ideal Mars design to be aimed for, AND for inspiring the population to buy into the vision and be willing to support it. (That doesn't mean it might not end up being necessary for the BFR to serve other uses.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 11/02/2015 01:38 pm
GregA, we dont necessarily have a disagreement here. I dont think that BFR will be derailed by requirements that are unrelated to Mars. Unlike the space shuttle, which was designed to do crazy stuff that never happened.
But I do think that SpaceX will take opportunities as they arise. And they can only take them with a satellite delivery system to LEO and GTO. It provides nice revenue for reentry and landing tests that would otherwise be without a paying customer. Therefore, I do expect SpaceX to create 5 versions for MCT, all based on the same concept.
1: MCT-Satellite: Satellite delivery system as a pathfinder to create revenue and as a test lab for the 3 following MCTs:
2: MCT-Tanker: Tanker version for refulling. Direct offspring of MCT-Satellite, initially tested with MCT-Satellite. Will enable MCT-Satellite to do deep space missions.
3: MCT-Cargo: Cargo version for Mars, no life support, no pressurized volume, pure cargo transport. Direct offspring of MCT-Satellite, will also be the first MCT to land on Mars
4: MCT-Crew: Early crew version of MCT. Very limited living room for exploration missions. Offspring of MCT-Cargo and Crew Dragon.
5: MCT-Coll: The true collonial transporter, designed for colonization and many people. Probably no cargo at all Direct offspring from MCT-Crew.

MCT-Tanker, MCT-Cargo and MCT-Coll are what SpaceX is aiming for. But they need MCT-Satellite as pathfinder, both for finencial and engineering reasons. I dont see them coming up with a ready to go Mars fleet. Doing MCT-Satellite can do a lot of the testing they need anyway. MCT-Crew is basically the same as MCT-Coll, just with less living space and more space for redundency, equipmit of all sorts and in general outfitted for high survivability instead of large number of crew. It will evenutally phase out. MCT-Satellite will probably be around for a long time, simply because it makes sense to use BFR to launch satellites. Once a reusable system is developed, it makes no sense to also create a disposable fairing-based launcher.

I also expect the performance of BFR and Raptor to increase over time, similarly to F9. For MCT-Satellite, not the same level of performance as for the others is needed. So it is ok if BFR is not up to the collonial task right from the beginning.

Still, all this development is pointed directly at Mars. But the steps I think will happen are a little smaller than most of the folk here think.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 11/02/2015 01:54 pm
If SpaceX went that route, I would expect the first version of the BFR would be a scaled up Falcon, but with Raptor engines. Nine engine first stage and one engine second stage. That would make a good reusable satellite launcher and a possible Falcon Heavy replacement. Once they have experience with that system, then it's time for a full up BFR and MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 11/02/2015 02:16 pm

Developing BFR and MCT is a huge investment by SpaceX. I dont think they can make it without picking up money in some fashion along the way. Even the internet satellite constellation cant do that much on the time scales that are envisioned. Hell, BFR might even be used to get it to orbit.

My expectation is, that the first version of BFR will be a vehicle, purely used for commercial satellites. BFRv1 would be shorter than the one used for Mars and less capable of course. I expect it to have an early version of the Raptor engine, maybe even less engines in total. I also expect that a cargo version of MCT will ride BFR as an integrated second stage. It would have no pressurized volume, but large cargo doors to release satellites in orbit, up to GTO. It would be re-usable, test reentry and landing systems and would be a precursor to MCT in general.

I dont think SpaceX will be able to fund BFR to Mars from the get go. Not even if NASA hitches a ride. Development and production of BFR is way too expensive. They need tons of tests before cargo can be send to Mars for real. Better use BFR commercially as early as possible and refine designes on the way. Thats how SpaceX operated in the past and I assume will continue to operate in the future. Look at the development of Falcon 9 and Dragon. Its the same story, I expect history to repeate it self.

I voiced that view in before and from experience, most users here on the forum disagree with that view.

I agree with much of this.
I am directly in the camp that the 1st BFR launches may have less engines.  I do not agree with those proposing a mini-BFR configured similar to the Falcon 9 8:1 1st stage and single Raptor 2nd.  That's a whole different airframe development & tooling and flight testing than starting right away testing a less engine equipped BFR using THE intended airframe design but not necessarily full up with engines.
Early commercial satellite launch flights will likely serve as boilerplate MCT Cargo config proof of concept tests and yes purchasers could not care less if the 2nd stage MCT is recovered or not except that they will welcome a future price cut.
I am in the camp that the biggest risk for BFR development aside from additional Falcon 9 RUDs is financing the expensive R&D.  Right now SX is WAY behind on planned Q3 and Q4 revenue and most certainly has encountered large additional engineering, manufacturing and operations expenses preparing for RTF.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/02/2015 11:53 pm
...The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover....

Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.


1) MRO can resolve objects of "about a meter across"...
MRO has a resolution of ~30cm per pixel. Multiple exposures of the same site from different angles and ESPECIALLY with the Sun at high angles (thus casting long shadows) can identify hazards.

Perhaps, but that kind of coverage does not exist.
What do you mean? You can, right now, go and request new images be taken of a certain area. There's plenty of "coverage" to take multiple images of the same small area at multiple times of day.
Quote
Yes. And even when it does, it tells you nothing about the relative strength of the surface. It could be the Martian equivalent of quicksand for all we know.
Untrue, we have ground-truthing of multiple sites on Mar that allow us to calibrate the orbital instruments with on-the-ground measurements. We have day and night thermal IR, which allows us to figure out thermal inertia, etc. And there isn't such a thing as "Martian Quicksand," which requires a lot of liquid water. We can identify sand dunes, etc.

Quote
But it is still irrelevant. MCT will need to be able to land on unprepared terrain, it will be necessary to allow of off-nominal EDL and abort scenarios. So it will need a sturdy gear, and you seem reluctant for some reason to admit that.
I am in favor of actual abort capability, instead of super heavy landing gear. Why do I need to "admit" something that has no basis in actual SpaceX communications, just some people's opinion on the internet? My mental model of MCT most resembles DC-Y and DC-I, which used fairly stubby landing gear and had real abort capability. (And yes, you'd need Soyuz-style cushioning thrusters on Mars in addition to a parachute. But the actual delta-v for that cushioning thrust is VERY low.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/02/2015 11:58 pm
Lars/RB:  Can you each state how massive you expect landing gear to be, I've estimated 10% of touchdown mass.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/03/2015 12:14 am
Probably because it's another nail in the idea that MCT will have single digit dry mass percentage.
Oh, give me a break. You have not come even CLOSE to establishing that single-digit-dry-mass percentage isn't possible. (Not that it'd be that bad... you can still get more than 6km/s out of it, thus within the range of my expectation for MCT of 6-8km/s.)

Quote
Lets look at what landing gear will likely mass.  The primary driver is touchdown mass which would be 100 mT + vehicle dry mass + reserves from the landing propellants.  I'd call that all 200 mT, and no we do not get to deduct because of mars gravity, the vehicle has kinetic energy at touchdown which is independent of gravity.
That's false. Mars' lower gravity makes it easier to zero out the velocity more precisely than on Earth. So you have proportionally less kinetic energy (or, since kinetic energy is proportional to velocity squared, perhaps much, much less kinetic energy).

Quote
The landing legs on F9R are said to be 10% of the empty stage mass (and that's with use of carbon-fiber) so I take this as my basis for MCT legs structure.  Around 20 mT, though I expect them to telescope inside the vehicle rather then be on the surface.
No, we can do much better. For a VTVL SSTO or similar, something like 3% is often assumed for parametric purposes in "common wisdom," but we can do much better.

"Gary Hudson pointed out a couple of years ago that, while 3% is common wisdom, the B-58 landing gear was 1.5%... and that was a very tall and mechanically complex gear designed in the 1950s. "

( http://yarchive.net/space/launchers/landing_gear_weight.html )

But why would the passenger version of MCT use the super heavy legs of the full payload version? F9R's legs are removable and added at the launch site, so it would make perfect sense to be able to use less massive legs if you aren't landing a huge payload and that was a big mass driver.

F9R's legs are very long due to the fact that F9R is very tall and skinny, and you would want a wide base for landing. While MCT will have around the same volume for tanks and such, it will likely have a much wider base, thus allowing an equivalently-wide stance while being very short, ala DC-X. That saves significant mass. If we can do 1.5% in the 1950s on Earth, then even a 1% mass for the landing legs (if they're short and you land on a prepared surface) is well within the realm of possibility. Though a 4% leg isn't a deal-breaker either.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/03/2015 12:19 am
SpaceX has not reached the pinnacle of landing leg design and manufacture; there's room for improvement. Others have done better.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/03/2015 12:21 am
Musk is borrowing somewhat from Mars Direct (or is it Semi-Direct?) where an already-fueled ascent vehicle is fueled up on the surface. I don't see a good reason not to have a fueled up vehicle ready when they arrive.

I see no reason why to land the fuel production equipment at all.
It can do the same job on orbit.

you have said it yourself:
 http://forum.nasaspaceflight.com/index.php?topic=17984.msg620589#msg620589
CO/O2 is really neat, but orbital propellant collection is very difficult, and although I certainly support its development, I have absolutely no reason to think that's what SpaceX is planning. In fact, we can be reasonably certain that Raptor will use methane (and certainly it will use some sort of hydrocarbon), and that's what MCT will use.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/03/2015 12:24 am
Subcooled ethylene isn't a horrible idea if you want to boost MCT's mass fraction. It's not a lot harder to make than methane on Mars, has similar Isp, but is much denser. It's also liquid at Mars ambient temperatures at ~1MPa, and requires less hydrogen than methane. And is really useful for making plastics and stuff for habitats, so you'd want to eventually make it anyway.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 11/03/2015 12:34 am
But why would the passenger version of MCT use the super heavy legs of the full payload version? F9R's legs are removable and added at the launch site, so it would make perfect sense to be able to use less massive legs if you aren't landing a huge payload and that was a big mass driver.

I haven't noticed this distinction before. Dramatically different masses for passenger vs cargo MCT - is that what you meant?

Earlier I'd raised this in a different way, saying that a cargo MCT would contain denser materials than a passenger MCT,  and thus to have the same mass in the same volume would have "free space" that would be better shared with a small passenger group who would greatly appreciate free space. Some people responded that the cargo MCT would just be packed with extra space.

But you seem to be saying they'd actually just have a heavier version. More fuel would be part of that too of course. A higher mass for cargo MCT would impact its velocity (is it a slow trajectory?) and EDL issues/differences as well as launch differences.

Actually... perhaps you're saying the opposite. You'd make a regular cargo MCT, but there'd be a low-load light version too for passengers? I would think you wouldn't travel light in a system capable of carrying more.

I'd like to read the arguments for this... where/when was it?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oiorionsbelt on 11/03/2015 12:38 am

and you land on a prepared surface.
Robotbeat, you have mentioned this 'prepared surface' in several posts. How this would be accomplished?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 11/03/2015 01:16 am
But why would the passenger version of MCT use the super heavy legs of the full payload version? F9R's legs are removable and added at the launch site, so it would make perfect sense to be able to use less massive legs if you aren't landing a huge payload and that was a big mass driver.

I haven't noticed this distinction before. Dramatically different masses for passenger vs cargo MCT - is that what you meant?

Earlier I'd raised this in a different way, saying that a cargo MCT would contain denser materials than a passenger MCT,  and thus to have the same mass in the same volume would have "free space" that would be better shared with a small passenger group who would greatly appreciate free space. Some people responded that the cargo MCT would just be packed with extra space.

But you seem to be saying they'd actually just have a heavier version. More fuel would be part of that too of course. A higher mass for cargo MCT would impact its velocity (is it a slow trajectory?) and EDL issues/differences as well as launch differences.

Actually... perhaps you're saying the opposite. You'd make a regular cargo MCT, but there'd be a low-load light version too for passengers? I would think you wouldn't travel light in a system capable of carrying more.

I'd like to read the arguments for this... where/when was it?

It would be the same base MCT, but since a load of passengers wouldn't have as much mass as a load of cargo, they could reduce some vehicle mass by using lighter landing legs. Maybe change out some other components too. Then you get better performance from the engines with an overall lighter vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 11/03/2015 02:03 am
...The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover....

Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.


1) MRO can resolve objects of "about a meter across"...
MRO has a resolution of ~30cm per pixel. Multiple exposures of the same site from different angles and ESPECIALLY with the Sun at high angles (thus casting long shadows) can identify hazards.

Perhaps, but that kind of coverage does not exist.
What do you mean? You can, right now, go and request new images be taken of a certain area. There's plenty of "coverage" to take multiple images of the same small area at multiple times of day.

No, it does not exist *now*. If you watched the streams, you might have missed the talk about additional coverage needed to get better coverage during various times of the day, including the benefit of satellites in near-polar orbits for this very purpose. Better coverage of the ground is needed for final analysis of landing sites... What we have now is not sufficient as you could not tell the difference between a flat ground and an even boulder field.

You may not recall this, but the MER scientists were *quite* surprised that the landscape was as flat and featureless as it turned out to be. (See image below) They expected lots of smaller boulders, but found practically nothing. And vice versa at the other rover site.  It was a real surprise, despite an in-depth analysis of the landing sites.

Quote
But it is still irrelevant. MCT will need to be able to land on unprepared terrain, it will be necessary to allow of off-nominal EDL and abort scenarios. So it will need a sturdy gear, and you seem reluctant for some reason to admit that.
I am in favor of actual abort capability, instead of super heavy landing gear. Why do I need to "admit" something that has no basis in actual SpaceX communications, just some people's opinion on the internet? My mental model of MCT most resembles DC-Y and DC-I, which used fairly stubby landing gear and had real abort capability. (And yes, you'd need Soyuz-style cushioning thrusters on Mars in addition to a parachute. But the actual delta-v for that cushioning thrust is VERY low.)

DC-X (and the planned derivatives) had smaller tiny gears because they were designed to land on... drum roll... hard concrete pads. (and they could not land outside a prepared pad)

This is not what early MCT's will encounter. Even if your fantasy of tiny ground-clearing robots delivered by Red Dragon's materialize, the ground is not hard as diamond. It won't be even close to a prepared landing pad on Earth. And you continue to dodge the fact that the MCT legs also need to support a full propellant load, this will require something significantly more than an "elephant on stilts" approach.

My view of the legs is that they need to be fairly short (to conserve mass) - but have very wide feet, to distribute the load.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/03/2015 02:32 am
....
You may not recall this, but the MER scientists were *quite* surprised that the landscape was as flat and featureless as it turned out to be.
So what? MER was before MRO....

Quote
But it is still irrelevant. MCT will need to be able to land on unprepared terrain, it will be necessary to allow of off-nominal EDL and abort scenarios. So it will need a sturdy gear, and you seem reluctant for some reason to admit that.
I am in favor of actual abort capability, instead of super heavy landing gear. Why do I need to "admit" something that has no basis in actual SpaceX communications, just some people's opinion on the internet? My mental model of MCT most resembles DC-Y and DC-I, which used fairly stubby landing gear and had real abort capability. (And yes, you'd need Soyuz-style cushioning thrusters on Mars in addition to a parachute. But the actual delta-v for that cushioning thrust is VERY low.)

DC-X (and the planned derivatives) had smaller tiny gears because they were designed to land on... drum roll... hard concrete pads. (and they could not land outside a prepared pad)

Quote
This is not what early MCT's will encounter. Even if your fantasy
Give me a break.
Quote
of tiny ground-clearing robots delivered by Red Dragon's materialize,
If you think a 10-ton bulldozer is "tiny"
Quote
the ground is not hard as diamond. It won't be even close to a prepared landing pad on Earth.
Yes, there will continue to be improvements, not just clearing land.
Quote
And you continue to dodge the fact that the MCT legs also need to support a full propellant load, this will require something significantly more than an "elephant on stilts" approach.
Enough with the dramatic rhetoric! I've not "dodged" anything. I haven't seen it come up to need to address it, though I have thought of it. Jeez. No, you wouldn't launch an MCT on its legs. You also need supports placed under the MCT before you fuel it up for launch, just like with DC-X (DC-X's legs could support a full load, but they were practicing for DC-Y/I).

https://www.youtube.com/watch?v=sCVpfZ351FQ

It's as if you and Impaler want MCT to be a non-viable, heavy monstrosity that barely can push its own weight around. It's almost as if you're not trying to imagine how to reduce dry mass in meaningful ways that just about any aerospace undergrad would think of (let alone a team of seasoned professionals).


Musk talks about 80,000 people per year going to Mars (look it up), which would mean hundreds if not thousands of MCTs going every synod. It's ridiculous to think that the first couple MCTs are going to dominate the design of the vehicle and its operational dry mass. If the first few MCTs need beefier/taller legs because they won't be landing on a fully prepared surface, then so be it. But such early mods won't be driving up the dry mass for the vehicles making Earth-to-Mars transits with 50-100 passengers in ~100 days.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/03/2015 02:40 am

and you land on a prepared surface.
Robotbeat, you have mentioned this 'prepared surface' in several posts. How this would be accomplished?
There are several methods. As I posted earlier, some of the guys from "Swampworks" are establishing a technique that could be built with a rover. I guarantee that SpaceX is working the problem and has their own ideas of how to solve the problem.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 11/03/2015 02:45 am

and you land on a prepared surface.
Robotbeat, you have mentioned this 'prepared surface' in several posts. How this would be accomplished?

NASA has some ideas so maybe SpaceX will get some advice from from them.

http://www.nasa.gov/content/landing-pads-being-designed-for-extraterrestrial-missions
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/03/2015 02:52 am

and you land on a prepared surface.
Robotbeat, you have mentioned this 'prepared surface' in several posts. How this would be accomplished?

NASA has some ideas so maybe SpaceX will get some advice from from them.

http://www.nasa.gov/content/landing-pads-being-designed-for-extraterrestrial-missions

Exactly, Dr. Phil is the guy I was thinking of.

Here's some quotes from the article:

"Robotic landers would go to a location on Mars and excavate a site, clearing rocks, leveling and grading an area and then stabilizing the regolith to withstand impact forces of the rocket plume," Mueller said. "Another option is to excavate down to bedrock to give a firm foundation. Fabric or other geo-textile material could also be used to stabilize the soil and ensure there is a good landing site."

...
""We've tested several types of materials and it seems that basalt regolith mixed with polymer binders hold up well," Metzger said."
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 11/03/2015 02:58 am
It's as if you and Impaler want MCT to be a non-viable, heavy monstrosity that barely can push its own weight around. It's almost as if you're not trying to imagine how to reduce dry mass in meaningful ways that just about any aerospace undergrad would think of (let alone a team of seasoned professionals).
I think it's about having "conservative" mass estimates instead of "optimistic" ones, a.k.a. the reason why Mars Direct in its original form was criticized, then revised (e.g. Semi-Direct, DRM 3.0).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oiorionsbelt on 11/03/2015 02:59 am

and you land on a prepared surface.
Robotbeat, you have mentioned this 'prepared surface' in several posts. How this would be accomplished?

NASA has some ideas so maybe SpaceX will get some advice from from them.

http://www.nasa.gov/content/landing-pads-being-designed-for-extraterrestrial-missions


Quote
"Of all the substances we studied, ablative materials seem to work best," Metzger said.

:) PICAX landing sites

Edit: or is it PIRAX Polymer Impregnated Regolith Ablator.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/03/2015 03:03 am
It's as if you and Impaler want MCT to be a non-viable, heavy monstrosity that barely can push its own weight around. It's almost as if you're not trying to imagine how to reduce dry mass in meaningful ways that just about any aerospace undergrad would think of (let alone a team of seasoned professionals).
I think it's about having "conservative" mass estimates instead of "optimistic" ones, a.k.a. why Mars Direct was revised (e.g. Semi-Direct, DRM 3.0).
The problem with that is "conservative" mass fractions are NOT realistic!

If NASA, for instance, were doing initial design of F9 v1.1 full thrust and Falcon Heavy, no way would they contemplate giving the boosters mass fractions of 25 and 30, respectively.

Heck, when NASA was trading ULA's Centaur for ESAS, they literally sandbagged the dry mass of Centaur 50% more than it actually weighs today! How they managed to do that, I do not know.

But "conservative" mass fractions are the least likely for a company that both prides itself in world-class mass-fractions and that can't afford building something much larger and with extra stages than necessary. SpaceX doesn't need to spread work amongst several Centers, there's no reason they'll want to expand the number of stages beyond what they think they can achieve. "Conservative" is not realistic when you don't have infinite money.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/03/2015 04:24 am
It's as if you and Impaler want MCT to be a non-viable, heavy monstrosity that barely can push its own weight around. It's almost as if you're not trying to imagine how to reduce dry mass in meaningful ways that just about any aerospace undergrad would think of (let alone a team of seasoned professionals).
I think it's about having "conservative" mass estimates instead of "optimistic" ones, a.k.a. why Mars Direct was revised (e.g. Semi-Direct, DRM 3.0).
The problem with that is "conservative" mass fractions are NOT realistic!

If NASA, for instance, were doing initial design of F9 v1.1 full thrust and Falcon Heavy, no way would they contemplate giving the boosters mass fractions of 25 and 30, respectively.

Heck, when NASA was trading ULA's Centaur for ESAS, they literally sandbagged the dry mass of Centaur 50% more than it actually weighs today! How they managed to do that, I do not know.

But "conservative" mass fractions are the least likely for a company that both prides itself in world-class mass-fractions and that can't afford building something much larger and with extra stages than necessary. SpaceX doesn't need to spread work amongst several Centers, there's no reason they'll want to expand the number of stages beyond what they think they can achieve. "Conservative" is not realistic when you don't have infinite money.

You've brought up this distinction before and I think it's a semantic waste of time.

Nobody's dropping the performance numbers they hope to achieve for the sake of "being conservative".  They're trying to build in a performance margin between "What we would need for this mission to go forward at all" and "What we're hoping to achieve".  They're trying to *overbuild*, because they know that any hundred out of ten thousand things could turn out to just not be achievable - this possibility is the price you pay for being on the forefront of engineering, for trying new things that have not been done before.

There are about four or five orders of magnitude of price reduction that SpaceX is hoping to achieve - right now we could expect to field around 5 billion dollars (if not 50 billion dollars) a ticket for tens to hundreds of tickets to Mars aboard an Apollo-like effort, while SpaceX wants to eventually achieve 500,000 dollars.

Let me say that again.

Four.  Or.  Five. Orders.  Of.  Magnitude.

Putting a 20% margin in (or a 50% margin) as allowance for unexpected roadblocks is not going to break the bank.  Assuming that every performance estimate you have will ultimately take the upper 95% error bound is dumb.  They're not going to get there on audacity alone.

People use "conservative" because they want to demonstrate that yes, even with what we know that we don't understand, we're pretty sure this can be done.  It shouldn't have to have [TRIGGER WARNING] attached.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 11/03/2015 04:26 am

Fix your quoting!  I'can't even reply to the rest with that quoting mess, but these nuggets...:

Quote
This is not what early MCT's will encounter. Even if your fantasy
Give me a break.
Quote
of tiny ground-clearing robots delivered by Red Dragon's materialize,
If you think a 10-ton bulldozer is "tiny"

10 tons? Since when can Red Dragon deliver a 10 ton payload to Mars?!? I'm not the one who raised the "Red Dragon" approach - you did. The Red Dragon proposal can only put 7.5t on the surface of Mars, and 6.5t would be the Dragon dry mass. That's one ton remaining.

It's as if you and Impaler want MCT to be a non-viable, heavy monstrosity that barely can push its own weight around. It's almost as if you're not trying to imagine how to reduce dry mass in meaningful ways that just about any aerospace undergrad would think of (let alone a team of seasoned professionals).

You couldn't be more wrong. (Heck, Impaler and I hardly agree on anything) I'm just trying to imagine a *VIABLE* vehicle with sufficient margins to be a reusable tool for opening up Mars and the solar system. Something closer to a utility truck rather than an extreme sports car with razor thin margins.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/03/2015 04:30 am
How many times we we have to explain that conservative means 'what were sure we can do at reasonable time and money' not 'an incorrect estimate of the best we could ever do', being conservative dose not cut off the future potential to exceed original goals either in the detailed design process or in subsequent upgrading campaigns.  Maybe your absurd dry mass fractions will be achieved some day, but no sane person would bet the company on hitting those targets on the initial design.

Your claim that single digit mass fractions and 8 km/s DeltaV were achievable in the MCT is absurd (It seems you decided not to back off to 6 km/s and 20% so be it)  because you ignore all the parasitic mass involved in keeping a vehicle alive during interplanetary transit, EDL, rough surface landing and launch, cargo-hold and unloading access.  If the MCT were just tanks and engines you would be right, but it's not.

In my own estimations if you removed all dry mass other then tanks and engines the dry mass fraction when fully fueled would be just 6%, right on par with SpaceX's established performance, but the total vehicle dry mass is 20% of the GTOW once you account for real world needs (and in all likelihood I am underestimating the dry mass fraction).  You have been repeatedly accusing me of sand-bagging SpaceX, but your wrong, I started with the same basic rocketry you did and accounted for real needs and the parasitic mass resulting from it.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/03/2015 04:33 am
To put it into another frame:

If you have estimates of achievable performance, and you hang error bounds on those estimates, and you decide that you're going to rely on the 95% high error bound being achieved, or the mission fails;  And you do this several times on several (n) different variables.  And the mission doesn't fail?

It's almost certain (1-0.05^n probability)  that the people who wrote the estimates were lying to you about what they thought was achievable.  Because you're a bad manager who won't accept reality.

Like James Tiberius Kirk and his "Two hours to fix the engines?  You have 30 seconds or we all die!"

https://www.youtube.com/watch?v=t9SVhg6ZENw
https://www.youtube.com/watch?v=8xRqXYsksFg
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/03/2015 12:10 pm
Lars-J:
I said: "If you think a 10-ton bulldozer is "tiny""

A typical 10-ton bulldozer on Earth is built using steel. Aerospace grade materials have 20 times the strength-to-weight ratio, so fitting something the size of a 10 ton bulldozer into the ~2 ton payload capability of Red Dragon is certainly feasible, especially with careful, topologically-optimized design. To gain the traction you'd need in the lightweighted bulldozer, use ballast boxes like is commonly used with Bobcats.

So you can build something the size of a 10-ton bulldozer using just 2 tons of payload mass (and yes, taking the rough physical dimensions of Red Dragon into account).

I am just repeating what I said earlier, but you must have missed it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/03/2015 12:12 pm
A heavy-duty "utility truck" would require multiple stages, thus losing all of its utility.

My opinion is that MCT may be capable of 6-8km/s. 8km/s is certainly within the range of possibility. DC-I was more ambitious than even that. But 8km/s is the upper range.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 11/03/2015 02:30 pm
Construction equipment taken to Mars will probably be made from aircraft aluminum or titanium to reduce weight.  If extra weight is needed, Martian regolith, or even a lox tank for extended durations on Mars can be added to it.  Also, Martian gravity being only 38% of earths will make lighter equipment capable of doing the same proportion of work as a steel earth moving piece of equipment.  Equipment will also probably be using something like a Tesla battery package with a solar charging station. 

Also landing on a fairly level plain with nearby mountains or craters for water access shouldn't be too hard to find. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 11/03/2015 03:09 pm
Construction equipment taken to Mars will probably be made from aircraft aluminum or titanium to reduce weight. 

I am not sure they will go that way. Such equipment will be extremely expensive to develop and build. Also regolith is not that dense. It will not be easy to add enough mass. Maybe they just send more standard equipment, adjusted to Mars conditions with electric drive. It does not need to be the 20 ton caterpillar early on. They can still go big when they are able to make at least the biggest heaviest components locally. But even if they go that heavy it would only be 20% of a full MCT cargo load. Maybe the beams of large cranes are worth making them of aluminium.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: meekGee on 11/03/2015 03:10 pm
Where is the 12 flight requirement coming from?

And suppose there is some requirement.  You're implying customer flights, and revenue-generating ones at that, are cheaper than SpaceX flight?   

For a reusable rocket, test flights are the cheapest option.   

Quote
"A rocket is typically tested only once with a dummy payload with subsequent launches being with paid customers who have satellites."

But the whole point was that this is a reusable rocket.  Your "typically" applies to expendable rockets that operate in a field where there are worthy second-rate payloads that can both generate revenue and be of lesser value if lost.

None of that applies here.

If you're building a reusable rocket, then you can test it like you test any aircraft.  Send it up (you can test the first stage independently of the rest of the rocket), certify it, then start using it.

You can't use "typically" across a paradigm shift.


But we know that SpaceX, even in the fast build-up scenario, needs to send multiple unmanned payloads to Mars first.

BFR is an Earth-to-orbit vehicle, and so you're not risking a two-year delay when you first launch it.  Yes, the first launch may not carry an MCT, but by the same token, it won't carry any other one-of-a-kind payload.  Being reusable, it's a complete non-brainer to fly a dummy payload.  If it works, you you relaunch.  It it doesn't, good thing you didn't.

Actually, once you're shifted to a reusable rocket, test flights are cheap enough that you could do multiple dummy payloads before you put an MCT on top - and it's not like you wasted multiple rockets doing it.

So I think the "build up flight history" argument doesn't apply.

It will be cheaper per kg to LEO, but it is by no means going to be cheap enough to build an adequate flight history (~12 launches) with nothing but dummy payloads all at SpaceX's own expense.  A rocket is typically tested only once with a dummy payload with subsequent launches being with paid customers who have satellites.  I expect prices of ~200 million per launch even with recovery (about $1000 per kg, Musk's optimistic goal) so it would cost Billions to do these launches without customers.

I expect that 1st stage recovered will be attempted on every single BFR flight with very likely full success from the start.  If first stage recovery works on the dummy flight and is declared a solved problem then the price point will likely be set such that SpaceX is fully covering the cost of the 2nd stage in case it is lost as I expect 2nd stage recover to require a long campaign of attempts with lots of failures and redesigns as we have seen with F9, the customer will not care any more about the success or failure of these recovery attempts any more then they care about 1st stage recovery attempts now. 

By the time you have your 12 flight history your close to getting the 2nd stage to recover reliably and can drop the price to perhaps 100 million and try to get more volume.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 11/03/2015 03:18 pm
Something closer to a utility truck rather than an extreme sports car with razor thin margins.

Maybe that's the problem. You're saying a utility truck while Musk, the person who's actually going to decide how the MCT is built, is saying a bus type vehicle (and maybe even a cruise ship vehicle later) that has access to landing pads. You're just on the wrong thread.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 11/03/2015 03:28 pm
Did not Musk say somewhere that there would be approximately 10 - 100 ton cargo flights for every one 100 passenger flight?  Cargo being necessary for living areas, food growing units, power stations, fuel manufacturing equipment, mining equipment, long term food storage, etc.  To me it would be safer and easier just to send 10 people with each MCT.  All vehicles would be the same.  All would have cargo and people to work, but not be overloaded with large expensive human habitat area on the vehicles.  At least until a fairly large viable colony is built for massive transfers of people. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/03/2015 03:37 pm
Easier to send cargo to the Mars surface with heavy reliance on human-unfriendly SEP.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 11/03/2015 03:42 pm
Did not Musk say somewhere that there would be approximately 10 - 100 ton cargo flights for every one 100 passenger flight?  Cargo being necessary for living areas, food growing units, power stations, fuel manufacturing equipment, mining equipment, long term food storage, etc.  To me it would be safer and easier just to send 10 people with each MCT.  All vehicles would be the same.  All would have cargo and people to work, but not be overloaded with large expensive human habitat area on the vehicles.  At least until a fairly large viable colony is built for massive transfers of people.

IMO one reason is because one human habitat in a MCT that can support 100 people is less expensive than 10 human habits that can support 100 people. I would also think maintenance costs would be less.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 11/03/2015 03:44 pm
He did say that but only as a very rough guess, not a well calculated engineering number. It can't be because that ratio will change over time and depends on technology development. Early on only small numbers of people would go and they would take a lot of cargo with them. Later, when the colony is ready to take in 100 persons or multiple of 100 persons in one synod then dedicated passenger MCT will be more efficient IMO. Facilities like showers, toilets, training equipment, kitchen, laundry, ECLSS with redundancy will scale less than proportional.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 11/03/2015 03:59 pm
Something closer to a utility truck rather than an extreme sports car with razor thin margins.

Maybe that's the problem. You're saying a utility truck while Musk, the person who's actually going to decide how the MCT is built, is saying a bus type vehicle (and maybe even a cruise ship vehicle later) that has access to landing pads. You're just on the wrong thread.

Ah, the lost art of intentionally mis-reading a post. ::)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/03/2015 04:16 pm
Something closer to a utility truck rather than an extreme sports car with razor thin margins.

Maybe that's the problem. You're saying a utility truck while Musk, the person who's actually going to decide how the MCT is built, is saying a bus type vehicle (and maybe even a cruise ship vehicle later) that has access to landing pads. You're just on the wrong thread.

Ah, the lost art of intentionally mis-reading a post. ::)
I was imagining more of a pickup, but, you know, one with an 8-foot bed *and* a crew cab.  Because those are nice.

But then I also like conversion vans & toy haulers.

Wait... What were we talking about?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 11/03/2015 04:43 pm
This is an MCT Speculation thread.  No one really knows for sure, but has their own ideas as to how it will look, what it will carry, etc, etc.  100 people at a time is way way out there.  We do not even have the BFR for launching the MCT yet.  Therefore we don't know what size it will be.  Like someone said, an awful lot of cargo can be carried via large SEP tugs to Mars before people land for colonization.  In 20 years we might have mastered fusion, or even positrons for space travel, even small compact fission reactors might be more practical.  We do know a large booster rocket can put large amounts of whatever we need into space especially if reusable. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 11/03/2015 04:59 pm
Ok, While this IS a bit off topic, I think that what should go up, at least in the first MCT test load to Mars, Should be some modular rovers, a multi-material smelting plant, (for refining usable solids, gases and liquids) multiple construction modules and bags for regolith counter weights for crane operations.

     As has been demonstrated on Earth, both 3d printing and robotic controlled construction is both possible and practical.  By using a series of combinations of equipment mentioned above, primary facilities can be established for initial basecamp structures and, with human guidance once the first exploration MCT lands, more elaborate structures can be constructed, primarily out of local materials.

     Mind you, I am assuming that in excess of 100 tons of material could be landed with this inital test flight, as food and life support would not be needed for an unmanned test flight.  (IE, it would be a pure cargo MCT, allowing substantially more than 100 tons to the surface).

     Personally, I would not be suprised to see both a manned and cargo version of the MCTs sent to Mars.  In fact, I could imagine after a set number of trips to Mars, a manned MCT is converted to a cargo version, as the tolerances for pure cargo are more relaxed, when it comes to such things as life support and consumibles.

     As I think that the MCT will in all likelyhood succeed, I can't imagine SpaceX sending a full crew to Mars without at least doing a full mission with no crew on board.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 11/03/2015 06:11 pm
Methane and O2 can be produced on orbit provided a supply of H2 from the surface.
that way you get 11 times the fuel on orbit then what you launch. Even better with longer hydrocarbons.
There is no reason to think they won't pursue such a technology if it shows to be even slightly possible, which, to me, it does.

Musk is borrowing somewhat from Mars Direct (or is it Semi-Direct?) where an already-fueled ascent vehicle is fueled up on the surface. I don't see a good reason not to have a fueled up vehicle ready when they arrive.

I see no reason why to land the fuel production equipment at all.
It can do the same job on orbit.

you have said it yourself:
 http://forum.nasaspaceflight.com/index.php?topic=17984.msg620589#msg620589
CO/O2 is really neat, but orbital propellant collection is very difficult, and although I certainly support its development, I have absolutely no reason to think that's what SpaceX is planning. In fact, we can be reasonably certain that Raptor will use methane (and certainly it will use some sort of hydrocarbon), and that's what MCT will use.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/03/2015 06:24 pm
Where is the 12 flight requirement coming from?

And suppose there is some requirement.  You're implying customer flights, and revenue-generating ones at that, are cheaper than SpaceX flight?   

For a reusable rocket, test flights are the cheapest option.   

Quote
"A rocket is typically tested only once with a dummy payload with subsequent launches being with paid customers who have satellites."

But the whole point was that this is a reusable rocket.  Your "typically" applies to expendable rockets that operate in a field where there are worthy second-rate payloads that can both generate revenue and be of lesser value if lost.

None of that applies here.

If you're building a reusable rocket, then you can test it like you test any aircraft.  Send it up (you can test the first stage independently of the rest of the rocket), certify it, then start using it.

You can't use "typically" across a paradigm shift.


But we know that SpaceX, even in the fast build-up scenario, needs to send multiple unmanned payloads to Mars first.

BFR is an Earth-to-orbit vehicle, and so you're not risking a two-year delay when you first launch it.  Yes, the first launch may not carry an MCT, but by the same token, it won't carry any other one-of-a-kind payload.  Being reusable, it's a complete non-brainer to fly a dummy payload.  If it works, you you relaunch.  It it doesn't, good thing you didn't.

Actually, once you're shifted to a reusable rocket, test flights are cheap enough that you could do multiple dummy payloads before you put an MCT on top - and it's not like you wasted multiple rockets doing it.

So I think the "build up flight history" argument doesn't apply.

It will be cheaper per kg to LEO, but it is by no means going to be cheap enough to build an adequate flight history (~12 launches) with nothing but dummy payloads all at SpaceX's own expense.  A rocket is typically tested only once with a dummy payload with subsequent launches being with paid customers who have satellites.  I expect prices of ~200 million per launch even with recovery (about $1000 per kg, Musk's optimistic goal) so it would cost Billions to do these launches without customers.

I expect that 1st stage recovered will be attempted on every single BFR flight with very likely full success from the start.  If first stage recovery works on the dummy flight and is declared a solved problem then the price point will likely be set such that SpaceX is fully covering the cost of the 2nd stage in case it is lost as I expect 2nd stage recover to require a long campaign of attempts with lots of failures and redesigns as we have seen with F9, the customer will not care any more about the success or failure of these recovery attempts any more then they care about 1st stage recovery attempts now. 

By the time you have your 12 flight history your close to getting the 2nd stage to recover reliably and can drop the price to perhaps 100 million and try to get more volume.

12 flights is what I believe BFR will need to do before SLS wll be canceled in the face in it's incredible political inertia that will denounce SpaceX's rocket as 'unproven' when it is initially introduced.  Not how many flights are necessary to start getting paid sat-launch customers, that will start with the 2nd flight.

We all agree BFR will be cheaper then SLS, that alone is not enough the SLS defenders will just fall back to hand-waving about 'reliability' and 'traditional aerospace companies with more experience' so I am factoring in the political reality that BFR must out perform SLS in every metric including a longer flight history.

Your continuing to pretend that BFR has aircraft like costs per launch, aka nothing but propellants that is not going to be the case, the vehicle needs to be reassembled and launch logistics are massive even if the vehicle is not destroyed in the process.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 11/03/2015 06:34 pm
You're implying customer flights, and revenue-generating ones at that, are cheaper than SpaceX flight?   
For a reusable rocket, test flights are the cheapest option.

Letting someone else pay for your test flight is not cheaper than paying for it yourself?

Methane and O2 can be produced on orbit provided a supply of H2 from the surface.
that way you get 11 times the fuel on orbit then what you launch.

Errr, where does the carbon and oxygen come from?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 11/03/2015 06:46 pm

Methane and O2 can be produced on orbit provided a supply of H2 from the surface.
that way you get 11 times the fuel on orbit then what you launch.

Errr, where does the carbon and oxygen come from?

from the CO2 in the thin atmosphere in LMO . where there is friction there are molecules.
 http://forum.nasaspaceflight.com/index.php?topic=17984.msg1311439#msg1311439
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 11/03/2015 07:09 pm
Fuel will be needed to maintain a low orbit, constant adjustments.  It would be easier and quicker just to land, refuel, then launch back.  Mars' atmosphere isn't that thick.  An orbit low enough to scoop enough atmosphere is probably going to be too low, like to stay in orbit maybe as low as 20 or 30 miles.  Might as well land and relaunch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 11/03/2015 08:12 pm
You should not be so easy to dismiss an idea. check out that thread and see that a lot of work was put into atmospheric scooping starting in the 60's or so.

1. Fuel will be needed to maintain a low orbit, constant adjustments.  It would be easier and quicker just to land, refuel, then launch back.
2. Mars' atmosphere isn't that thick.  An orbit low enough to scoop enough atmosphere is probably going to be too low, like to stay in orbit maybe as low as 20 or 30 miles.  Might as well land and relaunch.
1. fuel will be there. that's the point. some of it will be used to maintain altitude and some will be gained.
2. than have a bigger scoop or an eliptical orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 11/03/2015 08:20 pm
That is not what Musk wants.  He wants MCT to go to Mars, land, unload, refuel, relaunch directly back to earth.  Refueling will probably take place while the MCT is unloaded, and a beginning base camp is set up, ready for the next MCT.  Musk doesn't seem to believe that is proven enough to make fuel.  They have already made fuel on earth from water and air.  They have even considered making fuel from excess power on an aircraft carrier, strings of hydrocarbons to make jet fuel.  Musk wants to keep it simple and robust as possible. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 11/03/2015 09:14 pm
You should not be so easy to dismiss an idea. check out that thread and see that a lot of work was put into atmospheric scooping starting in the 60's or so.

1. Fuel will be needed to maintain a low orbit, constant adjustments.  It would be easier and quicker just to land, refuel, then launch back.
2. Mars' atmosphere isn't that thick.  An orbit low enough to scoop enough atmosphere is probably going to be too low, like to stay in orbit maybe as low as 20 or 30 miles.  Might as well land and relaunch.
1. fuel will be there. that's the point. some of it will be used to maintain altitude and some will be gained.
2. than have a bigger scoop or an eliptical orbit.

Can we leave the crackpot ideas off this forum thread? The idea that you can scoop enough enough atmosphere to generate enough propellant to overcome the friction and *also* generate extra propellant is just two degrees short of a perpetual motion machine. It has been studied many times and also immediately rejected as many times.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 11/03/2015 10:14 pm
Can we leave the crackpot ideas off this forum thread? The idea that you can scoop enough enough atmosphere to generate enough propellant to overcome the friction and *also* generate extra propellant is just two degrees short of a perpetual motion machine. It has been studied many times and also immediately rejected as many times.

Using SEP, assuming highest performance panels and highest possible thrust drive, the raw numbers just barely work. Although we're talking a scoop in the hundred of metres length range. TRL is maybe 2, if we're generous. It doesn't work with chemical engines, therefore you can't use the scooped fuel to power the SEP. So in practice, TRL is zero or negative. So yeah, it doesn't belong here.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/04/2015 02:59 am
Can we leave the crackpot ideas off this forum thread? The idea that you can scoop enough enough atmosphere to generate enough propellant to overcome the friction and *also* generate extra propellant is just two degrees short of a perpetual motion machine. It has been studied many times and also immediately rejected as many times.

Using SEP, assuming highest performance panels and highest possible thrust drive, the raw numbers just barely work. Although we're talking a scoop in the hundred of metres length range. TRL is maybe 2, if we're generous. It doesn't work with chemical engines, therefore you can't use the scooped fuel to power the SEP. So in practice, TRL is zero or negative. So yeah, it doesn't belong here.
There are ways to make it work. You need to use a tether (with existing materials, not exotics), thus reducing your relative velocity while also allowing your draggy power source to not slow you down. Practicality is still questionable, but it's an interesting idea.

I entirely agree it's off-topic.

Calling this "crackpot," though, is completely false. It's entirely within the laws of physics, no more a "perpetual motion machine" than a ramjet is. Calling ideas which are well within the laws of physics "crackpot" or akin to perpetual motion is a great way to give credence to truly crackpot ideas that truly do break the laws of physics (of which we have several in the "Advanced Concepts" section, sucking up the site's bandwidth).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/04/2015 01:08 pm
-snip-

From Hop_David's spreadsheet (http://forum.nasaspaceflight.com/index.php?topic=37536.msg1371984#msg1371984), I offer five cases:

Straight Hohmann with propulsive capture - 259 days
A straight-up Hohmann burn from a {1AUx1AU heliocentric, 300km x 300km altitude geocentric} orbit to a {1.524AUx1.524AU heliocentric, 3697x23459km semimajor axis aereocentric} coplanar orbit using a {1AUx1.5240001AU heliocentric} transfer costs 510m/s plus change on Earth departure, over and above the 3220m/s escape velocity burn.  Then to propulsively capture into a highly elliptical Mars orbit it costs 1021m/s.  Conservative aerobraking can reduce that ellipse down to LMO for another 668m/s that we don't need to pay, where standard EDL penalties apply (I'll assume them to be 2km/s for purposes of this discussion).

Total: 3220 + 510 + 1021 + 2000 = 6751m/s
Wet to drymass ratio at 380s Isp: 6.12 to 1

The spreadsheet author's suggested non-Hohmann trajectory with propulsive capture - 102 days
The author would reduce perihelion in order to balance the perigee and periaerion burn into something sensible, assuming that propulsive capture is necessary.  He uses non-prograde burns or a suboptimal burn time in Earth orbit, which is highly inefficient, to balance out the Earth and Mars sides for minimal total dV.  From a {1AUx1AU heliocentric, 300km x 300km altitude geocentric} orbit to a {1.524AUx1.524AU heliocentric, 3697x23459km semimajor axis aereocentric} coplanar orbit using a {0.87AUx1.8AU heliocentric} transfer orbit costs 3146m/s plus change on Earth departure, over and above the 3220m/s escape velocity burn.  Then to propulsively capture into a highly elliptical Mars orbit it costs 4668m/s.  Conservative aerobraking can reduce that ellipse down to LMO for another 668m/s that we don't need to pay, where standard EDL penalties apply (I'll assume them to be 2km/s for purposes of this discussion).

Total: 3220 + 3146 + 4668 + 2000 = 13034m/s
Wet to drymass ratio at 380s Isp: 33.1 to 1

A 100 day semi-Hohmann transit given perfect free aerocapture - 100 days
From a {1AUx1AU heliocentric, 300km x 300km altitude geocentric} orbit to a {1.524AUx1.524AU heliocentric, 3697x23459km semimajor axis aereocentric} coplanar orbit using a {1AUx3.31AU heliocentric} transfer orbit costs 2241m/s plus change on Earth departure, over and above the 3220m/s escape velocity burn.  Then to propulsively capture into a highly elliptical Mars orbit it costs 9276m/s, but we're not going to do that: Instead, magnetoshell or some other aerocapture technology is going to do that all in one go;  Then it's going to, in the same step, further reduce the elliptical orbit down to LMO  for another 668m/s that we don't need to pay, then go directly into EDL, where standard EDL penalties apply (I'll assume them to be 2km/s for purposes of this discussion).

Total: 3220 + 2241 + 2000 = 7461m/s
Wet to drymass ratio at 380s Isp: 7.41 to 1

A 100 day semi-Hohmann transit given propulsive capture - 100 days
Examining the previous proposition without the non-prograde burns that the spreadsheet author makes.  From a {1AUx1AU heliocentric, 300km x 300km altitude geocentric} orbit to a {1.524AUx1.524AU heliocentric, 3697x23459km semimajor axis aereocentric} coplanar orbit using a {1AUx3.31AU heliocentric} transfer orbit costs 2241m/s plus change on Earth departure, over and above the 3220m/s escape velocity burn.  Then to propulsively capture into a highly elliptical Mars orbit it costs 9276m/s.    Conservative aerobraking can reduce that ellipse down to LMO for another 668m/s that we don't need to pay, where standard EDL penalties apply (I'll assume them to be 2km/s for purposes of this discussion).

Total: 3220 + 2241 + 9276 + 2000 = 16737m/s
Wet to drymass ratio at 380s Isp: 89.3 to 1

A reasonable 180 day near-Hohmann transfer with mild aerocapture - 180 days
From a {1AUx1AU heliocentric, 300km x 300km altitude geocentric} orbit to a {1.524AUx1.524AU heliocentric, 3697x23459km semimajor axis aereocentric} coplanar orbit using a {1AUx1.652AU heliocentric} transfer orbit costs 655m/s plus change on Earth departure, over and above the 3220m/s escape velocity burn.  Then to propulsively capture into a highly elliptical Mars orbit it costs 2443m/s, but we're not going to do that: Instead, magnetoshell or some other aerocapture technology is going to do that.  Conservative aerobraking can reduce that ellipse down to LMO for another 668m/s that we don't need to pay, where standard EDL penalties apply (I'll assume them to be 2km/s for purposes of this discussion).

Total: 3220 + 655 + 2000 = 5875m/s
Wet to drymass ratio at 380s Isp: 4.84 to 1

Would anyone like to do the work of reversing that spreadsheet so we could look at more refined estimates of return delta V?  I might try it at some point, but not today.

Orbits are time reversible so don't we just need to look at the 'Vinf at mars' and calculate the DeltaV needed to archive that escape velocity from mars surface, then we would (if we pointed ourselves in the right direction) be headed back down the equivalent half of the outbound orbit and we should reach Earth in the specified time and with the specified Vinf so we know what we need to do to aerocapture at Earth as well.

It would be nice to have this done for us on the spreadsheet though.
They're reversible, but you're forgetting the Oberth effect: because on the way from Earth to Mars, you can dump your exhaust in a deeper gravity well than Mars to Earth, it takes less delta-v.

I was just referring to the heliocentric portion of the transit being reversible, we would obviously need to take mars's smaller gravity well into account, that's why I said the Vinf at mars is needs to be looked at.  Here let me take some of Burnate's example and reverse them into mars-Earth transits and show how I would do it.

Straight Hohmann with propulsive capture - 259 days
Vinf at mars is 2.652818827 km/s that is our velocity at this point in the heliocentric orbit before we enter the mars gravity well, naturally we accelerate when falling into that gravity well but we would just come out again with the same speed aka were hyperbolic.  To get back to Earth we need that same heliocentric speed (pointed back in now) when leaving mars to return to Earth in 259 days.  To determine this we just take the escape velocity at mars surface 5 km/s, square it along with the needed Vinf add them together and get the square root which is 5.660 km/s.

Likewise we can use the previously 'escape' burn from Earth to know how much deceleration we need to shed to go into that high orbit at Earth after which we will aerobrake down to LEO, I'll assume that we can be refueled by tanker at this point in order to do our Earth landing as that will avoid having to blast off from mars with propellant we wont need until now in LEO where we know their is a continuous refueling process in place.

Earth return reversal
Total: 5660 + 510 = 6170m/s
Wet to drymass ratio at 380s Isp:  5.24 to 1


The spreadsheet author's suggested non-Hohmann trajectory with propulsive capture - 102 days

Earth return reversal
Total 9241 + 3145 = 12386 m/s
Wet to drymass ratio at 380s Isp:  27.82 to 1


A 100 day semi-Hohmann transit given perfect free aerocapture - 100 days

Earth return reversal
Total 13816 m/s
Wet to drymass ratio at 380s Isp:  40.85 to 1

This can be improved over simply reversing the outbound orbit which was {1AUx3.31AU heliocentric}, I've found  {.76AUx1.67AU heliocentric} with the same travel time which can decrease the mars escape burn substantially but at the cost of raising Earth side capture needs.

Earth return reversal
Total 8792 m/s
Wet to drymass ratio at 380s Isp: 10.6  to 1


A 100 day semi-Hohmann transit given propulsive capture - 100 days

Earth return reversal
Total 13816 + 2241 = 16057 m/s
Wet to drymass ratio at 380s Isp:  74.57 to 1

Using my alternative trajectory
Total 8792 + 4597 m/s = 13389
Wet to drymass ratio at 380s Isp: 36.42  to 1


A reasonable 180 day near-Hohmann transfer with mild aerocapture - 180 days

Earth return reversal
Total 7047 m/s
Wet to drymass ratio at 380s Isp: 6.63 to 1


Conclusions:  There seems to be no viable fast (100 day) returns from mars, unlike on the outbound even with perfect free aerocapture doesn't allow it at any kind of propellant fraction and DeltaV which would be believable.  The problem is that were starting from mars surface unlike LEO in the the outbound assumptions, that's putting us around 3600 m/s behind where we would be.  If we had propellant depots in mars orbit fast return would be a reasonable number if we also had free aerocapture as the wet/dry ratio would be 4:1, which would require something around 300 mT of propellant in mars orbit a huge amount.

Given these, I'm going to ask for consensus from both sides of the debate:
Is it possible to conclude at this point that the *only way* to achieve 1 mission per synod per vehicle (given obvious assumptions like methalox + Raptor) is using high-velocity aerocapture as well as refueling from an already-prepared Mars surface fuel depot during a short (days-weeks) surface stay?

Note that I'm skeptical of this workflow being achieved, and I think in a realistic vehicle it probably requires LEO + LMO depots, if not HEO + HMO depots on top of that, but those things I am satisfied to leave unspecified.  I'm just asking for a verification that single-synod operation inextricably requires these three points given the realities of delta V and Earth-Mars phasing: 1) a method for extreme-velocity aerocapture, 2) a prepared surface propellant depot, and 3) A short-stay by the vehicle itself.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 11/04/2015 01:37 pm
Given these, I'm going to ask for consensus from both sides of the debate:
Is it possible to conclude at this point that the *only way* to achieve 1 mission per synod per vehicle (given obvious assumptions like methalox + Raptor) is using high-velocity aerocapture as well as refueling from an already-prepared Mars surface fuel depot during a short (days-weeks) surface stay?

I know no other way to achieve 1 mission per synod per vehicle than using opposition class missions. This requires refuelling from a Mars surface depot.

The NASA Tracjectory Browser (http://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=rendezvous&LD1=2025&LD2=2040&maxDT=1.9&DTunit=yrs&maxDV=15.0&min=DV&wdw_width=-1&submit=Search#a_load_results) can give useful results. Earth re-entry speeds may be pretty high.



Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 11/04/2015 01:40 pm
1) was not explicitly mentioned by someone SpaceX, as far as I know but yes it is a necessary requirement. That is if aerocapture includes the possibility of direct EDL from interplanetary speeds.

2) and 3) were both mentioned as part of the plan, so yes.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 11/04/2015 03:11 pm
So, a few robotic MCT's might have to land first to get fuel made before humans arrive.  SEP tugs might have to get fuel depots in place also.  I know a Martian GPS system and 24 hour communication system will have to be in place.  Why not fuel depots at either end as well as on the surface? 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 11/04/2015 03:48 pm
Given these, I'm going to ask for consensus from both sides of the debate:
Is it possible to conclude at this point that the *only way* to achieve 1 mission per synod per vehicle (given obvious assumptions like methalox + Raptor) is using high-velocity aerocapture as well as refueling from an already-prepared Mars surface fuel depot during a short (days-weeks) surface stay?

I know no other way to achieve 1 mission per synod per vehicle than using opposition class missions. This requires refuelling from a Mars surface depot.

The NASA Tracjectory Browser (http://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=rendezvous&LD1=2025&LD2=2040&maxDT=1.9&DTunit=yrs&maxDV=15.0&min=DV&wdw_width=-1&submit=Search#a_load_results) can give useful results. Earth re-entry speeds may be pretty high.

One other possibility involves LMO refuelling and cargo transfer to dedicated surface to LMO craft.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 11/04/2015 04:02 pm
Why not fuel depots at either end as well as on the surface?

It would require dedicated launch vehicles to fill up the depot on Mars. Early in colony development there will be no capability to service them.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: slavvy on 11/04/2015 04:06 pm
Don´t know if this fits in this thread. It is a speculation and it involves Mars and SpaceX...
Could they secretly plan and build a Mars bound payload for the next 2018 launch window?
Launch on a Falcon Heavy, a Mars communication satellite or even a small lander with, for example, an ISRU test payload?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jim_LAX on 11/04/2015 04:43 pm
Schedule-wise this is at least conceivable, but I think they will be focusing on first stage reuse and working through their launch manifest.  I could see their first Falcon Heavy sending something around the moon, but Mars is much farther into the future!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/04/2015 08:13 pm
Given these, I'm going to ask for consensus from both sides of the debate:
Is it possible to conclude at this point that the *only way* to achieve 1 mission per synod per vehicle (given obvious assumptions like methalox + Raptor) is using high-velocity aerocapture as well as refueling from an already-prepared Mars surface fuel depot during a short (days-weeks) surface stay?

I know no other way to achieve 1 mission per synod per vehicle than using opposition class missions. This requires refuelling from a Mars surface depot.

The NASA Tracjectory Browser (http://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=rendezvous&LD1=2025&LD2=2040&maxDT=1.9&DTunit=yrs&maxDV=15.0&min=DV&wdw_width=-1&submit=Search#a_load_results) can give useful results. Earth re-entry speeds may be pretty high.

One other possibility involves LMO refuelling and cargo transfer to dedicated surface to LMO craft.

If you think this is a legit alternative, could you expand on it sufficient to understand what you're proposing?  It doesn't seem to mitigate the need for extreme aerocapture or a Mars surface depot or a short stay, and it sounds fairly difficult on top of that.

Still waiting to hear acknowledgements or challenges from several others on my point.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/05/2015 12:31 am
It should be noted that the direct-entry trajectory that MSL Curiosity did (using a PICA heatshield, by the way...) or especially Pathfinder--7km/s entry--did weren't much more "extreme" than the aerocapture we're talking about here. Aerocapture on the first pass would only need to bleed enough velocity off to allow capture (and can do so over a longer distance because you have both sides of periapsis plus ability to use negative lift), whereas those had to bleed all the velocity at once. I know that parts of MSL's entry peaked at like 15 gees, briefly. An aerocapture from even a fast transit would be much lower acceleration.


...btw, I'm waiting for c3planner.com to return. It sure is nice to calculate ~100 day transits to Mars to see the required c3 and entry c3 (although even c3planner.com doesn't give the TRUE minimum c3...).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/05/2015 02:20 am
Given these, I'm going to ask for consensus from both sides of the debate:
Is it possible to conclude at this point that the *only way* to achieve 1 mission per synod per vehicle (given obvious assumptions like methalox + Raptor) is using high-velocity aerocapture as well as refueling from an already-prepared Mars surface fuel depot during a short (days-weeks) surface stay?

I know no other way to achieve 1 mission per synod per vehicle than using opposition class missions. This requires refuelling from a Mars surface depot.

The NASA Tracjectory Browser (http://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=rendezvous&LD1=2025&LD2=2040&maxDT=1.9&DTunit=yrs&maxDV=15.0&min=DV&wdw_width=-1&submit=Search#a_load_results) can give useful results. Earth re-entry speeds may be pretty high.

One other possibility involves LMO refuelling and cargo transfer to dedicated surface to LMO craft.

If you think this is a legit alternative, could you expand on it sufficient to understand what you're proposing?  It doesn't seem to mitigate the need for extreme aerocapture or a Mars surface depot or a short stay, and it sounds fairly difficult on top of that.

Still waiting to hear acknowledgements or challenges from several others on my point.

I would almost agree with this, if we were talking about a manned mission.  But if we relax the requirement to cargo and thus have nearly the entire snyod to spend in space we can take the slowest trajectories and arrive back at Earth just short of the next launch window.

Playing around with the NASA trajectory it looks like their is a class of trajectories that are longer then traditional opposition missions but just shy of a full synod.  The aerocapature on these trajectories is significantly easier particularly on Earth ( ~14 km/s most cases vs >16 for nearly all opposition returns), mars stay times are around 100 days (which still means having propellant ready on the surface before arrival), mars departure and capture DeltaV is lower too but the Earth entry velocity is always the going to be the more demanding one in any trajectory.  They generally consist of a slow outbound leg in which the spacecraft goes beyond mars orbit followed by a return in which the craft stay outside of Earth orbit rather then going through aphelion within the orbit of the Earth and often inside that of Venus on an opposition return.

I'm calling them "Syno-Max"  trajectories

 NASA trajectory Browser  (http://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=rendezvous&LD1=2015&LD2=2040&maxDT=2.1&DTunit=yrs&maxDV=18.0&min=DT&wdw_width=-1&submit=Search#a_load_results)

Earth Departure  Feb-20-2030  ->  Earth reentry Dec-24-2031      14.86 km/s reentry

Earth Departure Aug-02-2031  ->   Earth reentry Jul-22-2033      14.11 km/s reentry

Earth Departure  Sep-08-2033  ->  Earth reentry  Sep-14-2035     14 km/s reentry

Here are some examples that just about work though some departures are a few months from working, I think some additional tweaking could get these to dove-tail together as their is a lot of time on mars or outbound leg time that could be taken from.  At least a month on Earth seems a reasonable minimum to refurbish and relaunch.

To really find out what is possible we would need trajectory simulator that actually chains together the many back and forth legs and can find for minimizing both DeltaV, duration and entry velocity.  The optimum chain may actually consist of a mix of different trajectories from year to year.


Also if were talking SEP their may be 1 synod round trips their as well, but they would require a lot of power and would look mostly like classic opposition trajectories in which you do aphelion withing the orbit of Earth.  It requires some impressive DeltaV, 10 km/s outbound 22 inbound and this is just to go between High Earth orbit and mars obit with propulsive capture but the acceleration is fairly modest at only 0.40 mm/s outbound and 0.56 mm/s inbound.  If we were to do aerocapture (which would certainly require the magneto-plasma technique to brake a SEP vehicle) the DeltaV would drop considerably, and if we took on SEP propellants at Mars orbit (presumably from depots) we would be looking at very nearly 80% of the outbound mass being cargo.  I'm doubtful that it would be desirable for crew as the transit times are a year each way so this is best used a freight-hauling solution.

My solution would be to make a vehicle that splits in two, a large drive section and a simple freight section that is just a frame with cargo containers attached all over it's surface and propellant tanks.  Upon arrive at the destination the vehicles splits apart and changes out it's freight section and picks up a new one.  At Earth a freight section full of cargo and propellants is picked up, at mars this freight section is empty of propellant and is dropped off and a section full of return propellant is picked up.  With 3 freight sections per drive section you have one being loaded, one being unloaded and one in transit at all times, and the freight section acts as the propellant depot and the turn-around operation is simplified to a single docking and un-docking for the drive section.

https://engineering.purdue.edu/people/james.m.longuski.1/ConferencePapersPresentations/2005Low-ThrustRoundtripTrajectoriestoMarswithOne-Synodic-PeriodRepeatTime.pdf
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Sohl on 11/05/2015 04:57 pm
My solution would be to make a vehicle that splits in two, a large drive section and a simple freight section that is just a frame with cargo containers attached all over it's surface and propellant tanks.  Upon arrive at the destination the vehicles splits apart and changes out it's freight section and picks up a new one.  At Earth a freight section full of cargo and propellants is picked up, at mars this freight section is empty of propellant and is dropped off and a section full of return propellant is picked up.  With 3 freight sections per drive section you have one being loaded, one being unloaded and one in transit at all times, and the freight section acts as the propellant depot and the turn-around operation is simplified to a single docking and un-docking for the drive section.

Something like this?  ;D

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 11/05/2015 05:43 pm

Impaler, please shorten your URL, it is breaking the site layout. (using Chrome)

Use this syntax (without spaces): [ url = http://whatever ] link text [ url ]
Title: Re: MCT Speculation and Discussion Thread 4
Post by: meekGee on 11/05/2015 06:59 pm
Impaler's concept always made sense to me, but with VTVL.

I envisioned MCT as a fuel-and-propulsion central core, and then cargo/habitat all around it.

It lands, sheds the payload, and can fly back much lighter.

You automatically get the benefit of a large cross section for Mars EDL, and a smaller one when returning to Earth.

Basically, Mars needs enclosed volumes for habitation and storage.  It seems such a shame to haul back an empty cargo hold.

This configuration also solves the "how to get the payload to the ground" question.  It's already at ground level when you land.

Get back to earth, attach new "saddle bags", and lift off again.

IMO there won't be in-orbit refueling around Mars, and so it is important to minimize the empty mass of MCT on the flight back, so the same engine and tanks will give you more dV.

EDIT:  No SEP in my concept.  Just a rocket with about 5 km/sec outbound dV, and about 1.5 times that on the way back.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/05/2015 09:47 pm
My solution would be to make a vehicle that splits in two, a large drive section and a simple freight section that is just a frame with cargo containers attached all over it's surface and propellant tanks.  Upon arrive at the destination the vehicles splits apart and changes out it's freight section and picks up a new one.  At Earth a freight section full of cargo and propellants is picked up, at mars this freight section is empty of propellant and is dropped off and a section full of return propellant is picked up.  With 3 freight sections per drive section you have one being loaded, one being unloaded and one in transit at all times, and the freight section acts as the propellant depot and the turn-around operation is simplified to a single docking and un-docking for the drive section.

Something like this?  ;D

No nothing like that, it would look like this  8)

(http://vignette3.wikia.nocookie.net/memoryalpha/images/1/1b/USS_Enterprise-D_saucer_separation.jpg/revision/latest?cb=20120205044747&path-prefix=en)

You see I'm not proposing a landing craft, I'm proposing a pure spacecraft (did I not mention it was SEP propulsion based).  The landers stay at mars and unload it over the whole synod as well as refill the fuel tanks.  At Earth we have the BFR launching constantly and a smaller type of SEP tug that moves cargo from LEO up the high orbit staging area.

This old Russian concept is what it would most resemble, but rather then a habitat and lander it moves pure cargo  http://www.energia.ru/en/history/mars/concept.html


Impaler's concept always made sense to me, but with VTVL.

I envisioned MCT as a fuel-and-propulsion central core, and then cargo/habitat all around it.

It lands, sheds the payload, and can fly back much lighter.

You automatically get the benefit of a large cross section for Mars EDL, and a smaller one when returning to Earth.

Basically, Mars needs enclosed volumes for habitation and storage.  It seems such a shame to haul back an empty cargo hold.

This configuration also solves the "how to get the payload to the ground" question.  It's already at ground level when you land.

Get back to earth, attach new "saddle bags", and lift off again.

IMO there won't be in-orbit refueling around Mars, and so it is important to minimize the empty mass of MCT on the flight back, so the same engine and tanks will give you more dV.

You have it backwards I'm not proposing a lander that comes apart, that is a bad idea it makes the vehicle much weaker and complicates it a lot.  I think the lander would have an internal cargo-bay which is simply emptied at mars for a cargo flight and carries a small return habitat for a crew flight.  Also their is no reason to reduce cross-section at Earth, more cross-section is always better for aerocapture.  And yes I'm in favor VTVL.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 11/05/2015 10:35 pm
My solution would be to make a vehicle that splits in two, a large drive section and a simple freight section that is just a frame with cargo containers attached all over it's surface and propellant tanks.  Upon arrive at the destination the vehicles splits apart and changes out it's freight section and picks up a new one.  At Earth a freight section full of cargo and propellants is picked up, at mars this freight section is empty of propellant and is dropped off and a section full of return propellant is picked up.  With 3 freight sections per drive section you have one being loaded, one being unloaded and one in transit at all times, and the freight section acts as the propellant depot and the turn-around operation is simplified to a single docking and un-docking for the drive section.

Something like this?  ;D

No nothing like that, it would look like this  8)

(http://vignette3.wikia.nocookie.net/memoryalpha/images/1/1b/USS_Enterprise-D_saucer_separation.jpg/revision/latest?cb=20120205044747&path-prefix=en)

You see I'm not proposing a landing craft, I'm proposing a pure spacecraft (did I not mention it was SEP propulsion based). 
>

Not to pick nits, but Enterprise saucer section could land. The entire Intrepid Class (ex: Voyager) could land.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/06/2015 02:59 am
Impaler: So your spacecraft wouldn't land? Cool, so you're not actually describing Musk's MCT but something else. Musk pretty clearly said MCT would land.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/06/2015 03:38 am
The BFR first stage won't even reach Earth orbit, dose that mean it's not part of the Mars Colonial Transport SYSTEM?  I have already clearly described a landing craft (which you railed against most vehemently).

In-space only vehicles are more efficient mass movers, but need landers to be of any use.  A lander could operate initially on it's own all be it less efficiently so the logical development is to do the lander firs and then augment it will a freight hauler.  This is how you would get into the huge numbers per year colonization effort as they would be requiring huge cargo imports that are time-insensitive.


Not to pick nits, but Enterprise saucer section could land. The entire Intrepid Class (ex: Voyager) could land.

More of a survivable crash-landing that left the vehicle a total loss.  And Intrepid class landing sequence really makes no sense the landing-gear-area is orders of magnitude too small, the legs would be driven strait into anything softer then solid rock.  Which brings us back to the prepared/unprepared landing site distinction, Intrepid depicts the landing-gear appropriate for the former but performs the later.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 11/06/2015 10:28 am
The BFR first stage won't even reach Earth orbit, dose that mean it's not part of the Mars Colonial Transport SYSTEM?  I have already clearly described a landing craft (which you railed against most vehemently).
But.... "Land the whole thing", right?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 11/06/2015 12:02 pm
I'm one of those who in this thread adheres to Musk quotes like "land the whole thing" for the purpose of coherent speculation.  However I'll bet that most here agree that SX's concepts for MCT have likely evolved considerably from the few sometimes off the cuff statements by Elon, many several years old.  I'll state further that I believe it probable the MCT that actually flies will again have notable differences from the MCT concept that Musk reveals later this year, if he even meets that schedule.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 11/06/2015 04:25 pm
Since a lot more freight would have to be hauled to Mars than people.  In space could be done by SEP tugs on a continuous bases.  LEO to LMO via one or more SEP tugs.  A specialty lander for use on Mars could indeed take freight from LMO to the surface.  The lander could have ISRU equipment/solar panels to manufacture it's fuel from Martian atmosphere when not in use or there could be a separate fuel farm nearby.  Once refueled, it could go pick up another load. 

Humans could travel at a much faster rate with the MCT. 

This plan would require the BFR.
It would require a reusable second stage.
It would require a fleet of large SEP tugs.
A cargo carrier that can be transferred from the second stage to the SEP tug.
A re-usable lander at Mars.
A fuel farm at Mars or a lander large enough to have it's on ISRU equipment. 

An MCT that could be refueled in LEO and fly to Mars.  It might not need to land on Mars, just transfer the human habitation module to the lander.  MCT would fly back to earth.  Lander would take people to Mars surface.  The habitation module could be or would be about the same size as a cargo module. 

This plan might be cheaper to operate overall, but would require a lot of building and development of specialty components.  It would also require a lot of in space dockings and transfers.   However, these specialty components could be built by other companies or countries to have a stake in the colonialization process. 

On the other hand, if everything Musk wants to build is big, then It might be more simple to go directly from Earth to Mars will a couple of refueling stops for both humans and cargo an have contributors supply fuel or Martian surface cargo to have a stake in colonialization. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 11/06/2015 05:02 pm
Since a lot more freight would have to be hauled to Mars than people.  In space could be done by SEP tugs on a continuous bases.  LEO to LMO via one or more SEP tugs.  A specialty lander for use on Mars could indeed take freight from LMO to the surface.  The lander could have ISRU equipment/solar panels to manufacture it's fuel from Martian atmosphere when not in use or there could be a separate fuel farm nearby.  Once refueled, it could go pick up another load. 

Humans could travel at a much faster rate with the MCT. 

This plan would require the BFR.
It would require a reusable second stage.
It would require a fleet of large SEP tugs.
A cargo carrier that can be transferred from the second stage to the SEP tug.
A re-usable lander at Mars.
A fuel farm at Mars or a lander large enough to have it's on ISRU equipment. 

An MCT that could be refueled in LEO and fly to Mars.  It might not need to land on Mars, just transfer the human habitation module to the lander.  MCT would fly back to earth.  Lander would take people to Mars surface.  The habitation module could be or would be about the same size as a cargo module. 

This plan might be cheaper to operate overall, but would require a lot of building and development of specialty components.  It would also require a lot of in space dockings and transfers.   However, these specialty components could be built by other companies or countries to have a stake in the colonialization process. 

On the other hand, if everything Musk wants to build is big, then It might be more simple to go directly from Earth to Mars will a couple of refueling stops for both humans and cargo an have contributors supply fuel or Martian surface cargo to have a stake in colonialization.

If humanity truly becomes interplanetary, nobody doubts that there will be a zillion different kinds of transports and spacecraft types for all kinds of purposes, filling all kinds of niches. But this is not the "MCT"... it needs to be something that SpaceX can reasonably design/build/afford mostly by themselves.

So it won't be the most optimal solution. It won't be the most efficient solution. But it will be cost-effective solution. Sound familiar? The F9 is a prime example. Sometimes a more "brute force" approach is the best one.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 11/06/2015 08:31 pm
Yep, that is what the Russians did for years in their military, etc.  Used cheap brute force, from small arms, to fighter planes that can land and take off on an unimproved runway (dirt or wheat field).  BFR should be able to launch a very heavy payload and be reused.  MCT will be also and will be needed for fast transfer of people to Mars.  Cargo or freight on the other hand might travel a different way. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/06/2015 08:59 pm
The lander could have ISRU equipment/solar panels to manufacture it's fuel from Martian atmosphere when not in use or there could be a separate fuel farm nearby.  Once refueled, it could go pick up another load. 

I've run the numbers and integrating ISRU into a vehicle is prohibitively massive (consuming half the cargo capacity), and would keep the vehicle on the ground for years and eliminating the ability to rapidly cycle between surface and orbit.  Propellant farms are the only viable solution.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 11/06/2015 09:07 pm
Cargo or freight on the other hand might travel a different way.

I think that is very unlikely. Cargo and passenger will be basically the same design, with the obvious addons for passengers. That at least in the beginning. Later on the two can develop in different directions.

An obvious difference could be that passenger MCT is faster. But Elon Musk ruled that out by making clear that speed is not for the passengers but for one synod reuse.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 11/06/2015 09:13 pm
Impaler, Lars-J, spacenut, etc.,

I wonder if the following might be an 'evolutionary' path that SpaceX might pursue:  Have an MCT that initially is used for all phases of the mission (launched to Earth orbit via BFR, is refueled there, launches to Mars, lands, drops off cargo and some/most crew, is refueled via ISRU, launches and does a direct return to Earth, lands on Earth).  This MCT would not ever transport 100 passengers, much less 100 passengers plus their cargo.  Instead it would be used for all expeditionary missions - those used to perform discovery (find easily accessible water sources), setup habitation and other infrastructure (IRSU, comms, modest chemical plants), prepare launch/landing sites, etc.  This would proceed for several synods.  Crew would be on the order of 5-15 people.  Some staying, some rotating out.

Meanwhile, the SEP interplanetary transporter is being assembled in LEO (or other staging area).  When this is complete, and a sufficient number of expeditionary missions have transpired, the function of the MCT vehicles transforms:  At Earth, they are used to shuttle colonists and their cargo from the surface to the SEP transporter.  At Mars, they are used for the converse - they launch empty from the Mars surface, dock with the SEP transporter, offload passengers and cargo, and return to Mars surface.  Each SEP transporter will in fact transport 100 (or more) passengers, plus their cargo.

I think this minimizes the number of vehicles developed, stays consistent with SpaceX's reusability ethos, and is mostly consistent with all of the statements thus far ("land the whole thing", "100 passengers at a time", "we're looking at everything, including SEP", etc.)

Impaler, I know you doubt the technical feasibility of an MCT craft that could do all of the phases listed in the first paragraph, but if it only has to accommodate a max crew of, say, 12, does that change the outlook?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 11/06/2015 09:56 pm
Gordap, that is the way I see it except SEP is slow.  It would be good for cargo, but probably not so good for people.  Now, if the SEP can accelerate for half the trip, then decelerate as needed to throw it into orbit around Mars, then it might be as fast as direct.  I do not see 100 people at a time until well after a good Martian infrastructure is established.  Surface power stations, housing, water mining, base construction, greenhouse construction etc. Any initial crew who stay will be building the colony infrastructure first, and probably rotated out until adequate living, working, farming, and recreation facilities are built and operational. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 11/06/2015 10:39 pm
I'm one of those who in this thread adheres to Musk quotes like "land the whole thing" for the purpose of coherent speculation.  However I'll bet that most here agree that SX's concepts for MCT have likely evolved considerably from the few sometimes off the cuff statements by Elon, many several years old.  I'll state further that I believe it probable the MCT that actually flies will again have notable differences from the MCT concept that Musk reveals later this year, if he even meets that schedule.

Absolutely.

The problem is that we really need a different thread for some of these ideas - because some are good!

Basically we try to use everything we know SpaceX has said about the Mars colonial fleet. And we know that it's a moving target. And when we get BIG new news we might need a new thread. 

Then we need a thread for "contradictory Mars ideas that SpaceX might already realise work better than their early thoughts".

Bit of a mouthful. And still trying to stay true to the General SpaceX principles.

The themes and interest are distinctly different.

( also if anyone goes down the "this is how I'd do it" then the Mars HSF forum is better. )
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/07/2015 06:15 am
Impaler, Lars-J, spacenut, etc.,

I wonder if the following might be an 'evolutionary' path that SpaceX might pursue:  Have an MCT that initially is used for all phases of the mission (launched to Earth orbit via BFR, is refueled there, launches to Mars, lands, drops off cargo and some/most crew, is refueled via ISRU, launches and does a direct return to Earth, lands on Earth).  This MCT would not ever transport 100 passengers, much less 100 passengers plus their cargo.  Instead it would be used for all expeditionary missions - those used to perform discovery (find easily accessible water sources), setup habitation and other infrastructure (IRSU, comms, modest chemical plants), prepare launch/landing sites, etc.  This would proceed for several synods.  Crew would be on the order of 5-15 people.  Some staying, some rotating out.

Meanwhile, the SEP interplanetary transporter is being assembled in LEO (or other staging area).  When this is complete, and a sufficient number of expeditionary missions have transpired, the function of the MCT vehicles transforms:  At Earth, they are used to shuttle colonists and their cargo from the surface to the SEP transporter.  At Mars, they are used for the converse - they launch empty from the Mars surface, dock with the SEP transporter, offload passengers and cargo, and return to Mars surface.  Each SEP transporter will in fact transport 100 (or more) passengers, plus their cargo.

I think this minimizes the number of vehicles developed, stays consistent with SpaceX's reusability ethos, and is mostly consistent with all of the statements thus far ("land the whole thing", "100 passengers at a time", "we're looking at everything, including SEP", etc.)

Impaler, I know you doubt the technical feasibility of an MCT craft that could do all of the phases listed in the first paragraph, but if it only has to accommodate a max crew of, say, 12, does that change the outlook?

That is very nearly exactly what I have been saying, only with the MCT being slightly less capable. 

I think the MCT will be dependent on SEP tug assistance to do initial crew missions at an acceptable speed (for crew health/GCR issues), but may be able to do cargo missions on it's own.

We have argued a lot about achievable DeltaV values, let me lay down some numbers that express the DeltaV achieved from full propellant loads with different amounts of cargo, 100 mT (the outbound cargo goal), 25 mT (the return cargo goal which would be some kind of habitat), and 0 mT (presumably the return from a cargo mission).

100 mT Cargo + 300 mT propellant + 75 mT dry mass -> 3.7 km/s
25 mT Cargo + 300 mT propellant + 75 mT dry mass -> 5.1 km/s
0 mT Cargo + 300 mT propellant + 75 mT dry mass -> 6 km/s

These numbers are a lot lower then other people want to see but I think they are realistic and if intelligently combined an evolving set of missions can be created that serve both cargo and passenger missions.  The empty 6 km/s allows direct Earth return on a hohmann transfer of an empty cargo mission, if the 100 mT cargo is ISRU equipment which deploys to the surface, pumps propellants into the MCT and then remains behind on launch, then a propellant farm is built up without abandoning any vehicles and the return capability is well validated before humans are sent. 

The 4.9 km/s assent with 25 mT cargo is enough to reach mars orbit AND have enough propellant for another decent with FULL cargo (800 m/s propulsion), this allows the vehicle to be a reusable tanker to mars orbit depositing 25 mT per trip of any desired mass, and to act as a rapid reusable downward cargo hauler AT THE SAME TIME. 

Also it means that the MCT fully fueled in mars orbit can do rapid transit back to Earth (150 day) though this would require 12 tanker-up/cargo-down flights to get the necessary propellants in orbit (with the first flight staying in orbit to act as a depot), but this is consistent with the expected 10:1 crew/cargo ratio.  The very first exploration missions wouldn't have so many MCT's or propellants available and will refuel via SEP tugs sent to mars with propellants.  Only once a high rate of propellant production is in place could this many MCT's be refueled and relaunched.

This will also allow the unloading of cargo from an in-space-only freight vessel while simultaneously refilling that vessel with propellant for Earth return.  These large freight vehicles would be a later addition to the system and would greatly increase the cargo delivery rate and it's efficiency, but are not necessary for the initial deployment as cargo can be sent in the MCT directly all be it with poor amortization.

The 3.7 km/s when fully loaded allows the vehicle to make a fast transit to mars (150 day) from a high orbit (EML1 followed by lunar and Earth slingshot burns) while retaining enough propellants to land at mars.  It would be placed in high orbit and sent propellants by a SEP tug in the 1 MW power range, if we were sending cargo by slow hohmann transfer then only 1/6th of the full propellant load (~50 mT) is needed at EML1 which may be low enough to just have it carried in the MCT from LEO eliminating propellant transfer for such cargo missions.

It also makes the fully loaded MCT ideal for making the fast (3-5 day) transfer from LEO to EML1 to quickly ferry passengers when the numbers are great enough to make use of Dragon or other small taxi craft inconvenient.  Being such a short transit the accommodations can be far more cramped then would be possible for the full transit and I expect some from of transit-hab will be employed.  The MCT in question will likely be docked to and towed by the transit vehicle which would transfer the necessary landing propellants and passengers back to the MCT which would land and disembark the passengers at mars using the same short term accommodations.

It is all an extremely elegant arrangement, at each cargo loading point the vehicle has sufficient DeltaV for the critical mission legs it would actually face at that point while dove-tailing well with force-multiplier vehicles that would be added later like SEP tugs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/07/2015 09:16 am
Impaler, Lars-J, spacenut, etc.,

I wonder if the following might be an 'evolutionary' path that SpaceX might pursue:  Have an MCT that initially is used for all phases of the mission (launched to Earth orbit via BFR, is refueled there, launches to Mars, lands, drops off cargo and some/most crew, is refueled via ISRU, launches and does a direct return to Earth, lands on Earth).  This MCT would not ever transport 100 passengers, much less 100 passengers plus their cargo.  Instead it would be used for all expeditionary missions - those used to perform discovery (find easily accessible water sources), setup habitation and other infrastructure (IRSU, comms, modest chemical plants), prepare launch/landing sites, etc.  This would proceed for several synods.  Crew would be on the order of 5-15 people.  Some staying, some rotating out.

Meanwhile, the SEP interplanetary transporter is being assembled in LEO (or other staging area).  When this is complete, and a sufficient number of expeditionary missions have transpired, the function of the MCT vehicles transforms:  At Earth, they are used to shuttle colonists and their cargo from the surface to the SEP transporter.  At Mars, they are used for the converse - they launch empty from the Mars surface, dock with the SEP transporter, offload passengers and cargo, and return to Mars surface.  Each SEP transporter will in fact transport 100 (or more) passengers, plus their cargo.

I think this minimizes the number of vehicles developed, stays consistent with SpaceX's reusability ethos, and is mostly consistent with all of the statements thus far ("land the whole thing", "100 passengers at a time", "we're looking at everything, including SEP", etc.)

Impaler, I know you doubt the technical feasibility of an MCT craft that could do all of the phases listed in the first paragraph, but if it only has to accommodate a max crew of, say, 12, does that change the outlook?

That is very nearly exactly what I have been saying, only with the MCT being slightly less capable. 

I think the MCT will be dependent on SEP tug assistance to do initial crew missions at an acceptable speed (for crew health/GCR issues), but may be able to do cargo missions on it's own.

We have argued a lot about achievable DeltaV values, let me lay down some numbers that express the DeltaV achieved from full propellant loads with different amounts of cargo, 100 mT (the outbound cargo goal), 25 mT (the return cargo goal which would be some kind of habitat), and 0 mT (presumably the return from a cargo mission).

100 mT Cargo + 300 mT propellant + 75 mT dry mass -> 3.7 km/s
25 mT Cargo + 300 mT propellant + 75 mT dry mass -> 5.1 km/s
0 mT Cargo + 300 mT propellant + 75 mT dry mass -> 6 km/s

These numbers are a lot lower then other people want to see but I think they are realistic and if intelligently combined an evolving set of missions can be created that serve both cargo and passenger missions.  The empty 6 km/s allows direct Earth return on a hohmann transfer of an empty cargo mission, if the 100 mT cargo is ISRU equipment which deploys to the surface, pumps propellants into the MCT and then remains behind on launch, then a propellant farm is built up without abandoning any vehicles and the return capability is well validated before humans are sent. 

The 4.9 km/s assent with 25 mT cargo is enough to reach mars orbit AND have enough propellant for another decent with FULL cargo (800 m/s propulsion), this allows the vehicle to be a reusable tanker to mars orbit depositing 25 mT per trip of any desired mass, and to act as a rapid reusable downward cargo hauler AT THE SAME TIME. 

Also it means that the MCT fully fueled in mars orbit can do rapid transit back to Earth (150 day) though this would require 12 tanker-up/cargo-down flights to get the necessary propellants in orbit (with the first flight staying in orbit to act as a depot), but this is consistent with the expected 10:1 crew/cargo ratio.  The very first exploration missions wouldn't have so many MCT's or propellants available and will refuel via SEP tugs sent to mars with propellants.  Only once a high rate of propellant production is in place could this many MCT's be refueled and relaunched.

This will also allow the unloading of cargo from an in-space-only freight vessel while simultaneously refilling that vessel with propellant for Earth return.  These large freight vehicles would be a later addition to the system and would greatly increase the cargo delivery rate and it's efficiency, but are not necessary for the initial deployment as cargo can be sent in the MCT directly all be it with poor amortization.

The 3.7 km/s when fully loaded allows the vehicle to make a fast transit to mars (150 day) from a high orbit (EML1 followed by lunar and Earth slingshot burns) while retaining enough propellants to land at mars.  It would be placed in high orbit and sent propellants by a SEP tug in the 1 MW power range, if we were sending cargo by slow hohmann transfer then only 1/6th of the full propellant load (~50 mT) is needed at EML1 which may be low enough to just have it carried in the MCT from LEO eliminating propellant transfer for such cargo missions.

It also makes the fully loaded MCT ideal for making the fast (3-5 day) transfer from LEO to EML1 to quickly ferry passengers when the numbers are great enough to make use of Dragon or other small taxi craft inconvenient.  Being such a short transit the accommodations can be far more cramped then would be possible for the full transit and I expect some from of transit-hab will be employed.  The MCT in question will likely be docked to and towed by the transit vehicle which would transfer the necessary landing propellants and passengers back to the MCT which would land and disembark the passengers at mars using the same short term accommodations.

It is all an extremely elegant arrangement, at each cargo loading point the vehicle has sufficient DeltaV for the critical mission legs it would actually face at that point while dove-tailing well with force-multiplier vehicles that would be added later like SEP tugs.

Setting aside for the moment that you're assuming a free supply of propellant & probably a prepared pad on the surface...

Your whole architecture relies on very low dry mass, combined with very low descent delta V.  Descent propellant requirements are likely to be even higher with F9R-style SSRP than with conventional ablative heatshield.  Where are you getting 800m/s?  I've read one estimate that large sphere-cone Mars landers are likely to reach ~Mach 6 (~1500m/s) on heat shield alone, though using F9R-style SSRP instead of an ablative heatshield, gravity losses from sane acceleration rates, a lander as huge as MCT, and terminal landing requirements associated with unprepared pad, will likely increase that.  I've been using 2km/s propulsive dV until someone can show me better numbers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 11/07/2015 10:07 am
SSRP will not be used instead of a heatshield. It will be used once the speed has dropped so much that lift plus a heat shield are no longer useful. Only the landing will be propulsive. Propulsion will set in at super sonic speed, so SSRP.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/07/2015 02:08 pm
Burninate: Terminal velocity at Mars is much, much lower than 1.5km/s for any reasonable ballistic coefficient and for any of the low altitude landing sites that are likely to be used. For Dragon-like ballistic coefficient of 300kg/m^2, you have about 350m/s terminal velocity. And terminal velocity is proportional to the square root of ballistic coefficient, so even if you think I'm wrong about ballistic coefficient, it won't make much difference.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 11/07/2015 03:57 pm
Burninate: Terminal velocity at Mars is much, much lower than 1.5km/s for any reasonable ballistic coefficient and for any of the low altitude landing sites that are likely to be used. For Dragon-like ballistic coefficient of 300kg/m^2, you have about 350m/s terminal velocity. And terminal velocity is proportional to the square root of ballistic coefficient, so even if you think I'm wrong about ballistic coefficient, it won't make much difference.

From what I'm told, on Mars objects with that sort of BC tend to smack into the ground *long* before they reach terminal velocity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/07/2015 05:34 pm
That is from high speed direct entry and low L:D ratio, I am proposing just the opposite.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/07/2015 11:51 pm
That is from high speed direct entry and low L:D ratio, I am proposing just the opposite.
That's like a high speed direct entry straight into the planet and zero L/D ratio, and probably a relatively high altitude.

If you're coming in from a Mars orbit (anything less than escape, it doesn't really seem to matter), then a Dragon-like ballistic coefficient gives you about 500m/s velocity at -5km coming in totally ballistic with zero L/D. I simulated it.

With even a modest L/D, you should be able to get to whatever your terminal velocity is, though that's harder to simulate (I plan to do it). Ballistic entry is old EDL tech. MSL used a lifting trajectory, and I'm sure SpaceX will, too (like Dragon).

Even a very slightly lifting reentry (like 0.3) gives you most of the benefit. It means you can carefully guide your aerocapture and entry.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 11/10/2015 10:47 pm
I really can't see SEP being used. I'm sure they are considering/have considered it, but I expect it to be rejected as unnecessary complexity.

I think simplicity is more important than mass-efficiency since

- SpaceX will probably have limited development funds

- the LV is already supposed to be too big for existing infrastructure, so the marginal cost of making it even larger may be relatively small

100 mT Cargo + 300 mT propellant + 75 mT dry mass -> 3.7 km/s
25 mT Cargo + 300 mT propellant + 75 mT dry mass -> 5.1 km/s
0 mT Cargo + 300 mT propellant + 75 mT dry mass -> 6 km/s

If MCT has a 75 mT dry mass, I would expect it to have a much larger propellant capacity than 300 mT. SpaceX has very good tankage mass fractions.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/10/2015 11:12 pm
SEP is not a difficult technology and I propose HALL thrusters which SpaceX is going to produce for it's own satellite swarm, the Solar panels are likewise a well established technology, the only challenge is scale and SpaceX clearly is not afraid of large scale as they will be building rocket stages with masses on the range of 200 mT of dry mass.  A large SEP tug would come out to under 20 mT.


I estimated all tanks and propellant lines at 5% of the propellant mass for a total of 15 mT, and 6 mT of engines.  That is a mass fraction perfectly consistent with SpaceX performance, but their are lots of other parasitic masses involved in such a vehicle, it is not just a big rocket stage with single digit dry mass fraction.  This is the central flaw in your and other similar comments.



Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 11/10/2015 11:24 pm
SEP is not a difficult technology and I propose HALL thrusters which SpaceX is going to produce for it's own satellite swarm, the Solar panels are likewise a well established technology, the only challenge is scale

My objection is in creating/development an extra vehicle not the base technology itself needing development.

It's well withi [EDIT: well within their capabilities, certainly.]


Quote
I estimated all tanks and propellant lines at 5% of the propellant mass for a total of 15 mT,

That seems high. IIRC FH side booster is more like a mass ratio of 30 (at least that's what's been quoted on this forum) and that includes engines, etc.


Quote
and 6 mT of engines.

Assuming a TWR of 100:1 or better that seems reasonable


Quote
their are lots of other parasitic masses involved in such a vehicle, it is not just a big rocket stage with single digit dry mass fraction.

Certainly. It needs a heat shield, it needs landing legs and a cargo container, it needs better communication than a rocket stage so it can talk to Earth from Mars.

But I don't think those will force them to limit the delta-v drastically. They'll just end up with a huge vehicle.

(Passenger version needs a lot more stuff but that will come out of the cargo-version max capacity...)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 11/11/2015 12:36 am
I really can't see SEP being used. [....]
- the LV is already supposed to be too big for existing infrastructure, so the marginal cost of making it even larger may be relatively small

I'm not seeing your reasoning here. I would think that transferring much of the TMI and TEI requirements onto a separate SEP vehicle would allow the MCT (demoted to a lander) to be smaller, not larger. Ditto its Earth launcher.

It also means you only need to bring MCTs to Mars once. Afterwards they act as SSTO "orbital taxis", ferrying fuel up and cargo/people down; and that means that the SEP ships carry only payload/passengers from then on, increasing the mass between Earth and Mars.

As GORDAP noted, it also gives you a clear upgrade path. You build BFR with a reusable first stage. While launching commercially, other people are essentially paying you to develop a reusable second stage, and then upgrade that into the more capable MCT. Then you use MCT to develop the fuel infrastructure in Earth orbit. Then you use orbitally refuelled MCTs to directly carry small payloads to Mars. Much, much less than 100t or 100 people. NASA (or an international joint mission) might fund the first manned visits. Meanwhile, using BFR/MCT you assemble the SEP ships in Earth orbit. The MCTs are demoted to taxi duty and you can carry the fully payloads to Mars via the SEPs; and the real colonisation effort begins.

It reduces each step to a bite-sized piece. It allows SpaceX to make money out of most steps, paying for the development of the next. It constantly undermines potential rivals by always being two steps ahead, reducing the chance that someone else will eat SpaceX's markets. What's not to love?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/11/2015 01:58 am
MCT would be a heck of a lot better propellant taxi and tanker if it had good mass fraction.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/11/2015 04:35 am
I really can't see SEP being used. [....]
- the LV is already supposed to be too big for existing infrastructure, so the marginal cost of making it even larger may be relatively small

I'm not seeing your reasoning here. I would think that transferring much of the TMI and TEI requirements onto a separate SEP vehicle would allow the MCT (demoted to a lander) to be smaller, not larger. Ditto its Earth launcher.


I think he was referring to the launch vehicle, aka make an even large BFR to launch an enormous MCT which has the propellant capacity to do a direct departure to mars.  In other words he thinks doubling the size of the launch rocket is worth it to avoid making a SEP tub because you know 'fewer vehicles' logic.  ::)

MCT would be a heck of a lot better propellant taxi and tanker if it had good mass fraction.

That's backwards reasoning, you want MCT to be an all purpose vehicle so you presume it to have that mass fraction for no other reason then that it fulfills your desire, not because is supported by evidence that such a vehicle is possible.

My objection is in creating/development an extra vehicle not the base technology itself needing development.

It's well withi [EDIT: well within their capabilities, certainly.]

Total cost is the metric we care about, if it be 1 vehicle or 10.  The performance demands on and resulting size of a single vehicle area a much greater threat to break the bank then is a series of smaller less ambitious vehicles which can be attacked one at a time.  The SEP tug I'm looking at would be around 1 MW and doesn't need to be started for a decade.  NASA proposes a SEP vehicle in this paper http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140002512.pdf which would be chem-hybrid and used for a full their and back again architecture which is different then what I'm proposing, but the solar power and propellant tanks are comparable to what I'm proposing.


That seems high. IIRC FH side booster is more like a mass ratio of 30 (at least that's what's been quoted on this forum) and that includes engines, etc.

Keep in mind that tank is 100 mT larger and lacks any insulation.  The need to keep propellants (both of them) at cryogenic temperatures in space and on Mars for very long duration is going to demand considerable insulation.  Finally I expect their to be multiple smaller tanks through the vehicle to accommodate good weight distribution and avoid the cargo-holds large volume, this will cut down on the efficiency of the tank.


Assuming a TWR of 100:1 or better that seems reasonable

Actually it was 150:1 for 4 engines at 2300 kN and the factor that I'm most uncomfortable with, a 100:1 ratio would be much more appropriate considering the fuel change and a full-flow engine, high ISP generally comes at the cost of a lower T:W ratio.  At a 100:1 ratio I would be looking at 9 mT for engines.

Certainly. It needs a heat shield, it needs landing legs and a cargo container, it needs better communication than a rocket stage so it can talk to Earth from Mars. 

But I don't think those will force them to limit the delta-v drastically. They'll just end up with a huge vehicle.

(Passenger version needs a lot more stuff but that will come out of the cargo-version max capacity...)

You can't just scale the vehicle to conquer thouse factors, the parasitic stuff all grows with overall vehicle mass (except for com/computer systems which are negligible already).  Growing the vehicle only makes the payload small by comparison but were talking about the vehicle dry mass before payload even gets considered.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/11/2015 03:10 pm
I've done calculations, and yes, it's possible to build an MCT with very good mass fractions (and by mass fraction, I mean without cargo or supplies, etc). I can show you my work if you'd like. But it'll take a while.

But honestly, DC-Y/I is even more ambitious but is still possible. I don't get this idea that you can't build good mass fractions. If it were true, then a reusable upper stage on a reusable TSTO rocket would never be possible (and I do get the idea that many people think that is true).

Also, I object firmly to the word "possible." What you actually mean is "feasible," not "possible." There is no first-principles reason why MCT couldn't achieve a mass ratio as good as 10 (when lightweighted, no cargo, etc). At very least, you could use propellant densification techniques if you were marginal.

So show me a first-principles reason why a mass ratio of 10 is impossible.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/11/2015 08:04 pm
By all means show your work, I expect to see a mass allotment for each subsystem and a justification for each which totals to a vehicle capable of all the mission DeltaV segments your proposing.

Their are an ENDLESS list of 'more ambitious' vehicles that can to trotted out to make anything else look easy in comparison, but the problem is they are made of PAPER.

Delta Clipper Y was NEVER BUILT, all we saw was the sub-scale non-orbital test vehicle DC-X and it's purpose was to demonstrate VTVL and fast turn-around which it did, it did not come within a mile of the DeltaV needed for orbit.  Basically it did nothing more then SpaceX Grasshopper has done.

From http://www.astronautix.com/lvs/dcx.htm

Quote
The DC-X was specifically not designed to demonstrate the most critical issue for any practical SSTO: structural mass fraction

Did you even know that the DC-X dry mass fraction was a colossal 48% of the take off weight 9100 kg dry 18,900 gross take off.  According to http://www.astronautix.com/lvs/dcx.htm

On top of that it used the RL10A-5 engine which only get 368s in Vac (on HYDRO-LOX), that's a DeltaV of just over 2.6 km/s.  The full scale vehicle was aiming for a dry mass of 5x as much and a mere 10 mT payload, it would have needed a different engine, even with a good 450 ISP the vehicle would have a launch mass of around 500 mT to reach orbit and would need >50 RL10B-2 (the best in production engine from P&W) or 4 Shuttle main engines, which is also the only Hydro-Lox engine designed to operate continuously from Sea-level to to vacuum while being restart able & reusable, all necessary features of DC-Y.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/11/2015 08:48 pm
Again, first-principles reason why it's not possible. Mere historical analogy is not good enough to show it can't be done.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/11/2015 09:22 pm
First off you are the one repeatedly trying to argue from historical vehicles, pointing out various metrics of performance and claiming they are achievable all in a single vehicle without consideration of how they conflict.

Now with that line of logic thoroughly refuted your now abdicating any connection with real world materials or systems, and claim I need to show that the laws of physics alone invalidate your claims?

This is preposterous and insulting because you know very well that their is no first principle of physics that limits a vehicles DeltaV, only the speed of light is denied to us by the laws of physics.

You can always propose exponentially smaller and smaller dry mass fractions and higher and higher T:W ratio engines made from any theoretically possible material and any theoretically possible propellant we can imagine that will make any DeltaV achievable.  An anti-matter rocket made of neutronium is certainly allowed by the laws of physics but has no place in this this thread.

If this is your position then you have business posting in this thread as you have left the bounds of rational engineering discussion.  And I am still waiting for your actual calculations.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/11/2015 09:45 pm
First off you are the one repeatedly trying to argue from historical vehicles...
Because if you're trying to prove something is possible, a single example from history is sufficient. If you're trying to prove something isn't possible, historical analogy isn't useful.

Yup, there's asymmetry there.

Historical analogy may help you throw doubt on the feasibility of something, but it doesn't touch the possibility of something.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/11/2015 09:50 pm
First off you are the one repeatedly trying to argue from historical vehicles, pointing out various metrics of performance and claiming they are achievable all in a single vehicle without consideration of how they conflict.

Now with that line of logic thoroughly refuted your now abdicating any connection with real world materials or systems, and claim I need to show that the laws of physics alone invalidate your claims?

This is preposterous and insulting because you know very well that their is no first principle of physics that limits a vehicles DeltaV, only the speed of light is denied to us by the laws of physics.

You can always propose exponentially smaller and smaller dry mass fractions and higher and higher T:W ratio engines made from any theoretically possible material and any theoretically possible propellant we can imagine that will make any DeltaV achievable.  An anti-matter rocket made of neutronium is certainly allowed by the laws of physics but has no place in this this thread....
Okay, show that you cannot achieve a rocket that does a 10:1 mass fraction with available materials and using chemical propulsion.

And yes, you CAN get better and better mass fractions as we make manufacturing and materials science advances. Heck, we've barely touched a lot of materials science advances, not even achieving the levels of performance we can get out of the materials we already have.

This is my point: you can't sandbag a design, then claim it's not possible to significantly exceed that design. What you're doing is not demonstrating how high of performance you can get, instead, you are trying to show what can be done without any degree of cleverness. MCT will likely involve cleverness.

Do you have any reason to believe that SpaceX is not trying to advance the state of the art in materials science or mass fraction? Because I have evidence that they ARE.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/12/2015 03:58 am
Where do you get this belief that the burned of proof is on me?  You are the one claiming cutting edge performance on par with what a SSTO vehicle needs.  YOU need to prove that envelope pushing is possible and can be done at reasonable costs, I am STILL waiting for your numbers that you hinted at several posts ago.

You are basically admitting that your logical process consists of pushing every performance margin to to braking point and claiming THAT will be the MCT design, while I am intentionally try to find a conservative design that would not require as much 'cleverness' (all though far from none).  Other word for 'cleverness' is TIME and MONEY, and 'blowing up a few in development'.

If your next response doesn't contain actual calculations then this discussion is pointless.  I repeat SHOW YOUR WORK.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/13/2015 12:03 am
Where do you get this belief that the burned of proof is on me?...
Because you claim it's not possible. Not just unfeasible, but not possible.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/13/2015 12:05 am
Where do you get this belief that the burned of proof is on me?  You are the one claiming cutting edge performance on par with what a SSTO vehicle needs.  YOU need to prove that envelope pushing is possible and can be done at reasonable costs, I am STILL waiting for your numbers that you hinted at several posts ago.

You are basically admitting that your logical process consists of pushing every performance margin to to braking point and claiming THAT will be the MCT design
No I'm not. I don't claim to think I can predict MCT, just establish some bounds about what COULD be done.
Quote
.while I am intentionally try to find a conservative design that would not require as much 'cleverness' (all though far from none)....
...that line of thinking would never have produced Falcon 9 v1.1 or Full Thrust, which is necessary to do their partial reusability.


I said it'd take time. I may get to it this weekend.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 11/13/2015 01:12 am
Where do you get this belief that the burned of proof is on me?  You are the one claiming cutting edge performance on par with what a SSTO vehicle needs.  YOU need to prove that envelope pushing is possible and can be done at reasonable costs, I am STILL waiting for your numbers that you hinted at several posts ago.

You are basically admitting that your logical process consists of pushing every performance margin to to braking point and claiming THAT will be the MCT design
No I'm not. I don't claim to think I can predict MCT, just establish some bounds about what COULD be done.
Quote
.while I am intentionally try to find a conservative design that would not require as much 'cleverness' (all though far from none)....
...that line of thinking would never have produced Falcon 9 v1.1 or Full Thrust, which is necessary to do their partial reusability.


I said it'd take time. I may get to it this weekend.

Their is the rub, SpaceX didn't START at Full-thrust, they started at something like half as much and built up too it over several years.  They were CONSERVATIVE initially, which is exactly what I'm saying should be done, their will certainly be an attempt to improve performance over time and that could yield higher payloads, faster transit times or more safety and engine-out margin.  Your trying to pretend that a conservative start permanently cripples any future potential for improvement.


As for the numbers, sorry I though you had them ready already, we will rejoin this topic when you have them ready.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 11/13/2015 01:20 am
SpaceX only launched 5 F9 v1.0s. They were basically all dev vehicles. If you want to argue the first couple MCTs will have sandbagged weight fractions, then that's fine. I won't contradict you. But actual operational MCTs capable of the full mission cycle and of carrying passengers in both directions... That I am certain will /require/ cutting-edge capability to be both economical and safe.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 11/17/2015 02:52 pm
Just a musing, because I know the following concept has some big 'issues'. Nevertheless it's been in my head despite my own objections, and could do with others agreeing it isn't useful/workable :)

We've spoken about a BFR launching
- MCT cargo, MCT passenger.
- tankers for refueling (also versions of MCT)
and some have added:
- existing payloads, with multiple satellites in a single fairing etc
- big payloads (space station components etc)

If you were going to try to use earth based requirements to help fund your MCT... could a tanker upper stage be made that ALSO launches a single satellite (up to FH size)? 

You'd have 1 payload/satellite of variable mass, sitting on top of the tanker second stage, with the tanker filled to use up the rest of the launch capability (secondary payload). Instead of launching tanker-only missions a launch could position the payload, and then continue by shipping the reduced tanker payload to a depot.

ie: 2 payloads configured in a novel way.

I believe the difficulties of making this work outweigh the benefits.
..... There's less tanker fuel going up and it's going towards the wrong place. For each half-filled tanker you're doubling your refuelling stops and doubling your tanker numbers waiting to offload. The launch difficulties of a BFR are far higher than a F9 or FH (for now). And it locks you in to satellite launch timing rather than fuel launch requirements (or requires you to leave the tanker waiting in orbit).

So just thinking aloud... I'm 95% against but my 5% wants to play it out.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 11/17/2015 03:32 pm
If you were going to try to use earth based requirements to help fund your MCT... could a tanker upper stage be made that ALSO launches a single satellite (up to FH size)? 

Two reasons at least why it does not make sense. Minor, it would need development of a small fairing, which is still big and expensive. Such a fairing would otherwise not be needed. Major, as you already mentioned, the orbits will not match. Fuel will go to near equatorial LEO or to the easiest LEO reachable from the launch site. The payload will need a different inclination and transfer orbit. Changing inclination in LEO is HARD.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 11/22/2015 07:20 pm
I think he was referring to the launch vehicle, aka make an even large BFR to launch an enormous MCT which has the propellant capacity to do a direct departure to mars.  In other words he thinks doubling the size of the launch rocket is worth it to avoid making a SEP tub because you know 'fewer vehicles' logic.  ::)

Well, if you already have to build a custom factory and a custom launch pad, what's the marginal cost of increasing the rocket size? Materials are cheap.

Quote
Total cost is the metric we care about, if it be 1 vehicle or 10.

That's where I disagree. Development cost, early in the program, is far more critical since it will be easier to get investment once a functioning Mars transport system is demonstrated.

They may well use SEP tugs eventually, but the initial system should work without them.


Quote
Keep in mind that tank is 100 mT larger and lacks any insulation.

100 mT larger? I expect the propellant mass of MCT to be greater than that of F9.

 (if Isp is 380 and delta-v is 6 km/s, then mass ratio needs to be 5: with empty mass = 50 tons and payload mass = 100 tons that's 600 tons of propellant. If the empty mass is 100 tons that's 800 tons of prop. If the delta-v is larger it will be more, quite possibly over 1000 tons.)

Quote
Finally I expect their to be multiple smaller tanks through the vehicle to accommodate good weight distribution and avoid the cargo-holds large volume, this will cut down on the efficiency of the tank.

Why would it need multiple smaller tanks? I would expect it to be shaped rather like a Blue Origin New Shepard or Apollo Lunar Module - relatively wide fuel tank + engines at bottom, capsule at top.

I think you may be over complicating things.

[quote[
You can't just scale the vehicle to conquer thouse factors, the parasitic stuff all grows with overall vehicle mass (except for com/computer systems which are negligible already).[/quote]

Well I was thinking in square/cube law, minimum gauge terms but maybe not.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 11/25/2015 09:38 pm
If you were going to try to use earth based requirements to help fund your MCT... could a tanker upper stage be made that ALSO launches a single satellite (up to FH size)? 

Two reasons at least why it does not make sense. Minor, it would need development of a small fairing, which is still big and expensive. Such a fairing would otherwise not be needed. Major, as you already mentioned, the orbits will not match. Fuel will go to near equatorial LEO or to the easiest LEO reachable from the launch site. The payload will need a different inclination and transfer orbit. Changing inclination in LEO is HARD.

True, but let's assume for a moment they'll be launching from the Cape.  Most sats going to GTO launch from there, unless they are going to a a polar orbit, then they launch from Vandy.

You would need either a PLF that can mount on the nose of a reusable tanker stage.  Or perhaps a payload bay in the nose that could deploy a sat out a hatch in the nose.  Something like the Rocketplane Kistler K-1 was going to do. 
The stage with a D4H or FH class sat going to GTO (<13mt so far, historically) could launch directly to a transfer orbit, just as most sats going to GEO/GSO do now.  Once in the correct location, it deploys the sat which then does it's own propulsive acting to put it in the correct GEO/GSO orbit.  Again, like is usually done now.
The transfer orbit will take the tanker stage back close to Earth where it can do a small burn to deorbit itself and come back to the launch pad.   The trick is to have it come back and deorbit at the right time to is gets back to the launch site.
That's probably one reason SpaceX decided not to pursue a reusable F9US.  Other than Dragon, most payloads F9/FH will be launching will be going BLEO, and so getting them back could be tricky, where it's much easier if you aren't trying to get the upper stage back. 

Two things bring down costs.  Resuability and economics of scale.  If you make stages cheaper and churn out more, you can bring the cost per unit down, and SpaceX seems to have taken that path with F9US.

But, and internal payload bay on the nose of an MCT tanker could look something like this...with a payload bay behind the nose cap instead of a docking hatch.  The stage could use solar panels like this that could retract, or depending on how long it'll be up there, maybe methalox fuel cells or IVF to make electricity from residuals propellants so there's no solar panels to need to mess with for such missions.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/02/2015 08:04 pm
I did a small side calculation to see what kind of cargo delivery capacity MCT would have for a lunar landing.

Again 75 mt dry mass, maximum propellant load of 300 mt, I'll be assuming NO lunar derived propellants and a similar SEP tug that delivers to EML1.  Any crew reach EML1 via a Dragon capsule.

Lunar landing from EML1 is 2520 m/s, Earth return is via direct assent of 2740 m/s to an atmospheric intersecting swing buy in which aerobraking brings us to a LEO orbit.  As in the return from Mars the vehicle will be comply empty of propellants at this point and require a small additional refueling to land.

Working backward the empty vehicle would 80 mt propellant to perform Earth return so this much needs to be retained at landing.  If the vehicle starts full fueled at EML1 then it can land offload 85 mt cargo and still make Earth return.  If the SEP tug were to move the MCT past EML1 and down to a Low lunar orbit (decent of 1870 m/s at the cost of ~800 m/s at low thrust) then the cargo delivery would nearly double to 160 mt.

Now lets look at a manned landing an return, I'll assume the same 25 mt return mass goal for Mars that Musk has stated so this will presumably the mass of a habitation module being carried inside the MCT.  To return to Earth with this module the propellant requirement grows by 33% as our dry mass has increased from 75 to 100 mt.  At 107 mt of propellant from EML1 this is starting to cut into payload quite a lot, we have only 33 mt of cargo along with the 25 mt habitat. 

The benefit of coming from LLO is considerable for this mission, the MCT could offload 108 mt while carrying the 25 mt habitat their and back.  But the cost in time of having a SEP tug move the vehicle from EML1 to low lunar orbit is likely to be 2-3 months, while the crew habitat is certainly capable of this period of life-support (it can go to mars and back) it may not be worth it if the lunar stay is only going to be of only modest length.  If on the other hand the lunar stay is several months this delay might not be a problem.  Alternatively crew rendezvous could be moved to LLO itself to remove this period from the crew's mission duration.

In any event this type of lunar mission, even without crew would be an excellent shake-down mission for the MCT as it would duplicate many of the aspects of a Mars mission.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 12/03/2015 07:28 am

...

In any event this type of lunar mission, even without crew would be an excellent shake-down mission for the MCT as it would duplicate many of the aspects of a Mars mission.

Have you consider using unmanned MCT tankers in LEO and LLO to top off the MCT lunar lander's prop tanks? In case of LLO for both descent & ascent from the Lunar surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 12/03/2015 07:52 am
Have you consider using unmanned MCT tankers in LEO and LLO to top off the MCT lunar lander's prop tanks? In case of LLO for both descent & ascent from the Lunar surface.

I have thought of a fully refueled tanker and a fully fueled MCT going to TLI together. The tanker then transfers its fuel to the MCT and does a direct return to earth while the MCT goes to land and relaunch from the moon. It's the most fuel efficient mission profile. The tricky part is rendezvous and refuelling on the way to the moon.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/03/2015 08:09 am

...

In any event this type of lunar mission, even without crew would be an excellent shake-down mission for the MCT as it would duplicate many of the aspects of a Mars mission.

Have you consider using unmanned MCT tankers in LEO and LLO to top off the MCT lunar lander's prop tanks? In case of LLO for both descent & ascent from the Lunar surface.

No that would be very inefficient.  The MCT has a 75 mt dry mass which would be moved all the way to LLO to do a job that could easily be done by a mere tank with a ~5% dry mass fraction.

I would put that tank on a SEP tug which is how both the propellants and MCT will be moved from LEO to the staging point for the lunar landing.

If we need more propellant then I would just move the staging point closer to the moon as I described, this easily brings the cargo delivery mass to over the 100 mt design goal and the MCT will almost have a volume limit just like every vehicle which means we can't just arbitrarily increase useful cargo even if we have the DeltaV to push it on paper it still needs to fit into the vehicle.

Speculation about 'MCT Tanker' is in my opinion misguided, the vehicle would be a terrible tanker due to it's dry mass which is highly specialized for other functions.  The LEO tanker will be a stretched 2nd stage which will transfer propellant to SEP tugs which will move propellants beyond LEO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 12/03/2015 10:02 am
Have you consider using unmanned MCT tankers in LEO and LLO to top off the MCT lunar lander's prop tanks? In case of LLO for both descent & ascent from the Lunar surface.

I have thought of a fully refueled tanker and a fully fueled MCT going to TLI together. The tanker then transfers its fuel to the MCT and does a direct return to earth while the MCT goes to land and relaunch from the moon. It's the most fuel efficient mission profile. The tricky part is rendezvous and refuelling on the way to the moon.

Obviously you dual launched the MCT and the tanker from a couple of nearby launch facilities at the same time.  ;)

Unless you think there will only be one launch pad for the BFR.  :o
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 12/03/2015 10:24 am
I have thought of a fully refueled tanker and a fully fueled MCT going to TLI together. The tanker then transfers its fuel to the MCT and does a direct return to earth while the MCT goes to land and relaunch from the moon. It's the most fuel efficient mission profile. The tricky part is rendezvous and refuelling on the way to the moon.

Obviously you dual launched the MCT and the tanker from a couple of nearby launch facilities at the same time.  ;)

Unless you think there will only be one launch pad for the BFR.  :o

They can take a month or two to launch and refuel both in LEO, just the way they would assemble a Mars fleet to launch into a launch window. What's the problem?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 12/03/2015 10:38 am

...

In any event this type of lunar mission, even without crew would be an excellent shake-down mission for the MCT as it would duplicate many of the aspects of a Mars mission.

Have you consider using unmanned MCT tankers in LEO and LLO to top off the MCT lunar lander's prop tanks? In case of LLO for both descent & ascent from the Lunar surface.

No that would be very inefficient.  The MCT has a 75 mt dry mass which would be moved all the way to LLO to do a job that could easily be done by a mere tank with a ~5% dry mass fraction.

I would put that tank on a SEP tug which is how both the propellants and MCT will be moved from LEO to the staging point for the lunar landing.

If we need more propellant then I would just move the staging point closer to the moon as I described, this easily brings the cargo delivery mass to over the 100 mt design goal and the MCT will almost have a volume limit just like every vehicle which means we can't just arbitrarily increase useful cargo even if we have the DeltaV to push it on paper it still needs to fit into the vehicle.

Speculation about 'MCT Tanker' is in my opinion misguided, the vehicle would be a terrible tanker due to it's dry mass which is highly specialized for other functions.  The LEO tanker will be a stretched 2nd stage which will transfer propellant to SEP tugs which will move propellants beyond LEO.

Since you will need the tankers in whatever form for the Methane & Lox propellants for Mars missions anyway. Using them even inefficiently might be a better trade than developing a separate SEP inspace vehicle with a different propellant (Xenon) that is not readily available in large quantities.

IMO the MCT tanker will not be too different from the MCT. Otherwise you will be developing yet another vehicle that can be reuse. Presuming you version of the MCT tanker is not expendable.

It is cheaper to developed a single general purpose vehicle than 3 different specialized vehicles in parallel.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 12/03/2015 10:48 am
I have thought of a fully refueled tanker and a fully fueled MCT going to TLI together. The tanker then transfers its fuel to the MCT and does a direct return to earth while the MCT goes to land and relaunch from the moon. It's the most fuel efficient mission profile. The tricky part is rendezvous and refuelling on the way to the moon.

Obviously you dual launched the MCT and the tanker from a couple of nearby launch facilities at the same time.  ;)

Unless you think there will only be one launch pad for the BFR.  :o

They can take a month or two to launch and refuel both in LEO, just the way they would assemble a Mars fleet to launch into a launch window. What's the problem?

Was thinking of a LEO prop depot for the refueling. So if you dual launch, you minimized the time needed to complete the mission. 

You way is also workable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 12/03/2015 11:35 am
They can take a month or two to launch and refuel both in LEO, just the way they would assemble a Mars fleet to launch into a launch window. What's the problem?

Was thinking of a LEO prop depot for the refueling. So if you dual launch, you minimized the time needed to complete the mission. 

You way is also workable.

I fully expect some kind of depot to emerge sooner or later. I am just arguing that early missions to Mars or in this case to the moon with two or more MCT can be done without. Especially as the moon missions don't need to interfere with the Mars windows.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/03/2015 09:01 pm

Since you will need the tankers in whatever form for the Methane & Lox propellants for Mars missions anyway. Using them even inefficiently might be a better trade than developing a separate SEP inspace vehicle with a different propellant (Xenon) that is not readily available in large quantities.

IMO the MCT tanker will not be too different from the MCT. Otherwise you will be developing yet another vehicle that can be reuse. Presuming you version of the MCT tanker is not expendable.

It is cheaper to developed a single general purpose vehicle than 3 different specialized vehicles in parallel.

Tankers are needed but they are hardly a 3rd vehicle, they are just stretched 2nd stages with a nose cone covering a Xenon/Krypton tank and a hose port.  This can launch and deliver 100 mt of propellants of varying combinations, either all Metho-Lox from residuals or SEP propellants.

The SEP tugs would have an integrated Xenon/Krypton tank for it's own use or around 50 mt and a Metho-Lox tank for offloading to the MCT, around 150 mt would be sufficient.  These tanks should mass 5 and 2.5 mt respectively and the rest of the vehicle would only come out to around 10 mt meaning it can be launched mostly fueled on the BFR.

A vehicle this size is going to be a lot simpler to design and produce then the MCT itself which goes through incredible stresses and flight regimes.  The SEP is basically made of off the shelf satellite parts, Solar panels and Hall thrusters both of which are going to be mass produced by SpaceX in it's Satellite Swarm.

Two tankers refuel 1 SEP with MethoLox and Xenon to make a delivery of Metho-Lox to EML1.  One tanker refuels two SEPs with just Xenon to move two MCT's to EML1.  That's 3 fuel launches and 2 MCT so a 2:5 ratio for cargo delivery.  Nearly doubling the LEO to Mars efficiency at the cost of a small SEP tug that should be a fraction of the cost of the vehicles that are already necessary.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CuddlyRocket on 12/04/2015 06:39 am
With all this talk of tankers for in-orbit refueling of the MCT, I had the following thought concerning the Mars mission it was designed for:

If a two-stage BFR can launch both the second stage and the MCT into LEO with the MCT still attached then both can be refueled - though the MCT most likely will be fueled for the first time. The refueled second stage can then use some of that propellant to provide a substantial fraction of the TMI burn. When the MCT detaches to use its own engines and propellant to provide the remainder of the TMI burn, the second stage uses its remaining propellant to return to LEO orbit (it will obviously need much less propellant to return to LEO without the multi-hundred mt MCT attached!) and/or Earth ground return.

This also works with a one-stage BFR launching an MCT into LEO. Assuming reusable tankers to refuel the MCT, and which will need to securely dock for that purpose, then one such tanker (or more actually) can provide TMI boost assist before themselves detaching and returning to Earth.

My understanding of the minimum size of the MCT is determined by the requirement to carry sufficient propellant to both perform the TMI burn and land 100 mt cargo on Mars, any such craft will then have sufficient performance to launch from Mars directly to Earth given much less cargo and with ISRU refuelling. Any assist to the TMI burn external to the MCT will enable a reduction of the propellant it needs to carry and concomitant reduction in its size and mass with cascading effects on the BFR and tanker designs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 12/04/2015 08:12 am
Using SEP for moon missions would save propellant and hence the number of tanker flights. However, that may not make things cheaper.

The SEP stage is likely to be quite expensive, it is basically all electronics, solar panels and thrusters which are all expensive in $/kg, tanks which are cheap make up a small percentage of the total mass.

Using SEP for the MCT transfer to lunar orbit adds costs to the MCT as it would need fully rad-hard electronics. SEP cannot be used for manned transfer to lunar orbit, so there is the overhead of maintaining two systems. The length of time required > 6 months limits the reflight rate for the MCT which adds to the costs.

Finally SEP costs are mainly up-front while refuelling in LEO is pay-as-you-go. This means that near term costs for SEP are higher than all cryogenic. With an increasing flight rate the money spent at any point in time could quite well be more for SEP, even if it seems cheaper on a per flight basis. SEP also has more opportunity cost and more risk (suppose it is superseded before its payback time).

[As an aside, it does not seem possible to use SEP for Mars and maintain a one synod reuse of the MCT. Similar cost arguments mean that SEP is quite likely not cheaper either.]

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 12/04/2015 09:17 am
[snip]

IMO the MCT tanker will not be too different from the MCT. Otherwise you will be developing yet another vehicle that can be reuse. Presuming you version of the MCT tanker is not expendable.

It is cheaper to developed a single general purpose vehicle than 3 different specialized vehicles in parallel.

Tankers are needed but they are hardly a 3rd vehicle, they are just stretched 2nd stages with a nose cone covering a Xenon/Krypton tank and a hose port.  This can launch and deliver 100 mt of propellants of varying combinations, either all Metho-Lox from residuals or SEP propellants.

You are describing a new large expendable vehicle that can maneuver and loiter in orbit.

Quote
The SEP tugs would have an integrated Xenon/Krypton tank for it's own use or around 50 mt and a Metho-Lox tank for offloading to the MCT, around 150 mt would be sufficient.  These tanks should mass 5 and 2.5 mt respectively and the rest of the vehicle would only come out to around 10 mt meaning it can be launched mostly fueled on the BFR.

A vehicle this size is going to be a lot simpler to design and produce then the MCT itself which goes through incredible stresses and flight regimes.  The SEP is basically made of off the shelf satellite parts, Solar panels and Hall thrusters both of which are going to be mass produced by SpaceX in it's Satellite Swarm.

AIUI none of those COTS parts are design for BEO radiation and thermal environments. So you are basically doing a partial parallel MCT development. Also the Hall thrusters seems like a mismatch with the impulse required plus developing the solar arrays & radiator arrays infrastructure on the vehicle.

Quote
Two tankers refuel 1 SEP with MethoLox and Xenon to make a delivery of Metho-Lox to EML1.  One tanker refuels two SEPs with just Xenon to move two MCT's to EML1.  That's 3 fuel launches and 2 MCT so a 2:5 ratio for cargo delivery.  Nearly doubling the LEO to Mars efficiency at the cost of a small SEP tug that should be a fraction of the cost of the vehicles that are already necessary.

Count 3 expendable tankers of 2 different types and 3 semi-expendable SEP tugs. As compare to no expendable vehicles using MCT variants.

Plus how do you planned to transfer the propellants and do the orbital rendezvous of the various elements?



Darn @Mike Atkinsom beats me to respond to @Impaler
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/04/2015 05:58 pm
Expendable Tankers???  Of course not, this is just the BFR's normal reusable 2nd stage with a mission kit on the nose in the place the MCT would have been.  It would need some loiter time in orbit but is already part of being a reusable stage so you can make controlled re-entry and the mission kit would be used to extend that time.

The SEP mass is tiny compared to the MCT at 15 vs 75 mt, dry mass is the most reliable cost estimate basis and by that metric a SEP tug is far cheaper to develop and build then the MCT itself.  Each round trip from the tug will replace roughly one whole launch of the BFR which is likely to cost around $100 million, so they pay for themselves on the first or second trip and will well into net savings by the end of a Synod.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 12/04/2015 07:01 pm
@Impaler

My presumption is that the MCT is the upper stage. You think otherwise?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/04/2015 10:06 pm
Yes, that's something I've been saying for this whole thread.  It's necessary to make BFR a capable launcher for all uses and to allows actual revenue generation before 'tickets to mars' are being sold.

In addition it allows the MCT to be a fraction of the size of the combined concept which reduces propellant needs on the Martian surface AND makes it feasible to actually have a launch abort capability. 

The smaller MCT can actually put it's cargo close to the surface, rather then several floors off the ground making unloading much simpler via a deploy-able ramp.

Lastly such a MCT actually makes sense as a long term vehicle that takes on a surface-2-orbit shuttle role at mars as the whole system evolves, a huge vehicle for direct flight is far over-built for that role.

And finally a smaller vehicle with much less aggressive DeltaV targets makes for a vastly cheaper and faster development at lower risk, particularly if you have already learned from creating a reusable 2nd stage that uses the same engines and built a good flight history with it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 12/05/2015 12:02 am
* A single-stage BFR is not likely to be a good cargo or liquid ferry to LEO, much less to GTO.  Payload mass fractions on a single stage are very small.  You can expect a *reusable* single stage rocket-based launch vehicle to be extraordinarily difficult to do with any payload at only 360-380s Isp.

* The optimal designs for transporting large-diameter cargo and liquids start to diverge at scale, with very different needs because of differing densities.  A spherical tank the size of a payload fairing will always be way too heavy when full to transport in a reasonable vehicle for lofting that payload fairing.  As volume dictates reentry vehicle design, this becomes important when you want to reuse all stages.

* MCT is likely to require extensive design compromises and dry mass increases to achieve reusability, which makes it a very poor cargo ferry to LEO, and a moderately bad liquid ferry to LEO.

* Mars missions are always starved for mass, starting with the maximum structurally-integral amount that can be lofted by the largest launch vehicle available;  If you make launch cheap and can spend as many launches as you like in propellant and cargo, you still have this limit on the part of the vehicle that can't be divided.  It makes sense to spend this number on durable vehicular dry mass, and fill the rest of the mission on subsequent launches, because that maximizes the total payload that can be feasibly landed, which has a capped ratio to vehicular dry mass.

* BFR will need to loft many, many liquids payloads for every MCT departure.

* A stage which reaches Earth orbit and lands back at Earth, whatever way that occurs, has fairly high dry mass fraction.

* Their immediate business future, in Falcon Heavy, will be reliant on a stage that lands at the launchpad, another stage that lands far downrange, and another stage that reaches orbit;  This third stage is something which they would like to reuse, but can't square the circle economically, because of dry mass increases or propellant increases.

* The fewer the stages, the worse dry mass increases harm payload capacity.



The simplest, most efficient way to reuse a BFR and to launch Mars missions will be to cut it into two stages, with several modular options for third stages - MCT, a reusable liquids carrier, and a reusable large cargo carrier, with perhaps a fourth expendable boost stage for reaching GTO with smaller payloads inside that large cargo carrier.   The RTLS + barge landing system is preserved, and the reusable third stages reach orbit and then return at their leisure to the launchsite.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 12/05/2015 12:45 am
Are you on L2, Burninate?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/05/2015 12:58 am
A single-stage BFR is not likely to be a good cargo or liquid ferry to LEO, much less to GTO.  Payload mass fractions on a single stage are very small.  You can expect a *reusable* single stage rocket-based launch vehicle to be extraordinarily difficult to do with any payload at only 360-380s Isp.


Are you replying to me?  I've been saying all along that BFR will have 2 stages like Falcon, the MCT would be a 3rd stage on-top of that but the first two stages can be launched on their own just like Falcon to put payloads in LEO or beyond without using the MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 12/05/2015 01:07 am
MCT may be very stripped down when in cargo mode, essentially a reusable second stage with a long-loiter package and refueling capability. Don't know why you'd insist on yet another stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/05/2015 01:45 am
What are you stripping off and what kind of mass estimate do you have this before and after?

If MCT in it's normal state is overbuilt as a Tanker I find it very hard to believe that it could be stripped into
Quote
essentially a reusable second stage with a long-loiter package and refueling capability
for less money then just making exactly THAT from a clean sheet design with a common diameter and tank fabrication process shared with the first stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 12/05/2015 02:00 am
10:1 mass ratio. Maybe 600 tons totally full.

MCT in its normal state IS stripped down.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 12/05/2015 02:46 am
Are you on L2, Burninate?

Not at present, no.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: SolarExploration on 12/08/2015 07:01 am
Maybe from a more non technical angle, it could be done like this?...
 https://m.youtube.com/watch?v=z4h1mvyRIjc
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/09/2015 01:42 am
That is actually surprisingly like what I see the LONG term transit solution looking like.

Direct launch of capsule like vehicle with passengers in short term air-plane like accommodations.
Transit vehicle which remains in space and provides for all life-support during transit.
Return from the surface to this transit vehicle in mars orbit for return to Earth.
Re-entry at Earth in the capsule vehicle.

Key differences I see though..

Transit vehicle staging position is EML1 rather then LEO.
Passengers vehicle needs refueling in LEO to get to LEO and this means 3-4 days to the transit vehicle.
Transit vehicle won't stay at mars but will return immediately after picking up return passengers.

On a non-technical note the kind of 'scientific adventure tourism' sounds like promising intermediate between the first humans on mars which will be space agency Astronauts and later full on colonists.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: cscott on 12/11/2015 03:34 pm
"Big Falcon Spaceship"
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 12/11/2015 05:29 pm
A BFR can be conceived with lots less than 30 1st stage engines. 
As a point of reference, I’ve taken these Musk’s statements as a given even though I bet they’ll be modified at his supposed late 2015 (likely spring 2016) briefing.
100mT land on Mars cargo
Land the whole thing and re-use it; i.e. return it to Earth
“there's a booster rocket and there's a spaceship. So the booster rocket's just to get it out of Earth's gravity because Earth has a deep gravity well and thick atmosphere, but the spaceship can go from Mars to Earth without any booster”
Raptor thrust over 230mT; use a lot of them.
380 seconds ISP vacuum

My BFR is 12.5m diameter, making a relatively squat first stage under 30m tall.   Propellant tanks alone 23.5m.  Delivers ~2.8Km/sec after gravity losses.  The wider diameter leaves room for growth for later larger versions, allowing for lengthening the tanks in both stages, adding engines and lengthening the cargo hold.  Assumed a heavy dry weight of 90mT for stage 2 MCT.

No worries about pad towers for 100m high rockets.  BFR with MCT 2nd stage is shorter than the 70m F9 but 10 times more massive.  BFR’s multi Raptor engine driven 12.5m diameter is a nice size to fit living quarters and various colonial heavy equipment.

Don’t need 15 million LBS thrust, but with mass ratios ~4.3%  need a bit over 12 million LBS (54 million Newtons) thrust, 24 engines arranged in rings of 16 and 8 with room for a future center engine or 2.

Given the huge delta V requirements for both Mars departure from refueling at LEO AND later functioning as a SSTO taking off from Mars’ surface and return to Earth, I put the Km/sec budget into the 2nd stage.  Stage one goes low & slow, under 3 Km/sec, boosting the heavy 2nd stage before return to launch site, RTLS.  The dry weight plus fuel of the returning 1st stage exceeds Raptor thrust so any 2 of the 8 engine inner ring engines throttled down provide landing thrust.

Total BFR mass 4450mT or 9.8 million LBS.  LEO mass fraction 4.3%.

Stage One:
12.5m diameter with 23.5m length propellant tanks
3280mT   7.2 million LBS  1st stage fueled mass
230mT thrust engines  506K LBS
24 engines 56 million Newtons  12.2 million LBS Thrust; T/W 1.24
Rings of 16 engines, and 8 engines
Avg ISP from sea level to vacuum 325
After 1 Km/sec additional Delta V reserved for RTLS Rocket Equation gives 3.4 Km/sec but nets under 3 Km/sec Delta V after gravity losses

Stage Two The MCT:
Dry Mass 90mT; 100mT is cargo
12.5m diameter with 7.5 m length for propellant tanks. 
Cargo 8.5m length ; 1040 m3 volume
(Plenty of space for expanded fuel tanks in a simple modified tanker version.)
1165mT fueled mass (2.6 million LBS)
380 seconds ISP vac; Rvac engines assumed 14% higher thrust as with F9 FT
6 Rvac engines   3.5 million LBS Thrust
6.75Km/sec Delta V capability, via Rocket eq.
8.4Km/sec Mars liftoff with only 25mT return cargo

I also modeled another small version to see just how small a BFR could meet Elon’s goals. I optimistically lowered the MCT 2nd stage dry weight from 90mT to 75mT.  This minimal, 12m diameter optimistic version needs only 19 engines with rings of 12, 6 and two center engines.  The MCT stage 2 has only 5 engines, reducing the cost of building this BFR/MCT from 30 Raptors to 24.  Engines are the big cost driver for mass producing BFRs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 12/11/2015 05:55 pm
From another thread, here is a recent quote by Musk in an interview:

Direct quote from Elon implying no second stage, just booster and mars spacecraft from an article in GQ:

"Well, there's two parts of it—there's a booster rocket and there's a spaceship. So the booster rocket's just to get it out of Earth's gravity because Earth has quite a deep gravity well and thick atmosphere, but the spaceship can go from Mars to Earth without any booster, because Mars's gravity is weaker and the atmosphere's thinner, so it's got enough capability to get all the way back here by itself. It needs a helping hand out of Earth's gravity well. So, technically, it would be the BFR and the BFS." As in "Big frakking Spaceship."

http://www.gq.com/story/elon-musk-mars-spacex-tesla-interview?utm_source=10370

So... I guess we are back to basics, what many of us have arguing, it seems? This thread has been devalued (and made less interesting) in the last few months by people wanting to discuss their own architectures (yes, you know who you are), so hopefully this can narrow down the discussion again.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 12/11/2015 06:37 pm
He also stated it was a very unusual (crazy) architecture, so  I suspect many of the ideas put forward that are similar to 'large dragon' are likely to be wrong.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Occupymars on 12/11/2015 08:03 pm
So the second stage is the spaceship confirmed. The longer this speculation goes on the more people have complicated it. Second stage's third stage's ect. KISS
This is what we know about his mars architecture so far:
1. Fully reusable
2. Mars ISRU
3. Two stage's
4. 100mt to mars surface
From those points I think we can safely say that his architecture includes on orbit refueling probably with a second BFS to remain fully reusable.

Oh man can't wait to see his architecture presented just awesome.
I wonder if the BFS will be a biconical design(Mars thin atmosphere) like blue origin's spaceship or a capsule.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 12/11/2015 08:56 pm
A BFR can be conceived with lots less than 30 1st stage engines. 
As a point of reference, I’ve taken these Musk’s statements as a given even though I bet they’ll be modified at his supposed late 2015 (likely spring 2016) briefing.
100mT land on Mars cargo
Land the whole thing and re-use it; i.e. return it to Earth
“there's a booster rocket and there's a spaceship. So the booster rocket's just to get it out of Earth's gravity because Earth has a deep gravity well and thick atmosphere, but the spaceship can go from Mars to Earth without any booster”
Raptor thrust over 230mT; use a lot of them.
380 seconds ISP vacuum

My BFR is 12.5m diameter, making a relatively squat first stage under 30m tall.   Propellant tanks alone 23.5m.  Delivers ~2.8Km/sec after gravity losses.  The wider diameter leaves room for growth for later larger versions, allowing for lengthening the tanks in both stages, adding engines and lengthening the cargo hold.  Assumed a heavy dry weight of 90mT for stage 2 MCT.

No worries about pad towers for 100m high rockets.  BFR with MCT 2nd stage is shorter than the 70m F9 but 10 times more massive.  BFR’s multi Raptor engine driven 12.5m diameter is a nice size to fit living quarters and various colonial heavy equipment.

Don’t need 15 million LBS thrust, but with mass ratios ~4.3%  need a bit over 12 million LBS (54 million Newtons) thrust, 24 engines arranged in rings of 16 and 8 with room for a future center engine or 2.

Given the huge delta V requirements for both Mars departure from refueling at LEO AND later functioning as a SSTO taking off from Mars’ surface and return to Earth, I put the Km/sec budget into the 2nd stage.  Stage one goes low & slow, under 3 Km/sec, boosting the heavy 2nd stage before return to launch site, RTLS.  The dry weight plus fuel of the returning 1st stage exceeds Raptor thrust so any 2 of the 8 engine inner ring engines throttled down provide landing thrust.

Total BFR mass 4450mT or 9.8 million LBS.  LEO mass fraction 4.3%.

Stage One:
12.5m diameter with 23.5m length propellant tanks
3280mT   7.2 million LBS  1st stage fueled mass
230mT thrust engines  506K LBS
24 engines 56 million Newtons  12.2 million LBS Thrust; T/W 1.24
Rings of 16 engines, and 8 engines
Avg ISP from sea level to vacuum 325
After 1 Km/sec additional Delta V reserved for RTLS Rocket Equation gives 3.4 Km/sec but nets under 3 Km/sec Delta V after gravity losses

Stage Two The MCT:
Dry Mass 90mT; 100mT is cargo
12.5m diameter with 7.5 m length for propellant tanks. 
Cargo 8.5m length ; 1040 m3 volume
(Plenty of space for expanded fuel tanks in a simple modified tanker version.)
1165mT fueled mass (2.6 million LBS)
380 seconds ISP vac; Rvac engines assumed 14% higher thrust as with F9 FT
6 Rvac engines   3.5 million LBS Thrust
6.75Km/sec Delta V capability, via Rocket eq.
8.4Km/sec Mars liftoff with only 25mT return cargo

I also modeled another small version to see just how small a BFR could meet Elon’s goals. I optimistically lowered the MCT 2nd stage dry weight from 90mT to 75mT.  This minimal, 12m diameter optimistic version needs only 19 engines with rings of 12, 6 and two center engines.  The MCT stage 2 has only 5 engines, reducing the cost of building this BFR/MCT from 30 Raptors to 24.  Engines are the big cost driver for mass producing BFRs.

Just to confirm: you have the BFR contributing only 1km/s delta V before separation?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 12/11/2015 09:05 pm
From another thread, here is a recent quote by Musk in an interview:

"So, technically, it would be the BFR and the BFS." As in "Big frakking Spaceship.""
I'd just read that article and came here.

So new naming?
Mars Colonial Transport Architecture with the BFR and BFS? :-)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 12/11/2015 11:23 pm


Just to confirm: you have the BFR contributing only 1km/s delta V before separation?

Sorry about any confusion, "nets under 3 Km/sec Delta V after gravity losses"  So BFR goes low & slow (under 3 Km/sec)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/12/2015 03:38 am
philw1776:  Your engine count is off because you forgot to account for lower thrust at Sea-level, 230 mt is the VAC performance goal for Raptor.  I'm estimating that Sea-level thrust is ~77% of Vac which raises the engine count to ~30 to get very nearly identical total thrust as your estimate.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 12/12/2015 07:58 am
If there is going to be a BFR boosting a BFS.

Then someone can modified the BFS as part of a cislunar base station for small reusable Lunar landers. Along with a few BFS tanker variants docked to a frame (Space Dock :D) with solar power & station keeping capabilities. The BFS mods is mostly for lander handling and maintenance with modules in the cargo bay.

Should be available in about early mid to late mid  2020s IMO if SpaceX manages to be on schedule.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Dante80 on 12/12/2015 10:44 am
philw1776:  Your engine count is off because you forgot to account for lower thrust at Sea-level, 230 mt is the VAC performance goal for Raptor.  I'm estimating that Sea-level thrust is ~77% of Vac which raises the engine count to ~30 to get very nearly identical total thrust as your estimate.

A question. Do we know that the 230mt quoted (I assume in the reddit Q&A Elon did) was for Vac? Or has there been any more information on this elsewhere? I'm asking because Elon was answering a question that was about SL thrust.

The quote I remember.

Quote
Q: Has the Raptor engine changed in its target thrust since the last number we have officially heard of 1.55Mlbf SL thrust?

A: Thrust to weight is optimizing for a surprisingly low thrust level, even when accounting for the added mass of plumbing and structure for many engines. Looks like a little over 230 metric tons (~500 klbf) of thrust per engine, but we will have a lot of them :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 12/12/2015 04:49 pm
philw1776:  Your engine count is off because you forgot to account for lower thrust at Sea-level, 230 mt is the VAC performance goal for Raptor.  I'm estimating that Sea-level thrust is ~77% of Vac which raises the engine count to ~30 to get very nearly identical total thrust as your estimate.

A question. Do we know that the 230mt quoted (I assume in the reddit Q&A Elon did) was for Vac? Or has there been any more information on this elsewhere? I'm asking because Elon was answering a question that was about SL thrust.

The quote I remember.

Quote
Q: Has the Raptor engine changed in its target thrust since the last number we have officially heard of 1.55Mlbf SL thrust?

A: Thrust to weight is optimizing for a surprisingly low thrust level, even when accounting for the added mass of plumbing and structure for many engines. Looks like a little over 230 metric tons (~500 klbf) of thrust per engine, but we will have a lot of them :)

I read that same quote to refer to sea level thrust of Raptor over 230mT or over 507 KLBs.  I uprated the Rvac thrust by the same % as the Merlin Vac/SL.

Regardless, I'm in the camp that says the now Q1 2016 big reveal will have a higher thrust for Raptor than 230mT
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MichaelBlackbourn on 12/12/2015 05:52 pm
It would be amazing to one day see hardware with a giant 'SpaceX BFR' Decal on the side.   I wonder if the 'name' will survive that long... Of it gets renamed something else... 'Tiny' maybe.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jcc on 12/12/2015 10:51 pm
It would be amazing to one day see hardware with a giant 'SpaceX BFR' Decal on the side.   I wonder if the 'name' will survive that long... Of it gets renamed something else... 'Tiny' maybe.

Eagle!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 12/13/2015 03:50 pm
I understand that usually it is assumed that the first stage will give the upper stage/MCT a horizontal speed of ~3km/s, similar to what the Falcon first stage does. For RTLS of the first stage that needs to be reversed, cutting into payload.

I do wonder if another approach could be effective. MCT will have a very large delta-v budget. It needs it to perform its functions towards Mars. Could the first stage go up almost straight similar to the BO New Shepard, but maybe up to 150km peak altitude, eating all the gravity and air resistance losses and use the second stage for the task of building up orbital speed? On the way down with its large diameter it may not need a reentry burn or only a very small one. Reuse fuel would be mainly only the small amount of landing fuel.

Did anyone of those who did thorough analysis ever consider such a scenario or am I way off?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Dante80 on 12/13/2015 04:13 pm
I understand that usually it is assumed that the first stage will give the upper stage/MCT a horizontal speed of ~3km/s, similar to what the Falcon first stage does. For RTLS of the first stage that needs to be reversed, cutting into payload.

I do wonder if another approach could be effective. MCT will have a very large delta-v budget. It needs it to perform its functions towards Mars. Could the first stage go up almost straight similar to the BO New Shepard, but maybe up to 150km peak altitude, eating all the gravity and air resistance losses and use the second stage for the task of building up orbital speed? On the way down with its large diameter it may not need a reentry burn or only a very small one. Reuse fuel would be mainly only the small amount of landing fuel.

Did anyone of those who did thorough analysis ever consider such a scenario or am I way off?

The vast majority of the energy in a rocket launch is expended reaching orbital velocity, not orbital height. Getting to orbital velocity requires a large amount of horizontal velocity. Getting that horizontal velocity takes about the same amount of dV, no matter what altitude you are at. If you started at LEO altitude, and started accelerating horizontally, you'd still need to obtain 17,100 mph of horizontal velocity. Without the horizontal velocity, you're suborbital.

Also, take a look at this.
https://gravityloss.wordpress.com/2008/01/10/drag-loss-in-ascent-gain-in-descent-and-what-it-means-for-scalability/
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 12/13/2015 04:30 pm
The vast majority of the energy in a rocket launch is expended reaching orbital velocity, not orbital height. Getting to orbital velocity requires a large amount of horizontal velocity. Getting that horizontal velocity takes about the same amount of dV, no matter what altitude you are at. If you started at LEO altitude, and started accelerating horizontally, you'd still need to obtain 17,100 mph of horizontal velocity. Without the horizontal velocity, you're suborbital.

I know all of this. I even explicitly stated it in my post. So what's your point?

Usually, I understand, a first stage does a lot of delta-v towards orbital speed. The Falcon 9 does much less, to facilitate RTLS and leaves more of the buildup of orbital speed to the second stage. That is not the optimum approach for expendable vehicles. It is a better approach for reusable vehicles.

My suggestion was to carry the idea to the extreme. Let the first stage eat all the gravity loss and drag loss and leave all or almost all of the buildup of orbital speed to the second stage. MCT needs the big delta-v budget anyway to get to Mars from LEO and land.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 12/13/2015 04:52 pm
The vast majority of the energy in a rocket launch is expended reaching orbital velocity, not orbital height. Getting to orbital velocity requires a large amount of horizontal velocity. Getting that horizontal velocity takes about the same amount of dV, no matter what altitude you are at. If you started at LEO altitude, and started accelerating horizontally, you'd still need to obtain 17,100 mph of horizontal velocity. Without the horizontal velocity, you're suborbital.

I know all of this. I even explicitly stated it in my post. So what's your point?

Usually, I understand, a first stage does a lot of delta-v towards orbital speed. The Falcon 9 does much less, to facilitate RTLS and leaves more of the buildup of orbital speed to the second stage. That is not the optimum approach for expendable vehicles. It is a better approach for reusable vehicles.

My suggestion was to carry the idea to the extreme. Let the first stage eat all the gravity loss and drag loss and leave all or almost all of the buildup of orbital speed to the second stage. MCT needs the big delta-v budget anyway to get to Mars from LEO and land.

That is not a bad approach, it was used in The Rocket Company book (fiction, but at times read more like a design manual), but I don't think that is what SpaceX are doing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 12/13/2015 04:55 pm
"Big Falcon Spaceship"

'Falcon' is not what he was quoted as saying 'F' stood for throughout the interview. Quite the contrary.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Dante80 on 12/13/2015 05:02 pm
I know all of this. I even explicitly stated it in my post. So what's your point?

Usually, I understand, a first stage does a lot of delta-v towards orbital speed. The Falcon 9 does much less, to facilitate RTLS and leaves more of the buildup of orbital speed to the second stage. That is not the optimum approach for expendable vehicles. It is a better approach for reusable vehicles.

My suggestion was to carry the idea to the extreme. Let the first stage eat all the gravity loss and drag loss and leave all or almost all of the buildup of orbital speed to the second stage. MCT needs the big delta-v budget anyway to get to Mars from LEO and land.

The point I tried to make is that this is a lot of delta-v needed. MCT might be able to do it, if its designed to stage from LEO, but in that case it might be almost empty when it reaches orbital speed. You will then need to transfer more fuel to it so that it can start the mission to Mars.

At the same time, the "slingshot to orbital height S1" might make re-usability easier, but you would still have to design it so that it could carry other payloads than MCT (for example, a tanker, or a hub, or mars infrastructure, or commercial payloads etc). If S1 is designed to launch more things than strictly MCT, then it would not be easy (I think) to merge both capabilities in the same structure.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MichaelBlackbourn on 12/13/2015 05:31 pm
. Let the first stage eat all the gravity loss and drag loss and leave all or almost all of the buildup of orbital speed to the second stage. MCT needs the big delta-v budget anyway to get to Mars from LEO and land.

?? gravity is pretty much the same at 160km up as it is on the surface. Gravity losses starting from 0 or 160km up are very similar.  It's all about the orbital velocity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 12/13/2015 06:01 pm
. Let the first stage eat all the gravity loss and drag loss and leave all or almost all of the buildup of orbital speed to the second stage. MCT needs the big delta-v budget anyway to get to Mars from LEO and land.

?? gravity is pretty much the same at 160km up as it is on the surface. Gravity losses starting from 0 or 160km up are very similar.  It's all about the orbital velocity.

As I have already stated twice, I know that it is all about orbital velocity. I also know that gravity is almost as strong at 160km altitude. But I was not talking about gravaity, but about gravity losses. The difference is the vector at which the engines fire. However the first stage would fire vertical or almost vertical while the second stage could fire horizontal.

I will just wait for the first flights. I expect that MCT will stage at less than 3km/s, but we will see.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 12/13/2015 06:08 pm
The point I tried to make is that this is a lot of delta-v needed. MCT might be able to do it, if its designed to stage from LEO, but in that case it might be almost empty when it reaches orbital speed. You will then need to transfer more fuel to it so that it can start the mission to Mars.

Not necessarily. With the different trajectory it could have more fuel, the first stage less. It is a trade, and one, I openly admit, I cannot make. I am sure they will make that trade at SpaceX very thoroughly and suspect the optimum for the system with full reuse will be at less than 3km/s horizontal speed.

At the same time, the "slingshot to orbital height S1" might make re-usability easier, but you would still have to design it so that it could carry other payloads than MCT (for example, a tanker, or a hub, or mars infrastructure, or commercial payloads etc). If S1 is designed to launch more things than strictly MCT, then it would not be easy (I think) to merge both capabilities in the same structure.

Good point. However it was quite clearly said, BFR/MCT will be optimized only and really only for Mars. It also has so much capability that it can afford to operate at less than optimum in cislunar space. I am sure it will be a very inefficient system to deploy satellites to GTO without refuelling.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 12/13/2015 07:18 pm
The one design criteria most overlooked is minimum operating costs. This is probably the most significant item for the design and delta -V requirements that the BFR must meet. These operating costs are for sending an MCT to Mars meaning less tanker flights means much lower costs. An increase of the BFR's deliverable delta V by 750m/s increases the tanker prop load from 100mt to 200mt. This nearly halves the total cost for an MCT to Mars by almost 50% from 10 flights to only 5 flights. This is without any change to the design of the BFS itself. The BFS is fairly easily sized because the three design flight uses: as second stage, as EDS, and as Mars SSTO all are very close to the  same propellant loads requirements.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 12/13/2015 07:41 pm
. Let the first stage eat all the gravity loss and drag loss and leave all or almost all of the buildup of orbital speed to the second stage. MCT needs the big delta-v budget anyway to get to Mars from LEO and land.

?? gravity is pretty much the same at 160km up as it is on the surface. Gravity losses starting from 0 or 160km up are very similar.  It's all about the orbital velocity.

As I have already stated twice, I know that it is all about orbital velocity. I also know that gravity is almost as strong at 160km altitude. But I was not talking about gravaity, but about gravity losses. The difference is the vector at which the engines fire. However the first stage would fire vertical or almost vertical while the second stage could fire horizontal.

I will just wait for the first flights. I expect that MCT will stage at less than 3km/s, but we will see.

"less than 3km/h" is much more than almost zero horizontal velocity.

Making the first stage launch vertically and just eat the gravity and atmospheric losses would mean that
1) second stage would have to do all the work for the 7.5km/h horizontal delta-v
2) The trajectory of the rocket would be very inefficient. Doing the vertical and horizontal part of the acceleration totally separately means much more total delta-v is needed, pythagoras is our friend here. Just to get to 200km altitude 2km/s delta-v is needed for the first stage. And this is ignoring the gravity losses. With 45 degrees burn direction,  2.8km/s delta-v gives 2kms/s vertical AND 2km/s horizontal delta-v. The gravity turns real rockets are doing are even much better.



Please, try this in KSP. You will see that how inefficient your trajectory idea is.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 12/13/2015 08:02 pm
The one design criteria most overlooked is minimum operating costs. This is probably the most significant item for the design and delta -V requirements that the BFR must meet. These operating costs are for sending an MCT to Mars meaning less tanker flights means much lower costs. An increase of the BFR's deliverable delta V by 750m/s increases the tanker prop load from 100mt to 200mt. This nearly halves the total cost for an MCT to Mars by almost 50% from 10 flights to only 5 flights. This is without any change to the design of the BFS itself. The BFS is fairly easily sized because the three design flight uses: as second stage, as EDS, and as Mars SSTO all are very close to the  same propellant loads requirements.

Up til now we (or at least I have, and I think just about everyone else) have sized the BFS for the Mars mission, then sized the BFR to lift that, then sized the tanker based on what the BFR can lift.

If instead we size the BFR and tanker to be most efficient (cost wise) to refuel the FBS, it could quite well lead to a bigger BFR. The tanker would then make full use of the BFR's lift capability and the BFS only a part of it.

If this is the case I don't see any easy way of outsiders using analysis to determine the optimum BFR size, as this would depend on internal SpaceX cost data (size vs development facilities, manufacturing and operations costs).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 12/13/2015 08:11 pm
. Let the first stage eat all the gravity loss and drag loss and leave all or almost all of the buildup of orbital speed to the second stage. MCT needs the big delta-v budget anyway to get to Mars from LEO and land.

?? gravity is pretty much the same at 160km up as it is on the surface. Gravity losses starting from 0 or 160km up are very similar.  It's all about the orbital velocity.

Is it still inefficient if you take in to account the 1st stage needs to RTLS, and therefor needs some sort of burn to negate it's horizontal DV? In fact it needs to impart twice the horizontal DV to rtls as it used to get to separation. It's carrying less fuel so is a lot lighter however, so maybe its not that big of an ask.

As I have already stated twice, I know that it is all about orbital velocity. I also know that gravity is almost as strong at 160km altitude. But I was not talking about gravaity, but about gravity losses. The difference is the vector at which the engines fire. However the first stage would fire vertical or almost vertical while the second stage could fire horizontal.

I will just wait for the first flights. I expect that MCT will stage at less than 3km/s, but we will see.

"less than 3km/h" is much more than almost zero horizontal velocity.

Making the first stage launch vertically and just eat the gravity and atmospheric losses would mean that
1) second stage would have to do all the work for the 7.5km/h horizontal delta-v
2) The trajectory of the rocket would be very inefficient. Doing the vertical and horizontal part of the acceleration totally separately means much more total delta-v is needed, pythagoras is our friend here. Just to get to 200km altitude 2km/s delta-v is needed for the first stage. And this is ignoring the gravity losses. With 45 degrees burn direction,  2.8km/s delta-v gives 2kms/s vertical AND 2km/s horizontal delta-v. The gravity turns real rockets are doing are even much better.



Please, try this in KSP. You will see that how inefficient your trajectory idea is.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: joek on 12/13/2015 09:01 pm
Making the first stage launch vertically and just eat the gravity and atmospheric losses would mean that
...

I would not be too quick to dismiss.  A TSTO "pop-up" trajectory has advantages in some situations.  There are several variations from straight up ("elevator") to simply more vertical than would otherwise be optimal from a total orbital dV perspective.

These trajectories are typically discussed in the context of RLVs (e.g., Kistler K-1 and various fly-back and boost-back designs).   Such designs may be sub-optimal from overall dV, but optimal for other reasons.  Two common attributes are: a relatively oversized booster than typical; and a second stage with greater dV capability than typical.  BFR + BFS may fit that description.

Jon Goff over at Selenian Boondocks did a nice writeup in "Orbital Access Methodologies Part III: Pop-up TSTO" (http://selenianboondocks.com/2008/06/orbital-access-methodologies-part-iii-pop-up-tsto/). A number of other papers discuss specific RLVs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 12/13/2015 09:19 pm
I argued one extreme, straight up. I see the 3km/s I see used frequently as the other extreme and believe the optimum will be somewhere inbetween. It may be very hard to determine an optimum. To reach the best value both stages need to share the work and that work includes RTLS of the first stage. So the overall package will be designed for an optimum including RTLS. I guess Falcon was designed with that in mind but not yet really exclusively optimised for reuse. BFR/MCT will and I am looking forward to see how SpaceX decided.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: cscott on 12/14/2015 12:23 am
Huh, that's interesting. I should have read TFA.  But I think there is a little ambiguity: the writer appears to have prompted the answer, with the obscenity context, and they end up discussing the BFG from Doom, where the F definitely stood for "frakking".  We've heard SpaceX mince the middle F into Falcon, which is actually quite a nice fit when you consider it.  I'm certainly not convinced that SpaceX will use an obscenity when they finally introduce the BFR.  I suspect they will continue to (at least occasionally) use Falcon in public, if they give any expansion for BFR at all.

(Now that I think of it, if might have been Gwynne or Hans who used "Falcon" in the middle.  So maybe this is another of the nomenclature variances within SpaceX, like Dragon V2/2/Crew Dragon etc.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 12/14/2015 02:03 am
The one design criteria most overlooked is minimum operating costs. This is probably the most significant item for the design and delta -V requirements that the BFR must meet. These operating costs are for sending an MCT to Mars meaning less tanker flights means much lower costs. An increase of the BFR's deliverable delta V by 750m/s increases the tanker prop load from 100mt to 200mt. This nearly halves the total cost for an MCT to Mars by almost 50% from 10 flights to only 5 flights. This is without any change to the design of the BFS itself. The BFS is fairly easily sized because the three design flight uses: as second stage, as EDS, and as Mars SSTO all are very close to the  same propellant loads requirements.

Could not agree more.
I was in a high-tech industry engineering products where low production cost was paramount.  We did the same cost driver analysis on every single aspect that Musk does.
I see the 1st stage as going low & slow under 3 Km/sec while the delta V is in the MCT stage two which makes it utilitarian for all Mars purposes.  Large propellant tanks make 'mods" for a tanker minimal. 
I also think those speculating that the BFR might be larger than minimal models may be onto something as they reduce # of flights to refuel the MCT in LEO or wherever.  It's a complex system analysis whether to make a minimum parts cost re-useable BFR vs making one a bit larger (a bit more expensive per unit) that reduces # of flights to fuel up an MCT in orbit for a Mars journey.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 12/14/2015 04:25 am
I'm certainly not convinced that SpaceX will use an obscenity when they finally introduce the BFR.  I suspect they will continue to (at least occasionally) use Falcon in public, if they give any expansion for BFR at all.
I don't think it'll ever be an official name, but given Musk's personality I'd say it was definitely that at first. There'll be a rename, unless "Big Falcon" sticks.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: LastStarFighter on 12/14/2015 06:15 am
Direct quote from Elon implying no second stage, just booster and mars spacecraft from an article in GQ

I beleive you are misinterpreting him simplifying things for the magazine readers. He seems to just be saying there will be a independant spacecraft and rocket. Just like there is a Dragon spacecraft and Falcon "booster" rocket. Thats just my take on it though. I could be wrong and perhaps they have found a reliable supplier of unobtainium and dilithium crystals from which to build this single stage booster rocket out of.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 12/14/2015 09:37 am
I beleive you are misinterpreting him simplifying things for the magazine readers. He seems to just be saying there will be a independant spacecraft and rocket. Just like there is a Dragon spacecraft and Falcon "booster" rocket. Thats just my take on it though. I could be wrong and perhaps they have found a reliable supplier of unobtainium and dilithium crystals from which to build this single stage booster rocket out of.

I am at a loss here. I cannot understand where the idea of a second stage comes from.

The abilities of a second stage are a subset of what MCT needs to do going from LEO to Mars surface and, after refuelling, back to earth. So why duplicate that existing capability with a separate second stage?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Krevsin on 12/14/2015 01:57 pm
. Let the first stage eat all the gravity loss and drag loss and leave all or almost all of the buildup of orbital speed to the second stage. MCT needs the big delta-v budget anyway to get to Mars from LEO and land.

?? gravity is pretty much the same at 160km up as it is on the surface. Gravity losses starting from 0 or 160km up are very similar.  It's all about the orbital velocity.

As I have already stated twice, I know that it is all about orbital velocity. I also know that gravity is almost as strong at 160km altitude. But I was not talking about gravaity, but about gravity losses. The difference is the vector at which the engines fire. However the first stage would fire vertical or almost vertical while the second stage could fire horizontal.

I will just wait for the first flights. I expect that MCT will stage at less than 3km/s, but we will see.

"less than 3km/h" is much more than almost zero horizontal velocity.

Making the first stage launch vertically and just eat the gravity and atmospheric losses would mean that
1) second stage would have to do all the work for the 7.5km/h horizontal delta-v
2) The trajectory of the rocket would be very inefficient. Doing the vertical and horizontal part of the acceleration totally separately means much more total delta-v is needed, pythagoras is our friend here. Just to get to 200km altitude 2km/s delta-v is needed for the first stage. And this is ignoring the gravity losses. With 45 degrees burn direction,  2.8km/s delta-v gives 2kms/s vertical AND 2km/s horizontal delta-v. The gravity turns real rockets are doing are even much better.



Please, try this in KSP. You will see that how inefficient your trajectory idea is.
1) Given that the dV needed to pull a SSTE from Mars surface is about 8 km/s, I'd say you're set in the dV department.

2) This is less about having an efficient trajectory than it is simplifying first stage reuse. This way, you go directly up and directly down, with very little correction needed, as opposed to boosting back from a gravity turn.



A brief simulation in KSP confirms that a high delta V upper stage is required for this purpose (which then requires refueling to get anywhere but orbits and halfways and whatnot), but this method does in fact simplify the construction of the first stage (basically you don't need to obsess so much about the mass budget and you can fix most first stage problems by just throwing additional mass at them) and eases first stage recovery, at the expense of making the upper stage more mass sensitive.

Basically since the BFS seems to have to be a Not-Quite-SSTO by design (SSTE from Mars surface is a requirement), a pop-up TSTO makes a lot of sense, especially given how much it simplifies first stage recovery.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Dante80 on 12/14/2015 03:25 pm
Direct quote from Elon implying no second stage, just booster and mars spacecraft from an article in GQ

I beleive you are misinterpreting him simplifying things for the magazine readers. He seems to just be saying there will be a independant spacecraft and rocket. Just like there is a Dragon spacecraft and Falcon "booster" rocket. Thats just my take on it though. I could be wrong and perhaps they have found a reliable supplier of unobtainium and dilithium crystals from which to build this single stage booster rocket out of.

I'm willing to guess that SX will not make a S2 and put the spaceship on top of it. It will actually use the spaceship to finish the orbit, and then maybe re-fuel it there to get to mars (or an even higher staging point).

Remember, the spaceship we are talking about should be capable of some serious dv if it can reach mars from LEO/HEO and land (or launch from mars and return). You are not going to need another stage on the rocket to get it to LEO, unless in-orbit refueling is out of the question. A re-usable S1 is enough, dilithium crystals would be overkill at this point.. ;)   

Moreover, a second stage that reaches orbit is either very expensive (expendable), or very expensive and complex (re-usable). If BFR stays as an exclusive MCT booster (as has been hinted by SpaceX in the past), then its more safe to assume that there won't be a second stage.

In any case, we will have to see how this unfolds. We may get some information by Elon on the architecture by Q1 2016.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 12/14/2015 05:00 pm
The one design criteria most overlooked is minimum operating costs. This is probably the most significant item for the design and delta -V requirements that the BFR must meet. These operating costs are for sending an MCT to Mars meaning less tanker flights means much lower costs. An increase of the BFR's deliverable delta V by 750m/s increases the tanker prop load from 100mt to 200mt. This nearly halves the total cost for an MCT to Mars by almost 50% from 10 flights to only 5 flights. This is without any change to the design of the BFS itself. The BFS is fairly easily sized because the three design flight uses: as second stage, as EDS, and as Mars SSTO all are very close to the  same propellant loads requirements.

Could not agree more.
I was in a high-tech industry engineering products where low production cost was paramount.  We did the same cost driver analysis on every single aspect that Musk does.
I see the 1st stage as going low & slow under 3 Km/sec while the delta V is in the MCT stage two which makes it utilitarian for all Mars purposes.  Large propellant tanks make 'mods" for a tanker minimal. 
I also think those speculating that the BFR might be larger than minimal models may be onto something as they reduce # of flights to refuel the MCT in LEO or wherever.  It's a complex system analysis whether to make a minimum parts cost re-useable BFR vs making one a bit larger (a bit more expensive per unit) that reduces # of flights to fuel up an MCT in orbit for a Mars journey.
The range of LEO capability given by SpaceX way back for the MCT was 180-250mt. As we have discussed tremendous about what the BFS dry weight is possible 80mt is sort of a average or consensus value + 100mt of payload, making the 180mt to LEO the absolute minimum that the system must meet. But what if the performance was closer to the other end 250mt. That means that about 70mt of extra propellant is delivered per flight.

The whole reason for the larger BFR and less flights would be the same regardless of whether the BFR is reusable or expendable. If the minimum design BFR takes 10 flights to accomplish sending a single BFS to Mars but a bigger BFR with the exact same design BFS that takes only 5 flights although the BFR costs 50% more per flight still gives a reduction to per mission of 75% of the 10 flights configuration. There are other advantages to requiring half the flights and that is pad availability. In order to support sending 4 BFS's to Mars the 10 flights minimal BFR configuration would require 40 launches in the 780 day period (a launch every 19.5 days).  In order to support sending 4 BFS's to Mars the 5 flights large BFR configuration would require 20 launches in the 780 day period (a launch every 39 days). For the 10 cargo to 1 crew ratio of missions making the possibility of 20 cargo and 2 crew missions in a synod (780 day period) that would require
a) 10 flight config-> a launch every 3.5 days
b) 5 flight config-> a launch every 7 days

As mission counts increase the number of launches becomes a greater cost factor than any other consideration.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/14/2015 07:29 pm
Direct quote from Elon implying no second stage, just booster and mars spacecraft from an article in GQ

I beleive you are misinterpreting him simplifying things for the magazine readers. He seems to just be saying there will be a independant spacecraft and rocket. Just like there is a Dragon spacecraft and Falcon "booster" rocket. Thats just my take on it though. I could be wrong and perhaps they have found a reliable supplier of unobtainium and dilithium crystals from which to build this single stage booster rocket out of.

Their is a large group of people who are simply dead-set on this 'super-direct' architecture and always have been and will interpret everything as confirmation of that architecture, no amount of technical arguments on my part about it's in-feasibility, enormous cost and risk have dissuaded them.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 12/14/2015 08:38 pm
Direct quote from Elon implying no second stage, just booster and mars spacecraft from an article in GQ

I beleive you are misinterpreting him simplifying things for the magazine readers. He seems to just be saying there will be a independant spacecraft and rocket. Just like there is a Dragon spacecraft and Falcon "booster" rocket. Thats just my take on it though. I could be wrong and perhaps they have found a reliable supplier of unobtainium and dilithium crystals from which to build this single stage booster rocket out of.

Their is a large group of people who are simply dead-set on this 'super-direct' architecture and always have been and will interpret everything as confirmation of that architecture, no amount of technical arguments on my part about it's in-feasibility, enormous cost and risk have dissuaded them.

I think it's more of a case that the configuration of a single stage BFR booster with BFS on top, then BFS does the 'super-direct' stuff as you call it, is just the simplest configuration that happens to also be consistent with everything that SpaceX and Elon have stated.  Especially this last statement from Elon. 

I agree with you that eventually they will employ some type of cycling SEP craft for the 'long trip across the  pond'(and they will probably say that this was always planned for the MCT system), but that doesn't seem to be in the cards right now.  And it seems clear at this point that there will be no 2nd stage between the BFR booster and the BFS.

It will be interesting to see how your technical objections are met when Elon eventually unveils the system design.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 12/15/2015 02:01 am
From another thread, here is a recent quote by Musk in an interview:

Direct quote from Elon implying no second stage, just booster and mars spacecraft from an article in GQ:

"Well, there's two parts of it—there's a booster rocket and there's a spaceship. So the booster rocket's just to get it out of Earth's gravity because Earth has quite a deep gravity well and thick atmosphere, but the spaceship can go from Mars to Earth without any booster, because Mars's gravity is weaker and the atmosphere's thinner, so it's got enough capability to get all the way back here by itself. It needs a helping hand out of Earth's gravity well. So, technically, it would be the BFR and the BFS." As in "Big frakking Spaceship."

http://www.gq.com/story/elon-musk-mars-spacex-tesla-interview?utm_source=10370

So... I guess we are back to basics, what many of us have arguing, it seems? This thread has been devalued (and made less interesting) in the last few months by people wanting to discuss their own architectures (yes, you know who you are), so hopefully this can narrow down the discussion again.
Let me just say, in a totally mature manner (regarding BFS--what we used to call MCT--being the integrated second stage):

Neener.

:)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 12/15/2015 03:11 am
The one design criteria most overlooked is minimum operating costs. This is probably the most significant item for the design and delta -V requirements that the BFR must meet. These operating costs are for sending an MCT to Mars meaning less tanker flights means much lower costs. An increase of the BFR's deliverable delta V by 750m/s increases the tanker prop load from 100mt to 200mt. This nearly halves the total cost for an MCT to Mars by almost 50% from 10 flights to only 5 flights. This is without any change to the design of the BFS itself. The BFS is fairly easily sized because the three design flight uses: as second stage, as EDS, and as Mars SSTO all are very close to the  same propellant loads requirements.

Could not agree more.
I was in a high-tech industry engineering products where low production cost was paramount.  We did the same cost driver analysis on every single aspect that Musk does.
I see the 1st stage as going low & slow under 3 Km/sec while the delta V is in the MCT stage two which makes it utilitarian for all Mars purposes.  Large propellant tanks make 'mods" for a tanker minimal. 
I also think those speculating that the BFR might be larger than minimal models may be onto something as they reduce # of flights to refuel the MCT in LEO or wherever.  It's a complex system analysis whether to make a minimum parts cost re-useable BFR vs making one a bit larger (a bit more expensive per unit) that reduces # of flights to fuel up an MCT in orbit for a Mars journey.
The range of LEO capability given by SpaceX way back for the MCT was 180-250mt. As we have discussed tremendous about what the BFS dry weight is possible 80mt is sort of a average or consensus value + 100mt of payload, making the 180mt to LEO the absolute minimum that the system must meet. But what if the performance was closer to the other end 250mt. That means that about 70mt of extra propellant is delivered per flight.

The whole reason for the larger BFR and less flights would be the same regardless of whether the BFR is reusable or expendable. If the minimum design BFR takes 10 flights to accomplish sending a single BFS to Mars but a bigger BFR with the exact same design BFS that takes only 5 flights although the BFR costs 50% more per flight still gives a reduction to per mission of 75% of the 10 flights configuration. There are other advantages to requiring half the flights and that is pad availability. In order to support sending 4 BFS's to Mars the 10 flights minimal BFR configuration would require 40 launches in the 780 day period (a launch every 19.5 days).  In order to support sending 4 BFS's to Mars the 5 flights large BFR configuration would require 20 launches in the 780 day period (a launch every 39 days). For the 10 cargo to 1 crew ratio of missions making the possibility of 20 cargo and 2 crew missions in a synod (780 day period) that would require
a) 10 flight config-> a launch every 3.5 days
b) 5 flight config-> a launch every 7 days

As mission counts increase the number of launches becomes a greater cost factor than any other consideration.

@oldAtlas_Eguy By your argument for fewer BFR flights to support each BFS going to Mars. It seems to make sense to go bigger with the BFR to to take one less flight per Mars bound BFS. Especially since even the smaller BFR being discuss will need specialized logistics infrastructure anyway. Maybe a bigger 15+ meter diameter BFR is cheaper with fewer flights needed for each Mars bound BFS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 12/15/2015 11:06 am
Could the first stage go up almost straight similar to the BO New Shepard, but maybe up to 150km peak altitude, eating all the gravity and air resistance losses and use the second stage for the task of building up orbital speed? On the way down with its large diameter it may not need a reentry burn or only a very small one. Reuse fuel would be mainly only the small amount of landing fuel.

Everyone hit you over horizontal velocity, but there may also be an issue with the vertical. Going to 150km (rather than staging below 100km with enough vertical velocity to carry the two stages above 100km), means that the first stage will have a 100km free-fall before it hits the atmosphere.

While the entry speed may be technically lower than a 3km/s horizontal entry, the rate of atmospheric density increase will be extremely sharp. That induces stresses on the stage in addition to mere re-entry heating.

(Travelling 100km through the first ten kilometres of atmosphere, then 100km through the second 10km... vs travelling 30km through the first 30km.... See what I mean. 200km of deceleration before you reach 30km altitude, vs just 30km deceleration and you're already deep in the atmosphere at the 20km mark.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 12/15/2015 11:55 am
While the entry speed may be technically lower than a 3km/s horizontal entry, the rate of atmospheric density increase will be extremely sharp. That induces stresses on the stage in addition to mere re-entry heating.

(Travelling 100km through the first ten kilometres of atmosphere, then 100km through the second 10km... vs travelling 30km through the first 30km.... See what I mean. 200km of deceleration before you reach 30km altitude, vs just 30km deceleration and you're already deep in the atmosphere at the 20km mark.)

The vertical component is still the same, just a horizontal component added. I don't see at the moment how this could be less harsh. I am not 100% sure though.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OxCartMark on 12/27/2015 01:52 am
Just re-read parts of the GQ article.  Here is a bit that is just below the previous quote that I think belongs in this thread -


"Musk has previously said that he would publicly present some specifics of his Mars-colonization plans later this year, though he tells me that it may now be early next year. "Before we announce it, I want to make sure that we're not gonna make really big changes to it," he says. "Um, yeah. I think it's gonna seem pretty crazy, no matter what."

Just because it's so far beyond what people would imagine?

He laughs. "It's really big." And laughs again. "It's really big. There's not been any architecture like this described that I'm aware of."

That's from December 2015.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 12/27/2015 10:01 am
Just re-read parts of the GQ article.  Here is a bit that is just below the previous quote that I think belongs in this thread -


"Musk has previously said that he would publicly present some specifics of his Mars-colonization plans later this year, though he tells me that it may now be early next year. "Before we announce it, I want to make sure that we're not gonna make really big changes to it," he says. "Um, yeah. I think it's gonna seem pretty crazy, no matter what."

Just because it's so far beyond what people would imagine?

He laughs. "It's really big." And laughs again. "It's really big. There's not been any architecture like this described that I'm aware of."

That's from December 2015.

It's that quote that I keep thinking of when people start saying what they think the architecture will be, big capsules etc. I don't think anyone has yet described an architecture that would fit with Musk's statement.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/27/2015 06:55 pm
Is he saying it is bigger even then Nova?  Bigger then the UR-700M (http://www.astronautix.com/lvs/ur700m.htm)?   What is his limit for 'described'?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TheTraveller on 12/30/2015 04:25 am
SpX Mars suit worn by Elon Musk?
BFS in the background?

https://www.instagram.com/elonmusk/?hl=en

Is this a Martian rescue fleet arriving after a Earth comet slam?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Coastal Ron on 12/30/2015 05:01 am
SpX Mars suit worn by Elon Musk?
BFS in the background?

https://www.instagram.com/elonmusk/?hl=en

Is this a Martian rescue fleet arriving after a Earth comet slam?

Nice catch!  That must being showing Musk on Earth though with his helmet off, unless he figures he'll be able to terraform Mars before he gets there.

Also, the vehicle in the background has aerodynamic features, so it's not just ballistic like the Falcon 9 1st stage.

Of course all this assumes that the drawing reveals some real details, but it could be pure fantasy...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TheTraveller on 12/30/2015 05:10 am
SpX Mars suit worn by Elon Musk?
BFS in the background?

https://www.instagram.com/elonmusk/?hl=en

Is this a Martian rescue fleet arriving after a Earth comet slam?

Nice catch!  That must being showing Musk on Earth though with his helmet off, unless he figures he'll be able to terraform Mars before he gets there.

Also, the vehicle in the background has aerodynamic features, so it's not just ballistic like the Falcon 9 1st stage.

Of course all this assumes that the drawing reveals some real details, but it could be pure fantasy...

Elon is known to like dropping hints, bread crumbs, like he is doing with Chris on L2.

Time will tell if it is fantasy or not.

Elon's suit is bigger than Watney's Martian suit.

Is clear to see the bent traffic control stop light, left of his foot on the ladder. Also shattered buildings to his left & right. So not Mars.

Enhanced BFS image attached.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: cscott on 12/30/2015 08:04 am
Doesn't look like the SpaceX suit design to me.  Doesn't particularly look like Elon, either, for that matter.

The only thing that is familiar is the Dragon-like canted thruster arrangement.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TheTraveller on 12/30/2015 08:41 am
Doesn't look like the SpaceX suit design to me.  Doesn't particularly look like Elon, either, for that matter.

The only thing that is familiar is the Dragon-like canted thruster arrangement.

Looks like a surface / EVA suit and not a Crew Dragon flight suit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stardhingy on 12/30/2015 05:37 pm

It's that quote that I keep thinking of when people start saying what they think the architecture will be, big capsules etc. I don't think anyone has yet described an architecture that would fit with Musk's statement.

I'm just going to suggest an outrageous one. The MCT is an Earth SSTO vehicle sized near the weight limit of LC39A that can deliver 236mTons to LEO. With a BFR under it it reaches orbit high on fuel. Fuel capacity is significantly higher than required for the trip to Mars, so one BFR flight can fuel up more than one MCT. Early flights can de-risk ISRU by leaving an MCT in Mars orbit with fuel for TEI and landing with enough fuel to get back to orbit.

I think that's probably big enough.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 12/30/2015 07:59 pm

It's that quote that I keep thinking of when people start saying what they think the architecture will be, big capsules etc. I don't think anyone has yet described an architecture that would fit with Musk's statement.

I'm just going to suggest an outrageous one. The MCT is an Earth SSTO vehicle sized near the weight limit of LC39A that can deliver 236mTons to LEO. With a BFR under it it reaches orbit high on fuel. Fuel capacity is significantly higher than required for the trip to Mars, so one BFR flight can fuel up more than one MCT. Early flights can de-risk ISRU by leaving an MCT in Mars orbit with fuel for TEI and landing with enough fuel to get back to orbit.

I think that's probably big enough.
1) Um... why?
2) Deliver 236 tons payload?
2A) Assuming 'yes', and you mean 236 tons of bricks to orbit on top of the rocket:


The structural mass fraction of the F9 first stage is currently estimated here at 6.1% (http://spaceflight101.com/spacerockets/falcon-9-v1-1-f9r/).  The structural mass fraction of the Shuttle External Tank (SLWT edition) is estimated here at 3.5% (https://en.wikipedia.org/wiki/Space_Shuttle_external_tank).  Let's split the difference and call the estimated rocket structural mass fraction 5%.
  EDIT: Actually, the Shuttle tank's structural mass fraction should be higher (worse) than the Falcon tank according to first principles;  This is an apples to oranges comparison because the Shuttle External Tank had no engines.  Tank mass fraction is supposed to scale inversely with propellant density;  The density of methalox is lower than the density of RP-1-LOX.  Perhaps I should rerun this with 7% or 8%.

Assuming 5% structural mass fraction on the rocket:

The burn mass ratio for a liftoff burn of 9.2km/s at an average Isp of 370s, will be about 12.6:1 wet to dry.

Plug that into here (http://www.quantumg.net/rocketeq.html) with a 9200m/s LEO, and you need 7143mt launch mass to reach orbit with 236mt of payload atop an empty rocket with calculated mass 329mt.  Add about 25% for liftoff thrust margin, and you need 87.5MN liftoff thrust. Raptor thrust is ~= 2250kN;  That makes for 39 Raptors.

LC-39A is said to be designed to 12.5Mlbf == 55.6MN.

2B) Assuming 'no', and you meant 236t total mass to orbit:

Plugging the same parameters in (with a little iteration to work the linked calculator backwards) but with an m1 (total mass to orbit) of 236t, you get 98.6mt payload mass atop a 137.4mt empty rocket to orbit, using a launch mass of 2984mt.  With the same coefficient, that's 36.6MN launch thrust, which is within the scope of LC-39A.   That makes for 17 Raptors... but below 100mt to orbit.

EDIT: Updated calcs two posts down
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 12/30/2015 08:09 pm
SpX Mars suit worn by Elon Musk?
BFS in the background?

https://www.instagram.com/elonmusk/?hl=en

Is this a Martian rescue fleet arriving after a Earth comet slam?

Well that's interesting. Hard to believe that's just some fantasy vehicle.

Looks like a biconic to me, although its hard to tell.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 12/30/2015 08:41 pm

It's that quote that I keep thinking of when people start saying what they think the architecture will be, big capsules etc. I don't think anyone has yet described an architecture that would fit with Musk's statement.

I'm just going to suggest an outrageous one. The MCT is an Earth SSTO vehicle sized near the weight limit of LC39A that can deliver 236mTons to LEO. With a BFR under it it reaches orbit high on fuel. Fuel capacity is significantly higher than required for the trip to Mars, so one BFR flight can fuel up more than one MCT. Early flights can de-risk ISRU by leaving an MCT in Mars orbit with fuel for TEI and landing with enough fuel to get back to orbit.

I think that's probably big enough.
1) Um... why?
2) Deliver 236 tons payload?
2A) Assuming 'yes', and you mean 236 tons of bricks to orbit on top of the rocket:


The structural mass fraction of the F9 first stage is currently estimated here at 6.1% (http://spaceflight101.com/spacerockets/falcon-9-v1-1-f9r/).  The structural mass fraction of the Shuttle External Tank (SLWT edition) is estimated here at 3.5% (https://en.wikipedia.org/wiki/Space_Shuttle_external_tank).  Let's split the difference and call the estimated rocket structural mass fraction 5%.
  EDIT: Actually, the Shuttle tank's structural mass fraction should be higher (worse) than the Falcon tank according to first principles;  This is an apples to oranges comparison because the Shuttle External Tank had no engines.  Tank mass fraction is supposed to scale inversely with propellant density;  The density of methalox is lower than the density of RP-1-LOX.  Perhaps I should rerun this with 7% or 8%.

Assuming 5% structural mass fraction on the rocket:

The burn mass ratio for a liftoff burn of 9.2km/s at an average Isp of 370s, will be about 12.6:1 wet to dry.

Plug that into here (http://www.quantumg.net/rocketeq.html) with a 9200m/s LEO, and you need 7143mt launch mass to reach orbit with 236mt of payload atop an empty rocket with calculated mass 329mt.  Add about 25% for liftoff thrust margin, and you need 87.5MN liftoff thrust. Raptor thrust is ~= 2250kN;  That makes for 39 Raptors.

LC-39A is said to be designed to 12.5Mlbf == 55.6MN.

2B) Assuming 'no', and you meant 236t total mass to orbit:

Plugging the same parameters in (with a little iteration to work the linked calculator backwards) but with an m1 (total mass to orbit) of 236t, you get 98.6mt payload mass atop a 137.4mt empty rocket to orbit, using a launch mass of 2984mt.  With the same coefficient, that's 36.6MN launch thrust, which is within the scope of LC-39A.   That makes for 17 Raptors... but below 100mt to orbit.

Based on this report (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090037584.pdf), page 5 figure 4, 6.8% is a reasonable structural mass fraction for a typical expendable RP-1/LOX core stage;  In achieving 6.1% SpaceX invented an engine with record-setting TWR.  Raptor will end up being a more complex, heavier FFSC engine in the interest of high specific impulse.

This report (https://www.nasa.gov/pdf/382034main_018%20-%2020090706.05.Analysis_of_Propellant_Tank_Masses.pdf) contains a table on expendable hydrogen stages.  The largest ones have structural mass fractions of 6.25% (not a first stage though) to 10.1%.

This leads me to believe 7% is a decent optimistic estimate for structural mass fraction of an expendable methalox stage with no thermal management / insulation & Raptor engines.  The Big Question is how much propellant depot capability adds to that... but since that's hard to quantify, let's leave that aside for a while and work from a best case scenario where it adds nothing.

Going back to the calculator and subbing in 7%, I end up with:
2A)236mt payload to orbit
empty rocket mass of 1041mt
16100mt launch mass
197MN;  88 Raptors

2B)236mt mass to orbit
empty rocket mass of 192.4mt;  Payload of 43.6mt
2984mt launch mass (unchanged)
36.6MN; 17 Raptors (unchanged)

If you get pessimistic and raise structural mass fraction to 10% to account for thermal insulation etc, launch becomes impossible in either vehicle, anything below that 12.6:1 ratio we worked out earlier (~= 7.9%) hits an asymptote and can't reach orbit.

I think we're way too close to the wire here.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 12/30/2015 08:42 pm
Elon's Instagram acct image looks like it comes from anime or manga. It has that style. I can't find the series, but throwing it into Google image search only returns other manga images, suggesting the colour palette is the same.

As for the vehicle, rotate it to the right, and it's shape seems pretty aircraft/shuttle-like. Which is common in anime.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stardhingy on 12/30/2015 09:17 pm
>Why?

For 80,000 people per year at 100 per vehicle you would need to average two flights per day. Really though you need to do it over about 3-months or you leave passengers in Earth orbit for months before departure. So we get to 860 flights per day.

Then you need to fuel up to get to a high orbit, and fuel up again. So if its 5 flights to fill up in LEO and use use half the fuel to get to the staging orbit, then its probably another 10 to get fuel to the staging orbit. You could save on the high orbit fill ups by using SEP tugs, but a SEP tug can't make many trips.

It works, for dozens of ships, but it doesn't scale to thousands well. An SSTO would simplify ground operations, and you could start going to Mars without the BFR, since the MCT would be capable of taking fuel up.

Also... I just wanted to get a guess out there that we can be pretty sure is not an underestimate of what he means by BFS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 12/30/2015 09:50 pm
I think size estimates have generally been too low.  Start with Earth surface to Mars surface and back to Earth surface, only refueling on Mars surface, everything reusable.  BFS when it lands on Mars, dry of fuel, is going to be 300 MT or more.  Even an empty 747 is over 200 MT.  BFS will contain 100 MT cargo (100 passengers + life support, etc. will probably weigh the same) when it lands and have empty tanks+engines+heat shield+landing legs for return. 

Falcon Heavy is claimed (on Spacex website) to be able to send 13 MT to Mars with liftoff weight of 1463 MT, for liftoff to payload ratio of about 113 - not even clear if that includes reusability.  (That is a lot better than the ratio for MSL, which was about 167 using an Atlas V.) So, it seems like BFS+BFR at Earth liftoff will be at least 34,000 MT, but more likely a lot more.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 12/30/2015 10:26 pm
I think these wildly huge BFR/MCT estimates are way, way off.  The thing has to be affordable to build in quantity and has to be able to launch without evacuating the surrounding populace and rebuilding puny steel & concrete launch pads.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 12/30/2015 10:40 pm
I think these wildly huge BFR/MCT estimates are way, way off.  The thing has to be affordable to build in quantity and has to be able to launch without evacuating the surrounding populace and rebuilding puny steel & concrete launch pads.

Yeah, we keep pingponging between "But the math and some educated guesses say it has to be at least this big, even optimistically" and "But Musk said it would be $500k/ticket.  Hundreds of thousands of passengers.  To do that it has to be a quarter that mass and twice the speed!  Build it out of unobtainium!".

I think there may be some middle ground in having one vehicle with multiple *configurations* for different purposes.

The primary bottomline variable is delta-V capability.  I showed above that a 9.2km/s stage for MCT is extremely problematic, perhaps impossible depending on structural mass fraction.  There are several steps (starting with ISRU and working on up) where refueling can drop the dV capability needed of the vehicle by splitting the longest leg of the mission, very substantially.

It's not that an 88-Raptor MCT is definitely impossible, it's just impractical & unnecessary;  There are easier ways, lower-hanging fruit.  It doesn't make *sense* to avoid propellant depots, to avoid ISRU, to avoid LEO cargo loading.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 12/30/2015 11:08 pm
To get a lot smaller than 34,000 MT requires more smaller vehicles, rendezvous, etc. per flight.  It also likely increases total dV by increasing the number of different intermediate parking/rendezvous  orbits.  That likely increases total production and operation cost well over one giant stack vehicle for each 100 MT cargo (or 100 persons) mission.  In terms of affordable building in mass, WW II Liberty ships, produced cheaply in mass (2,700 built in only a few years), had deadweight over 10,000 MT.  An MCT stack 34,000 MT fueled would be less than 5,000 MT structural construction.  It seems like as hard as it is one giant stack is probably the best hope for $500k/person.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 12/31/2015 12:15 am
On the economics of $500k/person,  suppose $500k is in real (not inflated) dollars and each MCT stack makes 30 round trips, one every 26 months, over 65 years.  That may seem like a long operational life, but we are still flying B-52s and KC-135s constructed over 50 years ago. So, in real (but undiscounted) dollars total ticket revenue is $1.5 billion per stack.  Suppose that financing (real interest rate) and operational costs over 65 years eat up 2/3 of this, leaving $500 million for capital construction.  (Note, 2/3 operational finance might seem low for 65 years but there would possibly be extra revenue to partially offset costs by using the stack for other missions between Mars flights.) 

Could Spacex mass produce 333 MCT (BFS+BFR) stacks at $500 million a piece to transport 1 million colonists over 65 years?  That seems possible since they can make Falcon 9 for $60 million and there will be economies of scale.   

What is missing from the calculation is supply cargo, which Musk has estimated at 10 times the number of passenger missions (seems reasonable even with ISRU).  In fact there need to be a lot of early cargo flights just to build the refueling depot.

In summary the economics of $500k/person seems maybe feasible with only passengers, but I cannot get to $500k/(person + cargo allocation).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/31/2015 02:57 am
I think these wildly huge BFR/MCT estimates are way, way off.  The thing has to be affordable to build in quantity and has to be able to launch without evacuating the surrounding populace and rebuilding puny steel & concrete launch pads.

Yeah, we keep pingponging between "But the math and some educated guesses say it has to be at least this big, even optimistically" and "But Musk said it would be $500k/ticket.  Hundreds of thousands of passengers.  To do that it has to be a quarter that mass and twice the speed!  Build it out of unobtainium!".

I think there may be some middle ground in having one vehicle with multiple *configurations* for different purposes.

The primary bottomline variable is delta-V capability.  I showed above that a 9.2km/s stage for MCT is extremely problematic, perhaps impossible depending on structural mass fraction.  There are several steps (starting with ISRU and working on up) where refueling can drop the dV capability needed of the vehicle by splitting the longest leg of the mission, very substantially.

It's not that an 88-Raptor MCT is definitely impossible, it's just impractical & unnecessary;  There are easier ways, lower-hanging fruit.  It doesn't make *sense* to avoid propellant depots, to avoid ISRU, to avoid LEO cargo loading.

I think the latest round of speculation is quite over the top, people seem to have forgotten that the LAST round of speculation was already have been the largest launch vehicle ever built.  Musk's comments about really big are for a lay audience who's basis of comparison is the Saturn 5, the Shuttle and possibly SLS, they are not directed at this thread and should not be construed to mean the earlier speculations were too small.

I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

This vehicle dose initial missions but in order to scale up to huge colonization efforts you have to augment it with SEP transit vehicles and habitats which raise the efficiency by orders of magnitude by letting the BFS serve as a rapidly cycling landing craft at Mars.  Over 1 synod a MCT/BFS staying at Mars could make more then 100 surface-orbit-and-back-again runs meaning you can actually get more like 3000 uses of the vehicle over it's lifetime rather then a mere 30.

People need to stop pretending that the initial vehicle is the one and only thing that will ever be used and SpaceX would just manufacture zillions of copies of a vehicle and fly massive armadas of them at terribly bad amortization rates while never inventing another vehicle ever again.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 12/31/2015 05:59 am
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 12/31/2015 06:11 am
To get a lot smaller than 34,000 MT requires more smaller vehicles, rendezvous, etc. per flight.

Yes, but smaller vehicles will cost less. And a higher flight rate will lower costs. And geez, if we are still afraid of *rendezvous* (mentioned like a word that shall not be spoken in some circles), then we might as well give up on the whole space thing.

It also likely increases total dV by increasing the number of different intermediate parking/rendezvous  orbits.

Propellant is dirt CHEAP.

And there will be lots of propellant tanker missions for each "MCT" no matter how you slice it, the question is just how many. And if the BFR can't be reused and fly economically with a high flight rate, the whole Mars thing is not going to happen anyway.

In terms of affordable building in mass, WW II Liberty ships, produced cheaply in mass (2,700 built in only a few years), had deadweight over 10,000 MT.  An MCT stack 34,000 MT fueled would be less than 5,000 MT structural construction.  It seems like as hard as it is one giant stack is probably the best hope for $500k/person.

Your point would be well taken if we needed to build *thousands* of BFR/MCTs. Going oversized will A) cost more in development, B) cripple mass production benefits (raising costs), and C) reduce your flight rate (further increasing cost)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 12/31/2015 01:00 pm
My smallest BFR/MCT is 12.5m in diameter, has 25 engines and 4630mT GLOW. Delivers 180mT to LEO at a mass fraction of 3.9% or 26:1 wet to dry mass ratio.  Goes low & slow.  Propellant reserve for abort to Earth landing. Built for rugged quick turn RTLS and re-launch.  The 1st stage is the easier vehicle for SpaceX to design.  Meets the claimed requirement of 100mT cargo to LEO.

My larger preferred BFR/MCT is 15m diameter, has 28 engines and 5100mT GLOW. Delivers 185mT to LEO at a mass fraction of 3.6% or 28:1 wet to dry mass ratio.  Goes low & slow.  Built for rugged quick turn RTLS and re-launch. I think Musk goes 15m diameter to allow for future engine growth and provide margin when a 85mT dry weight MCT turns out to be too optimistic with complications from things like TPS and complex extra Mars landing engines located "higher" along the structure.

The 80-85mT dry weight upper stage is "near SSTO" with 7.7Km/sec capability fully fueled.  Allows for "fast" transits to Mars.  Less refueling for slower cargo flights to Mars.

When you calculate the mass of propellant for a 15m vehicle you realize that the "BFR" is short and stout, the opposite of the F9 family.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 12/31/2015 04:02 pm
At the time Saturn V was developed it was 5 times heavier than the next largest rockets, Titan III and Proton.  How, 45 years later, can building a rocket that is 10-20 times larger (only about twice as big as was confidently proposed in the 1960s and 1970s with Nexus, Sea Dragon, etc.) than Saturn V be such an incredibly hard challenge?  The Germans built 900 foot long airships 100 years ago.  We built Liberty ships as described above in WW II.  We have been building aircraft carriers at 100,000 MT dry mass since the 1960s.  We have been building super tankers 500 meters long and 300,000 MT dry since the 1970s. 

Empty mass of Saturn V was about 10% of GLOW.  Building for a 34,000 MT to 100,000 MT GLOW is building a 3,400 MT to 10,000 MT vehicle.  That is 1/5 to 1/2 the size of an Ohio class nuclear submarine.

The construction and operation of an elaborate network of smaller Saturn V or Nova class rockets, refueling tankers, inter orbital transfer vehicles, intermediate point space habitats, etc.  has got to be a lot more difficult and expensive than one big dumb rocket and one refueling depot on Mars for surface to surface and back transit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 12/31/2015 04:42 pm
Where do you launch this behemoth?  Not at Cape Canaveral or the new Texas site.  Too close to population.  Noise too.  And what magic materials to you construct your launch pad with?  Think thrust force & joules of heat energy.  TOTALLY impractical. 

A spacecraft is not like an ocean sailing vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 12/31/2015 04:52 pm
Here are some designs done by Boeing in the 1970s for launch and landing facilities at KSC:

http://www.pmview.com/spaceodysseytwo/spacelvs/sld043.htm (http://www.pmview.com/spaceodysseytwo/spacelvs/sld043.htm)

http://www.pmview.com/spaceodysseytwo/spacelvs/sld044.htm (http://www.pmview.com/spaceodysseytwo/spacelvs/sld044.htm)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 12/31/2015 05:01 pm
Umbrella, do you even read other posts, or is this a post-only thread for you?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 12/31/2015 07:12 pm
Umbrella, do you even read other posts, or is this a post-only thread for you?
(I think they were responding to philw1776 asking about where and how this "behemoth" would be launched)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stardhingy on 12/31/2015 09:50 pm
My smallest BFR/MCT is 12.5m in diameter, has 25 engines and 4630mT GLOW. Delivers 180mT to LEO at a mass fraction of 3.9% or 26:1 wet to dry mass ratio.  Goes low & slow.  Propellant reserve for abort to Earth landing. Built for rugged quick turn RTLS and re-launch.  The 1st stage is the easier vehicle for SpaceX to design.  Meets the claimed requirement of 100mT cargo to LEO.

My larger preferred BFR/MCT is 15m diameter, has 28 engines and 5100mT GLOW. Delivers 185mT to LEO at a mass fraction of 3.6% or 28:1 wet to dry mass ratio.  Goes low & slow.  Built for rugged quick turn RTLS and re-launch. I think Musk goes 15m diameter to allow for future engine growth and provide margin when a 85mT dry weight MCT turns out to be too optimistic with complications from things like TPS and complex extra Mars landing engines located "higher" along the structure.

The 80-85mT dry weight upper stage is "near SSTO" with 7.7Km/sec capability fully fueled.  Allows for "fast" transits to Mars.  Less refueling for slower cargo flights to Mars.

When you calculate the mass of propellant for a 15m vehicle you realize that the "BFR" is short and stout, the opposite of the F9 family.

I think that's a little optimistic on mass ratios, but I do expect that a 15m diameter vehicle is going to have a very low ballistic coeefficient, with good lift it can spend a lot of time in the upper atmosphere for a low g and thermal load entry, giving a it a very good mass fraftion for an entry vehicle. But I also expect a design that doesn't depend on a never before achieved mass ratio.

On the order of a .9 mass fraction MCT and a .92 mass fraction booster, you get 236mT to orbit with a 5800 GLOW, and a 107mTon dry MCT. The MCT should have enough dV to do a reentry and landing development program before committing to sizing the BFR. Maybe you could get it orbit with Falcon Heavy boosters.  If you can't make the mass fraction on the MCT you can cut the payload, or tweak the BFR design. Around that size the whole thing is fairly insensitive to weight on the MCT, you could add 50tons and push the booster to .94 and still get 200mTons to orbit.

I can see maybe overcoming the problems with a super massive launch vehicle on Earth but the ISRU requirements get out of control. Can you really make several thousand mTons of propellent on Mars for each MCT? What's the footprint for a solar array to get that done in 2 years?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 12/31/2015 10:37 pm
12m is about the largest diameter standard river barges are.  Thus allowing manufacturing of fuel tankage almost anywhere with the vast Mississippi/Great Lakes systems as well as coastal areas.  The eastern inter-coastal waterway is from Brownsville, Texas to Maine.  The Mississippi river system reaches to Pittsburg, Mineapolis, probably Lincoln, Nebraska, and ties-in with the Tennessee-Tombigbee waterway going as far inland as Knoxville, Tennessee.  Canals connect the Mississippi through Chicago to the Great Lakes.  Anything larger than 12m will probably have to be made on the coast.  A three 8m core heavy version could be make almost anywhere with an 8m core single version replacing Falcon heavy.  Three core heavy for MCT. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 12/31/2015 11:08 pm

Anything larger than 12m will probably have to be made on the coast.  A three 8m core heavy version could be make almost anywhere with an 8m core single version replacing Falcon heavy.  Three core heavy for MCT.

I don't think they are planning a heavy version of the "BFR". Too much complexity for little gain, plus 3x infrastructure needed at pad. Such a massive launcher needs a lot of flights to have any chance of being economical, so you fly more often instead and assemble + refuel in orbit instead.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 12/31/2015 11:09 pm
Shotwell & Musk have said that the BFR will be made on site so river barges are irrelevant.
I'd bet big $ that BFR is single not tri-core.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 12/31/2015 11:11 pm
My smallest BFR/MCT is 12.5m in diameter, has 25 engines and 4630mT GLOW. Delivers 180mT to LEO at a mass fraction of 3.9% or 26:1 wet to dry mass ratio.  Goes low & slow.  Propellant reserve for abort to Earth landing. Built for rugged quick turn RTLS and re-launch.  The 1st stage is the easier vehicle for SpaceX to design.  Meets the claimed requirement of 100mT cargo to LEO.

My larger preferred BFR/MCT is 15m diameter, has 28 engines and 5100mT GLOW. Delivers 185mT to LEO at a mass fraction of 3.6% or 28:1 wet to dry mass ratio.  Goes low & slow.  Built for rugged quick turn RTLS and re-launch. I think Musk goes 15m diameter to allow for future engine growth and provide margin when a 85mT dry weight MCT turns out to be too optimistic with complications from things like TPS and complex extra Mars landing engines located "higher" along the structure.

The 80-85mT dry weight upper stage is "near SSTO" with 7.7Km/sec capability fully fueled.  Allows for "fast" transits to Mars.  Less refueling for slower cargo flights to Mars.

When you calculate the mass of propellant for a 15m vehicle you realize that the "BFR" is short and stout, the opposite of the F9 family.

I think that's a little optimistic on mass ratios, but I do expect that a 15m diameter vehicle is going to have a very low ballistic coeefficient, with good lift it can spend a lot of time in the upper atmosphere for a low g and thermal load entry, giving a it a very good mass fraftion for an entry vehicle. But I also expect a design that doesn't depend on a never before achieved mass ratio.



Mass ratios are roughly equivalent to today's.  Probably among the most pessimistic/conservative cited here.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 12/31/2015 11:19 pm
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.


I can see maybe overcoming the problems with a super massive launch vehicle on Earth but the ISRU requirements get out of control. Can you really make several thousand mTons of propellant on Mars for each MCT? What's the footprint for a solar array to get that done in 2 years?


I've estimated ~40 acres when using thin-film solar with 10% efficiency, occupying 50% of the ground surface to produce the power necessary to both collect water from the atmosphere and create Methane-Lox propellants of 300 mt over 1 synod.  The equipment including power should mass around 50 mt.

For comparison philw1776 anticipates between 1,170 and 1,404 mt propellant capacity in the MCT, presumably full at mars for the fastest possible Earth return.  A factor of between 4x and 5x more then my own target and would require between 200-250 mt of equipment for the same refueling time if the same technique is used.  Direct ice-mining might substantially improve the efficiency but the scale of mining must be very high because you require 45% of your final propellant mass in water for stoichiometric combustion of Methane-Lox.  This means a total mass of 526 to 631 mt, a bit under 1 mt per day.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 12/31/2015 11:28 pm
What would be wicked pissah would be a well conceived poll where we could select our BFR/MCT parameters before Elon makes his BFR/MCT announcement* and see who is at least in the ballpark.


* OK, I'm optimistically assuming we'll still be alive at that time.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 12/31/2015 11:38 pm
It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Does that include your self-deployable, disposable, wire landing/launch pad?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stardhingy on 12/31/2015 11:49 pm
Mass ratios are roughly equivalent to today's.  Probably among the most pessimistic/conservative cited here.

Is that accurate? I thought the highest ratios were around .94, or 16:1.

Edit: Oh, you mean total mass fraction to orbit, not per vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/01/2016 12:06 am
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.
...
Not accurate.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stardhingy on 01/01/2016 01:11 am
If its a 15m section, a spherical tank works out to ~1000mt of propellent. You aren't going to save much drymass by going to smaller tanks, you either use tanks that don't take up the whole diameter and provide support, or you have mass inefficient pancake shaped tanks. What does a couple meters of mostly empty rocket weigh?

It seems to me if you can have a 75mt ship with 300mt of propellent, 1000mtof propellent is only going to bump the dry mass up to say, 80mt. That trade would be well worth it since it would bump your mass fraction up to .93. Now you may not even be able to launch it with full tanks, but fully fueled In GTO you could put 300 mt on trans-Jupiter insertion and boostback to orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: QuantumG on 01/01/2016 02:27 am
Even at 15m, it's still a baby compared to the Sea Dragon ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/01/2016 02:28 am
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.
...
Not accurate.

Can you be more specific?

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Does that include your self-deployable, disposable, wire landing/launch pad?

It is just for launch and would be directly under the engines with a total area of ~100 m^2, even thick 6 gauge steel wire at a 1 inch spacing would be only 1,220 kg, add in stakes and simple rams that push the wire onto the ground and pin it and your still looking at a tiny fraction of the cargo capacity which is where it is accounted for.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/01/2016 05:39 am
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

I was extremely critical of this aspect in the past on the basis that a habitat which needs to hold 100 passengers for 1000 days with 1000 days of food, survive reentry, and produce its own propellant on the other end is probably going to be several times that dry mass;  But I'm increasingly moving towards backing off this conjunction of requirements, and assuming they will not occur simultaneously.

Even so;  Something like the Bigelow BA-2100 is supposed to be heavier than this.  On what basis do you propose 75 tons instead of 9 tons or 400 tons?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 01/01/2016 05:47 am
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

I really expect it to be less - F9 has very good mass ratios IIRC, and MCT will be more like a stage (with cargo bay) than a capsule. (I would expect the passenger accommodations to count against the cargo-version 100mt payload.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/01/2016 06:07 am
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

I was extremely critical of this aspect in the past on the basis that a habitat which needs to hold 100 passengers for 1000 days with 1000 days of food, survive reentry, and produce its own propellant on the other end is probably going to be several times that dry mass;  But I'm increasingly moving towards backing off this conjunction of requirements, and assuming they will not occur simultaneously.

Even so;  Something like the Bigelow BA-2100 is supposed to be heavier than this.  On what basis do you propose 75 tons instead of 9 tons or 400 tons?

Yes the dry mass to cargo mass is optimistic as nothing so far has had a greater then 1:1 ratio.  The cargo mass though is just a little under half ~46% the mars atmospheric entry mass though as propellants would be ~18% and the lander dry mass would be 36% of the total.

Of the requirements you site I see almost none of these requirements being simultaneous.

I see a transit habitat being used for the 100 count passengers and their life-support needs with the landing vehicle holding them for only a few days at a time in something like air-plane densities.  I see re-entry being from much lower orbital speeds at Earth and Mars rather then direct entry.  The propellant production will be done with systems that take up most or all of a single landers cargo capacity, the system will be deployed to the surface and remain their, none of it will be integrated to the vehicle but the vehicle that landed it will remain connected and drink-up the first batch of propellant and use that to slowly return to Earth completely empty of cargo.  Crew return will be in two legs with the lander just returning to mars orbit and then using SEP to return to Earth orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 01/01/2016 06:11 am
It is just for launch and would be directly under the engines with a total area of ~100 m^2, even thick 6 gauge steel wire at a 1 inch spacing would be only 1,220 kg, add in stakes and simple rams that push the wire onto the ground and pin it and your still looking at a tiny fraction of the cargo capacity which is where it is accounted for.

So not only do you have to worry about rocks, you would also have the possibility of long stakes flying up at your spacecraft. Way to many variables in ground composition and installation among other issues to be a viable option. Permanent launch pads will have to be built and by default will become landing pads.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/01/2016 06:36 am
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

I was extremely critical of this aspect in the past on the basis that a habitat which needs to hold 100 passengers for 1000 days with 1000 days of food, survive reentry, and produce its own propellant on the other end is probably going to be several times that dry mass;  But I'm increasingly moving towards backing off this conjunction of requirements, and assuming they will not occur simultaneously.

Even so;  Something like the Bigelow BA-2100 is supposed to be heavier than this.  On what basis do you propose 75 tons instead of 9 tons or 400 tons?

Yes the dry mass to cargo mass is optimistic as nothing so far has had a greater then 1:1 ratio.  The cargo mass though is just a little under half ~46% the mars atmospheric entry mass though as propellants would be ~18% and the lander dry mass would be 36% of the total.

Of the requirements you site I see almost none of these requirements being simultaneous.

I see a transit habitat being used for the 100 count passengers and their life-support needs with the landing vehicle holding them for only a few days at a time in something like air-plane densities.  I see re-entry being from much lower orbital speeds at Earth and Mars rather then direct entry.  The propellant production will be done with systems that take up most or all of a single landers cargo capacity, the system will be deployed to the surface and remain their, none of it will be integrated to the vehicle but the vehicle that landed it will remain connected and drink-up the first batch of propellant and use that to slowly return to Earth completely empty of cargo.  Crew return will be in two legs with the lander just returning to mars orbit and then using SEP to return to Earth orbit.

Sounds intriguing.  Some of these ideas I have explored myself.  Got anything written up on this?

Note that a transit habitat tends to be mutually exclusive with a fast transit, which is required for 1-synod reuse.  SEP from LMO to Earth is also going to be fairly slow.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 01/01/2016 07:33 am
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

There are many previous estimates. Only with HIAD you get to 0.75 or better, from what I've seen. For a non-reusable lander.

I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

I really expect it to be less - F9 has very good mass ratios IIRC, and MCT will be more like a stage (with cargo bay) than a capsule. (I would expect the passenger accommodations to count against the cargo-version 100mt payload.)

The mass ratio you're talking about refers to the total mass divided by the dry mass. What I refer to is the dry mass divided by the payload mass. Apart from that F9 stats are not really applicable to a Mars lander.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/01/2016 07:48 am
It is just for launch and would be directly under the engines with a total area of ~100 m^2, even thick 6 gauge steel wire at a 1 inch spacing would be only 1,220 kg, add in stakes and simple rams that push the wire onto the ground and pin it and your still looking at a tiny fraction of the cargo capacity which is where it is accounted for.

So not only do you have to worry about rocks, you would also have the possibility of long stakes flying up at your spacecraft. Way to many variables in ground composition and installation among other issues to be a viable option. Permanent launch pads will have to be built and by default will become landing pads.

You just seem to be fishing for negatives at this point, stakes driven into the ground are not going to come out in the time scale of a 2g launch.  Ground composition could be an issue and this may mean that their will be a lower maximum boulder size at an acceptable landing site then otherwise.

Note that this wire-mesh is intended just for the initial automated landings in place of the pre-cursor vehicles favored by others.  Once settlements are established I would expect a more permanent pads to be built but they will most likely consist of a larger area of mesh put down over cleared and compacted regolith, not concrete or anything resembling a pad on Earth and the lander will simply omit the drop mesh I described.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/01/2016 07:53 am
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

There are many previous estimates. Only with HIAD you get to 0.75 or better, from what I've seen. For a non-reusable lander.


I'm looking at a kind of mechanical flap at the base of the vehicle and telescoping or umbrella-like system that performs as a HIAD while being fully retractable and reusable to achieve most deceleration down to sub-sonic followed by brief landing burn.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 01/01/2016 08:01 am
I see a GLOW of around 4,600 mt, 31 Raptor engines on the booster and a MCT/BFS of only 75 mt dry.  A vastly more achievable size.

Which assumes 75mt dry mass for a reusable 100mt Mars lander is realistic...

It's more realistic then most other proposals which presume the lander has >1000 mt of propellant tanks at the same mass.  I targeting just 300 mt for tank capacity resulting in a much smaller vehicle and a dry mass fraction of 20%.

Can you find any previous estimates of the mass ratio for dry mass to cargo mass for a (presumably non-reusable) Mars lander, or alternately if your architecture lands back at Earth, for a reusable Earth lander?

There are many previous estimates. Only with HIAD you get to 0.75 or better, from what I've seen. For a non-reusable lander.


I'm looking at a kind of mechanical flap at the base of the vehicle and telescoping or umbrella-like system that performs as a HIAD while being fully retractable and reusable to achieve most deceleration down to sub-sonic followed by brief landing burn.

Like TVG's Michelle-B?

http://www.thespacereview.com/article/409/1
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jabe on 01/01/2016 01:57 pm
Not sure if this video has been posted yet..but a schematic of a 100MT lander is illustrated at 46 min mark.
Interesting vid but warning lots of physics!! :)
Cheers
Jb
https://youtu.be/GQueObsIRfI
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 01/01/2016 04:06 pm
You just seem to be fishing for negatives at this point, stakes driven into the ground are not going to come out in the time scale of a 2g launch.  Ground composition could be an issue and this may mean that their will be a lower maximum boulder size at an acceptable landing site then otherwise.

A less than optimal launch, loose soil, or a manufacturing defect in your unproven wire mesh could lead to a very bad day. You still haven't explained exactly how this pad gets installed. Are you going to depend on a machine that can break down or crew members that might make a mistake? How to you handle quality control when your trying build a new pad for every MCT launch?

As long as your permanent mesh landing/launching pads can hold up to the weight of the MCT and can work for multiple landing and launches, I'm perfectly fine with that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/01/2016 07:36 pm
Not sure if this video has been posted yet..but a schematic of a 100MT lander is illustrated at 46 min mark.
Interesting vid but warning lots of physics!! :)
Cheers
Jb
https://youtu.be/GQueObsIRfI

Very passionate student, and a huge nerd. Watch his "resume" video for applying to the SpaceX internship position:
https://www.youtube.com/watch?v=Nwnv-QM9-NA
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/02/2016 01:32 am

Like TVG's Michelle-B?

http://www.thespacereview.com/article/409/1

Somewhat, I see a nose first entry with the decelerator hinged from a high position on the vehicle perhaps just behind the nose cone, the entire outer skin below that point lifts up and forms part of the decelerator.  This removes the need for a door as the interior of the vehicle is naturally opened by this action.  After deceleration to terminal velocity of around 500 m/s the vehicle then needs to turn to land on it's base, the decelerator might serve as a quasi parachute during the later stages of landing if it can spread far enough to be clear of the ground, ideally it would invert slightly to to put the vehicle mass at the bottom and allow unrestricted access to the vehicle interior after landing.

For a bit of a visual on what it might look like see this video on the large parasols in Meca, as far as I know these are the largest mechanical umbrella like devices in the world.  A vehicle of 200 mt would need an area of about 4 of these to reach a low ballistic coefficient comparable to prior mars landers like MER.  Naturally the ribs would need to be made of light materials like carbon-fiber and the fabric must be something like Nomex or some other high strength incombustible material.

https://www.youtube.com/watch?v=PWLldTTaB5M
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 01/02/2016 02:07 am
What would be wicked pissah would be a well conceived poll where we could select our BFR/MCT parameters before Elon makes his BFR/MCT announcement* and see who is at least in the ballpark.


* OK, I'm optimistically assuming we'll still be alive at that time.

I have been thinking about a poll just for number of engines on the first stage. I would choose 36.

Enjoy, Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: KelvinZero on 01/02/2016 02:53 am
What would be wicked pissah would be a well conceived poll where we could select our BFR/MCT parameters before Elon makes his BFR/MCT announcement* and see who is at least in the ballpark.


* OK, I'm optimistically assuming we'll still be alive at that time.

I have been thinking about a poll just for number of engines on the first stage. I would choose 36.

Enjoy, Matthew
More difficult: but I would like to see an enumeration of all the basic configurations that are popular.. though I accept the most straightforward design is probably correct. All those wacky ideas just give me a "magnificent men in their flying machines" moment.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/02/2016 04:02 am
You just seem to be fishing for negatives at this point, stakes driven into the ground are not going to come out in the time scale of a 2g launch.  Ground composition could be an issue and this may mean that their will be a lower maximum boulder size at an acceptable landing site then otherwise.

A less than optimal launch, loose soil, or a manufacturing defect in your unproven wire mesh could lead to a very bad day. You still haven't explained exactly how this pad gets installed. Are you going to depend on a machine that can break down or crew members that might make a mistake? How to you handle quality control when your trying build a new pad for every MCT launch?

As long as your permanent mesh landing/launching pads can hold up to the weight of the MCT and can work for multiple landing and launches, I'm perfectly fine with that.

Manufacturing defects in 6 gauge wire is your concern now?  Even the Russians have better quality control then that.  Seriously your practically trolling at this point.

I already described the deployment process it's in a roll under the vehicle and simply drops to the ground or is on a swing arm that releases to bring it to the ground.  It can be unrolled by having the the wire under tension so it wants to expand as soon as released, if that's not enough you inflating a tube that was wrapped inside the roll this will pneumatically extend it even rolling up and over small obstacles.  This is how you autonomously deploy a single use mesh for one vehicle.

To build permanent pads you have human crews operate heavy machinery like bull-dossers, rollers and compactors, then lay down the best covering material they can afford to bring or make and try to attach it as securely as possible to the surface.  Some kind of prefabricated interlinking metal object is the likeliest solution.  If mass budgets are low it's probably a welded wire mesh or chain-mail like material linked together into a single huge piece.  If mass budgets are more generous it might resemble a Marston Mat made from aluminum.  https://en.wikipedia.org/wiki/Marston_Mat
Title: Re: MCT Speculation and Discussion Thread 4
Post by: arnezami on 01/02/2016 09:35 am
Not sure if this video has been posted yet..but a schematic of a 100MT lander is illustrated at 46 min mark.
Interesting vid but warning lots of physics!! :)
Cheers
Jb
https://youtu.be/GQueObsIRfI

Here is the relevant paper:

http://www.ssdl.gatech.edu/papers/phdTheses/CordellC-Thesis.pdf (http://www.ssdl.gatech.edu/papers/phdTheses/CordellC-Thesis.pdf)

Maxwell is referring to the configuration where the nozzles are located in the afterbody. In the paper, chapter 4.3.2 introduces this concept and in chapter 6 goes much deeper into it.

Attached are two figures from the papers, one with the afterbody nozzles turned off, the other with the nozzles turned on.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Johnnyhinbos on 01/02/2016 02:27 pm
Though somewhat click bait-y, there's a few tidbits worth reading. (I'd inline quote, but iPhone Tapatalk makes it a pain...)

http://www.universetoday.com/126457/will-2016-be-the-year-elon-musk-reveals-his-mars-colonial-transporter/
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Miker66 on 01/02/2016 04:05 pm
MCT Daily Gravity Dose

This is probably a crazy idea, but how about this for simulating gravity on a Mars trip?

Around the inside of the hull is a circular rollercoaster track. On it is a bicycle, the sort you lie on your back to pedal, maybe with hand cranks too. Each astronaut does, say, 30 minutes a day on the bike. You start out stationary, pedal up to speed, keep going for your 30 minutes, then slow down and get off when stationary. Assuming an MCT internal diameter of 40 feet how fast would you need to go to experience 1g? Or maybe ˝g would be enough.

You’d be lying flat on your back, so your head and feet are travelling at the same speed, experiencing the same ‘gravity’. Though you could of course sit upright if you wanted to drain fluid down from your head or get some spine compression. EDIT: even 10 minutes on your back, 5 minutes on your left side, 5 minutes on your right side, 5 minutes on your front and 5 minutes bolt upright to get some g in all the directions you would on earth?

The "bicycle" is reversible – the next guy goes round in the opposite direction to avoid imparting cumulative spin to the rocket. Though would 'anti-pedalling' to slow down undo all the spin you imparted?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 01/02/2016 04:53 pm
You'd be lying flat on your back

Remember that laying flat is used as a crude proxy for weightlessness in research on Earth, precisely because it causes many of the issues experienced in space even though you are under 1g. Hence, your bike method will achieving no more than peddling on a stationary bike in weightlessness.

Better to simply have a ring-track around the widest inside diameter of the hab section. And use centripetal force to hold you down as you jog/run. A la Skylab & 2001.

Though would 'anti-pedalling' to slow down undo all the spin you imparted?

The total energy of the ship and rider (or runner in my case) are conserved, unless mass is thrown overboard. So there'll only be induced spin during the exercise itself; but zero net spin, regardless of which direction(s) you ride.

If you don't want the ship to spin at all, you would probably use a flywheel large enough to store the momentum during the exercise sessions, (reversed when they stop.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stan-1967 on 01/02/2016 05:32 pm
You'd be lying flat on your back

Remember that laying flat is used as a crude proxy for weightlessness in research on Earth, precisely because it causes many of the issues experienced in space even though you are under 1g. Hence, your bike method will achieving no more than peddling on a stationary bike in weightlessness.

Better to simply have a ring-track around the widest inside diameter of the hab section. And use centripetal force to hold you down as you jog/run. A la Skylab & 2001.

Though would 'anti-pedalling' to slow down undo all the spin you imparted?

The total energy of the ship and rider (or runner in my case) are conserved, unless mass is thrown overboard. So there'll only be induced spin during the exercise itself; but zero net spin, regardless of which direction(s) you ride.

If you don't want the ship to spin at all, you would probably use a flywheel large enough to store the momentum during the exercise sessions, (reversed when they stop.)

I like the idea of a bike track that the rider lays relatively "flat" to the outer circumference.   Quick calculations for a 40 ft inner diameter track says a rider needs to be going 25 feet per second ( 12 rpm ) inside the track for 1g, and 17 feet per second ( 8.4 rpm ) for .5g.      Those velocities ( 11.5 to 17 mph)  are easily achieved by a bicycle, but not to easy for a person to sustainable run and get any benefit of daily "g" doses.   

I'd minimize flywheel demands by having to tracks that different riders can go opposite directions to cancel out the angular momentum issues.   A computer could direct each occupant to step up the pace, or back off on the effort to keep things in balance.  Make it a game and take the boredom of out of going in circles.  Concurrent riders can match each other in weight.  Heck, there's even no reason you couldn't couple the forces produced by the rider to a counterweight rotating in the opposite direction that would cancel his own momentum.  It would just add resistance, which is the whole point of exercise.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Miker66 on 01/02/2016 06:02 pm
Quote
I like the idea of a bike track that the rider lays relatively "flat" to the outer circumference. Quick calculations for a 40 ft inner diameter track says a rider needs to be going 25 feet per second (12 rpm) inside the track for 1g, and 17 feet per second (8.4 rpm) for .5g. Those velocities (11.5 to 17 mph) are easily achieved by a bicycle, but not too easy for a person to sustainably run and get any benefit of daily "g" doses.   

I'd minimize flywheel demands by having two tracks that different riders can go opposite directions to cancel out the angular momentum issues. A computer could direct each occupant to step up the pace, or back off on the effort to keep things in balance. Make it a game and take the boredom of out of going in circles.  Concurrent riders can match each other in weight.  Heck, there's even no reason you couldn't couple the forces produced by the rider to a counterweight rotating in the opposite direction that would cancel his own momentum.  It would just add resistance, which is the whole point of exercise.

Thank you for your thoughts and for doing the sums.

One revolution every 5 seconds to get 1g is not too fast, and (say) 30 minutes at 1g a day (lying flat and/or sitting up) would hopefully help combat muscle and bone loss.

I like the idea of two competing tracks and so forth. However, simplicity/weight/space may mean a single, simple track. On reflection, one person accelerating to 17mph would not have much spin effect on a huge spaceship, and negligible once they have decelerated.

Maybe it's not such a crazy idea after all.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Mongo62 on 01/02/2016 06:17 pm
For artificial gravity, I would simply go with two MCTs linked by a long cable, spinning about each other. The longer the cable, the better.

This does imply that an MCT fleet would preferably consist of an even number of passenger vessels (although a passenger vessel linked to a cargo vessel should work too).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 01/02/2016 06:21 pm
For artificial gravity, I would simply go with two MCTs linked by a long cable, spinning about each other. The longer the cable, the better.


Not attempting to be rude, but wasn't this idea suggested a long time ago and debunked? It adds numerous mission complications (and contingency risks) and the absence of zero-G increases volume limitations to a spacecraft that is already volume limited.

As to the bike idea - if you were going to use flywheels for rotational control/pitch control anyway on the trip to Mars (no idea how it scales), then just connect the bike to that. Saves you an extra flywheel.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Miker66 on 01/02/2016 06:41 pm

As to the bike idea - if you were going to use flywheels for rotational control/pitch control anyway on the trip to Mars (no idea how it scales), then just connect the bike to that. Saves you an extra flywheel.

No flywheels involved! Please see original post:

https://forum.nasaspaceflight.com/index.php?topic=37808.msg1468713#msg1468713 (https://forum.nasaspaceflight.com/index.php?topic=37808.msg1468713#msg1468713)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stan-1967 on 01/02/2016 07:45 pm
I'm in agreement with making operation of a bike track impart as close to zero angular momentum to the spaceship whether it be by cancelling the effect of an rider on a track by coupling to a flywheel, or by having a counter rotating mass ( other rider) cancelling the same. 

Over even minutes of operation, I am pretty certain that significant angular motion would be imparted to even a large craft like an MCT.   Communication arrays, solar arrays etc. would go out of alignment if not compensated for.  Think of those "strongman" shows where some big huge dude pulls a semitruck with a rope.  I've seen one guy get a truck up to 5mph in very little time.   The key part is that if you just want to give a person exposure to g's, you can do it with very little change in momentum once they are moving.  That becomes a problem of minimizing drag/friction on the track.  If you want this to also be resistance training for muscle preservation, you need resistance, which require you to push against something (i.e the spaceship) and that will impart a large angular momentum change.   That is much different problem, hence the complexity I am imagining with multiple tracks.

My thoughts on multiple tracks was that this is being discussed in context of a MCT with upwards of 100 colonists on board.  If the goal is to give a daily dose of 1g, plus resistance training for preserving muscle mass, how are 100 colonist going to cycle through a single track in any frequency that gives regular benefit?   If each colonist were to be assigned 1 hr per day of exersise, that would require 6 tracks operating 18 hours per day.  The number of tracks could be reduced by putting multiple riders in the same loop.   ( computers are going to have to be involved for adjusting resistance for collision avoidance!) 

Furthermore, if the track resistance adjust to make the average energy output of each rider around 150-200 Watts, I'm going to think it is worth the effort to make this space hamster wheel an electromagnetically coupled generator.   It would deliver about the equivalent of a kilowatt of continuous power when operating.   That is worth some reduced weight in solar arrays to offset the weight of the track.

I also don't think a bike track contraption necessarily has to take up too much space.   Given you can constrain the tracks, each lane should not need to be more than 2 ft wide and maybe 3 ft high.  Think of each track as a tube around the inner circumference.   If you have 3 track ( 6 ft ) total, that are 3 ft high, that would be volume around 1100 ft^3 or 31 m^3.  Not a show stopper for the size of MCT and the importance of human health during the journey.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Miker66 on 01/02/2016 08:09 pm
Good point: if there are 100 on board, two tracks in opposite directions could be good. Tandems - nice idea. The tracks - two rails attached to the hull - would weigh very little and the bike(s) could be very light and indeed wouldn't take up much space.

Even if there was only one track, one person accelerating to 17mph against a ship with mass of 100 tonnes wouldn't have too much spinning effect on the ship. (Though if one track would induce spinning, I think by that logic two opposite-direction tracks would induce tumble? So you're back to reversing each bike's direction each time.)

There would be some friction loses, and of course air resistance, so some work for the cyclist to do even to maintain a steady speed. I suppose you could couple to a dynamo, but my instinct says just keep it simple. This is mostly about getting a dose of g - let's make that as easy as we can for the guys.

Original idea https://forum.nasaspaceflight.com/index.php?topic=37808.msg1468713#msg1468713 (https://forum.nasaspaceflight.com/index.php?topic=37808.msg1468713#msg1468713)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 01/02/2016 08:26 pm
Position relative to CoG would influence tumble.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stan-1967 on 01/02/2016 09:06 pm
Position relative to CoG would influence tumble.

Correct!   Isn't space fun!  All moments need to be accounted for and cancelled to maximize any such scheme.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: KelvinZero on 01/02/2016 09:09 pm
Would some sort of flywheel/gyroscope be implemented anyway?

I can imagine people building up habits of circulating in a specific way, statistically. This would slowly rotate the vehicle which might interfere with pointing antenna or keeping a certain orientation to the sun for thermal reasons. It might not be predictable. On different flights the passengers might develop different conventions.

So have some gyroscope that can deal with a bit of this. If passengers develop really peculiar habits that saturate the flywheel, such as they decide to have hundred person sprinting races, diplomatically instruct them to stop or how to do it without interefering with the ships orientation. If there is something like a bike track or running track they should join the emptier side that moves in the counter direction, which they would probably do anyway. Or there could be a little gyroscope status indicator on the wall and one civic minded jogger could unwind the angular rotation of 99 not quite randomly circulating co-passengers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/02/2016 09:46 pm
Because of Coriolis disorientation, only very small amounts of gravity (0.1g?) are practical within a single vehicle.  This is certainly useful for some things - showering, natural convection airflow, mechanical work - but probably not health-related things.

For higher gravity you're going to need multiple parts connected by long (100m - 1000m) tethers.

Why this design over something with a smaller overall diameter and spinning faster with a larger tube diameter, why so few spokes? Why not just go with the more common proposal of docking at the hub? It just looks like a pretty design with no engineering offered as to why that design is an improvement over countless others.
Coriolis Nausea (http://en.wikipedia.org/wiki/Artificial_gravity#Rotation) afflicts very small diameter designs.  Reasonable rotation rates are up to 2-4rpm;  Above 7rpm there seem to be intractable issues in the short term.

At 480m radius, you can get 1G at 1.365rpm - a guaranteed comfortable experience apparently
At 120m radius, you can get 1G at 2.73rpm - Some side effects, but everyone can acclimate to the condition eventually
At 60m radius, you can get 1G at 5.46rpm - Extremely uncomfortable, some people can eventually acclimate, some can't

Any sort of artificial gravity scheme requires major compromises and mitigations for things that need to be statically pointed, like comms, thermal shielding on prop depots, and SEP;  A tether system is the lightest-weight way to make long spans, but it also requires a greater degree of autonomous control in the slung loads (independent propulsion is preferable).

With that said:
For artificial gravity, I would simply go with two MCTs linked by a long cable, spinning about each other. The longer the cable, the better.


Not attempting to be rude, but wasn't this idea suggested a long time ago and debunked? It adds numerous mission complications (and contingency risks) and the absence of zero-G increases volume limitations to a spacecraft that is already volume limited.

As to the bike idea - if you were going to use flywheels for rotational control/pitch control anyway on the trip to Mars (no idea how it scales), then just connect the bike to that. Saves you an extra flywheel.



It adds lots of mission complications, but unlike the bike idea, it is mathematically adequate for achieving the gravity specified.  Are there any real *showstoppers* for it, in a situation where SEP is not used?

A "flywheel" in this instance, a 'control moment gyroscope', is a solid metal or perhaps carbon fiber cylinder spinning at tens of thousands of RPM so it takes up as little space as possible and can be turned on three or four axes.  From what I recall, the flywheels on the ISS are presently insufficient to handle active turning;  Instead, propulsive thrusters are used for both attitude change maneuvers, and for desaturating the CMG's when they reach their angular momentum limit;  mostly they only handle short-duration loads like someone moving around the station.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 01/03/2016 01:56 am
and the absence of zero-G increases volume limitations to a spacecraft that is already volume limited.

Yeah -- I think this would be more important than the health effects of zero-G on a trip of 3 - 8 months. (We know this duration of zero G is do-able from Mir and ISS.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: darkenfast on 01/03/2016 07:14 am
I'm pretty sure we've gone through this discussion before.  Attempts to simulate gravity on a Mars-bound spacecraft would take up mass and space that could be put to better uses.  Adjusting to Mars' lower gravity will not take long.  The crew does not need to rush out and do handsprings.  If they need to move around right after landing for an emergency, then they will do just as Soyuz passengers returning from the ISS have done after an off-target landing: they will cope. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/03/2016 10:23 am
I'm pretty sure we've gone through this discussion before.  Attempts to simulate gravity on a Mars-bound spacecraft would take up mass and space that could be put to better uses.  Adjusting to Mars' lower gravity will not take long.  The crew does not need to rush out and do handsprings.  If they need to move around right after landing for an emergency, then they will do just as Soyuz passengers returning from the ISS have done after an off-target landing: they will cope.

I fully agree. If we ever send a manned vehicle, refuelled at Mars orbit, to explore the outer planets on a multi year mission, we may need to think of artificial gravity, but not to Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Johnnyhinbos on 01/03/2016 12:47 pm
I think perhaps there's merits to it (artificial gravity on a Mars insertion/return), especially for paying colonists.

As a side note, this paper on one potential Mars exploration architecture - in part authored by Boeing - feels that AG was important enough to include...

https://www.researchgate.net/profile/Ruth_Bamford/publication/233988445_Modular_Space_Vehicle_Architecture_for_Human_Exploration_of_Mars_using_Artificial_Gravity_and_Mini-Magnetosphere_Crew_Radiation_Shield/links/09e4150dcdd2965e62000000.pdf?inViewer=0&pdfJsDownload=0&origin=publication_detail
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/03/2016 01:08 pm
NASA administrator Charles Bolden has declared this year in a Congress hearing that they know how to mitigate zero gravity effects for the duration of a Mars mission. Even an orbital missionon that does not land but goes to orbit, leaving them in micro gravity for almost two years.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/03/2016 02:05 pm
Getting back closer to MCT speculation.

I have been thinking about LAS function. For a long time I don't see LAS useful on MCT as a stand alone vehicle. Very little good on Mars if the landing point is not reached. Very little to no good on earth return. Redundancy and reliability will have to make it safe enough.

That leaves the question of LAS capability on earth ascend as desirable. I don't believe that carrying the LAS all the way to Mars and back to have that ability on earth ascent. Maybe a dedicated LAS capable vehicle could be designed for transfer of all 100 passengers to the waiting MCT. It could be lightweight enough that it would be possible to launch the passengers and do the final filling of the tanks for departure in one go.

Though I still believe that no dedicated LAS will be needed at all. BFR with enough thrust that it can launch even with an engine out seconds after launch. With engines that are reliable enough and equipped with sensors that shut off the engine without explosion strong enough to affect neighbouring engines.

MCT could not do LAS in the sense it speeds away from an explosion but capable of separating from BFR and doing RTLS after burning most of its fuel before landing. It would need landing gear strong enough to deal with the full weight of a launched MCT. Out of the box idea, maybe not feasible: Land MCT on a pad 10m deep in water. It destroys MCT but saves the passengers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 01/03/2016 08:17 pm
(Suggest moving this entire spin-gravity subject to Non-astronauts for months in cramped environments (http://"http://forum.nasaspaceflight.com/index.php?topic=39058.0") under Advanced Concepts.)

You'd be lying flat on your back
Remember that laying flat is used as a crude proxy for weightlessness in research on Earth, precisely because it causes many of the issues experienced in space even though you are under 1g. Hence, your bike method will achieving no more than peddling on a stationary bike in weightlessness.
I like the idea of a bike track that the rider lays relatively "flat" to the outer circumference.  Quick calculations [...] for 1g

You missed my point. You don't get the benefit of 1g when you are laying down (or even sitting.)

Hence riding at 1g on an recumbent bicycle might be the equivalent of jogging at a quarter or a tenth of 1g. And probably no better than using a stationary bike.

Running has the added benefit of impact on joints and bones reducing bone-loss. (Which is why there was so much effort figuring out how to build a micro-g treadmill on ISS.)

What I like about a running track is that there's no equipment to wear out. It's very self-paced. And it's very natural.

Aside: If you insist on a bike, the track itself is unnecessary. There's this:

(the rider creates artificial gravity for the platform, which is for high-impact resistance weight training, squats, lifts, etc.)

(http://images.onset.freedom.com/ocregister/kpiz9c-25spacecyclelg.jpg) (http://"http://images.onset.freedom.com/ocregister/kpiz9c-25spacecyclelg.jpg")
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/03/2016 08:38 pm
I agree that the only viable mars emergency system is to have engine-out capability ideally from the moment of lift-off.  Likewise you need lots of thrust to even think about separating from a booster even if it is not a fast separation, both these requirements would lead us to a MCT which has substantially higher thrust to weight ratio then a rocket would typically have. 

My own concept is for MCT to mass just 200 mt at launch due to being nearly empty of propellants, 4 Raptor engines give it an acceleration of 4.7 g's.   In the event of separation from the booster (which might need assistance from pressure-fed or solids to account for spin-up time of Raptor) a RTLS landing might be possible in the early phases of launch but a down range water landing is most likely.  I agree that this would likely result in a scrapping of the vehicle (just as we scrap an airplane that has had a water landing) but it will be well worth it if it saves lives.  I see the vehicle simply doing a landing burn to soft land in water (as early F9 tests did) and floating due to it's tanks, passengers will wait for rescue inside the vehicle rather then jumping into life-rafts.

On mars surface with 25 mt cargo and with full propellant tanks GLOW would be 400 mt and the vehicle would have 2.3 g's acceleration which is reduced by mars gravity to just under 2 g's upward at launch, if an engine is lost a diagonal engine must also be shut down to maintain balance and the upward acceleration is only .75 g upward at take off, still very fast by conventional launch standards and more then sufficient to reach orbit with minimal gravity losses.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 01/03/2016 10:03 pm
Not sure if this video has been posted yet..but a schematic of a 100MT lander is illustrated at 46 min mark.
Interesting vid but warning lots of physics!! :)
Cheers
Jb
https://youtu.be/GQueObsIRfI

The author of the thesis, Max Fagin, has been discussing it on this Reddit thread: https://www.reddit.com/r/spacex/comments/3z6tr2/thesis_defense_supersonic_retropropulsion_for/
(He says he cannot comment on his work for SpaceX though)
 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/04/2016 12:31 am
I agree that the only viable mars emergency system is to have engine-out capability ideally from the moment of lift-off.  Likewise you need lots of thrust to even think about separating from a booster even if it is not a fast separation, both these requirements would lead us to a MCT which has substantially higher thrust to weight ratio then a rocket would typically have. 

My own concept is for MCT to mass just 200 mt at launch due to being nearly empty of propellants, 4 Raptor engines give it an acceleration of 4.7 g's.   In the event of separation from the booster (which might need assistance from pressure-fed or solids to account for spin-up time of Raptor) a RTLS landing might be possible in the early phases of launch but a down range water landing is most likely.  I agree that this would likely result in a scrapping of the vehicle (just as we scrap an airplane that has had a water landing) but it will be well worth it if it saves lives.  I see the vehicle simply doing a landing burn to soft land in water (as early F9 tests did) and floating due to it's tanks, passengers will wait for rescue inside the vehicle rather then jumping into life-rafts.

On mars surface with 25 mt cargo and with full propellant tanks GLOW would be 400 mt and the vehicle would have 2.3 g's acceleration which is reduced by mars gravity to just under 2 g's upward at launch, if an engine is lost a diagonal engine must also be shut down to maintain balance and the upward acceleration is only .75 g upward at take off, still very fast by conventional launch standards and more then sufficient to reach orbit with minimal gravity losses.

7 engines at Mars surface just about fit into a 15m diameter.  With that many, engine failure where you (hypothetically) have to shut off the opposite thruster is at most a 28% drop, rather than a 50% drop.  I like the notion of abort to water during Earth ascent.

Launching with MCT nearly empty would be required to achieve high-G abort, but this would mean the BFR would nearly need to reach orbit.   That eliminates or makes very expensive the possibility of a 1-stage BFR.

I think we're probably going to see crew & bulk cargo launch separately from the MCT structure.  The largest mission feasible is going to be bottlenecked by the welded-together structural mass that can be sent up on a single launch vehicle.  You can only build tanks so big given a fixed structural mass, you can only build a hab so big, you can only land so much mass onto the Martian surface.

Hanging an abort requirement onto that shrinks the bottlenecking variable by an order of magnitude or so.  Putting bulk cargo (mostly food) in with the crew subtracts further.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/04/2016 12:49 am

7 engines at Mars surface just about fit into a 15m diameter.  With that many, engine failure where you (hypothetically) have to shut off the opposite thruster is at most a 28% drop, rather than a 50% drop.  I like the notion of abort to water during Earth ascent.

Launching with MCT nearly empty would be required to achieve high-G abort, but this would mean the BFR would nearly need to reach orbit.   That eliminates or makes very expensive the possibility of a 1-stage BFR.

I think we're probably going to see crew & bulk cargo launch separately from the MCT structure.

What kind of GLOW at Mars do you see that will utilize the 5 remaining engines?  I assume the engine arrangement honey-comb with a central engine.

A 1-stage BFR is of course not what I'm proposing as it by your own logic makes abort at Earth launch impossible, not to mention it is inefficient for propellant delivery to LEO.  I expect BFR to be 2 stages with a reusable orbital 2nd stage.

If bulk cargo is launched separately from the MCT vehicle then that mandates a 2 stage BFR as something other then the MCT vehicle needs to push the cargo to orbit.  This would be a very attractive architecture as it would cut the size of the BFR nearly in half.  I've thought it likely that this is going to be sufficiently difficult that SpaceX will not try it initially, but will rather defer it to later and use it to just ramp up the rate of delivery once it is mastered.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/04/2016 06:04 pm


My own concept is for MCT to mass just 200 mt at launch due to being nearly empty of propellants, 4 Raptor engines give it an acceleration of 4.7 g's.   In the event of separation from the booster (which might need assistance from pressure-fed or solids to account for spin-up time of Raptor) a RTLS landing might be possible in the early phases of launch but a down range water landing is most likely.  I agree that this would likely result in a scrapping of the vehicle (just as we scrap an airplane that has had a water landing) but it will be well worth it if it saves lives.  I see the vehicle simply doing a landing burn to soft land in water (as early F9 tests did) and floating due to it's tanks, passengers will wait for rescue inside the vehicle rather then jumping into life-rafts.

On mars surface with 25 mt cargo and with full propellant tanks GLOW would be 400 mt and the vehicle would have 2.3 g's acceleration which is reduced by mars gravity to just under 2 g's upward at launch, if an engine is lost a diagonal engine must also be shut down to maintain balance and the upward acceleration is only .75 g upward at take off, still very fast by conventional launch standards and more then sufficient to reach orbit with minimal gravity losses.

I'm interested in just what the numbers are for the lower stage or stages that put the nearly empty of propellant 200mT MCT into LEO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/04/2016 11:05 pm
It's 200 mt total, 75 for the vehicle, 100 for cargo and 25 propellant which would be just for final orbital insertion and maneuvering or for the landing burn into water in case of an abort.

1st Stage boosters is comparable to what you have discussed, 54,900 kN thrust, 180 tons dry, 3150 mt Propellant.  2nd Stage 16,100 kN, 72 mt dry, 1200 mt propellant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/05/2016 05:43 pm
So the MCT is the 3rd stage or am I mis-understanding?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/05/2016 05:59 pm
The BFS (fka MCT) is the 2nd stage according to recent comments by Musk. I don't know what it is in other peoples' fantasy architectures.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/05/2016 07:46 pm
So the MCT is the 3rd stage or am I mis-understanding?

Basically yes though the first 2 stages are a full orbital launch system capable of putting any payload into LEO.  Despite other folks desire to interpret Musk statements as unconditional support for their positions it is nothing of the sort, Musk simply said the mars spacecraft needs a booster on Earth, he did not specify the stages in said booster. 

The impracticality of a 1 stage booster that is dependent on being paired with a fully interplanetary spacecraft of gigantic size to do any launch at all is so high that the idea should be discounted until explicitly confirmed by Musk, and even then I would be highly doubtful such an architecture would successfully get out of development.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/05/2016 09:36 pm
So the MCT is the 3rd stage or am I mis-understanding?

Basically yes though the first 2 stages are a full orbital launch system capable of putting any payload into LEO.  Despite other folks desire to interpret Musk statements as unconditional support for their positions it is nothing of the sort, Musk simply said the mars spacecraft needs a booster on Earth, he did not specify the stages in said booster. 

The impracticality of a 1 stage booster that is dependent on being paired with a fully interplanetary spacecraft of gigantic size to do any launch at all is so high that the idea should be discounted until explicitly confirmed by Musk, and even then I would be highly doubtful such an architecture would successfully get out of development.

I think you are making a straw man there. There could be one booster paired with different reusable upper stages. An general purpose one for most LEO/GTO payloads (developed first), and a more specialized Mars variant. That's how I see it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/05/2016 10:31 pm
So the MCT is the 3rd stage or am I mis-understanding?

Basically yes though the first 2 stages are a full orbital launch system capable of putting any payload into LEO.  Despite other folks desire to interpret Musk statements as unconditional support for their positions it is nothing of the sort, Musk simply said the mars spacecraft needs a booster on Earth, he did not specify the stages in said booster. 

The impracticality of a 1 stage booster that is dependent on being paired with a fully interplanetary spacecraft of gigantic size to do any launch at all is so high that the idea should be discounted until explicitly confirmed by Musk, and even then I would be highly doubtful such an architecture would successfully get out of development.

I think you are making a straw man there. There could be one booster paired with different reusable upper stages. An general purpose one for most LEO/GTO payloads (developed first), and a more specialized Mars variant. That's how I see it.

No, many people have explicitly said that no separate 2nd stage will ever exist and all launches will be using MCT as the one and only 2nd stage.
 
If a reusable upper stage is produced first (which I expect) then it make no sense not to utilize it when launching the MCT vehicle regardless of how much deltaV the MCT itself may be capable of, you would simply design a larger MCT, or a smaller BFR if this was your plan and you would always use the 2nd stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/05/2016 10:49 pm
Then you are deliberately misreading people and interjecting your own ideas about how it must be done.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/06/2016 12:11 am
Then you are deliberately misreading people and interjecting your own ideas about how it must be done.

Misreading?  I'll provide quotes if you like, but it is indisputable that many people have adamantly rejected the idea of a 2 stage BFR and insist on an exclusive MCT as the only 2nd stage. 

MCT may be very stripped down when in cargo mode, essentially a reusable second stage with a long-loiter package and refueling capability. Don't know why you'd insist on yet another stage.

I am at a loss here. I cannot understand where the idea of a second stage comes from.

The abilities of a second stage are a subset of what MCT needs to do going from LEO to Mars surface and, after refuelling, back to earth. So why duplicate that existing capability with a separate second stage?

I'm willing to guess that SX will not make a S2 and put the spaceship on top of it. It will actually use the spaceship to finish the orbit, and then maybe re-fuel it there to get to mars (or an even higher staging point).

Remember, the spaceship we are talking about should be capable of some serious dv if it can reach mars from LEO/HEO and land (or launch from mars and return). You are not going to need another stage on the rocket to get it to LEO, unless in-orbit refueling is out of the question. A re-usable S1 is enough, dilithium crystals would be overkill at this point.. ;)   

Moreover, a second stage that reaches orbit is either very expensive (expendable), or very expensive and complex (re-usable). If BFR stays as an exclusive MCT booster (as has been hinted by SpaceX in the past), then its more safe to assume that there won't be a second stage.

In any case, we will have to see how this unfolds. We may get some information by Elon on the architecture by Q1 2016.

If you think I am misreading Musk statements I would argue that the other side has done the same and with far less justification on technical merits.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/06/2016 03:23 am
Geez, not this again. Read what I wrote closer. (Hint: I did not state that you misread *all*) Some have advocated that, but I certainly have not.

I have always advocated a BFR upper stage with a cargo bay, so good luck putting an MCT in or on top of that. An MCT would be an evolved version of such a stage. There is no reason to launch a Mars capable vehicle for most BFR missions, which will be LEO, GTO, and propellant deliveries.

But why do I bother. Will it be Impaler vs the world for another few weeks here? If so, let me know when the dust has settled.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 01/06/2016 03:50 am
Misreading?  I'll provide quotes if you like, but it is indisputable that many people have adamantly rejected the idea of a 2 stage BFR and insist on an exclusive MCT as the only 2nd stage. 

You're going to have to switch to the new nomenclature or things are going to get very confusing.

Musk's last statement makes it clear that what we've been calling "the MCT", Musk is obviously calling BFS. Hence, "MCT" is the whole system, BFR plus BFS plus whatever the system needs (fuel depots, etc.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/06/2016 04:46 am
Geez, not this again. Read what I wrote closer. (Hint: I did not state that you misread *all*) Some have advocated that, but I certainly have not.

I have always advocated a BFR upper stage with a cargo bay, so good luck putting an MCT in or on top of that. An MCT would be an evolved version of such a stage. There is no reason to launch a Mars capable vehicle for most BFR missions, which will be LEO, GTO, and propellant deliveries.

But why do I bother. Will it be Impaler vs the world for another few weeks here? If so, let me know when the dust has settled.

I think you should likewise re-read, I said 'many people' had said their would be no separate 2nd stage, you are basically saying that is correct.  But never said it was your position.  It seems you are staking out some kind of middle ground in which a less then mars capable vehicle is the normal 2nd stage for the many LEO/GTO launches (which in principle I agree with but most have rejected), but the MCT launch doesn't make use of this 2nd stage when it launches (which still seems illogical to me).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/06/2016 04:47 am
Impaler: There's literally no difference in my mind between a reusable second stage and a sufficiently stripped-down MCT (and I expect the first version they fly will be stripped down). That's what I meant, and I don't know what else you could take from what I said.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 01/06/2016 05:40 am
A human rated MCT needs a launch abort system.
The LAS will probably eject the crew compartment only, not the big engines and fuel tanks.
So
A mct\bfs will be built of two seperate parts - the propultion module and the utility module.
The propultion module is practically the BFR's 2nd stage and the utility module will be mission specific.
That's how I see it. Does it makes sence?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 01/06/2016 06:19 am
A human rated MCT needs a launch abort system.
The LAS will probably eject the crew compartment only, not the big engines and fuel tanks. So
A mct\bfs will be built of two seperate parts - the propultion module and the utility module.
The propultion module is practically the BFR's 2nd stage and the utility module will be mission specific.
That's how I see it. Does it makes sence?

This has come up before. The LAS-compartment will need to, in effect, be an independent spacecraft, capable of re-entry and landing.

In which case, why not just launch your humans on the "LAS" itself, and launch the BFS separately?

That way you're not trying to design a BFS that can safely split into two separate parts mid-launch, while still functioing as a single reentry vehicle (which, IMO, is going to be harder than simply having two independent vehicles.) It also means that the unmanned BFS can sit in LEO being refuelled before launching to Mars, without your passengers on board getting in the way and using up resources. At the 11th hour, the passengers are launched on the smaller crew-shuttle to the BFS.

The crew-shuttle is not only smaller than the full BFS. If you ferry the passengers up in groups of ten or twenty, it could be smaller still.

[Aside: My gut feeling is that if the BFS is the second stage on the BFR, then Musk will just have the whole BFS abort.]
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/06/2016 05:13 pm
Maybe it's just me but I read this as Elon saying that the BFR/MCT (now called BFS) is a 2 part entity which I interpret as that stage 2 IS the BFS.  A booster rocket (stage one with lots of engines) and a spaceship (stage 2).

"Well, there's two parts of it—there's a booster rocket and there's a spaceship. So the booster rocket's just to get it out of Earth's gravity because Earth has quite a deep gravity well and thick atmosphere, but the spaceship can go from Mars to Earth without any booster, because Mars's gravity is weaker and the atmosphere's thinner, so it's got enough capability to get all the way back here by itself. It needs a helping hand out of Earth's gravity well. So, technically, it would be the BFR and the BFS." As in "Big frakking Spaceship."

http://www.gq.com/story/elon-musk-mars-spacex-tesla-interview?utm_source=10370

This also pretty much says that the spaceship part needs to have the delta V capability for Mars surface to Earth (debatable Earth surface or LEO, maybe either).  That means more than small couple hundred mT propellant tanks.

Whether this is the best approach or the final architecture remains to be seen but it would be surprising to see a radical departure from this in the short term assuming there's a spring 2016 BFR/MCT information release.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/06/2016 05:39 pm
Maybe it's just me but I read this as Elon saying that the BFR/MCT (now called BFS) is a 2 part entity which I interpret as that stage 2 IS the BFS.  A booster rocket (stage one with lots of engines) and a spaceship (stage 2).

It's not just you. Though still even now some people disagree.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 01/06/2016 06:52 pm
Maybe it's just me but I read this as Elon saying that the BFR/MCT (now called BFS) is a 2 part entity which I interpret as that stage 2 IS the BFS.  A booster rocket (stage one with lots of engines) and a spaceship (stage 2).

"Well, there's two parts of it—there's a booster rocket and there's a spaceship. So the booster rocket's just to get it out of Earth's gravity because Earth has quite a deep gravity well and thick atmosphere, but the spaceship can go from Mars to Earth without any booster, because Mars's gravity is weaker and the atmosphere's thinner, so it's got enough capability to get all the way back here by itself. It needs a helping hand out of Earth's gravity well. So, technically, it would be the BFR and the BFS." As in "Big frakking Spaceship."

http://www.gq.com/story/elon-musk-mars-spacex-tesla-interview?utm_source=10370

This also pretty much says that the spaceship part needs to have the delta V capability for Mars surface to Earth (debatable Earth surface or LEO, maybe either).  That means more than small couple hundred mT propellant tanks.

Whether this is the best approach or the final architecture remains to be seen but it would be surprising to see a radical departure from this in the short term assuming there's a spring 2016 BFR/MCT information release.
Well, still,

It does not say whether the BFS is monolitic or modular.
It doesn't mention LEO refuel before mars injection and we know that from previos qoutes.
It does not say 'direct mars surface to earth' only 'from Mars to Earth without any booster' , so refuel in mars orbit is also an option.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/06/2016 09:23 pm
It does not say whether the BFS is monolitic or modular.

True. I bet on modular, have argued for that for a while.

Quote
It doesn't mention LEO refuel before mars injection and we know that from previos qoutes.

LEO refuel is a given. It is a requirement, no way to reach the target performance without it. And it was mentioned. There was talk about refuelling before leaving for Mars.

Quote
It does not say 'direct mars surface to earth' only 'from Mars to Earth without any booster' , so refuel in mars orbit is also an option.

Not an option, much too complex early on. Also not required. Much smaller payload back to earth was stated. That does not need Mars orbit refuelling. Though fuel ISRU on Phobos or Deimos is one of my pet ideas. It has potential to make things a lot easier. But certainly not a requirement and not part of the initial plan.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/06/2016 09:55 pm
Point is that the only thing definitively ruled out by Musk statement as a single-stage-to-mars vehicle.  Your interpreting every statement by Musk as total confirmation of your speculation but it's far from that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 01/06/2016 10:33 pm
Maybe it's just me but I read this as Elon saying that the BFR/MCT (now called BFS) is a 2 part entity which I interpret as that stage 2 IS the BFS.  A booster rocket (stage one with lots of engines) and a spaceship (stage 2).
"Well, there's two parts of it—there's a booster rocket and there's a spaceship. but the spaceship can go from Mars to Earth without any booster, because Mars's gravity is weaker and the atmosphere's thinner, so it's got enough capability to get all the way back here by itself. It needs a helping hand out of Earth's gravity well. So, technically, it would be the BFR and the BFS." As in "Big frakking Spaceship."

While I suspect your interpretation is correct, Musk wasn't talking to us, nor answering a question about whether there's a second stage. He was being very general and non-technical.

Hence, it's still possible that the "booster rocket" is a two stage launcher.

For example, "Well, there's two parts of it - there's a booster rocket, called Falcon 9, and there's a spaceship, called Dragon. The spaceship can return from orbit on its own. The velocity for deorbiting is less, so it's got enough capability to dock with ISS, then get back to Earth by itself. It just needs a helping hand out of Earth's gravity well."

[Edit: I mean, if we're going to be pedantic, a "booster rocket" should mean it's a side-mount. Ie, BFS will fire it's engines from launch to orbit, with a large "booster" to assists while it's fuel heavy. 1.5STO.]
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/06/2016 11:43 pm
I agree that those other interpretations are not definitively ruled out, hence "Maybe it's just me..."
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/07/2016 07:54 am
Point is that the only thing definitively ruled out by Musk statement as a single-stage-to-mars vehicle.  Your interpreting every statement by Musk as total confirmation of your speculation but it's far from that.

No, it is the other way around. I base my speculations on statements by SpaceX, you don't. Your concepts may be completely valid, I don't deny that. They are in conflict with SpaceX however.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 01/07/2016 05:04 pm
Point is that the only thing definitively ruled out by Musk statement as a single-stage-to-mars vehicle.  Your interpreting every statement by Musk as total confirmation of your speculation but it's far from that.

No, it is the other way around. I base my speculations on statements by SpaceX, you don't. Your concepts may be completely valid, I don't deny that. They are in conflict with SpaceX however.

Sorry guckyfan, ISTM that you take even the slightest off-the-cuff statements and hyperbolic tweets that Musk makes as always being absolute literal truth, with no margin for error. IMO you take some things far too literally and as absolutisms.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/07/2016 05:15 pm
Point is that the only thing definitively ruled out by Musk statement as a single-stage-to-mars vehicle.  Your interpreting every statement by Musk as total confirmation of your speculation but it's far from that.

No, it is the other way around. I base my speculations on statements by SpaceX, you don't. Your concepts may be completely valid, I don't deny that. They are in conflict with SpaceX however.

Sorry guckyfan, ISTM that you take even the slightest off-the-cuff statements and hyperbolic tweets that Musk makes as always being absolute literal truth, with no margin for error. IMO you take some things far too literally and as absolutisms.

You either A) take him and the folks at SpaceX by their word(s), or B) you do mental gymnastics to warp them to fit your own predetermined architecture. The sensible thing in this thread - based on its name - is to be closer to option A. If you prefer option B, there are other Mars related forums on this site.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 01/07/2016 10:17 pm
This is my idea of MCT, focusing on survival on all critical parts of Mars Journey, since there will multiple MCT on the way and they will not probably use 100 people before base is build and they could help each others.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/08/2016 06:12 pm
How does the MCT escape module land on Mars w/o killing everyone as it slams into the regolith?  Chutes ain't gonna git 'er done there.
Just make your upper stage like an airliner, either it gets there or you have no more worries at tax time, ever.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 01/08/2016 07:44 pm
MCT Escape system will have enough power to leave booster/MCT Engine and slow down using atmosphere and land using rocket engines.
On Earth more aerobraking
On Mars fight less gravity
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stardhingy on 01/08/2016 09:03 pm
How does the MCT escape module land on Mars w/o killing everyone as it slams into the regolith?  Chutes ain't gonna git 'er done there.
Just make your upper stage like an airliner, either it gets there or you have no more worries at tax time, ever.

That's my opinion as well. Build it stout. No matter how many Russian dolls of escape pods you have, the last one includes passengers and rocket fuel, if it lights up everyone dies.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/08/2016 11:34 pm
How does the MCT escape module land on Mars w/o killing everyone as it slams into the regolith?  Chutes ain't gonna git 'er done there....
...they will if you add a retro-rocket to them, like this:
https://www.youtube.com/watch?v=4uGfOppQD_g
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 01/09/2016 03:30 am

and you land on a prepared surface.
Robotbeat, you have mentioned this 'prepared surface' in several posts. How this would be accomplished?

NASA has some ideas so maybe SpaceX will get some advice from from them.

http://www.nasa.gov/content/landing-pads-being-designed-for-extraterrestrial-missions

Exactly, Dr. Phil is the guy I was thinking of.

Here's some quotes from the article:

"Robotic landers would go to a location on Mars and excavate a site, clearing rocks, leveling and grading an area and then stabilizing the regolith to withstand impact forces of the rocket plume," Mueller said. "Another option is to excavate down to bedrock to give a firm foundation. Fabric or other geo-textile material could also be used to stabilize the soil and ensure there is a good landing site."

...
""We've tested several types of materials and it seems that basalt regolith mixed with polymer binders hold up well," Metzger said."

Sulfer concrete might be a good solution too.

http://www.citylab.com/tech/2016/01/mars-build-house-concrete-sulfur-study/423288/?utm_source=yahoo

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Patchouli on 01/13/2016 12:49 am

Sulfer concrete might be a good solution too.

http://www.citylab.com/tech/2016/01/mars-build-house-concrete-sulfur-study/423288/?utm_source=yahoo



I wonder if it could be used for monolithic domes?
https://en.wikipedia.org/wiki/Monolithic_dome
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/13/2016 08:09 am
I wonder if it could be used for monolithic domes?
https://en.wikipedia.org/wiki/Monolithic_dome

We have extensive discussion of these things in the general Mars section. I suggest we keep it there and keep this thread closer to MCT. Sulphur concrete was not discussed there yet, I believe, but discussion should be there.

Just a short note, It has higher tensile strength than concrete and should enable domes to some extent. People tend to forget that tensile strength is what is required to build pressurized domes. Not so much compressive strength.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 01/13/2016 04:23 pm
...they will if you add a retro-rocket to them, like this...

That chute will help some after the heat shield reaches terminal velocity, but in an atmosphere that's 0.0059 X the density of Earth's atmosphere at the surface, you're still going to have a lot more velocity to overcome with retrorockets than that pallet has. Your gravity losses will be less, but you still have the inertia to kill off.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/13/2016 05:05 pm
How does the MCT escape module land on Mars w/o killing everyone as it slams into the regolith?  Chutes ain't gonna git 'er done there....
...they will if you add a retro-rocket to them, like this:
https://www.youtube.com/watch?v=4uGfOppQD_g

They're used every crew mission to the ISS, on the Soyuz lander.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 01/13/2016 05:18 pm
This is my idea of MCT, focusing on survival on all critical parts of Mars Journey, since there will multiple MCT on the way and they will not probably use 100 people before base is build and they could help each others.
That reminds me of the idea which was to fly a F9 reusable 2nd stage together with a dragon 2 as one spaceship.
How does the crew transfer between the escape pod and the hab module through the heat shield?
Is the heat shield necessary for an aerobreak?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 01/13/2016 06:02 pm
This is my idea of MCT, focusing on survival on all critical parts of Mars Journey, since there will multiple MCT on the way and they will not probably use 100 people before base is build and they could help each others.
That reminds me of the idea which was to fly a F9 reusable 2nd stage together with a dragon 2 as one spaceship.
How does the crew transfer between the escape pod and the hab module through the heat shield?
Is the heat shield necessary for an aerobreak?

Gemini-B would have had a hatch in the heat shield.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/13/2016 09:05 pm
...they will if you add a retro-rocket to them, like this...

That chute will help some after the heat shield reaches terminal velocity, but in an atmosphere that's 0.0059 X the density of Earth's atmosphere at the surface, you're still going to have a lot more velocity to overcome with retrorockets than that pallet has. Your gravity losses will be less, but you still have the inertia to kill off.
Smaller objects have lower terminal velocity and can reach terminal velocity quick enough. And yeah, you need more rocket impulse, but rockets scale well, as long as you're below like 100m/s.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/14/2016 02:53 am
I would ask that you guys focus for a bit on a problem that's been nagging me: the physical arrangement of mass on an MCT, versus the entry method.   During reentry and descent, the vehicle is going to shuttlecock - the center of mass will end up being in front of the rest of the vehicle.  During launches, shuttlecocking may or may not be an important element of stability, but much less so than during hypersonic entry.  Mass may be shifted around to control orientation, but it's going to need to be a *lot* of mass, and whatever faces forward needs heatshielding.  You can't heatshield engines.

The vehicle may have gliding entry, or may not.  Gliding entry is certainly not as useful during aerocapture.

The biggest deal is getting the engines pointed towards the ground in a retroburn, on the same vehicle that does the aerocapture and entry, without throwing anything away... when the center of mass was supposed to be on the other end of the vehicle.

And then there's the implicit assymmetries: full tanks will dominate mass considerations, but empty ones will shift mass to one end or the other.  Cargo unloading or Matryoshka-staging a subvehicle will drastically change center of mass.  The vehicle has to work in both orientations.

Where does that leave cargo & crew unloading?

I think this might end up being a greater concern than "But then the astronauts would be up in the sky!";  Ladders and lifts are trivial hacks relative to this issue.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 01/14/2016 03:22 am
Can it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/14/2016 03:43 am
Can it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...

If it was feasible to do so, why did we ever invent ablative heatshields?  Rocket engines deal with heat either ablatively or with regenerative cooling - heating up the propellant - in which case you need to expend the propellant steadily.

The guidance from the SSTO guys is that for Mars, direct retro burns basically overwhelm any drag benefit of the rest of the spacecraft;  You're left with a mass-intensive propulsive descent, as if Mars had no atmosphere.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/14/2016 05:37 am
My earlier thoughts had been towards a vehicle with cargo in the bottom, tanks above and heat-shields on the nose of an overall conical/bi-conical vehicle.  The entry is nose first with a a considerable lift component, the vehicle is stabilized by flaps at it's base that extend out mechanically, these create a lot of drag and move the center of drag to the read behind the center of mass and allow the vehicle to be steered and adjust to atmospheric conditions without moving mass internally.  After decelerating to under 1 km/s the vehicle flips from horizontal to vertical and lands on retro-rockets.

But I've begun to favor a far large umbrella of carbon-fiber fabric, a concept called ADEPT.  The vehicle would have a similar internal arrangement but the shell opens to become the center of the heat shield and the umbrella which is stowed underneath opens to a huge area for entry in a traditional 70 degree cone, adjusting the arm of the umbrella would give an off sent mass and a lift vector adjustable in real-time during entry.  The vehicle would again make a turn at a lower speed and would retain the umbrella in an open position but inverted so that it becomes an upward cone, some additional decent with deceleration purely from drag would occur and then finally rocket landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RanulfC on 01/14/2016 05:40 pm
Can it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...

If it was feasible to do so, why did we ever invent ablative heatshields?  Rocket engines deal with heat either ablatively or with regenerative cooling - heating up the propellant - in which case you need to expend the propellant steadily.

The guidance from the SSTO guys is that for Mars, direct retro burns basically overwhelm any drag benefit of the rest of the spacecraft;  You're left with a mass-intensive propulsive descent, as if Mars had no atmosphere.

That's because the exhaust creates a virtual "aerospike" which reduces the drag on the vehicle, but has nothing to do with the question. He didn't ask about using the engines but if they could stand the reentry temperatures and therefore have an "engines-forward" entry.

Engineers working on the SERV concept originally estimated that they would need TPS doors to cover the engine nozzles during reentry but subsequent testing showed that especially in SERVs case the overall base diameter was sufficient to reduce the heating load so that no TPS doors or special insulation was required. That's Earth though and Mars is a bit different but you should be able to, if the base is wide enough, to enter engines first as long as they are designed properly and integrated into the base of the vehicle. At worst you can probably cold-flow some propellant through the engine system during the period of highest heating, dumping it through the nozzle and overboard.

The benefit is once you're down far enough you only have to add in the other propellant to the engine and ignite it for the powered landing.

Randy
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 01/14/2016 06:05 pm
Randy, Speaking of the SSTO designs of the past, has it occured to anyone that the current design for the Dragon V2 could easily be the same basic design, externally, for the MCT?

    If SpaceX were to use a asymetrical aerospike system for each of the quads, the design would be very similar to many of teh SSTO designs of the 1960's and 70's.  I meantion this idea as what most people know is that exhaust effeciency at various altitudes changes as you get higher, resulting in teh need for a radically different exhaust bell than you'd have at sea level.  (Part of the reason we stage rockets).

     Aerospikes don't suffer this issue and asymetric aerospikes, using mostly Raptor components, should prove most effecient for Landings on both earth and Mars and launches from Mars.
     From what I've heard, it seems that the Raptor engines are primarily for the BFR first stage, while the same plumbing could be used for the MCT.  This should also give the advantage of less debris being kicked up under the MCT, as the exhaust would be spread and off to the sides, rather than concentrated underneith the craft, and having to make holes in the TPS.

     Making holes in the TPS adds mass for the hing and closing systems, (which would also have to be shielded against teh exhaust of engines cutting through the TPS) plus it complicates the landing sequence more than needed.

     I have further thoughts on the MCT design that I'll post later.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RanulfC on 01/14/2016 07:33 pm
Randy, Speaking of the SSTO designs of the past, has it occured to anyone that the current design for the Dragon V2 could easily be the same basic design, externally, for the MCT?

Probably, and probably quite often as well but not mentioned because calling something (or comparing it to, as well) "SSTO" carries a lot of baggage that can and often does get in the way :)

I've seen numerous "guesstimates" of the MCT/BFR design that basically simply scale up the Dragon V2 because it's a known design. (And it's easier to play-with-paint if someone else has made a picture of the design anyway :) )

Quote
    If SpaceX were to use a asymetrical aerospike system for each of the quads, the design would be very similar to many of the SSTO designs of the 1960's and 70's.  I meantion this idea as what most people know is that exhaust effeciency at various altitudes changes as you get higher, resulting in the need for a radically different exhaust bell than you'd have at sea level.  (Part of the reason we stage rockets).

     Aerospikes don't suffer this issue and asymetric aerospikes, using mostly Raptor components, should prove most effecient for Landings on both earth and Mars and launches from Mars.

Well I have to say that one of the first things "I" thought of when we began speculating on the design of the BFR and MCT was the German "BETA" SSTO design and variations thereof. But while true on Earth it's not as important on Mars and landing an MCT on Earth after a mission it's probably even less important. The cosign losses might overwhelm any benefit. On the other hand part of the draw of an aerospike type engine, (specifically any "plug" variety thereof) is an ability to use the "engine" as part of the heat-shield so you don't have two separate systems (and the mass that entails) on the vehicle. You get more advantage with locating the "plug" nearer the center of the heat shield than at the edges.

Still... You can actually use pretty much any engine as the basis of an aerospike or plug nozzle engine as the combustion chamber is the main component with most of the support systems (turbopumps, plumbing, controls, etc) as common parts. Hence we've had designs for J2, RL10, Atlas booster and sustainer, and even F1 engines as the basis for such engines.

Quote
     From what I've heard, it seems that the Raptor engines are primarily for the BFR first stage, while the same plumbing could be used for the MCT.  This should also give the advantage of less debris being kicked up under the MCT, as the exhaust would be spread and off to the sides, rather than concentrated underneith the craft, and having to make holes in the TPS.

     Making holes in the TPS adds mass for the hing and closing systems, (which would also have to be shielded against teh exhaust of engines cutting through the TPS) plus it complicates the landing sequence more than needed.

Actually my point was that the holes in the TPS weren't found to be that much of a problem and no doors were needed. The debris thing could go either way as I've seen comments on arrangements like the Dragon V2 SDs actually kicking debris farther and the more concentrated "blast" actually being easer to adjust for.

Quote
     I have further thoughts on the MCT design that I'll post later.

It's been like 10 minutes already, aren't you done yet? ;)

One of the things that comes to mind when you mentioned this as I noted was some of the work on the BETA SSTO and there was a "more-near-term" version that was actually an "assisted" SSTO using a zero-stage with engines such as you are talking about. However it wrapped a duct around the engines and created a air-augmented rocket system that boosted the thrust and ISP from zero to around Mach-2 where the augmentation dropped off till staging at around Mach-4/6. The augmentation more than covered the mass of the ducts and the ducting helped with landing the stage back at base as well. Of course at this point it begins to look like nothing we've been discussing :)

Randy
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/14/2016 11:52 pm
Can it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...

If it was feasible to do so, why did we ever invent ablative heatshields?  Rocket engines deal with heat either ablatively or with regenerative cooling - heating up the propellant - in which case you need to expend the propellant steadily.

The guidance from the SSTO guys is that for Mars, direct retro burns basically overwhelm any drag benefit of the rest of the spacecraft;  You're left with a mass-intensive propulsive descent, as if Mars had no atmosphere.

That's because the exhaust creates a virtual "aerospike" which reduces the drag on the vehicle, but has nothing to do with the question. He didn't ask about using the engines but if they could stand the reentry temperatures and therefore have an "engines-forward" entry.
I'm pointing out that the cooling mechanism on a regeneratively cooled engine, the thing that keeps it from melting during normal operation, is cold propellant flowing through it rapidly on the way to combustion.  You can't do that without having the engine turned on.  Having the engines directly in the flow poses perhaps the worst aerothermodynamic problem: a parachute-shaped facing surface with sharp frontal edges.
Quote
Engineers working on the SERV concept originally estimated that they would need TPS doors to cover the engine nozzles during reentry but subsequent testing showed that especially in SERVs case the overall base diameter was sufficient to reduce the heating load so that no TPS doors or special insulation was required. That's Earth though and Mars is a bit different but you should be able to, if the base is wide enough, to enter engines first as long as they are designed properly and integrated into the base of the vehicle. At worst you can probably cold-flow some propellant through the engine system during the period of highest heating, dumping it through the nozzle and overboard.

The benefit is once you're down far enough you only have to add in the other propellant to the engine and ignite it for the powered landing.

Randy

You're talking about engines arrayed in a ring around the edge of a large blunt heatshield, whose bow shockwave separation shields them.  These engines would have to have small bell nozzles (lower Isp), be tightly spaced, and have a limited thrust versus a vehicle with record-setting mass per cross-sectional area.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 01/15/2016 03:35 am
Can it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...

If it was feasible to do so, why did we ever invent ablative heatshields?

Well, a small dense capsule is a rather different case from a huge low-density rocket stage. And early reentry vehicles didn't have large rocket engines to use, either.


Quote
Rocket engines deal with heat either ablatively or with regenerative cooling

Radiative cooling also exists. It seems to be mostly nozzles, which suggests it's fairly limited. The question is how the heat flux on the rocket nozzle for a Mars entry compares to the heat flux in use.

Quote
- heating up the propellant - in which case you need to expend the propellant steadily.

How much propellant does it take if you are only cooling and not caring about thrust? Does film cooling change that?

I don't know the answers to any of these questions...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 01/15/2016 06:13 am
Can it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...

If it was feasible to do so, why did we ever invent ablative heatshields?  Rocket engines deal with heat either ablatively or with regenerative cooling - heating up the propellant - in which case you need to expend the propellant steadily.

The guidance from the SSTO guys is that for Mars, direct retro burns basically overwhelm any drag benefit of the rest of the spacecraft;  You're left with a mass-intensive propulsive descent, as if Mars had no atmosphere.

That's because the exhaust creates a virtual "aerospike" which reduces the drag on the vehicle, but has nothing to do with the question. He didn't ask about using the engines but if they could stand the reentry temperatures and therefore have an "engines-forward" entry.
I'm pointing out that the cooling mechanism on a regeneratively cooled engine, the thing that keeps it from melting during normal operation, is cold propellant flowing through it rapidly on the way to combustion.  You can't do that without having the engine turned on.  Having the engines directly in the flow poses perhaps the worst aerothermodynamic problem: a parachute-shaped facing surface with sharp frontal edges.

I know it's probably been mentioned many, many times now but it's something which SpaceX have already accomplished, several times now?

https://www.nasa.gov/press/2014/october/new-commercial-rocket-descent-data-may-help-nasa-with-future-mars-landings/
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/15/2016 07:21 am
Can it really not do Mars entry engines first? Rocket engines already deal with pretty intense heat...

If it was feasible to do so, why did we ever invent ablative heatshields?  Rocket engines deal with heat either ablatively or with regenerative cooling - heating up the propellant - in which case you need to expend the propellant steadily.

The guidance from the SSTO guys is that for Mars, direct retro burns basically overwhelm any drag benefit of the rest of the spacecraft;  You're left with a mass-intensive propulsive descent, as if Mars had no atmosphere.

That's because the exhaust creates a virtual "aerospike" which reduces the drag on the vehicle, but has nothing to do with the question. He didn't ask about using the engines but if they could stand the reentry temperatures and therefore have an "engines-forward" entry.
I'm pointing out that the cooling mechanism on a regeneratively cooled engine, the thing that keeps it from melting during normal operation, is cold propellant flowing through it rapidly on the way to combustion.  You can't do that without having the engine turned on.  Having the engines directly in the flow poses perhaps the worst aerothermodynamic problem: a parachute-shaped facing surface with sharp frontal edges.

I know it's probably been mentioned many, many times now but it's something which SpaceX have already accomplished, several times now?

https://www.nasa.gov/press/2014/october/new-commercial-rocket-descent-data-may-help-nasa-with-future-mars-landings/
No, SpaceX have been sidestepping reentry heating by starting off slow (I'd guess ~2-4km/s at separation instead of ~8km/s from LEO to ~12-14km/s Mars-Earth Transfer) and then spending reentry reducing speed propulsively behind the exhaust plume down to some velocity at which heating is not an issue.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Falcon H on 01/15/2016 02:53 pm
This is my idea of MCT, focusing on survival on all critical parts of Mars Journey, since there will multiple MCT on the way and they will not probably use 100 people before base is build and they could help each others.
That reminds me of the idea which was to fly a F9 reusable 2nd stage together with a dragon 2 as one spaceship.
How does the crew transfer between the escape pod and the hab module through the heat shield?
Is the heat shield necessary for an aerobreak?

Gemini-B would have had a hatch in the heat shield.
The Space Shuttle also had hatches in it's heat shield for landing gear, I believe. Since the Space Shuttle has flown 133 successful times, I think heat shields like this are very well proven.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 01/15/2016 03:18 pm
I'm a bit confused guys...

     When did SpaceX say that the MCT was going to be two sections, a main ship and an escape module?

     While, on the surface, this may seem like a good idea, the extra mass of a second heat shield would add tons of mass that likely wouldn't really be needed, as the MCT itself IS its' own escape craft.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/15/2016 03:47 pm
I'm a bit confused guys...
When did SpaceX say that the MCT was going to be two sections, a main ship and an escape module?

You are right, they have not said so.

However, there is a vast number of people who can't conceive of a crewed spacecraft without an abort module, so they believe it must be so.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/15/2016 05:42 pm
In my preferred architecture, the tip is not a launch abort precisely, but an Earth return capsule, a barebones backup MAV (which rendevous' with an LMO lifeboat), and maybe other things depending on configuration.  It may also serve as an independent crew launch vehicle to bring crew up to an unmanned MCT;  I'm not finished investigating which mission options are compatible with this, but there are enough of them that it makes a lot of sense to assume a nested capsule up there.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/15/2016 09:51 pm
An abort system would have a very limited advantage on Mars descent, ascent and earth reentry. I don't believe they would carry such a system all the way to Mars and back. If it is seen necessary on earth ascent, which I don't, then they would build a separate crew ascent vehicle that can cram 100 people in and get them to safety if necessary. Any excess lifting capability could go to a final top off for MCT.

It would be a lot less useless mass on the way to Mars and back.  So probably not even an additional launch because less fuel is needed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/16/2016 04:10 am
If you were to have an abort system on MCT, it'd have to work for Mars ascent (as well as Earth), and probably even terminal landing as well. No, this is not impossible. Hard, but not impossible.

Or just not have an abort system.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/16/2016 06:54 am
On the issue of an abort capsule I agree with guckyfan and Robotbeat, it is impractical and offers very little use at Mars while on Earth a whole vehicle abort is more practical.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/16/2016 09:43 am
If you were to have an abort system on MCT, it'd have to work for Mars ascent (as well as Earth), and probably even terminal landing as well. No, this is not impossible. Hard, but not impossible.

Or just not have an abort system.

Possible, no doubt. But with a massive payload penalty. Worst case payload back to earth would approach zero, meaning no return for humans.

I believe it will be engine out capability, high reliability and very, very low risk of explosive failure.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/16/2016 01:16 pm
On the issue of an abort capsule I agree with guckyfan and Robotbeat, it is impractical and offers very little use at Mars while on Earth a whole vehicle abort is more practical.
That's not what I think. I think you can do abort on Earth AND Mars. And "whole vehicle" abort is likely not appropriate.

But you don't HAVE to have an abort capability.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/20/2016 01:21 pm
Shotwell mentioned about BFR a few months ago at the South Summit 2015 (Oct 7-9), in Madrid, " [Falcon Heavy] This one is about 4M pounds of thrust, and the mock... the vehicle that takes us to Mars will be three or four times that size"

https://youtu.be/omBF1P2VhRI?t=10m46s

(original video, mostly Spanish-language conference proceeding, but Shotwell's voice still appears beneath a title graphic for the first ten minutes, though not her face.  The video I linked above seems to have been created a while after this one was promoted, and does a proper cut to her presentation alone)

I also vaguely remember her mentioning offhand that they were developing a 180-210t to LEO superheavy launcher.  I've been trying to find the interview, but can't turn anything up.

Above Quote from the Update thread

3 to 4 times FH thrust fits well with the 12.7-14.7 million pounds thrust BFR models I've built that conform to prior SX statements. 

It contradicts the ludicrous 15m wide 300+m tall !!! behemoths posted on Reddit which would require over 400 Raptors to lift off if the posters had simply calculated the propellant volume and subsequent mass.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/20/2016 02:54 pm
Shotwell mentioned about BFR a few months ago at the South Summit 2015 (Oct 7-9), in Madrid, " [Falcon Heavy] This one is about 4M pounds of thrust, and the mock... the vehicle that takes us to Mars will be three or four times that size"

https://youtu.be/omBF1P2VhRI?t=10m46s

(original video, mostly Spanish-language conference proceeding, but Shotwell's voice still appears beneath a title graphic for the first ten minutes, though not her face.  The video I linked above seems to have been created a while after this one was promoted, and does a proper cut to her presentation alone)

I also vaguely remember her mentioning offhand that they were developing a 180-210t to LEO superheavy launcher.  I've been trying to find the interview, but can't turn anything up.

Above Quote from the Update thread

3 to 4 times FH thrust fits well with the 12.7-14.7 million pounds thrust BFR models I've built that conform to prior SX statements. 

It contradicts the ludicrous 15m wide 300+m tall !!! behemoths posted on Reddit which would require over 400 Raptors to lift off if the posters had simply calculated the propellant volume and subsequent mass.
15m wide is pretty reasonable, but the main utility of that is to prevent it from being anywhere near 300m tall.  I don't expect it to be anywhere near the fineness ratio of F9.  A cylindrical rocket doesn't have infinite room to scale up;  The base grows as n^2 while mass grows as n^3, and eventually the base's space to fit rocket motors limits further growth.  Additionally, we have raised issues with eg the launch facilities here.

I suspect you can't build it much smaller than 12m and still have realistic height.

If you try to build it larger than a number somewhere in the 15m-18m range, then you run into issues where bridges need to be rebuilt to get the parts in place, and propellant tanks lose their cylindrical character.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: gadgetmind on 01/20/2016 02:56 pm
Why not make it into a flattened disk, and get it to spin while we're at it!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/20/2016 04:24 pm

Above Quote from the Update thread

3 to 4 times FH thrust fits well with the 12.7-14.7 million pounds thrust BFR models I've built that conform to prior SX statements. 

It contradicts the ludicrous 15m wide 300+m tall !!! behemoths posted on Reddit which would require over 400 Raptors to lift off if the posters had simply calculated the propellant volume and subsequent mass.
15m wide is pretty reasonable, but the main utility of that is to prevent it from being anywhere near 300m tall.  I don't expect it to be anywhere near the fineness ratio of F9.  A cylindrical rocket doesn't have infinite room to scale up;  The base grows as n^2 while mass grows as n^3, and eventually the base's space to fit rocket motors limits further growth.  Additionally, we have raised issues with eg the launch facilities here.

I suspect you can't build it much smaller than 12m and still have realistic height.

If you try to build it larger than a number somewhere in the 15m-18m range, then you run into issues where bridges need to be rebuilt to get the parts in place, and propellant tanks lose their cylindrical character.

Yes.  I start my models at 12.5m minimum (fit the engines) but believe they'll go for 15m but no larger, for reasons like future growth in # of engines.  I believe that the 15m "airframe" will be fabricated on-site as 15 is too large for ground transport on public roads and will also have problems on waterways with bridges.  The BFR will blow out steam singing, "I'm a little teapot, short and stout!"  Well under 100m tall with the MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/21/2016 12:57 am
~30 engines (+/-50%) sounds about right to me. Around the same as Falcon Heavy, but in a single core (which makes engine-out management a little simpler).

15m, too.


...by the way, we can know for a fact that if it's only 15m in diameter, it is going to be limited to around, say, 50 engines of about 500klbf each if they are squished together as close as they can go and have an exit pressure of around near sea level and a nice high chamber pressure of about 2000-3000psi. You cannot physically fit in more engines. For a lift-off T/W of 1.1 or more, that puts a hard upper bound of around 10,000 tons. So if 15m is the diameter (it probably is), then the lift-off mass cannot be more than 10,000 tons. And that leaves ZERO room for gimballing.

A more sane packing arrangement would leave them at around 6000 tons or less.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/21/2016 02:35 am
With ~30 engines you probably don't need gimbaling, or at least not on most of the engines.  Some variable thrust and a few engines along the edge that gimbal on just one axis should be sufficient and is the Russian way of doing it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/21/2016 04:08 am
With ~30 engines you probably don't need gimbaling, or at least not on most of the engines.  Some variable thrust and a few engines along the edge that gimbal on just one axis should be sufficient and is the Russian way of doing it.

That worked sooo great for the N1. :) I know that was failure of testing, but using variable thrust for control is a truly *terrible* idea. That's when you need more power, not less of it.

A few central engines may be fixed, but most should fully gimbal for general control authority and engine out capability. Having all the engines be identical (including their gimbal setups) also simplifies mass production and testing procedures, as SpaceX illustrate whenever their F9 rocket launches.

(it seems to be a VERY common misconception that some F9 engines are fixed, they are NOT)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/21/2016 04:34 am
With ~30 engines you probably don't need gimbaling, or at least not on most of the engines.  Some variable thrust and a few engines along the edge that gimbal on just one axis should be sufficient and is the Russian way of doing it.

That worked sooo great for the N1. :) I know that was failure of testing, but using variable thrust for control is a truly *terrible* idea. That's when you need more power, not less of it.

A few central engines may be fixed, but most should fully gimbal for general control authority and engine out capability. Having all the engines be identical (including their gimbal setups) also simplifies mass production and testing procedures, as SpaceX illustrate whenever their F9 rocket launches.

(it seems to be a VERY common misconception that some F9 engines are fixed, they are NOT)

Variable thrust on a big fat rocket like this is going to have fairly high control authority (unlike the high-fineness-ratio F9), so something like 'Right side -2% thrust" is enough.  Also, outward or inward-canted steering motors could be used for even greater effect, or the entire main engine bank could be inward-canted by a few degrees.

I don't think it's something to rule out either on first principles, or on the back of the N1 experience, a rushed-to-launchpad program using primitive computerization that decided to work out its kinks in live tests, but was deprived of funding and leadership before finishing its work.

With that said, I don't have any good reason to think non-gimballing engines are going to be a thing on BFR.  With MCT, on the other hand, there may be value in fixing the combustion chambers as well as the massive engine bells rigidly to the spacecraft;  Those gimbals are a source of potential failure with a few years of vacuum between uses, and whether the odds of that are greater than the odds of some other steering system failing, is a bit more of an open question than with BFR.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/21/2016 05:09 am
With that said, I don't have any good reason to think non-gimballing engines are going to be a thing on BFR.  With MCT, on the other hand, there may be value in fixing the combustion chambers as well as the massive engine bells rigidly to the spacecraft;  Those gimbals are a source of potential failure with a few years of vacuum between uses, and whether the odds of that are greater than the odds of some other steering system failing, is a bit more of an open question than with BFR.

I strongly disagree with that. I consider fixed engines more likely on a BFR booster than a MCT. First, the fewer engines you have, the more critical it is that they all gimbal. Otherwise you really have no engine out capability at all, a *long* way from home. Yes, your gimbal actuators need to be VERY reliable, but I think they need to be there to provider multiple levels of redundancy.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/21/2016 03:14 pm
~30 engines (+/-50%) sounds about right to me. Around the same as Falcon Heavy, but in a single core (which makes engine-out management a little simpler).

15m, too.


...by the way, we can know for a fact that if it's only 15m in diameter, it is going to be limited to around, say, 50 engines of about 500klbf each if they are squished together as close as they can go and have an exit pressure of around near sea level and a nice high chamber pressure of about 2000-3000psi. You cannot physically fit in more engines. For a lift-off T/W of 1.1 or more, that puts a hard upper bound of around 10,000 tons. So if 15m is the diameter (it probably is), then the lift-off mass cannot be more than 10,000 tons. And that leaves ZERO room for gimballing.

A more sane packing arrangement would leave them at around 6000 tons or less.

I believe that they're aiming for a decent T/W, certainly far higher than 1.1.  The old slow liftoff F9 had 1.19 I believe with the current F9 Full Thrust model considerably higher.  The issue is minimizing gravity losses.  I'm estimating they're going for 1.25 or better with the BFR.

One nice thing about 25-30 something engines at decent T/W is that one millisecond after Launch OK Release is that an engine can fail, well at least not catastrophically, and the mission continue.  I believe even the F9 with it's new higher T/W can lose an engine right away and complete most missions.

15 meter diameter initial design point allows for architectural growth with easy propellant tank elongation and future room to add engines beyond an initial 25-30.  Launch support towers don't need to be skyscrapers keeping launch operations simpler and more cost effective.

I'd estimate around 5,000 metric tons GLOW.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Arb on 01/21/2016 04:01 pm
Re the gimbal / variable-thrust steering discussion for the BFR (booster, not MCT). Given ~30 Raptors what would be the approximate weight saving of variable-thrust?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 01/21/2016 04:07 pm
I still think the BFR/MCT diameter will not exceed 10m.  There are many reasons for this.  I also think this version would be more economical in the long run.  A 3 core heavy for MCT launch.  Say 5.5m-8m for a single core for launching deep space probes, filling a fuel depot and other cash making activities.  The single core would be able to launch 80-100 tons.  A 3 core heavy version 250 tons.  A fully reusable 80 ton launcher might eliminate Falcon Heavy.  Say it had 9 engines at 550k lbs thrust or slightly more for a 5 million lb thrust reusable rocket.  This rocket can put up a lot of stuff to make money from the Air Force, NASA or others to help pay for MCT.  A single core could also be adapted to have two Falcon 9 cores attached for boosting slightly over 100 tons to LEO and could still launch from the cape.   

This size also would greatly expand locations for manufacturing and shipping via cheap barge and launch locations.  Otherwise if too wide it would have to be built at a shipyard and transported via ocean to various launch locations.  River and intercoastal barge widths in America are 36', or 10m maybe 11m.

This may make MCT cylindrical which might mean horizontal landing.  A try at using the vacuum Raptor in a reusable upper stage would be a good test for MCT cylinder design. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/21/2016 04:18 pm
Re the gimbal / variable-thrust steering discussion for the BFR (booster, not MCT). Given ~30 Raptors what would be the approximate weight saving of variable-thrust?

Not much, really. And the loss of performance would be severe. You are launching something massing on the order of thousands of tonnes, and the only way you can turn is to throttle down a lot of your engines!?!  :D That won't fly.

Steering by differential thrust is a *terrible* idea. It has always been, it will always be.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RoboGoofers on 01/21/2016 05:20 pm
If you were to have an abort system on MCT, it'd have to work for Mars ascent (as well as Earth), and probably even terminal landing as well. No, this is not impossible. Hard, but not impossible.

Or just not have an abort system.

"Work" would be subjective. ejecting and landing on mars with no supplies would leave you just as dead.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 01/21/2016 05:35 pm
I still think the BFR/MCT diameter will not exceed 10m.  There are many reasons for this.  I also think this version would be more economical in the long run.  A 3 core heavy for MCT launch.  Say 5.5m-8m for a single core for launching deep space probes, filling a fuel depot and other cash making activities.  The single core would be able to launch 80-100 tons.  A 3 core heavy version 250 tons.  A fully reusable 80 ton launcher might eliminate Falcon Heavy.  Say it had 9 engines at 550k lbs thrust or slightly more for a 5 million lb thrust reusable rocket.  This rocket can put up a lot of stuff to make money from the Air Force, NASA or others to help pay for MCT.  A single core could also be adapted to have two Falcon 9 cores attached for boosting slightly over 100 tons to LEO and could still launch from the cape.   


I buy these reasons, but a 3 core isn't what they're going for, and they've explicitly mentioned the core size .

We should work around what they're actually doing, or we have a 100% likelihood of being wrong.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/21/2016 07:26 pm
Attached are my latest BFR spreadsheet models. 

I have 2 core sizes, 12.5m and 15m.  I believe 15m will be the design center for SX because it allows growth.  All are TSTO with the MCT as stage 2. I have modeled various MCTs; all carry 100mT of cargo.  The different user selectable MCT masses simply mean different dry weight assumptions for the MCT.  From 25-30 Raptor engines.  You can vary most parameters including core size to design your own.

Most #s are citations from SX with others extrapolations based on F9 parameters.  Sources are below the main spreadsheet.

The BFR/MCT will likely be a stout vehicle under 100m height.
No pencil necked geek F9, but "I'm a little (sic) BFR, short & stout."
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/21/2016 07:33 pm
I still think the BFR/MCT diameter will not exceed 10m.  There are many reasons for this.  I also think this version would be more economical in the long run.  A 3 core heavy for MCT launch.  Say 5.5m-8m for a single core for launching deep space probes, filling a fuel depot and other cash making activities.  The single core would be able to launch 80-100 tons.  A 3 core heavy version 250 tons.  A fully reusable 80 ton launcher might eliminate Falcon Heavy.  Say it had 9 engines at 550k lbs thrust or slightly more for a 5 million lb thrust reusable rocket.  This rocket can put up a lot of stuff to make money from the Air Force, NASA or others to help pay for MCT.  A single core could also be adapted to have two Falcon 9 cores attached for boosting slightly over 100 tons to LEO and could still launch from the cape.   

This size also would greatly expand locations for manufacturing and shipping via cheap barge and launch locations.  Otherwise if too wide it would have to be built at a shipyard and transported via ocean to various launch locations.  River and intercoastal barge widths in America are 36', or 10m maybe 11m.

This may make MCT cylindrical which might mean horizontal landing.  A try at using the vacuum Raptor in a reusable upper stage would be a good test for MCT cylinder design.

You're absolutely right that business reasons make 3x10m a much, much easier sell than 15m.  But they have stated in the past three years that they changed their plans from the former to the latter (or at least, to "one big core").  My inferrence is either that they ran into trouble with mounting point load paths, or crossfeed was very important for their plans and that was dropped (unlikely given deep multiengine throttling & reliable restart requirements), or that they just needed the bigger fairing for the reusable Mars lander & MAV.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GregA on 01/21/2016 08:50 pm
I still think the BFR/MCT diameter will not exceed 10m.  There are many reasons for this.  I also think this version would be more economical in the long run.  A 3 core heavy for MCT launch.  Say 5.5m-8m for a single core for launching deep space probes, filling a fuel depot and other cash making activities.  The single core would be able to launch 80-100 tons.  A 3 core heavy version 250 tons.

One of the key principles of MCT design is that by designing it explicitly for Mars (not for anything else), it enables an optimisation that will make a big difference in costs.  If you're always launching for MCT, the costs of getting 3 cores ready for launch, retrieving and refurbing 3 cores is much higher than using a single more powerful core.  The only reason for doing it is to enable smaller launches, many of which the FH should be able to cover anyway.

(Before the standard replies that BFR will have to launch other payloads for whatever reasons - Yes, I suspect it will. The principle above was not to only USE the BFR for Mars, it was to DESIGN the BFR based on Mars requirements not other payloads.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/21/2016 10:32 pm
With ~30 engines you probably don't need gimbaling, or at least not on most of the engines.  Some variable thrust and a few engines along the edge that gimbal on just one axis should be sufficient and is the Russian way of doing it.

That worked sooo great for the N1. :) I know that was failure of testing, but using variable thrust for control is a truly *terrible* idea. That's when you need more power, not less of it.

A few central engines may be fixed, but most should fully gimbal for general control authority and engine out capability. Having all the engines be identical (including their gimbal setups) also simplifies mass production and testing procedures, as SpaceX illustrate whenever their F9 rocket launches.

(it seems to be a VERY common misconception that some F9 engines are fixed, they are NOT)

Lars you seem to have mentally dropped half of the proposal in your responses so that you can rail against throttling, I said gimbaled engines on the outer perimeter of the vehicle would be used and a vehicle so equipped would only need to vary thrust if these gimbaled engines are insufficient, just as ANY rocket with multiple engines can and would vary thrust beyond what it's gimbaling provides.

Your N-1 comparison is completely disingenuous by your own admission, the failure were not the result of insufficient control authority provided by fixed engines, the Russians knew this and continued to use fixed engines for decades because they are mechanically simpler.  And when engines do gimbal they generally do so on only one axis outward to provide maximum leverage again simplifying all the mechanics.  All engines being provided with 2 axis gimbaling is just an American excess not worth the cost and complexity much like Hydrogen fuel.

A 30 engine booster will have around a dozen engines on the out perimeter that can all gimbal on one axis.  Only the center engine would need 2 axis gimbaling for landing.  That leaves some ~18 engines that can be fixed and packed closer together for maximum thrust density.  This is very similar to the configuration the Soyuz uses 4 fixed nozzles and 4 small single axis vernier nozzles, and as we all know the Soyuz is the most successful Russian vehicle and one SpaceX would be wise to copy.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: KelvinZero on 01/21/2016 11:57 pm
Lars you seem to have mentally dropped half of the proposal in your responses so that you can rail against throttling, I said gimbaled engines on the outer perimeter of the vehicle would be used and a vehicle so equipped would only need to vary thrust if these gimbaled engines are insufficient, just as ANY rocket with multiple engines can and would vary thrust beyond what it's gimbaling provides.
I liked the idea of gimbaling but I have wondered about the effect of variations in thrust between different engines. They are still actually at full thrust so if variation is 1%, then if engines are gimballed fully outwards you still have sideways 'noise' in your signal equivalent to 1% full thrust, whereas a smaller downwards pointing engine would equivalently only have variation of 1% of its current thrust, and this variation almost entirely straight down in one dimension instead of sideways.

Also I imagine that balancing the thrust in the event of an engine out would be extremely difficult. Things could go sideways very rapidly ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/22/2016 12:01 am
If you were to have an abort system on MCT, it'd have to work for Mars ascent (as well as Earth), and probably even terminal landing as well. No, this is not impossible. Hard, but not impossible.

Or just not have an abort system.

"Work" would be subjective. ejecting and landing on mars with no supplies would leave you just as dead.
After a couple synods of crewed missions (assuming the number of BFSes each synod grows), there will be a sizable presence on Mars, and it would soon be cheap to have a "launch on need" BFS available (that would be used for a cargo flight back if not used for rescue during that synod, so doesn't use any resources other than space near the pad).

And an early abort would leave you close to base, within range of a rover. There's also the ability for the survivors to walk over and hook up into a group survival rebreather that would extend survivability on the surface for days (not fun, of course, but better than dead), allowing time for a rescue. Or for early flights with few passengers, even a small inflatable hab/"lifeboat" could be available.

I'm just spit-balling here. My main point is that abort modes for SpaceX's architecture are nothing like NASA's would be (where you wouldn't be able to afford the extra weight of an abort lifeboat, etc, and where there's no way you would have a launch-on-need ascent vehicle available).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/22/2016 12:12 am
With ~30 engines you probably don't need gimbaling, or at least not on most of the engines.  Some variable thrust and a few engines along the edge that gimbal on just one axis should be sufficient and is the Russian way of doing it.

That worked sooo great for the N1. :) I know that was failure of testing, but using variable thrust for control is a truly *terrible* idea. That's when you need more power, not less of it.

A few central engines may be fixed, but most should fully gimbal for general control authority and engine out capability. Having all the engines be identical (including their gimbal setups) also simplifies mass production and testing procedures, as SpaceX illustrate whenever their F9 rocket launches.

(it seems to be a VERY common misconception that some F9 engines are fixed, they are NOT)

Lars you seem to have mentally dropped half of the proposal in your responses so that you can rail against throttling, I said gimbaled engines on the outer perimeter of the vehicle would be used and a vehicle so equipped would only need to vary thrust if these gimbaled engines are insufficient, just as ANY rocket with multiple engines can and would vary thrust beyond what it's gimbaling provides.

I am not aware of ANY rocket steering with differential throttling, other than N-1. It just isn't done, because most engines don't have responsive enough throttling, nor accurate enough throttling.

Your N-1 comparison is completely disingenuous by your own admission, the failure were not the result of insufficient control authority provided by fixed engines, the Russians knew this and continued to use fixed engines for decades because they are mechanically simpler. And when engines do gimbal they generally do so on only one axis outward to provide maximum leverage again simplifying all the mechanics.  All engines being provided with 2 axis gimbaling is just an American excess not worth the cost and complexity much like Hydrogen fuel.

You are only looking at older designs from the early space age, where gimbaling was not developed for larger engines. But Energia and Zenit used/uses two axis gimbal, Angara uses two-axis gimbal, as will all future Russian LVs.

It is not an "American excess", it is common sense, especially if you want to have engine out capability.

A 30 engine booster will have around a dozen engines on the out perimeter that can all gimbal on one axis.  Only the center engine would need 2 axis gimbaling for landing.  That leaves some ~18 engines that can be fixed and packed closer together for maximum thrust density.  This is very similar to the configuration the Soyuz uses 4 fixed nozzles and 4 small single axis vernier nozzles, and as we all know the Soyuz is the most successful Russian vehicle and one SpaceX would be wise to copy.

Fixed engines with vernier nozzles was a limitation of early rocketry, not a desired outcome in itself, nor something that increased reliability. American LV's moved away from them vernier engines quickly, Russian LV's did as well too - it is just taking longer for Soyuz to be phased out due to other reasons. Falcon 9 is a clear demonstration that your line of thinking is opposite of SpaceX - and the rest of the industry.

Will all engines gimbal in a BFR? Maybe not - but those that do will use two-axis gimbal to allow the vehicle to survive engines out situations.

Edit: Added some images... First the RD-170 from Energia strap-ons (all 4 nozzles of the same engine had independent 2-axis gimbal), and Second - a picture from the SpaceX M1D production line, showing how the standard gimbal actuators look when installed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/22/2016 12:28 am
With that said, I don't have any good reason to think non-gimballing engines are going to be a thing on BFR.  With MCT, on the other hand, there may be value in fixing the combustion chambers as well as the massive engine bells rigidly to the spacecraft;  Those gimbals are a source of potential failure with a few years of vacuum between uses, and whether the odds of that are greater than the odds of some other steering system failing, is a bit more of an open question than with BFR.

I strongly disagree with that. I consider fixed engines more likely on a BFR booster than a MCT. First, the fewer engines you have, the more critical it is that they all gimbal. Otherwise you really have no engine out capability at all, a *long* way from home. Yes, your gimbal actuators need to be VERY reliable, but I think they need to be there to provider multiple levels of redundancy.

The only reason I mentioned "no gimballing" is just to say what the physical limits of 15m diameter rocket would be for lift-off weight. I definitely don't think SpaceX is going to pack the engines that close, and I don't think they'll rely on differential throttling at all. They'll gimbal the engines, because that's way more sensible and efficient.

I kind of wish I didn't bring that up. Just trying to cover the bases.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Chris Bergin on 01/22/2016 02:07 pm
Let's all use our inside voices. We're all rocket friends here.

(Really don't want to trim out long posts because one line was "OMG, OMG, O.M.G!" but we need to enforce civility here otherwise it'll quickly turn into the SDC days....and for you new people, that wasn't fun on that no-longer-around site!)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: launchwatcher on 01/22/2016 04:03 pm
"Work" would be subjective. ejecting and landing on mars with no supplies would leave you just as dead.
After a couple synods of crewed missions (assuming the number of BFSes each synod grows), there will be a sizable presence on Mars, and it would soon be cheap to have a "launch on need" BFS available (that would be used for a cargo flight back if not used for rescue during that synod, so doesn't use any resources other than space near the pad).
Another possibility would be an unmanned land-on-need BFS (or other vehicle) kept in Mars orbit with reserve supplies; after an abort you could drop it next to the survivors to give them additional supplies, shelter, and/or surface mobility.  It could also bail out the main settlement if something bad happened to their storage on the surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 01/22/2016 05:54 pm
It's been suggested before that a small number of the very first BFS's (formerly MCT) landers on Mars will not return to Earth. It shouldn't be hard to modify one or two into a point-to-point planetary hopper. It's a useful tool to have, and serves as a rescue vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/22/2016 09:07 pm
It's been suggested before that a small number of the very first BFS's (formerly MCT) landers on Mars will not return to Earth. It shouldn't be hard to modify one or two into a point-to-point planetary hopper. It's a useful tool to have, and serves as a rescue vehicle.

If they can do such hops, they can probably return to earth as well.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 01/22/2016 11:29 pm
It's been suggested before that a small number of the very first BFS's (formerly MCT) landers on Mars will not return to Earth. It shouldn't be hard to modify one or two into a point-to-point planetary hopper. It's a useful tool to have, and serves as a rescue vehicle.

If they can do such hops, they can probably return to earth as well.

Depends on the size of the hops Paul was going for, and... mathematically that doesn't seem logical. What's your reasoning, Guckyfan? Whilst I agree with you all BFSs will RTE, the margins to hop and the margins for Earth return are considerably far apart from each other.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/23/2016 08:47 am
Depends on the size of the hops Paul was going for, and... mathematically that doesn't seem logical. What's your reasoning, Guckyfan? Whilst I agree with you all BFSs will RTE, the margins to hop and the margins for Earth return are considerably far apart from each other.

My reasoning. BFS are capable of return to earth when functioning. They need to be functioning to make the hops.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 01/23/2016 09:09 am
It's been suggested before that a small number of the very first BFS's (formerly MCT) landers on Mars will not return to Earth. It shouldn't be hard to modify one or two into a point-to-point planetary hopper. It's a useful tool to have, and serves as a rescue vehicle.

If they can do such hops, they can probably return to earth as well.

Airplanes can 'hop' between continents. They cannot get in to orbit. One does not imply the other
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/23/2016 10:58 am

Depends on the size of the hops Paul was going for, and... mathematically that doesn't seem logical. What's your reasoning, Guckyfan? Whilst I agree with you all BFSs will RTE, the margins to hop and the margins for Earth return are considerably far apart from each other.

My reasoning. BFS are capable of return to earth when functioning. They need to be functioning to make the hops.

Being functioning and being supplied by an active ISRU facility is a wholly separate thing. Without propellant it doesn't matter.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/23/2016 12:47 pm

Depends on the size of the hops Paul was going for, and... mathematically that doesn't seem logical. What's your reasoning, Guckyfan? Whilst I agree with you all BFSs will RTE, the margins to hop and the margins for Earth return are considerably far apart from each other.

My reasoning. BFS are capable of return to earth when functioning. They need to be functioning to make the hops.

Being functioning and being supplied by an active ISRU facility is a wholly separate thing. Without propellant it doesn't matter.

Both return to earth and hops assume fuel ISRU in place. A safe assumption as this is the first thing to be installed. Operational according to Elon Musk before humans arrive.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 01/23/2016 01:43 pm
Or ISRU methane production is built into the early BFS's, or maybe all of them for redundancy. How large would the device  be?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/23/2016 01:57 pm
Or ISRU methane production is built into the early BFS's, or maybe all of them for redundancy. How large would the device  be?

This is one of the things we don't have a good credible estimate for. If you're harvesting water from the atmosphere, the device and its power needs get extremely large (eventually impacting mission design decisions), but if you're mining water... I'm not sure a mining layout has been defined, and what few people I have seen assuming numbers have been shots in the dark.

From a business reusability perspective, and from a safety perspective, the conservative option is for every single MCT to carry enough ISRU equipment that it can return to Earth, or at least return to LMO, after landing.  If you refrain from that you either need to hang a multiplier onto your MCT construction rate (eg send two for every one you get back, eliminating most of the point of reusability), or reuse existing landed ISRU gear to an extreme degree... with unknown wear, spare & repair characteristics.  On Earth, mining equipment starts out heavy as hell & large parts of it get beat up and replaced at a predictable rate.

An alternate safety precaution would be to land an MCT with a separating capsule tip of <2m3/person, not enough volume to live in, but enough to get to an LMO escape vehicle, that's landed with enough propellant that you could return without the habitat/lander.  This would resemble an Orion in accomodation level, and rendezvous with a hab & prop tank in orbit that returns to Earth.  It would be a reserve capacity, not usually used... although in some contingencies (like an atmospheric water-harvesting ISRU possibility that turns out to have low performance), it might be employed in a split mission capacity with the lander returning the following synod.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 01/23/2016 01:59 pm
All the more reason for FH precursor missions. Wonder if he has Tesla building the drive systems for the necessary 'bots.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 03:10 pm
About a Megawatt of power is needed to produce enough propellant for a MCT in a year. 40 tons unless you hook up to base-side infrastructure. If you have nuclear, you need huge radiators (or ground infrastructure) and shielding of some kind. Solar of 1MW requires even larger deployment on the ground. Electrolysis and Sabatier are a little smaller but still substantial.

It simply isn't a good idea to keep it on the MCTs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: llanitedave on 01/23/2016 03:47 pm
About a Megawatt of power is needed to produce enough propellant for a MCT in a year. 40 tons unless you hook up to base-side infrastructure. If you have nuclear, you need huge radiators (or ground infrastructure) and shielding of some kind. Solar of 1MW requires even larger deployment on the ground. Electrolysis and Sabatier are a little smaller but still substantial.

It simply isn't a good idea to keep it on the MCTs.


Yeah, that's the kind of equipment that's going to require multiple launches, be assembled on Mars, and then be able to operate during periods when no one is there to maintain it.  That's one reason why I expect that the first several BFS's are not going to return to Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/23/2016 04:07 pm

Or ISRU methane production is built into the early BFS's, or maybe all of them for redundancy. How large would the device  be?

Bingo. There will be a lot of cargo MCTs to develop a colony, very few will likely carry ISRU equipment.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 01/23/2016 04:20 pm
It's been suggested before that a small number of the very first BFS's (formerly MCT) landers on Mars will not return to Earth. It shouldn't be hard to modify one or two into a point-to-point planetary hopper. It's a useful tool to have, and serves as a rescue vehicle.

I don't get why using a huge interplanetary spacecraft for a rescue vehicle makes sense. All you want to do is get the people back to the base. A special purpose hopper could be way more efficient if built for this purpose. Of course, parts off MCT's or even Red Dragons could be useful.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 05:11 pm
The concept of "hoppers" for Mars is not really practical the way many people are throwing it around here. IF you expect the hopper to go point to point on Mars and return to the origin point without refuelling the range of a hopper that has enough ΔV to make it to low Mars orbit is less than 200km. The same hopper could go nearly 1000km if it can refuel at its destination, but that is not useful for exploration because you can't just go anywhere. For serious exploration by rocket powered craft what is needed is a craft that can descend from orbit fully fuelled to any location on Mars and, after landing have enough fuel to make it back to orbit.  If that can be achieved then there is a point to using that sort of craft to travel on Mars, otherwise the limitations on such craft is such that wheeled vehicles will be far more practical. Even so to make it work you would need fuel depots in Mars orbit.

A fully fuelled MCT (ΔV = 7.5km/s) on the surface of Mars could make a one way trip to any point on Mars most likely, but a two way trip would be limited to something around 700km.

Note MCT left at Mars for their use at Mars would make excellent support craft for a Mars Orbital Station/Depot and if a few dedicated smaller craft optimized for orbit-surface-orbit on a single load of propellant existed that depot could support exploration of any point on Mars surface, however every kilo of propellant used in that endeavour would represent 3 - 4 kilos of ISRU propellant and at say 200t of propellant per tanker flight, you are adding engine cycles on your reusable MCT's fairly quickly.

Still as pointed out above the real limit early on will be the ISRU capacity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 05:19 pm
A launch-on-need hopper can be a one-way trip. And if it has 7km/s of delta-V, it can go anywhere on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 05:20 pm
A launch-on-need hopper can be a one-way trip. And if it has 7km/s of delta-V, it can go anywhere on Mars.

Huh? what use is it if it can't return to where it started from?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 01/23/2016 05:53 pm
A launch-on-need hopper can be a one-way trip. And if it has 7km/s of delta-V, it can go anywhere on Mars.

Huh? what use is it if it can't return to where it started from?

It can carry enough supplies and solar power units to keep the stranded crew alive until a ground retrieve mission can reach them. If need be additional resupply flights.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 06:12 pm
A launch-on-need hopper can be a one-way trip. And if it has 7km/s of delta-V, it can go anywhere on Mars.

Huh? what use is it if it can't return to where it started from?

It can carry enough supplies and solar power units to keep the stranded crew alive until a ground retrieve mission can reach them. If need be additional resupply flights.

If it can only get as far as the stranded people it can't make subsequent flights. You are using up hoppers on a one way trip. So whether it is a custom designed hopper or an MCT that was left behind it is an emergency solution as much as a left behind MCT (and eventually several) will be the evac solution for a settlement if something makes it non viable early on.

If you want to use ballistic vehicles of any type for exploration you need an orbital depot and a craft designed to go from orbit to surface to orbit on a full propellant load since the requirements for that are less than the requirements for a hopper that can go more than 700km point to point and return on a single propellant load.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 01/23/2016 06:24 pm
If it can only get as far as the stranded people it can't make subsequent flights. You are using up hoppers on a one way trip. So whether it is a custom designed hopper or an MCT that was left behind it is an emergency solution as much as a left behind MCT (and eventually several) will be the evac solution for a settlement if something makes it non viable early on.

Isn't this highly dependent on how far the people are away from base and how the hopper is built? I would assume a custom hopper could weigh quit a bit less than an MCT. Even if it could only make a one-way trip, why couldn't a slow moving wheeled tanker just come along later and refuel it? Sure a orbital depot might make sense for exploration, but not IMO required for a rescue op.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/23/2016 06:27 pm

Or ISRU methane production is built into the early BFS's, or maybe all of them for redundancy. How large would the device  be?

Bingo. There will be a lot of cargo MCTs to develop a colony, very few will likely carry ISRU equipment.

Reasonable estimates for ISPP equipment necessary to refuel one vehicle over one synod once power sources and water collection equipment are included (which is where most of the mass is) is easily half of the 100 mt cargo capacity and may be several whole loads worth depending on how huge the vehicles propellant needs are.  It would be completely impractical to include this in every vehicle as it would cut deliverable payloads at a minimum in half.

In addition its simply inefficient because we want any ISPP equipment to stay on Mars FOREVER operating continuously and storing all that propellant for later use.  Integrated into the vehicle the equipment is dead-weight on every Earth return trip as well as a pure loss in potential propellant production by removing a functional system from the surface.

In the long run the fraction of cargo flights carrying ISPP equipment may be small because ideally the equipment will operate for decades and pay dividends of hundreds or thousands of times it's own mass in propellants.  But initially ISPP cargo will dominate and the ability to scale up propellant production will be a limiting factor in the ability to scale up the whole SpaceX transport infrastructure.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 01/23/2016 06:39 pm
...however every kilo of propellant used in that endeavour would represent 3 - 4 kilos of ISRU propellant and at say 200t of propellant per tanker flight, you are adding engine cycles on your reusable MCT's fairly quickly.

That's where the incentive for Phobos\Deimos\asteroid mining and atmospheric scooping lay.
If a mission like ARM is considered here, I bet it could be considered there, closer to the asteroid belt, as a viable solution for a LMO depot.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 06:43 pm
If it can only get as far as the stranded people it can't make subsequent flights. You are using up hoppers on a one way trip. So whether it is a custom designed hopper or an MCT that was left behind it is an emergency solution as much as a left behind MCT (and eventually several) will be the evac solution for a settlement if something makes it non viable early on.

Isn't this highly dependent on how far the people are away from base and how the hopper is built? I would assume a custom hopper could weigh quit a bit less than an MCT. Even if it could only make a one-way trip, why couldn't a slow moving wheeled tanker just come along later and refuel it? Sure a orbital depot might make sense for exploration, but not IMO required for a rescue op.

Actually once you are more than 700km away it takes more ΔV than orbital velocity to get there and land propulsively and the absolute limit of what is needed is somewhere between 6 and 7.5 km/s for an antipode(furthest point away on the surface of Mars - 10,000km) flight depending on how much aerodynamics can be used.

Basically the ΔV requirements look something like this for one way hops:

2km/s ~ 150km (aerolift/braking would make no difference)
4km/s ~ 750km (aerolift/braking would make no difference)
6km/s ~ 2500km (no aerolift/braking)
7.5km/s - 10,000km (no aerolift/braking)

So lets say your mission is more than 600km and your hopper can do 7.5 km/s of ΔV (limit for a two way flight) the amount of propellant required to refuel it and bring it back (at ISP 380) varies by fairly large factor but still is at least 2.5 times the total dry mass of the hopper, at the full range it would mass 7 times the mass of the hopper. So lets say the dry mass of the hopper is 10t (a very light craft if it is expected to land enough supplies for stranded people 10,000 km from base) you would need at least 25t of propellant that was trucked to the closest location and 70t to the furthest. That is an awful lot of extra mass to drag around on a rescue mission that needs to power itself all the way there and back.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 06:50 pm
So just go into very low Orbit and deorbit. That'd take less than ~5km/s delta-v.

btw, are you relying on Earth figures, or are you recalculating them for Mars? The lower gravity makes a huge difference here.

...BTW, this is all off-topic. I just brought up the idea to counter the false (but oft-repeated) claim that abort would be useless for MCT because there'd be no way to get to them.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 06:55 pm
So just go into very low Orbit and deorbit. That'd take less than ~5km/s delta-v.

btw, are you relying on Earth figures, or are you recalculating them for Mars? The lower gravity makes a huge difference here.

...BTW, this is all off-topic. I just brought up the idea to counter the false (but oft-repeated) claim that abort would be useless for MCT because there'd be no way to get to them.
I was using 4.1km/s for surface to LMO

yes I was calculating for Mars for the point to point distances
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 06:58 pm
So just go into very low Orbit and deorbit. That'd take less than ~5km/s delta-v.

btw, are you relying on Earth figures, or are you recalculating them for Mars? The lower gravity makes a huge difference here.

...BTW, this is all off-topic. I just brought up the idea to counter the false (but oft-repeated) claim that abort would be useless for MCT because there'd be no way to get to them.
I was using 4.1km/s for surface to LMO

yes I was calculating for Mars for the point to point distances
care to show your work?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/23/2016 07:00 pm
The concept of "hoppers" for Mars is not really practical the way many people are throwing it around here. IF you expect the hopper to go point to point on Mars and return to the origin point without refuelling the range of a hopper that has enough ΔV to make it to low Mars orbit is less than 200km. The same hopper could go nearly 1000km if it can refuel at its destination, but that is not useful for exploration because you can't just go anywhere. For serious exploration by rocket powered craft what is needed is a craft that can descend from orbit fully fuelled to any location on Mars and, after landing have enough fuel to make it back to orbit.  If that can be achieved then there is a point to using that sort of craft to travel on Mars, otherwise the limitations on such craft is such that wheeled vehicles will be far more practical. Even so to make it work you would need fuel depots in Mars orbit.

A fully fuelled MCT (ΔV = 7.5km/s) on the surface of Mars could make a one way trip to any point on Mars most likely, but a two way trip would be limited to something around 700km.

Note MCT left at Mars for their use at Mars would make excellent support craft for a Mars Orbital Station/Depot and if a few dedicated smaller craft optimized for orbit-surface-orbit on a single load of propellant existed that depot could support exploration of any point on Mars surface, however every kilo of propellant used in that endeavour would represent 3 - 4 kilos of ISRU propellant and at say 200t of propellant per tanker flight, you are adding engine cycles on your reusable MCT's fairly quickly.

Still as pointed out above the real limit early on will be the ISRU capacity.

Can you clarify how your calculation is performed?  Particularly are you assuming a fully propulsive landing equal in DeltaV to the take-off?  If landings are done with mostly atmospheric deceleration then this would greatly improve the range of the vehicle.   Also what if any cargo capacity are you assuming during the hop and is their any offloading or on-loading at the destination?

In any case the 700km figure that you came up with sounds adequate to do a down-range rescue of personnel from an aborted launch to orbit.  And it provides an excellent rescue option for ground vehicles, NASA plans limit ground vehicles to a 100km radius for logistics and safety reasons.  With a sub-orbital hop as a rescue and resupply option the vehicles could safely explore an area almost 50 times larger.  So all in all very useful even if it is of limited range.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 07:16 pm
It stands to reason that if a hopper over 700km exceeds orbital delta-V, then an aborted crew would not be more than ~700km away. That close, and a land-train of pressurized rovers would likely be able to meet them within a couple days of travel (or even 8-10 hours with a slightly prepared path, within EVA+contingency time). If the aborted crew aborted along with a rebreather system, they should be able to hang out in their spacesuits that long.

There would likely be only one orbital track for return from Earth, so you could possibly prepare a route before hand.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/23/2016 07:45 pm
I don't think their is that much of a rush with people having nothing but space suits on, I'm assuming the whole MCT/BFS aborted it's launch and simply landed down range, that means the personnel are in a fully functional habitat being carried inside the vehicle.  This might even be the 25 mt Earth-return habitat which would have sustained them for several months (in probably very Spartan conditions).  So life-support isn't as dire as Hollywood would like it to be. 

Now the rescue vehicle might have nothing in it but bucket seats that they strap themselves into while suited for the ~10 minute flight back to base but this is hardly much of a concern with an 8 hour EVA endurance and the personnel only need to leave the habitat on the aborted vehicle once the rescue vehicle has landed and gone through full diagnostics.

The main time pressure I see is getting the personnel back to base so they can be put into another vehicle for Earth return before the window closes so they are not stuck on Mars for another 2 years.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 07:51 pm
The BFS is a stage in and of itself. If it's intact enough to land, you'd likely be better off aborting to orbit.

BTW, MCT is the whole system, BFR and BFS together. What you call the MCT is what Musk calls the BFS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 01/23/2016 08:01 pm
The BFS is a stage in and of itself. If it's intact enough to land, you'd likely be better off aborting to orbit.

BTW, MCT is the whole system, BFR and BFS together. What you call the MCT is what Musk calls the BFS.

So in this case your looking at a crash sight where getting to the survivors as fast as possible is imperative. Don't want to use rovers for that. Although a BFS might work, seems like a specially built rescue hopper would be more appropriate.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 08:03 pm
So just go into very low Orbit and deorbit. That'd take less than ~5km/s delta-v.

btw, are you relying on Earth figures, or are you recalculating them for Mars? The lower gravity makes a huge difference here.

...BTW, this is all off-topic. I just brought up the idea to counter the false (but oft-repeated) claim that abort would be useless for MCT because there'd be no way to get to them.
I was using 4.1km/s for surface to LMO

yes I was calculating for Mars for the point to point distances
care to show your work?

rm (radius of Mars) = 3,400,000m

Mars orbital velocity at height h = sqrt(3.75m/s * rm2/(rm + h))

or 3570m/s at the surface of Mars

ΔΦ is defined as the "range angle" of the difference around the circumference of mars which, if we presume Mars is a perfect sphere and that launch and landing points are the same distance from the centre of Mars, gives us a range of 3,400 km per radian or 60km per degree.

YL is velocity at launch in multiples of orbital velocity at the surface of Mars

θL is the launch angle which the further we go is closer and closer to perpendicular to the ground for maximum range at launch

So the optimal launch angle (presuming vacuum of course) is

θL = (π - ΔΦ)/4

and the optimal launch velocity is

YL = SQRT(2*sin(ΔΦ/2)/(1+sin(ΔΦ/2)))

So plugging that into a table in excel gives me

Launch V (in m/s) for a given range

741m/s for 150km at 44.37 degrees
1590m/s for 750km at 41.84 degrees
2596m/s for 2500km at 34.47 degrees

I rounded up to 1km/s for the first one for gravity losses both on launch and landing since this isn't a canon shell so the first one is a boost of 1km/s at 1g  take off and landing it could be reduced to 875m/s at 2g etc.

you can see what I did for the rest.

Notes anyone who wants to can read far more about the math for less ideal cases at https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdf (https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdf)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 08:04 pm
The only reason the crew would be back on the surface is if the vehicle had a really bad day and the crew had to bail out, perhaps in a pod or ejection seats. Probably a pod, since it'd allow survival from Near Mars orbital velocity.

Then parachute down, with solid retrorockets to keep parachute size reasonable. The whole abort system could be relatively low mass. 2kg for the chute, 5-10kg for the rockets per passenger, plus whatever the suit would weigh and the pod to protect against the relatively modest Mars reentry (much more modest than. Typical Mars probe which comes in hyperbolically).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 08:12 pm
It stands to reason that if a hopper over 700km exceeds orbital delta-V, then an aborted crew would not be more than ~700km away.

HUH? where did you get that from? they could be anywhere from 0 to 10,000km away (any more than 10,000km away in one direction and they are closer on a different geodesic route) presuming that they had 7.5km/s of ΔV at launch they could have landed anywhere and survived.

That close, and a land-train of pressurized rovers would likely be able to meet them within a couple days of travel (or even 8-10 hours with a slightly prepared path, within EVA+contingency time). If the aborted crew aborted along with a rebreather system, they should be able to hang out in their spacesuits that long.

so you think that a path could be prepared that at .38g a rover train could motor along at 100km/h without rolling over?  I think over a prepared path a wheeled vehicle maximum speed will be on the order of 50km/h unless massively banked curves are put in, unprepared I wouldn't count on more than 15km/h average but obviously stretches of much faster could probably be practical.


There would likely be only one orbital track for return from Earth, so you could possibly prepare a route before hand.

With no depot that is not at all correct, if there were a depot then the tracks would have to match the depot and would be fairly close.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 08:16 pm
BFS should be able to get to orbit in a jiffy. They would only abort if they couldn't make it to orbit (even with secondary thrusters). It doesn't take 10,000km to get to orbit in a BFS with high thrust.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 08:17 pm
Impaler for the shorter distances aero lift and braking will not make any significant difference and have much less impact than gravity losses. Once you go above 2km/s in launch speed then it is possible that you can either use one of or  both lift and drag to somewhat reduce the amount landing ΔV required. But you will still need a significant proportion of your launch ΔV to land even at the antipode.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 08:18 pm
No evidence of a depot in LMO. Vastly more likely to launch directly to Earth or possibly visit a depot in high orbit like MSL-2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 08:23 pm
No evidence of a depot in LMO. Vastly more likely to launch directly to Earth or possibly visit a depot in high orbit like MSL-2.
Obviously there is no evidence of a depot in orbit around Mars yet, but there are no people, hoppers or vehicles returning to Earth. There is evidence that depots in LMO are a practical solution to a number of issues of the logistics of settling and exploring Mars. If you read the various threads on this forum there is as much evidence of depots as of other systems discussed here.

BFS should be able to get to orbit in a jiffy. They would only abort if they couldn't make it to orbit (even with secondary thrusters). It doesn't take 10,000km to get to orbit in a BFS with high thrust.

HUH again, if we are talking about a failure that causes an abort the failure could take place anywhere between launch and when the final orbit is achieved. So if that failure takes place at 95% of orbital velocity just 100km down range from the launch site, momentum would take them halfway around Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 08:24 pm
Yes, I think an average speed of over 70km/hr is feasible for a properly designed rover (huge wheels, low center of gravity) with a minimally prepared path I required. A much more leisurely rate (20-30km/hr) for an unprepared path. Eugene Cernan was able to tool around at nearly 20km/hr in half as much gravity and a rover designed only for 13km/hr.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 08:27 pm
No evidence of a depot in LMO. Vastly more likely to launch directly to Earth or possibly visit a depot in high orbit like MSL-2.
Obviously there is no evidence of a depot in orbit around Mars yet, but there are no people, hoppers or vehicles returning to Earth. There is evidence that depots in LMO are a practical solution to a number of issues of the logistics of settling and exploring Mars. If you read the various threads on this forum there is as much evidence of depots as of other systems discussed here.

BFS should be able to get to orbit in a jiffy. They would only abort if they couldn't make it to orbit (even with secondary thrusters). It doesn't take 10,000km to get to orbit in a BFS with high thrust.

HUH again, if we are talking about a failure that causes an abort the failure could take place anywhere between launch and when the final orbit is achieved. So if that failure takes place at 95% of orbital velocity just 100km down range from the launch site, momentum would take them halfway around Mars.
If you're that close, thrusters could get you to orbit. You just said that more than 700km would take more than orbital velocity, a claim I still have seen no calculations for that include lift.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 08:31 pm
If you're that close, thrusters could get you to orbit. You just said that more than 700km would take more than orbital velocity, a claim I still have seen no calculations for.

It is above! You can also do the math yourself see the link I quoted above along with my calculations:

https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdf (https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdf)

I said that it would take the same ΔV as going to orbit to launch and land 700km down range. You only need half orbital velocity to launch and crash 700km down range.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 01/23/2016 08:32 pm
The only reason the crew would be back on the surface is if the vehicle had a really bad day and the crew had to bail out, perhaps in a pod or ejection seats. Probably a pod, since it'd allow survival from Near Mars orbital velocity.

Then parachute down, with solid retrorockets to keep parachute size reasonable. The whole abort system could be relatively low mass. 2kg for the chute, 5-10kg for the rockets per passenger, plus whatever the suit would weigh and the pod to protect against the relatively modest Mars reentry (much more modest than. Typical Mars probe which comes in hyperbolically).

Not sure if you're arguing for or against a rescue hopper here. Are you assuming the crew would have enough supplies and be close enough to base that only a rover would be needed.?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 08:36 pm
I'm arguing that a rescue hopper is probably not required for 95% of abort scenarios.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 08:37 pm
Ok Robobeat you modified your post to say calculations with lift, that was not there when I replied. Lift is pretty irrelevant at lower speeds especially since to get efficient ballistic distances from your launch velocity you have to launch at an angle greater than 40 degrees (which means as you approach the surface (and lift can only play a role in the last 10 km or so) you are coming in at the same angle.  So lift is not going to increase your range significantly.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 08:38 pm
If you're that close, thrusters could get you to orbit. You just said that more than 700km would take more than orbital velocity, a claim I still have seen no calculations for.

It is above! You can also do the math yourself see the link I quoted above along with my calculations:

https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdf (https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdf)

I said that it would take the same ΔV as going to orbit to launch and land 700km down range. You only need half orbital velocity to launch and crash 700km down range.
What delta-V are you assuming is needed for landing?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 08:39 pm
If you're that close, thrusters could get you to orbit. You just said that more than 700km would take more than orbital velocity, a claim I still have seen no calculations for.

It is above! You can also do the math yourself see the link I quoted above along with my calculations:

https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdf (https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdf)

I said that it would take the same ΔV as going to orbit to launch and land 700km down range. You only need half orbital velocity to launch and crash 700km down range.
What delta-V are you assuming is needed for landing?
Equal to take off, particularly on hops that are less than 2km/s launch velocity since they are also really high angle
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 08:39 pm
Ok Robobeat you modified your post to say calculations with lift, that was not there when I replied. Lift is pretty irrelevant at lower speeds especially since to get efficient ballistic distances from your launch velocity you have to launch at an angle greater than 40 degrees (which means as you approach the surface (and lift can only play a role in the last 10 km or so) you are coming in at the same angle.  So lift is not going to increase your range significantly.
Boost-skip is one strategy to significantly increase point to point range. Lift is a big component of that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 08:41 pm
If you're that close, thrusters could get you to orbit. You just said that more than 700km would take more than orbital velocity, a claim I still have seen no calculations for.

It is above! You can also do the math yourself see the link I quoted above along with my calculations:

https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdf (https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdf)

I said that it would take the same ΔV as going to orbit to launch and land 700km down range. You only need half orbital velocity to launch and crash 700km down range.
What delta-V are you assuming is needed for landing?
Equal to take off, particularly on hops that are less than 2km/s launch velocity since they are also really high angle
Poor assumption. Lift changes the optimum angle significantly, can allow you to reach near terminal velocity.

Also, gravity losses would be quite small since Raptors will give BFS much, MUCH greater than T/W=1 on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 08:44 pm
I wrote a fairly simple simulator which allows you to take lift into consideration. It's currently setup for seeing max gee-loads during aerocapture, but can also be used for this sort of calculation:

https://repl.it/BXvp/15

(feel free to make changes and save. It will save it in a new spot by incrementing the number)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 08:50 pm
lift for skip is not significant at 2km/s it will not extend the range, if you launch at a 20 degree angle instead of 40 you don't go nearly as far ballistically so the net effect is to lower your range.  If you think angling a conic or biconic shape will allow you to fine tune your landing within a 30 or 40km radius at 700km ballistic range, I will say that is possible, if you say you will 'glide' a biconic shape 100km or more at 2km/s from where-ever you consider that enough lift starts above the Martian surface that is way off, even a winged vehicle would not get much further than that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 01/23/2016 08:55 pm

Nadreck, an abort scenario has to be realistic. If the BFS is able to be used as its own abort vehicle, it needs to be able to land. (If they crash, they die.) That means at least some engines are functional. So anything over half orbital velocity and your mission profile would be abort-to-orbit, then land at the base in the normal way once your orbit aligns with the base again.

During the first couple of minutes, you're close enough and slow enough to RTLS. After 5-6 minutes you default to abort-to-orbit. So there's a narrow window where you can't make orbit, but can land, but are too far from the base to RTLS. That's not going to be 10,000km.

Are you assuming the crew would have enough supplies

By definition, somewhere between 3 and 9 months worth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/23/2016 08:58 pm
Impaler for the shorter distances aero lift and braking will not make any significant difference and have much less impact than gravity losses. Once you go above 2km/s in launch speed then it is possible that you can either use one of or  both lift and drag to somewhat reduce the amount landing ΔV required. But you will still need a significant proportion of your launch ΔV to land even at the antipode.

I don't see why landing delta-V would be so high, if we can make a landing craft for Mars it's going to be capable of EDL landing on Mars at a minimum entry velocity of around 4 km/s (orbital velocity) with minimal propellant consumption, I'd say the landing Delta-V needs to be <1 km/s to be practical.

Now admittedly your entry angle is steeper on these re-entries but the velocities are considerably less so it seems reasonable that the vehicle can use lift to transition to a shallower entry and from then on the EDL would be just like any other landing.  So I see no more then 1 km/s for landing from any distance.

Likewise I can't see much gravity loss in this kind of hop, the atmosphere or Mars is so thin the vehicle should be able to start turning to the desired angle almost immediately upon launch and at 2g's acceleration you reach 2.5 km/s in only 2 minutes leaving virtually no time for gravity losses.

So for a 2.5 km/s launch and 1 km/s landing it looks to me that the 2500km range should be achievable with at 7 km/s vehicle.  And put half the planet within reach of one launch site.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 09:08 pm
With a light payload, decent lift and ballistic coefficient, You shouldn't need more than 1km/s to land from orbit. It takes 4.5km/s or less to get to low orbit. 7km/s would be enough delta-V to land anywhere on the planet, maybe except Olympus Mons.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 09:26 pm

Nadreck, an abort scenario has to be realistic. If the BFS is able to be used as its own abort vehicle, it needs to be able to land. That means at least some engines are functional. So anything over half orbital velocity and your mission profile would be abort-to-orbit, then land at the base in the normal way once your orbit aligns with the base again.

During the first couple of minutes, you're close enough and slow enough to RTLS. After 5-6 minutes you default to abort-to-orbit. So there's a narrow window where you can't make orbit, but can land, but are too far from the base to RTLS. That's not going to be 10,000km.

(If they crash, they die.)



By the same logic, if they could land at all, at any point, then they could also go on to orbit. But if you are going to pick outlandish scenarios that somehow an abort makes sense I don't see why you restrict it to a certain distance from the base. From a mathematical standpoint you might be anywhere along a geodesic based on the launch direction.

Look, I started here by trying to point out the ΔV requirements of a "hopper" because a variety of people had suggested it for a variety of purposes. That was my point, what are the real numbers around the performance of a ballistic point to point vehicle on Mars and the fact is once you are travelling more than about 700km, unless you are going to another base with propellant supplies, you could design a more efficient vehicle that orbits refuels lands anywhere on the surface (from a polar or high inclination orbit for true all planet access) and then takes off again to orbit.

At orbital speeds there is some benefit from aero drag/lift reducing ΔV requirements, but at low speeds (range under 700km) there is little benefit, gravity loss on take off and landing will be higher.

With a light payload, decent lift and ballistic coefficient, You shouldn't need more than 1km/s to land from orbit. It takes 4.5km/s or less to get to low orbit. 7km/s would be enough delta-V to land anywhere on the planet, maybe except Olympus Mons.

4.1Km/s at the most efficient to orbit the way I see it and I agree with 6 to 7.5km/s to get point to point to anywhere on Mars. You can review my posts above and I had stated that. 

I disagree about 1km/s to land from orbit I say 2 or more particularly if it is partly to fully fueled at atmospheric entry, and more importantly if I am only travelling I need much more than from orbit because to get anywhere near 700km balistically for less than 2km/s launch velocity I have to launch at a high angle which means I only have a very short time to have aerodynamic forces slow me SO I need more retropulsion proportionally than the low angle of an orbital entry.

Impaler see my responses above - but tl;dr  lift won't work nearly as much as you are imagining (except for winged craft); ΔV for EDL is more like 2km/s than 1km/s; gravity loss at 2.5g would be under 10% on launch; 1g would be a little over 20% presuming you translate immediately from vertical to the most efficient angle for the distance (see the formulae I posted above); landing at full thrust(hover slam) would always be less gravity losses than take off but if you throttle down for precision/translation or any other reason you increase the gravity losses.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 09:31 pm
  According to my simulations even 500 m/s is sufficient for landing at low altitude   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 09:36 pm
  According to my simulations even 500 m/s is sufficient for landing at low altitude

can you give me your assumptions for this: altitude where you start calculating drag and lift, angle of flight at that altitude, velocity at that altitude, cross section area, mass
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 01/23/2016 09:39 pm
Are you assuming the crew would have enough supplies

By definition, somewhere between 3 and 9 months worth.

Pretty obvious we were discussing a bail out scenario so I wouldn't assume these supplies would be available, but paint the scenario any way you want. That's what everybody else is doing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 09:54 pm
  According to my simulations even 500 m/s is sufficient for landing at low altitude

can you give me your assumptions for this: altitude where you start calculating drag and lift, angle of flight at that altitude, velocity at that altitude, cross section area, mass
And can you give me the results of your sim calculation with the same threshold altitude, an angle of 40 degrees, the shape was a cone with a rounded base with the height and diameter of the cone being 10 meters, and the mass was 60,000kg?

EDIT - oops and the velocity is 1.6km/s
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/23/2016 10:18 pm
No threshold, I use an exponential atmosphere model. I posted a link above. It contains all assumptions.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/23/2016 10:23 pm
No threshold, I use an exponential atmosphere model. I posted a link above. It contains all assumptions.

I have no experience in python, have you got it in Pascal?

Seriously I am not familiar with your software, you asked me to show you my work, you might be willing to come up with the numbers for your assumptions for me.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/24/2016 06:55 am
I should point out that their are MANY possible reason why we might wish to abort to surface other then loss of engines, anything which endangers the long term life-support capability, or compromises the heat-shield which would make Earth entry in that vehicle dangerous.   So I can't agree that any abort to surface is necessarily coming down with no propulsion and must therefore be a bailout.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/24/2016 02:40 pm
I should point out that their are MANY possible reason why we might wish to abort to surface other then loss of engines, anything which endangers the long term life-support capability, or compromises the heat-shield which would make Earth entry in that vehicle dangerous.   So I can't agree that any abort to surface is necessarily coming down with no propulsion and must therefore be a bailout.
Abort to orbit in most of those situations would be much safer since you're not risking landing in a compromised vehicle. The only reason you'd want to be on the surface rather than in orbit is if you literally can't get to orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/24/2016 05:14 pm
Hi everyone, I just made a design concept, I'm a product designer, not engineer.

Newest version: http://imgur.com/a/15fO2

Initial concepts and idea development: http://imgur.com/a/EtH8F
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 01/24/2016 05:58 pm
I should point out that their are MANY possible reason why we might wish to abort to surface other then loss of engines, anything which endangers the long term life-support capability, or compromises the heat-shield which would make Earth entry in that vehicle dangerous.   So I can't agree that any abort to surface is necessarily coming down with no propulsion and must therefore be a bailout.
Abort to orbit in most of those situations would be much safer since you're not risking landing in a compromised vehicle. The only reason you'd want to be on the surface rather than in orbit is if you literally can't get to orbit.

It depends on how the vehicle is compromised, if were in doubt of the vehicles thermal protection then aborting the launch immediately and landing propulsivly puts the vehicle through the least thermal load, less even then reaching orbit and then landing again.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/24/2016 07:14 pm
I should point out that their are MANY possible reason why we might wish to abort to surface other then loss of engines, anything which endangers the long term life-support capability, or compromises the heat-shield which would make Earth entry in that vehicle dangerous.   So I can't agree that any abort to surface is necessarily coming down with no propulsion and must therefore be a bailout.
Abort to orbit in most of those situations would be much safer since you're not risking landing in a compromised vehicle. The only reason you'd want to be on the surface rather than in orbit is if you literally can't get to orbit.

It depends on how the vehicle is compromised, if were in doubt of the vehicles thermal protection then aborting the launch immediately and landing propulsivly puts the vehicle through the least thermal load, less even then reaching orbit and then landing again.
No. Aborting to orbit puts the vehicle through the least thermal load. They would be rescued by another vehicle. That was the plan for Shuttle post-Columbia, and it'd likely be the case for BFS at Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 01/24/2016 07:46 pm
Hi everyone, I just made a design concept, I'm a product designer, not engineer.

Newest version: http://imgur.com/a/15fO2

Initial concepts and idea development: http://imgur.com/a/EtH8F

Nice pictures! Gives some idea of the sizes of craft that may be necessary!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: meetsitaram on 01/24/2016 07:59 pm
Why are all the rocket tall and cylindrical? What are the disadvantages of launching disc like space ships?
Is it possible to build a single stage spaceship that is capable of launching from earth and landing on mars?

(http://i.imgur.com/3RLvRoD.jpg) (http://i.imgur.com/peI5ICx.jpg)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/24/2016 08:16 pm
Higher costs for designing and building, basically.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/24/2016 08:50 pm
Why are all the rocket tall and cylindrical? What are the disadvantages of launching disc like space ships?
Is it possible to build a single stage spaceship that is capable of launching from earth and landing on mars?


Basic rocketry 101 doesn't really belong here, but respectively:

*Because it's the best way to defeat air resistance and the easiest to build.

*Drastically increased drag losses, massive logistical difficulty processing large flat sheets, increased weight from stiffening up large flat sheets (depending on construction techniques).

*Not really.  It's barely possible to build one to get to a 9km/s orbit, and although the math suggests SSTO is practical on an expendable rocket if you're satisfied with a low payload mass fraction, a reusable rocket stage which can survive reentry would be much heavier.  It costs more like 13km/s to get to Mars (*before* entry, descent, and landing is taken into account), which at 450s Isp is the difference between an 8:1 mass ratio and a 20:1 mass ratio.  There is a large segment of space enthusiasts that fixate on the dream they were sold in the 90's (and to some extent earlier) of reusable SSTO spaceplanes or VTVL craft, but now that we have reusable first stages, it basically always makes more sense to mount any such craft as an upper stage that only needs ~6km/s to reach orbit (a mass ratio at 450s Isp of 4:1).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: meetsitaram on 01/24/2016 11:21 pm
I appreciate that Burninate. I will follow up in the 'Basic Rocket Science Q&A' thread.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/25/2016 12:17 pm
Hi everyone, I just made a design concept, I'm a product designer, not engineer.

Newest version: http://imgur.com/a/15fO2

Initial concepts and idea development: http://imgur.com/a/EtH8F
I appreciate your excellent work to create superb renderings.

A rocket engineer would require some changes to the model based on his/her calculations and experience. You should be aware that a team of persons in the L2 section of this forum are also creating renderings based on expert opinion and hints from SpaceX. It would be worth your joining L2 just to review the large amount of information and the history behind their work.

I have also proposed some concepts on this forum that have received good reviews and critiques, but I have mostly relied on sketches. I would love to provide some ideas to you for your review and your rendering machine.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/25/2016 02:39 pm

I appreciate your excellent work to create superb renderings.

A rocket engineer would require some changes to the model based on his/her calculations and experience. You should be aware that a team of persons in the L2 section of this forum are also creating renderings based on expert opinion and hints from SpaceX. It would be worth your joining L2 just to review the large amount of information and the history behind their work.

I have aldo proposed some concepts on this forum that have received good reviews and critiques, but I have mostly relied on sketches. I would love to provide some ideas to you for your review and your rendering machine.

Thank you Ionmars, I appreciate your comments and loved to see your concept, I'll talk more about it later.
 
As I don't have the technical skills, I based this concept on other studies, my view of SpaceX' design philosofy, etc.
I think proportions would be very different, with the proper calculations, wind tunnel testing and right materials, I was tryng more to find a possible logic on the design, but this concept is not more than thinking aloud.

I've seen lots of articles and fan proposals, but every time it appears a new information that should change the basic design, so it's impossible to track everything. For me this is a funny guessing game and will be very interesting to see who had the technical skills and luck to be closer to the truth, when all is revealed.

For my design, specifically, I tried to keep it simple, so  it can be feasible on the development, costs and safety fields on a 15 years timeframe by now (more time than SpaceX exists).

IMO, not everything of what was said about the MCT will be achievable at the same time, it looks that the ship would become too heavy, expensive and complex, so I expect to see something brilliant and elegant, or something simplier, which is my approach.

I had seem some of your sketches before (nice to meet you finally) and I think that is the right bet if the MCT is the monolithic lander ship as the information goes. As you designed I also agree that they will rely on previous spacex's designs, evolutionary. I personaly bet on a modular ship instead. But as this is the main concept by this time, I'm thinking how to make a monolithic (almost) and refueling on orbit before going to mars. I assume it will be close to your design. But it'll have a difference, the propulsion module will not land back on earth as I presume you designed (I'm not sure if it's the case by the sketches I've seem by now). It would land here using the abort system, like the dragon.  The new BFR, on the second MCT mission would launch the lander + fuel + more cargo then before, to meet the MCT (propulsion + mars landing + crew hab and radiation shielding)already on orbit to refuel and servicing it.

I just saw your cargo unloading solution and is close of what I was thinking (attached rough). I think a car would ride on a leg or the side fuselage instead. Could I see the rough dimensions of your concept?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/25/2016 03:21 pm
Yes, BSenna. You and I are thinking alike.

I do not have a specific concept of the MCT design; I just react to new info as I discover it. I have some experience as a engineering project manager but my principle role now is "Idea Man." But as a team player I am ready to change my concepts when a better idea is presented. So if you and I were to work together, you should take the lead on what the MCT design is likely to be.

My arena would be an idea about a structure that the MCT architecture will require: an in-space propellant depot. If interested, it has 3 threads on this forum so far, starting with this:
http://forum.nasaspaceflight.com/index.php?topic=38146.0
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/25/2016 09:09 pm
Yes, BSenna. You and I are thinking alike.

I do not have a specific concept of the MCT design; I just react to new info as I discover it. I have some experience as a engineering project manager but my principle role now is "Idea Man." But as a team player I am ready to change my concepts when a better idea is presented. So if you and I were to work together, you should take the lead on what the MCT design is likely to be.

My arena would be an idea about a structure that the MCT architecture will require: an in-space propellant depot. If interested, it has 3 threads on this forum so far, starting with this:
http://forum.nasaspaceflight.com/index.php?topic=38146.0

Great, I'll love to colaborate as much I can! I'll take a look. The monolithic version of the previous concept:
http://imgur.com/a/CCtZ5
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/26/2016 04:06 pm
...
...
Great, I'll love to colaborate as much I can! I'll take a look. The monolithic version of the previous concept:
http://imgur.com/a/CCtZ5
OK, IMO your architecture reflects what most engineers are thinking is reasonable. MCT will be the second stage of a two-stage system with BFR as a muscular stage I. Both stages will have methane and LOX as fuels and Raptor engines. SI will only be used to launch from Earth and will return as a reusable SI, much like F9R.

The SII (MCT) will come in three varieties, a passenger vehicle. a cargo carrier and a fuel tanker. But they will have the same outer structure.

There will be differences in how the different versions will be utilized, but your stage 5, relaunch from Mars, seems pretty solid, at least for passenger and cargo versions. There are other observations to be made, but more appropriate for a section in L2.

Some differences: You show separation of a capsule from the main body when landing on Earth but both parts need to be landed for reusability and may likely land together. Also, you reasonably show refurbishment in step 8 but as time goes on Musk wants this to become minimal for rapid relaunch.

Musk is said to have ordered tooling for a 15 m fuel tank so I think this will be the diameter of main parts of SI and SII. Not so sure whether a wider 19 m capsule will sit on top.

I like your sketches.
Now it's your turn.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/26/2016 04:17 pm
PS. The L2 section of this forum carries a personal messaging service that makes inter-personal messaging very convenient. (No I get no commission) :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 01/26/2016 05:19 pm
Great, I'll love to colaborate as much I can! I'll take a look. The monolithic version of the previous concept:
http://imgur.com/a/CCtZ5

I like your concept - and your illustration style - but I have two areas of concern:
 - Abort capsule - I don't think it is necessary or helpful (lots of arguments over this I realize)
 - The raptors are canted outwards and lose efficiency
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/26/2016 05:28 pm
What do you guys think of a 'Return Capsule' plan of operations, where the tip of the MCT reenters with humans in Orion or Dragon-grade accomodations, but where the MCT hab + rocket itself never returns to the Earth Surface or to LEO, but stays in high orbit around Earth and receives repairs / refueling / cargo / passengers there?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/26/2016 05:31 pm
What do you guys think of a 'Return Capsule' plan of operations, where the tip of the MCT reenters with humans in Orion or Dragon-grade accomodations, but where the MCT hab + rocket itself never returns to the Earth Surface or to LEO, but stays in high orbit around Earth and receives repairs / refueling / cargo / passengers there?

Why not have the "return capsule" just be part of the vehicle that ferries crew/cargo up and where the BFS never comes back down and gets all its servicing in LEO or at LM-1 or 2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 01/26/2016 05:46 pm
What do you guys think of a 'Return Capsule' plan of operations, where the tip of the MCT reenters with humans in Orion or Dragon-grade accomodations, but where the MCT hab + rocket itself never returns to the Earth Surface or to LEO, but stays in high orbit around Earth and receives repairs / refueling / cargo / passengers there?

Why not have the "return capsule" just be part of the vehicle that ferries crew/cargo up and where the BFS never comes back down and gets all its servicing in LEO or at LM-1 or 2.

Having a separate vehicle (maybe a version of BFS) to transfer crew/cargo to a BFS Mars vehicle would help with planetary protection issues for Earth. A BFS returning from Mars would never land on Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/26/2016 05:54 pm


Musk is said to have ordered tooling for a 15 m fuel tank so I think this will be the diameter of main parts of SI and SII. Not so sure whether a wider 19 m capsule will sit on top.


I see no supporting quote for this in the SX MCT info thread...

http://forum.nasaspaceflight.com/index.php?topic=37839.0

Source?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/26/2016 06:15 pm
From what I gather there seem to be quite a few of us here who see the BFR/BFS assembly known as the MCT system as being a 2 stage to LEO vehicle with the BFR lofting the 2nd stage to LEO.  Stage 2 the MCS is almost but not quite a SSTO, although it IS a SSTO and beyond LMO to Earth when launching from Mars refueled.  Most of the delta V comes from the BFS.  This makes a RTLS or return to barge easier as the BFR lumbers along low & slow.

It's far easier to model & guess the 1st stage BFR's attributes than the complex, multi-faceted 2nd stage interplanetary BFS.  The BFS must have enough engines to deliver a T/W >1 as stage 2 on Earth launch.  Yet much lower thrust for Mars landing, never mind the problems of landing on unprepared sites.  Then there's TPS for Mars and Earth aerobraking.  I'd wager that this entire design continues to be in a strong state of flux.

I'm guessing that the plan is to announce the first details follows the 1st FH launch.  That would be an ideal time to talk "next" generation.  Don't know if Musk can restrain his marketing enthusiast CTO that long from premature ejaculation of some details.  In any case maybe we'll get some BFR details with the BFS being far less well described.  Maybe a poll forecasting Musk's coming out of the closet date?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 01/26/2016 06:50 pm
15 diameter will be great for aerobraking at Mars and back at Earth.
1/How much this diameter increase effect launch performance?
2/My estimate rocket will be only 70m tall(max 100m), how much make it easy to steering MCT during landing on Mars and Earth?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/26/2016 07:54 pm


Musk is said to have ordered tooling for a 15 m fuel tank so I think this will be the diameter of main parts of SI and SII. Not so sure whether a wider 19 m capsule will sit on top.


I see no supporting quote for this in the SX MCT info thread...

http://forum.nasaspaceflight.com/index.php?topic=37839.0

Source?

https://www.reddit.com/r/spacex/comments/3wl5iz/preliminary_mctbfr_information/

https://i.imgur.com/otQcEBs.png
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GalacticIntruder on 01/26/2016 07:56 pm
Hopefully find out in Sept.

https://www.youtube.com/watch?v=pIRqB5iqWA8\

http://www.iac2016.org/
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/26/2016 08:19 pm
Great, I'll love to colaborate as much I can! I'll take a look. The monolithic version of the previous concept:
http://imgur.com/a/CCtZ5

I like your concept - and your illustration style - but I have two areas of concern:
 - Abort capsule - I don't think it is necessary or helpful (lots of arguments over this I realize)
 - The raptors are canted outwards and lose efficiency

Thank you!
I think my concept is very conservative in terms of safety. The abort system is also for landing a smaller and lighter payload on earth. The raptors loose efficiency and add weigth as long as 6 are probably too many for launch the second stage, landing and then take-off from mars. But Its for redundancy and I tried to avoid moving parts on the heath shield for safety too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/26/2016 08:23 pm
PS. The L2 section of this forum carries a personal messaging service that makes inter-personal messaging very convenient. (No I get no commission) :)

I would love to, but this forum has already far more information that I can absorb...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/26/2016 09:37 pm
...
...
Great, I'll love to colaborate as much I can! I'll take a look. The monolithic version of the previous concept:
http://imgur.com/a/CCtZ5
OK, IMO your architecture reflects what most engineers are thinking is reasonable. MCT will be the second stage of a two-stage system with BFR as a muscular stage I. Both stages will have methane and LOX as fuels and Raptor engines. SI will only be used to launch from Earth and will return as a reusable SI, much like F9R.

The SII (MCT) will come in three varieties, a passenger vehicle. a cargo carrier and a fuel tanker. But they will have the same outer structure.

There will be differences in how the different versions will be utilized, but your stage 5, relaunch from Mars, seems pretty solid, at least for passenger and cargo versions. There are other observations to be made, but more appropriate for a section in L2.

Some differences: You show separation of a capsule from the main body when landing on Earth but both parts need to be landed for reusability and may likely land together. Also, you reasonably show refurbishment in step 8 but as time goes on Musk wants this to become minimal for rapid relaunch.

Musk is said to have ordered tooling for a 15 m fuel tank so I think this will be the diameter of main parts of SI and SII. Not so sure whether a wider 19 m capsule will sit on top.

I like your sketches.
Now it's your turn.

Thanks! I've been very consevative with the my proposal because of the time frame of midle 2020' to start colonization. Also I'm sckeptical with the 100 ton cargo payload, I imagine the entire system landing with this weigh, before refueling on mars. The designs I made so far:

V50: only 50 crew  (or cargo), 1 BFR and an expendable inflatable module for the earth - mars trip

http://imgur.com/T0COHsL

V100: a 100 crew  (or cargo) but modular bus, lanched on 1 BFR, with a mars lander

http://imgur.com/ngKKTEo

Mk.3: 100 crew (or cargo), 19m wide for a better heat shielding on 1 BFR

http://imgur.com/6Q2V5W9

Mk.4: 100 crew (or cargo), earth orbital, refueling on earth's orbit and the entire MCT/BFS lands on mars although just the abort capsule lans on earth. Launched by 1 BFR more another or more to Refueling.

http://imgur.com/a/CCtZ5

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stardhingy on 01/26/2016 10:02 pm
15 diameter will be great for aerobraking at Mars and back at Earth.
1/How much this diameter increase effect launch performance?
2/My estimate rocket will be only 70m tall(max 100m), how much make it easy to steering MCT during landing on Mars and Earth?

15m is still extremely small for aerobraking over 100 Mg on Mars. In mass per area, its an order of magnitude worse than anything we've ever sent to Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/26/2016 11:03 pm
15 diameter will be great for aerobraking at Mars and back at Earth.
1/How much this diameter increase effect launch performance?
2/My estimate rocket will be only 70m tall(max 100m), how much make it easy to steering MCT during landing on Mars and Earth?

15m is still extremely small for aerobraking over 100 Mg on Mars. In mass per area, its an order of magnitude worse than anything we've ever sent to Mars.
...because we've never ever had the ability to try SSRP, which allows you to land large payloads provided you use enough propellant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 01/26/2016 11:45 pm
Maybe a poll forecasting Musk's coming out of the closet date?

How about a poll with the top ten BFS/BFR designs and mission architectures?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/26/2016 11:51 pm
Maybe a poll forecasting Musk's coming out of the closet date?

How about a poll with the top ten BFS/BFR designs and mission architectures?

Who compiles the 1000 page pdf document detailing these?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 01/26/2016 11:54 pm
Musk already dropped a date for when he wants to reveal the architecture: September 26-30.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/27/2016 12:37 am
Musk already dropped a date for when he wants to reveal the architecture: September 26-30.

Great!  Let's hope he makes this date.  So much for the Big Reveal coming up Real Soon Now. :)

I think it's wise to hold off (Dammit!) because it's best done after a successful FH launch which hopefully will occur by then, although I'm concerned.  And it's best to thoroughly vet the major architecture points and sleep on them.  Also returning several cores and seeing what if any changes a BFR launcher would need.

No real point on a Poll for the date now. I of course was picking September.  :)
Let's hope that Lucy does not pull the football away from Charlie Brown a 4th time.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: DJPledger on 01/27/2016 08:29 am
Musk already dropped a date for when he wants to reveal the architecture: September 26-30.
Hopefully all the speculation on BFR/MCT system will end then.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/27/2016 01:29 pm
Musk already dropped a date for when he wants to reveal the architecture: September 26-30.
Hopefully all the speculation on BFR/MCT system will end then.

You mean just like all speculation on the Falcon 9, Dragon 2, and Falcon Heavy have stopped?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/27/2016 02:58 pm
Maybe a poll forecasting Musk's coming out of the closet date?

How about a poll with the top ten BFS/BFR designs and mission architectures?

Who compiles the 1000 page pdf document detailing these?

Maybe only the main features. Could be an spreadsheet with the info, data or ilustration of each part of the mission. Then, it woud be an Y or N for each point when the architecture is revealed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/27/2016 03:16 pm
Yes, BSenna. You and I are thinking alike.

I do not have a specific concept of the MCT design; I just react to new info as I discover it. I have some experience as a engineering project manager but my principle role now is "Idea Man." But as a team player I am ready to change my concepts when a better idea is presented. So if you and I were to work together, you should take the lead on what the MCT design is likely to be.

My arena would be an idea about a structure that the MCT architecture will require: an in-space propellant depot. If interested, it has 3 threads on this forum so far, starting with this:
http://forum.nasaspaceflight.com/index.php?topic=38146.0

I took a look at the propellant depot project and it looks great, very refined. But unfortunately is too much for my technical limitations, so, I didn't undestood it completely, but I trust on you guys!

I could start a 3d model, but my habilities are really limited. I have some doubts:

I assume that the MCTs which will trasport the fuel to LEO are of a similar size and mass of the crewed MCT, so, they're not full of fuel when reach the depot, right? If It's the case, would there be any advantage on leaving only a smaler fuel tank on each of these missions and returning to land to fly again on the same role, thus reducing the total fleet of MCT-SIIs) and also reducing the total mass of the complete transit to mars vehicle? Or The rockets on these MCTs are also necessary to throw the complete vehicle to Mars?

Once on Mars, just the crewd MCT would land, refuel and return to meet the rest of the vehicle?

Then, all 7 MCTs would land on Earth for refurbishing?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 01/27/2016 05:37 pm


You mean just like all speculation on the Falcon 9, Dragon 2, and Falcon Heavy have stopped?

People will stop suggesting completely alternative architectures and instead speculate about architecture upgrades. That will cut some of the 'Dastardly and Muttley in Their Flying Machines/Catch that pigeon' proposals.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/27/2016 05:55 pm


You mean just like all speculation on the Falcon 9, Dragon 2, and Falcon Heavy have stopped?

People will stop suggesting completely alternative architectures and instead speculate about architecture upgrades. That will cut some of the 'Dastardly and Muttley in Their Flying Machines/Catch that pigeon' proposals.

Excuse my cynicism but even before the USAF award to develop a raptor or raptor variant for FH and F9 upper stage use it had been discussed for a long time here along with potential F9 or FH new reusable US.  So I fully expect that whatever Musk announces in September some variants in both overall architecture (including depot/refuelling, upper stage types, dependencies on site preparation at Mars, Mars ISRU and depots, SEP on BFS, BFS return to Earth surface, LEO, LM-1/2, etc) and specific details (BFS engine arrangement, TPS, BFB recovery, BFS ECLSS, BFS cargo arrangemnt etc) will still get debated well outside guidelines of where SpaceX says it will be going.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/27/2016 09:32 pm
Excuse my cynicism but even before the USAF award to develop a raptor or raptor variant for FH and F9 upper stage use it had been discussed for a long time here along with potential F9 or FH new reusable US.  So I fully expect that whatever Musk announces in September some variants in both overall architecture (including depot/refuelling, upper stage types, dependencies on site preparation at Mars, Mars ISRU and depots, SEP on BFS, BFS return to Earth surface, LEO, LM-1/2, etc) and specific details (BFS engine arrangement, TPS, BFB recovery, BFS ECLSS, BFS cargo arrangemnt etc) will still get debated well outside guidelines of where SpaceX says it will be going.
The end of speculation lies just beyond Andromeda Galaxy.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/27/2016 11:10 pm
I took a look at the propellant depot project and it looks great, very refined. But unfortunately is too much for my technical limitations, so, I didn't undestood it completely, but I trust on you guys!

I could start a 3d model, but my habilities are really limited. I have some doubts:

I assume that the MCTs which will trasport the fuel to LEO are of a similar size and mass of the crewed MCT, so, they're not full of fuel when reach the depot, right? If It's the case, would there be any advantage on leaving only a smaler fuel tank on each of these missions and returning to land to fly again on the same role, thus reducing the total fleet of MCT-SIIs) and also reducing the total mass of the complete transit to mars vehicle? Or The rockets on these MCTs are also necessary to throw the complete vehicle to Mars?

Once on Mars, just the crewd MCT would land, refuel and return to meet the rest of the vehicle?

Then, all 7 MCTs would land on Earth for refurbishing?
Here's the way I see the Depot working:

The first half dozen or so trips to Mars will carry cargo to set up habitats, ISRU machinery, and remote-contolled equipment. These preliminary forays will prepare a base for humans who will arrive later. A cargo MCT launching from Earth will be heavily loaded; it will use up essentially all its fuel just to get to the depot in orbit. It will require a refill before proceeding any further.
 
We will have a tanker variant of MCT, which has the same basic outer shell as a cargo or passenger version, but will be hollowed out as a big fuel carrier. The volume that would otherwise be cargo volume will be devoted to big fuel tanks. This could be just an expansion of the the main tanks that extend into the the cargo space. Its principle function will be to haul fuel from Earth to the depot, probably about 250 tonnes of CH4 and LOX in each trip. . Three or four loads of fuel must be transferred to the cargo-MCT before it can proceed to Mars.

We could just make a series of trips to the waiting cargo ship and sequentially fill it up. But having a depot allows us to fill up multiple cargo ships and launch as a fleet to Mars. This is the stated intent of SpaceX.

So tanker #1 arrives at the depot and docks at a berth. Tanker #2 arrives at the depot and transfers its fuel load to tanker #1, reserving just enough fuel to return to Earth via propulsive landing. These tankers are highly reusable and require little maintenance between flights, like an airplane. Tanker #2 refills at the launch site and launches again to the depot. It again transfers its fuel load to tanker #1 and returns to the launch site. Now tanker # 1 has enough fuel in its tanks to service one cargo MCT. And because we have six berths at the depot, we can perform this procedure three times simultaneously using six tanker MCTs.

Now three cargo ships arrive at the depot and dock beside three refilled tankers. The tankers transfer their fuel loads to the cargo ships and return to Earth.

We have three cargo carriers ready to trek to Mars with full bellies.  :)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/28/2016 12:39 am
Here's the way I see the Depot working:

The first half dozen or so trips to Mars will carry cargo to set up habitats, ISRU machinery, and remote-contolled equipment. These preliminary forays will prepare a base for humans who will arrive later. A cargo MCT launching from Earth will be heavily loaded; it will use up essentially all its fuel just to get to the depot in orbit. It will require a refill before proceeding any further.
 
We will have a tanker variant of MCT, which has the same basic outer shell as a cargo or passenger version, but will be hollowed out as a big fuel carrier. The volume that would otherwise be cargo volume will be devoted to big fuel tanks. This could be just an expansion of the the main tanks that extend into the the cargo space. Its principle function will be to haul fuel from Earth to the depot, probably about 250 tonnes of CH4 and LOX in each trip. . Three or four loads of fuel must be transferred to the cargo-MCT before it can proceed to Mars.

We could just make a series of trips to the waiting cargo ship and sequentially fill it up. But having a depot allows us to fill up multiple cargo ships and launch as a fleet to Mars. This is the stated intent of SpaceX.

So tanker #1 arrives at the depot and docks at a berth. Tanker #2 arrives at the depot and transfers its fuel load to tanker #1, reserving just enough fuel to return to Earth via propulsive landing. These tankers are highly reusable and require little maintenance between flights, like an airplane. Tanker #2 refills at the launch site and launches again to the depot. It again transfers its fuel load to tanker #1 and returns to the launch site. Now tanker # 1 has enough fuel in its tanks to service one cargo MCT. And because we have six berths at the depot, we can perform this procedure three times simultaneously using six tanker MCTs.

Now three cargo ships arrive at the depot and dock beside three refilled tankers. The tankers transfer their fuel loads to the cargo ships and return to Earth.

We have three cargo carriers ready to trek to Mars with full bellies.  :)

Undesrtood!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/28/2016 08:39 am
Blah,, blah... blah
...
...

Undesrtood!
If you were to do a 3D model of the Depot it would just be a 2D (x,y) skeletal frame that is repeated into the third (z) dimension. Below is a sketch of the forward frame for one berth. The small circle is a "pad" for connecting to the nose of the MCT and the large circle is an imaginary volume representing one berth where one MCT is docked. The frames are connected by beams of a certain length in the z dimension. Then this 3D image is duplicated side-by-side to the right to make 5 additional berths until they join on the left side of the first berth. Voila!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stardhingy on 01/28/2016 05:54 pm

We will have a tanker variant of MCT, which has the same basic outer shell as a cargo or passenger version, but will be hollowed out as a big fuel carrier. The volume that would otherwise be cargo volume will be devoted to big fuel tanks. This could be just an expansion of the the main tanks that extend into the the cargo space. Its principle function will be to haul fuel from Earth to the depot, probably about 250 tonnes of CH4 and LOX in each trip. . Three or four loads of fuel must be transferred to the cargo-MCT before it can proceed to Mars.


Cargo density is far lower than fuel density,  so either the tanker is smaller or it has a lot of unused cargo volume.

I don't understand why you would need a depot though. Why not just have the tanker dock with the MCT and transfer propellent?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RocketmanUS on 01/28/2016 06:03 pm

We will have a tanker variant of MCT, which has the same basic outer shell as a cargo or passenger version, but will be hollowed out as a big fuel carrier. The volume that would otherwise be cargo volume will be devoted to big fuel tanks. This could be just an expansion of the the main tanks that extend into the the cargo space. Its principle function will be to haul fuel from Earth to the depot, probably about 250 tonnes of CH4 and LOX in each trip. . Three or four loads of fuel must be transferred to the cargo-MCT before it can proceed to Mars.


Cargo density is far lower than fuel density,  so either the tanker is smaller or it has a lot of unused cargo volume.

I don't understand why you would need a depot though. Why not just have the tanker dock with the MCT and transfer propellent?
TMI burn window. Need time to get the propellants and MCT in orbit before the window opens. Depot would be designed to store the propellants over a long period of time and could be used by other in space craft.

Launch cargo or crew MCT's to depot, fuel, then TMI burn.

With all the propellant in space before the TMI window opens up the MCT's to MArs just need to be launched and refueled at the depot. No waiting around for the propellants and no taking up launches for propellants in the TMI window.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/28/2016 07:32 pm
At some launch rate depots will make sense. They make it possible to have a steady launch sequence for tankers throughout the whole period between launch windows.

10 or maybe 20 launches can be done without depots.10 MCT will need a total number of 40 to 50 launches in ~25 weeks. That's only two per week. The numbers are quite arbitrary. Launching cargo MCT and starting to fuel them up might start early. There can be more launches a week. In that case more launches are possible without depots. The thousands of launches anticipated by Elon Musk would certainly need depots for efficiency.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/28/2016 07:52 pm
Another reason for a depot is to reduce risk in a way that might be specifically applicable to manned launches. This would actually be most important during the first few synods with manned flights.  I think it is safe to assume that for the first manned mission using the BFS that two BFS would be launched as simultaneously as possible and rendezvous very shortly after TMI to provide redundancy in ECLSS, and all other systems, and provide for alternative means of ensuring evacuation from the moment of rendezvous until another expedition with manned craft and supplies lands on Mars near them.  Along with the first two manned craft there might be support craft that were deemed important enough to be synchronized on the same path.  Obviously the bulk of cargo going to the first synod will probably be launched before the manned craft with only the most critical going on a route that gets them there as/more quickly as /than the manned craft.

For the craft that rendezvous or at least fly in close formation throughout the journey to Mars, you also reduce the risks to that effort by having ALL the fuel those specific craft need on orbit before you launch those craft.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/28/2016 09:40 pm
Blah,, blah... blah
...
...

Undesrtood!
If you were to do a 3D model of the Depot it would just be a 2D (x,y) skeletal frame that is repeated into the third (z) dimension. Below is a sketch of the forward frame for one berth. The small circle is a "pad" for connecting to the nose of the MCT and the large circle is an imaginary volume representing one berth where one MCT is docked. The frames are connected by beams of a certain length in the z dimension. Then this 3D image is duplicated side-by-side to the right to make 5 additional berths until they join on the left side of the first berth. Voila!

Is this?

http://imgur.com/a/KJRna
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/29/2016 01:16 am
Pick me up from the floor! Don't tell me you created all those images since my last post. It looks spot on.  :)  :)  :)

Edit: People in my generation will understand "Tinker-Toys" and that is exactly what the framework looks like.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 01/29/2016 04:48 am
I think after several cargo mission, first with FH and then MCT. When MCT successfully land on Mars. First crew will arrive without specified return day. There task will be prepare infrastructure and ask for additional resources in  preparation of infrastructure for return trip. Setup ice collection and build and maintain devices to create fuel,build tank for fuel. At the moment finishing task and prepare rocket  for return trip some of the crew will start their trip back to Earth. I think when first crew will arrive there  will be not enough fuel to bring them back, they have to build their "return ticket".
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/29/2016 10:07 am
I think after several cargo mission, first with FH and then MCT. When MCT successfully land on Mars. First crew will arrive without specified return day. There task will be prepare infrastructure and ask for additional resources in  preparation of infrastructure for return trip. Setup ice collection and build and maintain devices to create fuel,build tank for fuel. At the moment finishing task and prepare rocket  for return trip some of the crew will start their trip back to Earth. I think when first crew will arrive there  will be not enough fuel to bring them back, they have to build their "return ticket".

That was exactly my thougt too. However Elon Musk has stated that return fuel will be ready when the first crew arrives. Which means everything will need to be done by robots.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 01/29/2016 10:39 am
Blah,, blah... blah
...
...

Undesrtood!
If you were to do a 3D model of the Depot it would just be a 2D (x,y) skeletal frame that is repeated into the third (z) dimension. Below is a sketch of the forward frame for one berth. The small circle is a "pad" for connecting to the nose of the MCT and the large circle is an imaginary volume representing one berth where one MCT is docked. The frames are connected by beams of a certain length in the z dimension. Then this 3D image is duplicated side-by-side to the right to make 5 additional berths until they join on the left side of the first berth. Voila!

Is this?

http://imgur.com/a/KJRna
Nice skill, BSenna.

How many hardpoints per BFS on this structure do you guys envision?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/29/2016 01:09 pm
Now that BSenna has shown us what the propellant depot will look like in Reply #1497 above, we will need to make some adjustments.

First a note about adaptability. When I first proposed this type of depot last year it had an international flavor. I used the imaginary company "LEO Logistics International" as the entity to build and operate the Depot. This was to indicate that this should be an international project and not restricted to any one country. My feeling is that if we are to make the human species interplanetary, no nation and no people will be left behind. This may mean that vehicles constructed by other countries would share the use of the Depot. Because SpaceX is now involved in US military contracts it may not be the best entity to implement this project. Whatever international entity implements this project, it needs an adaptable design that accommodates different vehicles, within reason.

What is the main difference between an openly shared design and a one-country design? It is secrecy. SpaceX must keep under wraps its spacecraft designs and its extensive test results so as to maintain its competitive edge in rocketry. ITAR regulations also play a role. So the Depot should be able to service a vehicle at the Depot without requiring too much inside information: a service station that doesn't need to know what's under the hood.

What are the compatibility requirements for the Depot to service the MCT or a similar craft?
1. The craft must utilize LOX and LCH4 as fuel.
2. It must have a diameter compatible to the diameter of the Spacex MCT diameter. Today we think that will be about 15 m, but a range up to 19 m is probably doable. This is because the vehicle lies within a V-shaped berth without actually touching the framework; the only contact is a set of four flexible-length latches that extend from the framework to the vehicle.
3. Two Latch points on the exterior of the vehicle must be within the reach of the two robotic arms that pull the vehicle into its berth.
4. Four latch points on the exterior that are within reach of the four flexible-length latches.
5. Accessible fuel ports. The current Depot design assumes a capsule shape at the end and fuel ports through the nose cone. Alternatively, if MCT takes on an biconic shape with TPS on one side then fuel ports will be located on the dorsal (non-TPS) side) and propellant lines will need to be located along the interior cavity of the Depot.
6. Vehicle length within a range that the depot can accommodate. At this time I think about 60 m length is appropriate. If a vehicle is longer than the depot it will stick out at the aft end, but no harm there.  If it is shorter, it just needs to be within reach of the robotic arms and latches.

As much as possible we want the Depot design to adapt to the MCT design rather than vice-versa. Other than that we are "go" for launch and service.
 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 01/29/2016 02:00 pm
An international depot presupposes everyone using the same fuel, which doesn't look like the case at all. Assuming ULA gets ACES tankers off the ground they look to supply LH2. SpaceX is of course going  methane. The Russian Fenix looks  to be a methane "Zenit" (Sputnik News) and clustered for a heavy, but do we know what they'll use once in space if they even use tankers? China??
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CraigLieb on 01/29/2016 02:29 pm
Crazy idea number 854:
Could a fuel depot like this dip a "very long" stiff hose into the atmosphere, pump air up, and make fuel by processing CO2 and/or capturing methane?
Granted it might take a really long time, but is it even technically possible? I assume the power supply to run this would have to be solar. since if it is anything else, you use more fuel than you make most likely.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 01/29/2016 02:37 pm
How heavy would the hose and pumps be? How much drag would it add? How many decades would it need to be running for to manufacture significant fuel?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/29/2016 02:41 pm
An international depot presupposes everyone using the same fuel, which doesn't look like the case at all. Assuming ULA gets ACES tankers off the ground they look to supply LH2. SpaceX is of course going  methane. The Russian Fenix looks  to be a methane "Zenit" (Sputnik News) and clustered for a heavy, but do we know what they'll use once in space if they even use tankers? China??
Good point. Can't please everybody, but BE-4 methane engine will be used for something. What?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 01/29/2016 02:44 pm
The first stage of Vulcan and Blues own launcher, and their uppers use LH2. I haven't seen anything about a BE-4 Vac.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/29/2016 02:44 pm
Crazy idea number 854:
Could a fuel depot like this dip a "very long" stiff hose into the atmosphere, pump air up, and make fuel by processing CO2 and/or capturing methane?
Granted it might take a really long time, but is it even technically possible? I assume the power supply to run this would have to be solar. since if it is anything else, you use more fuel than you make most likely.
No, it isn't feasible. But I do like crazy ideas.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/29/2016 02:50 pm
The first stage of Vulcan and Blues own launcher, and their uppers use LH2. I haven't seen anything about a BE-4 Vac.
Ok, so not compatible with a MCT depot.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/30/2016 12:14 am
No word of a depot from SpaceX.

Depots have a big advantage with hydrogen since hydrogen wants to boil-off really bad, and it takes fancy equipment like a mult-layer sunshield and an active cooler to stop that. But both methane and oxygen are space-storable, meaning with the right type of paint and by keeping your tanks out of direct sunlight (point the long way, butt to the Sun), you can get passive zero boil-off.

So I really don't think SpaceX is planning a depot. But things change.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/30/2016 12:23 am
A depot for the MCT vs fuel transfer from a tanker could offer: slow rotational ulage, helium depot services, liquid nitrogen heat sink for propellant during transfer. If you made such a depot you could probably include liquid hydrogen support at a cost if someone were willing to pay that cost, though it would add complexity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 01/30/2016 12:26 am
No word of a depot from SpaceX.

Depots have a big advantage with hydrogen since hydrogen wants to boil-off really bad, and it takes fancy equipment like a mult-layer sunshield and an active cooler to stop that. But both methane and oxygen are space-storable, meaning with the right type of paint and by keeping your tanks out of direct sunlight (point the long way, butt to the Sun), you can get passive zero boil-off.

So I really don't think SpaceX is planning a depot. But things change.
Well, if an MCT is going to act as the second stage of the BFR, it has to refuel in orbit. And if people launch on the MCT, they can't wait for multiple tankers (i.e. MCTs acting as tankers) to come and fill it up.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: QuantumG on 01/30/2016 12:28 am
Well, if an MCT is going to act as the second stage of the BFR, it has to refuel in orbit. And if people launch on the MCT, it can't wait for multiple tanker MCTs to come and fill it up.

Why not? They're going to be in space for the whole trip to Mars, what's a few more weeks in LEO?  (Speaking of which, do we know if the refuelling is to be in LEO or somewhere else?)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 01/30/2016 12:32 am
Well, if an MCT is going to act as the second stage of the BFR, it has to refuel in orbit. And if people launch on the MCT, it can't wait for multiple tanker MCTs to come and fill it up.

Why not? They're going to be in space for the whole trip to Mars, what's a few more weeks in LEO?  (Speaking of which, do we know if the refuelling is to be in LEO or somewhere else?)
Waiting around in LEO when you're supposed to go to Mars is wasteful for the life support systems.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: QuantumG on 01/30/2016 12:34 am
Waiting around in LEO when you're supposed to go to Mars is wasteful for the life support systems.

Really? Seems like a much cheaper option than depots. Don't get me wrong, I'm all for depots - but because they imply a different architecture to "biggest rocket evar".
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/30/2016 12:37 am
Waiting around in LEO when you're supposed to go to Mars is wasteful for the life support systems.

Really? Seems like a much cheaper option than depots. Don't get me wrong, I'm all for depots - but because they imply a different architecture to "biggest rocket evar".
I don't get the impression that Musk is planning a big rocket just to have a big rocket, but that the size will be perfectly well-justified based on the total IMLEO needed for full-scale MCT operations (on the order of a million tons per year IMLEO).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/30/2016 01:16 am
What if...ionmars'll gonna hate that... The fuel carriers 2, 3 and 4 transfer The fuel directly to carrier 1 one carrier each time, then the 1 transfers to the incoming MCT? Is that feasible?

Concerning a fuel depot standard, soon there will be an international standard discussion, then anyone that intends to build something, will do it using The ISO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: launchwatcher on 01/30/2016 01:49 am
What if...ionmars'll gonna hate that... The fuel carriers 2, 3 and 4 transfer The fuel directly to carrier 1 each time, then 1 transfers to the incoming MCT? Os that feasible?
I was just about to suggest exactly that.   One tanker *is* the depot; you end up doing N launches to put a completely full tanker in orbit, then launch a crew+cargo MCT, fill it from the full tanker, and off we go..

alternatively, you could daisy-chain:
launch tanker #1
launch tanker #2 to rendezvous with #1; transfer from #1 to #2; land #1
launch tanker #3 to rendezvous with #2; transfer from #2 to #3; land #2
(repeat until there is a full tanker in orbit)

launch cargo/crew vessel to rendezvous with tanker #N; transfer fuel, land #N

With that scheme, you do more pumping, but all tankers spend about the same amount of time in orbit..
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/30/2016 03:29 am
What if...ionmars'll gonna hate that... The fuel carriers 2, 3 and 4 transfer The fuel directly to carrier 1 each time, then 1 transfers to the incoming MCT? Os that feasible?
I was just about to suggest exactly that.   One tanker *is* the depot; you end up doing N launches to put a completely full tanker in orbit, then launch a crew+cargo MCT, fill it from the full tanker, and off we go..

alternatively, you could daisy-chain:
launch tanker #1
launch tanker #2 to rendezvous with #1; transfer from #1 to #2; land #1
launch tanker #3 to rendezvous with #2; transfer from #2 to #3; land #2
(repeat until there is a full tanker in orbit)

launch cargo/crew vessel to rendezvous with tanker #N; transfer fuel, land #N

With that scheme, you do more pumping, but all tankers spend about the same amount of time in orbit..

My idea was that tankers reach their design limit of launches and landings. They then get a complete overhaul of the RCS and do their last launch to stay in orbit as depots.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 01/30/2016 07:16 am
Using a BFS tanker variant for orbital depot is thinking small.

Propose using a slightly modified BFR core as prop depot with one Raptor Vac engine.

Send it up to LEO as upper stage on top of a regular BFR with enough prop to make LEO orbit. Fill the depot core up with many later BFS tanker flights. Docked a combination sunshade, solar arrays, radiator arrays, refrigeration and  refueling structure with austere temporary accommodation to it in travel mode. Move to EML-2 assembly location for the Martian Colonial fleet. Detached the support superstructure and re-docked it in the depot mode with the prop depot core. Fill up to 2 BFS at the same time before the BFSs departed for Mars during a launch window.

Other prop depot cores will ferry more propellants to the EML-2 prop depot as needed.

The prop depot core will be able to land like the regular BFR cores for periodic servicing.

Dubbed this propsal as the BFD (Big F@#king Depot :) )


Also a stripped down expendable prop depot core or BFD could be use as a departure stage for high velocity missions to the outer Solar system from EML-2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/30/2016 07:51 am
Using a BFS tanker variant for orbital depot is thinking small.

 :)

I prefer to call it thinking efficiency. It would mainly use existing hardware that has been used to exhaustion for its original purpose. It would mean needing less ullage for fuel transfer. It would mean plenty of depots up there. A small delay in launch and you chose another depot to target. The method would serve well for a few hundred MCT. When it goes into the thousands a bigger depot may become more efficient.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/30/2016 06:08 pm
We've read elsewhere (Reddit) of really HUGE BFRs.  So large that if you filled even a fraction of their height with propellant way over 50 engines would be needed to lift off. Here, the speculation has mostly centered around BFRs with 25-30ish engines.  Still far larger than Saturn V or Nova class.
IF the optimum Raptor engine thrust size still remains ~230 metric tonnes force, is SX looking at possibly smaller, less engine/plumbing complex BFRs in the high teens to 21ish # of engines for most economical sized launchers?  As long as the BFR can put the 2nd stage dry weight into LEO it's big enough.  Or maybe even a couple launches plus in orbit assembly. Cargo, fuel, etc. could launch on subsequent flights.  Of course these "small" BFRs would have to be so much less expensive to build, maintain and fly that many times more refueling flights per Mars transit launch still makes economic sense.  Arguing against my own question, it seems to me that the largest launcher you can build and fly repeatedly would be the most economical.  Flight operations costs are not zero, plus they would include support of LEO propellant & cargo transfer ops.

Given Elon's Day One focus on economics, I find it difficult to believe that size/complexity/cost tradeoffs aren't fundamental to their ongoing architectural analysis.  September's reveal will be beyond interesting.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/30/2016 06:28 pm
And probably, the BFR 1st stage will not be designed for leaving the upper atmosphere.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/30/2016 06:38 pm
And probably, the BFR 1st stage will not be designed for leaving the upper atmosphere.
If you include the ionosphere in that you are correct, but like an F9 RTLS booster I expect it to go above 200km.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/30/2016 06:50 pm
I say, it doesn't have reentry capability. In the first reusable F9 or FH animation, the upper stage was also expected to reenter and landing, but then they decided it doesn't worth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 01/30/2016 07:18 pm
We've read elsewhere (Reddit) of really HUGE BFRs.  So large that if you filled even a fraction of their height with propellant way over 50 engines would be needed to lift off. Here, the speculation has mostly centered around BFRs with 25-30ish engines.  Still far larger than Saturn V or Nova class.

Do you know how big some Nova designs were? There were dozens and dozens of them.
http://astronautix.com/lvs/novamm1c.htm

Nova MM 1C:
Gross mass: 11,516,800 kg (25,390,100 lb).
Payload: 444,000 kg (978,000 lb).
Height: 119.00 m (390.00 ft).
Diameter: 21.00 m (68.00 ft).
Thrust: 144,157.50 kN (32,407,895 lbf).
And this wasn't some internet amateurs' fantasy. It was a study by Martin Marietta.
The F-1A engine was actually built and developmental work done on the M-2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/30/2016 07:45 pm
We've read elsewhere (Reddit) of really HUGE BFRs.  So large that if you filled even a fraction of their height with propellant way over 50 engines would be needed to lift off. Here, the speculation has mostly centered around BFRs with 25-30ish engines.  Still far larger than Saturn V or Nova class.
IF the optimum Raptor engine thrust size still remains ~230 metric tonnes force, is SX looking at possibly smaller, less engine/plumbing complex BFRs in the high teens to 21ish # of engines for most economical sized launchers?  As long as the BFR can put the 2nd stage dry weight into LEO it's big enough.  Or maybe even a couple launches plus in orbit assembly. Cargo, fuel, etc. could launch on subsequent flights.  Of course these "small" BFRs would have to be so much less expensive to build, maintain and fly that many times more refueling flights per Mars transit launch still makes economic sense.  Arguing against my own question, it seems to me that the largest launcher you can build and fly repeatedly would be the most economical.  Flight operations costs are not zero, plus they would include support of LEO propellant & cargo transfer ops.

Given Elon's Day One focus on economics, I find it difficult to believe that size/complexity/cost tradeoffs aren't fundamental to their ongoing architectural analysis.  September's reveal will be beyond interesting.
Shotwell mentioned about BFR a few months ago at the South Summit 2015 (Oct 7-9), in Madrid, " [Falcon Heavy] This one is about 4M pounds of thrust, and the mock... the vehicle that takes us to Mars will be three or four times that size"

https://youtu.be/omBF1P2VhRI?t=10m46s

(original video, mostly Spanish-language conference proceeding, but Shotwell's voice still appears beneath a title graphic for the first ten minutes, though not her face.  The video I linked above seems to have been created a while after this one was promoted, and does a proper cut to her presentation alone)

I also vaguely remember her mentioning offhand that they were developing a 180-210t to LEO superheavy launcher.  I've been trying to find the interview, but can't turn anything up.

There's still some play in those words if you stretch it - is the "vehicle" the stage 1 BFR?  the stage 2 MCT?  Is she referring to thrust or mass?  With that said... a reasonable interpretation is that BFR stage 1 will start out with 24 to 40 500klbf Raptors, with maybe a few extra if they don't start out operations at full thrust.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kch on 01/30/2016 07:49 pm
We've read elsewhere (Reddit) of really HUGE BFRs.  So large that if you filled even a fraction of their height with propellant way over 50 engines would be needed to lift off. Here, the speculation has mostly centered around BFRs with 25-30ish engines.  Still far larger than Saturn V or Nova class.

Do you know how big some Nova designs were? There were dozens and dozens of them.
http://astronautix.com/lvs/novamm1c.htm

Nova MM 1C:
Gross mass: 11,516,800 kg (25,390,100 lb).
Payload: 444,000 kg (978,000 lb).
Height: 119.00 m (390.00 ft).
Diameter: 21.00 m (68.00 ft).
Thrust: 144,157.50 kN (32,407,895 lbf).
And this wasn't some internet amateurs' fantasy. It was a study by Martin Marietta.
The F-1A engine was actually built and developmental work done on the M-2.

... and then there's this wee beastie:

http://astronautix.com/lvs/novagde.htm (http://astronautix.com/lvs/novagde.htm)

:)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/30/2016 07:53 pm
"There's always a bigger fishrocket"

There have been studies of all sorts of things, but the Nova we're talking about is the one that LC39a and b were sized for.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 01/30/2016 08:49 pm
...the Nova we're talking about is the one that LC39a and b were sized for.

My reply was not to you. It was to philw1776, re. his "Nova class":

...Nova class...
"
The stuff he's talking about is the stuff of internet fantasy and he claimed it's "way" bigger than anything of Nova class. It isn't. And these were studies done by aerospace companies, not amateur crowdsourcing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 01/30/2016 09:38 pm
Class was a bad choice of wording on my part.  To clarify, I intended to refer to the Nova that Robotbeat was referring to that NASA sized LC39a and b for.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 01/31/2016 03:00 pm
Since Shotwell has said BFR will be 3x - 4x FH (at most 2x Saturn V) and Musk describes tanker refueling in orbit in the Vance book, that looks like the way they will go.  However, this is going to require many tanker flights for each BFS transit.  Some people have estimated as few as 3-4 tanker flights, but when I run numbers 8 or more seems more realistic.  This means some significant cryocooling equipment to capture boil off for the 80% of propellant that is LOX.  This equipment has not been needed before since up to now cryo propellants have been burned shortly after liftoff.  Cryocooling has been used in orbit for the smaller amounts of cryo liquids used to cool sensitive instruments, but will it scale up very well to handle about 1,000 MT of LOX for a BFS ?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/31/2016 03:23 pm
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 01/31/2016 03:29 pm
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

BTW, note the cryocooling requirement kicks in with just about any orbital refueling architecture, probably even for just 1 tanker flight and propellant transfer.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 01/31/2016 03:31 pm
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

That has been speculated a lot a while back. But Elon Musk has explained that 100t it usable payload, not vehicle mass.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/31/2016 04:04 pm
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

BTW, note the cryocooling requirement kicks in with just about any orbital refueling architecture, probably even for just 1 tanker flight and propellant transfer.

Which argues strongly for a depot from my point of view along with the idea that in the early days when only a few BFRs exist having a depot could allow for a significant increase in the number of BFSs that can launch in one window.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 01/31/2016 04:17 pm
Which argues strongly for a depot from my point of view along with the idea that in the early days when only a few BFRs exist having a depot could allow for a significant increase in the number of BFSs that can launch in one window.

An orbital depot is probably a requirement just because it would be very inefficient for BFS and/or the tankers to have to lug around the cryocooling equipment. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/31/2016 04:29 pm
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 01/31/2016 04:29 pm
In regards to the MCT Depot, I think we are in the early planning stages where general issues can be discussed before any commitments will be made. I am trying to devise a few tools to help the discussion.

Attached is an simple Excel spreadsheet that calculates some data for this purpose. The inputs are the number of berths (Line 2), the assumed diameter of MCT (line3), and the minimum acceptable gravity force at the tank location closest to the depot center (line15). Some of the data of interest to me are depot diameter, the  highest gravity force that will be recorded at the outermost edge of each tank, and the rotational acceleration required to achieve these gravity forces. These are just a few of the factors to be considered. Please check it out.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/31/2016 04:30 pm
Which argues strongly for a depot from my point of view along with the idea that in the early days when only a few BFRs exist having a depot could allow for a significant increase in the number of BFSs that can launch in one window.

An orbital depot is probably a requirement just because it would be very inefficient for BFS and/or the tankers to have to lug around the cryocooling equipment.

It will have to cryocool propellant on Mars, which is more difficult than cryocooling in heliocentric orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/31/2016 04:50 pm
In regards to the MCT Depot, I think we are in the early planning stages where general issues can be discussed before any commitments will be made. I am trying to devise a few tools to help the discussion.

Attached is an simple Excel spreadsheet that calculates some data for this purpose. The inputs are the number of berths (Line 2), the assumed diameter of MCT (line3), and the minimum acceptable gravity force at the tank location closest to the depot center (line15). Some of the data of interest to me are depot diameter, the  highest gravity force that will be recorded at the outermost edge of each tank, and the rotational acceleration required to achieve these gravity forces. These are just a few of the factors to be considered. Please check it out.

That presumes that the depot is made up of BFS elements, one suggestion that I have seen on NFS was using the BFR as the initial tank - roughly the same volume as 4 or 5 BFSs, but now we eliminate a lot of complexity and if we roll the BFR for ulage we have far fewer structural issues.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 01/31/2016 05:04 pm
It will have to cryocool propellant on Mars, which is more difficult than cryocooling in heliocentric orbit.

Good point, The orbital depot is in addition to the depot on the Martian surface.  However, cryocooling on the surface might be easier since the atmosphere could be used for convection, avoiding large radiators that are necessary in a vacuum.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/31/2016 05:53 pm
PSA: Methane and oxygen don't need cryocooling to achieve zero boil off in orbit.

Thank you.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/31/2016 05:59 pm
PSA: Methane and oxygen don't need cryocooling to achieve zero boil off in orbit.

Thank you.

No but they do in transfer operations and to avoid the need for cryocooling to achieve zero boil off in orbit you need a attitude control and reflective shielding and radiative surface area that does not get that radiation reflected back at it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/31/2016 06:05 pm
PSA: Methane and oxygen don't need cryocooling to achieve zero boil off in orbit.

Thank you.

No but they do in transfer operations and to avoid the need for cryocooling to achieve zero boil off in orbit you need a attitude control and reflective shielding and radiative surface area that does not get that radiation reflected back at it.
They don't if both tanks are cool, which can be done passively and without a big sunshield.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/31/2016 06:06 pm
PSA: Methane and oxygen don't need cryocooling to achieve zero boil off in orbit.

Thank you.

No but they do in transfer operations and to avoid the need for cryocooling to achieve zero boil off in orbit you need a attitude control and reflective shielding and radiative surface area that does not get that radiation reflected back at it.
They don't if both tanks are cool, which can be done passively and without a big sunshield.

Excuse me how does it get from one tank to the other then?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/31/2016 06:09 pm
Pressure. Seriously, they already have to worry about hydrazine freezing in tanks. Just paint your spacecraft white and keep it out of the Sun except the skinny way. It'll naturally get that cold.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/31/2016 06:21 pm
Pressure. Seriously, they already have to worry about hydrazine freezing in tanks. Just paint your spacecraft white and keep it out of the Sun except the skinny way. It'll naturally get that cold.
Hydrazine freezes at 2 °C!  (not relevant)

Methane boils at -162 °C and freezes at -182 °C

Oxygen boils at -183 °C and freezes at -219 °C

Nitrogen boils at -196 °C and freezes at -210 °C

Oxygen could in theory with pumping and a heat exchange unit be your heat sink for the methane that was being moved around, but Nitrogen is more likely to be used just as it is here on earth.

If you use pressure then it is not zero boiloff you will be venting the destination tank, heat will still be added going through small openings, and the system still requires a lot more than just a coat of white paint and you can't be pointed away from both the sun and the earth at the same time.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 01/31/2016 06:33 pm
If the receiving tank is below boiling point, it'd have a lower pressure and could actually condense the propellant. No venting required.


Also remember that the figures you're using are at STP. Higher boiling point at 100psi ullage pressure.

Anyway, it's well understood that methane/LOx are "space storable" as XCOR advertises. Sick of arguing with people thinking that because boiloff s big for hydrogen that it must also be for methane and oxygen.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 01/31/2016 06:42 pm
If the receiving tank is below boiling point, it'd have a lower pressure and could actually condense the propellant. No venting required.


Also remember that the figures you're using are at STP. Higher boiling point at 100psi ullage pressure.

Anyway, it's well understood that methane/LOx are "space storable" as XCOR advertises. Sick of arguing with people thinking that because boiloff s big for hydrogen that it must also be for methane and oxygen.

Why has LOX/RP-1 (or even LOX/methane) historically not been used for delayed burn operations, which have almost always, if not always, used hydrazine?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 01/31/2016 06:45 pm
If the receiving tank is below boiling point, it'd have a lower pressure and could actually condense the propellant. No venting required.

So how did the pressure in the receiving tank drop so low that there is no displaced volume as you fill that tank?

So at what rate do you transfer so that the energy being added as you transfer the propellant is below the rate at which the added energy is radiated away?

How do you pressurize the source tank without heating the propellant being transferred?

Also remember that the figures you're using are at STP. Higher boiling point at 100psi ullage pressure.

100psi ulage pressure on the source tank, so now it needs to cool on the receiving side. How quickly can the heat added by transfer be radiated away? When the sun is above the horizon? or with just the radiative heat load from the earth.
Anyway, it's well understood that methane/LOx are "space storable" as XCOR advertises. Sick of arguing with people thinking that because boiloff s big for hydrogen that it must also be for methane and oxygen.

There is a difference between being storable 3 or 4 diameters out from Earth and in LEO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 01/31/2016 08:30 pm
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.
How do the rest of you account for this?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 01/31/2016 08:44 pm
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.
How do the rest of you account for this?

They are basing the number on a hypothetical 100 day one way flight to a Mars colony that is already operational. No need to send 100 crew if there is nowhere to go. Other flights and ISRU will provide the supplies at the colony.

25 tons / 100 people / 100 days = 2.5 kg / person / day for the BFS one way flight to Mars.

12 tons / 4 people / 1030 days = 2.9 kg / person / day for the NASA conjunction mission.

That's only a 16% difference. Close enough for an estimate.

Early BFS missions will have a small crew and will need supplies for the entire mission. Say about 24 tons for 8 crew.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 01/31/2016 09:19 pm
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.

Thanks for the article, I was asking because I really have no idea. Even the term consumables. I wasn't considering gases ansd water, and just on the first leg trip, about 6 months. Disposal manaement, personal pelongings, even clothes should be designed to fit in the mission imo, so it's maybe closer to 35 -40 t as I (not considering H˛O, O˛ et al).

Anyway, this 100 crew mission, is further in the future, not in the 11, 12 years time frame. I've just seen this:

http://www.thespacereview.com/article/2909/1
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 02/01/2016 02:29 am
In regards to the MCT Depot, I think we are in the early planning stages where general issues can be discussed before any commitments will be made. I am trying to devise a few tools to help the discussion.

Attached is an simple Excel spreadsheet that calculates some data for this purpose. The inputs are the number of berths (Line 2), the assumed diameter of MCT (line3), and the minimum acceptable gravity force at the tank location closest to the depot center (line15). Some of the data of interest to me are depot diameter, the  highest gravity force that will be recorded at the outermost edge of each tank, and the rotational acceleration required to achieve these gravity forces. These are just a few of the factors to be considered. Please check it out.
What is the safety circle in ths case?
What is the fuel volume/mass in the depot?
Are we talking about fuelling 9 ships at a time?
Is this a modification of the six shooter depot?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stardhingy on 02/01/2016 02:58 am

Why has LOX/RP-1 (or even LOX/methane) historically not been used for delayed burn operations, which have almost always, if not always, used hydrazine?

The ease of lighting and reliability of hypergolic engines is probably the major consideration.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 02/02/2016 12:37 am
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.
How do the rest of you account for this?

Depends on your assumptions for "closed loop".

3 tons per person for ~1000 days isn't a very good closed loop. A person needs about 5 kg/day of life support consumables, so 3000 kg for 1000 days means you only save 40% with the closed loop... huh?

Also, the MCT is probably carrying supplies for 100-250 days (depending on transit length) not 1000. Remember there are supposed to be ~10 cargo missions per crew mission (or something like that).

Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 02/02/2016 02:47 am
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.
How do the rest of you account for this?

Depends on your assumptions for "closed loop".

3 tons per person for ~1000 days isn't a very good closed loop. A person needs about 5 kg/day of life support consumables, so 3000 kg for 1000 days means you only save 40% with the closed loop... huh?

Also, the MCT is probably carrying supplies for 100-250 days (depending on transit length) not 1000. Remember there are supposed to be ~10 cargo missions per crew mission (or something like that).
As you can see in the joined graph (Ames research center trajectory browser), most synods offer 120 to 180 day missions to Mars.  So if you do the math, you will find 52 tonnes of consumables for 180 days with 5 kg/person.  As mentionned by others, you will only be having 100 passengers when there is a base in place, so the rest of the trip time is not applicable.
To reduce to 25 tonnes you need to go to dehydrated foods, and do some fierce water and atmospheric recycling.  But that equipement will be essential on Mars, so it should be part of a colony package.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 02/02/2016 03:05 am
My guess is the breakdown of the 5 kg is :
0,7 kg of oxygen, turned into CO2
3 kg of water
1,3 kg of food,
So there would be no allocation for recycling at all?

The oxygen can be recycled from CO2 using the sabatier process and some hydrogen, either stock of from the water coming from the food combustion.  As long as the unit weighs less that ,7*100*180 = 14 tonnes, including solar cells to run it, then we're ahead on that.

The water should be easy, the ISS already does that.  We need to treat 300 kg per day, plus whatever is used for sanitation and cleaning.  We can allow for some of it to get dirty, since even dirty water will be a good Martian import.  Again 5x100x180 = 52 tonnes, and we should be able to have a good cleaning system for much less mass than that.

The food will become compost.  It'll be recycled on the colony.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/02/2016 03:43 am
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.
How do the rest of you account for this?

Depends on your assumptions for "closed loop".

3 tons per person for ~1000 days isn't a very good closed loop. A person needs about 5 kg/day of life support consumables, so 3000 kg for 1000 days means you only save 40% with the closed loop... huh?

Also, the MCT is probably carrying supplies for 100-250 days (depending on transit length) not 1000. Remember there are supposed to be ~10 cargo missions per crew mission (or something like that).
As you can see in the joined graph (Ames research center trajectory browser), most synods offer 120 to 180 day missions to Mars.  So if you do the math, you will find 52 tonnes of consumables for 180 days with 5 kg/person.  As mentionned by others, you will only be having 100 passengers when there is a base in place, so the rest of the trip time is not applicable.
To reduce to 25 tonnes you need to go to dehydrated foods, and do some fierce water and atmospheric recycling.  But that equipement will be essential on Mars, so it should be part of a colony package.
...one of the reason I dislike that tool is that it isn't really made for looking for short transits, and the numbers you get can be very misleading (including how it optimizes things) unless you're really careful. Just keep in mind that it's not telling you the limits of what can be done. In actuality, 100 day transits are available except for maybe 20% of synods, and even then opportunities are available for less than 120 days.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 02/02/2016 07:03 am
Some people are getting way off base on consumables, here.  We already have nearly total water and air closure and dehydrated food of around a kg a day is already the norm.

We are on the verge of getting that to the point where the metabolic byproducts of the food will be able to make up the losses of air and water at which point these will become de-facto fully closed when packaged food is being consumed, and on Mars we can certainly obtain them from the environment at greater then the loss rate if we expect to be making return Propellants in volume.

Most of the remaining consumables are packaging materials, clothing, toiletries, and spare parts.  The way to drive them down is things like developing space-laundry, more efficient bulk food packaging rather then individual MRE like meals, and more reliable systems using a common pool of highly interchangeable spare-parts.

The consumable masses can certainly come down but it will be done with techniques that will be from the efficiency of scale associated with a large crew size where a true 'galley' and 'laundry' area can exist.  You won't see much per-capita consumable mass reductions until the crew sizes get up into the mid 20's.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/02/2016 02:18 pm
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.
How do the rest of you account for this?

Depends on your assumptions for "closed loop".

3 tons per person for ~1000 days isn't a very good closed loop. A person needs about 5 kg/day of life support consumables, so 3000 kg for 1000 days means you only save 40% with the closed loop... huh?

Also, the MCT is probably carrying supplies for 100-250 days (depending on transit length) not 1000. Remember there are supposed to be ~10 cargo missions per crew mission (or something like that).
My guess is the breakdown of the 5 kg is :
0,7 kg of oxygen, turned into CO2
3 kg of water
1,3 kg of food,
So there would be no allocation for recycling at all?

The oxygen can be recycled from CO2 using the sabatier process and some hydrogen, either stock of from the water coming from the food combustion.  As long as the unit weighs less that ,7*100*180 = 14 tonnes, including solar cells to run it, then we're ahead on that.

The water should be easy, the ISS already does that.  We need to treat 300 kg per day, plus whatever is used for sanitation and cleaning.  We can allow for some of it to get dirty, since even dirty water will be a good Martian import.  Again 5x100x180 = 52 tonnes, and we should be able to have a good cleaning system for much less mass than that.

The food will become compost.  It'll be recycled on the colony.
Why are you guys guessing and assuming and conjecturing when you could just be reading the NASA technical report on the subject I conveniently linked and picking apart individual numbers therein?

One snippet from the report states that water needs are filled mostly by food water content based on presentday space-food menus:
Quote
Although overall water recovery rates are less than 100% for the assumed ECLSS system, there is a net surplus of water produced. This surplus occurs because additional water is added to the system in the form of water in the food that the crew consumes. Although the food is “dehydrated” it still contains approximately 28% water. The result is that, under the assumptions made for the study, no additional water needs to be added to satisfy water or oxygen generation requirements. Further closure of the ECLSS system will not reduce total logistics requirements.

Quote
Water reclamation from H2O contained within food promotes water-rich operating conditions for the partially closed ECLSS. As such, only 30 days of contingency water and oxygen were required to be delivered with the habitat, resulting in 362kg and 99kg of water and oxygen required
respectively

On the other hand, long-run hygiene and laundry needs in excess of this report are something I've heard speculation about.

From their future possibilities section, it sounds like going from 3kg per person*day to 2kg per person*day is probably doable with compromises on food palatability, much better container design, better loop closure, lighter weight waste management, and a few other things, but more is pushing it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 02/02/2016 02:49 pm
>
On the other hand, long-run hygiene and laundry needs in excess of this report are something I've heard speculation about.

 A supercritical CO2 washer unit requires no water, which also eliminates the dryer and any humidity or airborn lint issues..
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/02/2016 03:08 pm
I drink Spylent quite often. Less than 500grams per day are needed for complete nutrition, and you should be able to get that safely less than 400 grams by replacing some of the carbs with more fats. Some people live solely off of Soylent.

It then just becomes a question of how good your water recycling system is, and there's no limit there except at some point improving it further isn't worth it from a mass standpoint.

There's no fundamental reason you can't get the consumables mass per person down below 1kg/day.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/02/2016 03:23 pm
One snippet from the report states that water needs are filled mostly by food water content based on presentday space-food menus:


"Water needs filled mostly by food water" and "presentday space-food menus". Two invalid assumptions if I ever saw any. Certainly for the 100 passenger transfer and probably for early flights too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/02/2016 03:53 pm
Maybe the "100 t payload" is the total land mass, a 60 t dry mass mct 25 t 100 people (+their goods and consumables) and 15t cargo or more cargo and less people. You engineering fellows, is that feasible with 3-4 refueling cargos?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf offers 12 tons consumables budget for a 4-person conjunction-class (1030 day) Mars mission using closed-loop ECLSS.  You're offering 25 tons for 100 people.
How do the rest of you account for this?

Depends on your assumptions for "closed loop".

3 tons per person for ~1000 days isn't a very good closed loop. A person needs about 5 kg/day of life support consumables, so 3000 kg for 1000 days means you only save 40% with the closed loop... huh?

Also, the MCT is probably carrying supplies for 100-250 days (depending on transit length) not 1000. Remember there are supposed to be ~10 cargo missions per crew mission (or something like that).
A) Where do you get 5kg/day?
B) Wait, what?  10 cargo missions per crew mission... of MCT?  1000 tons of cargo landed on the surface per 100 tons of manned mission?

And how many propellant missions per crew mission is that?  If you limited it to 6km/s each = 5:1 mass ratio @ 380s (probably not reasonable, given 3.2 C3, 0.5 minimum to MTO, more for single-synod reuse, and largely propulsive SSRP EDL), 40 prop launches to feed 10 cargo launches to feed 1 manned launch with its own 4 prop launches = 0.55 launches per person.

That would mean that a $500k ticket for 100 people per MCT needs to cost not $50M/launch, but ~$1M/launch.

Chain the math together.  Is this credible?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 02/02/2016 04:25 pm
One must have bulk food for proper intestinal function.  Fiber.  It can be filled with dry grains such as oatmeal, whole wheat, wild rice, and such.  But frozen vegetables also.  A space freezer can be an air lock opened to space for some foods. 

I think before 100 people can go to Mars, smaller 4-12 people will go to set up ISRU equipment, solar systems, find water, etc.  Then cargo ships will bring supplies for storage, habitation units, more solar power systems, etc.  After a base is established, then 100 people can come.  Then they can receive more cargo and set up more habitation units, greenhouse units, etc.  Like someone said 10-1 cargo vs people.  A few I think will come with the cargo to get everything set up for the first group of colonists.  Then they will return while these colonists set up everything for the next group and so on.  I see people only staying a few years at first, then return to earth. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/02/2016 04:28 pm
Soylent includes fiber.

Remember, this is for 3 months, not for surface living.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 02/02/2016 11:49 pm
Soylent includes fiber.

Remember, this is for 3 months, not for surface living.

Trying to save consumable mass by reducing the palatability of food ranks up their with pure oxygen atmospheres in the 'gram wise, kilo foolish' category of space speculation.

Food has been consistently rated the most important morale boosting thing Astronauts get, this is why NASA has spent so much effort in improving it's quality and done away with tubes of goo.  The mass is WELL worth it.  And it is not even a significant mass savings either, an astronaut on average consumes 1 kg per day of actual dry foodstuffs (an astronauts calorie consumption ranges from 2000 to 3000 calories a day a 50% increase over your calorie estimate).   The dry powder your proposing is going to be between 500g - 750g per day according to the products nutritional information.  Thus squares with the earlier reference that astronauts freeze-dried food still contains 28% water.  So the savings would only amount to that water difference because the powdered food product is completely desiccated.

So the savings are just 500g - 250g per day in the raw foodstuff itself at the cost of what would likely be a horrendous loss in morale.  While their would certainly be some potential for savings in packaging mass with a powdered product it would all come from using bigger pouches and containers, if it were packaged as individual servings it would be no improvement over the current food system of individual serving pouches.  Some packaging system that combines a full meal for several dozen people would be needed to get any real savings in packaging, but even this would have potential to negatively impact morale as individuals would lose the ability to choose what and when they eat individually.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/02/2016 11:55 pm
People can pay more for more food, then. Problem solved. But for those willing to skimp, save $10,000-100,000 and go with Soylent on the way there, that option should be available to them.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesG123 on 02/03/2016 02:29 am
People can pay more for more food, then. Problem solved. But for those willing to skimp, save $10,000-100,000 and go with Soylent on the way there, that option should be available to them.

And they'll be barking mad and stealing other people's food and toothbrushes by the time they get to Mars.

Besides, you would need to carry a lot of extra people if you are going to use Soylent as a food supply.  ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: llanitedave on 02/03/2016 02:35 am
Soylent tends to increase flatulence, from what I've read.  We really don't want unpleasant conditions for all during the trip.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesG123 on 02/03/2016 02:40 am
Soylent tends to increase flatulence, from what I've read.  We really don't want unpleasant conditions for all during the trip.

They can just open a window.  ;D
Title: Re: MCT Speculation and Discussion Thread 4
Post by: launchwatcher on 02/03/2016 02:58 am
Soylent tends to increase flatulence, from what I've read.  We really don't want unpleasant conditions for all during the trip.

They can just open a window.  ;D
They wouldn't let another methane source go to waste, would they?


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/03/2016 03:03 am
"Why would anyone want to live on Mars?? I wouldn't want to! This is a fool's errand and should be stopped!"
"Why would anyone want to just drink Soylent?? I wouldn't want to! This is a fool's errand and should be stopped!"



You all are going to make me into a Ron-Paul-loving libertarian!

(I can see QuantumG and jongoff smiling right now.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 02/03/2016 04:13 am
I agree that going to a super restricted diet wouldn't be good. But consumables mass could still be quite low without that extreme.

A) Where do you get 5kg/day?

Basic human life support requirements per day are about 5kg - less than 1kg oxygen, less than 1kg dry food, and over 3kg water (including water in food).

This assumes either doing something other than normal bathing, or 100% recycling of cleaning water.
Quote
B) Wait, what?  10 cargo missions per crew mission... of MCT?

I believe Musk tweeted that.

Quote
And how many propellant missions per crew mission is that?

I don't know... depends on the size of MCT and the architecture.

Quote
If you limited it to 6km/s each = 5:1 mass ratio @ 380s (probably not reasonable, given 3.2 C3, 0.5 minimum to MTO, more for single-synod reuse, and largely propulsive SSRP EDL), 40 prop launches to feed 10 cargo launches

That assumes that the MCT arrives in LEO empty.

If BFR is really too large for any existing pad, I would expect MCT to either go to a higher energy orbit than LEO or arrive with significant propellant.

But cost per launch will nonetheless have to be incredibly low by current standards.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 02/03/2016 04:15 am
"Why would anyone want to live on Mars?? I wouldn't want to! This is a fool's errand and should be stopped!"
"Why would anyone want to just drink Soylent?? I wouldn't want to! This is a fool's errand and should be stopped!"

Rare people will willingly do all kinds of bizarre things, but if Musk wants a colony of millions (who can all spend $500k - ruling out lots of the people who might want to go) the conditions have to be not *that* bad.

EDIT: For something like Mars Direct, austere conditions make sense, since you can be extremely selective if you're only sending 4 people.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/03/2016 04:45 am
If you're going to Mars for years, drinking a protein shake on the way is going to be the very least of your psychological worries, I PROMISE you. Ridiculous.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 02/03/2016 05:04 am
If you're going to Mars for years, drinking a protein shake on the way is going to be the very least of your psychological worries, I PROMISE you. Ridiculous.

Isn't that practically how some popular diets work these days? :)

And I agree with others... Flatulence is a great resource for ISRO production of propellant.  ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/03/2016 09:59 am
Flatulence is a great resource for ISRO production of propellant.  ;)

You think India is building a methane engine? ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/03/2016 10:42 am
If you're going to Mars for years, drinking a protein shake on the way is going to be the very least of your psychological worries, I PROMISE you. Ridiculous.

Might as well send people there naked too, or at least in briefs. The mass of clothes adds up. Shave everybody bald before the flight... could save 500gm or so for people with long hair. Offer lower prices to women since they have lower life support requirements and mass less and take up slightly less space. Pre-launch laxatives to clear the digestive systems of unneeded mass and minimise the upchuck on-orbit. Repurpose privacy partitions to be worn as clothes. Acceleration couches may as well be removed to be used as furniture on the surface. But why acceleration couches? Surely a hammock is just as good. Which can be turned into partitions. Which can be turned into clothes on arrival...

It will certainly be smelly aboard these MCTs.

Hmmm. Lots of unpleasant things I can do to these econocolonists.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Krevsin on 02/03/2016 11:18 am
If you're going to Mars for years, drinking a protein shake on the way is going to be the very least of your psychological worries, I PROMISE you. Ridiculous.
I am reminded of a proverb involving the backs of camels, straws and breaking.

People will tolerate a lot of discomfort, but what will finally break a person is usually something seeming relatively petty in the grand scheme of things.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/03/2016 11:29 am
I am reminded of a proverb involving the backs of camels, straws and breaking.

People will tolerate a lot of discomfort, but what will finally break a person is usually something seeming relatively petty in the grand scheme of things.

Yes, but we are talking about a few months of transfer. That the diet on Mars needs to be a lot better for colonists I think no one would dispute. I don't think that Soylent is the way to go but it is an option for the trip.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesG123 on 02/03/2016 11:44 am
Hmmm. Lots of unpleasant things I can do to these econocolonists.

It would make for spectacular "Mars One" ratings... :o
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Krevsin on 02/03/2016 12:48 pm
I am reminded of a proverb involving the backs of camels, straws and breaking.

People will tolerate a lot of discomfort, but what will finally break a person is usually something seeming relatively petty in the grand scheme of things.

Yes, but we are talking about a few months of transfer. That the diet on Mars needs to be a lot better for colonists I think no one would dispute. I don't think that Soylent is the way to go but it is an option for the trip.
"A few months" is still a very long time for a human to live through. Remember, there's not much to really do during the transfer. Sure, there's exercise, some leisure activities (reading, watching TV, various games, et cetera) and the occasional maintenance work to occupy your time. Boredom might be a serious morale issue and you do not want to compound that issue with a bland diet.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/03/2016 01:29 pm
I agree that going to a super restricted diet wouldn't be good. But consumables mass could still be quite low without that extreme.

A) Where do you get 5kg/day?

Basic human life support requirements per day are about 5kg - less than 1kg oxygen, less than 1kg dry food, and over 3kg water (including water in food).

This assumes either doing something other than normal bathing, or 100% recycling of cleaning water.
Quote
B) Wait, what?  10 cargo missions per crew mission... of MCT?

I believe Musk tweeted that.

Quote
And how many propellant missions per crew mission is that?

I don't know... depends on the size of MCT and the architecture.

Quote
If you limited it to 6km/s each = 5:1 mass ratio @ 380s (probably not reasonable, given 3.2 C3, 0.5 minimum to MTO, more for single-synod reuse, and largely propulsive SSRP EDL), 40 prop launches to feed 10 cargo launches

That assumes that the MCT arrives in LEO empty.

If BFR is really too large for any existing pad, I would expect MCT to either go to a higher energy orbit than LEO or arrive with significant propellant.

But cost per launch will nonetheless have to be incredibly low by current standards.

Why would an MCT arrive in LEO (with around 200 tons, per Shotwell) packing 50 tons of propellant in place of 50 tons of gear?  When half of you are performing increasingly desperate reasoning-from-first-principles and begging-the-question ("Oh come on, I can drink 3000 calories of vegetable oil...") to reject NASA's estimate of consumables?  When 50 tons of propellant would send MCT... directly into the inner Van Allen belt and no further?  What does BFR being too large for any existing pad have to do with it?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/03/2016 02:24 pm
I drink Soylent for lunch. This is not "drinking 3000 Calories of vegetable oil."

Building a colony transporter with the economics needed to make it feasible is not something that has ever been done before. It most CERTAINLY will involve thinking from first principles, as Musk is wont to do.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 02/03/2016 04:03 pm
I drink Soylent for lunch. This is not "drinking 3000 Calories of vegetable oil."

Building a colony transporter with the economics needed to make it feasible is not something that has ever been done before. It most CERTAINLY will involve thinking from first principles, as Musk is wont to do.
The first principle in Musk's mind is cost followed by almost eliminating training, which is also a major cost. That would include using normal diet, fresh like foods. Each MCT would need a core group that is the operator/maintainers but most of the group of 100 are just passengers along for the ride with little training. Many of the specialists/crew may not be colonists and return. Similar to a ocean passenger ship crew.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/03/2016 04:44 pm
I drink Soylent for lunch. This is not "drinking 3000 Calories of vegetable oil."

Building a colony transporter with the economics needed to make it feasible is not something that has ever been done before. It most CERTAINLY will involve thinking from first principles, as Musk is wont to do.
The first principle in Musk's mind is cost followed by almost eliminating training, which is also a major cost. That would include using normal diet, fresh like foods. Each MCT would need a core group that is the operator/maintainers but most of the group of 100 are just passengers along for the ride with little training. Many of the specialists/crew may not be colonists and return. Similar to a ocean passenger ship crew.
The NASA estimates are nowhere near a normal diet or fresh-like foods.  Those foods are shelf-stabilized in some way, and there's no food freezer or refrigerator, and they're dehydrated wherever it's practical.   28% water content by mass is extremely low for foods that can be eaten without only a minimal kitchen.

http://www.cnet.com/news/houston-we-have-a-tortilla-problem/

While we're on that example, how much water content is in the food *you* eat?

Let's take a typical flour tortilla from a supermarket:
http://www.caloriecount.com/calories-mission-foods-8-premium-flour-i99186

These are bland, highly refined foods that we would expect to be almost completely digestible;  Subtract the macronutrients from the weight and you will find a decent estimate for water content.  We actually tend to lump the indigestible vegetable matter into carbs as 'fiber'.

(47g weight - (18g carbs + 3g protein + 3g fat)) / 47g weight = 49% water by mass.  While typically you put something wet on one, I can just about palatably eat a flour tortilla dry (unlike a corn tortilla).


How about something we already dehydrate?  Grapes / raisins are probably the most popular.

http://nutritiondata.self.com/facts/fruits-and-fruit-juices/2050/2

(165g weight - 138g macronutrients) / 165g weight= 16% water by mass.


Maybe something we tend to keep on the shelf?  How about dry rice?  Hell, we use that to literally dehydrate things (like phones) that get too much water on them, by sucking moisture out of the air.

http://nutritiondata.self.com/facts/cereal-grains-and-pasta/5711/2

1 - 162/185 = 12.4% water by mass.

When we cook it:

http://nutritiondata.self.com/facts/cereal-grains-and-pasta/5804/2

we raise it to 1-(45+4)/158 = 69% water by mass.


Let's try a shelf-stabilized energy bar (designed to be a precooked meal replacement sitting next to your water bottle):

http://www.clifbar.com/products/clif-bar/clifbar/banana-nut-bread#nutrition

1-58/68= 15% water by mass.  Impressive.




Continuing on, how about what I just had for breakfast?


Eggs

http://nutritiondata.self.com/facts/dairy-and-egg-products/120/2

1-56/220 = 75% water


Bread

http://nutritiondata.self.com/facts/baked-products/4876/2

1-17/28 = 39% water


Banana

http://nutritiondata.self.com/facts/fruits-and-fruit-juices/1846/2

1 - 54/225 = 76% water
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/03/2016 04:50 pm
I drink Soylent for lunch. This is not "drinking 3000 Calories of vegetable oil."

Building a colony transporter with the economics needed to make it feasible is not something that has ever been done before. It most CERTAINLY will involve thinking from first principles, as Musk is wont to do.
The problem is not thinking from first principles, it's rejecting actual research that's been done and the optimum that's been chosen in a program where every kilogram costs $30,000 extra, which has plenty of incentive to minimize mass and ramp up the ECLSS;  And ensuring everyone that this is all an irrelevant, useless assessment, because you choose to drink Soylent for lunch sometimes.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 02/03/2016 05:05 pm
I drink Soylent for lunch. This is not "drinking 3000 Calories of vegetable oil."

Building a colony transporter with the economics needed to make it feasible is not something that has ever been done before. It most CERTAINLY will involve thinking from first principles, as Musk is wont to do.
The problem is not thinking from first principles, it's rejecting actual research that's been done and the optimum that's been chosen in a program where every kilogram costs $30,000 extra, which has plenty of incentive to minimize mass and ramp up the ECLSS;  And ensuring everyone that this is all an irrelevant, useless assessment, because you choose to drink Soylent for lunch sometimes.

Yes, a lot of effort has gone into this subject. No need to throw that reseach out the airlock. NASA has a variety of dehydrated foods that are very mass efficient. So does private industry. While Soylent or something like it can be part of the food selection, there is no reason to make it the only food.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/03/2016 05:45 pm
Another interesting food tidbit:

http://www.pbs.org/newshour/updates/astronauts-crave-tabasco/

Apparently microgravity nasal congestion dulls the sense of smell aboard the ISS, so despite problems with wafting odors, familiar foods tend to taste unpleasantly sweet or bland ("like plastic"), and astronauts tend to go in heavy on the spicy stuff.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 02/03/2016 08:13 pm
A space freezer can be an air lock opened to space for some foods.

No it can't. "Space" isn't cold. It's a vacuum. If you keep your food in an open airlock, it will have the same temperature as any other section of the ship's hull, which will be whatever temperature it is radiating at. (Probably room-temperature, for obvious reasons.)

Food has been consistently rated the most important morale boosting thing Astronauts get

Astronauts are crew. Crew morale is important. Colonists are cargo. Only their survival rates matter.

But seriously, I think people are getting themselves knotted up over this. Things like Soylent merely give you a simple number to use as your starting point. If you can't close your case with such products, you ain't gonna do better with more reasonable foods. Now once you've crossed your eyes and dotted your tea, if you still have mass budget left over, by all means add some tinned tomatoes or an entire greenhouse module. But you have to start somewhere.

(Musk himself may just end up adding an extra supply ship, because "fuel is cheap".)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/03/2016 09:11 pm
I drink Soylent for lunch. This is not "drinking 3000 Calories of vegetable oil."

Building a colony transporter with the economics needed to make it feasible is not something that has ever been done before. It most CERTAINLY will involve thinking from first principles, as Musk is wont to do.
The problem is not thinking from first principles, it's rejecting actual research that's been done and the optimum that's been chosen in a program where every kilogram costs $30,000 extra, which has plenty of incentive to minimize mass and ramp up the ECLSS;  And ensuring everyone that this is all an irrelevant, useless assessment, because you choose to drink Soylent for lunch sometimes.

Yes, a lot of effort has gone into this subject. No need to throw that reseach out the airlock. NASA has a variety of dehydrated foods that are very mass efficient. So does private industry. While Soylent or something like it can be part of the food selection, there is no reason to make it the only food.
Completely agree.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Hotblack Desiato on 02/03/2016 09:41 pm
Regarding weight and water content in food: how about freeze drying?

It can be done on earth, is a well understood process and reduces the weight of the food.

Of course, not everything can endure freeze drying, for example meat can be freeze-dried, but reconstituting it turns it into a slurry (still edible), although apparently it works with bacon. There are plenty of other types of food which can endure freeze-drying.

A system that cleans water (maybe via active coal, can be regenerated, and reverse osmosis) allows reduction of the mass without losing too much of the quality.

Okay, the quality will be like instant meals (add water and heat), but they are not so bad either. That stuff just needs adjustion to the different environment, as earlier pointed out, it needs to be spicier (will martians be chili-heads?).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 02/03/2016 09:46 pm
..meat can be freeze-dried, but reconstituting it turns it into a slurry.....

I spent a lot of summers of college and grad school working as a wilderness guide. I never had much problem with any kind of freeze dried meat: beef, chicken, ham, shrimp. And I ate a lot of it over the years.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 02/03/2016 09:50 pm
I drink Soylent for lunch. This is not "drinking 3000 Calories of vegetable oil."

Building a colony transporter with the economics needed to make it feasible is not something that has ever been done before. It most CERTAINLY will involve thinking from first principles, as Musk is wont to do.
The problem is not thinking from first principles, it's rejecting actual research that's been done and the optimum that's been chosen in a program where every kilogram costs $30,000 extra, which has plenty of incentive to minimize mass and ramp up the ECLSS;  And ensuring everyone that this is all an irrelevant, useless assessment, because you choose to drink Soylent for lunch sometimes.

Yes, a lot of effort has gone into this subject. No need to throw that reseach out the airlock. NASA has a variety of dehydrated foods that are very mass efficient. So does private industry. While Soylent or something like it can be part of the food selection, there is no reason to make it the only food.
Completely agree.

What's the sodium content of the NASA foods? The commercial versions have near edema inducing levels.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/03/2016 10:24 pm
Nobody seems to be reading the links I posted, so I'll post them again:

An assessment of long-run consumables needs:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150003005.pdf

Two articles on ISS food:

http://www.cnet.com/news/houston-we-have-a-tortilla-problem/

http://www.pbs.org/newshour/updates/astronauts-crave-tabasco/




Regarding weight and water content in food: how about freeze drying?
While freeze-drying saw a number of earlier applications in food processing & medical products, eating freeze-dried food was basically popularized by products developed for NASA's short-duration spaceflights in the 60's.  If you ever go to the NASM you'll probably walk away with souvenir 'Astronaut Ice Cream', developed under contract for NASA in 1968, or a package of freeze dried strawberries.

I think it's still used for some portion of the menu, but a lot of freeze dried food is not very palatable or is hard to rehydrate, per NASA's history of its space food program at:

http://www.nasa.gov/audience/forstudents/postsecondary/features/F_Food_for_Space_Flight.html


What's the sodium content of the NASA foods? The commercial versions have near edema inducing levels.
This is handled in the PBS link.

You can guess that it was roughly in line with the RDA before the ISS program, but... NASA decided during the ISS program that the optical hypertension they were observing in long-duration spaceflight was worrying enough that they cut planned sodium intake by half, eliminating basically all commercial food options.  In my experience commercial canned savory foods, and also many frozen prepared foods and restaurant dishes, tend to have 2 to 10 times as many miligrams of sodium as they have calories of macronutrients;  This ratio has been useful for me in cooking for someone with a 2000mg/d diet (the right ratio is 1:1 on average).  IMO, the only way the US gets away with an average as low as 3400mg a day is by replacement of many savory dishes with heavy use of sugary foods & soft drinks, which the American palate does not require to be salty.

A system that cleans water (maybe via active coal, can be regenerated, and reverse osmosis) allows reduction of the mass without losing too much of the quality.

You're pushing a steam engine on a rocketry program.  The ISS ECLSS is extremely sophisticated, and recovers (if the estimates in the first link are based on that, as I suspect), ~85% of water lost to the toilet, and ~100% of everything else.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 02/03/2016 10:39 pm
I'll eat most any food so long as the place is well stocked with sriracha or habańero sauce. Sign me up.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GalacticIntruder on 02/03/2016 11:11 pm
If you take COTS freeze dried food as an example, you get 1080 servings, which feeds one person 2000 calories per day for 200 days. All of that food only weights around 100kg, minus daily water rations. (which will be 5-10 Liters per person per day)

It is true, that prepared freeze dried meals have SCARY sodium levels. But basic freeze dried bulk staples, like chicken, rice, beans, milk, potatoes, eggs, and other common fruits and vegetables have very little sodium.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Hotblack Desiato on 02/03/2016 11:53 pm
..meat can be freeze-dried, but reconstituting it turns it into a slurry.....

I spent a lot of summers of college and grad school working as a wilderness guide. I never had much problem with any kind of freeze dried meat: beef, chicken, ham, shrimp. And I ate a lot of it over the years.

Good to know, never had to deal with this kind of products.

I worked with another type of freeze dried products (mostly before they were dried, sometimes afterwards). Freeze dried hemophilia products. Once bottled and lyophilized, they were stable for a long period of time. Because of the special nature of these proteins, creating processes was very tricky (A good friend created several of those processes).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 02/04/2016 12:16 am
I have my own dehydrator (nominally meant for making jerky) but I have used it with a variety of veggies to make up food for backpacking. Basically I often carry pasta and rice, packets of dried veggies, spices and herbs that I have mixed up with specific mains and soups in mind but made with what I consider appropriate levels of salt, shredded hard cheese, olive oil, powdered eggs and then sometimes I bring canned/pouched preserved meats and fish to use with all that. I have been known to make up stuff like linquine and clam sauce, vindaloo shrimp, pasta with meat sauce, wild rice with walnuts and cranberries (used up half the fuel I brought for cooking on that one!). But judicious work drying some of my own ingredients allows me the luxury of having less weight efficient meats/fish. Though I do often bring dried shrimp, and sometimes dried tuna flakes.

My friends have brought army rations (too heavy to carry and calorie wise), campers freeze dried foods (as others have pointed out too much salt in those for me to enjoy any amount of them), one friend brings in a thermos full of raw eggs shelled and puts it in a cool stream or spring at night to keep them cool.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/04/2016 06:46 am
I understand NASA requires all the meals to include the full complement of vitamins and minerals at the end of the projected shelf time. They won't consider supplements for that purpose. That will sure drive requirements.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 02/04/2016 10:40 am
ESA recently held a meeting to discuss possible human hibernation:
http://motherboard.vice.com/read/a-brief-history-of-cryosleep (http://motherboard.vice.com/read/a-brief-history-of-cryosleep)
Obviously, that is still fairly speculative technology.  But given the enormous practical burden of carrying large amounts of food/water and handling the resulting huge amount of human waste, it warrants serious consideration for MCT.  Hibernation would also eliminate potential psychological issues, like boredom, in transit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mikelepage on 02/04/2016 12:45 pm
It is stating the obvious IMO that at some point the Mars colony has to account for the system-level reality of growing real food and fully recycling the waste...  Ya know, an ecosystem.

Assuming this much, I think it's useful to ask at what point in time do you start planning for the initial steps to happen?  If you're going to have this discussion, it's also useful not to talk in absolutes, since it's likely even the first missions will at least have some experimental setup designed to produce something which can be consumed, and at the other end of the scale, even centuries from now, there will be some things which cannot be grown on Mars and are still imported from Earth.

Between those two points, theres a t50... at time point at which half the food is grown at Mars, and half is imported.

I think it's likely that if that t50 occurs during the operational lifetime of the MCT (say the next 3 decades), and it's probable that the MCT itself will incorporate a lot of that technology, in which case we can expect the design process would be in progress now.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/04/2016 12:50 pm
ESA recently held a meeting to discuss possible human hibernation:
http://motherboard.vice.com/read/a-brief-history-of-cryosleep (http://motherboard.vice.com/read/a-brief-history-of-cryosleep)
Obviously, that is still fairly speculative technology.  But given the enormous practical burden of carrying large amounts of food/water and handling the resulting huge amount of human waste, it warrants serious consideration for MCT.  Hibernation would also eliminate potential psychological issues, like boredom, in transit.
Hibernation is a dark horse option.  The tiny chance we can get it working multiplied by the huge difference it would make means scaling up a very large space program another 1% looks like a bad investment relative to taking the risk with low-hanging-fruit hibernation research... but it's much, much more speculative than MCT.  It cannot be a critical-path element.

Sci-fi gets exactly three plausible means of interstellar and outer-system spaceflight for biological humans: Hibernation, new-physics FTL or new-physics CoE/CoM breaking engines, and generation ships.  The payoff on hibernation is much, much larger than the payoff on a Mars colony, but the odds of it working are unknowable and only look good relative to the other two options for interstellar spaceeflight.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/04/2016 01:04 pm
It is stating the obvious IMO that at some point the Mars colony has to account for the system-level reality of growing real food and fully recycling the waste...  Ya know, an ecosystem.

Assuming this much, I think it's useful to ask at what point in time do you start planning for the initial steps to happen?  If you're going to have this discussion, it's also useful not to talk in absolutes, since it's likely even the first missions will at least have some experimental setup designed to produce something which can be consumed, and at the other end of the scale, even centuries from now, there will be some things which cannot be grown on Mars and are still imported from Earth.

Between those two points, theres a t50... at time point at which half the food is grown at Mars, and half is imported.

I think it's likely that if that t50 occurs during the operational lifetime of the MCT (say the next 3 decades), and it's probable that the MCT itself will incorporate a lot of that technology, in which case we can expect the design process would be in progress now.

I think Martian agriculture is especially difficult, and will probably not scale to t50 until there are more than 10^6 person-years spent on Mars, and they're in the process of industrializing.

This is a hell of a lot of food sent from Earth, but them's the breaks.  We won't be able to build greenhouses, LEDs, and solar panels from native materials without a large amount of bootstrapping, and I don't think they start to look especially promising to send from Earth, myself.  There's a lot of learning and a lot of adapting and a lot of failed crops to do to get agriculture to the point that Mars can *rely* on it, so even if they do experimental agriculture earlier on, that food won't be mission-critical resources.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 02/04/2016 02:03 pm
Mars could very quickly get to the point where more than 100% of the mass of food consumed on Mars was grown on Mars, and that should be an early goal along with exporting some of that food as soon as their packaging industry has hits the point where packaging materials are locally sourced.  There would still be food imported from earth, but by the time a serious volume of grains and legumes were produced the human diet on Mars could be, by mass, 80-90% locally sourced, that means producing 20% more than they need is all that is needed to go beyond that 100% I mentioned.  If it turns out that it is difficult to grow grains, legumes, fruit, rabbits, chickens, fish, etc in zero G then for a long time there will be a market for Mars produce for micro gravity outposts/expeditions and ones that have yet to develop the CHON ISRU to support their own food cultivation.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/04/2016 02:07 pm
There are other threads where agriculture on Mars would fit far better than here. Look in the general Mars section.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/04/2016 02:33 pm
There are other threads where agriculture on Mars would fit far better than here. Look in the general Mars section.

This is the active thread on those matters. Plenty of interesting posts. Please get the discussion there.

http://forum.nasaspaceflight.com/index.php?topic=35877.0

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 02/05/2016 03:15 am
Sci-fi gets exactly three plausible means of interstellar and outer-system spaceflight for biological humans: Hibernation, new-physics FTL or new-physics CoE/CoM breaking engines, and generation ships.

Interstellar, maybe, but the outer system is entirely plausible without any of the three. You can do Jupiter and Saturn systems at least with nuclear propulsion.

Now, the habitats would have to be long-term, but not generational. There was a NASA study (HOPE - Human Outer Planets Exploration) which had 4-5 year round trip times for Callisto with NTR and NEP, which are both things we could do with no breakthroughs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/05/2016 03:28 am
You don't need hibernation. With the propulsion systems in Avatar, the crew could be awake.

Beamed propulsion is a big enabler (not just for light sails... Could be dust accelerators, etc) and requires megastructures to harness Terawatts or Petawatts. You'd also need to brake against the interstellar medium. A refined sort of fusion rocket or fission fragment rocket might be useful in combination with those other things.

Another thing not mentioned: biological immortality. Engineer the human body to not age, or have an ability to replace tissue as needed (3D printer?).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mikelepage on 02/05/2016 04:00 am
There are other threads where agriculture on Mars would fit far better than here. Look in the general Mars section.

This is the active thread on those matters. Plenty of interesting posts. Please get the discussion there.

http://forum.nasaspaceflight.com/index.php?topic=35877.0

Thanks - I hadn't seen that one.

Last q for this thread: I only brought up the Martian agriculture aspect to ask the question about MCT.  The consensus here seems to be that all food for occupants of MCT will be prepared on either Earth or Mars and preserved for travel.  Does that not seem a strange assumption?  i.e. nothing fresh grown on MCT itself? - Granted if "landing the whole thing" is what's happening, then the mass cost of equipment for trying to grow things over periods of 3-6 months probably isn't worth it.  If however there is a part of the architecture that stays in space for years at a time, being reused constantly, then it will be a lot easier to implement some type of long term system.


 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Geron on 02/05/2016 04:00 am
Mayo clinic today announced they eliminated senescent cells in mice and added 35% more useful high quality life.

When this is applied to humans we could be looking at 120 years of useful life.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 02/05/2016 04:04 am
Why would an MCT arrive in LEO (with around 200 tons, per Shotwell) packing 50 tons of propellant in place of 50 tons of gear?

I was imagining something significantly more than 50 tons.

Quote
What does BFR being too large for any existing pad have to do with it?

Because if I run the rocket equation with 100 tons of payload, dV = 9500 m/s, Raptor's claimed Isp, and dry masses that I consider pretty conservative for SpaceX, I get a rocket that's not that big.

Which suggests to me that the delta-V will be a lot higher - either it'll go to a much higher energy orbit or have quite a bit left.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 02/05/2016 03:49 pm
Why would an MCT arrive in LEO (with around 200 tons, per Shotwell) packing 50 tons of propellant in place of 50 tons of gear?

I was imagining something significantly more than 50 tons.

Quote
What does BFR being too large for any existing pad have to do with it?

Because if I run the rocket equation with 100 tons of payload, dV = 9500 m/s, Raptor's claimed Isp, and dry masses that I consider pretty conservative for SpaceX, I get a rocket that's not that big.

Which suggests to me that the delta-V will be a lot higher - either it'll go to a much higher energy orbit or have quite a bit left.

You are not alone in getting such "not that big" results.  Right now we're all over the map with possibly conflicting  years old Elon statements and crazy big BFR/MCT rumors on Reddit.  But the bottom line is that it does not even take the "mid sized" :) 15 million LB thrust vehicle to meet the LEO payload claims.

Postponing the architecture announcement for the 3rd time indicates to me that everything is in a high state of flux.  They've likely done some next level of detail of engineering analysis and arrived at some key numbers different than expected, which iterates revisions.  With Musk the decisions will not be just space cadet tech driven but will also have a strong best economic model (as he best believes it) influencing size/capability tradeoffs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesG123 on 02/05/2016 11:41 pm

No it can't. "Space" isn't cold. It's a vacuum. If you keep your food in an open airlock, it will have the same temperature as any other section of the ship's hull...


But vacuum is a great insulator. All you need is a layer or two of mylar and minimal contact with the hull and your cold stuff will stay cold for a very long time.


Quote
Astronauts are crew. Crew morale is important. Colonists are cargo. Only their survival rates matter.

I read that novel too.  But...  Colonists are people. It will only take one going koo-koo to jeopardize everyone and the ship.   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stardhingy on 02/06/2016 12:52 am
Why would an MCT arrive in LEO (with around 200 tons, per Shotwell) packing 50 tons of propellant in place of 50 tons of gear?

I was imagining something significantly more than 50 tons.

Quote
What does BFR being too large for any existing pad have to do with it?

Because if I run the rocket equation with 100 tons of payload, dV = 9500 m/s, Raptor's claimed Isp, and dry masses that I consider pretty conservative for SpaceX, I get a rocket that's not that big.

Which suggests to me that the delta-V will be a lot higher - either it'll go to a much higher energy orbit or have quite a bit left.

Don't forget to save fuel for reuse.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/06/2016 12:57 am
BFR is much more than 100 tons to LEO. That much is clearly established.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/06/2016 08:04 am
Don't forget to save fuel for reuse.

Yes, for the tanker. The MCT going forward is something else.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 02/06/2016 08:30 am

You are not alone in getting such "not that big" results.  Right now we're all over the map with possibly conflicting  years old Elon statements and crazy big BFR/MCT rumors on Reddit.  But the bottom line is that it does not even take the "mid sized" :) 15 million LB thrust vehicle to meet the LEO payload claims.

Postponing the architecture announcement for the 3rd time indicates to me that everything is in a high state of flux.  They've likely done some next level of detail of engineering analysis and arrived at some key numbers different than expected, which iterates revisions.  With Musk the decisions will not be just space cadet tech driven but will also have a strong best economic model (as he best believes it) influencing size/capability tradeoffs.

Further analysis and high levels of design flux would mean to me that the architecture is not the kind of brutally simple von Braun eat-your-heart-out kind of thinking most people are imagining.  If that was the design they could announce it now and no one would care if the rockets final size is +/-10%.  I think Musk is going to come up with something vastly more creative then that, something that is to rocketry what hyper-loop is to trains.

I've always said that I see SEP as a big part of the solution and I'd also new and radical EDL solutions, automated propellant production, containerized cargo logistics in the mix as well.  To get anywhere near an efficient low cost system requires full integration of all of these elements together into a fundamentally new arrangement.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 02/06/2016 12:37 pm
BFR is much more than 100 tons to LEO. That much is clearly established.

The 100 tonnes figure was the useful payload landed on Mars IIRC. This is by a ship/lander that will refuel and depart sans 100 tonnes payload. The mass to LEO will vary considerably(though always be much larger than 100 tonnes) depending how refueling is incorporated and how you account for the spaceship itself.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 02/06/2016 01:32 pm
BFR is much more than 100 tons to LEO. That much is clearly established.

The 100 tonnes figure was the useful payload landed on Mars IIRC. This is by a ship/lander that will refuel and depart sans 100 tonnes payload. The mass to LEO will vary considerably(though always be much larger than 100 tonnes) depending how refueling is incorporated and how you account for the spaceship itself.

Yes. The 100 metric tons is payload landed on Mars according to Musk.  The understandable controversy is the dry mass of the stage that makes it to LEO.  I think most estimates are too optimistic (light) for the 1st versions.
 
I see a largish 1st stage booster that goes relatively low & slow as being the easier of the engineering challenges.  The 2nd stage of this supposed TSTO has near but not equal to Earth SSTO performance and is a SSTO when departing Mars' surface.  Add in life support, re-entry speeds and mechanisms for landing on unprepared Mars sites and it's a huge architectural and developmental challenge.  I think that's the part that's in flux, not so much the 1st stage.

I'm also intrigued by the possibility of SEP (mentioned by Gwynne Shotwell) for interplanetary transit and EDL as well, but I'm skeptical because it's yet another R&D $ challenge and I sense from his philosophical comments that Musk wants to keep development architecture as simple, at least in its first decade.  Especially with Musk's avowed 2015 target, I don't see lots of sexy stuff being part of the architecture.  I hope he makes a crewed landing by 2033.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kicaj on 02/06/2016 04:57 pm
Hello.
I have a question, I know you had probably talk about this but I cant find it.
What kind of propulsion will have second stage?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/06/2016 05:06 pm
Hello.
I have a question, I know you had probably talk about this but I cant find it.
What kind of propulsion will have second stage?
We think a bunch of Raptors.  The Falcon 9 uses nine Merlin 1D's in the first stage and a single slightly different Merlin 1D (Vacuum Optimized) in the second stage.

The number of Raptors in the upper stage is a bit dependent on the scale of BFR, and we're in quite some disagreement about that.  With that said, 7 is a nice number that permits a fairly large upper stage (2500 tons or so at Mars Ascent for MarsG+15%, 1000 tons or so at Earth Ascent for EarthG+15%) even with one engine-out & the opposite number throttled.  It's also a convenient packing to fit a vacuum-optimized nozzle as large as possible.

I also harbor admittedly exotic theories that some SuperDracos might come in handy as secondary propulsion.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 02/06/2016 05:22 pm
Technical query for my BFS models.
What's a rational target range for T/W of the 2nd stage at ignition taking into account gravity losses, etc.?
I would expect it could be less than a 1st stage's preferred T/W.
How low can it be at ignition?

I'd also assumed RTLS in my past calculations but have come to believe that the 1st stage will instead land on a floating platform, as less propellant is needed with no boost-back.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 02/06/2016 05:34 pm

I'd also assumed RTLS in my past calculations but have come to believe that the 1st stage will instead land on a floating platform, as less propellant is needed with no boost-back.
Once they came back, they can never come back...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 02/06/2016 06:30 pm
Technical query for my BFS models.
What's a rational target range for T/W of the 2nd stage at ignition taking into account gravity losses, etc.?
I would expect it could be less than a 1st stage's preferred T/W.
How low can it be at ignition?


That really depends on the amount of energy imparted by the first stage, and to a lesser extent the angle: if the first stage leaves off at 3km/s at a 45° angle, then the vertical component is 2.1km/s which on its own would allow the craft to coast to an altitude 210 km higher over a period of 210 seconds (rounded and ignoring the already reduced gravity loss from it trajectory around a sphere). If we had a 2nd stage with an initial T/W ratio of .75 and a final one of 3 then after 210 seconds it would roughly have added 3km/s, be travelling at a velocity that already cuts further gravity losses by more than 50% as it goes around the curved surface of the Earth and have a T/W ratio of more than 1.5 and need to simply maintain altitude so at the start of this period it is moving about 5.1km/s down range, needs to add another 3km/s as its T/W goes from 1.5 to 3 so initially the angle it needs at 5.1km/s headed down range with a 1.5 T/W ratio is 23° to stay at the same altitude which reduces to 0° a mere 2 minutes and 20 seconds later. The gravity loss would be something like 120m/s.

If instead the separation occured at 5km/s at a 20° angle then the vertical component is still over 1.5km/s but your downrange component is around 4.5km/s so you only need another 3.5km/s while you have more than 5 minutes coasting upward on the current trajectory a T/W ratio of less than .25 going to 1 would give you close to the same gravity loss as the previous case.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 02/08/2016 05:55 am
The 3 km/s separation seems to be the more likely scenario and the T/W ratio sounds reasonable at 0.75 so we can extrapolate different masses for the 2nd stage at separation based on an engine count and the target Raptor thrust.

7 Raptors:  16100 kN thrust,  2200 mt mass at separation.
6 Raptors:  13800 kN thrust,  1880 mt mass at separation.
5 Raptors:  11500 kN thrust, 1570 mt mass at separation.
4 Raptors:  9200 kN thrust, 1260 mt mass at separation.

I believe the 5 engine configuration is getting on the small end, my bet would be to use a hexagonal 6 engine arrangement which would provide a space for a smaller central landing engine (I dub this mini engine 'Robin').
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 02/08/2016 06:02 am
The 2nd stage of this supposed TSTO has near but not equal to Earth SSTO performance and is a SSTO when departing Mars' surface.

Can you clarify if you actually mean SSTLMO (to Low Mars Orbit) or SSTTEI (to trans-Earth-Injection).  The latter is what everyone claiming integrated 2nd stage seems to be aiming for and it tends to yield a mars take off mass >1000 mt.  The former is my position and involves SEP transit vehicles or refueling in mars orbit with SEP delivered propellants and keeps mars take-off mass to ~400 mt.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 02/08/2016 02:04 pm
The 2nd stage of this supposed TSTO has near but not equal to Earth SSTO performance and is a SSTO when departing Mars' surface.

Can you clarify if you actually mean SSTLMO (to Low Mars Orbit) or SSTTEI (to trans-Earth-Injection).  The latter is what everyone claiming integrated 2nd stage seems to be aiming for and it tends to yield a mars take off mass >1000 mt.  The former is my position and involves SEP transit vehicles or refueling in mars orbit with SEP delivered propellants and keeps mars take-off mass to ~400 mt.

Sorry about my mis-statement.  I meant SSTEI, the latter with the larger mass at take off.
I'm simply trying to model vehicles based on as I best understand what Musk has said.
However, I believe that the September 2016 mission architecture reveal, raptor thrust, whatever will have changed in the years since the early statements.
It's possible that SEP which SX says they're "looking at" is part of the architecture but given the incredibly early 2025 target date I doubt that additional R&D expense for an interplanetary SEP vehicle will be included.
I continue to believe that available cash flow will be a serious limit to any Mars architecture taking hardware form.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 02/09/2016 03:29 pm
My part in the architecture speculation is the LEO propellant depot. Propellant transfers can be accomplished with little or no depot as long as there are only a few missions during each synod. But when will the volume of traffic to Mars require a larger depot?

To address this question I have been developing a worksheet - see the file attachment below.

The number of launches to LEO and the number of Mars trips will depend on the volume of MCTs of the various types that are produced, the current inventory of each type on Earth, and the rate of return of vehicles from Mars. In table 1 below is a projection over 4 synods, beginning with the first introduction of a prototype during “Synod 0.” In this somewhat conservative projection I assumed a constant production rate of 2 MCTs per year or 4 per 26-month synod with no increase in the rate. I also do not account for any contribution from preliminary Dragon missions that could set up small ISRU propellant facilities on Mars. How realistic is this?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 02/09/2016 04:19 pm
... How realistic is this?

I don't expect an MCT to return until there are people there, various bits of logic for that, but one is inspecting engines, and another is that in the timeline the way I see it that by the time one fully fueled MCT is ready to go, the people are arriving and that means that fuel is reserve for returning crew in a catastrophic situation.

I don't see them sending just one passenger MCT when they first send people. Having an MCT that can support say 24 people to Mars loiter and return to Earth should then suggest sending 24 people in two such MCTs, or if you sent 3 that could hold 12 each then send 8 per MCT for a total of 24. The logistics of returning people then would allow for return flights of manned MCT's part way through the 2nd synod of manned occupation while still maintaining a 100% evacuation fleet on Mars through the next 5 synods, while still returning a large portion of the passenger MCTs (though I see sending them back at conjunctions not doing the rapid return thing).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 02/09/2016 04:28 pm
I think the first MCT will be cargo only.  Solar panels for power and ISRU equipment.  The second one may have a small crew 6-12 people to stay for about 18 months to two years.  They would make sure all equipment works.  MCT for themselves is refueled for return, and also the second one would carry additional equipment and habitat.  This will probably be true for the first few arriving.  Then as equipment for ISRU is operational for fuel, oxygen, water, and modules for living and possibly growing algae with some food, people will start arriving with additional MCT's with even more equipment. 

Maybe even 9-10 MCT's landing robotically with all equipment food, etc, necessary for 100 people to arrive.  Depends on how many MCT's can be built before the first synod, to how many can be build between each synod.  Some people might want to return home, some will stay, some will rotate.  A lot of unknowns. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CraigLieb on 02/09/2016 06:17 pm
...
I read that novel too.  But...  Colonists are people. It will only take one going koo-koo to jeopardize everyone and the ship.   

And if you catch the kook in time, you run a quick experiment to determine how long someone lasts outside the airlock.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 02/09/2016 07:40 pm
...
I read that novel too.  But...  Colonists are people. It will only take one going koo-koo to jeopardize everyone and the ship.   

And if you catch the kook in time, you run a quick experiment to determine how long someone lasts outside the airlock.

HAL9000 did just this in '2001 A Space Odyssey'.  His altruistic research motives were mis-understood by the audience.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: QuantumG on 02/10/2016 11:22 pm
I like the way he listed space tourism as something *other* companies are doing.. and he specifically mentioned orbital space tourism in that list. I'd love to know when SpaceX decided they were too good for this market.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 02/10/2016 11:32 pm
I like the way he listed space tourism as something *other* companies are doing.. and he specifically mentioned orbital space tourism in that list. I'd love to know when SpaceX decided they were too good for this market.

Probably because space tourism doesn't help them with their long term projects. They may have deduced that the cost for SpaceX to get a working tourism architecture going wouldn't equate to a big enough end profit to be worth it in the end. Besides, they have enough projects in the pipeline as-is, including trying to get their LVs off the ground (which has been a little shaky this year so far).

It makes sense for Blue and for VG because they can repurpose architectural elements to help them learn enough to get to orbital launch. SpaceX already knows this. Why would they go back? It doesn't help them to get to BFR.


And yes, Steve counts as a source since he's a major SpaceX investor along with a close business friend of Elon. He watches the space sector closely and has at least a moderate knowledge of how the field works from a technical level and a dominant one from a financial level.  It's safe to hazard that he has access to information that we do not, since he has access to Elon and SpaceX generally that we do not.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/11/2016 12:14 am
It counts as a source, but this page isn't for discussion.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 02/11/2016 10:26 am
I like the way he listed space tourism as something *other* companies are doing.. and he specifically mentioned orbital space tourism in that list. I'd love to know when SpaceX decided they were too good for this market.

By too good, do you really mean not really interested in it because it's not what they want to do?

Or did you deliberately use the phrase "too bad" just to have a strawman dig at SpaceX?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: llanitedave on 02/11/2016 02:23 pm
I like the way he listed space tourism as something *other* companies are doing.. and he specifically mentioned orbital space tourism in that list. I'd love to know when SpaceX decided they were too good for this market.

By too good, do you really mean not really interested in it because it's not what they want to do?

Or did you deliberately use the phrase "too bad" just to have a strawman dig at SpaceX?


"Strawman Digs" is a good user name.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: A_M_Swallow on 02/12/2016 08:35 am
I like the way he listed space tourism as something *other* companies are doing.. and he specifically mentioned orbital space tourism in that list. I'd love to know when SpaceX decided they were too good for this market.


Airlines and aircraft builders like Boeing and Airbus are different companies. The same applies to the builders and operators of ships, buses, trains and taxis. It was only a matter of time before space tourism was separated from launch vehicle construction.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 02/12/2016 12:47 pm

Airlines and aircraft builders like Boeing and Airbus are different companies. The same applies to the builders and operators of ships, buses, trains and taxis. It was only a matter of time before space tourism was separated from launch vehicle construction.

Indeed, they were separate since inception. The world's first  (sorta) hypothetical space tourist vessel (Space Ship 1), could hardly be regarded as something optimised for commercial orbital use. It was however optimised to do what it was meant to do - do multiple big ballistic arcs in a short period of time. Space Adventures are the only ones to use traditional LVs, but only to fill an opportunity left by a pre-existing service.

Blue are some of the first would-be tour providers to step away from rockets with wings (barring Space Adventures) and to head to single stage VTVL suborbital launchers for capsules, which is certainly on the same evolutionary path to commercial orbit, but again, you wouldn't use a New Shepherd to launch crew into LEO or higher.

We can safely divide at this stage commercial rocket manufacturers who make use of their own hardware between those focused on tours, and those focused on transport, with Blue the obvious hybrid.


For English people: You wouldn't take your children for the back of an EWS train, but you would take them on the back of Thomas the Tank engine.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 02/12/2016 01:42 pm
The 3 km/s separation seems to be the more likely scenario and the T/W ratio sounds reasonable at 0.75 so we can extrapolate different masses for the 2nd stage at separation based on an engine count and the target Raptor thrust.

7 Raptors:  16100 kN thrust,  2200 mt mass at separation.
6 Raptors:  13800 kN thrust,  1880 mt mass at separation.
5 Raptors:  11500 kN thrust, 1570 mt mass at separation.
4 Raptors:  9200 kN thrust, 1260 mt mass at separation.

I believe the 5 engine configuration is getting on the small end, my bet would be to use a hexagonal 6 engine arrangement which would provide a space for a smaller central landing engine (I dub this mini engine 'Robin').

Isn't that a bit too big? Wouldn't a 1260 mt BFS second stage, fully fueled, be enough to lift ~200 mt (50% of it being structural mass)?

And for the return trip, a 4 Raptor BFS would have a T/W > 1 in Mars anyway, even with full tanks and cargo.

I like your 'Robin' idea, I wonder if it could be a pressure fed, for safety reasons, lox/methane engine, a bit like the Superdracos but using a different propellant (Hyperdracos, anyone?). You don't need super efficient engines to reach LMO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/12/2016 03:44 pm
The 3 km/s separation seems to be the more likely scenario and the T/W ratio sounds reasonable at 0.75 so we can extrapolate different masses for the 2nd stage at separation based on an engine count and the target Raptor thrust.

7 Raptors:  16100 kN thrust,  2200 mt mass at separation.
6 Raptors:  13800 kN thrust,  1880 mt mass at separation.
5 Raptors:  11500 kN thrust, 1570 mt mass at separation.
4 Raptors:  9200 kN thrust, 1260 mt mass at separation.

I believe the 5 engine configuration is getting on the small end, my bet would be to use a hexagonal 6 engine arrangement which would provide a space for a smaller central landing engine (I dub this mini engine 'Robin').

Isn't that a bit too big? Wouldn't a 1260 mt BFS second stage, fully fueled, be enough to lift ~200 mt (50% of it being structural mass)?

And for the return trip, a 4 Raptor BFS would have a T/W > 1 in Mars anyway, even with full tanks and cargo.

I like your 'Robin' idea, I wonder if it could be a pressure fed, for safety reasons, lox/methane engine, a bit like the Superdracos but using a different propellant (Hyperdracos, anyone?). You don't need super efficient engines to reach LMO.

Two broad groups of ideas form, with a compromise in between:

Alpha
Two stages to LEO with one RTLS (or possibly barge landing), and one upper stage to orbit
LEO, MS-ISRU refueling
Terminal stage needs ~7km/s for Mars Ascent to Earth Return, plus Earth Return Capture
May be capable of fairly fast transits if a high-efficacy aerocapture method can be found (like MAC).  Earth to Mars quickly is easier than Mars to Earth quickly.

Beta
Three stages to LEO with one RTLS, one barge landing, and one upper stage to orbit
LEO, MS-ISRU, LMO refueling
Terminal stage needs ~4.5km/s for Mars Ascent to LMO (and possibly a little more if Mars EDL is expensive)
Not capable of especially fast transits

And the compromise position, which exerts some pressure on BFR first stage to overperform (4.5km/s plus entry?  dunno), and on MCT to pack lots of thrust (+ dry mass of engines):

Gamma
Two stages to LEO with one barge landing, and one upper stage to orbit
LEO, MS-ISRU, LMO refueling
Terminal stage needs ~4.5km/s for Mars Ascent to LMO (and possibly a little more if Mars EDL is expensive)
Not capable of especially fast transits

Right now I'm leaning towards Gamma but kicking it up to 5.5km/s or 6km/s to deal with pessimistic Mars EDL while reducing pressure on BFR first stage.  The past few weeks, I've been forking on the overall mission mode though, and whether to return hab to HEO & separate a crew capsule to Earth EDL, or return the entire hab to Earth EDL.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 02/12/2016 10:21 pm
jsgirald:
Yes with a 1260 mt mass you would be looking at around a ~200 mt burn out mass at LEO assuming that acceleration after separation is 6 km/s.  At 1880 mt separation mass the burn out mass it approaching 375 mt but that is an upper limit.  A 6 engine configuration allows for engine out (which after symmetrically shut down drops us to 4 engines).  As I expect the vehicle to be launched with cargo that requires a dry mass delivery in LEO of nearly 200 mt, thus the 4 engine configuration provides no margin for a shutdown not to mention the need to retain landing propellant when the goal is to delivery propellant to a depot.  Lastly I see the robin engine as being a sub-scale Raptor running on Methane and Lox.

Burnate:
If favor the Beta configuration but with some minor alterations. 

First I don't believe barge landing a 2nd stage is reasonable because the barge would need to be in the Indian Ocean considering the acceleration and downrange velocity the 2nd stage will achieve.  A once around the Earth orbit and landing at the launch site is more likely.

Second the terminal stage DeltaV I would target is 5.1 km/s because this would allow a launch to LMO with 25 mt of cargo and then (by my estimates) a return to mars surface with another 100 mt of cargo.  In addition with no cargo at all the DeltaV would reach 6 km/s which would be enough for a slow Hohmann transfer back to Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/12/2016 10:27 pm
"Symmetrical shutdown" is not required unless you're not gimbaling your engines.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 02/13/2016 05:42 am
Unlikely, most engines can only gimbal a few degrees, not enough to maintain the thrust axis through the vehicles center of mass which for a short second stage is considerably closer to the engines then it is on a long first stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 02/13/2016 10:43 am
jsgirald:
Yes with a 1260 mt mass you would be looking at around a ~200 mt burn out mass at LEO assuming that acceleration after separation is 6 km/s.  At 1880 mt separation mass the burn out mass it approaching 375 mt but that is an upper limit.  A 6 engine configuration allows for engine out (which after symmetrically shut down drops us to 4 engines).  As I expect the vehicle to be launched with cargo that requires a dry mass delivery in LEO of nearly 200 mt, thus the 4 engine configuration provides no margin for a shutdown not to mention the need to retain landing propellant when the goal is to delivery propellant to a depot.  Lastly I see the robin engine as being a sub-scale Raptor running on Methane and Lox.

Well, engine out capability is nice to have, but maybe the MCT needs to be designed simply for safe abort, i.e. if you have engine trouble you won't be going to space, but it doesn't need to end in a wreck.

Regarding tanker missions, a fully fledged, Mars capable, vehicle seems a bit of an overkill for that, probably they'll either use future iterations of Falcon, or more likely a stripped down BFR upper stage that will be their design for common 'bread and butter' missions. I'm assuming here that MCT will be a specialised upper stage for BFR.

The already famous tweet of Chris Bergin, and the last I've heard from Musk et al. make me think that BFR/MCT will represent a break from the past in terms of configuration and design, rather than simply being a bigger rocket. The reduction of the projected power of the Raptor engines also points to this. I think it won't be much heavier than an Energia/Buran stack, probably close to N1.

I suggested the secondary engine idea based on a set of beefed up Superdracos because a 'simple' pressure fed set of engines for Mars landing and take off look more reliable than a single FFSC engine.
The idea is that secondary engines get the ship airborne and then you light up the big ones for the push to orbit. As an added benefit, you don't need a launch pad equiped for big rockets. This also opens the possibility of landing the ship in a horizontal position, an idea already considered for lunar and Mars landers, which simplifies unloading, something like the Centaur derived lander proposed by Masten.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/13/2016 10:47 pm
After reading many articles/posts on Raptor, MCT, etc. and applying what I know and what I remember (which is a lot given I have an eidetic memory), I decided to throw in my .02 worth.  Basically, I put some thought as to how a Mars architecture could work.  Decidedly, I took a page out of Elon's book and went to fundamentals.  By this I mean actually functional hardware or could-be functional hardware for the task at hand.  This means reasonably sized tanks, engines, and all the subsystems necessary for a Mars mission, Earth & Mars EDL, and long term on orbit operations.  Of course, I made several assumptions which are:
* Everything is reusable; no stages, fairings, etc. jettisoned and everything has to be serviceable on surface or on orbit.
* Long term on surface or on orbit.
* Upper stage Raptor (vacuum) with CH4 Draco thrusters.  Assumed fuel depots and ISRU.  Required Integrated Vehicle Fluids (IVF) system and closed loop ECLSS.
* Efficient ascent via optimized engine nozzles and EDL via Supersonic Retro-Propulsion (SRP) using only ONE set of engines.  Engine nozzles/bells optimized for thin to no atmosphere (aka Mars thin).
* Common modules; one size fits all.  Cost efficient components in manufacturing.

Given these assumptions I dreamed up the attached image.  Of course, there is a lot more detail that I didn't include.  For example, at the top there would be an "auxiliary control" module which would contain ECLSS components and spacecraft control (aka pilot seats).  The pilot seat(s) is needed since on orbit operations could be complicated.  Like the engine bay, this module would also have a CBM ring with connection ports for fuel/electrical & ECLSS supply.  This "upper stage" is actually a spacecraft but with the benefit of have different payloads attached to the top of it (for launch; fuel, cargo, passenger modules) or can switch around on orbit, aka attach to a BA-330, the ISS, or the fuel depot.

BTW: I didn't add any technical details but the model is sized according to my best guess (via calculations) an upper stage.  4 x Raptor 4400kN@380s (vacuum); 1:3.8 CH4 to LOX ratio with densification.  Combined LOX/CH4 tanks are 31.21m long at 8.4m diameter (common tooling with SLS).  Actual external diameter > 8.4m due to insulation/shielding (micrometeoroid) and solar panels.  Assumed CBMs rated for stresses/loading with supplemental connection points.  Engine module is 8.68m long at 8.4 diameter.  Total length is 41.68m NOT including the upper module (aux control or cargo/fuel).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/13/2016 11:21 pm
-snip-

* It's very difficult to parse your diagram.  You should illustrate some more of the things you're captioning.

* I'm not sure anyone really considers an 8.4m diameter plausible for this vehicle anymore.  What we know of the requirements imposed on the vehicle by most the mission architectures suggests there's too much rocket here for things to fit into 8.4m without making the vehicle extraordinarily long and thin and difficult to land.  We examined 10, 12.5, and 15 meters and mostly concluded that we were looking at the upper part of that range, just based on how big the BFR would need to be to get it into LEO.

* If you could include more of your figures and timelines for the mission architecture, we would be able to critique that a lot more productively.

It's nice to see more people thinking about the problem constructively, in any case.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/14/2016 12:29 am

* It's very difficult to parse your diagram.  You should illustrate some more of the things you're captioning.

* I'm not sure anyone really considers an 8.4m diameter plausible for this vehicle anymore.  What we know of the requirements imposed on the vehicle by most the mission architectures suggests there's too much rocket here for things to fit into 8.4m without making the vehicle extraordinarily long and thin and difficult to land.  We examined 10, 12.5, and 15 meters and mostly concluded that we were looking at the upper part of that range, just based on how big the BFR would need to be to get it into LEO.

* If you could include more of your figures and timelines for the mission architecture, we would be able to critique that a lot more productively.

It's nice to see more people thinking about the problem constructively, in any case.
Thank you, the intent is to think about the problem constructively.  I'm sure that Elon's MCT architecture will be completely different but you never know where ideas come from.

Yes, a picture is worth a thousand words, however, the cliche says nothing on how long it takes to document a visual idea from one's mind and put it a 3D model.  Unfortunately, a lot of time especially when your learning new software (aka SketchUp).  I would love to visualize the picture in my head, I just don't have the resources quite as yet.  This is a work in progress to be shared/worked on by all.

I'm more conservative regarding sizes (see my assumption about cost efficiencies).  8.4 diameter means existing tools and knowledge in handling, aka friction stir welding machines, transport (NASA Pegasus Barge), etc.  No matter how you slice and dice the numbers, you can't launch everything at one go.  Either you launch fuel, launch cargo, or launch butts-in-seats.  This "upper stage" is the common part to those three modes using the least amount of dry mass, reuse of proven technology, and within the limitations of existing/known infrastructure.  Going larger diameters may have devils in the details; it's the devils that are the problem.

This idea of an upper stage (but really a spacecraft in its own right) assumes a BFR first stage that's extremely large.  The engine module is not just 4 engines with a really good TWR and simple gimbal.  The engines have to adjust to the atmosphere or lack there of with best efficiencies.  The gimble/cant is for the different flight regimes.  For this reason, the module has to have a lot of structure for SRP (to cant the engines, heat shielding, deflectors), on orbit (IVF, ECLSS, pressurization, CBMs, pumps, shielding, insulation, extra baffles, etc.), and on Mars (cargo movement, fuel movement, airlock, "mud" room, immediately usable solar panels, etc.).  This is all dry mass so bigger means an even bigger first stage which I think is bordering on ridiculous.

As for figures and timelines, I concede that there are folks here better than me in such things.  My figures is based on a slew of posts and articles I've read, which I mashed together using first principals and simple calculations (mostly ratios of known values) to arrive at what I would call an "informed" guess.  Since I can't provide accreditation for everything and my figures are only guesses, I use them in my model but everything is up to interpretation.  Again it's a work-in-progress... Unfortunately, .skp files is not in the allowed file types for attachments.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 02/14/2016 03:02 am
There is not really an such thing as a standard tank (LV) manufacturing equipment. Every provider uses a different machining/setup customized for the tank design even if it happens to be the same diameter of other providers. Making the diameter 8.4m will not save anything. The reasoning behind the SLS being 8.4m is that NASA was experienced with the handling of this size plus having existing transportation assets that is geared for that size. Since SpaceX's experience is with tanks of only 3.66m any size larger is equally plausible from a cost evaluation standpoint.

But here is the kicker. NASA's experience with tank manufacturing equipment for even the 8.4m tank size has been a significant problematic experience. SpaceX's design and subsequent manufacturing equipment design would evaluate the trade-offs between ease of manufacture/light weight/capitol costs into a solution that has the lowest life cycle costs development and operational costs. If you reuse each vehicle 10 times then slightly higher manufacturing costs are not as significant as other operational costs. So SpaceX assumption of the vehicle being operated sole as a reusable vehicle will weigh heavily on how it is designed and how it would be manufactured. Here is the assumptions on manufacturing the tank vertically or horizontally. A horizontally manufactured large diameter tank would be differently designed and possibly weigh more than a vertically manufactured tank like the SLS. Given the problems with getting the vertical manufacturing setup to stay in alignment it may be easier to do the manufacturing horizontally (lower floor weight support required, easier to maintain alignment).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/14/2016 05:19 am
The problems experienced by NASA (Boeing is doing the tanks I believe at Michoud) is the devils in the details.  I chose 8.4 diameter to leverage the knowledge NASA has.  Of course, you could go with larger but why reinvent the wheel.  Also, dry mass is important for upper stages.  From my calculation, using NASA sleep station dimension plus some (5 cubic meters) per person.  Butts-in-seats (more like first class suite) for 100 passengers only require 500 cubic meters.  13.5m @ 8.4m dia. is 2993 cubic meters which is more than enough for passenger sleep stations, isles/passway, hygiene stations, common/work stations, and recreation stations (which includes ECLSS).  The consumables (fuel, water, air) come from tanker modules in something like the six shooter depot and/or the upper stage.  Note that the "six shooter" would never deorbit and require berths for the tankers, multi-CBM ports a la Unity, and a "auxiliary control" module.  Basically, the entire MCT is a train concept where everything is reusable that needs to be.

Here is an updated model showing the upper stage (the "engine room") and a basic tanker module.  The actual passenger module and auxiliary control module are still works-in-progress.

Note that the legs would have to be little more bigger/beefier with double articulation/shock absorbing.  What's picture is just a copy from another model I found.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/14/2016 08:30 am
If you reuse each vehicle 10 times then slightly higher manufacturing costs are not as significant as other operational costs. So SpaceX assumption of the vehicle being operated sole as a reusable vehicle will weigh heavily on how it is designed and how it would be manufactured.

Their declared goal is for 100 reuses. That's for the first stage obviously. A second stage MCT that goes to Mars will have less reuses. If the stage can do mixed service going to Mars and as a tanker they may get 50 reuses.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/15/2016 01:01 am
I'm late to this but I wonder, apart from Karou's estimate has anyone looked at physically how 100 people lying down map into a cylinder? I'm guessing about 8'x3'. A square 8.2m gives 24 spaces, a circle is likely to give substantially less.

I expect the accumulated water, food and air will be much heavier than the passenger (without heavy recycling of all consumables) but occupy less volume (given the density of those items.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/15/2016 02:09 am

I'm late to this but I wonder, apart from Karou's estimate has anyone looked at physically how 100 people lying down map into a cylinder? I'm guessing about 8'x3'. A square 8.2m gives 24 spaces, a circle is likely to give substantially less.

I expect the accumulated water, food and air will be much heavier than the passenger (without heavy recycling of all consumables) but occupy less volume (given the density of those items.
I got my numbers from NASA for the sleep stations on ISS.  I assume that if one can live aboard ISS for months on end, it's good for MCT passengers.  The sleep station is more than a bed, it doubles as a work/relaxation space. It doesn't have to be rectangle or box.  Think of it being an enclosed first class suite on a AirBus A380. 

A Dragon V2 has 10 cubic meters of pressurized space for seven people, 5 m3 for one person seems reasonable.   Layout of the stations would be interesting since you don't need floors in zero g.  The stations would have to be oriented for ascent/EDL and require access ways in gravity.

A good question is if the MCT will be used for temporary living space on Mars or just be a transport.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 02/15/2016 02:41 am
5 m^3 per person is reasonable if the trip lasted a couple of weeks, but this is going to be at least 3-4 months or more.

Based on diagrams of the original Mars Direct plan, I had calculated (http://forum.nasaspaceflight.com/index.php?topic=37733.msg1393316#msg1393316) the volume of the Earth Return Vehicle crew cabin for each of the four astronauts: 36 m^3. And for 6 months, that (https://www.google.com/search?newwindow=1&q=mars+direct+erv+cabin+too+small) was thought to be too small.

ISS total habitable volume is 388 m^3 (http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html). For 6-7 people (permanent crew, living on the station for months at a time), that is 55-65 m^3 per person.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/15/2016 05:03 am
5 m^3 per person is reasonable if the trip lasted a couple of weeks, but this is going to be at least 3-4 months or more.

Based on diagrams of the original Mars Direct plan, I had calculated (http://forum.nasaspaceflight.com/index.php?topic=37733.msg1393316#msg1393316) the volume of the Earth Return Vehicle crew cabin for each of the four astronauts: 36 m^3. And for 6 months, that (https://www.google.com/search?newwindow=1&q=mars+direct+erv+cabin+too+small) was thought to be too small.

ISS total habitable volume is 388 m^3 (http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html). For 6-7 people (permanent crew, living on the station for months at a time), that is 55-65 m^3 per person.
There's a difference between personal space and common space.  The personal space aboard the ISS is less than 5 m3, the rest is work space and Scott Kelly has gone almost a year with only that amount of personal space.  This is not an airplane, think of it more like a submarine with a lot more personal space (at least they're not hot racking).  AFAICR, ISS in the beginning didn't have (may still not have) not enough sleep stations; 2 stations I believe in the beginning for three astronauts.  One of them just had to sleep wherever they could be tied down.

Not sure about my previous post numbers, the cargo module (top; shown in attachment) is 13m by 8.4 dia cylinder with a 12m cone which is a pressure vessel of 720 m3 + 221 m3 = 941 m3.  Obviously, some of that is taken up by mechanicals and such but there should be a good chunk left over.  Of course, my concept is modular so there's no reason why a BA330 couldn't be added to the MCT.

I'm interested in modelling what the passenger module would look like.  Note that my "engineering" service module has most of the mechanicals for the passenger module.  I'm still working on the models, but here is what I envision as MCT would be (using a "train" paradigm):

Service Module #1 (as shown in attachment) -> Service Module #2 -> Service Module #3 -> Fuel/Consumables Carrier (never lands; contains tanker/cargo modules that can land w/ service module) -> Orbital Habitat Module (i.e. BA330; never lands) -> "Aux Control" module (for on orbit ops; never lands) -> Passenger Module (lands w service module).

At Earth:  Launch modules aux. control, module carrier, and orbital habitat module (i.e.) with two service modules kept in orbit.  Launch fuel & cargo modules to fill up service modules and carrier.  Launch passenger module, service module refuels.  All modules are now in orbit and ready to depart to Mars.

At Mars:  Enter Mars orbit.  Service Module #1 -> Cargo module is lander #1.  Service Module #2 -> Passenger Module is lander #2.  Both land at landing site.

That's an example regime from my ideas.  Here's the updated model (by no means finished) with sudo-Raptors (vacuum nozzle minus extension) added; I haven't put the nacelles on.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/15/2016 04:31 pm
Here's an updated model with the nacelles.  I assume that the Raptors won't cant more of an angle than that of crew Dragon's Super Dracos.  The only thing missing is heat shielding and external gimbal bellows.  To make a better depiction, I'm going to work on modelling the Command & Control module (was auxiliary control; a better name), Consumables Carrier module, and the Passenger module.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/15/2016 06:10 pm
5 m^3 per person is reasonable if the trip lasted a couple of weeks, but this is going to be at least 3-4 months or more.

Based on diagrams of the original Mars Direct plan, I had calculated (http://forum.nasaspaceflight.com/index.php?topic=37733.msg1393316#msg1393316) the volume of the Earth Return Vehicle crew cabin for each of the four astronauts: 36 m^3. And for 6 months, that (https://www.google.com/search?newwindow=1&q=mars+direct+erv+cabin+too+small) was thought to be too small.

ISS total habitable volume is 388 m^3 (http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html). For 6-7 people (permanent crew, living on the station for months at a time), that is 55-65 m^3 per person.
Musk keeps saying 3 months or 100 days. Some opportunities require a little more energy, but 120 days is fine. So not more than 4 months (except with reduced crew).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 02/15/2016 08:15 pm
5 m^3 per person is reasonable if the trip lasted a couple of weeks, but this is going to be at least 3-4 months or more.

Based on diagrams of the original Mars Direct plan, I had calculated (http://forum.nasaspaceflight.com/index.php?topic=37733.msg1393316#msg1393316) the volume of the Earth Return Vehicle crew cabin for each of the four astronauts: 36 m^3. And for 6 months, that (https://www.google.com/search?newwindow=1&q=mars+direct+erv+cabin+too+small) was thought to be too small.

ISS total habitable volume is 388 m^3 (http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html). For 6-7 people (permanent crew, living on the station for months at a time), that is 55-65 m^3 per person.
Musk keeps saying 3 months or 100 days. Some opportunities require a little more energy, but 120 days is fine. So not more than 4 months (except with reduced crew).
For a 100 crew size with a 15m diameter 50m^3 /person is a crew cabin of 30m tall. For 30m^3 it is 17m tall.
If it is such a short duration of travel then a crew cabin size of 3000m^3 may work. Even a possible 2000m^3 may work. But for the first missions the MCT crew cabin will be the on surface HAB module as well so if the volume is 2000m^3 then the crew numbers would need to be less than 40 for initial trips. Crew sizes of 25 has been batted around a lot for these missions.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 02/15/2016 08:46 pm
5 m^3 per person is reasonable if the trip lasted a couple of weeks, but this is going to be at least 3-4 months or more.

Based on diagrams of the original Mars Direct plan, I had calculated (http://forum.nasaspaceflight.com/index.php?topic=37733.msg1393316#msg1393316) the volume of the Earth Return Vehicle crew cabin for each of the four astronauts: 36 m^3. And for 6 months, that (https://www.google.com/search?newwindow=1&q=mars+direct+erv+cabin+too+small) was thought to be too small.

ISS total habitable volume is 388 m^3 (http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html). For 6-7 people (permanent crew, living on the station for months at a time), that is 55-65 m^3 per person.
Musk keeps saying 3 months or 100 days. Some opportunities require a little more energy, but 120 days is fine. So not more than 4 months (except with reduced crew).
I'd like to know where and when did he actually say this. Because I'm not finding it (https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=%22musk%22%20%22100%20days%22%20%22mct%22).

Also, with that fast trajectory, what will the heating loads be as the vehicle gets aerocaptured by the Martian atmosphere? And can that thin atmosphere slow it down enough?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 02/15/2016 08:58 pm
5 m^3 per person is reasonable if the trip lasted a couple of weeks, but this is going to be at least 3-4 months or more.

Based on diagrams of the original Mars Direct plan, I had calculated (http://forum.nasaspaceflight.com/index.php?topic=37733.msg1393316#msg1393316) the volume of the Earth Return Vehicle crew cabin for each of the four astronauts: 36 m^3. And for 6 months, that (https://www.google.com/search?newwindow=1&q=mars+direct+erv+cabin+too+small) was thought to be too small.

ISS total habitable volume is 388 m^3 (http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html). For 6-7 people (permanent crew, living on the station for months at a time), that is 55-65 m^3 per person.
Musk keeps saying 3 months or 100 days. Some opportunities require a little more energy, but 120 days is fine. So not more than 4 months (except with reduced crew).
I'd like to know where and when did he actually say this. Because I'm not finding it (https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=%22musk%22%20%22100%20days%22%20%22mct%22).

Also, with that fast trajectory, what will the heating loads be as the vehicle gets aerocaptured by the Martian atmosphere? And can that thin atmosphere slow it down enough?

http://shitelonsays.com/transcript/raw-science-elon-musk-on-mars-2013-12-09
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/16/2016 12:03 am
5 m^3 per person is reasonable if the trip lasted a couple of weeks, but this is going to be at least 3-4 months or more.

Based on diagrams of the original Mars Direct plan, I had calculated (http://forum.nasaspaceflight.com/index.php?topic=37733.msg1393316#msg1393316) the volume of the Earth Return Vehicle crew cabin for each of the four astronauts: 36 m^3. And for 6 months, that (https://www.google.com/search?newwindow=1&q=mars+direct+erv+cabin+too+small) was thought to be too small.

ISS total habitable volume is 388 m^3 (http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html). For 6-7 people (permanent crew, living on the station for months at a time), that is 55-65 m^3 per person.
Musk keeps saying 3 months or 100 days. Some opportunities require a little more energy, but 120 days is fine. So not more than 4 months (except with reduced crew).
For a 100 crew size with a 15m diameter 50m^3 /person is a crew cabin of 30m tall. For 30m^3 it is 17m tall.
If it is such a short duration of travel then a crew cabin size of 3000m^3 may work. Even a possible 2000m^3 may work. But for the first missions the MCT crew cabin will be the on surface HAB module as well so if the volume is 2000m^3 then the crew numbers would need to be less than 40 for initial trips. Crew sizes of 25 has been batted around a lot for these missions.
Right, I'm sure the crew size would be much less than 100 at first. And I used to be pretty sure 500m^3 was about the right size for cabin for MCT, squished, yes, but doable for the short trip. And I still stand by that as a possible minimum size per person, at least if you're really clever with how you utilize the space (with sleep schedules rotating, everyone having their own small personal space that they spend at least 12 hours a day in), but I no longer think SpaceX is thinking as small as 500m^3. Probably 1000m^3 or perhaps more. 2000m^3 is perhaps on the high end of what I think SpaceX is thinking of, but I wouldn't argue too much with it until we get more information.

3000m^3 is starting to get too big (IMHO) to be practical (at some point, you're better off lowering the price and sending more people if you have that much room).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/16/2016 12:08 am
5 m^3 per person is reasonable if the trip lasted a couple of weeks, but this is going to be at least 3-4 months or more.

Based on diagrams of the original Mars Direct plan, I had calculated (http://forum.nasaspaceflight.com/index.php?topic=37733.msg1393316#msg1393316) the volume of the Earth Return Vehicle crew cabin for each of the four astronauts: 36 m^3. And for 6 months, that (https://www.google.com/search?newwindow=1&q=mars+direct+erv+cabin+too+small) was thought to be too small.

ISS total habitable volume is 388 m^3 (http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html). For 6-7 people (permanent crew, living on the station for months at a time), that is 55-65 m^3 per person.
Musk keeps saying 3 months or 100 days. Some opportunities require a little more energy, but 120 days is fine. So not more than 4 months (except with reduced crew).
I'd like to know where and when did he actually say this. Because I'm not finding it (https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=%22musk%22%20%22100%20days%22%20%22mct%22).

Also, with that fast trajectory, what will the heating loads be as the vehicle gets aerocaptured by the Martian atmosphere? And can that thin atmosphere slow it down enough?
The heating loads can be dealt with using PICA-X, and yes the thin atmosphere is enough to slow it down since you can dive deeper in. You're right to mention aerocapture, though, as you likely would want to do an aerocapture pass (perhaps two, one to capture in a high orbit, then another to put you in low orbit before doing the final descent), not go straight in for a landing like most Mars probes have done (on a hyperbolic trajectory, it's harder to slow down in time).

...and to make things even easier for you, it'd probably make sense to restrict large payload landings to very low altitude sites (below -3 or -4 km altitude).

And yes, I've calculated that it can be done with a simple 2D simulation I whipped up in Python, so I'm not COMPLETELY just pulling that out of my butt (not that there's any kind of real hardcore fidelity in the simulation, it uses an exponential atmosphere and many other oversimplifications, but it is a /tiny/ bit better than a hand-wave).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 02/16/2016 03:18 am
Some far out speculation.... Everything points to Brownsville for the MCT launch site.  But could the VAB and pad 39a at KSC do the job, at least as a backup option ?  The shuttle fuel tank and SRBs were 15.8 m wide.  So, the VAB doors are about 16m wide and 139m tall (Wikipedia).  Unless there is some reason 39a could not handle 2x Saturn V thrust, it seems doable.  The factory would have to be close to the VAB.  If SLS is cancelled could VAB itself be converted into an MCT factory? One problem might be that VAB is designed for vertical integration and Spacex is geared  to horizontal integration with an erector transporter.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/16/2016 03:28 am
Too high thrust for LC39A. also, SpaceX filled in one of the two flame trenches at LC39a with cement, a difficult action to reverse. a kind of "burn the ships" approach, maybe.

And no way in heck will BFR be built/assembled/etc in the VAB.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/16/2016 03:56 am
3000m^3 is starting to get too big (IMHO) to be practical (at some point, you're better off lowering the price and sending more people if you have that much room).

I am quite sure Elon Musk recently said just that. That 100 people may not be the upper limit forever and they may offer "economy class" trips with more. My guess is that they would need some advances in ECLSS to pull that off.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/16/2016 04:51 am
3000m^3 is starting to get too big (IMHO) to be practical (at some point, you're better off lowering the price and sending more people if you have that much room).

I am quite sure Elon Musk recently said just that. That 100 people may not be the upper limit forever and they may offer "economy class" trips with more. My guess is that they would need some advances in ECLSS to pull that off.
I think they may start at trips less than 100. Musk originally gave a range for # of passengers, like 50-100 or something like that. So start with 50, say, and grow to 100 as you become more efficient.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/16/2016 06:32 am
5 m^3 per person is reasonable if the trip lasted a couple of weeks, but this is going to be at least 3-4 months or more.

Based on diagrams of the original Mars Direct plan, I had calculated (http://forum.nasaspaceflight.com/index.php?topic=37733.msg1393316#msg1393316) the volume of the Earth Return Vehicle crew cabin for each of the four astronauts: 36 m^3. And for 6 months, that (https://www.google.com/search?newwindow=1&q=mars+direct+erv+cabin+too+small) was thought to be too small.

ISS total habitable volume is 388 m^3 (http://www.nasa.gov/mission_pages/station/main/onthestation/facts_and_figures.html). For 6-7 people (permanent crew, living on the station for months at a time), that is 55-65 m^3 per person.
Musk keeps saying 3 months or 100 days. Some opportunities require a little more energy, but 120 days is fine. So not more than 4 months (except with reduced crew).
For a 100 crew size with a 15m diameter 50m^3 /person is a crew cabin of 30m tall. For 30m^3 it is 17m tall.
If it is such a short duration of travel then a crew cabin size of 3000m^3 may work. Even a possible 2000m^3 may work. But for the first missions the MCT crew cabin will be the on surface HAB module as well so if the volume is 2000m^3 then the crew numbers would need to be less than 40 for initial trips. Crew sizes of 25 has been batted around a lot for these missions.
Right, I'm sure the crew size would be much less than 100 at first. And I used to be pretty sure 500m^3 was about the right size for cabin for MCT, squished, yes, but doable for the short trip. And I still stand by that as a possible minimum size per person, at least if you're really clever with how you utilize the space (with sleep schedules rotating, everyone having their own small personal space that they spend at least 12 hours a day in), but I no longer think SpaceX is thinking as small as 500m^3. Probably 1000m^3 or perhaps more. 2000m^3 is perhaps on the high end of what I think SpaceX is thinking of, but I wouldn't argue too much with it until we get more information.

3000m^3 is starting to get too big (IMHO) to be practical (at some point, you're better off lowering the price and sending more people if you have that much room).

According to NASA, 5m^3 over a few months is about the size volume where trained astronauts will go bonkers and kill each other, the survivors turning into Reavers who will prey on hapless interplanetary vessels. I've stayed in a capsule hotel before - that's 2.7m^3 of space per capsule, and that's really not a lot.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070023306_2007019854.pdf

The only way 5m^3 will work is if the passengers are in hibernation or some advanced form of VR or other disruptive future tech. 10m^3 *might* be doable. Nuclear submarines have 10m^3 per person with hot bunking. Certainly you will want shifts so the passengers don't get in each other's faces too much.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/16/2016 06:53 am
According to NASA, 5m^3 over a few months is about the size volume where trained astronauts will go bonkers and kill each other, the survivors turning into Reavers who will prey on hapless interplanetary vessels. I've stayed in a capsule hotel before - that's 2.7m^3 of space per capsule, and that's really not a lot.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070023306_2007019854.pdf

The only way 5m^3 will work is if the passengers are in hibernation or some advanced form of VR or other disruptive future tech. 10m^3 *might* be doable. Nuclear submarines have 10m^3 per person with hot bunking. Certainly you will want shifts so the passengers don't get in each other's faces too much.

Much of the stress factor would be the small number of 4 Astronauts. Yes, 4 Astronauts in 20mł is a no go. Or 3 in an Orion capsule, which would give slightly over 5mł per person.

But 20 in 100mł would be a totally different situation, especially if almost always at least half of them would be in their private 2mł space. But we are not talking about such a small space. MCT will give much more space, the only question is how much more. Low estimates were ~800m, but now with a diameter of 15m 1500mł seem reasonable which is 15mł per person.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/16/2016 08:14 am
A horizontally manufactured large diameter tank would be differently designed and possibly weigh more than a vertically manufactured tank like the SLS. Given the problems with getting the vertical manufacturing setup to stay in alignment it may be easier to do the manufacturing horizontally (lower floor weight support required, easier to maintain alignment).
I always suspected a big part of NASA's vertical tank mfg approach was the tank sections would "sag" under their own weight in different ways and NASA (during Saturn/Apollo) did not feel it had the time to investigate and decided to side step the problem altogether (and continue to do so).

That said given the much lower cost of non high bay work area and ease of movement I wonder if it would have really been that hard to devise a set of movable, adjustable bracing struts to get it back into a circle for the welding.

Incidentally on another thread it was noted that you could move a 10m dia structure around Texas fairly easily.  On that basis a build and fly out of Texas for a 10m MCT design would seem quite feasible, not easy, but feasible.
The only way 5m^3 will work is if the passengers are in hibernation or some advanced form of VR or other disruptive future tech. 10m^3 *might* be doable. Nuclear submarines have 10m^3 per person with hot bunking. Certainly you will want shifts so the passengers don't get in each other's faces too much.
I thought only the British did hot bunking on nuclear submarines, and they'd abandoned it as well in their latest generation boats
[EDIT I've just looked through the study, reading the the firs section in full and skimming the appendices and I can't find the section about metal well being. Could you give a  page number ]
That finding about astronauts (after extensive psychological screening) not being able to cope is pretty worrying.  :(

Not exactly the approach that most shipping companies to the New World operated is it?
There's was more on the lines of "If you have the fare, we do not care."
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/16/2016 10:56 am
Sorry, wrong link.

http://msis.jsc.nasa.gov/sections/section08.htm#Figure 8.6.2.1-1

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2011-217352.pdf

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2015-218564.pdf

I'm being flippant when I talk about the passengers/crew wigging out, but this is something crews on nuclear subs have to be carefully screened for. The British still do hot bunking - it's just the junior crew who have to suffer through it. About 1/3 of submariners are discharged for psychological reasons after their first tour. It may be lower (I didn't check the figures) but it's still a terrible psychological toll. Put your average hipster in there and you may find a gibbering mess coming out.

Assuming 18 people can use the same communal space as 6, then 15m^3 looks possible.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 02/16/2016 11:10 am
Sorry, wrong link.

http://msis.jsc.nasa.gov/sections/section08.htm#Figure 8.6.2.1-1

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2011-217352.pdf

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2015-218564.pdf

I'm being flippant when I talk about the passengers/crew wigging out, but this is something crews on nuclear subs have to be carefully screened for. The British still do hot bunking - it's just the junior crew who have to suffer through it. About 1/3 of submariners are discharged for psychological reasons after their first tour. It may be lower (I didn't check the figures) but it's still a terrible psychological toll. Put your average hipster in there and you may find a gibbering mess coming out.

I suspect the average hipster is already a gibbering mess. Putting on in a spaceship will just make him/her gibberouser.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/16/2016 12:22 pm
Well too bad, Boomers. The young folk are going to be the ones going to Mars.

Maybe you would've gotten the chance if you hadn't been messing around with drugs in your youth (then racking up a big national debt and environmental damage in your adult lives) instead of building spaceships like these fantastically hard-working and bright young engineers at SpaceX (and other Newspace companies), you would've been able to go. You can just deal with it. :P

(You aren't all bad, Boomers, but if you're going to dish it out, you better be able to take it...)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/16/2016 01:37 pm
Well too bad, Boomers. The young folk are going to be the ones going to Mars.

Maybe you would've gotten the chance if you hadn't been messing around with drugs in your youth (then racking up a big national debt and environmental damage in your adult lives)
At those prices it sounds like Mars will be the first new territory by trust fund beneficiaries,retirees and ex caregivers.

Which will make for an interesting experience all round.  :(
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/16/2016 01:48 pm
To return to MCT..

When you do the really broad brush analysis of this stuff you see what really matters.

Firstly for any chemical (and I think most nuclear) missions propellant is the #1. Almost anything that reduces this is good. I think most people here have no issues about spitting the load by various propellant depot/drop tank architectures.

Perhaps surprisingly #2 is consumables.  A person on a 100 day flight would consume 500Kg of water, air and food open loop.  So say a 100 people are 9 tonnes, their consumables are 50 tonnes.

This suggests ISS grade recycling at a minimum is a good idea as the mass per passenger for the systems is charged once and does not rise on a daily basis. Of course you've got to power that but PV cell & radiator designs have improved since ISS was implemented.

An interesting thought would be what if you launch with the Mars landing vehicle tanks dry and mfg the propellant on route from a stream in the ECLSS?

You've got to take it anyway, why not use it multiple times first?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 02/16/2016 02:01 pm
Well too bad, Boomers. The young folk are going to be the ones going to Mars.

Maybe you would've gotten the chance if you hadn't been messing around with drugs in your youth (then racking up a big national debt and environmental damage in your adult lives) instead of building spaceships like these fantastically hard-working and bright young engineers at SpaceX (and other Newspace companies), you would've been able to go. You can just deal with it. :P

(You aren't all bad, Boomers, but if you're going to dish it out, you better be able to take it...)

You got a point, but don't count your chickens before they hatch. Elon and SpaceX still have to raise the money for MCT. That's not guaranteed. Thirty to forty years from now you might be in the same boat as us boomers, wondering what happened to our dream.

I wish you luck. I'd love to see a Mars landing during my life.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: llanitedave on 02/16/2016 03:09 pm
Sorry, wrong link.

http://msis.jsc.nasa.gov/sections/section08.htm#Figure (http://msis.jsc.nasa.gov/sections/section08.htm#Figure) 8.6.2.1-1

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2011-217352.pdf (http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2011-217352.pdf)

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2015-218564.pdf (http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2015-218564.pdf)

I'm being flippant when I talk about the passengers/crew wigging out, but this is something crews on nuclear subs have to be carefully screened for. The British still do hot bunking - it's just the junior crew who have to suffer through it. About 1/3 of submariners are discharged for psychological reasons after their first tour. It may be lower (I didn't check the figures) but it's still a terrible psychological toll. Put your average hipster in there and you may find a gibbering mess coming out.

Assuming 18 people can use the same communal space as 6, then 15m^3 looks possible.


I never had to hot bunk on the sub I was on, but some of the crew did.  This was in the mid to late 1970's, in an FBM submarine that was large for its day.  I worked and bunked in the missile compartment, the largest space on the boat, so my conditions were better than most.  But it's true that even there, after a few weeks of submerged patrol, some people did start to wig out, and there were some major confrontations that developed over the most trivial triggering incidents.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/16/2016 03:48 pm
I don't think they'll be hot-bunking on MCT. But sleeping in shifts (and spending time in personal bunk reading, etc) would still improve space per passenger in the common areas.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/16/2016 04:17 pm
Hot bunking should not even be considered on MCT. In a sub it can work because when not sleeping they have a station to attend to. Passengers on MCT don't. So a private sleeping place is the most volume efficient way. People can sleep, watch a movie, use the computer for entertainment or learning, without taking up space in the communal area.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/16/2016 06:33 pm
Sorry, wrong link.

http://msis.jsc.nasa.gov/sections/section08.htm#Figure 8.6.2.1-1

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2011-217352.pdf

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2015-218564.pdf
Assuming 18 people can use the same communal space as 6, then 15m^3 looks possible.
Much more helpful but quite disturbing. I note 2 things.

5 m^3 is the very low end of the range for missions about 3 months.

But more worryingly there is a sense in the 2 reports that this is just a placeholder as there has simply been
been no research in this area to find out what the minimum really is.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/16/2016 06:46 pm
Sorry, wrong link.

http://msis.jsc.nasa.gov/sections/section08.htm#Figure 8.6.2.1-1

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2011-217352.pdf

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2015-218564.pdf
Assuming 18 people can use the same communal space as 6, then 15m^3 looks possible.
Much more helpful but quite disturbing. I note 2 things.

5 m^3 is the very low end of the range for missions about 3 months.

But more worryingly there is a sense in the 2 reports that this is just a placeholder as there has simply been
been no research in this area to find out what the minimum really is.
1)Yes, you start out looking at the minimum to bound the problem. Obviously, there's not really a maximum.
2) Studies almost always are looking at crews of 3-8, not 50-100. With small crews, rotating sleep schedules don't make much sense as the crew is working together. So most studies would miss some ways that space can be used more effectively.
3) it's wrong to say no research has been done. Reality is that soft sciences often have problems whose solutions are really hard to nail down.
4) There are no doubt countermeasures and techniques that would effect what the minimum space per passenger is. The hard physiological limit is obviously much less than 5m^3 per person, but it's really hard to say for sure what the true psychological minimum is.
5) SpaceX is probably thinking more than 5m^3 per passenger, at least for the first iterations of MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 02/16/2016 07:44 pm

I suspect the average hipster is already a gibbering mess. Putting on in a spaceship will just make him/her gibberouser.

 Excreting indignance is for youtube, not here.

It would be a mistake to assume people are going to walk through the door with the correct mindstate, as everyday life doesn't foster the required mindstate for Mars. People are going to be trained over a number of months, perhaps years at first, for a considerable period of time. The years will  be long before a ticket to mars is as simple as flashing your boarding pass.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/16/2016 11:48 pm
I never had to hot bunk on the sub I was on, but some of the crew did.  This was in the mid to late 1970's, in an FBM submarine that was large for its day.  I worked and bunked in the missile compartment, the largest space on the boat, so my conditions were better than most.  But it's true that even there, after a few weeks of submerged patrol, some people did start to wig out, and there were some major confrontations that developed over the most trivial triggering incidents.
It's kind of worrying that would happen despite what I presume was fairly extensive screening for the roles.  :(

The worst aspect of this is that in extreme conditions the boat could surface and request help.

An MCT en route may never be out of radio range of Earth but once the first TMI burn begins Mr Newton is in the driving seat. There is no concept of turnaround.   :(
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/16/2016 11:49 pm
Sorry, wrong link.

http://msis.jsc.nasa.gov/sections/section08.htm#Figure 8.6.2.1-1

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2011-217352.pdf

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2015-218564.pdf

Much better.

The bottom line of those 2 reports seems to be that that they are recommending just the personal space be somewhere between 7-8 m^3.

Unless this MCT comes with a big blow up section that's going to have a pretty sizeable impact on vehicle size.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/17/2016 12:12 am
Sorry, wrong link.

http://msis.jsc.nasa.gov/sections/section08.htm#Figure 8.6.2.1-1

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2011-217352.pdf

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2015-218564.pdf

Much better.

The bottom line of those 2 reports seems to be that that they are recommending just the personal space be somewhere between 7-8 m^3.
...
...it should be noted that the last report (2015) is referencing ~5m^3 of person space for missions 912 days in duration. That's an order of magnitude greater duration than the MCT's 3 month trip. Also, everything seems quite hand-wavy as to why /exactly/ that much space is needed.

In the 2011 report, most of those problems seem better mitigated by things other than simply having more per-person volume. For instance, sending always two or more MCTs at once (with margin for both) would provide full backup capability without adding extra space required just for backup use. Customizability is something that is also not volume-dependent. Having sufficient mental tasks can be accomplished by providing stimulating training during the transit, including perhaps group projects to prepare for life on Mars. VR headsets could help with mental stimulation, as well as having the entire Netflix catalogue available.

Proper layout of the cabin itself as well as good sleep schedule management (with some freedom to change sleep shift if you want) could help relieve congestion in common areas without needing any more volume per person.

...again, those reports don't at all seem definitive about what exactly is the minimum per-passenger space needed for a short 90-100 day transit.


...and remember also that for the same mass, allocating less volume will improve the radiation protection automatically.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/17/2016 01:07 am
After reading the NASA reports/specs for "orbital" modules and reading the posts here, there seems to be a disjoint.  The MCT has to ascend and land which means passengers will need a seat.  Moreover, the MCT will be on Earth and Mars (in the vertical position) therefore orientation is predetermined.  This means that the vertical height will be fixed, most likely 7 feet.  The area (not volume) for a crew/sleep station should the size of a bed and storage.  The bed would articulate into a seat and workstation (aka cubicle).  Think of like a first class seat on a long haul aircraft.  Bed at (simulated) night and cubicle by day.  Not that different from my life if you minus my commute.  :)

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 02/17/2016 01:08 am
Sorry, wrong link.

http://msis.jsc.nasa.gov/sections/section08.htm#Figure 8.6.2.1-1

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2011-217352.pdf

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2015-218564.pdf

Much better.

The bottom line of those 2 reports seems to be that that they are recommending just the personal space be somewhere between 7-8 m^3.

Unless this MCT comes with a big blow up section that's going to have a pretty sizeable impact on vehicle size.

I don't see that.
Assuming that the MCT or BFS is 15 meters in diameter an 8 meter long passenger section has 1415 m^3 or 14 m^3 per person. 
Alternatively, three ~two meter high decks give 1062 m^3 or 10 m^3 per person.  That's a pretty small length 6 or 8 meters relative to the behemoths people are modeling.
Yes I know that walls and floors are not zero thickness, etc.  The numbers are approximations.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 02/17/2016 05:16 am
That's an order of magnitude greater duration than the MCT's 3 month trip. Also, everything seems quite hand-wavy as to why /exactly/ that much space is needed.


90 day transit is insanely expensive in propellant, and while it might be possible to do it from LEO at huge cost in propellant.  But the longest leg of the journey is what you need to plan around and that is likely to be the Earth return leg.

Do your remember the discussion we had back on page 39 & 40 when we found that just 100 days Earth return launches from Mars surface would require 8.8 km/s DeltaV and significant aero-braking or propulsive capture at Earth.


Transit times of 120-180 days for Earth return are the range that's actually achievable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/17/2016 05:34 am
You'll have fewer crew for the return journey. Thems the rules or this whole thing doesn't work.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/17/2016 06:09 am
You'll have fewer crew for the return journey. Thems the rules or this whole thing doesn't work.

Why even bother returning the vehicles?  We could just scale up Mars One by a factor of 30?

"But it's necessary for the price to drop to $500k..."

Strong guarantees of a round-trip ticket are necessary to get a million people to pay $500k to go to Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/17/2016 07:49 am
Strong guarantees of a round-trip ticket are necessary to get a million people to pay $500k to go to Mars.

Certainly not! It is obvious that a million people, or even 10,000 cannot be brought back. The return guarantee is important early on, not when the colony is established. Or maybe for everyone but not for all.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/17/2016 09:13 am
Sorry, wrong link.

http://msis.jsc.nasa.gov/sections/section08.htm#Figure 8.6.2.1-1

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2011-217352.pdf

http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2015-218564.pdf

Much better.

The bottom line of those 2 reports seems to be that that they are recommending just the personal space be somewhere between 7-8 m^3.
...
...it should be noted that the last report (2015) is referencing ~5m^3 of person space for missions 912 days in duration. That's an order of magnitude greater duration than the MCT's 3 month trip. Also, everything seems quite hand-wavy as to why /exactly/ that much space is needed.

In the 2011 report, most of those problems seem better mitigated by things other than simply having more per-person volume. For instance, sending always two or more MCTs at once (with margin for both) would provide full backup capability without adding extra space required just for backup use. Customizability is something that is also not volume-dependent. Having sufficient mental tasks can be accomplished by providing stimulating training during the transit, including perhaps group projects to prepare for life on Mars. VR headsets could help with mental stimulation, as well as having the entire Netflix catalogue available.

Proper layout of the cabin itself as well as good sleep schedule management (with some freedom to change sleep shift if you want) could help relieve congestion in common areas without needing any more volume per person.

...again, those reports don't at all seem definitive about what exactly is the minimum per-passenger space needed for a short 90-100 day transit.


...and remember also that for the same mass, allocating less volume will improve the radiation protection automatically.

The data is based on confinement studies, analogues and historical spaceflight. When we talk of 5m^3 per person, let's not forget that shuttle missions ran to 10m^3 per person. 5m^3 is Apollo CSM+LSM. The SEALAB II clocked in at 17m^3 with 10 people and by all accounts it seemed awful. I think MCTs at these volumes will have to have separate male and female flights, or at least have separate bunkroom & washroom sections according to gender.

https://books.google.co.za/books?hl=en&lr=&id=vEkQFWgN5WsC&oi=fnd&pg=PR9&dq=Groups+under+stress:+Psychological+research+in+SEALAB+II&ots=14xol7gZkQ&sig=D41SgF9xNRd4oI-IHN0MqnQQsM4#v=onepage&q&f=false

http://www.spacearchitect.org/pubs/ICES2008/Abstracts/08ICES-0046.pdf

The references are extensive in the previous docs I linked... worth checking out.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/17/2016 11:44 am

90 day transit is insanely expensive in propellant, and while it might be possible to do it from LEO at huge cost in propellant.  But the longest leg of the journey is what you need to plan around and that is likely to be the Earth return leg.

Do your remember the discussion we had back on page 39 & 40 when we found that just 100 days Earth return launches from Mars surface would require 8.8 km/s DeltaV and significant aero-braking or propulsive capture at Earth.
That's huge emphasizing the need to make ECLSS closed loop as much as possible.
Quote
Transit times of 120-180 days for Earth return are the range that's actually achievable.
These are the figures I was thinking about.  Do you happen to have the Delta V to give a 100 day to Mars trip?
That also hint SX might like to make it an uncrewed return, but then how do  you get the crew back for the next one?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/17/2016 12:32 pm
You'll have fewer crew for the return journey. Thems the rules or this whole thing doesn't work.

Why even bother returning the vehicles?  We could just scale up Mars One by a factor of 30?

"But it's necessary for the price to drop to $500k..."

Strong guarantees of a round-trip ticket are necessary to get a million people to pay $500k to go to Mars.
If the crew modules are unloaded for surface habitation, then you can use some of the cargo vehicles. If you're talking evacuating the entire planet, that would take longer than a single synod anyway, an impossible standard if you really believe in establishing a city.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 02/17/2016 01:57 pm

90 day transit is insanely expensive in propellant, and while it might be possible to do it from LEO at huge cost in propellant.  But the longest leg of the journey is what you need to plan around and that is likely to be the Earth return leg.

Do your remember the discussion we had back on page 39 & 40 when we found that just 100 days Earth return launches from Mars surface would require 8.8 km/s DeltaV and significant aero-braking or propulsive capture at Earth.
That's huge emphasizing the need to make ECLSS closed loop as much as possible.
Quote
Transit times of 120-180 days for Earth return are the range that's actually achievable.
These are the figures I was thinking about.  Do you happen to have the Delta V to give a 100 day to Mars trip?
That also hint SX might like to make it an uncrewed return, but then how do  you get the crew back for the next one?

First Elon has said 25 tonnes cargo on transit back from Mars.  Makes a significant rocket equation difference from the 100 tonnes outbound.  I don't think the MCT will have a crew in the sense we're used to.  No "astronauts".  No "test pilots" especially after the first few flights.  Cargo flights may be unmanned.  Even passenger flights will be automated and each shipment of passengers will have several passenger engineers cross trained to be flight engineers for the trip, skilled enough to implement directions from the ground for ECLS, etc. repairs in flight.  This won't be difficult as especially in the early days the vast majority will be STEM folk & a few construction folk to work with the robots.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/17/2016 11:48 pm
Here's a model of the passenger module (the nose cone is just for show).  The area per seat/bed is way more than 5m^3 but I still have a lot of things to put in like walls, storage, ducting, electronics, etc..  There is more than enough room for those items, the nose cone area will contain the hygiene/food prep./common stations (I haven't modelled it yet).  Total passenger stations is 96.  Of course, this is just a module with is part of a larger architecture.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/18/2016 05:56 am
The bunks will almost certainly be vertical. Say 1.5m in from the wall, 1.5m of wall circumference, and then you can do an inner ring of bunks with similar dimensions. With such an arrangement you can easily fit 30 people in a 12m diameter floor, half that for your 8.3m radius tank. Also, the central corridor and doors are wasted space. Doors need space to open and if they open into a corridor can smack an unsuspecting passenger or snag some cargo being pushed along. All you need is a standard door-sized hole to make a corridor.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/18/2016 06:29 am
The bunks will almost certainly be vertical. Say 1.5m in from the wall, 1.5m of wall circumference, and then you can do an inner ring of bunks with similar dimensions. With such an arrangement you can easily fit 30 people in a 12m diameter floor, half that for your 8.3m radius tank.
That might have worked on Shuttle but how were you going to handle launch?
Quote
Also, the central corridor and doors are wasted space. Doors need space to open and if they open into a corridor can smack an unsuspecting passenger or snag some cargo being pushed along. All you need is a standard door-sized hole to make a corridor.
Perhaps but a single depressurization event anywhere in this connected space now threatens everyone.

Yes it's probably the number of headaches caused by people being hit by closing compartment doors will be higher than the number of blow outs on any given flight but the consequences if one did happen are much more severe.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/18/2016 06:49 am
The bunks will almost certainly be vertical. Say 1.5m in from the wall, 1.5m of wall circumference, and then you can do an inner ring of bunks with similar dimensions. With such an arrangement you can easily fit 30 people in a 12m diameter floor, half that for your 8.3m radius tank.
That might have worked on Shuttle but how were you going to handle launch?

It did work on shuttle too. The spare seats are folded and stowed.

(http://www.spaceflightnow.com/shuttle/sts134/120808gallery/03.jpg)

Launch/landing is the least of the worries for layout. We're not going to be pulling 20g like Tintin on the way to the moon - maybe 3 or 4.

Quote
Quote
Also, the central corridor and doors are wasted space. Doors need space to open and if they open into a corridor can smack an unsuspecting passenger or snag some cargo being pushed along. All you need is a standard door-sized hole to make a corridor.
Perhaps but a single depressurization event anywhere in this connected space now threatens everyone.

Yes it's probably the number of headaches caused by people being hit by closing compartment doors will be higher than the number of blow outs on any given flight but the consequences if one did happen are much more severe.

Sorry, I was not clear - a door in the floor and ceiling, which can close. In kaoru's design, a blowout could depressurise the corridor and leave everybody trapped (assuming they shut all ~50 doors). Also, it has the problem of opening a pressure-sealed door to get to your cabin, when a simple zip-up soundproofed flap works just as well.

You just need one door in the floor, one in the ceiling. And if you seal off every floor (fire is a lot more likely on a spaceship than a blowout), you have the tricky problem of what to do about reaching survivors in a trapped compartment. Airlocks on every floor? Suits? Docking ports? These will need to be trade spaced for the best solution.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/18/2016 06:50 am
BTW

100 people weigh somewhere around 9-10 tonnes. Open loop LSS is 50 tonnes of consumables (hopefully 1/2 that or less with SoA ECLSS closing most of the loops)

But whats the power  & thermal situation?

I mean what are current figures of merit for PV arrays and radiators? In 2008 80-100W/Kg for a rigid array was SoA.  The same report gave thin film systems around 2000W/Kg It lists ISS as roughly 1W/Kg, a staggeringly low number IMHO.

http://www.spacefuture.com/archiveearly_commercial_demonstration_of_space_solar_power_using_ultra_lightweight_arrays.shtml

But what about radiators.

On Earth a human being has been simulated by a 400W incandescent lamp. So figure 40Kw for humans alone?  It's also likely to be low temperature heat, so radiation efficiency is likely to be low.

Does anyone have some actual numbers? IIRC ISS is about 40W/m^2 but that sounds like garbage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/18/2016 07:04 am
BTW

100 people weigh somewhere around 9-10 tonnes. Open loop LSS is 50 tonnes of consumables (hopefully 1/2 that or less with SoA ECLSS closing most of the loops)

But whats the power  & thermal situation?

I mean what are current figures of merit for PV arrays and radiators? In 2008 80-100W/Kg for a rigid array was SoA.  The same report gave thin film systems around 2000W/Kg It lists ISS as roughly 1W/Kg, a staggeringly low number IMHO.

http://www.spacefuture.com/archiveearly_commercial_demonstration_of_space_solar_power_using_ultra_lightweight_arrays.shtml

But what about radiators.

On Earth a human being has been simulated by a 400W incandescent lamp. So figure 40Kw for humans alone?  It's also likely to be low temperature heat, so radiation efficiency is likely to be low.

Does anyone have some actual numbers? IIRC ISS is about 40W/m^2 but that sounds like garbage.

400W? No, more like 100W. 400W is like a champion cyclist going full tilt. 40W/m^2 sounds about right on average for low-temperature ammonia radiator panels. Google is your friend. Each radiator panel can dump a maximum of about 200W/m^2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 02/18/2016 08:15 am

400W? No, more like 100W. 400W is like a champion cyclist going full tilt. 40W/m^2 sounds about right on average for low-temperature ammonia radiator panels. Google is your friend. Each radiator panel can dump a maximum of about 200W/m^2.

You are confusing mechanical power created vs heat energy generated. Humans have only about 30-40% energy efficiency when converting food to mechanical work, the rest is going to heat.

Top cyclist full power is about 1 kW, sustainable aerobic power about 400W. (I can do 700W on sprint and 300W sustained and I'm not a top cyclist.) Multiply that by 3 to get the total energy consumed(and heat generated assumed the work goes to heat) and that champion cyclist created 3 kW of heat on full spring, or 1.2 kW sustained.

But the 100 watts is still quite close to the idle consumption of humans,
women might be able to produce just 100 watts, men are typically bigger and heavier and produce something like 120-130 watts.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/18/2016 12:27 pm
2000kcal diet works out to 100Watts average. Conversion efficiencies irrelevant, it all becomes heat. :P
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 02/18/2016 02:38 pm
After reading the NASA reports/specs for "orbital" modules and reading the posts here, there seems to be a disjoint.  The MCT has to ascend and land which means passengers will need a seat.  Moreover, the MCT will be on Earth and Mars (in the vertical position) therefore orientation is predetermined.  This means that the vertical height will be fixed, most likely 7 feet.  The area (not volume) for a crew/sleep station should the size of a bed and storage.  The bed would articulate into a seat and workstation (aka cubicle).  Think of like a first class seat on a long haul aircraft.  Bed at (simulated) night and cubicle by day.  Not that different from my life if you minus my commute.  :)

Kaoru

The seat will need to oriented properly for takeoff and landing, but in microgravity during flight it can be moved to the wall. That will allow the personal space to be more vertical than horizontal. There will need to be enough room for a computer and storage of some personal items along the walls. 1.5m by 1m by 2.25m high totaling 3.375m^3 should be plenty of volume for personal space.

Sleeping and working in shifts can easily result in a crewperson spending 50% of their time in their personal space. With that in mind, 15m^3 per person would be about the same as 27m^3 per person if there was only one shift. That's a comfortable volume for a few months in microgravity. Going from 15m^3 down to 12m^3 would still be reasonable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/18/2016 08:00 pm
The bunks will almost certainly be vertical. Say 1.5m in from the wall, 1.5m of wall circumference, and then you can do an inner ring of bunks with similar dimensions. With such an arrangement you can easily fit 30 people in a 12m diameter floor, half that for your 8.3m radius tank. Also, the central corridor and doors are wasted space. Doors need space to open and if they open into a corridor can smack an unsuspecting passenger or snag some cargo being pushed along. All you need is a standard door-sized hole to make a corridor.
Obviously, I thought about making the bunks vertical (a la NASA) but that mode is only good for orbit/space.  What about when landed on Mars.  You can't move 100 people plus cargo when no or a limited hab is in place.  You'll need a place and do a migration over time; that means normally oriented beds.

As for doors, notice how they open.  I oriented the doors so that they are inline.  Why?  My intent was to model a top to bottom grab rail for traversing the core *on orbit* without being in the way of the doors.  The grab rails are door guards.  Also, the grab rails will do double duty as rails for a elevator/lift when *on surface*.

The doors can be auto-closing in case of depressurization.  As for case of the central core or any passenger station being depressurized, the NASA standard of wearing a pressure suit (like SpaceX's one) on ascent/EDL ops is given.  The suit will be stored under the seats when not in use.  If a emergency depressurized occurs, doors automatically close and occupants would don their suits.  Software can control the locking/unlocking of the doors via simple rules.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/18/2016 08:11 pm
The seat will need to oriented properly for takeoff and landing, but in microgravity during flight it can be moved to the wall. That will allow the personal space to be more vertical than horizontal. There will need to be enough room for a computer and storage of some personal items along the walls. 1.5m by 1m by 2.25m high totaling 3.375m^3 should be plenty of volume for personal space.

Sleeping and working in shifts can easily result in a crewperson spending 50% of their time in their personal space. With that in mind, 15m^3 per person would be about the same as 27m^3 per person if there was only one shift. That's a comfortable volume for a few months in microgravity. Going from 15m^3 down to 12m^3 would still be reasonable.
You still need a bed in the horizontal position if one of the modes is to use the module as a temporary hab on Mars.  It is *great* idea to allow the seat/bed to be reconfigured for more space while on orbit.  With an articulating frame you can have a normal (horizontal) seat, horizontal bed (for Mars surface; temporary), and a vertical bed for on orbit.  I'll see if I can work that into my module.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RocketmanUS on 02/18/2016 08:18 pm
The seat will need to oriented properly for takeoff and landing, but in microgravity during flight it can be moved to the wall. That will allow the personal space to be more vertical than horizontal. There will need to be enough room for a computer and storage of some personal items along the walls. 1.5m by 1m by 2.25m high totaling 3.375m^3 should be plenty of volume for personal space.

Sleeping and working in shifts can easily result in a crewperson spending 50% of their time in their personal space. With that in mind, 15m^3 per person would be about the same as 27m^3 per person if there was only one shift. That's a comfortable volume for a few months in microgravity. Going from 15m^3 down to 12m^3 would still be reasonable.
You still need a bed in the horizontal position if one of the modes is to use the module as a temporary hab on Mars.  It is *great* idea to allow the seat/bed to be reconfigured for more space while on orbit.  With an articulating frame you can have a normal (horizontal) seat, horizontal bed (for Mars surface; temporary), and a vertical bed for on orbit.  I'll see if I can work that into my module.

Kaoru
Inflatable mattress would work on Mars if needed for sleeping. Low mass, small volume when not inflated.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/18/2016 09:11 pm
From the comments given on my model, I got some ideas on how to improve space and access.  The idea RonM gave me got me thinking on how to have the seat/bed articulate horizontal to vertical.  For a display/workstation, I always planned to make it part of the seat/bed with an overhead console that contains air vent/fan (on orbit will always be on; got to move air around), lighting, connections (for pressure suit), and communications.  The pressure suit can be store in the overhead console/bin.  Think like an airplane.  However, this seat/bed with overhead console/storage would be fully integrated together.  This means that it will be functional as a horizontal bed, seat, or vertical bed.  Using this fold-away notion other equipment can now fold into this space for use.

One possible uses for this space is for exercise.  For example, an exercise treadmill will be necessary for everyone to stave off the effects of weightlessness.  However, having equipment as such per passenger station or in a common area has pros and cons.  I would like hear people opinions on how the space could be utilized (without costing a lot of mass) vis-ŕ-vis common areas like food prep, eating, hygiene, exercise, etc.

Update:  I forgot to mention my idea for the doors.  Originally I oriented the doors so that I could do a grab rail/lift rail that extends from the top to the bottom.  However, I like the idea of having a large central core but having the 8 doors latching onto the 4 rails shrinks the core space.  I got a brilliant idea from the Model X, make the doors double hinged (aka a folding door) and automatic (with sensors).  This effectively doubles the core space and doubles the elevator/lift area.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 02/18/2016 09:55 pm
That's an order of magnitude greater duration than the MCT's 3 month trip. Also, everything seems quite hand-wavy as to why /exactly/ that much space is needed.


90 day transit is insanely expensive in propellant, and while it might be possible to do it from LEO at huge cost in propellant.  But the longest leg of the journey is what you need to plan around and that is likely to be the Earth return leg.

Do your remember the discussion we had back on page 39 & 40 when we found that just 100 days Earth return launches from Mars surface would require 8.8 km/s DeltaV and significant aero-braking or propulsive capture at Earth.


Transit times of 120-180 days for Earth return are the range that's actually achievable.
I think this is no problem since you will land on Earth and you could easy recover from long voyage. What is important is trip to Mars, when arrived you have to be ready to work hard make colony alive.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 02/18/2016 10:46 pm
From the comments given on my model, I got some ideas on how to improve space and access.  The idea RonM gave me got me thinking on how to have the seat/bed articulate horizontal to vertical.  For a display/workstation, I always planned to make it part of the seat/bed with an overhead console that contains air vent/fan (on orbit will always be on; got to move air around), lighting, connections (for pressure suit), and communications.  The pressure suit can be store in the overhead console/bin.  Think like an airplane.  However, this seat/bed with overhead console/storage would be fully integrated together.  This means that it will be functional as a horizontal bed, seat, or vertical bed.  Using this fold-away notion other equipment can now fold into this space for use.

One possible uses for this space is for exercise.  For example, an exercise treadmill will be necessary for everyone to stave off the effects of weightlessness.  However, having equipment as such per passenger station or in a common area has pros and cons.  I would like hear people opinions on how the space could be utilized (without costing a lot of mass) vis-ŕ-vis common areas like food prep, eating, hygiene, exercise, etc.

Update:  I forgot to mention my idea for the doors.  Originally I oriented the doors so that I could do a grab rail/lift rail that extends from the top to the bottom.  However, I like the idea of having a large central core but having the 8 doors latching onto the 4 rails shrinks the core space.  I got a brilliant idea from the Model X, make the doors double hinged (aka a folding door) and automatic (with sensors).  This effectively doubles the core space and doubles the elevator/lift area.

Kaoru

I think as much as possible should be in common areas.

Having three shifts as Robotbeat suggested would get the maximum use out of the space. If a crewperson had to exercise for about one hour a day and if treadmills were available 24 hours a day, then the ship would only need five or six treadmills (some spare capacity for when one needs repair). A mess room for meals would only need to handle about fifteen people at a time. It could be larger if they wanted to avoid a strict schedule. There would just have to be a schedule for using these areas. Generic common areas would be larger for people to social, have meetings, etc.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/19/2016 01:33 pm
2000kcal diet works out to 100Watts average. Conversion efficiencies irrelevant, it all becomes heat. :P

OK so a baseline radiator needs to dump 10Kw from LEO out to Mars. I don't have a good number for specific power. 40W/m^2 from ISS gives 250 m^2 but what's that in mass? A quarter tonne? 25 tonnes? More?

I know over the years there have various proposals for tricky high efficiency space radiators using molten metals etc but AFAIK none of these have flown. Any updates on that would be greatly appreciated.

IMHO it's going to be liquids in a loop or vapors cooling back to liquids for the foreseeable future. I think tricks could be played with the surface properties to "tune" the IR emission frequency to most probable temperature, but I'm not sure how much that buys you in efficiency terms.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/19/2016 09:42 pm
For a radiator, the figure of merit you want is mass per unit area. State of the art experimental radiators can do 1.5-2kg/m^2. I think older heritage designs are more like 6kg/m^2.

Power per unit area is determined by the Stefan-Boltzmann law:

Power/area = 5.67*10^-8 W/(m^2*K^4)*T^4
(Use absolute temperature, i.e. Kelvin)
So to reject 10kW using state of the art radiator at 300 Kelvin (10 degrees below body temp) is about 32 kilograms.

More realistically, 273Kelvin rejection temp (0Celsius) and 100kW of heat and a more conservative (but still aggressive) 2kg/m^2 requires 635kg.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/19/2016 10:25 pm
But note that the body of the spacecraft itself emits heat, though it's insulated for reentry. Which is a good argument for putting the crew quarters inside a cargo bay with doors that can open to space like Shuttle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/20/2016 07:04 am
For a radiator, the figure of merit you want is mass per unit area. State of the art experimental radiators can do 1.5-2kg/m^2. I think older heritage designs are more like 6kg/m^2.
That's what I was looking for. Indicates propellant and HSF consumables are still the big mass items.
Quote
More realistically, 273Kelvin rejection temp (0Celsius) and 100kW of heat and a more conservative (but still aggressive) 2kg/m^2 requires 635kg.
I think the Shuttle payload bay door radiators worked around 60-80c
But note that the body of the spacecraft itself emits heat, though it's insulated for reentry.
True. I wanted to start with the human thermal load as we know the design is expected to support 100 people.

Above that will be heat from all the hardware in the system and solar radiation, close to 1300 W/m^2 above the  atmosphere at LEO.

That said I will note 2 things.

Heat can be treated as a resource. IIRC Shuttle hydraulic fluid circulated continuously on orbit to keep the actuators (out in the wings and tail) warm. I'm thinking better thermal control on mechanical stuff like aerial bearings perhaps.

Another option would be to use human power. 

Instead of packages of motors/gearboxes/sensors/power/data cabling just have someone pull on a lanyard at the right moment.  :)

I know. Very low tech. Very steam punk. But light weight, mechanically simple (theres a really neat way to transmit rotary motion through a solid metal wall which completely air tight) and with fault reporting just needs an intercom channel.
Quote
Which is a good argument for putting the crew quarters inside a cargo bay with doors that can open to space like Shuttle.
Maybe, but that would add substantial complexity and significant power requirements.

Worst case failure mode. Doors can't close. What do you do about Mars entry? Can you still do it?  Can you carry enough supplies for a free return back to Earth?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/20/2016 03:09 pm
You'll have failure modes like that no matter what because you need doors to open for the radiators and solar arrays. There are ways to deal with such failure modes. And actually, back shell temperatures are quite modest.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 02/21/2016 06:50 pm
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity, and using that to power a laser that they simply shone in to space.

Is that even theoretically possible?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Hauerg on 02/21/2016 06:59 pm
Usually when converting you have losses which express themselves as .... heat.
But SF might have "found" a better process.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jim on 02/21/2016 07:01 pm
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity,

How was the electricity produced?  Conversion of energy produces heat.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/21/2016 08:34 pm
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity, and using that to power a laser that they simply shone in to space.

Is that even theoretically possible?
No

The classic version of this is the Theremo Electric Modules used in RTGs to turn the decay heat from Plutonium directly into electricity. You're looking at about 8% efficiency.

So you need a smaller radiator, but you still need a pretty big one.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/21/2016 09:17 pm
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity, and using that to power a laser that they simply shone in to space.

Is that even theoretically possible?
No

The classic version of this is the Theremo Electric Modules used in RTGs to turn the decay heat from Plutonium directly into electricity. You're looking at about 8% efficiency.

So you need a smaller radiator, but you still need a pretty big one.
Nope! You need a larger radiator because you're rejecting the heat at a lower temperature (all methods of extracting useful energy from heat require some sort of thermal gradient or thermodynamically equivalent).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/22/2016 06:02 am
Here's another quick grab of improvements to my passenger model.  The biggest change is the diameter which is now 10.1 meters, the same as the Saturn V first stage.  With this diameter, each deck holds 24 sleep stations and 24 seats (fold-away).  That means only 4 decks for 96 passengers.  The deck features an airlock door.  Being a work in progress, still got fill out the sleep stations and put in a fold-away ladder for up and down on surface access.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/22/2016 07:15 am
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity, and using that to power a laser that they simply shone in to space.

Is that even theoretically possible?

Nope because the electrical side gets hot and that needs its own set of radiators. Basically you make more waste heat than you throw overboard.

I read a paper ages ago which described a "laser radiator" which basically a very complex gasdynamic laser. Essentially it produced a beam of light with a blackbody radiation curve which carried the waste heat away (so not really a radiator which shoots heat away as a laser beam).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/22/2016 07:44 am
Here's another quick grab of improvements to my passenger model.  The biggest change is the diameter which is now 10.1 meters, the same as the Saturn V first stage.  With this diameter, each deck holds 24 sleep stations and 24 seats (fold-away).  That means only 4 decks for 96 passengers.  The deck features an airlock door.  Being a work in progress, still got fill out the sleep stations and put in a fold-away ladder for up and down on surface access.

Kaoru

Unless you are designing for extended surface operations, you don't need the under-bed drawers, and you don't need the "dressing space" between the beds and the door. Designing for zero-g allows you to cheat by using a lot less space than normal. People don't stretch out in bed in zero gee - they float in foetal position, meaning your sleeping compartments are that much smaller. They can also go anywhere - wall, floor, ceiling. Lockers too can go anywhere. You don't need "floor" space where you can have a dual usage area - vertical corridors don't need landings, etc. Since your walls are all just partitions, you can just take them down and stow them for atmospheric entry and landing.

(http://images.spaceref.com/news/2011/iss026e012169.jpg)

The 100-person MCT will only be operational much later in the 21st century. By then, Mars will have landing pads and domes / underground tunnels / modules/ whatever to handle an influx of colonists. Many of the initial colonists will earn their money by continually building colony habitats for the newcomers.

Now of course if you want to design for an artificial gravity environment during the trip, then that's going to change things and naval designs may be the better option (ie your current layout).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/22/2016 10:40 am
The 100-person MCT will only be operational much later in the 21st century.
And you know this how exactly? Musk seems quite clear on getting this up and running fairly soon.
Quote
By then, Mars will have landing pads and domes / underground tunnels / modules/ whatever to handle an influx of colonists. Many of the initial colonists will earn their money by continually building colony habitats for the newcomers.
Quite possibly.
Quote
Now of course if you want to design for an artificial gravity environment during the trip, then that's going to change things and naval designs may be the better option (ie your current layout).
It's a fair point that Musk does not not seem to have mentioned AG, although it would simplify some problems and effectively give everyone a workout without exercise machines.

But that would be a really bleeding edge design given our experience of in space AG systems to date IE one of the Geminis spinning on a tether with their booster.  :(
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/22/2016 02:18 pm
The 100-person MCT will only be operational much later in the 21st century.
And you know this how exactly? Musk seems quite clear on getting this up and running fairly soon.
Quote

I have a soothsayer that says so. His name on these forums is Jim. :P

Some people would say AG would be less bleeding edge than landing a first stage rocket on a barge at sea. Or a reusable surface-to-surface Mars Colony Transport.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/22/2016 03:04 pm
Just because we COULD do AG doesn't mean we SHOULD. If your trip is short, you don't need it and probably shouldn't use it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 02/22/2016 03:34 pm
From one of the ISS videos, they show people sleeping in a bag attached to the wall.  This keeps them from floating around and touching something.  You don't need bunks in zero g.  I even saw one lady astronaut who designed a double bag for a husband/wife team for privacy.  Their work stations can double as their quarters like cubicles in large offices and they could have bags to sleep in and work quarters that also have doors for privacy.

If these living quarters could also be offloaded on Mars for habitats it would save a lot of money and trouble, even if you can only get 50 colonists at a time.   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/22/2016 04:24 pm
Just because we COULD do AG doesn't mean we SHOULD. If your trip is short, you don't need it and probably shouldn't use it.

I agree. Short as in not much more than one year. We may need AG when we send people out to the asteroid belt or beyond.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/22/2016 05:20 pm
Unless you are designing for extended surface operations, you don't need the under-bed drawers, and you don't need the "dressing space" between the beds and the door. Designing for zero-g allows you to cheat by using a lot less space than normal. People don't stretch out in bed in zero gee - they float in foetal position, meaning your sleeping compartments are that much smaller. They can also go anywhere - wall, floor, ceiling. Lockers too can go anywhere. You don't need "floor" space where you can have a dual usage area - vertical corridors don't need landings, etc. Since your walls are all just partitions, you can just take them down and stow them for atmospheric entry and landing.

The 100-person MCT will only be operational much later in the 21st century. By then, Mars will have landing pads and domes / underground tunnels / modules/ whatever to handle an influx of colonists. Many of the initial colonists will earn their money by continually building colony habitats for the newcomers.

Now of course if you want to design for an artificial gravity environment during the trip, then that's going to change things and naval designs may be the better option (ie your current layout).
I agree with you if the passenger module was going to be on orbit exclusively.  However, the modes that the passenger module will be employed is for both on orbit and on surface.  My take is that it will take lots of man power to build the first habitat on Mars.  This means the passenger module, as part of the Mars landing, will be the habitat for some time.  When on orbit, orientation or areas as you describe are meaningless.  However, on the surface it does matter so my layout inherently supports both on orbit and on surface modes.

Also, the use of walls and auto closing cabin doors (like a hotel room door) is for safety.  Ascent and EDL ops means that everyone will don their pressure suits (which are IVA only) and strapped in their fold-away seats.  The rest of the time, if a depressurization event occurs due to micro-meteoroid impact, etc. closed cabin doors prevent total loss of atmosphere.  In the event that the central core is loses pressure, the IVA suits and the deck doors (which can be made to close on pressure loss) can be used to get around and effect repairs.

Of course, my model is still a work-in-progress.  I had a lot done but now have to redo it for the new diameter.  Also, I'm adding interactive things like opening/closing doors.  I'm refining the model trying to be mass conscious.  My experience so far has shown me that building a BFR and BFS for 96-100 persons to Mars is doable, aka not outrageous to the extreme.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 02/22/2016 09:37 pm
I don't believe we will see a large habitat that is intended for surface AND space usage.

Rather we will see SMALL (~10 person) habitats that are usable in both environments for early missions when their is no pre-existing base to move into.  And in this role I foresee a large wheeled habitat/rover filling the entire cargo bay and simply rolling out onto the surface as the ideal solution as it provides instant and maximum mobility for exploration.  The rover can act as the habitat for transit to mars, on mars and then back to Earth and the landing vehicles can all be of an identical nature with large empty cargo holds ideal for the heavy machinery and equipment that would dominate the early missions.  This also adds redundancy by allowing any of the landing vehicles to be the one used for return should one suffer a breakdown.

But that will be a VERY short-lived phase, maybe just 1-3 missions to do scouting, once real base building is done they will consist of  habitat structures permanently left on Mars with arriving persons immediately moving from the vehicle into these surface habitats. 

The vehicle will thus NOT need to be lived in under gravity.  At most the vehicle needs some kind of seating for experiencing g-forces on entry but that is it, it would otherwise be a habitat designed fully for zero-g living, much like the space shuttle.

Further I expect these later missions to use a larger space-only transit habitat as in Semi-Direct DRM mission plans, that will allow the landing vehicle to be designed around much much shorter duration usage, on the order of 3 days at most.  People can be packed in at around 1 m^3 each or less which will make it quit easy to understand how the same size vehicle can accommodate a 10 fold increase in head count, we must relax the time constraint proportionally. 

In something like coach air-plane densities the lander in this configuration is also an excellent high volume LEO taxi craft for rendezvous with the rest of the mission elements which will proceed to TMI (propellants habitats, cargo), thouse elements will have been built up over the 26 month period between departure windows and passengers must be brought to these elements only just before the TMI to minimize time in space and deleterious health effects of such so a high density taxi launched last is the most efficient solution.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: darkenfast on 02/23/2016 04:33 am
Here's another quick grab of improvements to my passenger model.  The biggest change is the diameter which is now 10.1 meters, the same as the Saturn V first stage.  With this diameter, each deck holds 24 sleep stations and 24 seats (fold-away).  That means only 4 decks for 96 passengers.  The deck features an airlock door.  Being a work in progress, still got fill out the sleep stations and put in a fold-away ladder for up and down on surface access.

Kaoru

Try stacking the bunks three-high, with pan lockers under the mattresses.  That will give you basically what enlisted personnel live in on U.S. Navy ships and better than some submarines.  You can put a surprising amount of stuff in one of those lockers.  Allow 100mm for the pan, 100mm for the mattress an .5 - .55 meters for the person.  Deck to overhead distance totals 2.1 - 2.25 meters.  For width and length, try .7m by 2 - 2.1m.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/23/2016 06:45 am
Just because we COULD do AG doesn't mean we SHOULD. If your trip is short, you don't need it and probably shouldn't use it.
Most people would not consider 3-4 months a short trip.

However the practical work on AG is so limited it would absurd to bet your plans on it working.

If space exploration were done logically it's a technique that would have been tried decades ago and its benefits and problems already found. Yet in 2016 it still has had no full scale test.  :(
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/23/2016 07:15 am
Just because we COULD do AG doesn't mean we SHOULD. If your trip is short, you don't need it and probably shouldn't use it.
Most people would not consider 3-4 months a short trip.

However the practical work on AG is so limited it would absurd to bet your plans on it working.

If space exploration were done logically it's a technique that would have been tried decades ago and its benefits and problems already found. Yet in 2016 it still has had no full scale test.  :(

Why do such a test? We do know for a fact that 1 year is not a problem. Advocates of AG should get over it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: QuantumG on 02/23/2016 08:34 am
Yeah, I agree. Robotbeat convinced me of this years ago. Zero-g mitigation is now sufficient for exploration missions in the inner solar system. You could make the argument that it always has been.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/23/2016 11:13 am
Zero-g certainly allows a much more compact ship than would otherwise be the case.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/23/2016 02:59 pm
I agree that AG should not be in the critical path.  With that said...

Zero-g certainly allows a much more compact ship than would otherwise be the case.

Please convince me of this.  The counterpoint would be a bolo made of two MCTs connected by tether at the nose.  Spinup and spindown by synchronized use of RCS thrusters.

Assume MCT will not employ SEP, obviously.  Are booms to extend a small solar panel + radiator curtain roll so mass-expensive?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 02/23/2016 04:34 pm
How was the electricity produced?  Conversion of energy produces heat.

The question is  good one, however conversion of energy in an endothermic reaction absorbs heat. I do not know what their supposed mechanism is, however people who continue to claim that it is impossible due to violation of second law of thermodynamics are incorrect. When you smash a cold pack and put it on a sprained ankle, it gets cold due to ambient heat driving the endothermic reaction. Ambient heat is converted into potential energy and locked up in the molecules created. Most mechanical conversions usually are exothermic due to inefficiencies of the conversion mechanism, however endothermic chemical reactions do exist. Photovoltaic panels convert visible electromagnetic energy into electricity. I would think that conversion of the infrared portion of the electromagnetic spectrum into electricity should be theoretically possible. A heat pump might assist in concentrating the thermal energy prior conversion, but that is a separate mechanism with its own set of issues.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Krevsin on 02/23/2016 04:47 pm
The cold pack dumps its heat to the surrounding air. The heat is still present, it's just been moved, namely from the pack and to the surrounding air. It's why the backs of fridges are hot. Because the fridge is merely dumping the heat, not unmaking it.

"Endothermic" does not mean "laughs in the face of entropy", rather it states that a certain reaction requires heat to happen and it most certainly does not remove the heat, merely moves it around.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 02/23/2016 05:37 pm
Just because we COULD do AG doesn't mean we SHOULD. If your trip is short, you don't need it and probably shouldn't use it.
Most people would not consider 3-4 months a short trip.

However the practical work on AG is so limited it would absurd to bet your plans on it working.

If space exploration were done logically it's a technique that would have been tried decades ago and its benefits and problems already found. Yet in 2016 it still has had no full scale test.  :(

It doesn't matter. It's a voluntary trip. If the people decide, with the evidence to date, that this is a non-issue, more power to them. If lack of AG kills them it's no fault but their own. If you're not convinced that it's safe (as I am far from being) you shouldn't of signed up for the ride.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 02/23/2016 07:51 pm
The cold pack dumps its heat to the surrounding air. The heat is still present, it's just been moved, namely from the pack and to the surrounding air. It's why the backs of fridges are hot. Because the fridge is merely dumping the heat, not unmaking it.

"Endothermic" does not mean "laughs in the face of entropy", rather it states that a certain reaction requires heat to happen and it most certainly does not remove the heat, merely moves it around.

You are simply wrong. The heat pump on a refrigerator does move the heat, but that is not what happens in an endothermic reaction. I used to teach both chemistry and physics, as well as biology. When carbon oxidizes, potential energy is given off as heat. In an endothermic reaction, ambient heat is absorbed and changed into potential energy in the new chemical bonds that are created. The energy changes from thermal energy to potential energy. A cold pack does not dump heat; it soaks it up. You are absolutely and totally W...R...O...N...G ! ! !  Go look it up. Exo thermic means puts out heat. Endo thermic literally means that heat goes into the reaction. Quit arguing and go do the research.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 02/23/2016 09:17 pm
I doubt that Musk is planning to use AG, however...

a bolo made of two [MCTs BFSs] connected by tether at the nose. Spinup and spindown by synchronized use of RCS thrusters.
[my edit]

A tether is almost certainly not necessary. If the crew can tolerate/adapt to higher RPM as easily as they are expected to adapt to micro-g, and if 1/3-1/2g is sufficient to offset micro-g damage, then a single BFS spinning around its long axis should be sufficient. Put the work and exercise areas against the hull, with the sleep areas down the centre (low-g sleep is more pleasant, and gravity works less when you are reclining anyway). (Sorry Kaoru, I guess you need to redesign the ship again.)

If higher-g or lower RPM is required, spinning the BFS around its short axis (tumbling pigeon) would allow up to 1g at 6RPM or 1/2g at 4RPM. (Depending on the length of the BFS, I've arbitrarily used 50m.) Work/exercise areas at the nose, sleeping areas towards the CoM. (Engines/cargo as countermass.) And if you dock two BFSs together by their aft ends, spinning them end-over-end, the fore-end of each will be able to reach half a g from just 3RPM, and 1g from just over 4RPM.

If you need a lower RPM and higher g-load, then frankly AG is really not worth the effort. (As JS19 notes, it would be nice to have some firm figures by now. Especially given how small an experiment it would be compared to Apollo/STS/ISS/SLS development costs.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/23/2016 09:20 pm
Having looked a little more into the ISS ECLSS system it looks like they have a long way to go on weight reduction.

My very rough estimate is at present we're looking about 333Kg/person of ECLSs hardware per person.

Reading the descriptions of the hardware is quite odd. All the systems seem to have been built completely separately and some of the design choices seem strange. The trace gas monitor, that monitors 8 (and no other) airborne species, weighs 58Kg and is a sort of mass spectrometer IE needs high vacuum to operate without destroying filaments and a 5000psi gas canister to regularly re-calibrate it.

This is despite the fact people have been shrinking gas chromatographs (as in systems that analyse gas) from silicon wafers down to chips since the 1970's. Likewise optical sensors have improved beyond all recognition.

And the commode weighs 50Kg. ::)  A 110lb toilet.  I get it, gas,water and solid separation is complex. But 50Kg. Really?

[EDIT An interesting special case. Hair & nail clippings. Keratin is a tough protein and can foul equipment but could make the raw material for say 3d printing objects. Or should it be broken down to its elements? ]

It's pretty clear they're going to need a lot more work toward integrating these systems, tapping heat released from some cycles to drive others, common design elements so basic units can be repurposed as necessary.

The SoA in this stuff is the use of integrated  heat exchangers and chemical reactors mfg using diffusion bonded metal foils. These units are typically 1/3 the size of more conventionally built systems. It's referred to as "process intensification" and several chemical plant mfg do this.

My instinct is somewhere between the current system and the highly integrated PI systems is a system efficient enough to get the job done and light enough to make it worthwhile.

Personally I quite like photocatalyst systems built around flowing most of the stuff through a reactor loaded with TiO powder and exposed to UV light. IIRC this has been used to rip most molecules down to CO2, H2O and various metal salts, although I'd guess N2 is a probably end point as well.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RocketmanUS on 02/23/2016 11:46 pm
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity,

How was the electricity produced?  Conversion of energy produces heat.
Thermocouple
https://en.wikipedia.org/wiki/Thermocouple

Thermopile
https://en.wikipedia.org/wiki/Thermopile

Radioisotope_thermoelectric_generator
https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

Stirling_engine
https://en.wikipedia.org/wiki/Stirling_engine

May not be mass and or volume efficient inside the MCT. Radiators might be better.

The electrical energy produced could then be used to help run the heat pump ( A/C ). I don't know if this could generate more or less power than what is needed to run the heat pump ( A/C ).

There would need to be a study to see if this could remove all the heat or just some of it ( still needing some amount of radiators ).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 02/23/2016 11:50 pm
the commode weighs 50Kg. ::)  A 110lb toilet.  I get it, gas,water and solid separation is complex. But 50Kg. Really?

I wonder if it needs to be that size just to do the job, regardless of whether it is used by 6 people or 60 people. If more people can use some of these systems, the needed mass per person could go down
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/24/2016 12:25 am
The cold pack dumps its heat to the surrounding air. The heat is still present, it's just been moved, namely from the pack and to the surrounding air. It's why the backs of fridges are hot. Because the fridge is merely dumping the heat, not unmaking it.

"Endothermic" does not mean "laughs in the face of entropy", rather it states that a certain reaction requires heat to happen and it most certainly does not remove the heat, merely moves it around.

You are simply wrong. The heat pump on a refrigerator does move the heat, but that is not what happens in an endothermic reaction. I used to teach both chemistry and physics, as well as biology. When carbon oxidizes, potential energy is given off as heat. In an endothermic reaction, ambient heat is absorbed and changed into potential energy in the new chemical bonds that are created. The energy changes from thermal energy to potential energy. A cold pack does not dump heat; it soaks it up. You are absolutely and totally W...R...O...N...G ! ! !  Go look it up. Exo thermic means puts out heat. Endo thermic literally means that heat goes into the reaction. Quit arguing and go do the research.
I know what you're talking about WRT endothermic reactions. These do not violate the laws of thermodynamics because entropy still increases, and you soon run out of the little reservoir of low entropy.

This other device you're talking about, a device that's able to generate useful energy by absorbing waste heat indefinitely would clearly NOT obey the laws of thermodynamics.

Please realize that this device that you keep defending is not possible.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 02/24/2016 02:17 am
I know what you're talking about WRT endothermic reactions. These do not violate the laws of thermodynamics because entropy still increases, and you soon run out of the little reservoir of low entropy.

This other device you're talking about, a device that's able to generate useful energy by absorbing waste heat indefinitely would clearly NOT obey the laws of thermodynamics.

Please realize that this device that you keep defending is not possible.

I have not defended any device. I stated above that I do not know the methodology by which it supposedly works, however, such a device is theoretically possible.

Photosynthesis is classified as an endothermic reaction, even though the energy input is in the visible range of the spectrum rather than the infrared portion. While lacking in efficiency, photovoltaic cells convert the visible portion of the electromagnetic spectrum into electricity as photons elevate electrons across a barrier. The electricity can then drive a chemical reaction that builds potential energy in a battery or stores the electrons in a capacitor.

Now I am not aware of a mechanism whereby infrared energy in the spectrum can excite electrons and move them across a photovoltaic membrane, however the second law of thermodynamics would not preclude it. It would likely be inefficient. A good deal of heat still would radiate away, just as it does in a normal photovoltaic cell, but there is no theoretical reason that thermal energy could not be converted back into potential energy by mechanisms other than endothermic chemical reactions. You are simply converting some kinetic energy to potential energy and losing some of it through inefficiencies and conversion.

In endothermic chemical reactions, heat is absorbed, the temperature of the reactants drops as measured in a calorimeter, and potential energy is created in bonds and in valences which have exothermic bonding potential. The second law of thermodynamics is not violated. In like manner, there could exist other mechanisms which perform a similar function.

I don't know anything about the device that has been mentioned. I haven't looked at the purported mechanisms at all. All I am saying is that in theory, thermal energy can be converted to potential energy without violating the 2nd law of thermodynamics, and that this principle is verified in endothermic chemical reactions.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lampyridae on 02/24/2016 08:47 am
I agree that AG should not be in the critical path.  With that said...

Zero-g certainly allows a much more compact ship than would otherwise be the case.

Please convince me of this. 

Essentially, the difference between playing Tetris and playing Tetris without being able to rotate the bricks.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 02/24/2016 01:34 pm
[Put this in a single post to make it easier for mods to remove, when they finally get sick of this off-topic argument. Sure, I'm a jerk, but I'm a considerate jerk.]

Thermocouple
Thermopile
Radioisotope_thermoelectric_generator
Stirling_engine
May not be mass and or volume efficient inside the MCT. Radiators might be better.

Bothą require radiators. They operate by exploiting the temperature difference between a hot-side and a cold-side. Without a radiator, the two sides will equalise in temperature. In order to do work, you have to constantly pump concentrated heat in and pump/radiate waste heat out. You need a heat source and a heat sink, and the heat source must be a higher grade of energy (more concentrated) than the heat sink. To do work, you turn the high-grade source heat into lower-grade waste heat.

ą Both thermopiles and sterling engines. The other two are redundant. Thermocouples use the same principle as thermopiles (or vice versa). And RTGs use thermopiles to actually produce electricity (research RTGs (https://en.wikipedia.org/wiki/Stirling_radioisotope_generator) have also used sterling engines).

The electrical energy produced could then be used to help run the heat pump ( A/C ). I don't know if this could generate more or less power than what is needed to run the heat pump ( A/C ).

Always less. Laws of physics.

Please realize that this device that you keep defending is not possible.
I have not defended any device. I stated above that I do not know the methodology by which it supposedly works, however, such a device is theoretically possible.

Not really. It must violate thermodynamics.

It's possible to develop a refrigerator (obviously) which concentrates heat energy to allow it to radiate away. And perhaps it's possible to develop a refrigeration laser (Brin was obviously riffing on the then newly invented laser doppler cooling), which concentrates its waste heat as a beam. But thermodynamics requires that the heat output is in a lower grade form than the total energy input.

In a refrigerator, you can "cheat" to turn low grade room-termperature heat into higher-grade hot-radiator and cold-interior by stealing very-high-grade electricity and turning it into more low grade waste heat. The waste-heat created at the power-plant to generate electricity is not being pumped into the fridge interior along with the electricity. It's the decoupling that allows the system to work.

[Think about it. The compressor (or other heat-pump) of a standard fridge uses a certain amount of electricity (or other power source) in order to cool the interior from room-temp to 3-4℃. If you pumped in the waste-heat from the power-production as well, the compressor would clearly need to work harder to get rid of that heat too, which means using more electricity, which means more waste heat, which means yet more electricity, which means... You can't close the loop unless you have a method of creating high-grade energy which the heat-pump doesn't have to deal with.]

In Brin's ship, where does the high-grade energy coming from to power the laser? A reactor of some kind inside the ship? The waste heat from that reactor must also be disposed of by the same refrigeration-laser that is cooling the ship.

Forget the internals. You've got a closed box that is not only cooler than the environment, but outputs a concentrated beam of high-intensity energy. Clearly you could use that super-high-grade energy to generate power to run the refrigeration-laser. Hence you've invented a free energy machine, and Maxwell's Demon is sadly shaking his head no.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/24/2016 02:31 pm
This is dumb. Can we get back on topic instead of giving a platform to people (who ought to understand thermodynamics) to demonstrate that they don't understand thermodynamics?

You can't make your radiator smaller by trying to get free energy. Argue about it in the New Physics section if you like.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH on 02/24/2016 03:14 pm
This is dumb. Can we get back on topic instead of giving a platform to people (who ought to understand thermodynamics) to demonstrate that they don't understand thermodynamics?

You can't make your radiator smaller by trying to get free energy. Argue about it in the New Physics section if you like.

No, it's not dumb. Because most people don't understand the laws of thermodynamics. But should be elsewhere, certainly.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/24/2016 04:25 pm
I agree that AG should not be in the critical path.  With that said...

Zero-g certainly allows a much more compact ship than would otherwise be the case.

Please convince me of this. 

Essentially, the difference between playing Tetris and playing Tetris without being able to rotate the bricks.

So you're talking about increased packing efficiencies from being able to store things in the ceiling/floor racks?

You know we get to build lower ceilings (and more floors) if we remove those, right?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/24/2016 04:30 pm
I'd like to say a few words about laundry.

Assuming people wear their clothes for a week each that's a minimum of 1500 sets of clothes you'll be taking to Mars unless something gets done about reusing them.

Remember this is not the ISS, where stocks can be substantial and resupply is (relatively) easy.  :(

Before we get to all the tricky techno solutions (BTW still waiting for my waterless ultrasonic clothes cleaner) could I suggest a simple, clear heavish grade plastic bag you stick your stuff in with a waterproof closure, hook up to water & soap connectors then knead the water & soap in to hand wash.

Personally I think it could be quite theraputic.  :)

Now the rinsing and drying stuff looks a bit harder. A waste connector to flush the water then transfer to a warm dry air cabinet to gradually suck the water off the fabric?

Naturally this all has to be plumbed into the ECLSS to to work.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 02/24/2016 04:34 pm
Here's another quick grab of improvements to my passenger model.  The biggest change is the diameter which is now 10.1 meters, the same as the Saturn V first stage.  With this diameter, each deck holds 24 sleep stations and 24 seats (fold-away).  That means only 4 decks for 96 passengers.  The deck features an airlock door.  Being a work in progress, still got fill out the sleep stations and put in a fold-away ladder for up and down on surface access.

Kaoru

This is great, however I don't think your floor will be able to stand up to the differential pressure if you close the door. The floor will become a pressure bulkhead and need to be rounded. At 1 atmosphere there will be about 750 tones of load on the floor. 101 kpa per m2, or 10 tonnes.  Even at 1/2 atmosphere you get a lot of load.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 02/24/2016 04:41 pm
I'd like to say a few words about laundry.

Assuming people wear their clothes for a week each that's a minimum of 1500 sets of clothes you'll be taking to Mars unless something gets done about reusing them.

Remember this is not the ISS, where stocks can be substantial and resupply is (relatively) easy.  :(

Before we get to all the tricky techno solutions (BTW still waiting for my waterless ultrasonic clothes cleaner) could I suggest a simple, clear heavish grade plastic bag you stick your stuff in with a waterproof closure, hook up to water & soap connectors then knead the water & soap in to hand wash.

Personally I think it could be quite theraputic.  :)

Now the rinsing and drying stuff looks a bit harder. A waste connector to flush the water then transfer to a warm dry air cabinet to gradually suck the water off the fabric?

Naturally this all has to be plumbed into the ECLSS to to work.
You can vacuum dry most things, at low pressure the water will boil away from its own heat. You can put the water back into the eclss. Cleaning a sleeping bag may be a chore though.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 02/24/2016 04:42 pm
This other device you're talking about, a device that's able to generate useful energy by absorbing waste heat indefinitely would clearly NOT obey the laws of thermodynamics.

Please realize that this device that you keep defending is not possible.

No, it's not dumb. Because most people don't understand the laws of thermodynamics. But should be elsewhere, certainly.

I never said anything about absorbing waste heat endlessly. I in fact stated that any such mechanism would likely be very inefficient. I am not the person who proposed such a device. All I have ever posited is that some heat can be captured and converted to potential energy through endothermic means which differ from things like heat pumps (which require more total heat to be added to a system and just move heat from one place to another).

As far as people not understanding thermodynamics, give me a break. There are people here who seem to think that heat and energy are limited to the simplistic closed systems that are theoretically examined in Physics 102. There are people other than thermodynamicists who examine and calculate the flow of heat and energy. The canopy of a tropical rain forest lowers the ambient temperature as much as 20-30 degrees F as solar energy is converted to chemical potential energy in sugars. Ecologists calculate the flow of energy from producers through primary, secondary, and tertiary consumers in an ecosystem. At each level, only about 10% of the energy is transferred to the next level up the food chain.

Some heat can be captured and converted to potential energy through endothermic chemical reactions and endothermic mechanical processes. Most of these are rather inefficient and impractical. I am not saying you do not lose energy. I am not saying you can recapture and reuse the same energy endlessly. I know you cannot. I am simply saying there is more to thermodynamics than the simplistic calculations that are done with simple closed systems that involve nothing more than conduction, convection, radiation, and evaporation.

When astronauts eat, metabolism of glucose going through the Krebs Citric Acid Cycle changes potential energy in the glucose into thermal energy that is added to the system. Batteries release thermal energy into the system as electricity experiences resistance. Heat can be added to a system, and small amounts of heat can be removed from a system through endothermic chemical reactions as well as endothermic physical mechanisms which change some of the energy back to potential energy. Is there anything that I know of that has enough efficiency to be of practical usefulness on a spacecraft in the near future? Frankly, no; I do not know of anything that would be practical. OTOH, those who say that no thermal energy whatsoever can be converted into potential energy, that is incorrect. You are limiting you overall system to subsystems that are not endothermic.  These mechanisms, though inefficient, do not violate the second law of thermodynamics. The heat simply changes from thermal energy to potential energy.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 02/24/2016 04:56 pm
Zero-g certainly allows a much more compact ship than would otherwise be the case.
Please convince me of this.
Essentially, the difference between playing Tetris and playing Tetris without being able to rotate the bricks.
So you're talking about increased packing efficiencies from being able to store things in the ceiling/floor racks?

It's mainly the efficiency inherent in being able to change your own orientation.

How much more "benchtop" would you have in your kitchen if you could use the cupboard doors, the walls and the ceiling and floor as a work surface. And hence how many more people could work comfortably in that space without crowding each other.

[edit: Although, that said, the "not going crazy" volume requirements eliminate any packing-efficiency from micro-g anyway. So I don't think that's a vote against AG.]

Before we get to all the tricky techno solutions (BTW still waiting for my waterless ultrasonic clothes cleaner) could I suggest a simple, clear heavish grade plastic bag you stick your stuff in with a waterproof closure, hook up to water & soap connectors then knead the water & soap in to hand wash.
Now the rinsing and drying stuff looks a bit harder. A waste connector to flush the water then transfer to a warm dry air cabinet to gradually suck the water off the fabric?

There's a big gap between a sci-fi waterless ultrasonic cleaner and "stick it in a bag with some soapy water".

A water efficient combination washer/dryer seems pretty trivial compared to everything else that'll need to work. It doesn't need to be as fast or heavy as anything we use in the home. Hell, if you must, it can even be spun by hand (or foot (http://1.bp.blogspot.com/-DnJHnHn3X24/VXsTw5BQOII/AAAAAAAAEhM/vsIyWM4jLS0/s1600/Maquina%2Bde%2Blavar%2Bbicicleta.jpg))
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 02/24/2016 05:03 pm
TomH,
If you melt 1 kg of ice you will be transforming it from lower potential, a solid, to higher potential, a liquid. To reuse it you will need to re freeze it.  To do so on a spaceship you will need a radiator. Same thing with chemical potential.
I've done a bit of math and I find about 10  kW of lighting, 10 kW of crew heat, another 10 kW of electronics and 20 kW of miscellaneous gains such as pumping, conductor resistance, water heating,  food heating, washing, air scrubbing, etc  So at least 50 kW of thermal load on the radiators, since all this heat comes from combustion of food, or the solar cells. As the hull needs to be insulated for re entry, it will be at low temperture and likely not a good radiator, so we will need a lot of radiators.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RocketmanUS on 02/24/2016 05:26 pm
{snip for length }
We are considing the possible design for removing excess heat from the MCT , that is part of the MCT's design.

I did put in the disclosures in my post above of what you replied to, agreeing to some or all of what you stated.

Thermopile and Stirling_engine, yes I know they both need to be cooled on the other side. However it could possible have an over all reduction the temperature in the cabin.

And I did say help in powering the heat pump, meaning it would not be able to supply all the needed power. The rest of the power would need to come from the MCT's power source ( solar panels ).

Research still would need to be done. However it is possible to be done to reduce the heat in a given area, but do to size and mass it may not be possible on something like the MCT. Radiators would most likely for now be the most mass efficient way to get ride of the excess heat in the cabin.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jim on 02/24/2016 05:53 pm

And I did say help in powering the heat pump, meaning it would not be able to supply all the needed power. The rest of the power would need to come from the MCT's power source ( solar panels ).


The only way of removing heat from the MCT is by radiators or dumping mass.  There is no way around it.   A "heat pump" by definition moves heat from a cold region to a hot region and it consumes energy in the process which generates more heat.  A heat pump does not use direct heat for power.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 02/24/2016 06:19 pm
Here is a little spreadsheet about radiators, solar cells and energy use.

Basically, I propose 100 kW of electric peak power at Mars, so almost 200 at Earth; 70 kW of radiators, about 50 kW of peak energy use in the ship habitat.

Anyone have a suggestion about the energy required to recycle CO2 back into O2?

Radiators would be attached to cargo bay door, as for the shuttle, or extend out like the ISS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RocketmanUS on 02/24/2016 06:45 pm

And I did say help in powering the heat pump, meaning it would not be able to supply all the needed power. The rest of the power would need to come from the MCT's power source ( solar panels ).


The only way of removing heat from the MCT is by radiators or dumping mass.  There is no way around it.   A "heat pump" by definition moves heat from a cold region to a hot region and it consumes energy in the process which generates more heat.  A heat pump does not use direct heat for power.
Jim in an above post I did stay a Stirling engines and not heat heat pump for producing power from the waste heat, the heat pump just moves heat from one point to another. For the tech we have today I agree with you that the heat pump would most likely produce more heat than the Stirling engine would convert to electrical power. That making this not work on a space craft meant to land on a planet. But that does not mean sometime in the future it will not be possible to have such a system be able to work on a craft such as the MCT concept. People are working on the concept, it may or may not ever work.

And some heat pumps do use heat for power. Look up motor home refrigerators and how they use heat from propane to work ( this would not work for MCT ).

So for now I agree the MCT would be using radiators for getting rid of excess heat.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jim on 02/24/2016 07:00 pm

1.  Jim in an above post I did stay a Stirling engines and not heat heat pump for producing power from the waste heat,

2.   the heat pump just moves heat from one point to another. For the tech we have today I agree with you that the heat pump would most likely produce more heat than the Stirling engine would convert to electrical power. That making this not work on a space craft meant to land on a planet. But that does not mean sometime in the future it will not be possible to have such a system be able to work on a craft such as the MCT concept. People are working on the concept, it may or may not ever work.


1.  The Stirling still needs a radiator to work. 

2. Technology today or tomorrow isn't going to change things. 

There is no way around it, there always will be radiators on spacecraft.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 02/24/2016 07:25 pm
And some heat pumps do use heat for power. Look up motor home refrigerators and how they use heat from propane to work

Yes, look up how they work. Study it until you intuitively understand it. You should eventually realise why you are wrong about being able to replace radiators with "something like a sterling engine"; why that concept doesn't make any sense whatsoever.

Propane- or kerosene-burning fridges exploit the difference between the high-grade heat of the burner and the lower-grade heat-sink of the radiator coil/fins in order to do work. If you removed the radiator, the inside of the fridge would just heat up.

A sterling engine likewise exploits the difference between a heat source and a heat-sink. The heat-sink is normally produced via a radiator coil/fins radiating lower-grade heat into the environment. Something must take the heat away from the system or else the two sides will simply come to equilibrium and the engine will stop working.

You can't have a refrigeration system that doesn't have some kind of heat sink to eliminate the waste heat.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/24/2016 07:52 pm
Before we get to all the tricky techno solutions (BTW still waiting for my waterless ultrasonic clothes cleaner) could I suggest a simple, clear heavish grade plastic bag you stick your stuff in with a waterproof closure, hook up to water & soap connectors then knead the water & soap in to hand wash.
Now the rinsing and drying stuff looks a bit harder. A waste connector to flush the water then transfer to a warm dry air cabinet to gradually suck the water off the fabric?

There's a big gap between a sci-fi waterless ultrasonic cleaner and "stick it in a bag with some soapy water".
True. Mostly that the bag solution already exists, which I'd forgotten when I originally posted.  Something like it is sold as a gadget for backpackers and lightweight travelers.
Quote
A water efficient combination washer/dryer seems pretty trivial compared to everything else that'll need to work. It doesn't need to be as fast or heavy as anything we use in the home. Hell, if you must, it can even be spun by hand (or foot (http://1.bp.blogspot.com/-DnJHnHn3X24/VXsTw5BQOII/AAAAAAAAEhM/vsIyWM4jLS0/s1600/Maquina%2Bde%2Blavar%2Bbicicleta.jpg))
Well there was something in the 2011 ISS budget for this but it never happened.  :(

You're right it can be slower and hence lower power than an Earth unit.

But I'd caution that one recurring lesson of all the ECLSS development efforts is that it was the "little things" that caused the most trouble, such as catalytic beds releasing dust into the environment, or valves needing redesign to ensure they seal properly (to be fair quite a bit of that was due to the dust).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 02/24/2016 07:54 pm

And I did say help in powering the heat pump, meaning it would not be able to supply all the needed power. The rest of the power would need to come from the MCT's power source ( solar panels ).


The only way of removing heat from the MCT is by radiators or dumping mass.  There is no way around it.  A "heat pump" by definition moves heat from a cold region to a hot region and it consumes energy in the process which generates more heat.  A heat pump does not use direct heat for power.

There are methods which convert heat directly to electricity (though with low efficiencies so far). See this:
http://spectrum.ieee.org/nanoclast/semiconductors/materials/optical-rectenna-could-doube-solar-cell-efficiency
If it could be used to convert some IR to DC, wouldn't it would count as "a way around it"?
*I realise that lowering the working temperature may necessitate a bigger radiator, but technically less heat will be lost so less electricity needs to be produced.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/24/2016 08:09 pm
You can vacuum dry most things, at low pressure the water will boil away from its own heat. You can put the water back into the eclss. Cleaning a sleeping bag may be a chore though.
Agreed. The challenge is to retain the water for reuse.

Bizarre as it may seem I think the simplest option may be to use some vacuum accumulator tanks. Vent them to vac for use, then use them to collect the vapor for later reuse on a pulse basis.

Sizewise I guess the sleeping bag would be the challenge for any system. Obviously zero g helps a lot in this but since I presume  people will be staying in the ship on Mars and hence touching the surface a lot during sleep it will need to be washed more frequently.

Consider how long you'd be comfortable sleeping in the same bed linen.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 02/24/2016 08:15 pm

There are methods which convert heat directly to electricity (though with low efficiencies so far).

No, there are NOT. There are methods than convert heat DIFFERENCE directly into electricity.

In order to have that considerable heat DIFFERENCE, big radiators are needed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 02/24/2016 09:39 pm

There are methods which convert heat directly to electricity (though with low efficiencies so far).

No, there are NOT. There are methods than convert heat DIFFERENCE directly into electricity.

In order to have that considerable heat DIFFERENCE, big radiators are needed.
There are methods than convert heat DIFFERENCE directly into electricity. These are called heat pumps and  are disscussed above.
Less discussed are direct methods like IR photovoltaic cells which dont use heat difference and don't require radiators themselves.
Anyway, IMO,  when talking about a system which has a raditor, and someone suggests to add a heat pump,  it is correct to say that the heat pump requires a radiator only if the combined system's raditor is bigger then the original ststem's radiator, which is probably the case, but the total system efficiency may still be better if you count the energy production part too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 02/24/2016 10:11 pm
You can vacuum dry most things, at low pressure the water will boil away from its own heat. You can put the water back into the eclss. Cleaning a sleeping bag may be a chore though.
Agreed. The challenge is to retain the water for reuse.

Bizarre as it may seem I think the simplest option may be to use some vacuum accumulator tanks. Vent them to vac for use, then use them to collect the vapor for later reuse on a pulse basis.

Sizewise I guess the sleeping bag would be the challenge for any system. Obviously zero g helps a lot in this but since I presume  people will be staying in the ship on Mars and hence touching the surface a lot during sleep it will need to be washed more frequently.

Consider how long you'd be comfortable sleeping in the same bed linen.
It would seem we shed 10grams of skin per day, for a total of 3.6 kg per year.  So 100 crew would produce 1 kg per day of skin flakes, and for a 200 day trip 200 kg.

So basically at the end of the trip you have two extra crew members made of dead skin!!!!  Plus at least the same amount of hair, so you really need to clean the ship and wash the linen.  I guess the skin mites will get a lot of it and transform it into CO2 and skin mite shit.  Beaurk.
Most of the skin will wash off in showers though.  So bacteria will get it instead?

And there is all that urea from sweat that condenses in the linen as well.  Definitively need washing machines ;-)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/24/2016 10:15 pm

There are methods which convert heat directly to electricity (though with low efficiencies so far).

No, there are NOT. There are methods than convert heat DIFFERENCE directly into electricity.

In order to have that considerable heat DIFFERENCE, big radiators are needed.
There are methods than convert heat DIFFERENCE directly into electricity. These are called heat pumps and  are disscussed above.
Less discussed are direct methods like IR photovoltaic cells which dont use heat difference and don't require radiators themselves.

Nope.  As previously mentioned, there aren't.  We're just far enough from the fundamental laws to make things really confusing for people;  Many things that are not technically impossible end up being practically impossible or impossible by virtue of secondary laws formed out of the core axioms.  Sorry if you misunderstood, but this is not the place for thermodynamic engineering 101;  I would start with the Wikipedia entry on Carnot heat engines and work your way up from there.  It may help to consider how IR photovoltaic cells would work at an equilibrium temperature, or consider where the energy is supposed to go after you 'generate' it with magical IR photovoltaic cells that do work (spent inside, it heats up the interior).  Please seek other resources than this thread.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 02/24/2016 11:10 pm

There are methods which convert heat directly to electricity (though with low efficiencies so far).

No, there are NOT. There are methods than convert heat DIFFERENCE directly into electricity.

In order to have that considerable heat DIFFERENCE, big radiators are needed.
There are methods than convert heat DIFFERENCE directly into electricity. These are called heat pumps and  are disscussed above.
Less discussed are direct methods like IR photovoltaic cells which dont use heat difference and don't require radiators themselves.

Nope.  As previously mentioned, there aren't.  Sorry if you misunderstood, but this is not the place for thermodynamic engineering 101;  I would start with the Wikipedia entry on Carnot heat engines and work your way up from there.  It may help to consider how IR photovoltaic cells would work at an equilibrium temperature, or consider where the energy is supposed to go after you 'generate' it with magical IR photovoltaic cells that do work (spent inside, it heats up the interior).  Please seek other resources than this thread.

Well , perhaps just a bit of thermo: The Carnot equation is Work=Heat*(1-Tcold/Thot)

So for a ship wall at 20C, or 293K, and exchanging heat with an exterior at 200K, the maximum work that could be done (or rate of energy extraction and transformation) is 1-200/293=32%  so the rest of the energy, 68% would leave the ship at external radiators.  This is for an ideal Carnot cycle.  Real cycles are about 50% of these efficiences or less.  so we might extract 15%.  Of course the radiators themselves would exchange heat with deep space according to the Stephan boltzman law of radiation, and would need to be very large since the temperature difference with space (200K to 180 K) would be very small.  In fact these radiators would be much larger than if we had just radiated away all the heat in the first place.  How much larger?  Well radiateor surface is to the fourth of the temperature difference, so 293 to 180 vs 200 to 180 is 5 times more, so 5^4 is 625 times.
So we would get 15% back, at the cost of radiators 625 times larger.
Not worth it, is it?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/24/2016 11:46 pm

There are methods which convert heat directly to electricity (though with low efficiencies so far).

No, there are NOT. There are methods than convert heat DIFFERENCE directly into electricity.

In order to have that considerable heat DIFFERENCE, big radiators are needed.
There are methods than convert heat DIFFERENCE directly into electricity. These are called heat pumps and  are disscussed above.
Less discussed are direct methods like IR photovoltaic cells which dont use heat difference and don't require radiators themselves.

Nope.  As previously mentioned, there aren't.  Sorry if you misunderstood, but this is not the place for thermodynamic engineering 101;  I would start with the Wikipedia entry on Carnot heat engines and work your way up from there.  It may help to consider how IR photovoltaic cells would work at an equilibrium temperature, or consider where the energy is supposed to go after you 'generate' it with magical IR photovoltaic cells that do work (spent inside, it heats up the interior).  Please seek other resources than this thread.

Well , perhaps just a bit of thermo: The Carnot equation is Work=Heat*(1-Tcold/Thot)

So for a ship wall at 20C, or 293K, and exchanging heat with an exterior at 200K, the maximum work that could be done (or rate of energy extraction and transformation) is 1-200/293=32%  so the rest of the energy, 68% would leave the ship at external radiators.  This is for an ideal Carnot cycle.  Real cycles are about 50% of these efficiences or less.  so we might extract 15%.  Of course the radiators themselves would exchange heat with deep space according to the Stephan boltzman law of radiation, and would need to be very large since the temperature difference with space (200K to 180 K) would be very small.  In fact these radiators would be much larger than if we had just radiated away all the heat in the first place.  How much larger?  Well radiateor surface is to the fourth of the temperature difference, so 293 to 180 vs 200 to 180 is 5 times more, so 5^4 is 625 times.
So we would get 15% back, at the cost of radiators 625 times larger.
Not worth it, is it?
8)

Thank you for doing what I (or someone else) should have done a couple pages ago to put this topic to bed. You probably were clearer than I would've been, too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 02/25/2016 03:40 am
Agreement on my part. Not impossible, but extremely impractical. Doesn't violate thermodynamics, but surely not worth extra mass. I am satisfied with that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BobCarver on 02/25/2016 01:02 pm
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity, and using that to power a laser that they simply shone in to space.

Is that even theoretically possible?

Nope because the electrical side gets hot and that needs its own set of radiators. Basically you make more waste heat than you throw overboard.

I read a paper ages ago which described a "laser radiator" which basically a very complex gasdynamic laser. Essentially it produced a beam of light with a blackbody radiation curve which carried the waste heat away (so not really a radiator which shoots heat away as a laser beam).

Actually, it can be done, but some claim it's a violation of the 2nd law. However, in reality, it is not. An electroentropic or magnetoentropic device can do it. It generates electricity without using a temperature differential by directly converting heat into electricity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/25/2016 02:10 pm
It would seem we shed 10grams of skin per day, for a total of 3.6 kg per year.  So 100 crew would produce 1 kg per day of skin flakes, and for a 200 day trip 200 kg.

So basically at the end of the trip you have two extra crew members made of dead skin!!!!  Plus at least the same amount of hair, so you really need to clean the ship and wash the linen.  I guess the skin mites will get a lot of it and transform it into CO2 and skin mite shit.  Beaurk.
Most of the skin will wash off in showers though.  So bacteria will get it instead?
Keep in mind the ISS has been in continuous occupation for 1-2 decades and this is not a show stopper.

However I think managing this issue needs to become a bit more sophisticated than " clean the place with wipes, stick them in the cargo vehicle, let them burn on re-entry."  :(

Good point about the skin mites. All humans carry a substantial micro climate of assorted creatures with them. True most of them need an electron microscope to see clearly but they are  there and long term operations away from Earth will need to take this into account.
Quote
And there is all that urea from sweat that condenses in the linen as well.  Definitively need washing machines ;-)
I kind of like the washing bags idea because
a) it's likely to be much easier (and cheaper) to engineer this as a low risk solution for what is a non core (but still pretty important) task and
b)At a subconscious level it would get people used to the idea that they are personally responsible for their own well being.

In some ways the more interesting question is what do  you do with the waste from such bags? IE the dead skin, urea etc.

Incidentally people seem to be thinking that a 100 day journey is it and things will get a lot easier once landed.

Once landed it would be possible to deploy much bigger solar arrays and radiators. [EDIT So power and thermal control would not be show stoppers. ] Inflatable habitats could  increase habitable area substantially as well.

But now anything that's been floating in the atmosphere will settle on the nearest surface.

What happens next will depend on how abrasive, chemically or bio active the are.

The other joker is that we know Martian surface dust is very chemically aggressive. I'm not sure there any area on Earth quite like it.  The design must therefor ensure either the dust cannot foul mechanisms or that such mechanisms can be cleaned. Otherwise if you can't close all doors and re-stow all equipment you may not be able to take off.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/25/2016 04:10 pm
Forgive my naivety.

In the novel Sundiver (David Brin), they dumped excess heat by converting to electricity, and using that to power a laser that they simply shone in to space.

Is that even theoretically possible?

Nope because the electrical side gets hot and that needs its own set of radiators. Basically you make more waste heat than you throw overboard.

I read a paper ages ago which described a "laser radiator" which basically a very complex gasdynamic laser. Essentially it produced a beam of light with a blackbody radiation curve which carried the waste heat away (so not really a radiator which shoots heat away as a laser beam).

Actually, it can be done, but some claim it's a violation of the 2nd law. However, in reality, it is not. An electroentropic or magnetoentropic device can do it. It generates electricity without using a temperature differential by directly converting heat into electricity.
Explain how heat can conduct or radiate without a temperature differential.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 02/25/2016 05:29 pm
Would putting the linens out the airlock and in full sunlight be the ultimate "dry cleaning?" I have no idea if this would work or not, but i love the idea of the MCT strung with clothes lines and festooned with dirty laundry.

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 02/25/2016 06:59 pm
Weird thought here;

     Anybody ever consider that the BFR could be an up scaled Falcon 9 configuration, using 9 Raptor engines for the first stage and possibly a couple of BFR's as strap on boosters?  Or even a configuration using six or more Falcon 9 first stages as strap ons as an alternative?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/25/2016 07:02 pm
Weird thought here;

     Anybody ever consider that the BFR could be an up scaled Falcon 9 configuration, using 9 Raptor engines for the first stage and possibly a couple of BFR's as strap on boosters?  Or even a configuration using six or more Falcon 9 first stages as strap ons as an alternative?
A big scaled up Methane Falcon heavy type design was originally the thought of BFR according to Musk in the R*ddit AMA, but in the AMA, Musk said they opted to instead go the single-core route with LOTS of Raptors.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 02/26/2016 02:33 pm
It seems, based on dV requirements, that BFR will likely need to land on a drone ship.  Would the existing drone ships be big enough?  If not, how big would a new drone ship need to be?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/26/2016 03:08 pm
It seems, based on dV requirements, that BFR will likely need to land on a drone ship.  Would the existing drone ships be big enough?  If not, how big would a new drone ship need to be?
What delta-V requirements? Are you thinking BFR is going to launch all the way to Mars? BFR would likely just be launching to LEO. No, return to launch site is much more likely. This way you can have much faster turnaround time of the BFR stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 02/26/2016 03:17 pm
It seems, based on dV requirements, that BFR will likely need to land on a drone ship. 

Not only operational aspects are against this. Also the 30% payload loss mentioned by Elon Musk are not laws of nature, they are roughly the result of Falcon 9 design.

More lightweight build, higher ISP of the engines and probably staging even earlier than Falcon 9 will reduce the losses by a lot, making barge landing unnecessary.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/26/2016 05:07 pm
Would putting the linens out the airlock and in full sunlight be the ultimate "dry cleaning?" I have no idea if this would work or not, but i love the idea of the MCT strung with clothes lines and festooned with dirty laundry.

Matthew
Interesting idea. Something that should be testable on the ISS.

The joker in the pack is not the vacuum. It's the temperature in the lock. IIRC in full sunlight you're talking c200c, in full shadow -200c.

I think cold would do less damage but I'd still suspect it would do so much damage they would literally crumble in your hands.

But note it's still basically an open loop system and the goal should always be to close the loops.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 02/26/2016 05:36 pm
It seems, based on dV requirements, that BFR will likely need to land on a drone ship.  Would the existing drone ships be big enough?  If not, how big would a new drone ship need to be?
What delta-V requirements? Are you thinking BFR is going to launch all the way to Mars? BFR would likely just be launching to LEO. No, return to launch site is much more likely. This way you can have much faster turnaround time of the BFR stage.

According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.  BFR+BFS need to put at least 200 MT in LEO just to cover empty BFS+payload.  And all this has to be done with no more than 4 times FH lift off thrust.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 02/26/2016 07:08 pm
According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.

Source? That seems incredibly unlikely. 9km/s at staging is enough to carry the fully fuelled ~100 tonne second stage into LEO without firing its engines. That would make the F9 first stage a 110 tonne to LEO SSTO!

(Sorry, a 110 tonne to LEO reusable SSTO.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/26/2016 09:39 pm
According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.

Source? That seems incredibly unlikely. 9km/s at staging is enough to carry the fully fuelled ~100 tonne second stage into LEO without firing its engines. That would make the F9 first stage a 110 tonne to LEO SSTO!

(Sorry, a 110 tonne to LEO reusable SSTO.)
Indeed.

I'd settle for a reusable TSTO.

BTW has anyone mentioned the mass fraction this thing needs?

AIUI people have said a 100 day trip needs 8.8Km/s from LEO. Raptors Isp is suggested at 363secs in Vac, which should be OK in the Mars atmosphere as well, given its pressure.

Putting those into the the rocket eqn gives 11.81:1 or a mass fraction of about 8.5%, giving a gross launch mass (from LEO) is 709 tonnes for a 60 tonne payload IE about 12x the size of the FH. Once again closing the ECLSS loops with an integrated mass efficient ECLSS will pay big dividends on size needed, possibly bigger than getting an extra second of Isp on the engines. Likewise cutting that delta V to 8 Km/s cuts gross mass by 20%.

This is still less than 1/2 the GTOW of the Shuttle stack, so big but not enormous. However that's raw payload, without structure, and I've no real sense what fraction that would be. 10% of payload mass IE 6 tonnes? 10 tonnes?

So cutting delta V, improving ECLSS closure and lowering transit time are all good things, but some are more good than others. for a fully open ECLSS 1 day --> 500Kg of supplies but ISS can already do better, therefor 50 tonnes of supplies is conservative for a 100 day trip (but what'll you eat there & on the way back?)

I think I'm going to have to revise my game a bit more.  :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 02/26/2016 10:42 pm
AIUI people have said a 100 day trip needs 8.8Km/s from LEO. Raptors Isp is suggested at 363secs in Vac, which should be OK in the Mars atmosphere as well, given its pressure.

I seem to recall that Tom Mueller said that they aimed for 380 secs of vac Isp.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DJPledger on 02/27/2016 07:12 am
AIUI people have said a 100 day trip needs 8.8Km/s from LEO. Raptors Isp is suggested at 363secs in Vac, which should be OK in the Mars atmosphere as well, given its pressure.

I seem to recall that Tom Mueller said that they aimed for 380 secs of vac Isp.
363 sec. in vac. for SL Raptor. 380 sec. in vac. for the vac. Raptor.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 02/27/2016 09:03 am
363 sec. in vac. for SL Raptor. 380 sec. in vac. for the vac. Raptor.
Running with 380sec gives a mass ratio of 10.57:1 and a mass of about 714 tonnes to LEO, IE about 14x the size of the expendable FH.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 02/27/2016 11:41 am
According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.

Source? That seems incredibly unlikely. 9km/s at staging is enough to carry the fully fuelled ~100 tonne second stage into LEO without firing its engines. That would make the F9 first stage a 110 tonne to LEO SSTO!

(Sorry, a 110 tonne to LEO reusable SSTO.)

It was 9000 km/hr:
Quote
It's flying away from the pad in this case at 5000 km/h. In the upcoming flight it'll be going 8 or 9000 km/h, or roughly 5000 mph, in the wrong direction.
http://shitelonsays.com/transcript/postlanding-teleconference-with-elon-musk-2015-12-22
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 02/27/2016 11:53 am
Apologies, my fault,  the difference was 9000 km/hr down to 6000km/hr.  This was based on a Musk tweet on 1/17/2016.  Still, I think the dV penalty of dry landing of BFR makes drone ship landing worth consideration.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/27/2016 03:34 pm
Yet another lesson in why we should all be using metric, and we should be using m/s.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Prettz on 02/27/2016 03:52 pm
Apologies, my fault,  the difference was 9000 km/hr down to 6000km/hr.  This was based on a Musk tweet on 1/17/2016.  Still, I think the dV penalty of dry landing of BFR makes drone ship landing worth consideration.
It's not a "penalty" if the first stage is sized to allow for it from the beginning.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 02/27/2016 04:07 pm
Yet another lesson in why we should all be using metric, and we should be using m/s.

I'll let Elon know!


(I agree wholeheartedly)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Umbrella on 02/27/2016 04:49 pm
Apologies, my fault,  the difference was 9000 km/hr down to 6000km/hr.  This was based on a Musk tweet on 1/17/2016.  Still, I think the dV penalty of dry landing of BFR makes drone ship landing worth consideration.
It's not a "penalty" if the first stage is sized to allow for it from the beginning.

Even if the BFR is relatively a smaller proportion of the stack, it is hard to see cutoff not being at least a little bit down range.  So, I would claim you can push the design for a somewhat smaller penalty for dry landing - but not penalty free.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/27/2016 05:12 pm
Would putting the linens out the airlock and in full sunlight be the ultimate "dry cleaning?" I have no idea if this would work or not, but i love the idea of the MCT strung with clothes lines and festooned with dirty laundry.

Matthew
Interesting idea. Something that should be testable on the ISS.

The joker in the pack is not the vacuum. It's the temperature in the lock. IIRC in full sunlight you're talking c200c, in full shadow -200c.

I think cold would do less damage but I'd still suspect it would do so much damage they would literally crumble in your hands.

But note it's still basically an open loop system and the goal should always be to close the loops.
200C is actually fine for cotton as long as it's fairly quick. Keep it out there too long and it'd degrade at those temperatures. Anyway, the actual temperature would depend on the color of the cloth and other aspects.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/27/2016 05:18 pm
According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.

Source? That seems incredibly unlikely. 9km/s at staging is enough to carry the fully fuelled ~100 tonne second stage into LEO without firing its engines. That would make the F9 first stage a 110 tonne to LEO SSTO!

(Sorry, a 110 tonne to LEO reusable SSTO.)
Indeed.

I'd settle for a reusable TSTO.

BTW has anyone mentioned the mass fraction this thing needs?

AIUI people have said a 100 day trip needs 8.8Km/s from LEO. ...
Not right. More like 5-7km/s from LEO if you aerocapture at the other end. 8.8km/s would be doing a propulsive capture, which simply isn't going to happen. SpaceX will be doing aerocapture for the majority of the capture delta-v.

This is what happens when people (not saying this is you, john smith) use an online tool or online numbers without reading the fine print or understanding where the numbers come from.

http://trajbrowser.arc.nasa.gov/
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 02/27/2016 05:21 pm
Even if the BFR is relatively a smaller proportion of the stack, it is hard to see cutoff not being at least a little bit down range.  So, I would claim you can push the design for a somewhat smaller penalty for dry landing - but not penalty free.

I've been wondering myself what might be the ideal proportion. Playing around with the equations I got stage 1 to something below 60% of the total mass (the whole stack would have a mass similar to a Saturn V for ~200 mt to LEO), and a staging altitude similar to Falcon 9, which I admit looks wrong. This would need about 5 tanker missions to refuel before TMI.

Perhaps a more knowlegeable member could provide a better solution??
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/27/2016 05:35 pm
According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.

Source? That seems incredibly unlikely. 9km/s at staging is enough to carry the fully fuelled ~100 tonne second stage into LEO without firing its engines. That would make the F9 first stage a 110 tonne to LEO SSTO!

(Sorry, a 110 tonne to LEO reusable SSTO.)
Indeed.

I'd settle for a reusable TSTO.

BTW has anyone mentioned the mass fraction this thing needs?

AIUI people have said a 100 day trip needs 8.8Km/s from LEO. ...
Not right. More like 5-7km/s from LEO if you aerocapture at the other end. 8.8km/s would be doing a propulsive capture, which simply isn't going to happen. SpaceX will be doing aerocapture for the majority of the capture delta-v.

This is what happens when people (not saying this is you, john smith) use an online tool or online numbers without reading the fine print or understanding where the numbers come from.

http://trajbrowser.arc.nasa.gov/

In a 2-dimensional simplification, we go over the dV's required here:

http://forum.nasaspaceflight.com/index.php?topic=37808.msg1436054#msg1436054

http://forum.nasaspaceflight.com/index.php?topic=37808.msg1436460#msg1436460

0) You are correct, we find only about 3.2+2.2=5.4km/s for LEO to Mars 100d-transit escape burn, before accounting for EDL & without accounting for capture.  EDL dV needs seem to be contentious, I add a conservative 2km/s for 7.4km/s total.  Note again this is a circular coplanar simplification with launch direct to ecliptic; Reality is likely to be a little bit worse.

1) We have never aerocaptured at Mars before

2) We expect the Mars aerocapture to be especially difficult because the Martian atmosphere's thickness is apparently somewhat variable.

3) The required aerocaptures on a 100d Earth-Mars trip are rather extreme for aerocaptures, probably requiring MAC or some novel means;  I have read published suggestions that this is unfeasible in a traditional heatshielded lander, though I cannot verify them.  It needs to dissipate 9.3km/s of velocity in one pass to get into a high elliptical, but captured orbit, and more if you're doing a direct entry.  A minimum aerocapture from slow Hohmann transfer is more like 1.0km/s.

4) A 100d direct return trip with 'free' aerocapture at Earth is likely to require extreme amounts of dV for the Mars launch + escape burn, the link mentioned 8.8km/s.

Therefore:

I consider 100d transfers a bit of a silly overreach, at least at the beginning;  We know that the extra 80 days of microgravity and radiation isn't statistically prohibitive, and I fear that the changes required for fast transfers, at least ones in the mission architecture that has been described (LEO & MS refueling only) would be economically and physically prohibitive.  The goal being asserted on the business end, single-synod reuse, is probably unfeasible without a large propellant production facility already emplaced on the Mars surface with a hard pad - ISRU cannot be reasonably accomplished in a short-stay.  And something's going to need to build that facility;  If that something never gets off the ground because the design is unworkable at 100d transits, then this all fails to happen.

SEP methane propellant depots to LMO, then HEO, then HMO, let you cut the dV needs substantially if you're willing to set up a Conga line of them and give each one 2-5 years to get in place.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/27/2016 07:45 pm
I've simulated Mars aerocapture coming in from many different hyperbolic velocities. 100 day transfers DO NOT need MAC. PICA-X is what will be used.

2km/s is ridiculously conservative. More like 0.5-1.5km/s.

Who cares if we've never aerocaptured at Mars before? It's certainly possible. Why must our decisions be constrained by the same kind of compound conservatism that continuously makes NASA choose battlestar galactica expendable architectures with a billion different components and vehicle configuration changes (thus defeating any supposed safety advantage)?

100 day is to Mars, as Musk has REPEATEDLY said. NEVER has Musk said 100 days /back/. That means it'd be longer back.

Mars' atmosphere is plenty thick enough for aerocapturing.

100 day transfers is not silly anything and would not be even close to the most difficult entry/reentry ever attempted, though I would expect early missions would use lower energy transfers.

And yes, MCT will need ISRU infrastructure in place. That has been clear since forever, so why would you question that?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 02/27/2016 07:47 pm
Using several conservative assumptions is a good way to guarantee you'll develop an architecture which has no bearing on SpaceX's actual plans.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 02/27/2016 08:54 pm
With all the concerns (valid) about closed systems, why not consider CO2 washing machines for MCT or BFS whatever-it's-called passengers?

http://e3tnw.org/ItemDetail.aspx?id=512

"About 32 dry cleaning companies in the country are currently cleaning with the Glacier liquid CO2 system supplied by Solvair of Naperville, Illinois. The load capacity of their machine is about 25 kg or 55 pounds.  CO2Nexus of Littleton, Colorado has developed three models of their TERSUS® system. These supercritical carbon-dioxide based laundry systems are suitable for commercial and industrial uses and can accommodate loads of 100 and 200 pounds per cleaning cycle.  At high pressures, CO2 enters a liquid supercritical state and can serve as a washing fluid. The liquid CO2 has low viscosity and surface tension allowing for superior pore penetration and better cleaning action. After cleaning is completed, the pressure is reduced and the CO2 flashes to a gaseous state, eliminating the need for a drying cycle. The gaseous CO2 is captured, filtered and distilled, and then reused. The units are compact, save both energy and water, and extend garment life due to the lack of need for high temperatures and agitation."

Another article...

http://www.trendhunter.com/trends/supercritical-washing-machine



Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/28/2016 07:19 pm
Here's a pic of my upper stage/BFS engine module so far.  The volume of the LOX tank is ~581 m3 and for the CH4 tank it's ~360 m3.  This is to contain densified LOX at -205C (1248.9 kg/m3) or 725,773 kg of LOX.  For CH4 tank, it's densified at -180C (448.31 kg/m3) or 161,503 kg of liquid CH4.  Of course, this assumes the following values: a LOX to CH4 ratio of 3.5:1 where the vacuum Raptors are 2300 kN (x4) at ISP of 380 s (vac) for 397 seconds burn time.

I've loaded an extension to SketchUp that computes the dry weight of the model.  Unfortunately, having complex models really takes a long time to compute weight so I don't have the weights yet; it's still running.

Everything in the model is a component and have an assigned material density.  For the most part, I using an aluminium alloy 7075-T6 which has a density of 2810 kg/m3; tracking down densities of aluminium lithium alloys is little harder so I assume that the structure could be made lighter (T6 is at the higher end weight wise).

My goal is to model all the major components for the engine module that has weight:
* 4 X Vacuum Raptors (with cantilever mounts for Supersonic Retro-Propulsion SRP)
* 4 X Retractable landing legs (leveling & shock absorbing)
* Integrated Vehicle Fluids (CH4 ICE for compressors and electricity generator)
* Cargo-level ECLSS
* CBM/Airlock & PICAX heat shield hatch, pressurized tunnel.
* Service deck with aux. control.
* Batteries, Control Moment Gyroscopes (4 x CMG).
* Solar panels and heat radiators.

Of course, modelling all of that takes a bit of creative license and time.

Diameter: 10.1 meters
Height:  My system is busy calculating weight; but I believe it's 22 meters give or take.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Long EZ on 02/28/2016 08:31 pm
When MCT departs for Mars the propellant tanks will be mostly empty, having only enough for Mars EDL + reserve. To keep these from boiling off during Mars transit it will require active cooling. My thought is that perhaps it would be better to store these is separate tanks. A tank in a tank? The point being that the inner tank would have additional insulation to reduce the active cooling energy required. My first thought was that the tank in a tank could be a central column inside methane and LOX tanks. Another thought was that these could be large insulated pressure vessels in a lower equipment bay. After landing these tanks could be removed and used as habitation module: large insulated pressure vessels.

Has this been suggested already? Is it a reasonable idea?
Thanks
Long EZ builder / pilot
Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 02/28/2016 08:48 pm
According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.

Source? That seems incredibly unlikely. 9km/s at staging is enough to carry the fully fuelled ~100 tonne second stage into LEO without firing its engines. That would make the F9 first stage a 110 tonne to LEO SSTO!

(Sorry, a 110 tonne to LEO reusable SSTO.)
Indeed.

I'd settle for a reusable TSTO.

BTW has anyone mentioned the mass fraction this thing needs?

AIUI people have said a 100 day trip needs 8.8Km/s from LEO. ...
Not right. More like 5-7km/s from LEO if you aerocapture at the other end. 8.8km/s would be doing a propulsive capture, which simply isn't going to happen. SpaceX will be doing aerocapture for the majority of the capture delta-v.

This is what happens when people (not saying this is you, john smith) use an online tool or online numbers without reading the fine print or understanding where the numbers come from.

http://trajbrowser.arc.nasa.gov/

In a 2-dimensional simplification, we go over the dV's required here:

http://forum.nasaspaceflight.com/index.php?topic=37808.msg1436054#msg1436054

http://forum.nasaspaceflight.com/index.php?topic=37808.msg1436460#msg1436460

0) You are correct, we find only about 3.2+2.2=5.4km/s for LEO to Mars 100d-transit escape burn, before accounting for EDL & without accounting for capture.  EDL dV needs seem to be contentious, I add a conservative 2km/s for 7.4km/s total.  Note again this is a circular coplanar simplification with launch direct to ecliptic; Reality is likely to be a little bit worse.

1) We have never aerocaptured at Mars before

2) We expect the Mars aerocapture to be especially difficult because the Martian atmosphere's thickness is apparently somewhat variable.

3) The required aerocaptures on a 100d Earth-Mars trip are rather extreme for aerocaptures, probably requiring MAC or some novel means;  I have read published suggestions that this is unfeasible in a traditional heatshielded lander, though I cannot verify them.  It needs to dissipate 9.3km/s of velocity in one pass to get into a high elliptical, but captured orbit, and more if you're doing a direct entry.  A minimum aerocapture from slow Hohmann transfer is more like 1.0km/s.

4) A 100d direct return trip with 'free' aerocapture at Earth is likely to require extreme amounts of dV for the Mars launch + escape burn, the link mentioned 8.8km/s.


umm. Are you calculating delta-v by calculationg sums of partial delta-v:s from a delta-v map even when you can do the whole thing in one burn?

In those cases Oeberth effect gives huge benefit and the required delta-v is only the Pythagoran sum of partial delta-v's that are done together, not direct sum of those.

3.2km/s + 2.2 km/s done together at pegiree, high speed velocity, costs only sqrt(3.2^2 + 2.2^2) = 3.88 km/s.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 02/28/2016 08:59 pm
When MCT departs for Mars the propellant tanks will be mostly empty, having only enough for Mars EDL + reserve. To keep these from boiling off during Mars transit it will require active cooling. My thought is that perhaps it would be better to store these is separate tanks. A tank in a tank? The point being that the inner tank would have additional insulation to reduce the active cooling energy required. My first thought was that the tank in a tank could be a central column inside methane and LOX tanks. Another thought was that these could be large insulated pressure vessels in a lower equipment bay. After landing these tanks could be removed and used as habitation module: large insulated pressure vessels.

Has this been suggested already? Is it a reasonable idea?
Thanks
Long EZ builder / pilot

I have thought ever since we heard of MCT that secondary tanks may be used. As well as the advantages for cooling I can think of three other reasons, which I'll leave as an exercise for the reader.

The big question is whether the added mass and complexity of the extra tanks is worth it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 02/28/2016 10:09 pm
According to Musk, Falcon 9 1st stage separation velicity drops from 9 km/s with drone landing to 6km/s with dry landing.

Source? That seems incredibly unlikely. 9km/s at staging is enough to carry the fully fuelled ~100 tonne second stage into LEO without firing its engines. That would make the F9 first stage a 110 tonne to LEO SSTO!

(Sorry, a 110 tonne to LEO reusable SSTO.)
Indeed.

I'd settle for a reusable TSTO.

BTW has anyone mentioned the mass fraction this thing needs?

AIUI people have said a 100 day trip needs 8.8Km/s from LEO. ...
Not right. More like 5-7km/s from LEO if you aerocapture at the other end. 8.8km/s would be doing a propulsive capture, which simply isn't going to happen. SpaceX will be doing aerocapture for the majority of the capture delta-v.

This is what happens when people (not saying this is you, john smith) use an online tool or online numbers without reading the fine print or understanding where the numbers come from.

http://trajbrowser.arc.nasa.gov/

In a 2-dimensional simplification, we go over the dV's required here:

http://forum.nasaspaceflight.com/index.php?topic=37808.msg1436054#msg1436054

http://forum.nasaspaceflight.com/index.php?topic=37808.msg1436460#msg1436460

0) You are correct, we find only about 3.2+2.2=5.4km/s for LEO to Mars 100d-transit escape burn, before accounting for EDL & without accounting for capture.  EDL dV needs seem to be contentious, I add a conservative 2km/s for 7.4km/s total.  Note again this is a circular coplanar simplification with launch direct to ecliptic; Reality is likely to be a little bit worse.

1) We have never aerocaptured at Mars before

2) We expect the Mars aerocapture to be especially difficult because the Martian atmosphere's thickness is apparently somewhat variable.

3) The required aerocaptures on a 100d Earth-Mars trip are rather extreme for aerocaptures, probably requiring MAC or some novel means;  I have read published suggestions that this is unfeasible in a traditional heatshielded lander, though I cannot verify them.  It needs to dissipate 9.3km/s of velocity in one pass to get into a high elliptical, but captured orbit, and more if you're doing a direct entry.  A minimum aerocapture from slow Hohmann transfer is more like 1.0km/s.

4) A 100d direct return trip with 'free' aerocapture at Earth is likely to require extreme amounts of dV for the Mars launch + escape burn, the link mentioned 8.8km/s.


umm. Are you calculating delta-v by calculationg sums of partial delta-v:s from a delta-v map even when you can do the whole thing in one burn?

In those cases Oeberth effect gives huge benefit and the required delta-v is only the Pythagoran sum of partial delta-v's that are done together, not direct sum of those.

3.2km/s + 2.2 km/s done together at pegiree, high speed velocity, costs only sqrt(3.2^2 + 2.2^2) = 3.88 km/s.

That is already factored in to the spreadsheet tool I used.  Not using Oberth, the figures would be much, much higher.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 02/29/2016 02:35 am
When MCT departs for Mars the propellant tanks will be mostly empty, having only enough for Mars EDL + reserve. To keep these from boiling off during Mars transit it will require active cooling. My thought is that perhaps it would be better to store these is separate tanks. A tank in a tank? The point being that the inner tank would have additional insulation to reduce the active cooling energy required. My first thought was that the tank in a tank could be a central column inside methane and LOX tanks. Another thought was that these could be large insulated pressure vessels in a lower equipment bay. After landing these tanks could be removed and used as habitation module: large insulated pressure vessels.

Has this been suggested already? Is it a reasonable idea?
Thanks
Long EZ builder / pilot
My model shown in my previous post addresses this by an Integrated Vehicle Fluids (IVF) system.  Though speculation on my part, something like this would have to be implemented.  First, the Dracos (RCS) would be converted to CH4/LOX with electric ignition since hydrazine is hard to come by on Mars.  This means that pressurized CH4/LOX is required (doing away with helium).  The IVF is what would maintain these tanks using the boil off of the main tanks.  The IVF would use some of the CH4/LOX boil off to run the Internal Combustion Engine (ICE) that generates electricity and runs compressors to pressurize those tanks and chillers to cool/maintain the fuels in the main tanks.  The trick is to build a system that is light (plumbing/compressors can be heavy) and have really good heat radiators.

In my model, my plan is to have the IVF system in the stern (bottom) in a pressurized section.  The reason is to take advantage of the main tank plumbing (for the Raptors) and there is room for tankage, etc.  Also, since this system would be just as critical as ECLSS, the central tunnel can access the equipment for service if need be.  The central tunnel serves multiple purposes beyond just being a way to get to the surface.  It's also a gangway for plumbing, etc. to the bow.  The idea is that multiple of these modules can link up end on end, like Lego bricks.  Update:  Also, having the IVF and all the plumbing for connections to other modules also means that on the surface of Mars it can connect up to ISRU equipment for refuelling.  Going to need that big time.

Also, it's already a given that it'll take multiple LEO launches to get fuel, cargo, and passengers into orbit.  Having one upper stage (like my model) reusable for multiple purposes (that have some commonality) is the most efficient means (in both cost and weight).

BTW, I was calculating the weight of my model but the numbers were wildly off.  Turns out the plugin I was using can only calculate object as if they are solid, aka my tanks were being treated as solid aluminium.  I may have to do this old school... find the surface area of tanks, account for the thickness and compute the volume.

Update: Here's my latest snapshot with a man to show scale.
Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 03/01/2016 09:09 am
Quote from: John Smith 19

Interesting idea. Something that should be testable on the ISS.

The joker in the pack is not the vacuum. It's the temperature in the lock. IIRC in full sunlight you're talking c200c, in full shadow -200c.

I think cold would do less damage but I'd still suspect it would do so much damage they would literally crumble in your hands.

But note it's still basically an open loop system and the goal should always be to close the loops.
200C is actually fine for cotton as long as it's fairly quick. Keep it out there too long and it'd degrade at those temperatures. Anyway, the actual temperature would depend on the color of the cloth and other aspects.
I did not know cotton was good to 200c.  Working out it's actual final temperature inside an airlock would be difficult enough but once you're in direct sunlight then you're into the spectral absorbance and emissivity of the fabrics. Has anyone even measured these factors?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 03/01/2016 09:12 am
This is what happens when people (not saying this is you, john smith) use an online tool or online numbers without reading the fine print or understanding where the numbers come from.

http://trajbrowser.arc.nasa.gov/
True.

Different assumptions can have a very large impact on what people think is and is not possible.

I merely took the figures given and ran with them. The MCT tab of the next version of my costing game will let people put their own numbers in and see what comes out in terms of expected size.


As promised here is the new version. As usual date entry is to the Blue bordered cells.

The MCT tab let's you put in choose a delta V and see what that does to your expected gross weight needed in LEO. Note while the figure for resource use per day is the NASA standard (11lb or 5Kg/day) it can be changed, reflecting peoples beliefs in how much (or little) closed loop life support can improve on it. Likewise although it's labelled "Raptor Vac Isp" you can provide any Isp you want. It's pretty astonishing what a 4000sec engine (IE an Ion thruster) can to size to LEO, but this is just the rocket equation, and does not take into account any tricky orbital mechanics, multiple burns, slingshots etc.

I've also finally gotten round to fleshing out the "design your rocket" tab. This uses the ULA chart for the cost and weight of 2 stage LV components as a starting point for seeing how different assumptions affect the final outcome. If you use the UL defaults and start with a gross takeoff weight and cost that's how the different parts will break out in terms of mass and cost.

I encourage anyone who thinks they can do better than ULA to do so and to give me any feedback.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 03/02/2016 04:05 pm
An item is that the colonization policy would be a strict 50/50 male/female ratio. For there and back mission the ratio could be anything but for colonization it would have to be 50/50.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 03/02/2016 04:31 pm
An item is that the colonization policy would be a strict 50/50 male/female ratio. For there and back mission the ratio could be anything but for colonization it would have to be 50/50.

Excuse me but that was not the sort of ratio seen in historical colonization efforts and I really doubt that it would pertain today. What justification do you have for imposing such a ratio? Is sexual orientation going to be a selection criteria for colonization? Is intention to have children going to be a selection criteria? Is fertility? Is philosophical commitment to monogamy going to be a selection criteria?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 03/02/2016 06:27 pm
An item is that the colonization policy would be a strict 50/50 male/female ratio. For there and back mission the ratio could be anything but for colonization it would have to be 50/50.

Excuse me but that was not the sort of ratio seen in historical colonization efforts and I really doubt that it would pertain today. What justification do you have for imposing such a ratio? Is sexual orientation going to be a selection criteria for colonization? Is intention to have children going to be a selection criteria? Is fertility? Is philosophical commitment to monogamy going to be a selection criteria?

If anything a sexual vetting process would be unethical by the standards of most. You can't turn away people because they might have had partners on Earth who they preserve long distance relationships with, are sterile, are asexual, simply enjoy sex for pleasure rather than reproduction, don't want any more kids, are LGBT+, are polyamorous or simply want to spend their time working rather than spending time intimately with other people whilst their on mars (as many choose to do on Earth).

Certainly, if you end up with 80% male applicants all from the same small town in the same part of the world there will need to be some filtering - but you can't invalidate skilled, intelligent people because of deeply personal elements of their life that they have no control over. If a Mars colony is going to be representative of humanity, you're going to get people from every walk of life (who can afford the trip) applying.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Hauerg on 03/02/2016 06:43 pm
Getting a tiny little bitt off course, aren't we.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 03/02/2016 06:52 pm
If left alone, the natural selection process of humans ends up being close to 50-50.  Only in the 20th century have these changes taken place, like birth control, nuclear families, then other choices.  Most all world societies traditionally have had a male-female relationship selection process.  Occationally there were deviations from the norm like Rome with gay Ceasars, and multiple wives like Islamic countries, but almost all of humanity societies have been 50-50 man-woman relationships.  It will probably require this for colonization to take hold.  Otherwise it will be like Europe, Japan, and American whites today with decreasing populations. 

Sure there will be a need for all types of educated people to make it work, but they will have to have families for colonization to take hold.  Something interesting I learned, when America declared it's independence from England, America had the most educated population in the world at the time.  More Americans could read and write than Europeans.  Because of religious freedom coupled with the "age of enlightenment" education was important.  Most of the original universities were started by various churches.  "Sunday School" was started to teach kids how to read.  So it is with Martian colonization, the most educated people, with various skills, will have to be the ones to colonize and grow the colony. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 03/02/2016 11:37 pm
Continuing the gender and reproductive discussion here: http://forum.nasaspaceflight.com/index.php?topic=39719.msg1498881#msg1498881 (http://forum.nasaspaceflight.com/index.php?topic=39719.msg1498881#msg1498881)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 03/03/2016 04:19 pm
Back to BFR/MCT. I believe I have heard about MCT using densified subcooled propellant but may remember wrong. The discussion about the SES flight showed that subcooling is not compatible with self pressurizing. So what do you think? Falcon 9 needs densification to have more propellant in the available volume. MCT would not be volume restricted in the same way so it seems to me they will not use subcooling to enable self pressurizing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 03/03/2016 04:40 pm
The discussion about the SES flight showed that subcooling is not compatible with self pressurizing.

Subcooled prop won't work with VaPak style self pressurization but it does not prevent autogenous pressurization where the propellant is pumped by the engine and then some of it gets boiled and ducted back to the prop tank to keep it pressurized.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 03/03/2016 05:55 pm
 My understanding from what I researched (for my model), for long term storage in zero g requires autogenous pressurization with either ullage motors and special channels (to utilize surface tension to keep the propellant together), or an inflating bladder.  The point of the pressurization is to get the propellant to the pump intake.

In my model, the main tanks will be the first method and the RCS would be the second method.  To maintain the pressures, a ICE (part of IVF) running compressors, etc. to cool and pressurize the system.  The CO2 produced could be used in the RCS tanks bladders and slush tanks with excess vented.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 03/03/2016 07:07 pm
Subcooled prop won't work with VaPak style self pressurization but it does not prevent autogenous pressurization where the propellant is pumped by the engine and then some of it gets boiled and ducted back to the prop tank to keep it pressurized.

Thanks for the explanation. Do I understand this correctly? The tanks would be brought to flight pressure with inert gas, probably from ground support equipment. Then in flight the pressure would be maintained using hot propellant from the engines?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 03/03/2016 08:08 pm
Subcooled prop won't work with VaPak style self pressurization but it does not prevent autogenous pressurization where the propellant is pumped by the engine and then some of it gets boiled and ducted back to the prop tank to keep it pressurized.

Thanks for the explanation. Do I understand this correctly? The tanks would be brought to flight pressure with inert gas, probably from ground support equipment. Then in flight the pressure would be maintained using hot propellant from the engines?
Correct, and that's basically how it's ALREADY done, except you'd use hot/warm methane/oxygen instead of hot/warm helium for the system we're talking about.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 03/04/2016 07:16 pm
A speculation piece re the MCT on SpaceFlightInsider.com

http://www.spaceflightinsider.com/organizations/space-exploration-technologies/spacexs-mars-colonial-transporter-rumors-realities/
Note the kicker at the end

"his facility will be powered by a compact nuclear reactor (6 meters tall and 5 meters in diameter) "

If people the BFR & MCT are going to cost a lot, wait till they see the fill for that
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 03/05/2016 03:24 am
Right. Doesn't have to be a lot, should be less than BFR/MCT. Small modular reactors are supposed to be around $5000/kW (much of that site fees, etc), and I expect SpaceX would be working with some other company, so there'd be development cost sharing for the reactor portion. There are some as small as 11MWe, so about the right size.

...got to solve that heat transfer problem, though, with Mars' thin atmosphere.
This article

http://www.theguardian.com/environment/2015/nov/24/mini-nuclear-reactors-answer-to-climate-change-crisis

from the UK quotes a Rolly Royce engineer (who develop British navy reactors) that SMR's will need about Ł500m to do the DDT&E with a market of 40-70 units. That's $710m.

While these designs are relatively small they are not mass constrained and may be surprisingly heavy.

The real question would be can an Earth based SMR design be adapted for Mars, because the market for Mars specific inits will be very small.  :(

OTOH like IVF "waste" heat is (potentially) a valuable resource for site heating, ice melting and some lower temp chemical reactions, softening plastics etc.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 03/05/2016 04:49 am
What about getting the permits to launch a nuclear reactor, though?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 03/05/2016 07:16 am
What about getting the permits to launch a nuclear reactor, though?

Why would that be difficult? Provided you haven't run it before launch, it's a big lump of metal and ceramic, with some low-level radioactive fuel which is routinely transported around the world. (And the fuel rods/pellets can be launch separately from the reactor itself.) Should be easier than getting permission to launch an RTG.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 03/05/2016 07:57 am
Only the fuel would need permission for launch. And you'd likely want a high burn-up ratio. That means either highly enriched uranium or a partially breeding/high-burn-up design.

To ensure safety, fuel would likely be encased in steel and perhaps even launched in a Dragon with abort capability.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sghill on 03/05/2016 12:32 pm
I was in institution-scale solar for years. There's a bunch of over thinking the MCT ground use-panels on this thread (plus it's OT, we have a thread for solar panels on Mars in that area).

Instead of complicated schemes to deploy PV panels or schemes like reflectors to get more power out them, it is far easier and cheaper to just have a longer spool of thin film panels to make up for inefficiencies.

Additionally,  no automated unfurling system is needed. Just set the spool on the ground and roll it out- over the rocks and everything, then plug it in to the junction box (on board power will be DC). Hammer in some ground stakes every 2m.

A UV coating will be needed. They make that stuff in "space application" strength, so there's no new technology there.

Quote
...However, while fine in space, I do have to ask how you intend to structurally support all those PV panels while the MCT is on the martian surface?  They'd have to have support arms underneath, or else lay flat on the dirt and roll out like a tongue ...

I absolutely NAILED this one last year!

http://www.nasa.gov/mission_pages/station/research/experiments/2139.html

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 03/05/2016 11:02 pm
Although I like and agree with your idea (Cooper at MIT published a paper on the topic), I'm not sure ROSA shows you're such a prophet. Roll-out arrays were used originally for Hubble.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 03/06/2016 03:20 am
I was in institution-scale solar for years. There's a bunch of over thinking the MCT ground use-panels on this thread (plus it's OT, we have a thread for solar panels on Mars in that area).

Instead of complicated schemes to deploy PV panels or schemes like reflectors to get more power out them, it is far easier and cheaper to just have a longer spool of thin film panels to make up for inefficiencies.

Additionally,  no automated unfurling system is needed. Just set the spool on the ground and roll it out- over the rocks and everything, then plug it in to the junction box (on board power will be DC). Hammer in some ground stakes every 2m.

A UV coating will be needed. They make that stuff in "space application" strength, so there's no new technology there.

Quote
...However, while fine in space, I do have to ask how you intend to structurally support all those PV panels while the MCT is on the martian surface?  They'd have to have support arms underneath, or else lay flat on the dirt and roll out like a tongue ...

I absolutely NAILED this one last year!

http://www.nasa.gov/mission_pages/station/research/experiments/2139.html

erm... (https://www.sbir.gov/sbirsearch/detail/144778)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 03/07/2016 06:30 pm
Back to BFR/MCT. I believe I have heard about MCT using densified subcooled propellant but may remember wrong. ...MCT would not be volume restricted in the same way (as F9) so it seems to me they will not use subcooling to enable self pressurizing.

This brings up a related point in my mind.

Obviously, ISRU will be used to manufacture prop on Mars. Given the constraints of being on Mars (low density atmosphere, limited power supply) vs. being on Earth, how much more difficult would it be to super-cool/densify the prop as opposed to only chilling it to standard cryo temperatures. IOW, you can densify by supercooling on Earth, but is doing the extra cooling going to be more difficult on Mars due to the low density atmosphere as a heat dump and by not being on a massive power grid?

If it is a problem, could BFS use super cryo temp on Earth launch, but only normal cryo temp. on Mars launch?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 03/07/2016 07:26 pm
'Subcooling' is actually easier on Mars because the sub part refers to temperatures below the nominal boiling point at 1atm. Or boiling points at subatmospheric pressures. On Mars the low pressure of ambient atmosphere means you can drop pressures inside your LV (during prop load) and storage tanks below 1atm without fear of imploding things. Wiki says average surface pressure on Mars is 600Pa. LOX boils at 59K in this pressure, only five Kelvins above freezing point.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 03/07/2016 07:30 pm
However that still leaves the problems of dust storms for solar arrays

http://www.nasa.gov/feature/goddard/the-fact-and-fiction-of-martian-dust-storms

It looks like you'd have to wait it out, but it could be weeks or months worst case.

However this really comes under payloads for an MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 03/07/2016 08:02 pm
'Subcooling' is actually easier on Mars because the sub part refers to temperatures below the nominal boiling point at 1atm. Or boiling points at subatmospheric pressures. On Mars the low pressure of ambient atmosphere means you can drop pressures inside your LV (during prop load) and storage tanks below 1atm without fear of imploding things. Wiki says average surface pressure on Mars is 600Pa. LOX boils at 59K in this pressure, only five Kelvins above freezing point.

I am aware of the Ideal Gas Law and how that works. I didn't know there's only 5 degree K difference between the two state changes. How much difference is there for methane? Also, once you hit the state change temperature between liquid and freezing, how much enthalpy of state change is there?  i.e. how much do you have to worry about a shock that solidifies the liquid? As either of these enters the enthalpy of state change to solid, do they expand, contract, remain same volume? You surely wouldn't want to tip over into solid, especially if it expands. A cracked tank would be catastrophic.

In any case, it sounds like the lower atmospheric pressure of Mars will not allow the liquids to be densified as much there, thus the energy density will be less? It also sounds like you need to be really careful about keeping the O2 between those state change temps on Mars due to the narrow temperature difference and not having the degree of mechanical control you have over the process on Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 03/07/2016 08:16 pm
They will have plenty of nitrogen from processing the atmosphere for CO2. Venting liquid nitrogen to near vacuum Mars atmosphere can provide subcooling. If they want to go through a complex process like this on Mars is another matter.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 03/07/2016 09:50 pm
'Subcooling' is actually easier on Mars because the sub part refers to temperatures below the nominal boiling point at 1atm. Or boiling points at subatmospheric pressures. On Mars the low pressure of ambient atmosphere means you can drop pressures inside your LV (during prop load) and storage tanks below 1atm without fear of imploding things. Wiki says average surface pressure on Mars is 600Pa. LOX boils at 59K in this pressure, only five Kelvins above freezing point.

Can I get a factcheck / primer on this?

Is 'slush propellant' the same concept as 'subcooled propellant', or is it a subset?  Does propellant ever actually see 1atm?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 03/08/2016 09:24 am
What about getting the permits to launch a nuclear reactor, though?

Why would that be difficult? Provided you haven't run it before launch, it's a big lump of metal and ceramic, with some low-level radioactive fuel which is routinely transported around the world. (And the fuel rods/pellets can be launch separately from the reactor itself.) Should be easier than getting permission to launch an RTG.
That's pretty wishful thinking.

Historically space reactors have used HEU IE bomb grade enriched Uranium which makes the fuel very expensive and governments very twitchy about who uses and who has it. The reactors themselves will probably need to meet standards for on orbit radiation affecting other payloads as they pass by them so they don't fry other peoples electronics as they get where they're going. If launched loaded with fuel extensive modelling will be needed to show it won't go critical if it crashes in the sea, given seawater makes a good moderator. This includes if the coolant (even a molten metal that will be frozen at launch) is fully replaced by seawater.

Ground reactor certification has also been geared toward big static power generators which have issues which (in principal) small ones can avoid.

And of course there is the market for the design.

When you've done all that work how many? 2? 4? 10?

The nearest "off the shelf" you could get to this would be the units in nuclear submarines.  These units are roughly in the 10s of MW range (so plenty of power) and historically have been sealed-for-life (I think modern ones are refuelable about every decade)  but expect a very plentiful supply of seawater and because of their use are highly classified. I've no idea what one weighs but being for use in submarines mass was not a key driver.

Has any small reactor reached prototype stage yet? I mean actually built. Toshiba have been talking about their 4S design but AFAIK the only small reactor design that's gone critical was a pebble bed design in South Africa.


I mean what are current figures of merit for PV arrays and radiators? In 2008 80-100W/Kg for a rigid array was SoA.  The same report gave thin film systems around 2000W/Kg It lists ISS as roughly 1W/Kg, a staggeringly low number IMHO.

http://www.spacefuture.com/archiveearly_commercial_demonstration_of_space_solar_power_using_ultra_lightweight_arrays.shtml
The MIT report on a potential 6Kw/Kg is interesting. That would make the ISS array weigh about 36Kg. However t there is much more to a full array than just the blanket.

A key question would be should such an array be able to survive launches & landings?

In principal given the MIT technique uses high vacuum (readily available on orbit) you could make them single use and discard after every trip. Attaching them to the MCT on orbit for the trip and setting up a PV array mfg unit in Mars orbit for the return journey.

I'm not advocating it. I merely point it out as an option. Seems wasteful but if you can recycle the materials after use you get a fresh array for each journey. A copy of the array mfg unit would probably be needed to mfg cells for Mars, which could be more robust or also single use (during the visit).

Assuming a reusable blanket (the conservative option) you're going to need a)Storage containers b)Unroll mechanism c)Roll up mechanism and (probably) d) Power transfer coupling so the array can track the sun independently of MCT orientation. All of which will knock down specific power.

Some of these can be varied, for example the aspect ratio of the array will affect the shape (but not the overall volume) of the storage box, which has implications on materials selection for the box, array stiffness and surface area of the MCT taken up by the array storage versus other uses for the same surface, like radiators, antenna etc.

Note that a transformer based coupling design from NASA and the University of Bangor in Wales has shown data transfer rates in the mbs and power transfer in the 100s of Kw with no rubbing contacts.

Note that even if this reduced array specific power 6x (using the MIT technology) it would still be 1000x better than ISS specific power (if the figures in the original article are correct), provided the array itself can survive launch and landing.  :(

Which sounds like a good candidate for a small test payload for a recoverable F9 first stage to carry.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 03/08/2016 04:15 pm
'Subcooling' is actually easier on Mars because the sub part refers to temperatures below the nominal boiling point at 1atm. Or boiling points at subatmospheric pressures. On Mars the low pressure of ambient atmosphere means you can drop pressures inside your LV (during prop load) and storage tanks below 1atm without fear of imploding things. Wiki says average surface pressure on Mars is 600Pa. LOX boils at 59K in this pressure, only five Kelvins above freezing point.

Granted you must think about tank implosion, but also about explosion. The temperatures you cited are open system, but you are not going to put LOX in an open vat and allow it to evaporate/boil away. It is going into closed tanks and will have to be chilled to lower temperature as well as under some pressure in order to fit more density into the tank. Lacking the 1 atm. of pressure on the outside of the tank, the amount of interior pressure the tanks can withstand would be offset by an equal counter-pressure. So we still arrive back at the question of how cold you can get the prop when you are on Mars. You still have the limitations of a much lower electrical power supply than the North American electrical grid and you also have to dump the heat you withdraw from the prop as you chill it. With almost no atmosphere to run through a radiator from a heat pump, the heat has to be dumped into the ground or allowed to radiate directly into space or something. So I am back to wondering whether creating super-cryo prop in situ on Mars is going to be significantly harder than more typical cryo temperature prop.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 03/08/2016 06:29 pm
I mean what are current figures of merit for PV arrays and radiators? In 2008 80-100W/Kg for a rigid array was SoA.  The same report gave thin film systems around 2000W/Kg It lists ISS as roughly 1W/Kg, a staggeringly low number IMHO.
We have some distinctions to make:
1. Raw solar cells
2. UV-Coated/encapsulated & wired solar cells
3. Coated, wired, structurally supported solar panels
4. Solar panels mounted in an array
5. Solar panels mounted in an array mounted on a a deployment mechanism
6. A solar panel array on a deployment mechanism mounted on a large motorized rotation spindle/axle
7. The above arrangement mounted on a truss to extend away from the station
8. That truss being modular and heavy-duty enough to support indefinite amounts of length, and having additional motorized axles
9. That truss also having batteries, radiators, and substantial station infrastructure mounted on it

We launched the last one on the Shuttle for the ISS four times.  It was very heavy.  Comparing the Shuttle's payload with the power output of the truss gives a ludicrously low number even with 1980's technology.

2kw/kg probably refers to item 1.

There are two projects (https://www.nasa.gov/offices/oct/home/feature_sas.html#.Vt8jzPkrLcs) currently deployed from NASA to satisfy an eventual desire for a 300kw 'Government Reference Array' (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140000360.pdf), with minimum 100w/kg at EOL, probably at about the scope of item 6.  One firm is selling the prospect of 200w/kg, and the other is matching 200w/kg with some notation about the future possibility of 400-600w/kg.  Funding is currently focused on interim products far below this scale.  The ROSA tech has not been flown to my knowledge, while the Ultraflex tech has seen use (https://www.orbitalatk.com/space-systems/space-components/solar-arrays/docs/FS007_15_OA_3862%20UltraFlex.pdf) in several missions in the last two decades - the Phoenix Lander achieved 103w/kg with 1G deployment.

The commercial sector is presently pushing the Boeing 702SP with all-SEP GTO->GSO transition.  Its solar arrays come in at 130w/kg (http://www.lpi.usra.edu/meetings/lpsc2013/eposter/1486.pdf), again probably at about the scope of item 6.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 03/08/2016 06:33 pm
Raw solar cells can be made as good as 40-100kW/kg.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 03/08/2016 06:36 pm
Raw solar cells can be made as good as 40-100kW/kg.

Cite?

The present hype in lightweight encapsulated solar cells seems to have only demonstrated 6kw/kg and at that thickness, will float on a soap bubble:
http://news.mit.edu/2016/ultrathin-flexible-solar-cells-0226
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 03/08/2016 06:58 pm
Thin film cells themselves, not counting contacts and substrate, are about a micron thick. At 1300kW/kg and 10-30% efficiency gives on the order of 40-100kW/kg.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 03/08/2016 07:07 pm
The actual absorption thickness is on the order of 50-100nm, actually. If we're talking about fundamental limits, here.

...think like a solar sail designer!!!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 03/08/2016 10:03 pm
The actual absorption thickness is on the order of 50-100nm, actually. If we're talking about fundamental limits, here.

...think like a solar sail designer!!!
Actually I was. IIRC KE Drexlers Masters thesis was on the idea of mfg solar sails by vacuum deposition onto a wax layer, then dissolving the wax layer.  In principle excellent performance but far too fragile to survive launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 03/09/2016 03:09 am
The actual absorption thickness is on the order of 50-100nm, actually. If we're talking about fundamental limits, here.

...think like a solar sail designer!!!
Actually I was. IIRC KE Drexlers Masters thesis was on the idea of mfg solar sails by vacuum deposition onto a wax layer, then dissolving the wax layer.  In principle excellent performance but far too fragile to survive launch.
Neat idea, I was thinking of something similar (but I was just thinking regular acid etching... wax is cleverer than what I was thinking). You could launch it with some sort of waxlike material that would sublimate away once heated in space.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 03/09/2016 06:47 am
The actual absorption thickness is on the order of 50-100nm, actually. If we're talking about fundamental limits, here.

...think like a solar sail designer!!!
Actually I was. IIRC KE Drexlers Masters thesis was on the idea of mfg solar sails by vacuum deposition onto a wax layer, then dissolving the wax layer.  In principle excellent performance but far too fragile to survive launch.
Neat idea, I was thinking of something similar (but I was just thinking regular acid etching... wax is cleverer than what I was thinking). You could launch it with some sort of waxlike material that would sublimate away once heated in space.
Drexlers thesis should still be available at Stamford Princeton, however it'll date from the late 70's so I've no idea if it's been scanned and available online.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jim_LAX on 03/09/2016 02:22 pm
How about launching a 3D printer that takes advantage of the vacuum of outer space to do the vacuum deposition on wax.  And then melt and recycle the wax.  You would just need to launch fresh supplies of Silicon.  This might even work for Space Based Solar Power.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 03/09/2016 05:21 pm
The actual absorption thickness is on the order of 50-100nm, actually. If we're talking about fundamental limits, here.

...think like a solar sail designer!!!
Actually I was. IIRC KE Drexlers Masters thesis was on the idea of mfg solar sails by vacuum deposition onto a wax layer, then dissolving the wax layer.  In principle excellent performance but far too fragile to survive launch.
Neat idea, I was thinking of something similar (but I was just thinking regular acid etching... wax is cleverer than what I was thinking). You could launch it with some sort of waxlike material that would sublimate away once heated in space.
Drexlers thesis should still be available at Stamford, however it'll date from the late 70's so I've no idea if it's been scanned and available online.

Most masters' theses are not published in peer-reviewed journals, today.  The overwhelming majority of papers published in the late 70's have not been scanned and made available online and transferred to a paper repository we can access.

Fortunately, this is an exception to the rule:
https://dspace.mit.edu/handle/1721.1/16234
https://dspace.mit.edu/bitstream/handle/1721.1/16234/06483741-MIT.pdf?sequence=2
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 03/09/2016 06:59 pm
Most masters' theses are not published in peer-reviewed journals, today.  The overwhelming majority of papers published in the late 70's have not been scanned and made available online and transferred to a paper repository we can access.

Fortunately, this is an exception to the rule:
https://dspace.mit.edu/handle/1721.1/16234
https://dspace.mit.edu/bitstream/handle/1721.1/16234/06483741-MIT.pdf?sequence=2
Excellent work.  That's the one I was thinking of.

MIT

Well I completely screwed up that reference  :-[
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 03/09/2016 08:11 pm
'Subcooling' is actually easier on Mars because the sub part refers to temperatures below the nominal boiling point at 1atm. Or boiling points at subatmospheric pressures. On Mars the low pressure of ambient atmosphere means you can drop pressures inside your LV (during prop load) and storage tanks below 1atm without fear of imploding things. Wiki says average surface pressure on Mars is 600Pa. LOX boils at 59K in this pressure, only five Kelvins above freezing point.

Granted you must think about tank implosion, but also about explosion. The temperatures you cited are open system, but you are not going to put LOX in an open vat and allow it to evaporate/boil away. It is going into closed tanks and will have to be chilled to lower temperature as well as under some pressure in order to fit more density into the tank. Lacking the 1 atm. of pressure on the outside of the tank, the amount of interior pressure the tanks can withstand would be offset by an equal counter-pressure. So we still arrive back at the question of how cold you can get the prop when you are on Mars. You still have the limitations of a much lower electrical power supply than the North American electrical grid and you also have to dump the heat you withdraw from the prop as you chill it. With almost no atmosphere to run through a radiator from a heat pump, the heat has to be dumped into the ground or allowed to radiate directly into space or something. So I am back to wondering whether creating super-cryo prop in situ on Mars is going to be significantly harder than more typical cryo temperature prop.

This isn't true.
The tanks can (and probably will) be kept near Mars atmospheric pressure, but sub-cooled to slightly below saturation temperature.  Saturation temperature at that pressure is near the triple point as stated -- and LOX is an essentially incompressible fluid, so its density is set by its temperature.  Nearest analogy is keeping a pot of water on the stove just below boiling temperature... it will remain liquid unless you add energy.

On the closed tank comment, this will be a necessity because the CO2 (and a bit of water) in Martian atmosphere will freeze-out in a LOX bath, so the tanks must remain sealed to maintain purity of the LOX.  A slight pressure might be used, but nothing is sacred about or 'easier' at one Earth atmosphere.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 03/10/2016 06:29 am
Most masters' theses are not published in peer-reviewed journals, today.  The overwhelming majority of papers published in the late 70's have not been scanned and made available online and transferred to a paper repository we can access.

Fortunately, this is an exception to the rule:
https://dspace.mit.edu/handle/1721.1/16234
https://dspace.mit.edu/bitstream/handle/1721.1/16234/06483741-MIT.pdf?sequence=2
Just had a chance to skim it.

I think Drexler ran tests that showed you can mfg thin metal films by depositing them on a wax layer and then removing the layer but I don't think he ever built an actual machine.

Possibly his neatest feature is the idea of deliberately introducing cuts and waves into the film to stop tears and absorb stress without stiffeners. I was sort of reminded of the cuts made in foils to make flexure bearings.

I'll also note that such a device would scale down quite well, making it an interesting (but very challenging) project for someone to pursue. Rotary motion in UHV is tricky. With a lubricant on the bearings you run the risk of it vaporizing and contaminating the system (give the oils on a fingerprint can certainly do this). Without it you risk ceasing up.

Keep in mind that on orbit the vacuum is effectively outside the container and hence the various "chambers" in the machine would be more there to stop various vapors mixing and depositing in the wrong places, more like partitions than actual mini vacuum chambers.

There is also a PV cell architecture that uses the difference between the work functions of two dissimilar metals to make electricity. The metal thicknesses would be in this order of magnitude, although one of them would be thinner to let the light get to the junction area.

One thing I'm not clear on. Do solar sails open up the launch windows to other planets?

Could you set up a pipeline of sail vehicles leaving say every month to the same destination? AFAIK solar sails are the only technology that can return the core structure of the vehicle [EDIT without any infrastructure at the destination for refueling ] ready for another trip.

Ongoing support to remote settlements has to be sustainable. Such a fleet of vehicles would might be one way to do this.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 03/12/2016 01:41 pm
I just stumbled upon an old soviet idea for a reusable space shuttle:
(http://www.astronautix.com/nails/m/mtkva1.jpg)

Although it's not designed for anything Mars related, it rather looks like an elongated Kliper, I found a couple interesting points that might be relevant re MCT.

1. I like the skids idea, it's relatively lightweight and if needed wheels can be attached to them for ground operation. These need not be carried by the vehicle after the first trip, in fact a single set of wheels can be shared by all the fleet.

2. The rounded triangle profile looks interesting, apparently was designed for hypersonic flight above 12km. Below that, it used parachutes with small rockets just before touching the ground. Remove the parachutes and add bigger rockets and it might work in Mars lower gravity. Problem is, they'd have to be used for take off too, and the main engine would be fired for the big push only.
This sort of horizontal landing makes a lot easier the unloading of payload in Mars, this is usually not mentioned, but a tall lander makes handling cargo a lot harder.

3. It was about 34 m long, and weighed 200 mt(!!). I find this quite unbelievable given that the shuttle orbiter weighed a lot less and had wings. But probably a fully loaded MCT (sans TMI propellant) would be that heavy, probably not much bigger than this either.

Obviously, the main problem would be the need for quite powerful landing/take off rockets that don't appear to be something that SpaceX may be considering. Personally I think an expander cycle variant of their Raptors (downsized perhaps) might work, but this is just my MCT not Musk's.

For more info, have a look at these:
http://forum.nasaspaceflight.com/index.php?topic=30044.0
https://falsesteps.wordpress.com/2012/10/06/mtkvp-glushkos-opening-gambit/
http://www.buran.ru (https://translate.google.com/translate?depth=1&hl=en&prev=/search%3Fq%3Dburan.ru%26hl%3Den%26biw%3D1680%26bih%3D904%26prmd%3Dimvns&rurl=translate.google.ca&sl=ru&u=http://www.buran.ru/htm/str124.htm)
http://www.astronautix.com/craft/mtkva.htm
Title: Re: MCT Speculation and Discussion Thread 4
Post by: R7 on 03/18/2016 09:11 am
Can I get a factcheck / primer on this?

Is 'slush propellant' the same concept as 'subcooled propellant', or is it a subset?  Does propellant ever actually see 1atm?

NIST databooks are excellent;

Oxygen properties (http://www.nist.gov/srd/upload/jpcrd423.pdf)
Alkane (methane-butane) properties (http://www.nist.gov/srd/upload/jpcrd331.pdf)
Nitrogen properties (http://www.nist.gov/data/PDFfiles/jpcrd39.pdf)

Slush propellant is a 2-phase mixture, fine solid particles in a liquid. The idea is to increase density because most substances are denser in solid phase. Kind of special case of subcooling, subcooled so close to melting point that has partially frozen.

AFAIK never used in flight. Would be even more problematic to handle than subcooled pure liquid, special problems like how to keep the solid particles from settling out of the mixture (agitation?) and pumping said mixture in the engine.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 03/19/2016 08:52 am
Here is my engineering module (upper stage Raptor engines & tanks) to date.  The person at the top shows scale.  The airlock/doors are dynamic which mean they actually open/close.  The engine canting mount also works, canting the Raptor 15 degrees with the engines retaining gimbal room.  The nacelles internally have ablative nozzle extension which also cants with the engine.  Next up is landing legs and filling in the engineering spaces with IVF, Draco methlox tankage, plumbing.  Also have to finish the upper deck with ECLSS, tankage (water & nitrogen), batteries, etc.  The only thing I don't like is the separated tanks; I should have made a common bulkhead/dome.  Less weight and height but would have more time to resize everything.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 03/19/2016 10:50 am
Here is my engineering module (upper stage Raptor engines & tanks) to date.  The person at the top shows scale.  The airlock/doors are dynamic which mean they actually open/close.  The engine canting mount also works, canting the Raptor 15 degrees with the engines retaining gimbal room.  The nacelles internally have ablative nozzle extension which also cants with the engine.  Next up is landing legs and filling in the engineering spaces with IVF, Draco methlox tankage, plumbing.  Also have to finish the upper deck with ECLSS, tankage (water & nitrogen), batteries, etc.  The only thing I don't like is the separated tanks; I should have made a common bulkhead/dome.  Less weight and height but would have more time to resize everything.

Kaoru

What use do you envision for the airlock tunnel when the airlock itself is not in use? I mean, it is a lot of space in a space constrained design...

Edit: since it runs by the engines, wouldn't it make sense to allow engine compartment access from the tunnel?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 03/19/2016 11:05 am
Here is my engineering module (upper stage Raptor engines & tanks) to date. [...]

You don't need to overdo the symmetry. Provided you don't have a shifting CoM during delicate manoeuvres (like landing), a rocket design can cope if specific elements aren't physically symmetrical.

Hence, I'd run that airlock access tunnel along the outside of the vehicle. Being a long vertical tube, it isn't aerodynamically harmful during launch/landing. (And assuming the re-entry attitude is off-centre (to add lift), the tunnel can be on the dorsal side; protected from re-entry heating.)

It removes that hole through the tanks. And it removes issues with either having warm air piped to the centre of the cryo-tanks, or allowing the tunnel to reach cryo-temps during the flight -- both of which I suspect are bad choices.

More broadly, have you been thinking about the cargo version? There will be a lot more of those than crewed ships. IIRC, Musk talked of 10:1. How does your design allow cargo to be unloaded?

What use do you envision for the airlock tunnel when the airlock itself is not in use? I mean, it is a lot of space in a space constrained design...

Storage of ground equipment not needed in flight? EVA suits, etc.

Plus supplies and parts during the trip. These would be transferred to the hab sections after landing, to allow the airlock to be used, then moved outside.

Edit: since it runs by the engines, wouldn't it make sense to allow engine compartment access from the tunnel?

{laughs} I really like the idea, but suspect that the amount of maintainable systems you could access would be limited, and number of situations where you have the vehicle safe in space but with an engine failure would be even more limited.

The only scenario that's realistic is on the Martian surface, where they landed safely but either something glitched or they just want to do a check-out and service before lift-off for Earth-return. In which case, you'd be better off designing for access to the entire engine system from outside (as you would on Earth for a first stage after a launch-abort).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 03/19/2016 03:34 pm

What use do you envision for the airlock tunnel when the airlock itself is not in use? I mean, it is a lot of space in a space constrained design...

Edit: since it runs by the engines, wouldn't it make sense to allow engine compartment access from the tunnel?
You hit the nail on the head.  The space where the engine nacelles and tankage (gaseous methane/oxygen, nitrogen, etc.) are are unpressurized.  However, the IVF and other equipment would be pressurized and accessible.  The intent is to be able to service (everything that's serviceable) from the inside; important for long term trips where everything is in-situ.

In doing the model, it was just easier to stretch the tunnel.  I'll be updating it with a pressure vessel and bulkheads for the engines.

Kaoru
 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 03/29/2016 11:42 am
Nice rendering, though I agree with others that the airlock tunnel is structurally impractical. Just have an ordinary airlock above the tanks and a ladder down the side, with a flip-out hook for hoisting down stuff.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 03/29/2016 02:12 pm
Guys, what happened to "Keep It Simple Stupid"?

The design concepts I've seen presented of late are more and more complex, with many added potential points of failure on items that, while convenient, also become mission critical failure points.

The base outer design of the MCT will most likely be something like a jumbo sized Dragon 2 capsule, (assuming the Dragon 2 works as planned) combined with a separate living quarters module and strongback structure to which propulsion, fuel and cargo modules would be attached.  Sending a single MCT at a time to Mars, with 100 colonists each, would take many decades to achieve the population intended.  Likely, when the actual colonial effort starts, they will effectively be building a "Liner" style system, carrying hundreds of people for each trip.

Obviously, the first expeditions will likely be single craft, small crews as more proof of concept and scouting type missions, but later flights will be for the establishment of the initial "beach head" colony.

Adding things like internally stored cargo, skyscraper tall landers, and elevators, amongst many other concepts, simply adds to the overall complexity of the mission profile, as well as adding unneeded dangers to an already very dangerous operation.

Something similar to the old, post Apollo capsule based lander design, (except as a SSTO Mars design) seems the most simple and least failure prone type of craft.  (The addition of inflatable Hypersonic decelerator systems would be a help too).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 03/29/2016 04:32 pm
The base outer design of the MCT will most likely be something like a jumbo sized Dragon 2 capsule, (assuming the Dragon 2 works as planned) combined with a separate living quarters module and strongback structure to which propulsion, fuel and cargo modules would be attached.  Sending a single MCT at a time to Mars, with 100 colonists each, would take many decades to achieve the population intended.  Likely, when the actual colonial effort starts, they will effectively be building a "Liner" style system, carrying hundreds of people for each trip.

It is quite reasonable, the problem here is Musk saying that they intend to 'land the whole thing'.
Also, the 100 colonists per ship looks more a like long term goal (for future versions of the system) rather than a requirement. A bit like the 80000 persons/year.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 03/29/2016 04:45 pm
The base outer design of the MCT will most likely be something like a jumbo sized Dragon 2 capsule, (assuming the Dragon 2 works as planned) combined with a separate living quarters module and strongback structure to which propulsion, fuel and cargo modules would be attached.  Sending a single MCT at a time to Mars, with 100 colonists each, would take many decades to achieve the population intended.  Likely, when the actual colonial effort starts, they will effectively be building a "Liner" style system, carrying hundreds of people for each trip.

It is quite reasonable, the problem here is Musk saying that they intend to 'land the whole thing'.
Also, the 100 colonists per ship looks more a like long term goal (for future versions of the system) rather than a requirement. A bit like the 80000 persons/year.

He's also said that the design is currently fluid.  It's likely to change before they start cutting metal for it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 03/29/2016 05:13 pm
He's also said that the design is currently fluid.  It's likely to change before they start cutting metal for it.

Functionally we may define three modules: lander/payload delivery, propulsion and living quarters/ECLSS. If you separate them you'll need to duplicate, e.g. in space propulsion vs landing. It may be simpler in the end to build a jack-of-all-trades ship, it won't be optimal but it will be simple to operate as a system and require a lot less mass.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 03/29/2016 11:03 pm

...

Edit: since it runs by the engines, wouldn't it make sense to allow engine compartment access from the tunnel?

{laughs} I really like the idea, but suspect that the amount of maintainable systems you could access would be limited, and number of situations where you have the vehicle safe in space but with an engine failure would be even more limited.

The only scenario that's realistic is on the Martian surface, where they landed safely but either something glitched or they just want to do a check-out and service before lift-off for Earth-return. In which case, you'd be better off designing for access to the entire engine system from outside (as you would on Earth for a first stage after a launch-abort).

Humbly, I disagree with this assertion. It seems you are looking for scenarios under the streetlight of status quo, while the vastness of a space mass-transport system, comprised of reusable components contains plenty of them, if a bit concealed by the contrast :).

I am sure you can appreciate maximum access when changing on orbit a couple of Raptors after an unfortunate MMOD event on one of a couple of hundreds of craft you total fleet comprises. Btw, my suggestion was made with engine room being unpressurised in mind, not part of the interior, but rather the exterior of the ship for that matter.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 03/29/2016 11:11 pm


Guys, what happened to "Keep It Simple Stupid"?

...

Not to disagree with the rest of your post, I'd like to suggest that by the time this thing gets built, Musk's and his engineers' concept of Simple will be interesting to behold.

Also, completely aside, I'd note that that phrase, addresses stupid, which people building MCT are not

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 03/30/2016 04:44 am
Adding things like internally stored cargo

Where else would you put the cargo for a vehicle capable of EDL on a planet with an atmosphere?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 03/30/2016 04:56 am
I am sure you can appreciate maximum access when changing on orbit a couple of Raptors after an unfortunate MMOD event on one of a couple of hundreds of craft you total fleet comprises.

You aren't going to be transporting spare Raptors inside the passenger ship, nor moving them through a crew-access tunnel. (Nor even the major parts of the engine.) They'd be stored in one of the cargo ships. So the repair crew still need to exit the ship.

Having a crew access tunnel that opens inside the engine area offers a trivial advantage over an EVA-airlock anywhere else on the ship.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 03/30/2016 06:14 am
I am sure you can appreciate maximum access when changing on orbit a couple of Raptors after an unfortunate MMOD event on one of a couple of hundreds of craft you total fleet comprises.

You aren't going to be transporting spare Raptors inside the passenger ship, nor moving them through a crew-access tunnel. (Nor even the major parts of the engine.) They'd be stored in one of the cargo ships. So the repair crew still need to exit the ship.

Having a crew access tunnel that opens inside the engine area offers a trivial advantage over an EVA-airlock anywhere else on the ship.

Not in the design discussed, though
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 03/30/2016 04:55 pm
After reading the past few posts, there seems some disjoint between the opinions put forward and reality of the requirements and the technology available.  First, scaling up the Dragon 2 spacecraft to be an upper stage, lander, and long term spacecraft is impractical.  However, scaling up an traditional upper stage isn't and it's because of the requirements.  Any design will be a trade off but there are some absolutes imposed by the requirements and the available technology.  I identify the requirements as these:

Starting with propellants & propulsion, CH4/LOX is required since ISRU/refuelling has to be employed.  Propulsion has to work efficiently in thin atmosphere to vacuum and have highest ISP (for CH4/LOX).  The modes are ascent, injection, entry, descent, and landing.  Ascent and injection requires high thrust and specific impulse which means no cosine/expansion thrust loss and using a lot of propellant.  Using a lot of propellant means "independent" refuelling on surface and in orbit with all the plumbing/pumps, etc. on board the spacecraft.  The remaining modes entry, descent, and landing requires throttling/control for supersonic retro-propulsion (EDL) which means adaptable nozzles and canting of the engines (with cosine loss to lower thrust).

As well, RCS/ullage propulsion has to be based on CH4/O2 (gaseous) in bladder/piston tanks, as hydrazine/nitrogen/helium can't be refueled (aka CO2 can be used as the pressurizing gas).  Also, momentum wheels will have to be employed for stability to lower propellant expenditures.  Of course, main propulsion (aka the US Raptors) will require cryogenic CH4/LOX storable for long term which means cryogenic plant (aka IVF) with pumps, compressors, etc.  Also, for a closed loop ECLSS and for ISRU, a Sabatier reactor also has to be included.  All of this will take a lot of energy and being pure solar is impractical both on orbit and on surface.  The energy budget will have to be balanced.  This most likely means a hybrid solution between solar/batteries and an ICE running the pumps/compressors and generator.  All of these technologies will be used on orbit and on surface and are absolutely critical/high maintenance.  This maintenance requirement assumes access to the technology timely/effectively and in any mode, in other words, in a pressurized environment.

My design speculates the above requirements and provides a solution to each as simply as possible and with the least amount of dry mass (that can be speculated).  Also, the "tunnel" provides a lot of advantages.  First, the tanks are a torus which are structurally stronger than a straight tank.  It also provides a more direct path for plumbing/wiring which means less mass (the Saturn V had the same idea for the fuel lines passing thru the tanks, five pipes in total).  The bottom airlock and tunnel provides the means to off-load cargo without a heavy crane or such.  My idea is to use an electro-magnetic lift system (like on the US Ford class carrier) installed in the tunnel to a bottom airlock area.  Then a simple pulley/cable system lowers to the ground.  This bottom pressurized area also allows access to the afore mentioned system like IVF/Sabatier reactor, ICE generator, batteries, etc. for maintenance on orbit or on surface.  Also, the systems can be connected/plumbed externally for Mars ISRU operations.

I'm still devoted to finishing my model.  I must be since I bought the Pro version of SketchUp to the tune of $700.  My justification to my wife was that my daughter (who's doing computer science/game development) can use it for game modelling.  She seemed to buy that.

My .02 worth or more,
Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 03/30/2016 05:27 pm
  This most likely means a hybrid solution between solar/batteries and an ICE running the pumps/compressors and generator.  All of these technologies will be used on orbit and on surface and are absolutely critical/high maintenance.  This maintenance requirement assumes access to the technology timely/effectively and in any mode, in other words, in a pressurized environment.

I'm still devoted to finishing my model.  I must be since I bought the Pro version of SketchUp to the tune of $700.  My justification to my wife was that my daughter (who's doing computer science/game development) can use it for game modelling.  She seemed to buy that.

My .02 worth or more,
Kaoru


I'm still on the free Sketchup ;-)  Am I missing anything except for the converters?

Did you check the fuel and oxygen requirements for the ICE (Internal Combustion Engine)?  for the 100 kW power level I chose for my own design, I calculated about 2 tonnes of solar arrays and converters.
When I checked the power to mass ratio of CH4+3O2=CO2+2H2O in an ICE, I found I would only get 7.1 Mj/kg, or 7100 MJ per tonne.  This works out at about 1 tonne per day of combustion required for 40 kW of power + 60 kW of heat, so it was really bad choice. The oxygen is very heavy.

You might choose to pressurize your RCS ullage gas tanks with methane and oxygen and avoid pressurants altogether?

looking forward to seeing the whole model!




Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 03/30/2016 06:28 pm
I'm still on the free Sketchup ;-)  Am I missing anything except for the converters?

Did you check the fuel and oxygen requirements for the ICE (Internal Combustion Engine)?  for the 100 kW power level I chose for my own design, I calculated about 2 tonnes of solar arrays and converters.
When I checked the power to mass ratio of CH4+3O2=CO2+2H2O in an ICE, I found I would only get 7.1 Mj/kg, or 7100 MJ per tonne.  This works out at about 1 tonne per day of combustion required for 40 kW of power + 60 kW of heat, so it was really bad choice. The oxygen is very heavy.

You might choose to pressurize your RCS ullage gas tanks with methane and oxygen and avoid pressurants altogether?

looking forward to seeing the whole model!
I was on the SketchUp Pro trial which expired and then I used SketchUp Make for a while to see the differences.  While on the Pro trial, I implemented dynamic components for the engines, airlocks, and hatches; they actually move when clicked.  Also, I used the solid tools (intersect/union, etc.) for implementing a lot of the components.  When I went to the free version, those tools were unavailable. I could still model but it was more time consuming/tedious and I couldn't modify the dynamic components I done.  I researched around for various modelling software and SketchUp is the only one that was applicable with a reasonable price (perpetual license; no subscription required).  All other software was subscription based and way to expensive anyway (aka Autodesk wanted $700 per year).

To keep on point, the energy requirements (for a Sabatier reactor, compressors, pumps) are substantial.  I have some good ideas for light but large/efficient solar panels but that's stretching things.  An ICE will be needed and it'll burn CH4/O2.  Your right that the RCS/ullage can be autogenously pressurized but the waste CO2 would also work and be available (as well as the ECLSS CO2) to the Sabatier reactor to make CH4 and O2 from CO2 and H2O.  The challenge is the energy required, which is obvious.  Solar panels and radiators can only be so big, batteries are only a buffer, and ICE generator requires fuel.

I haven't run the numbers to size the employed technologies because there are too many unknown factors.  However for speculation, I just know that it will be an interesting balance.  I akin this to the systems on a boat, where you have to budget your energy/fuel over time between refueling.  My design will most likely run at a net energy loss for an individual module but with other modules can be made self-sufficient.

Kaoru.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 03/30/2016 08:24 pm
An ICE is a really bad idea. Batteries work great. Solar panels also work great. 100 days is much too long to be using a ICE. An ICE throws away 70-80% of your energy. At least a fuel cell only throws away half. And you already have to throw away about half your energy to produce the methane and oxygen in the first place. So you're left with a round-trip efficiency of between 10 and 25%, ie you're left with only one tenth to one fourth of the energy you started with. Bad bad bad. Solar panels, on the other hand, are producing energy and are also improving all the time.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 03/30/2016 09:45 pm
An ICE is a really bad idea. Batteries work great. Solar panels also work great. 100 days is much too long to be using a ICE. An ICE throws away 70-80% of your energy. At least a fuel cell only throws away half. And you already have to throw away about half your energy to produce the methane and oxygen in the first place. So you're left with a round-trip efficiency of between 10 and 25%, ie you're left with only one tenth to one fourth of the energy you started with. Bad bad bad. Solar panels, on the other hand, are producing energy and are also improving all the time.

I take it this applies to ACES IVF system as well? AIUI, its powered by a Roush Racing built ICE.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 03/30/2016 10:18 pm
An ICE is a really bad idea. Batteries work great. Solar panels also work great. 100 days is much too long to be using a ICE. An ICE throws away 70-80% of your energy. At least a fuel cell only throws away half. And you already have to throw away about half your energy to produce the methane and oxygen in the first place. So you're left with a round-trip efficiency of between 10 and 25%, ie you're left with only one tenth to one fourth of the energy you started with. Bad bad bad. Solar panels, on the other hand, are producing energy and are also improving all the time.

I take it this applies to ACES IVF system as well? AIUI, its powered by a Roush Racing built ICE.
No, because the IVF is lasting for hours, maybe a few days. It'd need like a 50th the fuel of a 100 day trip that we're talking about.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 03/30/2016 10:32 pm
That's not what Boeing says.They say weeks, and mission descriptions out as asteroids sound longer than that.

http://spaceflightnow.com/2015/04/16/ula-gets-futuristic/

Quote
“We can take our first launch, big fuel tanks, supplies, food, water, if it’s a manned mission. And the next mission will bring up the spacecraft or the astronauts in their capsule. With this advanced upper stage, which can fly around for weeks, it’s up there waiting, we can put these pieces together, and outside the deep part of Earth’s gravity well with that much impulse and propellant, we can do anything.

“We can go out and tap the resources that are in space. We can asteroid mine, we can build the infrastructure required for a real and permanent human presence. Fuel depots, water depots, commercial human habitats. This is truly a game-changer and I couldn’t be more excited about what this will do for the future of space, all enabled by that advanced, high-performance, ultralong-duration upper stage,” Bruno said.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jg on 03/30/2016 11:04 pm
That's not what Boeing says.They say weeks, and mission descriptions out as asteroids sound longer than that.

http://spaceflightnow.com/2015/04/16/ula-gets-futuristic/

Quote
“We can take our first launch, big fuel tanks, supplies, food, water, if it’s a manned mission. And the next mission will bring up the spacecraft or the astronauts in their capsule. With this advanced upper stage, which can fly around for weeks, it’s up there waiting, we can put these pieces together, and outside the deep part of Earth’s gravity well with that much impulse and propellant, we can do anything.

“We can go out and tap the resources that are in space. We can asteroid mine, we can build the infrastructure required for a real and permanent human presence. Fuel depots, water depots, commercial human habitats. This is truly a game-changer and I couldn’t be more excited about what this will do for the future of space, all enabled by that advanced, high-performance, ultralong-duration upper stage,” Bruno said.

Note that the ICE has very high dynamic range (output power).  It can idle at very low power levels.  And the fuel used is not wasted: venting the water vapor overboard gives you just enough thrust to keep the propellants settled in the tanks, which also means that the boiloff from the tanks is much less due to lower heat loss.

This is more important when you have H2 stages, since H2 is so cold that you'll have significant boiloff otherwise which you now avoid by the constant tiny thrust available.  For methane and O2, it's less clear, since with good sunshading/orientation you can maintain low enough temperatures to avoid most/all of the fuel boil off problem of long missions.

The really huge benefits of ACES?IVF are on several fold: 1) much better mass fractions, as you save a lot of weight over conventional stages, 2) flexibility without reconfiguration of the stage, since so long as you have fuel available, you can power your stage, for days, weeks, or months; with existing upper stages, if you can do the mission at all, you may need different amounts of helium/tanks, etc, making a lot of non-leo missions one-off problems, and 3) you can get a lot of power when you need it.

So I'm a real fan of the idea, and find the slowness of ULA to get it into flight frustrating.  I had the chance to have dinner once at a meeting with the IVF inventor, Frank Zegler and hear a talk from him; IVF is a true step forward, and innovation of first order.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: john smith 19 on 04/03/2016 11:19 am
JG has it mostly right about IVF.

IVF seems to have gone through several revisions over the years as ULA have refined the concept. Key parts of it are.

Thrusters drive by the boiloff can be run in a pulsed mode to settle the propellants into 2 big single balls. This cuts boiloff by 1/2. Longer missions were always expected to have more layers of multilayer insulation that current ones. I think the current level is 5 but ULA have suggested somewhere between 19 and 34 IIRC.

The biggest discovery (when ULA analyzed all their peripheral systems for a stage) was the GHe tanks to do tank pressurization were the biggest item, yet with cryogenic propellants all you need to pressurize the tanks is something to heat them. In a normal ICE heat is a waste products you send to the radiator. In IVF it is a critical resource to the whole mission.

BTW IVF does have a battery sized mostly for (internal combustion) engine startup.

I think it's a tricky modelling task to trade IVF alone against IVF + solar for an uncrewed stage.

However once you have crew on board your power needs rise substantially and some kind of PV system seems pretty much essential unless you have a convenient sized nuclear reactor available. Very nice to have. Very doubtful you'll get it. :(

Moving to more use of momentum control devices for attitude control seems a pretty good idea but the preferred device is a Control Moment Gyroscope, not a Momentum Wheel. They run at constant (high) speed on 2 axis bearings. Such units were used on Skylab and do run on the ISS.

Replacing hypergols with O2/CH4 is an excellent idea to create a single system that can be reloaded through ISRU. Actually I think you can do hypergols from the Martian atmosphere but the very low level of N2 present would make it a very slow process.

The issue with O2/CH4 is ignitions. Mission planners like their RCS to be reliable and O2/CH4 probably complicates each thruster with spark plugs and support electronics unless you have a catalyst that can operate on the fluids as they come out of the tanks, or maybe a resonance tube ignitor, which needs enough tank pressure on at least one of the propellants to get supersonic flow in a nozzle.   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: the_other_Doug on 04/03/2016 02:08 pm
In terms of RCS fuel (where you really like the hypergolic, no-igniter-required aspect of current fuels), and in terms of ISRU production, what about hydrogen peroxide?  It has been successfully used as a monopropellant in RCS systems, notable for Mercury spacecraft but in many others, as well.

You do need a catalyst for peroxide monopropellant systems, which I imagine would reduce their service lives, but you don't need to find scarce nitrogen to make it with ISRU techniques.  And it is easier to maintain for long timeframes since it is not cryogenic and doesn't have the boiloff issue you have with LOX.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 04/03/2016 02:32 pm
The Morpheus moon lander testbed uses methane/LOX RCS thrusters and does just fine. That problem is solvable and I am convinced they will not use another fuel for that purpose.

Will they use sparkplugs or laser igniters? The russians are working on or already have laser igniters. Spark plugs do an impressive number of ignitions in ICE motors.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 04/03/2016 03:37 pm
An ICE is a really bad idea. Batteries work great. Solar panels also work great. 100 days is much too long to be using a ICE. An ICE throws away 70-80% of your energy. At least a fuel cell only throws away half. And you already have to throw away about half your energy to produce the methane and oxygen in the first place. So you're left with a round-trip efficiency of between 10 and 25%, ie you're left with only one tenth to one fourth of the energy you started with. Bad bad bad. Solar panels, on the other hand, are producing energy and are also improving all the time.

I take it this applies to ACES IVF system as well? AIUI, its powered by a Roush Racing built ICE.

It's hard to imagine Elon Musk taking SpaceX down the internal combustion engine road (i.e., Tesla, Giga-battery factories, Solar City, ZBO Methlox, minimal mass-to-orbit limitations, etc.), but the remaining ACES/IVF concepts are great and almost can be assumed to be part of BFS/MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 04/04/2016 12:36 am
It's hard to imagine Elon Musk taking SpaceX down the internal combustion engine road (i.e., Tesla, Giga-battery factories, Solar City, ZBO Methlox, minimal mass-to-orbit limitations, etc.), but the remaining ACES/IVF concepts are great and almost can be assumed to be part of BFS/MCT.
Elon did say that you can make all modes of transportation electric on the exception of rockets.  A rocket engine by definition is a combustion engine, adding an internal combustion engine to MCT is no big deal.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 04/04/2016 12:53 am
It's hard to imagine Elon Musk taking SpaceX down the internal combustion engine road (i.e., Tesla, Giga-battery factories, Solar City, ZBO Methlox, minimal mass-to-orbit limitations, etc.), but the remaining ACES/IVF concepts are great and almost can be assumed to be part of BFS/MCT.
Elon did say that you can make all modes of transportation electric on the exception of rockets.  A rocket engine by definition is a combustion engine, adding an internal combustion engine to MCT is no big deal.

Kaoru

I imagine the advantage of using an ICE is much bigger with LH/LOX than methane/LOX. It is not that hard to get methane/LOX to zero boil off and purely for electric power I believe solar is the better solution, especially beyond LEO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 04/04/2016 01:00 am
It's hard to imagine Elon Musk taking SpaceX down the internal combustion engine road (i.e., Tesla, Giga-battery factories, Solar City, ZBO Methlox, minimal mass-to-orbit limitations, etc.), but the remaining ACES/IVF concepts are great and almost can be assumed to be part of BFS/MCT.
Elon did say that you can make all modes of transportation electric on the exception of rockets.  A rocket engine by definition is a combustion engine, adding an internal combustion engine to MCT is no big deal.

Kaoru

I imagine the advantage of using an ICE is much bigger with LH/LOX than methane/LOX. It is not that hard to get methane/LOX to zero boil off and purely for electric power I believe solar is the better solution, especially beyond LEO.

Hmm I think LH/LOX makes for better efficiency in a fuel cell than ICE and methane/lox could be used that way too, however there are lots of methane powered diesels out there.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 04/04/2016 02:12 am
ICE is super dumb for MCT.

The specific energy of methane with stoic oxygen (best case) is 11MJ/kg. At an optimistic 33% efficiency, it's 3.7MJ/kg of electricity (A lithium-ion battery is 1MJ/kg, by the way, though there are some better ones in the lab). You know how long it'd take a 120W/kg solar array to make that much electricity? Less than 9 hours. And that's assuming the actual ICE and dynamo and tanks are massless!

Using an ICE (or even a fuel cell) to provide power for 100 days when you have access to solar energy without any clouds is the height of stupidity. Just use a solar panel! It's literally over a hundred times better!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 04/04/2016 02:39 am
It's hard to imagine Elon Musk taking SpaceX down the internal combustion engine road (i.e., Tesla, Giga-battery factories, Solar City, ZBO Methlox, minimal mass-to-orbit limitations, etc.), but the remaining ACES/IVF concepts are great and almost can be assumed to be part of BFS/MCT.
Elon did say that you can make all modes of transportation electric on the exception of rockets.  A rocket engine by definition is a combustion engine, adding an internal combustion engine to MCT is no big deal.

Kaoru

Yes it is.  A typical orbital insertion burn for MCT uses 700 tonnes of propellant, producing 15 GW for 320 seconds.
A short transit of 150 days to Mars is 12 960 000 seconds.  divide 15 GW by the travel time and you will find that the same 700 tonnes will only produce a continuous output of 300 kW.  And that's 300 kW of heat.  The electrical power will be about 100 to 130 kW.  So you need to burn 700 tonnes of methane and oxygen to produce 100 kW continuously.
With solar cells, supposing 4 kg/m2 (conservative) 800 m2, or 3.2 tonnes of cells, will produce 260 kW continuously at Earth, and still produce 100 kW when you reach Mars.
ICE just don't make sense.  700+ tonnes compared to 3 or 4 tonnes.

It does make for large panels though, and likely a pain to deploy and furl in.  But certainly doable.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 04/04/2016 05:58 pm
Of course, I have no special insight or secret sauce for knowing the power requirements for MCT.  However, doing a scale model is providing insight on how large and number of solar panels are possible (assuming roll-up/flexible panels with good efficiency).  Look at the ISS, its panels are huge for just 6 people and modest demand.  MCT will have a huge demand for energy (IVF/ISRU/Sabatier reactor) both on orbit and on surface.  Given the requirements of having panels deployed on orbit AND ON Mars surface, there's not enough to generate the necessary energy and/or impractical due to the required size/surface area.  However, a combination of solar/battery power and an efficient ICE generator with offloading of pumps/compressors to ICE *may* be the secret sauce in meeting the power requirements "in the different modes".  Yes, you'll be burning CH4/O2 (fuel) for electricity and/or to run pumps/compressors but that would only be on peak/active demand.  The best analogy would be a hybrid car.

Also, fundamentally the MCT will require refuelling both from a depot and ISRU.  Obviously, the architecture is geared to provide the required energy accordingly.  Having lived up north where the only electricity is from an old diesel generator running 7/24 for months on end with fuel deliveries every 6 months, I know it can be done.  The trick is knowing how much energy is needed then planning ahead.  I speculate that using an ICE to supplement solar power/batteries and using it in on demand situations where you need mechanical energy (ie. pumps/compressors) is how the energy budget will be balanced.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 04/04/2016 07:12 pm
Adding things like internally stored cargo

Where else would you put the cargo for a vehicle capable of EDL on a planet with an atmosphere?

As the cargo won't be returning to Earth, how about in a separate one shot landing module?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 04/04/2016 07:17 pm


Guys, what happened to "Keep It Simple Stupid"?

...

Not to disagree with the rest of your post, I'd like to suggest that by the time this thing gets built, Musk's and his engineers' concept of Simple will be interesting to behold.

Also, completely aside, I'd note that that phrase, addresses stupid, which people building MCT are not

     Never said that they were, but engineers just LOVE to add new and useful features!  As has been said. "the question isn't weather we can do a thing, the question is whether we SHOULD do a thing".

     Sometimes, people, (myself included) will look at a project and come up with some tremendously complex and unwieldy ways of doing something when a much simpler approach would be both cheaper and easier.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 04/05/2016 05:00 am
Here is the latest model of my design speculation.  For context, the attached image shows the engineering module focusing on the lower part.  Specifically I'm only showing the pressure vessel which would contain (not shown) IVF, Sabatier reactor, batteries, pumps/compressors, etc. which are serviceable.  The very lower part would be storage/cargo containing hoses/lines, etc. to hook up the systems externally/on surface or to another module via the CBM ring.  Outside the pressure vessel, would contain structure and tankage for various systems, mostly CH4, O2, CO2, etc..  The top deck (which is not done yet) will contain removable water tanks, ECLSS, and other life support systems.  Total height as shown is 26.5 meters (87 feet) which obviously does not include the payload (aka crew decks or cargo/consumables/propellants).

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 04/06/2016 02:31 am
Here is the latest model of my design speculation.  For context, the attached image shows the engineering module focusing on the lower part.  Specifically I'm only showing the pressure vessel which would contain (not shown) IVF, Sabatier reactor, batteries, pumps/compressors, etc. which are serviceable.  The very lower part would be storage/cargo containing hoses/lines, etc. to hook up the systems externally/on surface or to another module via the CBM ring.  Outside the pressure vessel, would contain structure and tankage for various systems, mostly CH4, O2, CO2, etc..  The top deck (which is not done yet) will contain removable water tanks, ECLSS, and other life support systems.  Total height as shown is 26.5 meters (87 feet) which obviously does not include the payload (aka crew decks or cargo/consumables/propellants).

Kaoru

A 10m core diameter?  Have you provided for extra insulation for the tanks?
Where does the cargo go?  And how does it all fit on the BFR?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 04/06/2016 04:03 pm
Elon has said the Raptor thrust would not be the previously cited 1.5 million lbf but would be "over 230 metric tons" or around 515 Klbf.  Optimal point for T/W ratio for an engine compared to the previous 3x greater design point.

SPECULATION:
Given that rival Bezos is in the news again with another successful re-use of his BE-3 engine rocket and that the Blue Origin BE-4 methalox engine is reported to have 550 Klbf thrust, I wonder if Elon's September reveal will have Raptor at higher than 515 Klbf, maybe ~600 Klbf?  Reduces the ~27 engine BFR to the low 20s at similar total thrust.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 04/07/2016 08:03 am
I see no reason for Raptor thrust or any other part of Musks design to change in response to Bezos's rocket design, if anything the comparable thrust levels mean both engines could be interchangeable on ULA's Vulcan which the Airforce would would look upon very favorably.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Craig_VG on 04/09/2016 01:26 am
Hi! Elon just said this on Twitter, do we think he could be talking below the $500,000 point?

https://twitter.com/elonmusk/status/718598761832968192

"Tickets to orbital hotels, the moon and Mars will be a lot less than people think."
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 04/09/2016 12:59 pm
Hi! Elon just said this on Twitter, do we think he could be talking below the $500,000 point?

https://twitter.com/elonmusk/status/718598761832968192

"Tickets to orbital hotels, the moon and Mars will be a lot less than people think."

First time Elon talking about orbital hotels and the moon, to my knowledge. Might indicate a shift towards more "attainable" goals. As for "what people think". NASA will pay $58m per seat on average to LEO. That's the reality.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: su27k on 04/09/2016 01:56 pm
Hi! Elon just said this on Twitter, do we think he could be talking below the $500,000 point?

https://twitter.com/elonmusk/status/718598761832968192

"Tickets to orbital hotels, the moon and Mars will be a lot less than people think."

First time Elon talking about orbital hotels and the moon, to my knowledge.

He mentioned the Moon several times before, you can find it on http://shitelonsays.com/, a very good example that explains Moon's place perfectly is

Quote
I don't think the Moon is a necessary step, but I think if you've got a rocket and spacecraft capable of going to Mars, you might as well go to the Moon as well - it's along the way. That's like crossing the English Channel, relative to Mars. So, it's like, if you have these ships that could cross the Atlantic, would you cross the English Channel? Probably. It's definitely not necessary, but you'd probably end up having a Moon base just because, like, why not, ya know.

As for space hotels, that's probably because BEAM is in this mission.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 04/09/2016 03:15 pm
Hi! Elon just said this on Twitter, do we think he could be talking below the $500,000 point?

https://twitter.com/elonmusk/status/718598761832968192

"Tickets to orbital hotels, the moon and Mars will be a lot less than people think."

First time Elon talking about orbital hotels and the moon, to my knowledge. Might indicate a shift towards more "attainable" goals. As for "what people think". NASA will pay $58m per seat on average to LEO. That's the reality.

You mean revenue, right?
NASA won't be the only customer for long.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 04/09/2016 03:43 pm
https://twitter.com/NASASpaceflight/status/718570618917150725 (https://twitter.com/NASASpaceflight/status/718570618917150725)

Mr Bergin, I'd just like to take this moment to ask you to stop giving us heart attacks. We do need to sleep sometimes if we're going to make it through to 2025. Thank you.

~ Yours truly, everyone.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ben Hawes on 04/09/2016 04:24 pm
Chris, and I'll report my own post so Chris reads it. You seem to know things about SpaceX's Mars plans. Is it true you've kept some of it to yourself or is it all in L2?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Chris Bergin on 04/09/2016 04:50 pm
Chris, and I'll report my own post so Chris reads it. You seem to know things about SpaceX's Mars plans. Is it true you've kept some of it to yourself or is it all in L2?

Yeah, I've had to keep a lot to myself, working to the guidelines provided when it was shown to me (that's totally natural on the process for a lot of things....in fact it's almost a set response of "what can I actually use" with most things). With L2, we already had an envisioning process going on (really cool work by clever folk, both in numbers and renders) and we mixed in, with permission, some of the planning phase into that to aid the accuracy of the envisioning. Naming no names, but we sent the rendering envisioning on a particular (you'd know the name) person at SpaceX I've chatted with and that got some thumbs up (probably because they look super cool, not making any claims here ;))

The notable caveats to everything include that they will be evolving their plans all the time (and getting "crazier" by the month apparently, which I'm sure Elon was alluding to yesterday) and only Elon will be the one to show off the actual plans - and that's only right.

Sometimes you have to remember you're a fan of rockets first and foremost and I prefer to watch history evolve with the rest of the community. That will apply in Mexico. Sh-ts about to get real folk.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: WBY1984 on 04/09/2016 05:04 pm
I'm confused, what's going on on Mexico?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ben Hawes on 04/09/2016 05:15 pm
Thanks Chris!

I'm confused, what's going on on Mexico?

Elon said he's going to give details at the IAC in Mexico this year.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bubbinski on 04/09/2016 09:32 pm
When is the IAC?!? I will be staying tuned!

Will I need to pick my jaw up off the floor after that unveiling Chris?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Retired Downrange on 04/09/2016 09:41 pm
http://www.iac2016.org

Every year, the International Astronautical Federation together with the International Academy of Astronautics and the International Institute of Space Law (IISL), holds the International Astronautical Congress (IAC) which is hosted by one of the national society members of the IAF.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 04/12/2016 04:09 am
Here are some screen shots of my model.  The engineering/service module, which is the workhorse of the BFS, is coming along.  In the shots shows the major areas which would contain the following components (not shown but coming): ECLSS (closed loop O2/H2O generation & CO2 scrubbing) with removable H2O/air tanks, ISRU/Sabatier reactor, IVF(cyrogenic plant), mechanical/electrical power generation (solar/batteries & ICE), and thermal management.  Of course, these systems are within the deck's pressure vessel to allow service.  The removable tanks allows them to be off-loaded to the surface via the tunnel.  The service module has some permanent tanks for the trip back to earth (assuming less passengers/crew only); they're outside the engineering deck.

Other additions include the heat shield cover for the aft airlock door, which is a dynamic component (ie. it opens/closes with a click on the model).

What I have remaining is the landing legs, solar panels, radiators, Draco thrusters, control moment gyroscopes, communication array, and CBM rings.  This will complete the module.  Next up is to do the crew module & cargo/fuel module which is the payload; this would complete the upper stage.

What do you think?
Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 04/12/2016 06:02 am
What do you think?
Kaoru

I'm not an expert on reentry, but this doesn't look like a viable reentry shape.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Cinder on 04/12/2016 06:05 am
Would an inflatable heat shield stowed in that hatch not be feasible either?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 04/12/2016 06:53 am
This is just an over-complicated design IMO. There is no need for a hatch at the bottom like that. And all that around the engines - the exhaust deflector housing - is going to need some *SERIOUS* active cooling to not melt during Raptor burns. Simplify. Remove the bottom hatch/tunnel. Remove the tunnel in the middle of the tanks. Increase tank volume.

It looks like you decided on 4 raptors in such an arrangement early on (with engine cowlings - why?) and you don't want to let go of it. That shape doesn't make much sense.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 04/12/2016 03:22 pm
This is just an over-complicated design IMO. There is no need for a hatch at the bottom like that. And all that around the engines - the exhaust deflector housing - is going to need some *SERIOUS* active cooling to not melt during Raptor burns. Simplify. Remove the bottom hatch/tunnel. Remove the tunnel in the middle of the tanks. Increase tank volume.

It looks like you decided on 4 raptors in such an arrangement early on (with engine cowlings - why?) and you don't want to let go of it. That shape doesn't make much sense.
I value your feedback as it questions my design choices, which in turn, validates the reason why I made those design choices.  Of course, my design is still very much a thought exercise until I model it.  Until then, my design choices are obviously unclear so I'll make a mental note to show why I decided that way (or clarify the choice).

In regards to the hatch, tunnel, and associated placement of the engines, this choice is born out of the idea of a "space train".  Having done some calculations on mass, I concluded that's it borderline impractical mass wise, even assuming refueling, for a full up BFS holding 100 passengers/crew, cargo, and consumables for the following modes: ascent, trans-Mars-injection, long term flight, Mars EDL, long term surface ops, and return to Earth.  Of course, the base assumption that everything is to be reused and play a role in the entire mission.  My idea for a "space train" is a cool way to address the requirements hence I chose to break up the dry mass into modules.  This choice requires a means to "link" the modules together (link a train) and this is where the aft hatch, tunnel, etc. come into play.

To visualize this, I envision four separate modules: service (the current model), cargo/consumables, fuel, and crew.  A single crew module will hold 48-52 people with life support supplied by the service module.  Given this, I envision that 4 launches (4 BFR with RTLS; upper stages are 2 x service + crew, 1 x service + cargo, 1 x service + fuel) would occur for a single Mars mission.  All the modules would link up like a train, aka 2 x crew, 1 x cargo, 1 x fuel, and 4 x service modules.  The tunnel and forward/aft CBM/hatches allows traversal (consumables/fuel/cargo) across all the modules on orbit/in-flight and servicing of all critical systems.  Prior to arriving at Mars, the train would break up into 3 or 4 landing units (1 service + module each) depending if fuel will remain orbiting Mars or land if needed (aka ISRU failed).

The engines can cant 15 degrees to do retro-propulsion (EDL) and for trans-Mars injection.  The exhaust deflector is essentially PICAX (no regenerative cooling required) and is primarily for retro-propulsion to maximize the plasma plume/atmosphere interface.  The aft CBM/hatch heat shield is obvious but has to open as not to impede the "train" link up.  Once on Mars surface, the hatch and tunnel is how cargo will be lowered to the surface; that's why the airlock has a large diameter.  Water tanks, air tanks, BEAM-like habitats, etc. is capable of fitting through the tunnel/airlock.  The engineering deck has ISRU, water/air generators to support on surface ops x 4 for redundancy.  The crew modules provide habitat while the base is being built.

As you can see, that's a lot of detail I put thought into when I made my design choices.  Of course, this is all speculation on my part but it does confirm in my mind that Elon's MCT is quite doable and at a fairly low cost (as costs go for Mars; at least lower than the wild projections being posted).

Food for thought,
Kaoru 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: biosehnsucht on 04/12/2016 11:49 pm
With regards to canting the engines within the engine nacelles / fairings / whatever they are, for EDL purposes, I recall reading that in order to benefit you need them to be operating from behind the shock front during EDL, not in the middle of it, so they would need to be further up the body (sort of Super Draco style).

As I understand it, with them at the shockfront, running the engines will _reduce_ the aerodynamic deceleration and  require greater thrust from the engines to make up for the loss of aerodynmic deceleration (which, if you can afford more propellant than heat shielding might be useful) and not go splat.

The obvious downsides of course with placing the engines higher so that they can operate behind the shockfront is that you are probably stuck with sizable cosine losses, and potentially more complicated plumbing (if the tanks are at the bottom, must pump up), etc ...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 04/13/2016 03:38 pm
I have a hard time envisioning a Mars base constructed with elements limited in size by having to pass through a tunnel such as the one in your plans.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 04/13/2016 04:40 pm
I have a hard time envisioning a Mars base constructed with elements limited in size by having to pass through a tunnel such as the one in your plans.
If you look at the dimensions of BEAM, it's not small by any standard (once expanded) but small enough to pass thru my modeled tunnel.  My thoughts stem from the requirement in building any habitat, either here on Earth or Mars, is that your materials have to be transported to your job site.  Here on Earth we have the luxury of heavy machinery.  On Mars, you're not going to have that luxury thus moving building materials is going to be manual labour which in turn means the size/weight will have to be limited.  Using BEAM like components is like using IKEA flat packs, some assembly required...  :D  Since a BEAM like component will fit thru the tunnel with a simple lift/pulley (or magnetic lift) system, you eliminate heavy equipment (like a crane, cargo doors, ramps).  With a small motorized dolly, building a habitat from small modules is more practical but time consuming.

Since your going to be on Mars for awhile, time to move and assemble a lot of small modules/components is not an issue... You'll have plenty of time.  This is why my model speculates that it (the service module/lander) will be a temporary habitat while on surface.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 04/13/2016 06:40 pm
The train idea is interesting, and you've obviously quite a attached to it. But I don't think the added complexity and compromises is worth it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 04/13/2016 08:37 pm
The train idea is interesting, and you've obviously quite a attached to it. But I don't think the added complexity and compromises is worth it.
Thank you for finding the "space train" idea interesting, but I'm not attached to it.  It's only choices which I made that, IMHO, is a possible and plausible MCT architecture.

Of course, I don't disagree that there is added complexity to my speculative design.  It's easy to fall into the trap of solving a problem for the sake of the model and not necessarily the requirements of the assumed mission (aka 100 people to Mars).

However, the underlying point of doing a speculative model is to test all the possibilities, assuming some set conditions.  It's the set conditions (which are speculative too but assumed to be correct) that pre-determine the model.  For example, what's needed for the ascent after BFR MECO?  How MCT will prep for trans-Mars injection?  The journey there and Mars EDL?  How surface ops/building a habitat occur?  Finally, how to ascend from Mars surface, do trans-Earth injection, and finally complete Earth EDL?

When asking these questions or pondering them in relation to the other speculative designs, I seem to come up short on the design being a plausible implementation.  My design and the choices are all founded on *existing* implementations that are modified/interpreted (aka speculated) by myself to answer the above questions.  Things being equal, you may find aspects of my design not plausible and that's feedback that I value.  It's the peer review of speculation.  ;D
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 04/13/2016 09:39 pm
If an inflatable unit can fit the tunnel, is the lander going to be high enough for it to turn 90 degrees after exiting the spacecraft to get out?  If some items can't make the 90 degree turn, they would have to be offloaded from the top via a crane.  Then weight and balance can become a problem.  Maybe if the fuel is placed higher, payload at the bottom, with people at the top, and they can come down the tunnel. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 04/14/2016 02:31 am
If an inflatable unit can fit the tunnel, is the lander going to be high enough for it to turn 90 degrees after exiting the spacecraft to get out?  If some items can't make the 90 degree turn, they would have to be offloaded from the top via a crane.  Then weight and balance can become a problem.  Maybe if the fuel is placed higher, payload at the bottom, with people at the top, and they can come down the tunnel.
Great insight!  I'm glad you mentioned it because I've already put some thought into the two necessary components to handle this.  The first component is the tunnel and the lift system which I believe can be made as a electromagnetic rails/lift system with a special platform.  This I already mentioned.  What I didn't mention is my design for the legs.  All the designs I've seen use the same style of SpaceX landing legs.  The reality is that they would have to be completely redesigned to work on Mars.  First they have to extend and then retract on demand.  Secondly, and more germane to your insight, the legs will have to auto-level lifting the weight of the lander (in Earth gravity).  Obviously, to aid in the unloading of items on Mars the legs would have the strength to jack up the ship and/or there is a height restriction on the cargo matched to the clearance the legs provide.  In either case the legs will require an interesting design due to these requirements.  My yet-to-be-modeled legs will be pure speculation but founded in the above realization.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 04/14/2016 07:32 am
I have a hard time envisioning a Mars base constructed with elements limited in size by having to pass through a tunnel such as the one in your plans.
If you look at the dimensions of BEAM, it's not small by any standard (once expanded) but small enough to pass thru my modeled tunnel.  My thoughts stem from the requirement in building any habitat, either here on Earth or Mars, is that your materials have to be transported to your job site.  Here on Earth we have the luxury of heavy machinery.  On Mars, you're not going to have that luxury thus moving building materials is going to be manual labour which in turn means the size/weight will have to be limited.  Using BEAM like components is like using IKEA flat packs, some assembly required...  :D  Since a BEAM like component will fit thru the tunnel with a simple lift/pulley (or magnetic lift) system, you eliminate heavy equipment (like a crane, cargo doors, ramps).  With a small motorized dolly, building a habitat from small modules is more practical but time consuming.

Since your going to be on Mars for awhile, time to move and assemble a lot of small modules/components is not an issue... You'll have plenty of time.  This is why my model speculates that it (the service module/lander) will be a temporary habitat while on surface.

Kaoru

While your right that standardized cargo modules that can be linked together to form habitats, your size is much too small.  The BEAM module is a mere 2.36 m in diameter and 1.7 tall when compressed for a volume of ~7.5 m^3.  ISS cargo has a fairly low average density so your looking at many dozens of such modules needing to be unloaded from each ship and then linked together.  As these modules are already too large to be moved by anything other then cranes their is every incentive to go bigger as the usefulness of the modules increases as well as the speed of unloading.

I favor a module size comparable to a TEU shipping container which is  6.1 m x 2.44 m x 2.59 m totaling 38.5 m^3 roughly 5 times larger then BEAM when compressed and about twice as large as BEAM when expanded.  If a module this size expanded with the same ratio as BEAM the resulting interior space would be 80 m^3 a very generous and spacious habitat indeed.

Containers this size will necessitate a side door and a cargo bay of around 500 m^3 in which containers can be stacked and secured by bolting them to structural hard-points as in modern containerized cargo on ships, planes, trains etc etc.  This is very similar to the Space Shuttle which had 300 m^3 internal cargo bay and similar hard-point mountings.  Cargo would be loaded/unloaded by a gantry crane in the roof of the cargo bay and extends out to clear the edge of the vehicle.  First a flat bed truck is unloaded, then modules are unloaded onto the truck which take them away.

Remember we need to think about the entire SYSTEM in MCT including logistics of ground transportation on Mars, we can't just dump stuff right at the landing site, we need the habitat a safe distance of a few miles away.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 04/14/2016 03:37 pm
I have a hard time envisioning a Mars base constructed with elements limited in size by having to pass through a tunnel such as the one in your plans.
If you look at the dimensions of BEAM, it's not small by any standard (once expanded) but small enough to pass thru my modeled tunnel.  My thoughts stem from the requirement in building any habitat, either here on Earth or Mars, is that your materials have to be transported to your job site.  Here on Earth we have the luxury of heavy machinery.  On Mars, you're not going to have that luxury thus moving building materials is going to be manual labour which in turn means the size/weight will have to be limited.  Using BEAM like components is like using IKEA flat packs, some assembly required...  :D  Since a BEAM like component will fit thru the tunnel with a simple lift/pulley (or magnetic lift) system, you eliminate heavy equipment (like a crane, cargo doors, ramps).  With a small motorized dolly, building a habitat from small modules is more practical but time consuming.

Since your going to be on Mars for awhile, time to move and assemble a lot of small modules/components is not an issue... You'll have plenty of time.  This is why my model speculates that it (the service module/lander) will be a temporary habitat while on surface.

Kaoru

While your right that standardized cargo modules that can be linked together to form habitats, your size is much too small.  The BEAM module is a mere 2.36 m in diameter and 1.7 tall when compressed for a volume of ~7.5 m^3.  ISS cargo has a fairly low average density so your looking at many dozens of such modules needing to be unloaded from each ship and then linked together.  As these modules are already too large to be moved by anything other then cranes their is every incentive to go bigger as the usefulness of the modules increases as well as the speed of unloading.

I favor a module size comparable to a TEU shipping container which is  6.1 m x 2.44 m x 2.59 m totaling 38.5 m^3 roughly 5 times larger then BEAM when compressed and about twice as large as BEAM when expanded.  If a module this size expanded with the same ratio as BEAM the resulting interior space would be 80 m^3 a very generous and spacious habitat indeed.

Containers this size will necessitate a side door and a cargo bay of around 500 m^3 in which containers can be stacked and secured by bolting them to structural hard-points as in modern containerized cargo on ships, planes, trains etc etc.  This is very similar to the Space Shuttle which had 300 m^3 internal cargo bay and similar hard-point mountings.  Cargo would be loaded/unloaded by a gantry crane in the roof of the cargo bay and extends out to clear the edge of the vehicle.  First a flat bed truck is unloaded, then modules are unloaded onto the truck which take them away.

Remember we need to think about the entire SYSTEM in MCT including logistics of ground transportation on Mars, we can't just dump stuff right at the landing site, we need the habitat a safe distance of a few miles away.
We have some evidence/conjecture for the notion that BFR is going to be 15m diameter.  MCT is going to require lots of space for vacuum bell nozzles to achieve high Isp with enough engines for redundancy, so it will probably be about the same 15m diameter.  A side-loading cargo dispenser at 15m overall diameter might have six <=5m diameter cargo pods arrayed along the outer edge, of indefinite length, around a central structural core + crane system.  We know that ISS modules have already been designed at 4.1 to 4.5m diameter for 10 to 20 tons of mass, and that MCT is targeting 100 tons 'useful cargo'  to the Martian surface.  This provides a cargo footprint that is usefully similar to the Shuttle's payloads.

Lower these standard cargo pods to the ground, and you can have vehicles drive out of their ends, just like a new automobile might drive out of an ISO container coming off the shipyard stacks in Baltimore.  ISO containers are built of the cheapest materials that will take the load of intermodal shipping, and weigh about 10% of their rated maximum load.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RanulfC on 04/14/2016 04:27 pm
Unless the Raptor engines consist of combustors around a plug-nozzle which doubles as a heat shield :)

Added: ROMBUS style lander for the win:
http://www.fantastic-plastic.com/IthacusSSTOCatalogPage.htm
http://www.pmview.com/spaceodysseytwo/spacelvs/sld008.htmhttp://www.spacefuture.com/archive/single_stage_to_orbit_vertical_takeoff_and_landing_concept_technology_challenges.shtml
http://www.spacefuture.com/archive/history_of_the_phoenix_vtol_ssto_and_recent_developments_in_single_stage_launch_systems.shtml

Randy
Note in Project Selene using ROMBUS the drop tanks were replaced by hab modules that were lowered onto wheels and driven into place for use. Just saying :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 04/14/2016 04:30 pm
While your right that standardized cargo modules that can be linked together to form habitats, your size is much too small.  The BEAM module is a mere 2.36 m in diameter and 1.7 tall when compressed for a volume of ~7.5 m^3.  ISS cargo has a fairly low average density so your looking at many dozens of such modules needing to be unloaded from each ship and then linked together.  As these modules are already too large to be moved by anything other then cranes their is every incentive to go bigger as the usefulness of the modules increases as well as the speed of unloading.

I favor a module size comparable to a TEU shipping container which is  6.1 m x 2.44 m x 2.59 m totaling 38.5 m^3 roughly 5 times larger then BEAM when compressed and about twice as large as BEAM when expanded.  If a module this size expanded with the same ratio as BEAM the resulting interior space would be 80 m^3 a very generous and spacious habitat indeed.

Containers this size will necessitate a side door and a cargo bay of around 500 m^3 in which containers can be stacked and secured by bolting them to structural hard-points as in modern containerized cargo on ships, planes, trains etc etc.  This is very similar to the Space Shuttle which had 300 m^3 internal cargo bay and similar hard-point mountings.  Cargo would be loaded/unloaded by a gantry crane in the roof of the cargo bay and extends out to clear the edge of the vehicle.  First a flat bed truck is unloaded, then modules are unloaded onto the truck which take them away.

Remember we need to think about the entire SYSTEM in MCT including logistics of ground transportation on Mars, we can't just dump stuff right at the landing site, we need the habitat a safe distance of a few miles away.
This is good feedback, though I don't believe my tunnel/small cargo pallets is too small.  I sized it to be practical for a spacecraft landing on Mars.  While the idea of "cargo containers" are practical here on Earth using airplanes, it's not even remotely practical for mass limited landing spacecraft on Mars.  First, such rigid containers represent a lot of dead weight.  Add to that the weight of the crane, cargo doors, and the mechanics to support all of that.  Of course, you still have the problem of transporting all the cargo to the base site.  Obviously, the base site will not be next to the MCT as it has to launch again and you would want to avoid hot exhaust and flying rocks/debris.

My solution is to have light weight cargo "bags" or no container at all but just a light weight platform (pallet) with straps/wrap.  The dimensions would be sized according to the allowances of the tunnel (which is 2.5 m in diameter; height is dependent on the height of the cargo deck).  To transport the pallets (bags), I take a page from Mammoset.  Mammoset uses small independent mobile carriers which link up, the result being able to lift and move the most massive things (aka buildings, etc.).  Shrink the concept down and you can have a cargo transporter that is completely flexible and carry tremendous weight while being small, light, and modular for many tasks.  The cargo transporter can deploy the same way as the cargo, thru the tunnel, then assemble as a bigger carrier or a number of smaller carriers.  The only trade off with this solution is time, it will take more time to unload and transport the small cargo pallets.  However, time is something that the colonists will have plenty of.

Thinking of the cargo carrier and BEAM, the two could be married to create a rover.  For example, the base module could consist of 4 movement modules (4 wheels each with 360 degree rotation) that hard link to an expandable module (like a small BEAM) and a service module (batteries/ECLSS).  It's easily transportable, light, and practicable.

Expanding the concept, a mobile robotic "construction" worker could be formed from the modules.  This "construction" robot would have a 3D printer and could "print" an exterior structure which then have an expandable interior (aka like a tent) to form the inside.  The materials used would be Mars regolith and some kind of binder; aka Mars cement.  None of these ideas require massive or heavy equipment.

In fact, I hail from northern Canada and have journeyed to the most in-hospitable of places, the artic.  I'm used to planning trips where life and death is actually dependent on well you plan.  I actually know how to build an igloo (because all Canadians live in igloos  ;D ) and actually you could do the same on Mars.  Igloos are extremely strong structures and they can be made simply if you have the knowledge.  I could build a Mars igloo by hand (wearing a -50 degree rated snowsuit is like wearing a space suit) as long as I could form a block/brick (in a specific shape dynamically; in the snow I use a machete to carve).  On Mars, building such an igloo (which is a dome) for a small 8 foot high is easy (again assuming specific shaped blocks).  A larger dome will take more time and a ladder.  My father has done an igloo that was about 10 ft high, 20 ft in diameter with only compacted snow (using a form), a machete, a ladder, and time.  It lasted several months until it had to be knocked down for safety reasons; warm weather.  He did it at the airport as a display for the World Cup Cross Country Skiing Races hosted in my hometown (Labrador).

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 04/14/2016 05:09 pm
Talking about cargo and how to unload it, you first has to get back to fundamentals.  Yes, the BFR will most likely be 15 m diameter.  However, BFS may not be 15 m diameter because of mass limitations.  A 15 m diameter upper stage/BFS is a lot of dry mass, which mean more engines and more fuel.  Of course, those engines will have to work in multiple modes, of which the nozzles and engine would have to change dramatically.  You can't get around this unless you have multiple engines for *each* mode.  This means more mass/dead weight for the other modes.  Abort engines would only be practical on Earth but not on Mars ascent (where would you abort too?).  My design speculates 4 Raptor vacuum engines with adaptable nozzle/exhaust deflector and a canting/gimbal mount in a protective nacelle.  There are no abort engines because it's not practical to have them.  It's easy to build the Raptors to be as robust as possible.  I calculate that the four engines, dry mass, propellants, and payload (as MCT goes; aka 48 person crew module, cargo module, or fuel only module which link up in orbit) which roughly is attainable by the 4 engines in all the modes.  Obviously, refueling in Earth orbit, Mars surface, and possible Mars orbit would be required.

Given this, every bit of mass has to be accounted for.  Large cargo carriers, cranes, etc. is just a Earth way of thinking.  On Mars with the gravity being .38 that of Earth, small cargo pallets weighing 150 kg on Earth could be lifted manually (57 kg) on Mars.  However, in space all the extra mass (ie. cargo carriers, cranes, doors, etc.) will require more energy in the engines (aka ISP) in order to get to Mars in a reasonable time, not to mention decelerate and land with only to launch into orbit again.  My speculation is small and light hence why I chose a 10 m diameter, 4 US Raptors, no aborts, and complicated nozzles/nacelles.

Kaoru   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 04/14/2016 05:56 pm
Yes, the BFR will most likely be 15 m diameter.  However, BFS may not be 15 m diameter because of mass limitations.  A 15 m diameter upper stage/BFS is a lot of dry mass, which mean more engines and more fuel.

Que? A shorter, wider stage is closer to a sphere, therefore more mass-efficient than a longer narrower stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 04/14/2016 06:58 pm
Yes, the BFR will most likely be 15 m diameter.  However, BFS may not be 15 m diameter because of mass limitations.  A 15 m diameter upper stage/BFS is a lot of dry mass, which mean more engines and more fuel.

Que? A shorter, wider stage is closer to a sphere, therefore more mass-efficient than a longer narrower stage.

A 15 m diameter stage could quite easily be longer as well.

When the MCT was first talked about by Elon, I thought that the most likely shape of its spaceship (now called the BFS) would be a bullet (fairing) shape of about 10 m diameter and 30 - 40 m tall. Now, I think it is likely to be bigger 13 - 15 m and 40 - 60 m tall.

To put a 15 m diameter 60 m tall stage into context, its cargo area would hold three fully expanded BA2100 or seven Falcon 9 first stages (may not quite fit lengthwise, but volume would fit). Elon has said that it will be big, and this is super big.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 04/15/2016 06:27 am

We have some evidence/conjecture for the notion that BFR is going to be 15m diameter.  MCT is going to require lots of space for vacuum bell nozzles to achieve high Isp with enough engines for redundancy, so it will probably be about the same 15m diameter.  A side-loading cargo dispenser at 15m overall diameter might have six <=5m diameter cargo pods arrayed along the outer edge, of indefinite length, around a central structural core + crane system.  We know that ISS modules have already been designed at 4.1 to 4.5m diameter for 10 to 20 tons of mass, and that MCT is targeting 100 tons 'useful cargo'  to the Martian surface.  This provides a cargo footprint that is usefully similar to the Shuttle's payloads.

Lower these standard cargo pods to the ground, and you can have vehicles drive out of their ends, just like a new automobile might drive out of an ISO container coming off the shipyard stacks in Baltimore.  ISO containers are built of the cheapest materials that will take the load of intermodal shipping, and weigh about 10% of their rated maximum load.

I don't like the arrangement your proposing, I see cargo containers in a horizontal orientation with overhead crane attaching to each end and lifting/lowering them without rotation as is done in modern container ships.  At a width of 2.4 m and with half a meter between we can lay 3 containers alongside each other creating a footprint 8.3 m by 6 m (the container length).  Stacked 3 high would give a height of 7.7 m and a total of 9 containers with a storage volume inside the containers of ~300 m^3.  This container block easily fits within the proposed vehicle diameter and should fit in a vehicle as narrow as 13 m in diameter.

I also think we will see an arrangement where cargo is low and close to the ground rather then high, possibly with engines flanking the cargo hold rather then directly under it so cargo can be practically in the belly of the vehicle and as close to the ground as possible, landing gear that can squat down could bring it to practically in contact with the ground.  Propellant would be above the cargo (aka nose) and/or in flanking locations in the cord shaped spaces that don't contribute to the usable cargo bay.

Entry to the cargo bay is a simple door on the side of the vehicle and a fold down ramp.  If desirable their can even be doors on opposite sides making the whole cargo bay a tunnel (like a C5 Galaxy which is coincidentally about the logistical scale were talking about).  This also allows the cargo bay to hold alternative cargo like large monolithic vehicles for exploration or mining as they can simply drive down the ramp.  From the perspective of the door containers are in profile and the crane system only needs to extend a short distance to clear the vehicle and lower a container to a waiting truck pulled up along side.  Unloading should take only a mater of hours allowing the vehicle to get turn around rapidly, remember time IS critical because of launch windows back to Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RanulfC on 04/15/2016 09:12 pm
Time to bring up the "Stanley Shuttle" concept again for reference, (posted here: http://forum.nasaspaceflight.com/index.php?topic=33224.msg1134071#msg1134071, presented by TaylorR137 and loved by all who see it, no really it's a requirement :) )

VTOL take-off/landing, cargo bay on the OTHER side, (no TPS penetration with a big door, thanks) propellant tanks around, and above cargo compartment with crew compartment near the nose. Side-entry increases surface area and works both on Mars and Earth. We need an update on it from TaylorR137 at some point :)

Randy
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 04/15/2016 11:10 pm
Yes that is certainly closer to what I'm envisioning, though it still has an engine directly under cargo configuration where I think that will not work due to the length of engine nozzles and the combustion chamber hardware, a rocket engine has a considerable 'root' which most folks fail to take into account when thinking about a vehicle.

I'm also doubtful of any kind of bridge/habitat being integrated into the vehicle like that of the Space Shuttle.  It's not necessary from a flight control perspective because their will not be a runway landing necessitating a forward view, Astronauts (actually computers watched by Astronauts) will control the vehicle fine from within a habitation module that is simply loaded into the cargo hold.  This will simply the vehicle by eliminating any cargo/passenger variations and simply the logistics of setting up a colony.  Travel to mars in a habitat in the cargo-hold, unload habitat onto surface, send empty ship back to Earth, rinse, repeat.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 04/16/2016 12:51 am
1/If MCT will have diameter 15m, then height will be under 35 meters. It will looks more like  lunar lander, from doimension point of view.
2/Maybe they will not have retractable legs, but fixed, because  diameter and to avoid point of failure, as part of the heat shield
3/MCT maybe will have skirt deployed after landing, to have sleeves free environment to work on maintenance of engines and expand living spaces.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: biosehnsucht on 04/17/2016 02:47 am
I started working on this almost 2 months ago, but then didn't touch it for over a month... have recently been inspired to mess about with it some more. Fair warning, I'm not as skilled as some here.. okay.. most. These are some very rough designs.

So I shall too throw my hat into the "Armchair MCT design" ring.

This is a 15m (except Raptor nacelle protrusion) bullet-shaped "capsule", almost 50m tall. 8 Raptors surround the capsule similar to an overgrown Crew Dragon. Due to the positioning of the engines relative to the tanks, some creative design may be required (perhaps shared turbopumps or simply remote turbopumps below the tanks, feeding "up" to the engines, to avoid having pumps that just feed turbopumps).

Tanks are sized with the assumption that we will get to orbit with enough fuel to land propulsively on Earth if necessary if we launched succesfully, but otherwise must be topped off with several fueling flights (basically similar design but no cargo / crew decks, just more tanks with fuel).

Solar panels and radiators will be extended from the side of it ... someplace. Probably between the Raptor nacelles someplace. This is one of those details I'm not worrying about, along with specifics of life support systems etc. There's plenty of unused volume around the fuel tanks and other than an airlock the service deck is "empty" (since I haven't defined any space usage for specific ECCLS systems or such, just assume they'll fit in there).

No attempt at dedicated launch abort is made or assumed. I make the assumption that the BFR will be so highly sensored that nothing should go wrong (if it does, no launch), and should anything go terribly wrong anyways, the MCT will either abort to launch site or suborbital somewhere using the Raptor engines, or just an unusually low orbit (where it could be refuelled or deorbited on it's fuel reserves depending on how much fuel remains). Either crew are onboarded via another craft (perhaps shrunk MCT variant with actual (Super?)SuperDraco LES and no cargo or crew/etc decks, just seating for launch), via many Crew Dragons, or simply we assume LOC won't happen or be so rare that anyone flying on it is willing to take the risk.

A central tunnel runs from the Service Deck to the Flight Deck. It does not connect directly to either the Bulk Cargo or Upper Airlock areas. Automated hatches slide horizontally into the tunnel to seal it in case of emergency between decks. The tunnel is accessed at each deck it services by an opening in the side, there is not any additional hatch in the side of the tunnel. The tunnel runs through the middle of the LOX/CH4 tanks. Power, life support, etc run along the inside of the tunnel wall.

For surface operation, a winch system combined with a platform that runs along the tunnel handrails creates an effective elevator (the winch can be used separately as well). Same type (and interchangeable) winch is available from the Service Deck airlock to the Bulk Cargo area as well as to the outside (same winch, mounted to a gantry).

Bulk cargo section has a door which operates like a giant inside out passenger van door, or a really big version of some of the doors on the ISS. It pulls in and then slides around the interior to get out of the way. When closed, any positive pressure inside vs the exterior will help keep it sealed closed. Bulk cargo section has a gantry crane which can extend outside the craft to place containers on the ground, which can then be moved by a container moving device (sort of like the wheeled devices PODS uses to deliver a container to your house). Cargo can either be intermodal-like (though probably more mass-efficient construction etc) or simply have a frame around or on it that the crane and container mover can use as if it were an intermodal container. Cargo may also not need crane at all, in which case it can be in whatever form is best packed for transport to Mars.

With the exception of the service and cargo decks, all decks are 2.5m high (which is for maximizing personal space in the cabins, ~3.5m2 x 2.5m of space should be fairly roomy as space travel goes). Service deck is 3m and bulk cargo is 5.4m. Upper airlock area is not exactly defined, other than that it should be around 2m at least (for entry into the airlock) - much of the apparently empty space up there will be taken up with various infrastructure and such.

The common decks are used for exercise, eating, and socializing, etc. The service deck contains an airlock that can either open to the exterior (and use a gantry crane or ladder/stairs to access on surface) or into the bulk cargo area (same gantry crane can allow surface access, or a ladder/stairs). The airlock in the nose is intended normally only for space use, but if necessary a tripod or similar structure can be erected above it with winch attached if there is an issue with the service deck airlock.

For the crew / passenger decks, partitions (both regular walls and door sections) are attached using L-track (like that used in aircraft or the ISS for attaching things) to make individual cabins. L-track is in both the "floor" and "ceiling", spaced radially every 15 degrees from the center tunnel to the exterior wall. L-track is also positioned along the two inner circles depicted (they are 1.5m apart, making for a 1.5m wide hallway).

Cabins along the outer wall can be only 15 degrees wide and fit a bed, whereas cabins along the inner wall will need 45 degrees (see mct_crewdeck.png blue shaded areas, the rectangle is a bed)

Some elements not depicted such as toilets / washrooms will be permanently installed at various locations, but generally the crew decks are re-configurable as needed. For couples or families, multiple adjacent sections can be made into a single large cabin but simply removing some partitions.

Not depicted is the BFR itself, but just imagine a great big giant 15m stick with a ton of Raptors under it, etc. Also not depicted are almost any details, I'm sure you noticed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sanman on 04/18/2016 05:15 am
It may not be part of the existing design plan, but why couldn't MCT have some temporarily expandable section, a la Bigelow, which could be temporarily expanded during transit to Mars in order to provide necessary interior space during the months-long journey, and which could then be un-expanded or jettisoned before Mars arrival?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: GabrielP on 04/18/2016 05:54 am
It may not be part of the existing design plan, but why couldn't MCT have some temporarily expandable section, a la Bigelow, which could be temporarily expanded during transit to Mars in order to provide necessary interior space during the months-long journey, and which could then be un-expanded or jettisoned before Mars arrival?

Another alternative to using that would be to just launch it separately and have MCT dock with it in LEO before heading out.
Would it then be possible to just leave it in orbit around Mars then pick it up again on the way back? (fully reusable and all that...)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sanman on 04/18/2016 07:33 am
It may not be part of the existing design plan, but why couldn't MCT have some temporarily expandable section, a la Bigelow, which could be temporarily expanded during transit to Mars in order to provide necessary interior space during the months-long journey, and which could then be un-expanded or jettisoned before Mars arrival?

Another alternative to using that would be to just launch it separately and have MCT dock with it in LEO before heading out.
Would it then be possible to just leave it in orbit around Mars then pick it up again on the way back? (fully reusable and all that...)

Wouldn't that then alter the flight-trajectory away from the Mars-Direct approach favored by Musk, and also add risk to the mission?

Maybe if the walls of the mid-section could swing outward like Elon's gull-wing doors, then some expandable hab could mushroom outwards.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: QuantumG on 04/18/2016 07:35 am
Mars-Direct? What's Mars Direct about MCT?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sanman on 04/18/2016 09:48 am
I thought MCT is supposed to fly to Mars directly, with no stops in between (like what Zubrin originally suggested)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 04/18/2016 12:40 pm
I thought MCT is supposed to fly to Mars directly, with no stops in between (like what Zubrin originally suggested)

No-one really knows (publically) what Musk has in mind.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 04/18/2016 01:25 pm
I thought MCT is supposed to fly to Mars directly, with no stops in between (like what Zubrin originally suggested)
It will probably get refueled in Earth orbit, unlike MD. Otherwise you either have a vehicle that is "mass-starved" for its intended purpose or a launcher that is impractically huge for ground handling.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 04/18/2016 03:26 pm
The Moon MethaLOX ISRU thread got me thinking about the MCT as passenger service vehicle from Earth to Moon surface. For a short trip < 1week the volume needed per passenger is lot less than the volume per passenger needed for a Mars trip. If The MCT is designed for a crew volume area of 2000-3000 m^3 to support the transport of 100 passengers to Mars how many person could be sent on a short trip to just the Moon?

My estimate was numbers of passengers as low as 250 and as high as 750.

2000m^3/8m^3(per person) = 250
3000m^3/4m^3(per person) = 750
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 04/18/2016 04:24 pm
The Moon MethaLOX ISRU thread got me thinking about the MCT as passenger service vehicle from Earth to Moon surface. For a short trip < 1week the volume needed per passenger is lot less than the volume per passenger needed for a Mars trip. If The MCT is designed for a crew volume area of 2000-3000 m^3 to support the transport of 100 passengers to Mars how many person could be sent on a short trip to just the Moon?

My estimate was numbers of passengers as low as 250 and as high as 750.

2000m^3/8m^3(per person) = 250
3000m^3/4m^3(per person) = 750

What would they do? Would all of them be trained as astronauts? If they are tourists, you may have problems with them wandering off. OTOH, I could see a tourism vendor using the first several flights to carry expandable modules for a hotel, along with extra cargo, setting up a base, then offering vacation travel to the Heavenly Honeymoon Hotel.

I would surely go and take my wife if we could afford it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RanulfC on 04/19/2016 07:26 pm
Impaler:
The shown engines are based on engines capable of being used on Mars or Earth as needed, somewhat on the described Raptors, something of the Merlin, with a little SSME thrown in so they are probably representative :)

While it shows a "cockpit/flight deck" area it's probably more of an observation area and/or 'cap' point for the ladder from the crew area to the cargo deck. The illustrator was going for a "Shuttle" look to indicate that it would be a reusable space vehicle after all so from that point-of-view it makes sense even if it's not actually the control area of the vehicle :)

The "crew-in-hab-in-cargo-bay" concept is nice but I'm of the mind that the basic MCT design will be based on the BFS which in and of itself will be more than just a cargo hold and propellant tankage. So it would stand to reason the basic BFS design would be capable of more than just hauling cargo.

Randy
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 04/20/2016 06:34 am
BFS?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RotoSequence on 04/20/2016 11:13 am
BFS?

Big Freakin' Spaceship
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 04/20/2016 01:59 pm
BFS?

Big Freakin' Spaceship

That's not exactly how Musk worded it in GQ ;)

http://www.gq.com/story/elon-musk-mars-spacex-tesla-interview
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 04/20/2016 06:42 pm
BFS?

MCT = BFR + BFS.

People previously assumed just the Mars stage was the "MCT", but apparently Musk uses that name for the whole system. IMO, it's less confusing for everyone to adopt Musk's nomenclature, since he's not likely to adopt ours; unfortunately most posters persist in using "MCT" for just the BFS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RanulfC on 04/20/2016 08:41 pm
"Best Friend Spaceship?" No, I suspect down that path we'd end up somewhere dark and dangerous... Spaceship Friendship is Magic and all that... :::Shudder::: ;)

Randy
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 04/21/2016 12:28 am
It may not be part of the existing design plan, but why couldn't MCT have some temporarily expandable section, a la Bigelow, which could be temporarily expanded during transit to Mars in order to provide necessary interior space during the months-long journey, and which could then be un-expanded or jettisoned before Mars arrival?
Because 1) un-expanding is problematic. Needs to be carefully refolded. 2) jettisoning it makes it expensive.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 04/21/2016 01:17 am
BFS?

MCT = BFR + BFS.

People previously assumed just the Mars stage was the "MCT", but apparently Musk uses that name for the whole system. IMO, it's less confusing for everyone to adopt Musk's nomenclature, since he's not likely to adopt ours; unfortunately most posters persist in using "MCT" for just the BFS.

I remember back a year or so ago when people argued that Elon's MCT nomenclature implied a single monolithic vehicle which was clearly absurd.  Unfortunately most speculation today is hardly much improved with a compulsive desire to make simplistic and monstrously large 'direct' approaches.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 04/21/2016 02:14 am
BFS?

MCT = BFR + BFS.

People previously assumed just the Mars stage was the "MCT", but apparently Musk uses that name for the whole system. IMO, it's less confusing for everyone to adopt Musk's nomenclature, since he's not likely to adopt ours; unfortunately most posters persist in using "MCT" for just the BFS.

I remember back a year or so ago when people argued that Elon's MCT nomenclature implied a single monolithic vehicle which was clearly absurd.  Unfortunately most speculation today is hardly much improved with a compulsive desire to make simplistic and monstrously large 'direct' approaches.
They still do, you know? They think the development will cost less because it is only one vehicle design.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 04/21/2016 08:22 am
And yet Musk himself has said that the concept is a bit off the wall (cannot remember exact phrase). Just building a big rocket is not 'off the wall'.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 04/21/2016 05:38 pm
Landing the same spacecraft on Mars that was launched from Earth and returning it to Earth or LEO would be "off the wall".  Even with LEO refueling before Mars transit.
I think there will be additional "enhancements" in the plan.
Elon says 2025, but in Elon time that means mid 2030s, even his 2:1 schedule slip would be fantastic.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sanman on 04/21/2016 10:38 pm
Landing the same spacecraft on Mars that was launched from Earth and returning it to Earth or LEO would be "off the wall".  Even with LEO refueling before Mars transit.
I think there will be additional "enhancements" in the plan.
Elon says 2025, but in Elon time that means mid 2030s, even his 2:1 schedule slip would be fantastic.

Meh, a guy like him won't be satisfied with waiting until the 2030s - and SpaceX will be continually ramping its talent and expertise over the next 10 years - so how will SpaceX maintain the buzz if they don't keep making steady progress toward Mars? MCT and Mars colonization are the brass ring or the carrot that Musk keeps holding out in front of everyone, so he can't afford to lose cred on that.

In the meantime, I'd like to ask if MCT would make use of Propellant Densification, or would that be too difficult to manage for methalox, given that it also has to be refueled and launched from the Mars environment?
Would it be possible to do Propellant Densification just for the Earth-Mars leg, and go with regular undensified propellant for the return journey from Mars to Earth? (Then later on, as Mars-side infrastructure builds up, you could upgrade to Propellant Densification for Mars liftoff as well.)




Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 04/21/2016 10:57 pm
I like the MCT with the 8 engines around.  I still think that sending 10-20 people with cargo would be the norm for several years in order to build the colony.  Lots of equipment, habitats, greenhouse units, roving vehicles, earth moving vehicles, and lots of solar panels to power everything, etc, to unload.  I also think they will not send 100 people and 100 tons of cargo to Mars on one spacecraft, but far more cargo than people initially.  Like Musk said, 10 cargo flights for every 100 people.  So, why not put 10 people on each cargo flight?  Then some type of LES capsule could be at the top, and if something happened on the way, only 10 people would be in danger instead of 100. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 04/22/2016 02:07 am
BFS?

MCT = BFR + BFS.

People previously assumed just the Mars stage was the "MCT", but apparently Musk uses that name for the whole system. IMO, it's less confusing for everyone to adopt Musk's nomenclature, since he's not likely to adopt ours; unfortunately most posters persist in using "MCT" for just the BFS.

I remember back a year or so ago when people argued that Elon's MCT nomenclature implied a single monolithic vehicle which was clearly absurd.  Unfortunately most speculation today is hardly much improved with a compulsive desire to make simplistic and monstrously large 'direct' approaches.
They still do, you know? They think the development will cost less because it is only one vehicle design.
It probably would. If you're going to do refueling, and you're going to be doing ISRU, and you're going to be building a high-performance TSTO fully reusable HLV, then you basically can skip much the rest. No need for a Battlestar Galactica style architecture with 10 different elements to satisfy the 10 different NASA centers, incorporating everyone's pet technology, etc.

Refueling makes it possible to reuse the same hardware for multiple purposes without ballooning the costs. Several years ago, I realized (with another member... mmeijeri?) that a reusable 5km/s lander/ascender (I think we picked a lander with balloon tanks to improve mass fraction) can do a whole bunch of mission tasks and simplify the overall architecture dramatically, including serving as its own upper stage, etc. Something like this is the logical conclusion of refueling and reuse.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 04/22/2016 03:44 am
RB:  You completely inverted the meaning of 'Battlestar Galactica'.  That was Zubrin's pejorative term for a single huge vehicle that carries all propellant from Earth which was the NASA plan in the 90 day report.

Zubrin's argument was two fold, use insitu propellant on mars to reduce outbound propellant needs (which we all agree Musk is doing) AND using a number of smaller modular elements that serve specific roles and provide redundancy.  The Battlestart Galactica term was specifically about not making a single all inclusive budget busting vehicle designed to perform multiple tasks.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 04/22/2016 04:22 am
Another thing that virtually no one here talks about is MARS ORBITAL RENDEZVOUS.

If the BFS can be refueled in LEO then it can likewise be refueled in LMO if propellant can be brought their.

This would break the DeltaV budget for Earth return into two legs, assent to LMO and then TEI resulting in a vastly smaller vehicle AND a faster Earth return then would be possible with a single direct launch of even a huge vehicle.

To make the vehicle capably of departing for Mars it must start at EML-1 fully fueled which again will allow for a faster transit then a large vehicle starting in LEO.

To get the propellants to LMO and the vehicle to EML-1 you use the same solution a SEP tug, fist it moves the BFS to EML-1, picks up and drops off fuel between LEO and EML-1, then makes a fuel run all the way out to mars to rendezvous with the BFS a second time and finally returns to Earth to repeat the cycle.

The BFS would only need around 4-5 km/s DeltaV capability in this scenario which makes it hugely smaller and simpler, to launch to LEO the BFR is a 2 stage rocket like F-9 but with reusable 2nd stage which can carry payloads other then the BFS on top.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 04/22/2016 12:58 pm
The Battlestar Galactica thing made me think and put some numbers, just plug data in the rocket equation to see what happens. I'm assuming the 'land the whole thing' architecture because, in order to transport a lot of cargo and people to Mars, you need a big and heavy lander anyway, so it does make sense to use the same ship to make the interplanetary part as well. I'm also assuming a pure chemical rocket propulsion system, although G Shotwell mentioned other possibilities being studied.

As a reference I used Saturn V (I'm taking Apollo XVII numbers), obviously the only comparable succesfull system so far, yes the Nova designs where more like it, but they remained paper rockets, no ppt in those happy days.

Plugging the Saturn IC data in the rocket equation shows that deltaV was just over 3.3 Km/s, it also staged at a pretty low altitude (good for the RTLS thing). Let's assume that the MCT booster does likewise, that leaves about 7 Km/s deltaV to the second stage (aka BFS) which is ok if you plan to refuel and do a TMI burn.

As per word of Musk, the ship will be capable of putting 100 t of useful mass on Mars, so let's make it another 100 t for structure (engines, TPS, legs, you name it). So that leaves a 200 t dry mass vehicle, capable of 7 km/s deltaV, with engines giving a Isp of 380 s you need a whopping 1150 t of propellant and a total BFS mass at lift off of about 1350 t. This also pushes the BFR mass to 3200 t, more than a Saturn V GLOW.

Indeed, it's not a small ship, so the term Battlestar does apply here.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 04/22/2016 02:05 pm
Another thing that virtually no one here talks about is MARS ORBITAL RENDEZVOUS.

If the BFS can be refueled in LEO then it can likewise be refueled in LMO if propellant can be brought their.

This would break the DeltaV budget for Earth return into two legs, assent to LMO and then TEI resulting in a vastly smaller vehicle AND a faster Earth return then would be possible with a single direct launch of even a huge vehicle.

To make the vehicle capably of departing for Mars it must start at EML-1 fully fueled which again will allow for a faster transit then a large vehicle starting in LEO.

To get the propellants to LMO and the vehicle to EML-1 you use the same solution a SEP tug, fist it moves the BFS to EML-1, picks up and drops off fuel between LEO and EML-1, then makes a fuel run all the way out to mars to rendezvous with the BFS a second time and finally returns to Earth to repeat the cycle.

The BFS would only need around 4-5 km/s DeltaV capability in this scenario which makes it hugely smaller and simpler, to launch to LEO the BFR is a 2 stage rocket like F-9 but with reusable 2nd stage which can carry payloads other then the BFS on top.

Questions arise...
How long does the SEP tug take to bring the BFS and/or the propellant to EML-1 and return to LEO? 
How many SEP trips to EML-1 per single BFS launch to Mars and return?
How efficient are SEP solar panels after numerous long trips thru the Van Allen belts? 
How many BFTanker flights to re-fuel the SEP tug itself for its various transits to support one Mars round trip mission?  Including bringing up the BFS propellant that the SEP carries all the way to Mars orbit.
Besides the added expense, resources and complexity of developing the SEP tug.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 04/22/2016 02:18 pm
Another thing that virtually no one here talks about is MARS ORBITAL RENDEZVOUS.

If the BFS can be refueled in LEO then it can likewise be refueled in LMO if propellant can be brought their.

This would break the DeltaV budget for Earth return into two legs, assent to LMO and then TEI resulting in a vastly smaller vehicle AND a faster Earth return then would be possible with a single direct launch of even a huge vehicle.

To make the vehicle capably of departing for Mars it must start at EML-1 fully fueled which again will allow for a faster transit then a large vehicle starting in LEO.

To get the propellants to LMO and the vehicle to EML-1 you use the same solution a SEP tug, fist it moves the BFS to EML-1, picks up and drops off fuel between LEO and EML-1, then makes a fuel run all the way out to mars to rendezvous with the BFS a second time and finally returns to Earth to repeat the cycle.

The BFS would only need around 4-5 km/s DeltaV capability in this scenario which makes it hugely smaller and simpler, to launch to LEO the BFR is a 2 stage rocket like F-9 but with reusable 2nd stage which can carry payloads other then the BFS on top.
Orbital rendezvous and refueling does make things more mass efficient, but I think ferrying fuel from earth may not be the right approach. Instead consider a tanker variant of the BFS which is sent to Mars and uses local ISRU to loft fuel to LMO for refueling the returning BFS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 04/22/2016 02:39 pm
Another thing that virtually no one here talks about is MARS ORBITAL RENDEZVOUS.

If the BFS can be refueled in LEO then it can likewise be refueled in LMO if propellant can be brought their.

This would break the DeltaV budget for Earth return into two legs, assent to LMO and then TEI resulting in a vastly smaller vehicle AND a faster Earth return then would be possible with a single direct launch of even a huge vehicle.

To make the vehicle capably of departing for Mars it must start at EML-1 fully fueled which again will allow for a faster transit then a large vehicle starting in LEO.

To get the propellants to LMO and the vehicle to EML-1 you use the same solution a SEP tug, fist it moves the BFS to EML-1, picks up and drops off fuel between LEO and EML-1, then makes a fuel run all the way out to mars to rendezvous with the BFS a second time and finally returns to Earth to repeat the cycle.

The BFS would only need around 4-5 km/s DeltaV capability in this scenario which makes it hugely smaller and simpler, to launch to LEO the BFR is a 2 stage rocket like F-9 but with reusable 2nd stage which can carry payloads other then the BFS on top.
Orbital rendezvous and refueling does make things more mass efficient, but I think ferrying fuel from earth may not be the right approach. Instead consider a tanker variant of the BFS which is sent to Mars and uses local ISRU to loft fuel to LMO for refueling the returning BFS.

Is LMO refueling likely to be necessary? Musk has stated that the Mars return payload will be on the order of 25t. Staging velocity to LEO and LEO to TMI with 100t are both considerable more constraining than Mars surface direct return of 25t. Any ship that can sent 100t through TMI (about 3.6 kms dV) or from BFR staging to LEO (at least 4.5 kms dV) will be able to easily send 25t from Mars surface to TEI (about 5.3 kms dV but 1/4 the payload).

The most constraining leg seems to be getting from BFR staging velocity to LEO with 100t of payload.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 04/22/2016 03:30 pm
The Battlestar Galactica thing made me think and put some numbers, just plug data in the rocket equation to see what happens. I'm assuming the 'land the whole thing' architecture because, in order to transport a lot of cargo and people to Mars, you need a big and heavy lander anyway, so it does make sense to use the same ship to make the interplanetary part as well. I'm also assuming a pure chemical rocket propulsion system, although G Shotwell mentioned other possibilities being studied.

As a reference I used Saturn V (I'm taking Apollo XVII numbers), obviously the only comparable succesfull system so far, yes the Nova designs where more like it, but they remained paper rockets, no ppt in those happy days.

Plugging the Saturn IC data in the rocket equation shows that deltaV was just over 3.3 Km/s, it also staged at a pretty low altitude (good for the RTLS thing). Let's assume that the MCT booster does likewise, that leaves about 7 Km/s deltaV to the second stage (aka BFS) which is ok if you plan to refuel and do a TMI burn.

As per word of Musk, the ship will be capable of putting 100 t of useful mass on Mars, so let's make it another 100 t for structure (engines, TPS, legs, you name it). So that leaves a 200 t dry mass vehicle, capable of 7 km/s deltaV, with engines giving a Isp of 380 s you need a whopping 1150 t of propellant and a total BFS mass at lift off of about 1350 t. This also pushes the BFR mass to 3200 t, more than a Saturn V GLOW.

Indeed, it's not a small ship, so the term Battlestar does apply here.

SpaceX pushes mass fractions to the limit so a 100t empty mass is probably conservative, but lets go with that. However, Saturn V was a 3 stage to orbit system, so the comparisons to a TSTO aren't really accurate.

BFR will likely have mass fractions much closer to Falcon 9 than Saturn V, but with a better ISP than either. Falcon 9 stages at around 2.2 to 2.5 kms, and the upper stage adds about 5.3 kms to get it to LEO. With Raptor's higher ISP, it only takes about 625t of prop to get a 200t ship+payload into LEO.

If they can stage at 3.5 kms (with enough prop in the BFR to boostback to reentry at a survivable Mach 6 or 2 kms), then the upper stage/ship only has to add about 4.5 kms to LEO, which happens to be about the same performance it needs to sent 100t through TMI and do a 1 kms (ish) EDL burn at Mars. That only takes about 500t of prop.

The other question is how they will want to size the Raptor. At the currently stated 2300kN a single Raptor would be rather underpowered for throwing 100t into LEO, although probably not worse than the Centaur US. A single 2300 kN engine would be ideal for TMI and Mars return though, and dragging extra engines to Mars and back isn't ideal.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 04/22/2016 04:36 pm

The other question is how they will want to size the Raptor. At the currently stated 2300kN a single Raptor would be rather underpowered for throwing 100t into LEO, although probably not worse than the Centaur US. A single 2300 kN engine would be ideal for TMI and Mars return though, and dragging extra engines to Mars and back isn't ideal.

You're going to need multiple engines to propulsively land BFS back at KSC, Brownsville or wherever, which is absolutely critical for the economics of the architecture. I'm assuming extendable/discardable nozzle extensions on the BFS raptor, which may be a distinctive variant from the initial upper stage raptor vac.

Besides, if I was the commander of a 100 individual interplanetary spaceship, I'd either want engines with a ludicrous reliability or a few with a wide gimbal so I have engine out redundancy. Nobody wants to be marooned.

They are going to be carting a few unnecessary engines with them, I bet the most edible of my cowskin hats on it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 04/22/2016 06:05 pm

The other question is how they will want to size the Raptor. At the currently stated 2300kN a single Raptor would be rather underpowered for throwing 100t into LEO, although probably not worse than the Centaur US. A single 2300 kN engine would be ideal for TMI and Mars return though, and dragging extra engines to Mars and back isn't ideal.

You're going to need multiple engines to propulsively land BFS back at KSC, Brownsville or wherever, which is absolutely critical for the economics of the architecture. I'm assuming extendable/discardable nozzle extensions on the BFS raptor, which may be a distinctive variant from the initial upper stage raptor vac.

Besides, if I was the commander of a 100 individual interplanetary spaceship, I'd either want engines with a ludicrous reliability or a few with a wide gimbal so I have engine out redundancy. Nobody wants to be marooned.

They are going to be carting a few unnecessary engines with them, I bet the most edible of my cowskin hats on it.

A single 2300 kN SL Raptor would be about as much overkill for a ~120t BFS as a single Merlin is for an empty Falcon S1, so I don't know that you need multiple engines to land. BFS will likely do a fully aerobraking reentry with minimal reentry burning, so the 3-engine Falcon burns don't have a BFS parallel. If you want to land 100t of payload on Earth, you might need more Raptors, but I can't imagine a non-abort scenario where that's likely. And I don't see Raptors as feasible launch abort propulsion, so any LAS will need SuperDracos or similar.

Redundancy is a good point, but would have to be optimized against available abort modes and payload reduction. If there's always a viable abort and the engines are highly reliable it might make sense to axe the dead weight. Or they might reoptimize to 150 kN at SL and always use 2 Raptors thrusting through the BFS COM.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 04/22/2016 07:39 pm
Another thing that virtually no one here talks about is MARS ORBITAL RENDEZVOUS.

If the BFS can be refueled in LEO then it can likewise be refueled in LMO if propellant can be brought their.

This would break the DeltaV budget for Earth return into two legs, assent to LMO and then TEI resulting in a vastly smaller vehicle AND a faster Earth return then would be possible with a single direct launch of even a huge vehicle.

To make the vehicle capably of departing for Mars it must start at EML-1 fully fueled which again will allow for a faster transit then a large vehicle starting in LEO.

To get the propellants to LMO and the vehicle to EML-1 you use the same solution a SEP tug, fist it moves the BFS to EML-1, picks up and drops off fuel between LEO and EML-1, then makes a fuel run all the way out to mars to rendezvous with the BFS a second time and finally returns to Earth to repeat the cycle.

The BFS would only need around 4-5 km/s DeltaV capability in this scenario which makes it hugely smaller and simpler, to launch to LEO the BFR is a 2 stage rocket like F-9 but with reusable 2nd stage which can carry payloads other then the BFS on top.

Questions arise...
How long does the SEP tug take to bring the BFS and/or the propellant to EML-1 and return to LEO? 
How many SEP trips to EML-1 per single BFS launch to Mars and return?
How efficient are SEP solar panels after numerous long trips thru the Van Allen belts? 
How many BFTanker flights to re-fuel the SEP tug itself for its various transits to support one Mars round trip mission?  Including bringing up the BFS propellant that the SEP carries all the way to Mars orbit.
Besides the added expense, resources and complexity of developing the SEP tug.

For fast transits you want to go nuclear. See for example the DRM 5 Addendum 2. In fact I don't think one synod return is possible without EP or refueling in LMO, because the delta-v is SSTO-level or higher. From both options, EP or LMO refueling, I would pick EP because it also saves you a ton of mass in LEO and it doesn't require a huge launch infrastructure on Mars. Note that you would not refuel the BFS in LMO, the EP would bring it back. In fact all in-space propulsion would be done with EP, however the BFS would do aerocapture at Mars.

If SpaceX plans to use a reactor on Mars they could use it for NEP too, if it has sufficiently low mass.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 04/22/2016 08:48 pm
SpaceX pushes mass fractions to the limit so a 100t empty mass is probably conservative, but lets go with that. However, Saturn V was a 3 stage to orbit system, so the comparisons to a TSTO aren't really accurate.
Well, actually I thought 100t estimate to be optimistic!
I was using the Saturn thing just to make sure the numbers did make sense. Agreed, they'll be different, but actually, the SIC did stage very low, not too different from Falcon 9 on that, and this also makes RTLS easier (for a barge landing they'd need a Nimitz class barge!) which was the point really.

Quote
BFR will likely have mass fractions much closer to Falcon 9 than Saturn V, but with a better ISP than either. Falcon 9 stages at around 2.2 to 2.5 kms, and the upper stage adds about 5.3 kms to get it to LEO. With Raptor's higher ISP, it only takes about 625t of prop to get a 200t ship+payload into LEO.

If they can stage at 3.5 kms (with enough prop in the BFR to boostback to reentry at a survivable Mach 6 or 2 kms), then the upper stage/ship only has to add about 4.5 kms to LEO, which happens to be about the same performance it needs to sent 100t through TMI and do a 1 kms (ish) EDL burn at Mars. That only takes about 500t of prop.

The other question is how they will want to size the Raptor. At the currently stated 2300kN a single Raptor would be rather underpowered for throwing 100t into LEO, although probably not worse than the Centaur US. A single 2300 kN engine would be ideal for TMI and Mars return though, and dragging extra engines to Mars and back isn't ideal.

Aren't you cutting deltaV too low for comfort? I'd actually estimated a total > 9km/s just to be safe. That makes the second stage almost 7 km/s with a huge but manageable BFR, over 200t empty mass. With that you're ok with a single Raptor (2300 kN) for landing, maybe three for RTLS (again not too different from Falcon 9).

You can get to Mars from LEO with less than 4.5 km/s, but there are not many options (I've checked NASA's Trajectory Browser) and it puts a very narrow constraint. With the extra deltaV you get better margins for braking and EDL too.

Besides, if I was the commander of a 100 individual interplanetary spaceship, I'd either want engines with a ludicrous reliability or a few with a wide gimbal so I have engine out redundancy. Nobody wants to be marooned.

They are going to be carting a few unnecessary engines with them, I bet the most edible of my cowskin hats on it.
Mostly agree with that, better safe than sorry. But being Raptors an overkill, I also wonder if they will use Raptors for landing, either on Mars and on Earth. Probably smaller and lightweight pressure fed engines for landing might work too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 04/23/2016 12:00 am
More than 9 kms total dV is needed for orbit, but that includes drag and gravity losses largely borne by the first stage before staging. Falcon 9 stages at about 2.5 kms horizontal velocity, but expends well over 4 kms total dV to get there... So the 2nd stage only needs to add about 5.3 kms to orbit.

All Mars injections for the next 4 synods can be done with 3.5 to 4 kms of dV from 200 km LEO:
http://trajbrowser.arc.nasa.gov/traj_browser.php?
NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&
chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list
=Mars&mission_class=oneway&mission_type
=rendezvous&LD1=2015&LD2=2025&maxDT=1&DTunit=yrs&maxDV=6.0&min
=DV&wdw_width=365&submit=Search#a_load_results

100t might be optimistic. To baseline, the Falcon S2 is 8t with a fairing and can deliver at least 17t to LEO (possibly much more depending on staging velocity). Terminal landing fuel and legs add about 10% each to the F9 S1, which would bring the S2 to 9.6t. Estimates of heatshield mass vary, but typically range from 1 to 4t, or 10.6 to 13.6 total dry mass. Assuming the pressure vessel, life support, and consumables count as payload, the empty stage could carry roughly its dry mass in payload, or a 100t stage for a 100t payload.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 04/23/2016 04:56 am
Another thing that virtually no one here talks about is MARS ORBITAL RENDEZVOUS.

If the BFS can be refueled in LEO then it can likewise be refueled in LMO if propellant can be brought their.

This would break the DeltaV budget for Earth return into two legs, assent to LMO and then TEI resulting in a vastly smaller vehicle AND a faster Earth return then would be possible with a single direct launch of even a huge vehicle.

To make the vehicle capably of departing for Mars it must start at EML-1 fully fueled which again will allow for a faster transit then a large vehicle starting in LEO.

To get the propellants to LMO and the vehicle to EML-1 you use the same solution a SEP tug, fist it moves the BFS to EML-1, picks up and drops off fuel between LEO and EML-1, then makes a fuel run all the way out to mars to rendezvous with the BFS a second time and finally returns to Earth to repeat the cycle.

The BFS would only need around 4-5 km/s DeltaV capability in this scenario which makes it hugely smaller and simpler, to launch to LEO the BFR is a 2 stage rocket like F-9 but with reusable 2nd stage which can carry payloads other then the BFS on top.

Questions arise...
How long does the SEP tug take to bring the BFS and/or the propellant to EML-1 and return to LEO? 
How many SEP trips to EML-1 per single BFS launch to Mars and return?
How efficient are SEP solar panels after numerous long trips thru the Van Allen belts? 
How many BFTanker flights to re-fuel the SEP tug itself for its various transits to support one Mars round trip mission?  Including bringing up the BFS propellant that the SEP carries all the way to Mars orbit.
Besides the added expense, resources and complexity of developing the SEP tug.

1)  I'd aim for each tug to complete 3 round trips between LEO and EML-1 per synod which would be 260 days each round trip, likely 200 outbound and 60 inbound due to lower mass.

2)  It differs for crew vs cargo missions, for crew you need BFS full of propellant at EML-1 which would be 2 propellant loads plus BFS itself, then another 2 loads of propellant delivered to EML-1 for transit to Mars which means 5 total LEO->EML-1 trips per 1 crew mission. 

For a cargo mission the slow hohomann trajectory should allow 2 BFS to be fueled from one propellant load at EML-1 and no propellant is needed at mars because a BFS on mars surface without any return cargo should make direct earth return so 3 LEO->EML-1 trips do 2 cargo deliveries or 1.5 per cargo delivery.

3)  Amorphous silicon solar panels can be self healing under the radiation environment of space and make many passes through the belts, eventually though the panels and likely thrusters will need replacement perhaps every other synod or two, the EML-1->Mars transits won't involve the belts and will likely be less stressful, I could see a tug doing one transit for the first synod then the 3 LEO->EML-1 trips the second as this keeps it closer to Earth and more easily put into unscheduled maintenance if needed.

4)  Ideally one Tanker flight corresponds to one tugs propellant load and it is a direct vehicle to vehicle transfer to avoid the need for a depot.  A load is probably around 150 mt of Metho-Lox propellant and 20-30 mt of Xenon.  Possibly the BFR simply launches a self-contained insulated tri-propellant cylinder which is equipped with all necessary transfer and cooling equipment (a bit like a self contained depot), the tug simply pushes this around while drawing the Xenon (though the tug has an integral tank too), this would avoid the need for perfect synchronicity between the launches and the tug pick ups as well as allow propellant to be accumulated in mars orbit or on Demos without requiring the tugs to loiter there.



Finally note that the above scenario would be used as a boot strapping method with the goal of getting the propellant depot in place in mars orbit and making the first few crewed missions safer.  Then we would transition to stockpiling propellant in Mars orbit sourced from Mars using the 25 mt cargo capacity from the mars surface that we know is planned.  When sufficient cargo volume is being shipped and propellant on the surface is plentiful the SEP tugs move cargo (without it being in a BFS) to mars rather then propellant, the cargo is placed into empty BFS in mars orbit and is landed.  Then the BFS is launched back to mars orbit with 25 mt extra propellant (rather then return crew) and this is offloaded when the next cargo is on-loaded.  After 12 such cycles enough propellant is accumulated to perform 1 fast crew return which roughly matches the expected crew:cargo ratio.  From this point on crew missions only need 3 SEP tug loads to EML-1 and cargo loads are better then 1:1 because the BFS itself is being omitted.

The very first crewed mission can also avoid landing on Mars as well and instead conduct an exploration of Phobos and then return via the pre-delivered propellants.  This would fit with the NASA plans which call for a gradual build up of capabilities, meanwhile the ISPP systems can be getting set up on the surface with the assistance of tele-robotic operation from the Demos crew.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 04/23/2016 02:32 pm
Thank you for your thoughtful response.
If I understand correctly one tanker load to LEO is 150 + 30 = 180 mt cargo.  Big BFR especially if you downsize your stage 2 as proposed for the BFS.  Or maybe your tanker version has larger propellant tanks to supply more delta V to LEO for the heavy cargo payload.

I see a SEP hauler approach as a follow on after initial synod missions as I am in the camp that the most likely disaster/delay scenario for SX is the huge R&D costs to develop the BFR (easier) and BFS (more difficult & riskier).  Adding a SEP increases R&D costs considerably.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 04/23/2016 06:16 pm
Yes around 180 mt for a propellant tanker load, but that is comparable to the mass of the BFS + 100 mt of Cargo.  I expect the BFR to have two stages like F-9 with the 2nd stage holding around 1000 mt of propellant.  BFS and the propellant tankers are both a payloads upon the BFR and of comparable mass, likewise when the SEP tug itself is launched perhaps two at a time as they won't be very massive. 

I see BFR as stand alone universal hyper-heavy lift vehicle able to carry a payload fairing up to 15m in diameter and ~40 m tall (7000 m^3) within which just about anything can be launched.

This is the safest development track because the BFR can be completed first and enter service to generate revenue and compete with SLS for any beyond Earth or heavy lift missions NASA attempts, this will basically kill the SLS and give SpaceX a monopoly on this size class of launch vehicle.  Then the BFS and SEP tugs can be developed for less then the proposed single huge BFS due to considerably lower mass and lower propellant fractions of the BFS, my calculations show a BFS of 75 mt dry mass with 300 mt propellant capacity will do the job where as the huge BFS will likely mass closer to 150 mt and hold 1000 mt of propellant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 04/23/2016 08:03 pm
Not totally bought in, but the much smaller BFS with Mars orbit SEP capture has a big advantage in that far less Mars colony energy and ISRU is needed per flight.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 04/24/2016 12:26 am

For fast transits you want to go nuclear. See for example the DRM 5 Addendum 2. In fact I don't think one synod return is possible without EP or refueling in LMO, because the delta-v is SSTO-level or higher. From both options, EP or LMO refueling, I would pick EP because it also saves you a ton of mass in LEO and it doesn't require a huge launch infrastructure on Mars. Note that you would not refuel the BFS in LMO, the EP would bring it back. In fact all in-space propulsion would be done with EP, however the BFS would do aerocapture at Mars.

If SpaceX plans to use a reactor on Mars they could use it for NEP too, if it has sufficiently low mass.

Fast in this context means faster then Hohmann transfer, I'm aiming for 150 days.  From EML-1 the DeltaV is modest around 4 km/s, if this were attempted from LEO it would indeed be SSTO levels of DeltaV and a one synod round trip is even more brutal, I have dismissed this as a possibility long ago even with unlimited propellants, the vehicles are just too large and have too high a propellant fraction to be reasonable.

An all EP for ex-atmospheric propulsion would indeed be the most efficient solution and I see that being done for cargo with something like a container ship going from LEO->LMO and chemical rockets staying at Earth and Mars and shuttling between surface and orbit to load and unload cargo.  Combining EP with aerocapture is also highly desirable as it would eliminate the need to brake into orbit via EP, saving both time and propellant but it may require advancements in solar array stiffening to achieve. 

For crew transport I suspect the speed of chemical may be necessary to beat the radiation threat, should a radiation mitigation (shielding, drugs, etc etc) be found then EP would be preferred their as well.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 04/24/2016 04:30 am
Plugging the Saturn IC data in the rocket equation shows that deltaV was just over 3.3 Km/s, it also staged at a pretty low altitude (good for the RTLS thing). Let's assume that the MCT booster does likewise, that leaves about 7 Km/s deltaV to the second stage (aka BFS) which is ok if you plan to refuel and do a TMI burn.

Well, depends what kind of orbit it goes to. If it goes into a pretty low orbit (maybe 9.5 km/s or so) to be refueled, and the first stage does 3.3 km/s, that only leaves 6.2 for the second stage.

Or are you counting the propulsive landing delta-v into the 3.3?

Quote
As per word of Musk, the ship will be capable of putting 100 t of useful mass on Mars, so let's make it another 100 t for structure (engines, TPS, legs, you name it). So that leaves a 200 t dry mass vehicle, capable of 7 km/s deltaV, with engines giving a Isp of 380 s you need a whopping 1150 t of propellant and a total BFS mass at lift off of about 1350 t.

Sounds pretty reasonable.

If the needed delta-v can drop to 6.2 km/s, the propellant mass can go down to about 860 tons.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: su27k on 04/24/2016 05:04 am
RB:  You completely inverted the meaning of 'Battlestar Galactica'.  That was Zubrin's pejorative term for a single huge vehicle that carries all propellant from Earth which was the NASA plan in the 90 day report.

Zubrin's argument was two fold, use insitu propellant on mars to reduce outbound propellant needs (which we all agree Musk is doing) AND using a number of smaller modular elements that serve specific roles and provide redundancy.  The Battlestart Galactica term was specifically about not making a single all inclusive budget busting vehicle designed to perform multiple tasks.

I think the BSG comment was referring to a big NTR vehicle that is assembled in orbit, especially if the assembly also requires the space station, which I assume would be a major cost driver. Neither the "big" BFS as 2nd stage, nor the "small" BFS as payload with a separate 2nd stage qualifies as BSG.

The BFR/BFS is only big because SpaceX's cargo requirement is hugely ambitious (100t to Mars surface), it wouldn't be so big if the cargo requirement was reduced to be inline with what Zubrin or NASA imagined. I don't think he overall dry mass of the entire system would change much between "big" BFS and "small" BFS, the only difference would be the mass you send through TMI.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 04/24/2016 02:18 pm
The BFR/BFS is only big because SpaceX's cargo requirement is hugely ambitious (100t to Mars surface), it wouldn't be so big if the cargo requirement was reduced to be inline with what Zubrin or NASA imagined.

I'd say NASA is currently downsizing its Mars plans, not in terms of payload landed on Mars (still ~80t), but in terms of the size of the individual elements. It's now considering 27t or even 18t landers (instead of 40t), chemical in-space stages with masses around 40t, SEPs with a few hundred kw. Nothing monstrous. In fact the only thing monstrous left is SLS.

All that I suppose in an effort to save cost. SpaceX does exactly the opposite, it's going very big (of course SpaceX attempts to colonize Mars instead of sending 4 people every few years).

That's why I fear that SpaceX will present a paper at IAC but since it's so diametrically opposed to NASA's evolvable Mars campaign it won't have any impact. In fact it might even give congress more legitimation to push forward with SLS (Look! SpaceX wants to build an ever bigger rocket!).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: the_other_Doug on 04/24/2016 05:40 pm
The BFR/BFS is only big because SpaceX's cargo requirement is hugely ambitious (100t to Mars surface), it wouldn't be so big if the cargo requirement was reduced to be inline with what Zubrin or NASA imagined.

I'd say NASA is currently downsizing its Mars plans, not in terms of payload landed on Mars (still ~80t), but in terms of the size of the individual elements. It's now considering 27t or even 18t landers (instead of 40t), chemical in-space stages with masses around 40t, SEPs with a few hundred kw. Nothing monstrous. In fact the only thing monstrous left is SLS.

All that I suppose in an effort to save cost. SpaceX does exactly the opposite, it's going very big (of course SpaceX attempts to colonize Mars instead of sending 4 people every few years).

That's why I fear that SpaceX will present a paper at IAC but since it's so diametrically opposed to NASA's evolvable Mars campaign it won't have any impact. In fact it might even give congress more legitimation to push forward with SLS (Look! SpaceX wants to build an ever bigger rocket!).

Yeah, I don't think the SpaceX Mars architecture is going to be anything that even remotely resembles the NASA Mars DRA.  Which, I will argue, is designed to land four people on Mars not once every few years, but once every decade or two, at best.  The only big plus to NASA's Mars DRA is the potential build-up of infrastructure in cis-lunar space, which is useful for both Mars and Moon exploration support, regardless of which program it is built up under.  (Note that all Musk has ever said about the Moon is, paraphrasing, "it's on the way, I guess we should look at how to get there, but it's not anything like a goal of the architecture to be able to go to the Moon".)

I, for one, would like to see a new interplanetary transportation architecture be designed to support more than one possible destination, I guess... ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CuddlyRocket on 04/24/2016 08:39 pm
(Note that all Musk has ever said about the Moon is, paraphrasing, "it's on the way, I guess we should look at how to get there, but it's not anything like a goal of the architecture to be able to go to the Moon".)

I, for one, would like to see a new interplanetary transportation architecture be designed to support more than one possible destination, I guess... ;)

Just because going to the Moon is not a goal of the MCT architecture doesn't mean the system won't be capable of being used to go to the Moon. I'm sure people will come up with all sorts of non-Mars uses for the MCT architecture once it's in existence (or even before).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 04/27/2016 01:03 am
(Note that all Musk has ever said about the Moon is, paraphrasing, "it's on the way, I guess we should look at how to get there, but it's not anything like a goal of the architecture to be able to go to the Moon".)

I, for one, would like to see a new interplanetary transportation architecture be designed to support more than one possible destination, I guess... ;)

Just because going to the Moon is not a goal of the MCT architecture doesn't mean the system won't be capable of being used to go to the Moon. I'm sure people will come up with all sorts of non-Mars uses for the MCT architecture once it's in existence (or even before).
Imagine Hubble in the Smithonian.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 04/27/2016 01:34 am
(Note that all Musk has ever said about the Moon is, paraphrasing, "it's on the way, I guess we should look at how to get there, but it's not anything like a goal of the architecture to be able to go to the Moon".)

I, for one, would like to see a new interplanetary transportation architecture be designed to support more than one possible destination, I guess... ;)

Just because going to the Moon is not a goal of the MCT architecture doesn't mean the system won't be capable of being used to go to the Moon. I'm sure people will come up with all sorts of non-Mars uses for the MCT architecture once it's in existence (or even before).
Imagine Hubble in the Smithonian.
Imagine Hubble keeps operating nearly indefinitely. Much better, IMHO... ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 04/27/2016 08:38 am
Imagine Hubble keeps operating nearly indefinitely. Much better, IMHO... ;)

Nah, we all love it but it's old. Build a one significantly newer and 4x the size. Hell, with that kind of capacity you could have a dedicated manned observatory station, or even throw a hubble-esque telescope into a solar orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: su27k on 04/27/2016 10:02 am
That's why I fear that SpaceX will present a paper at IAC but since it's so diametrically opposed to NASA's evolvable Mars campaign it won't have any impact. In fact it might even give congress more legitimation to push forward with SLS (Look! SpaceX wants to build an ever bigger rocket!).

Well Bolden already used this line of argument a few weeks ago, so the cat is definitely out of the bag...

I do wonder if the paper will include some cost estimates, on one hand cost will be a major justification for the architecture, on the other hand realistic cost estimate may give their commercial competitors some unique insights into their operations.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 04/27/2016 10:22 am
Imagine Hubble keeps operating nearly indefinitely. Much better, IMHO... ;)

Nah, we all love it but it's old. Build a one significantly newer and 4x the size. Hell, with that kind of capacity you could have a dedicated manned observatory station, or even throw a hubble-esque telescope into a solar orbit.

You wouldn't want a manned observatory station - too much vibration and other interference. Better to have an unmanned observatory which can reached and upgraded quickly and cheaply, as needed. Which is exactly what a "cislunar" BFS could provide.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Cinder on 04/27/2016 01:15 pm
Imagine Hubble keeps operating nearly indefinitely. Much better, IMHO... ;)

Nah, we all love it but it's old. Build a one significantly newer and 4x the size. Hell, with that kind of capacity you could have a dedicated manned observatory station, or even throw a hubble-esque telescope into a solar orbit.

You wouldn't want a manned observatory station - too much vibration and other interference. Better to have an unmanned observatory which can reached and upgraded quickly and cheaply, as needed. Which is exactly what a "cislunar" BFS could provide.
The manned portion could float nearby.  As far as that issue ruling out that particular use of non-Mars MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sanman on 05/05/2016 06:51 am
Will MCT use methalox for all parts of its Earth-Mars trip? If so, then is that volatile methalox supposed to last all the way until the Mars EDL burn? Or will hypergolics be used for the ending burn instead?
Likewise, what about for return trip back to Earth? There likely won't be a way to manufacture traditional hypergolics on Mars for the return trip, so it sounds like Methalox will need to survive from Mars all the way to Earth.

How will that methalox be preserved across the entire journey?

Will MCT use the same very-low-temperature cryo approach as Falcon FT?


Title: Re: MCT Speculation and Discussion Thread 4
Post by: TheTraveller on 05/05/2016 08:53 am
Will MCT use methalox for all parts of its Earth-Mars trip? If so, then is that volatile methalox supposed to last all the way until the Mars EDL burn? Or will hypergolics be used for the ending burn instead?
Likewise, what about for return trip back to Earth? There likely won't be a way to manufacture traditional hypergolics on Mars for the return trip, so it sounds like Methalox will need to survive from Mars all the way to Earth.

How will that methalox be preserved across the entire journey?

Will MCT use the same very-low-temperature cryo approach as Falcon FT?

Have read no plans to manufacture hypergolics on Mars, plus those engines have low ISPs. Storing methalox is just an engineering issue in optimal insulation techniques.

Reddit info said BFS was 15 x 60m, so a big space for heavily insulated fuel tanks during the transit. Another thought is only the Mars descent & LEO insertion / Earth descent fuel needs to be long time insulated so maybe large low insulation TMI / TEI burn tanks and small high insulation Mars descent, LEO insertion / Earth descent burn tanks?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Space OurSoul on 05/05/2016 05:07 pm
I think this counts as MCT speculation:

While reading this:
There is speculation that MCT might be built/tested/flown all at the Cape.

There is no way SpaceX would do that unless the range is ready to support daily flights.
It occurred to me that it's *technically feasible* to build BFR and BFS at the cape and have them both self-ferry to Brownsville... in fact this is feasible from any eastern-seaboard location.
Perhaps this side-steps the problem of needing a large skilled workforce in an out-of-the-way place like Brownsville.


Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/05/2016 05:17 pm
I think this counts as MCT speculation:

While reading this:
There is speculation that MCT might be built/tested/flown all at the Cape.

There is no way SpaceX would do that unless the range is ready to support daily flights.
It occurred to me that it's *technically feasible* to build BFR and BFS at the cape and have them both self-ferry to Brownsville... in fact this is feasible from any eastern-seaboard location.
Perhaps this side-steps the problem of needing a large skilled workforce in an out-of-the-way place like Brownsville.

Shipping large rockets by sea is a problem that has been solved many times. It's not only *technically feasible* but SOP.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TheTraveller on 05/05/2016 06:26 pm
I think this counts as MCT speculation:

While reading this:
There is speculation that MCT might be built/tested/flown all at the Cape.

There is no way SpaceX would do that unless the range is ready to support daily flights.
It occurred to me that it's *technically feasible* to build BFR and BFS at the cape and have them both self-ferry to Brownsville... in fact this is feasible from any eastern-seaboard location.
Perhaps this side-steps the problem of needing a large skilled workforce in an out-of-the-way place like Brownsville.

Shipping large rockets by sea is a problem that has been solved many times. It's not only *technically feasible* but SOP.

SpX / Elon has breadcrumbed for a dedicated island site for MCT.

Where else can SpX build a 15m diameter core that is maybe 60m or 120m long and transport it to the launch pad?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 05/05/2016 10:45 pm
(Note that all Musk has ever said about the Moon is, paraphrasing, "it's on the way, I guess we should look at how to get there, but it's not anything like a goal of the architecture to be able to go to the Moon".)

I, for one, would like to see a new interplanetary transportation architecture be designed to support more than one possible destination, I guess... ;)

Well, if MCT has the delta-v to SSTO from Mars and go to Earth, it should be able to land on and take off from the Moon just fine, even if it's not really designed for that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 05/06/2016 03:28 am
Regarding the BFS TPS, I always thought the best place to put it was on the bottom.  This way force is always in the same direction (same for launch and EDL) and it would enable to lowest possible structural mass and simplist cargo/passenger stowage.  This also means that the TPS will look like Swiss cheese to allow openings for the engines (or alternatively nacelles).

If we put the TPS on top, it solves some of those headaches but creates a few new ones.  Engines would be protected during descent and TPS would be protected during landing.  However,  would a blunt TPS designed for Mars EDL have too much drag during earth ascent?  Does anyone have a drag coefficient by mach number graph for a blunt body?  Things like a lofted trajectory and throttling near max Q would help, but would add to gravity losses.

Assuming it does create too much drag during Earth assent (likely), would the mass penalty of adding a fairing be worth it?  Although i couldnt find any historical precedent, I think it could even be inflatable.  Inflatables have been proposed for mars descent, which should have higher mechanical and thermal loads than earth ascent.  Being inflatable could also make recovery easier by passively surviving descent and splashdown (or make a big slow target for a helicopter mid air grab.)

The last paragraph is outside my area of expertise, so I thought I would bounce the idea off the NSF community.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 05/06/2016 07:24 am
Drag in these kinds of situations basically boils down to cross-sectional area.

The design I think would be most efficient is to use an ADEPT type system of carbon cloth on tensioned carbon-fiber arms on the top/sides of the vehicle which opens like an umbrella.  Entry would be nose first and the base of the vehicle is clear for engines and landing gear.  The opening and closing of the decelerator also acts as the door to the cargo hold as the vehicles outer skin segments are attached to the arms and are carried out to the perimeter of the umbrella shape.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 05/07/2016 08:29 am
Regarding the BFS TPS, I always thought the best place to put it was on the bottom.
[...] and it would enable [the] simplist cargo/passenger stowage.

What's the reasoning for that?

If we put the TPS on top,

I've assumed if the TPS isn't at the bottom, it'll be down the ventral side. With a biconic or lifting-body forward shape, allowing lift/drag type EDL, extending the deceleration, reducing the amount of supersonic retropropulsion required, and lowering the final speed before the landing burn, both reducing fuel demand.

It also allows a longer glide, improving safety for suboptimal entry timing. (For eg, uneven upper atmosphere means the BFS decelerates earlier than expected, losing speed before reaching the intended landing area. BFS lands short, necessitating a rescue scenario. With a longer glide, you can stretch the descent.)

I think it could even be inflatable.

Doubtful. It would need to be repacked on Mars to allow for the Earth-return EDL. Or you'd need to carry two expendable inflatable heat-shields (one for Mars, one for return to Earth.)

(It just doesn't fit the typical SpaceX architecture.)

(or make a big slow target for a helicopter mid air grab.)

Errr, no. IMO, ULA's engine pod for Vulcan will end up being be too large for helicopter aerial recovery, the BFS would be too large for capture even by a giant transport plane.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/07/2016 04:19 pm
I think it could even be inflatable.

Doubtful. It would need to be repacked on Mars to allow for the Earth-return EDL. Or you'd need to carry two expendable inflatable heat-shields (one for Mars, one for return to Earth.)

(It just doesn't fit the typical SpaceX architecture.)

Inflatables are preferable for Mars because of the very high terminal velocity (compared to the same mass and shape on Earth reentry), so it may have an inflatable for Mars entry but drop it at Mars and use a traditional heat shield for Earth return.

If the inflatable has a secondary use on Mars or enroute (Raw material? Habitat?) it could be considered payload and wouldn't be just so much dead weight.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 05/07/2016 05:11 pm
Regarding the BFS TPS, I always thought the best place to put it was on the bottom.
[...] and it would enable [the] simplist cargo/passenger stowage.
What's the reasoning for that?
If acceleration is always in the same direction, then you only need to support cargo from one direction.  If not, straps / bolts have to be beefier and more numerous.  Not a huge issue.  Slightly more problematic is passengers after the flip maneuver and landing.  Their high-g chairs need to flip around.   I think some kind of swinging hammock would work, but as I said, acceleration in only one direction is simpler to design for.
I've assumed if the TPS isn't at the bottom, it'll be down the ventral side. With a biconic or lifting-body forward shape, allowing lift/drag type EDL, extending the deceleration, reducing the amount of supersonic retropropulsion required, and lowering the final speed before the landing burn, both reducing fuel demand.

It also allows a longer glide, improving safety for suboptimal entry timing. (For eg, uneven upper atmosphere means the BFS decelerates earlier than expected, losing speed before reaching the intended landing area. BFS lands short, necessitating a rescue scenario. With a longer glide, you can stretch the descent.)
Certainly all valid points.  I think everyone agrees that lift is pretty much required to minimize prop.

The craft I am describing is very similar in shape to the F9 S2 in the S2 landing video. I didn't mention this in my original post in the interest of keeping it short, but during descent,  BFS would need to tilt slightly to provide lift and would therefore need to have at least a thin heat shield along one side to protect it.

I think our two proposals are similar, but just vary in shape of the craft and angle during descent.  The shape you describe certainly has the advantage of the nose of the craft being appropriate for both ascent and descent.

Doubtful. It would need to be repacked on Mars to allow for the Earth-return EDL. Or you'd need to carry two expendable inflatable heat-shields (one for Mars, one for return to Earth.)
...
(It just doesn't fit the typical SpaceX architecture.)
...
Errr, no. IMO, ULA's engine pod for Vulcan will end up being be too large for helicopter aerial recovery, the BFS would be too large for capture even by a giant transport plane.

Maybe I wasn't clear enough.  This fairing would be jettisoned right around S1 separation.  The TPS is a rigid blunt shape underneath.  Fairing is not required in mars ascent because the thin atmosphere creates little drag even for a blunt nose.   
BFS would land vertically at the earth launch site.

Thanks for the feedback.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: drzerg on 05/08/2016 10:37 am
what do you think about tripropellant engine for long duration missions?
i know that lox+RP+H2 gives some good results but could lox+methane+H2 do that?

for example (engine is the same):

for BFR first stage: start on methane 66-75% + 33-25% H2 for best thrust, then high isp flight on pure H2 and landing on pure methane (no need for high insulation for H2)

for MCT: start to mars on pure H2 and landing on mars on pure methane. start from mars on methane or mix if it possible to produce H2. landing on earth on pure methane.   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DJPledger on 05/08/2016 06:52 pm
what do you think about tripropellant engine for long duration missions?
i know that lox+RP+H2 gives some good results but could lox+methane+H2 do that?

for example (engine is the same):

for BFR first stage: start on methane 66-75% + 33-25% H2 for best thrust, then high isp flight on pure H2 and landing on pure methane (no need for high insulation for H2)

for MCT: start to mars on pure H2 and landing on mars on pure methane. start from mars on methane or mix if it possible to produce H2. landing on earth on pure methane.   
Ain't going to happen. BFR+MCT will be 100% LOx/LCH4. Elon is staying away from H2 because of it's difficulties.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 05/08/2016 07:18 pm
I kind of doubt the BFR will require inflatable decelerators or anything like that. Looking at some delta-v maps, LEO to Mars transfer orbit is a lot less delta-v than Mars surface to Earth transfer, so a little extra propulsive landing delta-v probably will be fine.

Given SpaceX's good mass ratios, I think accepting a requirement for a bit more delta-v/performance for architecture simplicity is the way to go, anyway.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/09/2016 03:32 am
Putting 100t from LEO through TMI is about the same as putting 25t from Mars surface to TEI (exact number depends on non payload masses). The extra Delta v comes out in the payload.

That said, I agree that inflatables don't seem to be a thing at SpaceX.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 05/10/2016 07:49 pm
This is more BFR than MCT speculation. I believe a three core arrangement uses about a third more metal to hold the same amount of propellant at about the same strength as a single core of the same capacity, so it is no surprise they are not considering multiple cores in this clean sheet design. If logistics of ground or sea transport are discarded, the remaining major trade would seem to be between flight dynamics and tank efficiency.

More squat designs hold more liquid with less metal. I was thinking of the growing waste of space/added structure  as tanks get more spherical and remain stacked. I then imagined the ideal would be a sphere of LOX inside a sphere of methane. Inner sphere situated at the bottom of the outer sphere.

Fooling around with various layouts, I am wondering if it would make sense to have the LOX tank be an uninsulated cylinder inside of a cylindrical liquid methane tank, both with normal domes. Would seem to have some structural and plumbing benefits.

I am sure this has been thought of in the past, but I have not found references to it. What are the downsides?

Enjoy, Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/10/2016 08:00 pm
Matt, that's exactly what a common bulkhead propellent tank design does. Look up the Saturn V second stage tank common bulkhead.

http://www.alternatewars.com/Games/KSP/Tut2/KSP_Tutorial_2-6.htm
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 05/11/2016 12:08 am
Matt, that's exactly what a common bulkhead propellent tank design does. Look up the Saturn V second stage tank common bulkhead.

http://www.alternatewars.com/Games/KSP/Tut2/KSP_Tutorial_2-6.htm

Yup, common bulkheads have been around a long time. S-IVB (Saturn IB's second stage and Saturn V's third stage) had one too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 05/11/2016 12:37 am
Pressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics.  I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 05/11/2016 01:08 am
I am familiar with common bulkheads, especially in the Saturn V, I am asking about nested cylinders. At very least it eliminates the plumbing from the top tank to the engines.

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 05/11/2016 01:11 am
I too have asked in the past about concentric nested cylinders for metholox.  Both are about the same temperature, I think about 20 Degrees different.  Plumbing would be short and would add to vertical strength of the rocket or stage. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/11/2016 02:18 am
Strength isn't as important as strength/weight or strength/volume ratios. A short nested cylinder is basically a common bulkhead. A full length nested cylinder loses most of the volumetric advantage because the inner cylinder has a slender aspect ratio.

If you think about what a nested cylinder becomes if you take the exact same parts and stack them, it's easier to visualize: you would have one half-full large tank and one completely full smaller tank. It will be hard for this arrangement to beat two properly sized tanks.

That said, there is an advantage in that the smaller tank has very little pressure or temperature differential radially... It could even be an inflatable membrane while the outer tank is the pressure vessel. I'll do a fist pass later with real(ish) numbers to see how the strength, volume and weight optimize...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 05/11/2016 05:35 am
The volume of LOX would be much smaller than the volume of the Methane, so the inner tank would be sized so that tanks of the same length contain the proper ratio of propellants.

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/11/2016 12:33 pm
What you said is true for hydrolox. It is not true for methalox. It takes 3.4kg of lox to burn 1kg of liquid methane, but lox is only about 2.6 times denser. If you have equal volume tanks you will have methane left over.

If your outer cylinder diameter is 10m, the same-length inner cylinder needs to be 7.5m in diameter to hold enough lox for complete combustion.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 05/11/2016 01:31 pm
What you said is true for hydrolox. It is not true for methalox. It takes 3.4kg of lox to burn 1kg of liquid methane, but lox is only about 2.6 times denser. If you have equal volume tanks you will have methane left over.

If your outer cylinder diameter is 10m, the same-length inner cylinder needs to be 7.5m in diameter to hold enough lox for complete combustion.

I may have used incorrect numbers. If I understand your numbers correctly, LOX/liquid methane tanks would have about 1.3 cubic meters of LOX per cubic meter of liquid methane?

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 05/11/2016 02:30 pm
For a wider BFR and BFS, I think two nested cylinders would be the best design.  Cross section would be two concentric circles.  There would be no horizontal common bulkhead.  The side walls would no longer have to support the weight of the upper tank.  The new vertical common bulkhead would actually add to compressive strength of the rocket.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/11/2016 04:41 pm
Matt, yes it should be about 1.3 or so. The exact volume ratio will depend on the temperature of each fuel (subcooled is denser) and the optimum engine fuel:oxidizer mass ratio which in turn depends on chamber pressure.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 05/11/2016 05:24 pm
I guess the fuel has to go in the inside tank. If the inner tank is 10 meters in diameter, then the outside tank would be 15.1 meters or so. Conventional stacking architecture, for the same tankage, would of course be the same height as the nested design, so aside from getting rid of the feed tube from the top tank to the engine cluster, the nesting design would have a lot more surface area of aluminum. The nesting design could use thinner elements all around though and and have strengths not present in the stacked design.

The BFR is likely in my opinion, to have a center engine plus two concentric rings of engines. The inner tank can be the load path for the inner engines, saving structure that would carry the load out to the outer tank walls in a conventional design. That structure is potentially quite heavy. I don't have the chops to spec the whole design out, but I think there is something here.

What I would really like to know is if this has been explored before by professional rocket designers. On the one hand this seems likely, but on the other, how many steely eyed rocket designers have set out to design a first stage with dozens of engines? A few for sure, (N-1) but not many.

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/11/2016 08:39 pm
Pressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics.  I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.
Your logic is correct, but your statement isn't correct.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 05/11/2016 10:19 pm
The BFR is likely in my opinion, to have a center engine plus two concentric rings of engines

My guess is that they will consider the ideal T/W for landing and base the configuration decision on that. If one engine is ideal, there will be one center engine. If three engines burning at landing is ideal, I would not be surprised to see an equilateral triangular cluster in the center with that surrounded by concentric rings. The engines fired for boost back and/or entry may not even be the same engines used for landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 05/11/2016 11:10 pm
Pressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics.  I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.
Your logic is correct, but your statement isn't correct.

I can assure that is my real opinion and I am not secretly expecting a different size, so this would be considered a correct statement of my opinion.  Now if you a different opinion then by all means present it.

Also with regard to this idea of nested propellant tanks, my understanding of pressure vessels is that the outer tank would need to have the full mass and strength of a single tank with the combined volume of them both because the mass in the inner tank still contributes to the forces trying to burst the outer tank.

With regard to engine arrangement the central engine with 2 (or more) concentric rings of engines around it makes for the most flexible arrangement so long as the rings are hexagonal (which is most efficient anyway).  You can fire one central engine, 2 opposite flanking engines, 3 engines in a triangle, 4 engines etc etc.  In fact you should be able to fire a symmetrical group of engines in every single increment from one up to the total engine count so I see this as the optimal arrangement unless it presents some difficulty in propellant piping.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 05/12/2016 03:38 pm
Pressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics.  I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.

IF the Rvac engine approaches the 5m width some have computed, 10m will be too small.
I figure the BFR/BFS as just under 100m tall but maybe 15m wide, certainly at least 12.5m.  If narrower, then taller.
In any case, it will look very different from the pencil necked geek Falcon9.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 05/12/2016 03:47 pm
Pressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics.  I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.

I doubt the tank is going to dominate the structural mass of the vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/12/2016 03:49 pm
Pressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics.  I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.

I doubt the tank is going to dominate the structural mass of the vehicle.
Efficient rocket stages are pretty much just giant tanks. Think again.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/12/2016 04:12 pm
Pressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics.  I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.

I doubt the tank is going to dominate the structural mass of the vehicle.
Efficient rocket stages are pretty much just giant tanks. Think again.

The Shuttle orbiter structure massed twice as much as it's external tank. That may not reflect MCT's design, but there aren't a lot of other baselines for very large reusable upper stages.

The MCT booster, however, will certainly be a giant tank with lots of engines and little else.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 05/12/2016 04:15 pm
Pressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics.  I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.

I doubt the tank is going to dominate the structural mass of the vehicle.
Efficient rocket stages are pretty much just giant tanks. Think again.

I thought he meant BFS, my fault.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/12/2016 04:22 pm
Pressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics.  I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.

I doubt the tank is going to dominate the structural mass of the vehicle.
Efficient rocket stages are pretty much just giant tanks. Think again.

I thought he meant BFS, my fault.
BFS requires rocket-stage-like performance and so will have to be built like a rocket stage. Tank mass is very important.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: aameise9 on 05/13/2016 12:33 am
May I ask if anyone has a conception how MCT is supposed to RETURN from Mars?

It was mentioned a few times that the return leg, surface to LMO and LMO to TEI, constitutes the most challenging aspect ('long pole') for the entire architecture.  Yet I have read almost no discussion of how this could be achieved.  Basically, there seem to be two extreme possibilities, plus a range of intermediates.

1) Mars surface is reached by a larger version of the Dragon, with engines suitable for precision landing.  But can the same engines take the craft back to orbit?

2) Mars surface is reached by a larger version of the F9R, with engines suitable for both orbital launch and precision landing.  But can such a craft launch without a launch complex and its infrastructure?  And can such a craft return to earth without replenishing propellants from a tanker in LMO?

Apologies if I have overlooked any information pertaining to these points!





Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 05/13/2016 01:01 am
Pressure vessel mass to volume ratios don't change much with total volume, and narrower tanks give better airodynamics.  I think we will see BFR at around 10 m to 12.5 m in diameter and 90 m tall.

IF the Rvac engine approaches the 5m width some have computed, 10m will be too small.
I figure the BFR/BFS as just under 100m tall but maybe 15m wide, certainly at least 12.5m.  If narrower, then taller.
In any case, it will look very different from the pencil necked geek Falcon9.

2nd stage engine bells might indeed be an issue, but we need to know how many engines the 2nd stage would have.  If it's 4 engines then the 12.5m should work, if it's 5-7 then 15m would indeed be necessary.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/13/2016 01:50 am
A lot of hints point to BFR as a F9 scaled up 10x. 15m lbf thrust vs. 1500; 100t to LEO with RTLS vs. 10t plus a margin for reuse. That would make BFR a 12.6m diameter at the same height if methalox is 20% less dense.
But Raptor is supposed to be scaled up about 3x, so for the same staging points the US needs 3 Raptors to match the Mvac. Three 5m bells should fit nicely on a 12.6 m stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/13/2016 02:17 am
May I ask if anyone has a conception how MCT is supposed to RETURN from Mars?

It was mentioned a few times that the return leg, surface to LMO and LMO to TEI, constitutes the most challenging aspect ('long pole') for the entire architecture.  Yet I have read almost no discussion of how this could be achieved.  Basically, there seem to be two extreme possibilities, plus a range of intermediates.

1) Mars surface is reached by a larger version of the Dragon, with engines suitable for precision landing.  But can the same engines take the craft back to orbit?

2) Mars surface is reached by a larger version of the F9R, with engines suitable for both orbital launch and precision landing.  But can such a craft launch without a launch complex and its infrastructure?  And can such a craft return to earth without replenishing propellants from a tanker in LMO?

Apologies if I have overlooked any information pertaining to these points!
Neither. Or rather, something in between.

You need maybe 6-7km/s to return to Earth from the surface of Mars. You can do that in a single stage with TPS, though it is hard.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jet Black on 05/13/2016 08:08 am
For example, one of the chips I like to use the most in residential downlighting applications, masses 3kg per 100 units. including shipping packaging. Something even lighter, like a Bridgelux COB array comes in at 130-150 lumens per watt, ~1300-2500 lumens delivered, ....

Most while light LED units have an annoying peak around 450nm or so which is not good for the circadian rhythm (I work in this area). iirc the ISS replaced all their lighting with a custom system to attempt to simulate the changes in chromaticity that you would normally experience through the day. This is probably going to be something needed both in transit and on mars (since the changes in colour throughout the day there will be very different to earth).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jet Black on 05/13/2016 01:18 pm
Or for 400kg extra, have a backup solar array that can provide 20-40kW indefinitely. A solar array and a generator have about the same mass, but the solar array isn't going to explode, won't wear out or require maintenance or fluid, and needs no fuel and can operate indefinitely, and doesn't have exhaust.

Just. Stop. Stop trying to make "internal combustion engine in space" happen. It's not happening.


What about in a dust storm on mars? Your solar panels probably aren't going to be much use then.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 05/13/2016 01:34 pm

What about in a dust storm on mars? Your solar panels probably aren't going to be much use then.

Batteries whilst the storm lasts, shrouds to close over the panels before the storm happens/orient the panels away from the wind/roll the panels back in/put something over them. Any of these objects are less resource intensive than an ICE.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 05/13/2016 01:56 pm
May I ask if anyone has a conception how MCT is supposed to RETURN from Mars?

It was mentioned a few times that the return leg, surface to LMO and LMO to TEI, constitutes the most challenging aspect ('long pole') for the entire architecture.  Yet I have read almost no discussion of how this could be achieved.  Basically, there seem to be two extreme possibilities, plus a range of intermediates.

1) Mars surface is reached by a larger version of the Dragon, with engines suitable for precision landing.  But can the same engines take the craft back to orbit?

2) Mars surface is reached by a larger version of the F9R, with engines suitable for both orbital launch and precision landing.  But can such a craft launch without a launch complex and its infrastructure?  And can such a craft return to earth without replenishing propellants from a tanker in LMO?

Apologies if I have overlooked any information pertaining to these points!

Well Martian ISRU helps out a great deal, and gravity and atmospheric losses on mars are considerably lower - the lowered gravity losses are especially helpful when it comes to exiting the gravity well.

As for launching without a launch complex, the craft is going to require fueling whilst on mars, and perhaps a rudimentary pad of some kind - quite likely the area will need to be cleared of potentially harmful debris that could be kicked up when the engines fire.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/13/2016 02:05 pm
Or for 400kg extra, have a backup solar array that can provide 20-40kW indefinitely. A solar array and a generator have about the same mass, but the solar array isn't going to explode, won't wear out or require maintenance or fluid, and needs no fuel and can operate indefinitely, and doesn't have exhaust.

Just. Stop. Stop trying to make "internal combustion engine in space" happen. It's not happening.


What about in a dust storm on mars? Your solar panels probably aren't going to be much use then.
If you're landing away from the pad, you're in a survival situation. You're going to be dead very soon, power or no, without a rescue party. You may have even needed to bail out of the vehicle.

Wasting tons on the corner-case of a corner-case (in a way that still is inferior to other solutions) is not a good idea.

An internal combustion engine on MCT is a bad idea that simply won't die. People keep bringing it back up. It's a zombie idea.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jet Black on 05/13/2016 02:30 pm

What about in a dust storm on mars? Your solar panels probably aren't going to be much use then.

Batteries whilst the storm lasts, shrouds to close over the panels before the storm happens/orient the panels away from the wind/roll the panels back in/put something over them. Any of these objects are less resource intensive than an ICE.

The limitation of a battery is that it can hold as much power as the capacity of the battery. For something that is fuelled, the limitation is the amount of fuel that you have (that can be built up in situ for a methane burner on mars). Wind's not an issue, just the dust, though there is probably an element of abrasion in the long term. (iirc the most violent storms on mars would feel light a light breeze, because the air is so thin)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jet Black on 05/13/2016 02:32 pm
Or for 400kg extra, have a backup solar array that can provide 20-40kW indefinitely. A solar array and a generator have about the same mass, but the solar array isn't going to explode, won't wear out or require maintenance or fluid, and needs no fuel and can operate indefinitely, and doesn't have exhaust.

Just. Stop. Stop trying to make "internal combustion engine in space" happen. It's not happening.


What about in a dust storm on mars? Your solar panels probably aren't going to be much use then.
If you're landing away from the pad, you're in a survival situation. You're going to be dead very soon, power or no, without a rescue party. You may have even needed to bail out of the vehicle.

Wasting tons on the corner-case of a corner-case (in a way that still is inferior to other solutions) is not a good idea.

An internal combustion engine on MCT is a bad idea that simply won't die. People keep bringing it back up. It's a zombie idea.

even on-pad. Though that depends on what the constituents of the base are early on. You're right about it generally being useless in space, but if it's worth having one on mars, then it may as well be compatible with the rest of the infrastructure.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: baldusi on 05/13/2016 02:58 pm
If you're landing away from the pad, you're in a survival situation. You're going to be dead very soon, power or no, without a rescue party. You may have even needed to bail out of the vehicle.

Wasting tons on the corner-case of a corner-case (in a way that still is inferior to other solutions) is not a good idea.

An internal combustion engine on MCT is a bad idea that simply won't die. People keep bringing it back up. It's a zombie idea.
You keep saying that. But there are engineering methods to define when something makes sense and when it doesn't. It's called a trade. So help him make the technical trade on mass and simply let the numbers speak for themselves.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Johnnyhinbos on 05/13/2016 03:03 pm
Interesting, so what's being said is that it is impossible for a scenario, say an explosion, which both sets up an uncontrolled rotation and takes out the roll control system. This prevents the solar panels from operating with any efficiency, if at all. So you're willing to bet the life and safety of the crew of the MCT on one single mode of power generation.

I deal with critical life support where failure isn't an option, and would result in certain death. A proposal that's analogous to a single mode of power generation would simply not be  entertained.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jet Black on 05/13/2016 03:05 pm
Interesting, so what's being said is that it is impossible for a scenario, say an explosion, which both sets up an uncontrolled rotation and takes out the roll control system. This prevents the solar panels from operating with any efficiency, if at all. So you're willing to bet the life and safety of the crew of the MCT on one single mode of power generation.

I deal with critical life support where failure isn't an option, and would result in certain death. A proposal that's analogous to a single mode of power generation would simply not be  entertained.

Surely that scenario would also create problems for a liquid fuel system too, since the forces in the lines would keep changing directions. Additionally how long would you expect such a scenario to last? would it be longer than the on-board battery supply?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/13/2016 03:19 pm
If you're landing away from the pad, you're in a survival situation. You're going to be dead very soon, power or no, without a rescue party. You may have even needed to bail out of the vehicle.

Wasting tons on the corner-case of a corner-case (in a way that still is inferior to other solutions) is not a good idea.

An internal combustion engine on MCT is a bad idea that simply won't die. People keep bringing it back up. It's a zombie idea.
You keep saying that. But there are engineering methods to define when something makes sense and when it doesn't. It's called a trade. So help him make the technical trade on mass and simply let the numbers speak for themselves.
I already have done that. Doesn't seem to matter, the zombie idea keeps coming up.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/13/2016 03:26 pm
Interesting, so what's being said is that it is impossible for a scenario, say an explosion, which both sets up an uncontrolled rotation and takes out the roll control system. This prevents the solar panels from operating with any efficiency, if at all. So you're willing to bet the life and safety of the crew of the MCT on one single mode of power generation.

I deal with critical life support where failure isn't an option, and would result in certain death. A proposal that's analogous to a single mode of power generation would simply not be  entertained.
What. I can tell you didn't actually read what I wrote, just what people snipped. I don't care that you work with critical life support systems, because your analysis is ridiculous.

When you include the overhead and the inefficiency of small IC, lithium batteries are actually superior from a mass and energy standpoint besides being far more reliable. I SHOWED THIS ABOVE (15% typical efficiency for small IC, plus methane--or diesel--operating at stoichiometric mix gets you about 400Wh/kg plus the mass of the tanks and the actual ICE itself, primary lithium can do up to 700Wh, state-of-the-art rechargable can do 300-400Wh/kg). And if you want long-term use, solar array beats everything.

The problem here is that everyone is using their intuition from Earth, where you get free oxygen (which is a kind of ISRU). Oxygen is the vast majority of the mass.

It's a freaking zombie idea. LET IT DIE.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Johnnyhinbos on 05/13/2016 03:28 pm

Interesting, so what's being said is that it is impossible for a scenario, say an explosion, which both sets up an uncontrolled rotation and takes out the roll control system. This prevents the solar panels from operating with any efficiency, if at all. So you're willing to bet the life and safety of the crew of the MCT on one single mode of power generation.

I deal with critical life support where failure isn't an option, and would result in certain death. A proposal that's analogous to a single mode of power generation would simply not be  entertained.

Surely that scenario would also create problems for a liquid fuel system too, since the forces in the lines would keep changing directions. Additionally how long would you expect such a scenario to last? would it be longer than the on-board battery supply?
I would expect the lines to be pressurized. And I'd expect the time to resolution to be sometime just past the capacity of the battery backup, because that's exactly how Murphy works. And yes, there's a careful balance in trade offs between redundancy and practicality. I'm not saying that an IC engine is the solution (though I could be), rather I'm saying its foolhardy to have only one method to generate power.

I dive in circumstances where if your LSS has an issue, heading to the surface is certain death. So you build in redundancy that is variable. Example: my rebreather has not one but three separate and different methods for checking on CO2 buildup. It has a chemical sensor (so think of that as the solar panels, as it would get the job done). But it also knows my metabolic rate because it counts the number of times the O2 solenoid fires. From this the amount of CO2 generated can be calculated. Completely independent of the first method. Finally, there is a series of temperature probes mounted inside the CO2 scrubber canister that are used to quantify the chemical reaction between absorbent and CO2, thereby determining efficiency of system and potential for CO2 breakthrough. Again, fully independent and functionally different.

Don't even get me started on the O2 system.

Point being, when you are in a hostile environment that a human body can not possibly survive on its own, and where's there's zero chance of someone coming to your aid, you don't put all your critical eggs in one basket...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/13/2016 03:29 pm
Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.

NO ONE is saying not to have redundancies and margin. What we're saying is ICE is the wrong solution.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Johnnyhinbos on 05/13/2016 03:42 pm

Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.
Sigh. I'm not sure why you are being so aggressive here. It's a conversation. I did mention that the focus is not on using an IC, rather that there should be a completely independent power generator that shares no commonality with solar.

But to answer your question, my rebreather uses three battery systems, all independent and in physically different enclosures. Each is rated to power the system longer than the consumables could last (O2, diluent, and scrubber). With the loss of one the system can feed off the others. The system uses a digital bus called DiveCAN derived from the ubiquitous auto CAN bus and even with a physical cut between main computer and O2 delivery system, O2 will continue to inject at the current set point. I also have a 100% independent system (literally everything is independent) which allows me to fly the unit manually in the advent of complete system failure. Finally there's an orifice in the O2 side that delivers, depth independent, metabolic rate O2 into the loop (0.6 l/m).

Anyway, I've no desire to argue with you. I respect your posts. I just humbly suggest, IMO, that the real MCT will no doubt have an independent power generator to solar.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jet Black on 05/13/2016 03:43 pm
Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.

NO ONE is saying not to have redundancies and margin. What we're saying is ICE is the wrong solution.

Yeah I'm struggling to think what other options there are beyond solar/battery power combo and an ICE, unless there is some useful power that can be dragged out of the cooling system (I'm assuming that there won't be nuclear power or RTG on the crew transports)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/13/2016 03:53 pm

Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.
Sigh. I'm not sure why you are being so aggressive here. It's a conversation. I did mention that the focus is not on using an IC, rather that there should be a completely independent power generator that shares no commonality with solar.

But to answer your question, my rebreather uses three battery systems, all independent and in physically different enclosures. Each is rated to power the system longer than the consumables could last (O2, diluent, and scrubber). With the loss of one the system can feed off the others. The system uses a digital bus called DiveCAN derived from the ubiquitous auto CAN bus and even with a physical cut between main computer and O2 delivery system, O2 will continue to inject at the current set point. I also have a 100% independent system (literally everything is independent) which allows me to fly the unit manually in the advent of complete system failure. Finally there's an orifice in the O2 side that delivers, depth independent, metabolic rate O2 into the loop (0.6 l/m).

Anyway, I've no desire to argue with you. I respect your posts. I just humbly suggest, IMO, that the real MCT will no doubt have an independent power generator to solar.
As I said, the backup would be batteries. But you'd also build-in redundancy in the solar array. For life support, no doubt you'd actually have a few oxygen candles and chemical scrubbers, or rely on the large volume of the MCT as a buffer.

EDIT: And you could have a completely passive and manually operated system for life support if you wanted. A certain type of regenerative scrubber, if you have access to vacuum, just needs some valves opened and closed. That could be done manually. You could also dispense oxygen manually as well, though that would be tougher. In any case, such things only need a tiny amount of power.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: belegor on 05/13/2016 03:56 pm
Is there a guess on the minimum power required to maintain basic functionality of the craft? (I.e. basic life support, basic thermal control, minimal comms, emergency lighting only, basic GNC, etc.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 05/13/2016 03:57 pm
Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.

NO ONE is saying not to have redundancies and margin. What we're saying is ICE is the wrong solution.

Yeah I'm struggling to think what other options there are beyond solar/battery power combo and an ICE, unless there is some useful power that can be dragged out of the cooling system (I'm assuming that there won't be nuclear power or RTG on the crew transports)
Methane/oxygen fuel cells
Hydrogen/oxygen fuel cells
Stirling engine based on catalytic Methane/Oxygen reaction
Turbine based on Methane/Oxygen combustion
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/13/2016 04:00 pm
Is there a guess on the minimum power required to maintain basic functionality of the craft? (I.e. basic life support, basic thermal control, minimal comms, emergency lighting only, basic GNC, etc.)
Passive thermal control, manually operated life support or oxygen candles and chemical scrubbers. Windows. gravity-stabilized orientation or manual operation of thruster valves (not a terribly good idea, but possible). Except for comms, basically everything could be done with zero electrical power (though relying on manual operations).

But that's unnecessary.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jet Black on 05/13/2016 04:01 pm
Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.

NO ONE is saying not to have redundancies and margin. What we're saying is ICE is the wrong solution.

Yeah I'm struggling to think what other options there are beyond solar/battery power combo and an ICE, unless there is some useful power that can be dragged out of the cooling system (I'm assuming that there won't be nuclear power or RTG on the crew transports)
Methane/oxygen fuel cells
Hydrogen/oxygen fuel cells
Stirling engine based on catalytic Methane/Oxygen reaction
Turbine based on Methane/Oxygen combustion

I was subconsciously including all combustion in that... but yep. Once you can split your water back into Hydrogen and oxygen again (using solar) then the fuel cells are an interesting backup, since it's in principle replenishable and probably easier to do than making more methane and the components either side of the reaction are useful.

There's ammonia to burn too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/13/2016 04:01 pm
Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.

NO ONE is saying not to have redundancies and margin. What we're saying is ICE is the wrong solution.

Yeah I'm struggling to think what other options there are beyond solar/battery power combo and an ICE, unless there is some useful power that can be dragged out of the cooling system (I'm assuming that there won't be nuclear power or RTG on the crew transports)
Methane/oxygen fuel cells
Hydrogen/oxygen fuel cells
Stirling engine based on catalytic Methane/Oxygen reaction
Turbine based on Methane/Oxygen combustion
Or use independent batteries. The simplest, most reliable solution.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 05/13/2016 04:02 pm
Something like a Redox low temp solid oxide fuel cell. A 1 m3 450kg Cube runs on NG and delivers 25kw. Much more efficient than an ICE generator.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/13/2016 04:02 pm
Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.

NO ONE is saying not to have redundancies and margin. What we're saying is ICE is the wrong solution.

Yeah I'm struggling to think what other options there are beyond solar/battery power combo and an ICE, unless there is some useful power that can be dragged out of the cooling system (I'm assuming that there won't be nuclear power or RTG on the crew transports)
Methane/oxygen fuel cells
Hydrogen/oxygen fuel cells
Stirling engine based on catalytic Methane/Oxygen reaction
Turbine based on Methane/Oxygen combustion

I was subconsciously including all combustion in that... but yep. Once you can split your water back into Hydrogen and oxygen again (using solar) then the fuel cells are an interesting backup, since it's in principle replenishable and probably easier to do than making more methane and the components either side of the reaction are useful.

There's ammonia to burn too.
Regenerative fuel cells have very low round-trip efficiency. Use frakking batteries, you'll get a lot more power for your trouble and no moving parts (regenerative fuel cells need pumps, etc).

There seems to be some sort of allergy to batteries here.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 05/13/2016 04:07 pm

I was subconsciously including all combustion in that... but yep. Once you can split your water back into Hydrogen and oxygen again (using solar) then the fuel cells are an interesting backup, since it's in principle replenishable and probably easier to do than making more methane and the components either side of the reaction are useful.

There's ammonia to burn too.

There is methane, and oxygen, for propellant. Methane is currently a byproduct of the oxygen generation of one LSS system in the ISS IIRC.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 05/13/2016 04:25 pm
Guys, be excellent to each other. I won't single any one person out, although I could.

Terms like "zombie idea" are not helpful.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: baldusi on 05/13/2016 05:43 pm
Do you have an IC in your rebreather to act as a backup to the battery? No? Of course not, because that'd be ridiculous. It'd be dangerous, complicated, and would probably end up adding more failure modes than it'd save. You use backup batteries.

NO ONE is saying not to have redundancies and margin. What we're saying is ICE is the wrong solution.

Yeah I'm struggling to think what other options there are beyond solar/battery power combo and an ICE, unless there is some useful power that can be dragged out of the cooling system (I'm assuming that there won't be nuclear power or RTG on the crew transports)
Methane/oxygen fuel cells
Hydrogen/oxygen fuel cells
Stirling engine based on catalytic Methane/Oxygen reaction
Turbine based on Methane/Oxygen combustion
Or use independent batteries. The simplest, most reliable solution.
I might have missed the lines in so many posts. But what are the requirements exactly on this discussion? Backup for what phase of the trip, for how long, considering which contingencies? I understand that nuclear power will be prepossitioned. And I'm assuming a certain amount of CH4/LOX is supposed to be on the Mars pad, but the MCT would have some margin on its own storage tanks.
So again, what are the requirements. I don't feel like stating an educated guess (some call it an opinion) if I don't fully understand the requirements.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jet Black on 05/13/2016 07:56 pm

I was subconsciously including all combustion in that... but yep. Once you can split your water back into Hydrogen and oxygen again (using solar) then the fuel cells are an interesting backup, since it's in principle replenishable and probably easier to do than making more methane and the components either side of the reaction are useful.

There's ammonia to burn too.

There is methane, and oxygen, for propellant. Methane is currently a byproduct of the oxygen generation of one LSS system in the ISS IIRC.

sure, but is the methane as easy to replenish as hydrogen/oxygen would be? If something is going to be used in a burning system, then you want to be able to replenish it when you have spare energy again.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/13/2016 08:00 pm

I was subconsciously including all combustion in that... but yep. Once you can split your water back into Hydrogen and oxygen again (using solar) then the fuel cells are an interesting backup, since it's in principle replenishable and probably easier to do than making more methane and the components either side of the reaction are useful.

There's ammonia to burn too.

There is methane, and oxygen, for propellant. Methane is currently a byproduct of the oxygen generation of one LSS system in the ISS IIRC.

sure, but is the methane as easy to replenish as hydrogen/oxygen would be? If something is going to be used in a burning system, then you want to be able to replenish it when you have spare energy again.
But then you have to reclaim the exhaust, include an electrolysis kit, a compressor... which adds a bunch of mass. So much that you get better storage capacity per mass with... *dundundun* ...a lithium rechargable battery.

(not to mention much better round-trip efficiency)

If you're using a fuel cell (which is much better than a small IC, though still bad IMO), just vent the exhaust or possibly use the water for crew use (like on Shuttle). Anything else will just result in a lithium battery being a much better option.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 05/13/2016 08:06 pm

I was subconsciously including all combustion in that... but yep. Once you can split your water back into Hydrogen and oxygen again (using solar) then the fuel cells are an interesting backup, since it's in principle replenishable and probably easier to do than making more methane and the components either side of the reaction are useful.

There's ammonia to burn too.

There is methane, and oxygen, for propellant. Methane is currently a byproduct of the oxygen generation of one LSS system in the ISS IIRC.

sure, but is the methane as easy to replenish as hydrogen/oxygen would be? If something is going to be used in a burning system, then you want to be able to replenish it when you have spare energy again.
But then you have to reclaim the exhaust, include an electrolysis kit, a compressor... which adds a bunch of mass. So much that you get better storage capacity per mass with... *dundundun* ...a lithium rechargable battery.

(not to mention much better round-trip efficiency)

If you're using a fuel cell (which is much better than a small IC, though still bad IMO), just vent the exhaust or possibly use the water for crew use (like on Shuttle). Anything else will just result in a lithium battery being a much better option.

Unless of course your LSS is already processing the CO2 and water vapor in the air into CH4 and O2 then there is no added mass. I would favor a methane fuel cell if it had a decent electrolyte lifespan.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 05/13/2016 08:37 pm
As I said, the backup would be batteries. But you'd also build-in redundancy in the solar array. For life support, no doubt you'd actually have a few oxygen candles and chemical scrubbers, or rely on the large volume of the MCT as a buffer.
As mentioned previously, the concern is power "generation" for all modes/situations; in space or on Mars.  In a life critical context, having two or more independent power generation capabilities is obvious.  However, batteries are for power "storage", not generation.  Sure you can use batteries when your power generation fails but only to the extend of the amount of power stored in the batteries and the number of physical batteries you have.

In other words, we're talking energy density, aka how much power you can store or is stored.  Granted that batteries are extremely efficient, for their mass, in providing the stored energy but fails in another metric, energy density.  Batteries just don't have the energy density to even come close to Methane LOX, either by combustion or reaction, mass for mass.  That's why a ICE sedan (aka Audi or BMW) similar to Tesla Model S weighs half as much and has twice (give or take) the range.  It's also why Methane LOX is rocket fuel and a battery powered rocket engine will never exist.

In short, batteries are excellent "buffers" in power generation to maintain supply during deterministic lapses in power generation.  They are useless for "non-deterministic" lapses (in power generation) as there is always the possibility of running out of energy.  A dust storm on Mars (which have covered the entire planet) is possibly one of those "non-deterministic" lapses that could last months.  Though I'm not for or against any technology, I do hold the opinion that an ICE (or derivative technology) genset is the best, simplest, non-nuclear solution.

Kaoru   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CuddlyRocket on 05/14/2016 01:16 am
What about in a dust storm on mars? Your solar panels probably aren't going to be much use then.

Dust storms don't completely block the Sun. The maximum reduction in power from the Mars rovers' solar cells was ~80%.

In a life critical context, having two or more independent power generation capabilities is obvious.

I agree; for safety reasons there needs to be a source of electric power that is not derived either directly or indirectly from your main source. It may be less efficient, but it is independent and that is a worthwhile feature in its own right to be factored into any engineering trades.

Unfortunately, it is difficult to think of any independent source of power to solar other than nuclear, or vice-versa. (For very small amounts of power there are the crew members (https://www.k-tor.com/).)

Quote
Though I'm not for or against any technology, I do hold the opinion that an ICE (or derivative technology) genset is the best, simplest, non-nuclear solution.

ICE and associated fuel/oxygen stocks is a power storage method and needs to be traded against other storage methods. That said, if on the surface of Mars you're going to be producing large amounts of methalox propellant, it would seem a shame if you had no means to use it to generate electricity in an emergency! Zubrin noted the back-up possibilities in his Case for Mars, although he assumed ICE-powered vehicles whose engines could do dual duty as generators. How much this applies to the MCT is another matter.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: biosehnsucht on 05/14/2016 03:48 am
TL;DR: If there's an ICE to be found, I think it's most reasonable to put it in a long/medium range rover (for distances greater than half a day's walk, or less if your backpack life support doesn't last that long) to be used for recharging the batteries (sized for normal close range stuff but not for long range, due to mass) in a series hybrid arrangement (it would be a plug-in as well, and can use ICE to feed power back to whatever and can be refilled from either ground side tanks of liquid or gaseous CH4/O2 or from MCT's tanks)

--

In space, ICE just as backup (or really, any) source doesn't make sense unless it's part of your overall IVF system and a necessary part of it (I recall reading about an ICE in the IVF of ... was it the ACES upper stage?).

On the surface of Mars, ICE isn't a terrible backup system if you want to eliminate "eggs in one basket" scenario, but obviously you can't take enough of it to power everything at once (would mass too much plus where would you get the fuel?). You'll have to generate it's fuel from ISRU which means it's really another kind of solar power.

So, it would seem obvious that batteries make a better choice, but batteries have mass, and an empty tank doesn't have near as much.

If for example you can pull the fuel back out of your partially-refueled MCT to run the ICE, then the overall additional mass of the ICE and it's available runtime is far more mass efficient than batteries. You might also be able to have some kind of expandable or otherwise lightweight gaseous (rather than liquid) storage for CH4 and O2, which might or might not be better than batteries for mass (since it's now something you weren't going to bring). Whether an ICE and storage (either additional or siphoning off the MCT) is more mass efficient than enough batteries to outlast whatever issue (may not just be storms, maybe damage to solar panels etc) is dependent on how "bad" you think the bad can possibly be.

The "obvious" choice for where to make the ICE useful for more than just backup would be to have your surface vehicles use ICE as some kind of series hybrid setup and be able to feed power into whatever else you need it for, but realistically you're likely to find batteries a better use for such a use.

However, a longer range rover (in which you might possibly go more than half a day's walk) might be a good place to put an ICE. The energy density of ICE without the mass (at launch from earth) of batteries (you'd still need some, but not as much) might make that worthwhile. A large enough solar array to recharge it for such a range may not be feasible to make portable, so an ICE would win if you want to risk venturing too far to walk back safely, then when you need emergency power (more than say overnight or a day) you can by then get the rover back and use it's ICE to convert fuel (either stored onboard or via ground side tanks or the MCT's tanks) back into energy.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 05/14/2016 04:17 am
Regenerative fuel cells have very low round-trip efficiency. Use frakking batteries, you'll get a lot more power for your trouble and no moving parts (regenerative fuel cells need pumps, etc).

There seems to be some sort of allergy to batteries here.

Their is one motivation I can see for chemical energy storage.  When a solar powered ISRU process is being run continually and we want to avoid the need to store the large amounts of energy needed to run the process at night the best solution is to immediately use all solar power for water electrolysis (which is most of the energy input to the whole process) and store the excess hydrogen during the day as it is being produced faster then it is being consumed.  Because the remaining chemo-synthesis steps to create methane are exothermic after Hydrogen creation it can run with little power input (compressing the methane will require some power).

Now admittedly you could just size the system such that all hydrogen produced during the day is immediately consumed and then their is a full shutdown at night.  But this would introduce thermal cycling to the synthesis equipment as well as a daily startup process both of which would certainly cause wear on it, so keeping the process continuous would be advantages to both mass and lifespan of the equipment.  Depending on latitude a seasonal shutdown due to lower solar power might still be necessary and their are dust-storms too, but that's still about a 700 fold reduction in cycling.

Now all of that being justified on it's own ground I can running the stored Hydrogen/Oxygen through a fuel-cell as a back up power-source after batteries are depleted, at any one time their will be only 1 day's worth of Hydrogen stored but this may constituted several days worth of emergency power needs if their is a sudden failure of solar and or batteries.  Hydrogen/Oxygen fuel cells would be preferable to a Methane/Oxygen ones because the source fuel Hydrogen has gone through less conversions steps and thus has a higher storage efficiency, Hydrogen/Oxygen fuel-cells are also a more refined technology.

Internal combustion is an absolute non-starter as it would be just a fraction of the efficiency of a fuel-cell and as the only conceivable use is as an emergency backup you want electricity to run a base while repairs are made a stationary system is ideal, not one mounted to a vehicle which might be absent right when it is needed most.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: randomly on 05/14/2016 05:47 am
Just remember it takes about 75-80kw/hr of electrical energy to produce 1kg of hydrogen, and a fuel cell only extracts about 16 kwh from that 1kg of hydrogen. so you are throwing away 80% of your energy.
as Robotbeat mentioned, the round trip energy efficiency of fuel cells sucks. You'd have equivalent results if you only stored 20% of the power in lithium batteries.

I wouldn't dismiss methane fuel cells. The hydrogen storage problem is substantial. It may be a better over all system trade to use methane/oxygen.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 05/14/2016 08:29 am
Batteries just don't have the energy density to even come close to Methane LOX, either by combustion or reaction, mass for mass.  That's why a ICE sedan (aka Audi or BMW) similar to Tesla Model S weighs half as much and has twice (give or take) the range.

Cars on Earth don't have to carry their own oxygen. As RB said, you are letting your experience on Earth mislead you.

It's also why Methane LOX is rocket fuel and a battery powered rocket engine will never exist.

Solar electric propulsion has vastly better "range" than any chemical rocket.

A dust storm on Mars (which have covered the entire planet) is possibly one of those "non-deterministic" lapses that could last months.

Solar panels still work during dust storms. (Dust is actually easier for modern solar panels than water-droplet clouds on Earth.)

The power generated will drop, of course. But most of the power required on Mars will be for ISRU. You simply suspend power hungry ops during the worst of the storm. (Which, judging by MER-Opportunity, is only a few days even in a month long dust storm.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jdeshetler on 05/14/2016 02:27 pm

A dust storm on Mars (which have covered the entire planet) is possibly one of those "non-deterministic" lapses that could last months.

Solar panels still work during dust storms. (Dust is actually easier for modern solar panels than water-droplet clouds on Earth.)


The biggest concern is that the "Mars Dust" is more of salty (sticky), abrasive (sharp edges) and much smaller particles (talcum powder sized) which is electrically charged attracted to any man-made elements, not the "Earth dust" we think of ones from the dry deserts.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: aameise9 on 05/14/2016 05:54 pm
1) Mars surface is reached by a larger version of the Dragon, with engines suitable for precision landing.

2) Mars surface is reached by a larger version of the F9R, with engines suitable for both orbital launch and precision landing.
Neither. Or rather, something in between.

You need maybe 6-7km/s to return to Earth from the surface of Mars. You can do that in a single stage with TPS, though it is hard.

Thank you!  So something in between a squat capsule and a pencil-shaped booster.

Presumably with short, stubby legs to support the weight of a fully tanked craft?

Presumably with engines angling outward (Dragon-style) to direct blast debris away from craft?

I am not sure that I understood the relevance of TPS (temperature protection system)?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 05/14/2016 06:21 pm


The biggest concern is that the "Mars Dust" is more of salty (sticky), abrasive (sharp edges) and much smaller particles (talcum powder sized) which is electrically charged attracted to any man-made elements, not the "Earth dust" we think of ones from the dry deserts.

So effectively nothing you want in joins, bearings, panels engines or lungs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/14/2016 06:38 pm
1) Mars surface is reached by a larger version of the Dragon, with engines suitable for precision landing.

2) Mars surface is reached by a larger version of the F9R, with engines suitable for both orbital launch and precision landing.
Neither. Or rather, something in between.

You need maybe 6-7km/s to return to Earth from the surface of Mars. You can do that in a single stage with TPS, though it is hard.

Thank you!  So something in between a squat capsule and a pencil-shaped booster.

Presumably with short, stubby legs to support the weight of a fully tanked craft?

Presumably with engines angling outward (Dragon-style) to direct blast debris away from craft?

I am not sure that I understood the relevance of TPS (temperature protection system)?
Needs to be able to withstand entry to Mars, reentry back to Earth, and perhaps aerocapture. Definitely need a thermal protection system for that. But it'll have to be extremely lightweight.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 05/14/2016 08:09 pm
I am not sure that I understood the relevance of TPS (temperature protection system)?

Thermal protection system.  Thermal relates to heat. Though temperature and heat are related, they are not the same thing. Termerature is a measure of intensity. In comparing a match to an electric blanket, the lit match will have a higher temperature, while the electric blanket will put out more total heat, though at a lower temperature. One will keep you warm; the other will burn you, yet not keep you warm.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Long EZ on 05/14/2016 09:23 pm
Question: what is the best material to make MCT out of?

The options that I come up with are:

1) Aluminum - Lithium alloy just like Falcon.
2) Carbon Fiber composite using a honeycomb core.
3) Titanium single shell.
4) Titanium double shell with a core of some kind.

Considerations include heat tolerance, insulation needed, corrosion on Mars and Earth.
Stiffness when not pressurized. Thick core walls are much stiffer.
The material that I like is Titanium with hollow spaces to form a a 2 wall Ti sandwich with a Ti honeycomb core.
Obviously this is very difficult to make as it is hard to weld Ti alloys in air. But if that could be worked out it would seem to be the most durable.
Insulation is needed not only on Earth, but on Mars when accumulating ISRU propellants, so an inner layer of insulation is needed. For Carbon Fiber or Al-Li an outer layer of insulation would also be needed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kaoru on 05/14/2016 09:28 pm
Cars on Earth don't have to carry their own oxygen. As RB said, you are letting your experience on Earth mislead you.
No I'm not...  I'm directly looking at the modes of the entire mission and matching it with existing technology or technology that could be applied.  Energy density per kilogram mass and the efficiency of turning that energy into useful work is the factors to determine the viability of using the solution for the mission.
The mission calls for at least two methods of power generation.  Solar will be the primary method with batteries as the primary storage to buffer normal usage.
I rule out nuclear since mixing humans with radioactive isotopes just have too many failure modes with no solution within the context of the mission. 
That leaves chemical reaction as the backup method.  This is obvious since the mission requires ISRU technology.  Since ISRU is energy storage, adding a way to make it useable in case of emergency requires very little extra mass since you already have most of it including the mass for CH4-O2/tanks.
Using batteries as a backup for X time beyond the normal usage would be more massive and you still need bigger solar panels to cover all current needs plus charging.
So in space, you have large pool of stored energy, CH4/LOX, to tap into in an emergency.  For on surface, as long as your ISRU is budgeted correctly that large pool of stored energy is available.
This is the basis of my opinion that some form of ICE or fuel cell will be included in the mission.  Since ICE is the most mature and well known technology, adds the least mass, and is flexible in application, it gets my vote.
Solar electric propulsion has vastly better "range" than any chemical rocket.
Yes, SEP has great ISP but no thrust because the amount of energy required to ionize a larger reaction mass to provide greater thrust is ridiculous.  SEP is great for low mass long duration flights measured in years.  It's not practicable for high mass "as short as possible" duration flights like a manned Mars mission.
Solar panels still work during dust storms. (Dust is actually easier for modern solar panels than water-droplet clouds on Earth.)

The power generated will drop, of course. But most of the power required on Mars will be for ISRU. You simply suspend power hungry ops during the worst of the storm. (Which, judging by MER-Opportunity, is only a few days even in a month long dust storm.)
So you lose some power...  How much power and for how long?  No one can answer this question because it's non-deterministic and we have little experience to fall back to.  Remember you have power ECLSS and ISRU because your lives depend on it.  This is why two primary methods of power generation is required.

Kaoru
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 05/14/2016 10:53 pm
Question: what is the best material to make MCT out of?

The options that I come up with are:

1) Aluminum - Lithium alloy just like Falcon.
2) Carbon Fiber composite using a honeycomb core.
3) Titanium single shell.
4) Titanium double shell with a core of some kind.

Considerations include heat tolerance, insulation needed, corrosion on Mars and Earth.
Stiffness when not pressurized. Thick core walls are much stiffer.
The material that I like is Titanium with hollow spaces to form a a 2 wall Ti sandwich with a Ti honeycomb core.
Obviously this is very difficult to make as it is hard to weld Ti alloys in air. But if that could be worked out it would seem to be the most durable.
Insulation is needed not only on Earth, but on Mars when accumulating ISRU propellants, so an inner layer of insulation is needed. For Carbon Fiber or Al-Li an outer layer of insulation would also be needed.
The simplicity of your initial question is daunting. For me, it would have to be broken down into a long list, just for the major components, because each one will require drastically different engineering considerations. (Then I would duck and defer to a materials specialist.)
 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Long EZ on 05/15/2016 08:38 pm
I had in mind the structure of the propellant tanks and possibly the crew area. If the vehicle does atmospheric entry nose first, then it either needs a heat shield or be a material that can take the heat. Also of concern is micrometeorite  protection. There is a region just short of Mars that has a high concentration of them. A double wall structure is preferred for that. A double wall also has better stiffness for the weight.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jjwaDal on 05/15/2016 08:44 pm
Basically for the MCT to be real SpaceX has  to answer one question : « How do you make a HLV (possibly larger than the « Saturn-5 » rocket) both cheaper and reliable ?

There's an easy answer which is that to absorb the cost of development and the overall costs to keep  the whole system going you need to fly often. Mandatory but not sufficient.
Reusability is also an important point and they are working on that.
But strategy is paramount.

Looking at the numbers given for Falcon Heavy is telling…
If anyone had proposed at ESA or ULA or Roskosmos 7 years ago to build a rocket capable to lift 54 mT to LEO or 22 mT to GTO he would have been told there is no market for those capacities and the cost of development for a few launches (possibly to deep space or the army) doesn't justify that.
Well SpaceX is telling us FH can do that and will probably never do that.
But… Can lift 20 to 30 mT to LEO or 8 mT to GTO for 90 million $ and there's a market for that.
Because it is based on a rocket often flown, because it will have commercial customers and fly often too, and because first stages will be recovered and refly, Shotwell told us they were thinking of flying rocket in the long run for less than 10 million $…

Let's consider they can refly their first stages on a regular basis.

The next step should be the recovery of the second stage and RTLS for all first stages, and FH can't do that without losing too much lift capacity and too many customers.
But Raptor will come along and we can think of a single stick able to essentially return all stages to launch site and make more than the max capacities of FH in full expendable mode.
Full reusability and a very large fairing (let's say 10m +) should give it a commercial use given its price (including price/pound).
But such a rocket would enable travel to Mars in a Mars Direct style 10 years from now. Anyhow Elon is not going to send to Mars 100 people at a time  without lots of stuff on the ground and selected first tiny crews to tend the « shop »…
Bind three of these boosters and you would have the BIG ONE, cheap and reliable before sending anybody to Mars.

I think it would be suicide to build directly the BFR.  :o
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 05/21/2016 10:00 pm
Trip Harris is celebrating 9 with SpaceX today, and is currently is Manager of Falcon landings. The YouTube clip he chose to link to his celebratory tweet is....interesting.

https://twitter.com/SpaceXTrip/status/733869950067036160 (http://"https://twitter.com/SpaceXTrip/status/733869950067036160")

Quote
@SpaceXTrip
Today I celebrate nine years @SpaceX! It's amazing how much it's changed, and I am excited for what the future holds https://t.co/oNLgPQM9my (http://"https://t.co/oNLgPQM9my")

Quote
Picard:"Somehow I doubt this will be the last ship to carry the name Enterprise."

http://youtu.be/Gc1yBSUev7g
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 05/22/2016 01:06 pm
Trip Harris is celebrating 9 with SpaceX today, and is currently is Manager of Falcon landings. The YouTube clip he chose to link to his celebratory tweet is....interesting.

https://twitter.com/SpaceXTrip/status/733869950067036160 (http://"https://twitter.com/SpaceXTrip/status/733869950067036160")

Quote
@SpaceXTrip
Today I celebrate nine years @SpaceX! It's amazing how much it's changed, and I am excited for what the future holds https://t.co/oNLgPQM9my (http://"https://t.co/oNLgPQM9my")

Quote
Picard:"Somehow I doubt this will be the last ship to carry the name Enterprise."

There were a lot of other good quotes in this strip. Doesn't mean its this one. And maybe he just liked the scene a lot without deeper meaning. I wouldn't read too much into it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: spacenut on 05/22/2016 01:30 pm
Solar panels for MCT could be made to flip upside down at night to keep potential dust off, then flip back during the day.  They are going to be packed for flight, so a few adjustments on the design of them can flip the panels.  I also think a mixture of materials for MCT.  Seems like titanium around the bottom sensitive areas would be better than aluminum, based on what we have seen with Falcon 9.  At one time on the proposed X-33 or Oriental Clipper a titanium wire fabric was to be used on the skin of this spacecraft. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 05/22/2016 05:27 pm
Such frequent cleaning is not needed and dust is likely to have enough electrostatic cling that it will not fall off simply by flipping something upside down (try this with a dusty object on Earth if your not convinced).

The only reliable way to remove dust is brush or blow it off, as the solar panels need to have a retraction system simply put at air-knife along the hull so that the panel is blown clean when retracted.  Periodically retract and redeploy the panel as needed and you avoid any need to turn or rotate the panel either under gravity or in space.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: sanman on 05/25/2016 06:52 am
I don't know if it's been talked about yet - but what about MCT/BFS and the hoverslam? As F9R is showing, hoverslam can be pretty damn rough/tough on the rocket. So what would MCT/BFS face during descent on Earth or Mars, and would hoverslam be feasible? Or are you just going to need much more deeply throttleable engines?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/26/2016 12:18 am
I don't know if it's been talked about yet - but what about MCT/BFS and the hoverslam? As F9R is showing, hoverslam can be pretty damn rough/tough on the rocket. So what would MCT/BFS face during descent on Earth or Mars, and would hoverslam be feasible? Or are you just going to need much more deeply throttleable engines?
It's not necessarily the hoverslam that is rough on the rocket, it's the reentry. Shield from reentry heating, and hoverslam is simply a more efficient way to land (though maybe a bit sketchy with crew).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 05/26/2016 02:26 am
I don't know if it's been talked about yet - but what about MCT/BFS and the hoverslam? As F9R is showing, hoverslam can be pretty damn rough/tough on the rocket. So what would MCT/BFS face during descent on Earth or Mars, and would hoverslam be feasible? Or are you just going to need much more deeply throttleable engines?
It's not necessarily the hoverslam that is rough on the rocket, it's the reentry. Shield from reentry heating, and hoverslam is simply a more efficient way to land (though maybe a bit sketchy with crew).

Brace everyone properly in comfy chairs (with lots of straps), ensure you have maximal confidence, have engines that throttle deeper than merlins, and try not to think about the three figure ton bullet you're sitting in hurtling towards the concrete. Hopefully (going out on a limb to say certainly) BFS will have a lower thrust-to-weight ratio compared with a F9 stage one.

It's -just- a D2 (with a foot about a 13th of the area of a Manhattan city block and about as heavily populated) with less margins and no chutes - for that reason, they better be damn sure everything works according to plan.

That's partly why we have D2 and F9r, of course. I for one look foreward to watching gigantic martian apartments dropping out of the sky. It'd probably be the most watchable component of the whole program.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/27/2016 02:59 pm
...
Hopefully (going out on a limb to say certainly) BFS will have a lower thrust-to-weight ratio compared with a F9 stage one.

We can put some rough bounds on that. Musk said the Raptor is targeting about 230t of thrust at SL, which should give about 280t thrust in vacuum. To deliver 100t to Mars surface will take about 100t of dry mass (more or less). The same dry mass is supposed to return 25t to Earth. BFS is supposed to have "multiple" engines, which based on possible core diameters and vac bell sizes probably means 3 engines.

Put all those together (total thrust / total mass - local gravity) and the net acceleration at the Mars surface is 3.8g, and the net acceleration at the Earth's surface is 4.5g.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 05/28/2016 02:08 am
What do you mean 3.8g and 4.5g, thouse are incredible acceleration rate and likely beyond what crew could tolerate, did you mean m/s of net upward acceleration at launch, aka how fast you will move away from the ground?  Even then they are incredible and imply crushing burnout acceleration rates, please show your formula for deriving these values.

When looking at vehicle acceleration rates the acceleration at burn out is very important too as it determines a lot of the strength requirements of the vehicle and it's cargo.  Throttling down or shutting down engines can keep the acceleration reasonable a triangular 3 engine configuration is poor as it permits no shutdown.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 05/28/2016 07:02 am
What do you mean 3.8g and 4.5g, thouse are incredible acceleration rate and likely beyond what crew could tolerate,

I don't think so... 4 g isn't that big of a deal with correct positioning. The Shuttle was limited to 3, but Apollo astronauts took way more g's than that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Elmar Moelzer on 05/28/2016 07:52 am
Some rollercoasters pull higher g loads (I heard of up to 7 though only for a short time).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/28/2016 01:00 pm
Humans can handle 8-9 gees just fine if oriented the correct way.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Hyperion5 on 05/28/2016 02:04 pm
Humans can handle 8-9 gees just fine if oriented the correct way.

Not for very long, though.  NASA limited sustained gees on Apollo flights to 4.5 g and Shuttle flights to 3 g for very good physiological reasons.  Spacex should be aiming for a similar sustained g load for manned launches and reentries for the same reasons.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/28/2016 02:48 pm
We were discussing the hover slam landing, which is essentially at burnout since only marginal fuel is remaining.

That's also open throttle on all engines. I'm sure they would be throttled to within crew acceptable limits for landing.

Liftoff accelerations would probably net less than 1/3g with a full fuel load.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 05/28/2016 04:47 pm
Humans can handle 8-9 gees just fine if oriented the correct way.

Not for very long, though.  NASA limited sustained gees on Apollo flights to 4.5 g and Shuttle flights to 3 g for very good physiological reasons.  Spacex should be aiming for a similar sustained g load for manned launches and reentries for the same reasons.

Sure, for long term/sustained... but ~4 g for a hoverslam landing just isn't that big of a deal at all.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 05/28/2016 05:08 pm
Humans can handle 8-9 gees just fine if oriented the correct way.

Not for very long, though.  NASA limited sustained gees on Apollo flights to 4.5 g and Shuttle flights to 3 g for very good physiological reasons.  Spacex should be aiming for a similar sustained g load for manned launches and reentries for the same reasons.

Sure, for long term/sustained... but ~4 g for a hoverslam landing just isn't that big of a deal at all.
8gees would be fine, too. But I suspect if they limit it, they'll do it for structural reasons, i.e. they could have a lighter structure if they limited hoverslam acceleration to, say, 5 gees vs 8 gees.

Humans can withstand WAY higher limits than we often assume, and I think the weak point may actually be the non-human parts.

For Shuttle, if I recall correctly, the seats were NOT oriented in the most optimum position for withstanding gee-loads. They needed a good orientation for gliding the orbiter back, so they couldn't be lying on their back like for capsules.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 05/28/2016 08:42 pm
I'm still looking for a clarification by envy887, is this a calculation of the vehicles acceleration rate during a hover-slam landing?  I had though he meant a launch but as a landing g force that makes a lot more sense. 

Still we need to remember that the crew/cargo inside the vehicle gets an additional local g worth of force upon them (sanity check, if the rocket were hovering we would feel 1 g, not weightlessness).  So that means a force of 5.5 g at Earth and around 4.1 g on Mars.  In practice I'm sure you would see throttling of engines and a gentler deceleration in the 3 g neighborhood.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 05/28/2016 10:40 pm
I'm still looking for a clarification by envy887, is this a calculation of the vehicles acceleration rate during a hover-slam landing?  I had though he meant a launch but as a landing g force that makes a lot more sense. 

Still we need to remember that the crew/cargo inside the vehicle gets an additional local g worth of force upon them (sanity check, if the rocket were hovering we would feel 1 g, not weightlessness).  So that means a force of 5.5 g at Earth and around 4.1 g on Mars.  In practice I'm sure you would see throttling of engines and a gentler deceleration in the 3 g neighborhood.

Not sure how you are calculating that. Everything else about the vehicle in question being equal (particularly its mass and engine thrust) an occupant of that vehicle will experience the same feeling of acceleration at full thrust whether they are taking off from Earth, going for TMI from LEO, Landing on Mars or taking off from Mars. As was pointed out above as the propellant mass drops off as you are burning it, then acceleration increases. Also has been discussed if your vehicle has the same thrust and mass taking off from Earth or Mars the gravity loss would be much less from Mars. A craft that could take off with a TMR (thrust to mass ratio) of 1.3 would accelerate at .3g initially as it took off from Earth and at .92g from the surface of Mars. The gravity loss at the start of the launch would go from 77% on Earth to 23% on Mars. Now once you start pitching over from the vertical, and also as propellant load drops off, your real acceleration relative to the point you started from increases and the acceleration the occupants feel moves up at the same curve (presuming the same thrust, ISP and vehicle mass) on either location. Throttling would most likely happen on the MCT though, and also dropping the number of engines firing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/28/2016 11:10 pm
I'm still looking for a clarification by envy887
....
See my reply above. I was figuring a hover-slam at burnout mass, not a launch.

Not sure how you are calculating that.
....
He added local gravity to my calculations above, which were based on my rough estimates of MCT dry mass, engine count, and engine thrust. That is indeed the perceived acceleration during landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 05/28/2016 11:15 pm
Not sure how you are calculating that.
....
He added local gravity to my calculations above, which were based on my rough estimates of MCT dry mass, engine count, and engine thrust. That is indeed the perceived acceleration during landing.

Different payloads? if the mass and thrust are the same then perceived acceleration will be the same.  If the craft is nearly empty (of propellant) has the same payload and can thrust at 4g in free fall, then in a hover slam the passengers experience 4g on Mars or Earth but on Mars they are decelerating at 3.62g and on Earth at 3g.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 05/28/2016 11:31 pm
What do you mean 3.8g and 4.5g, thouse are incredible acceleration rate and likely beyond what crew could tolerate,

I don't think so... 4 g isn't that big of a deal with correct positioning. The Shuttle was limited to 3, but Apollo astronauts took way more g's than that.

Humans can handle 8-9 gees just fine if oriented the correct way.


Not for very long, though.  NASA limited sustained gees on Apollo flights to 4.5 g and Shuttle flights to 3 g for very good physiological reasons.  Spacex should be aiming for a similar sustained g load for manned launches and reentries for the same reasons.

Mercury-Atlas astronauts withstood 11g. But they were test pilots made of The Right Stuff.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/28/2016 11:34 pm
Not sure how you are calculating that.
....
He added local gravity to my calculations above, which were based on my rough estimates of MCT dry mass, engine count, and engine thrust. That is indeed the perceived acceleration during landing.

Different payloads? if the mass and thrust are the same then perceived acceleration will be the same.  If the craft is nearly empty (of propellant) has the same payload and can thrust at 4g in free fall, then in a hover slam the passengers experience 4g on Mars or Earth but on Mars they are decelerating at 3.62g and on Earth at 3g.
Yes. 100t to Mars, 25t to Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 05/29/2016 06:29 am
Not sure how you are calculating that.
....
He added local gravity to my calculations above, which were based on my rough estimates of MCT dry mass, engine count, and engine thrust. That is indeed the perceived acceleration during landing.

Different payloads? if the mass and thrust are the same then perceived acceleration will be the same.  If the craft is nearly empty (of propellant) has the same payload and can thrust at 4g in free fall, then in a hover slam the passengers experience 4g on Mars or Earth but on Mars they are decelerating at 3.62g and on Earth at 3g.
Yes. 100t to Mars, 25t to Earth.

nadreck your forgetting that the passengers are not part of the vehicle, the vehicle acceleration upward towards the occupants but the occupants are still affected by gravity and are accelerated downward into the vehicle too, the sum of the forces are what they feel.

Consider a vehicle putting out just enough thrust to hover, inside you would feel the local gravity field acceleration, any acceleration of the vehicle is going to be added to that, so if the vehicle accelerates upward at 1 g your going to feel 2 g inside.

Formula for how quickly the whole vehicle accelerates upward:  (Thrust - (Gravity * Mass) ) / Mass

Formula for the force felt inside the vehicle by passengers:  (((Thrust - (Gravity * Mass) ) / Mass ) + Gravity
which can be shortened by cancellation to just Thrust / Mass

Thus the passengers would experience a force of 4.2g when landing on Mars due to the expected landing mass of 200 mt, on Earth the landing mass is expected to be a lower 125 mt resulting in a higher 6.7g force, but this is due ONLY to the lower mass and has nothing to do with differences in gravity fields. 

And again I reiterate I expect throttle-down of rockets to give a gentler ~3g landing at all locations.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 05/29/2016 08:03 am

Impaler, the vehicle is also fighting against gravity, it's burning 1g just to stay up.

Hence, a rocket capable of accelerating at say 3g's will, using the same amount of thrust, accelerate linearly at 2g's relative to the ground while under a 1g gravitational acceleration in the opposite direction. The rocket (and passengers) will experience the same 3g's as they would in open space, even though the rocket is accelerating upwards linearly at 2g's from Earth.

A rocket capable of accelerating at 2g's will, using the same amount of thrust, linearly accelerate at 1g relative to the ground. The rocket and passengers will experience the same 2g's as they would in space, even though the rocket is rising at just 1g from Earth.

A rocket capable of accelerating at only 1g will not linearly accelerate relative to the ground. It will hover, making no net linear acceleration, and yet the rocket and the passengers experience the same 1g as they would in space.

And a rocket with its engines off will fall at 1g towards the ground (ignoring air resistance.) Yet the rocket and passengers will experience zero-g, just as if the rocket was drifting in space with its engines off, even though they are actually linearly accelerating at 1g relative to the ground. (Until they hit the ground.)

If you calculate that a rocket is capable of accelerating at 3.5g's in open space, then it will accelerate linearly at 2.5g's on Earth, and roughly 3.1g's on Mars. The rocket and crew will experience 3.5g's.

The rocket and crew will not experience 4.5g's (3.5+1) on Earth, unless the rocket increases its thrust to 4.5g's.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 05/29/2016 09:00 am
Paul re-read what your replying too, your simply reiterating my argument and producing the same result. 

envy887's original method was incorrect and I demonstrated why his subtraction of local gravity was wrong for g-force upon crew and he was instead calculating vehicle acceleration relative to the ground in his original post.

You seem to have misinterpreted my reply as saying that crew g-forces exceed what would be felt by firing the vehicle in open space, that is not the case as I stated the force is a simple Thrust / Mass relationship. 

The correct g-forces felt in envy887's hypothetical rocket are different from his original numbers due to correction, the values of 4.2g and 6.7g with 100 and 25 mt cargo loads respectively are the rockets acceleration in open-space given the stated thrust and vehicle mass.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 05/29/2016 04:03 pm

nadreck your forgetting that the passengers are not part of the vehicle, the vehicle acceleration upward towards the occupants but the occupants are still affected by gravity and are accelerated downward into the vehicle too, the sum of the forces are what they feel.

No we are in violent agreement here, it has nothing to do with the force of gravity, you cancel it out in your own equation. It was difference in payload that gave different results which was what I was looking for and had missed in the discussion. 

Gravity only enters into the calculation of what real acceleration your vehicle has relative to a point, but as long as the  vehicle is not on the ground it makes no difference what angle the craft is pointing at. Whatever the angle, if the engines are on the occupants feel an acceleration force equal to thrust/mass(including their own mass) if the engines are off they are in free fall. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 05/31/2016 07:18 am
To better understand the MCT (specifically the portion that lands on Mars often called the BFS) we should examine an Earth analog aircraft with a comparable payload.  The best analog is the 777F, the freight version of the Boeing 777.

http://www.boeing.com/commercial/aeromagazine/articles/qtr_02_09/article_02_1.html

http://www.boeing.com/assets/pdf/commercial/airports/acaps/777_2lr3er.pdf

The cargo capacity is 102 mt and cargo volume comes out to 635 m^3 even in the containers which means the interior volume of the vehicle is slightly higher due to square-ish containers not fully filling the round fuselage.  This yield a density of just 160 g/L, most people don't realize how low density most air cargo is and space cargo is likely to be comparably low density requiring high volume to utilize.

(http://theaviationspecialist.com/777F_CSECTION.jpg)


This gives us a good idea what kind of physical volume and containerization system is going to be needed for any kind of efficient logistics.  Now consider total vehicle cost, Musk expects to ultimately build rockets for about the same cost as jets and this one costs around $300 million, we can expect the Mars landing vehicle to have a per unit cost around that once produced in volume.  The mass is 144 mt empty which is a bit more then most are expecting for the BFS, if vehicle cost is directly proportional to dry weight then prices of $200 million would be consistent with at 100 mt dry mass, note that the per unit cost to make the Shuttle orbiter was around $200 million though that was decades ago with lots of inflation between then and now, it was certainly not the cost of a comparable jet aircraft of the day so this would be consistent with a considerable decline in price if a space vehicle matches a commercial aircraft in cost per pound.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 05/31/2016 12:53 pm
on Earth the landing mass is expected to be a lower 125 mt resulting in a higher 6.7g force, but this is due ONLY to the lower mass and has nothing to do with differences in gravity fields. 

And again I reiterate I expect throttle-down of rockets to give a gentler ~3g landing at all locations.

6.7g would be the vacuum burnout acceleration with 25t payload given my estimated vehicle parameters, but at Earth landing the ambient sea level pressure will reduce thrust. I estimated 230t SL and 280t vacuum thrusts, so unthrottled perceived acceleration would only be ~5.5g and local acceleration (relative to Earth's surface) would be ~4.5g assuming thrust and gravity are antiparallel.

I agree it would likely be throttled, not only to keep passengers happy, but to give more control authority.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Toast on 05/31/2016 02:55 pm
Humans can handle 8-9 gees just fine if oriented the correct way.

Not for very long, though.  NASA limited sustained gees on Apollo flights to 4.5 g and Shuttle flights to 3 g for very good physiological reasons.  Spacex should be aiming for a similar sustained g load for manned launches and reentries for the same reasons.

Sure, for long term/sustained... but ~4 g for a hoverslam landing just isn't that big of a deal at all.

To add to this, Soyuz capsules experience double that acceleration when landing (http://www.space.com/5574-rides-soyuz-spacecraft-rocky-risky.html), so it really isn't a problem so long as it's limited in duration.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 06/02/2016 04:59 am
@CNBCNow
SpaceX's Elon Musk says could launch flight to Mars with people aboard in 2024 and they would arrive in 2025. #CodeCon
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 06/02/2016 03:02 pm
@CNBCNow
SpaceX's Elon Musk says could launch flight to Mars with people aboard in 2024 and they would arrive in 2025. #CodeCon

Interesting. That particular deadline hasn't shifted for years - if anything, it's been progressively elaborated upon.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 06/03/2016 12:03 pm
After Elon's Mars schedule announcement, I was wondering about this (I don't know if this has been discussed before, I presume so but perhaps not in this specific context) :

A way to speed up the development of the first manned Mars mission (to keep up with the aggressive 2024/5 schedule) would be to bring molecular H to the Martian surface (which could also serve as a radiation shield on the way there). If the BFS must have a dV capacity of 6 km/s and has a dry mass of 200 tons, it will need about 800 tons of fuel for the return journey. Since only about 5% of a stochiometric Methane/LOX fuel is hydrogen, they could bring down about 40 tons of molecular H with each BFS, well within its payload capacity (of 100 tons). Even if we add a few percent of that for the mass of the tank, this is still very feasible.

All that the first SpaceX astronauts would then have to do after landing is react the H with the atmospheric CO2 in the Sabatier reaction - this could virtually been done without any human supervision or involvement. This is also a much simpler and cleaner (and less energy intensive) process than having the crew looking for water ice, digging it out, cleaning it, testing it for any potential chemical agents (e.g., peroxides, salts, etc.) and removing them before electrolysis, etc. This is also a technology that 1) is already in development and 2) would be reasonably easy to demonstrate with a precursor Red Dragon mission. The same cannot be said of actively digging for water ice on Mars.

While I am certain the plan is for a Mars base to eventually provide BFS's with fuel synthesized from martian water ice and atmospheric CO2, the very first landings could / should skip this step and bring the H from Earth instead.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/03/2016 01:12 pm
...
 Since only about 5% of a stochiometric Methane/LOX fuel is hydrogen, they could bring down about 40 tons of molecular H with each BFS, well within its payload capacity (of 100 tons). Even if we add a few percent of that for the mass of the tank, this is still very feasible.
...
40 tonnes of LH2 needs a 575 m^3 tank kept below 30K... the tankage and cooling are going to weigh a lot more than a few percent.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kch on 06/03/2016 01:36 pm
After Elon's Mars schedule announcement, I was wondering about this (I don't know if this has been discussed before, I presume so but perhaps not in this specific context) :

A way to speed up the development of the first manned Mars mission (to keep up with the aggressive 2024/5 schedule) would be to bring molecular H to the Martian surface (which could also serve as a radiation shield on the way there). If the BFS must have a dV capacity of 6 km/s and has a dry mass of 200 tons, it will need about 800 tons of fuel for the return journey. Since only about 5% of a stochiometric Methane/LOX fuel is hydrogen, they could bring down about 40 tons of molecular H with each BFS, well within its payload capacity (of 100 tons). Even if we add a few percent of that for the mass of the tank, this is still very feasible.

All that the first SpaceX astronauts would then have to do after landing is react the H with the atmospheric CO2 in the Sabatier reaction - this could virtually been done without any human supervision or involvement. This is also a much simpler and cleaner (and less energy intensive) process than having the crew looking for water ice, digging it out, cleaning it, testing it for any potential chemical agents (e.g., peroxides, salts, etc.) and removing them before electrolysis, etc. This is also a technology that 1) is already in development and 2) would be reasonably easy to demonstrate with a precursor Red Dragon mission. The same cannot be said of actively digging for water ice on Mars.

While I am certain the plan is for a Mars base to eventually provide BFS's with fuel synthesized from martian water ice and atmospheric CO2, the very first landings could / should skip this step and bring the H from Earth instead.

It's been mentioned:

https://en.wikipedia.org/wiki/Mars_Direct (https://en.wikipedia.org/wiki/Mars_Direct)

;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 06/03/2016 03:22 pm
@kch: sure, I am aware that the idea of bringing in H is from Mars Direct (and as such I should perhaps have said so), but I mean in the specific context of the BFS and speeding up the schedule to make a 2024/5 manned SpaceX mission to Mars feasible. ISRU is (well, presumably so) an integral part of the SpaceX architecture, but some of it (like digging up water ice) has very low technological readiness and this is unlikely to change before 2024/5. Also, consider that the initial crew would have to dig up 360 tons of water ice to produce the fuel, or 60 tons each if they are 6 astronauts.... Hard even if you bring some landmoving equipment....

Envy887 made an excellent point on the volume and cooling systems this would require. This is the kind of answer and input I was going after. A tank this size would only be 3 m high at 15 diameter for the BFS. Even if cooling etc take up 10 tons or more, at 100 tons total you still have some serious payload capacity left.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/03/2016 03:41 pm
Also, consider that the initial crew would have to dig up 360 tons of water ice to produce the fuel, or 60 tons each if they are 6 astronauts.... Hard even if you bring some landmoving equipment....

Worse.  :)

Elon Musk has once mentioned that crew would only be sent when return fuel is waiting for them. Not sure if this stands. If I had to decide I would opt for producing it during their 2 year stay. And prepare for worst case with 4 year supplies if anything goes wrong with production during this time. But that's just me and I have no say fortunately.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/03/2016 03:58 pm
@kch: sure, I am aware that the idea of bringing in H is from Mars Direct (and as such I should perhaps have said so), but I mean in the specific context of the BFS and speeding up the schedule to make a 2024/5 manned SpaceX mission to Mars feasible. ISRU is (well, presumably so) an integral part of the SpaceX architecture, but some of it (like digging up water ice) has very low technological readiness and this is unlikely to change before 2024/5. Also, consider that the initial crew would have to dig up 360 tons of water ice to produce the fuel, or 60 tons each if they are 6 astronauts.... Hard even if you bring some landmoving equipment....

Envy887 made an excellent point on the volume and cooling systems this would require. This is the kind of answer and input I was going after. A tank this size would only be 3 m high at 15 diameter for the BFS. Even if cooling etc take up 10 tons or more, at 100 tons total you still have some serious payload capacity left.

I really doubt that they won't have return an Earth return capability in place before they land (not necessarily 100% ready before they get there). So the first people going to Mars are to arrive with the capability to return to Earth already in place, or they bring it with them. To arrive to it already in place then the most likely scenario is that an automated ISRU system was sent the previous launch window and took nearly two years to produce enough propellant to return a single, occupied, MCT to Earth (one ton per day roughly). Note, I also consider that this is a back up plan only and that the arriving manned expedition plans to stay through the next return window, (though sending back as many craft as they can refuel less one kept in reserve for their return) and that more people and supplies arrive the next Earth - Mars window, and that by then there is more robust ISRU with more capacity, more habitat space and quite a bit of propellant stored up ready to send a large portion of the arriving craft back the following window, and probably some of the people from each expedition.

The other option is to land enough propellant on Mars for the ascent of the escape vehicle. This is possible, but not nearly as economical, potentially requiring one MCT to stay in low Mars Orbit with its payload of propellant that came from Earth and 3 or 4 cargo MCTs arriving with just propellant for the emergency ascent vehicle. The complexity of this is that propellant transfer from landed craft is required. The ISRU example might be accomplished with the ISRU MCT refueling itself and it being the emergency return vehicle not just an ascent to orbit vehicle.

As an aside there is an old song about a miner loading 16 tons of coal each day. I don't think they will be doing it by pick and shovel, but really they could, the power is more gating I think. Going from ISRU water and atmospheric CO2 to several hundred tons of propellant, only costs about 25% to 33% more power than going from transported H2 and atmospheric CO2 and still requires the electrolysis step on the water vapour produced in the Sabatier reaction. As well to get the proper mixture ratio of Oxygen to Methane you need to separate some oxygen from CO2 or collect local water, even if you brought hydrogen because going with the Sabatier reaction and electrolysing the water from that only gives you a stochiometric ratio.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/04/2016 12:24 am
Did Musk say humans would LAND on Mars, or just be sent TO Mars in 2024?  That later leaves open a purely orbital mission.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AC in NC on 06/04/2016 01:15 am
Did Musk say humans would LAND on Mars, or just be sent TO Mars in 2024?  That later leaves open a purely orbital mission.

He said "to".  Arriving in 2025.  Musk doesn't mince words so suspect strongly that Mars means the planet not an orbit around the planet.  Underpromise, Overdeliver. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 06/04/2016 08:47 am
Assuming its a landing in 2025, ISRU water from martian ground ice has still extremely low technological readiness, much less doing it fully automated (for prepositioning)! The energy required is also much more than the one needed for electrolysis, its also the digging itself, warming up the ice to form water (in a -55C environment), cleaning and chemically purifying it (by destillation?), etc. And all that without human supervision? If we take Elons requirement of prepositioned fuel serious, I see no other way than to bring in H with an unmanned mission in 2022/3 and producing the fuel during the two years that follow. In any case, this would mean the very first BFS landing to be in 2023 (I can't imagine a Red Dragon producing 800 tons of fuel....).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/04/2016 09:10 am
Assuming its a landing in 2025, ISRU water from martian ground ice has still extremely low technological readiness,

Supersonic Retropropulsion was too, until SpaceX just did it. I say with absolute confidence they will not transport H2 to Mars. That concept was always the weak spot of Mars direct by Robert Zubrin IMO. And he proposed that because at the time it was not known how much water there is on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 06/04/2016 01:15 pm
I would go as far as saying the trade-offs of transporting H2 offset the advantages of having a less complex ISRU system. It seems like a waste of volume and mass.

There's nothing inherently unproven about ISRU processes (it's well understood science after all), the problem is conducting the same familiar chemical processes on Mars, adapted to the unique conditions of the on-site martian materials. That's something surveying missions will help to answer and a role red dragon can fill.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 06/04/2016 01:22 pm
Another issue with ISRU is reliability. Can an unmanned mission fill the tanks before the system breaks down? Will a crew be required to do repairs, can the repairs be automated, or will there be enough redundancy?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 06/04/2016 02:00 pm
I don't think we can speak with confidence right now (in neighter direction), except if you had some insider knowledge.

Supersonic retropropulsion is close to the core competence of SpaceX, while teleoperation of ISRU units autonomously extracting water ice from soils on another planet isn't, really. But we will see in September.

Why do you think bringing down H to the surface is a weak point of Mars Direct? The motivation is not so much that there is no H on Mars, it's that this allows you to take one big unknown (how youw get from sub-surface dirty ice to CH4 in your tanks) out of the equation.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: the_other_Doug on 06/04/2016 02:29 pm
I'd think SpaceX would have a Plan A -- if the ISRU works fine and they'e pumping out fuel for the following synod -- and Plan B, if ISRU falls short for any reason.  And Plan B may have any number of sub-plans, to cope with a variety of potential issues.

As I've said on a number of occasions, we won't be able to intelligently address SpaceX's Mars architecture, including all Plans A, B, etc., until they announce it, hopefully this coming September.  And if what Chris has hinted about it is in any way representative, I think we'll have an awful lot to discuss then.

In any event, once we know what the architecture actually is, then we can see what the various plans are for cases where ISRU doesn't work as planned, or where not all of the planned pre-landed cargo makes it through, etc., etc.

So... while SpaceX may get plenty of kudos for landing the first humans on Mars, it will pretty much kill their colonization plans if those first humans end up on a one-way trip with no hope of either survival or return.  I'm therefore awfully confident that they will have anticipated most, if not all, of the obvious common-sense precautions we're all coming up with here, and will have plans in place to cope with those situations if they arise.  :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: su27k on 06/04/2016 02:48 pm
If ISRU didn't work for the first time, they'll just have to postpone the manned mission and try again, they don't have to make the 2024 date (and it may be delayed for other reasons anyway). The problem with LH2 is that it's a dead end for them, they don't plan to use it in the future so it would be just a waste of resources to develop it, unless someone else (ULA?) can provide a low cost turnkey solution.

I think ISRU would definitely be challenging for them, mainly because the feedback cycle is very long (2 years), they couldn't use their iterative test some/fix some approach easily. Maybe they'll need to send plan A/B/C together and test them one by one. Some capable telerobotics would also be very useful, I wonder if Elon is an investor in Boston Dynamics...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 06/04/2016 03:29 pm

 I wonder if Elon is an investor in Boston Dynamics...

That rings a bell - will do some searching and report back if it turns out to be factual.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: geza on 06/04/2016 03:40 pm
The other option is to land enough propellant on Mars for the ascent of the escape vehicle. This is possible, but not nearly as economical, potentially requiring one MCT to stay in low Mars Orbit with its payload of propellant that came from Earth and 3 or 4 cargo MCTs arriving with just propellant for the emergency ascent vehicle. The complexity of this is that propellant transfer from landed craft is required. The ISRU example might be accomplished with the ISRU MCT refueling itself and it being the emergency return vehicle not just an ascent to orbit vehicle.
The emergency ascent spacecraft can be very small, like a Dragon, without the heat-shield and SDs. Launch it to reach the Earth-return MCT in low Mars orbit will not require an enormous amount of fuel. If the capsule + ascent stage is 10 t dry, then 30 t wet is enough. The ascent stage can be derived (shortened) from F9 second stage, so the ascent vechicle need not be developed from scratch. A single MCT can land the fueled ascent vechicle together with extra cargo, or even the hab modul.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: pobermanns on 06/04/2016 03:43 pm
So... while SpaceX may get plenty of kudos for landing the first humans on Mars, it will pretty much kill their colonization plans if those first humans end up on a one-way trip with no hope of either survival or return.  I'm therefore awfully confident that they will have anticipated most, if not all, of the obvious common-sense precautions we're all coming up with here, and will have plans in place to cope with those situations if they arise.  :)

Dumb question - if the first people there had some really serious problem, that would force them to evacuate after the return launch window ended and before the next synod started, would they even be able to return?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/04/2016 04:00 pm

 I wonder if Elon is an investor in Boston Dynamics...

That rings a bell - will do some searching and report back if it turns out to be factual.

Google bought Boston Dynamics in 2013 and has put it up for sale now (http://www.bloomberg.com/news/articles/2016-03-17/google-is-said-to-put-boston-dynamics-robotics-unit-up-for-sale) (and it looks like Toyota might buy (https://www.google.ca/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=boston+dynamics+sale&tbm=nws&tbs=sbd:1))
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/04/2016 04:06 pm
Why do you think bringing down H to the surface is a weak point of Mars Direct? The motivation is not so much that there is no H on Mars, it's that this allows you to take one big unknown (how youw get from sub-surface dirty ice to CH4 in your tanks) out of the equation.

Because storing LH is hard. SpaceX avoids it for their propulsion for a good reason. They won't introduce it through the back door, that's my rationale.

Water ISRU is a problem that needs solving. Not only for a future colony with many people. Even NASA included it in their Mars mission architecture. And that's for a small group of astronauts. It is much more important for SpaceX because I am sure even their first group will be much bigger than NASA plans for.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: nadreck on 06/04/2016 04:25 pm
The other option is to land enough propellant on Mars for the ascent of the escape vehicle. This is possible, but not nearly as economical, potentially requiring one MCT to stay in low Mars Orbit with its payload of propellant that came from Earth and 3 or 4 cargo MCTs arriving with just propellant for the emergency ascent vehicle. The complexity of this is that propellant transfer from landed craft is required. The ISRU example might be accomplished with the ISRU MCT refueling itself and it being the emergency return vehicle not just an ascent to orbit vehicle.
The emergency ascent spacecraft can be very small, like a Dragon, without the heat-shield and SDs. Launch it to reach the Earth-return MCT in low Mars orbit will not require an enormous amount of fuel. If the capsule + ascent stage is 10 t dry, then 30 t wet is enough. The ascent stage can be derived (shortened) from F9 second stage, so the ascent vechicle need not be developed from scratch. A single MCT can land the fueled ascent vechicle together with extra cargo, or even the hab modul.

Fleshing this out a little more:

First, I am happy to entertain this for the first expedition so that they can leave scale ISRU until people are there.

2nd, for this to be worth more savings than the cost of sending enough propellant for an MCT return, the development has to be truly minimal, as well the development of this becomes critical path for the Mars Mission and either has to fly with the 2024 armada or the window before.

3rd, having a single one of these limits the first expedition crew to 7 (presuming that is still the maximum complement on a D2) 2 limit it to 14.  By the time you have 2 the development cost really has to be just about zero because 3 or 4 and you just use MCTs to ferry propellant down for 1 MCT to make orbit again.

technical difficulties that may push the development from minimal to too complex to be worth doing:

1. Modifying MCT to not only accommodate and land this craft without damaging it but to support its launch
2. keeping RP-1 from freezing/gelling (doable but needs design and development work)
3. modifying D2 to have the lifespan needed for this (going from nominally 9 months or so to 4 years)
4. modifying Falcon S2 to short length required
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/04/2016 05:41 pm
Check L2 and tell me that SpaceX isn't seriously looking at how to process water for ISRU on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CuddlyRocket on 06/04/2016 05:43 pm
Assuming its a landing in 2025, ISRU water from martian ground ice has still extremely low technological readiness, much less doing it fully automated (for prepositioning)! The energy required is also much more than the one needed for electrolysis, its also the digging itself, warming up the ice to form water (in a -55C environment), cleaning and chemically purifying it (by destillation?), etc. And all that without human supervision? If we take Elons requirement of prepositioned fuel serious, I see no other way than to bring in H with an unmanned mission in 2022/3 and producing the fuel during the two years that follow.

You cane extract water from the Martian atmosphere. It requires power (you get about 1.5 kg/kW/sol, if I remember correctly), but the equipment is not particularly massive. It has the advantage of simplicity (little need for purification) and may be preferable for initial missions, switching to local mined water once it has been located and characterised etc.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/04/2016 05:46 pm
SpaceX is definitely going to do water ISRU. Here are some of the early instruments that are proposed to fly on Red Dragon:
http://digitalvideo.8m.net/SpaceX/RedDragon/karcz-red_dragon-nac-2011-10-29-1.pdf
slide 8
"Water extraction system &
propellant production system.
HEOMD funded KSC & JSC
ISRU activity at TRL 5."

And Musk has said they want robotic mining to produce propellant on Mars. You cannot get more direct than that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Elmar Moelzer on 06/04/2016 08:16 pm
Another interesting tidbit to take away from the RecodeDotNet interview with Musk is that the trip will (initially) take less than 90 days. We should be able to deduct how much propellant would be needed to do such a short trip time with that much payload. He also said that they want to get to shorter trips (less than 30 days) at a later time. I presume that this would require some change to the whole architecture, though.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/04/2016 09:11 pm
Another interesting tidbit to take away from the RecodeDotNet interview with Musk is that the trip will (initially) take less than 90 days. We should be able to deduct how much propellant would be needed to do such a short trip time with that much payload. He also said that they want to get to shorter trips (less than 30 days) at a later time. I presume that this would require some change to the whole architecture, though.

If the BFS is the second stage to the BFR it needs about 5.5 - 6.5 km/s of delta-v, this is enough to give 90-120 days transit to Mars for most synods. If the BFS also carries extra tankage, so that it can act as a tanker carrying 100+ tonnes of extra propellant to LEO, then it should be able to do 90 day transits to Mars on most if not all synods. Some of these transits have high entry velocities at Mars which might be too much for the thermal protection system (but as we know little about such details it is impossible to say whether this is the limiting factor.

The journey back might be a different matter. I've tried and failed to work out a consistent set of trajectories which allow next synod reuse and allow return with 25 tonnes of payload and have 90-120 day transits. Some synods seem easy, others do not seem to allow next synod reuse without about 9 km/s delta-v and extremely high entry velocities.

Cargo flights can have relaxed delta-v requirements, but still need relatively fast transits to allow next synod reuse.

One limiting factor is how fast they can unload cargo, refuel and refly the BFS on Mars. Return is much easier if this can be a few days, rather than a few months.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/04/2016 09:16 pm
Assuming its a landing in 2025, ISRU water from martian ground ice has still extremely low technological readiness, much less doing it fully automated (for prepositioning)! The energy required is also much more than the one needed for electrolysis, its also the digging itself, warming up the ice to form water (in a -55C environment), cleaning and chemically purifying it (by destillation?), etc. And all that without human supervision? If we take Elons requirement of prepositioned fuel serious, I see no other way than to bring in H with an unmanned mission in 2022/3 and producing the fuel during the two years that follow.

You cane extract water from the Martian atmosphere. It requires power (you get about 1.5 kg/kW/sol, if I remember correctly), but the equipment is not particularly massive. It has the advantage of simplicity (little need for purification) and may be preferable for initial missions, switching to local mined water once it has been located and characterised etc.

The equipment may not be particularly massive, but it is large as you have to process a lot of Martian atmosphere (both volume and mass as the martian atmosphere is thin and very dry).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/04/2016 09:27 pm
The other option is to land enough propellant on Mars for the ascent of the escape vehicle. This is possible, but not nearly as economical, potentially requiring one MCT to stay in low Mars Orbit with its payload of propellant that came from Earth and 3 or 4 cargo MCTs arriving with just propellant for the emergency ascent vehicle. The complexity of this is that propellant transfer from landed craft is required. The ISRU example might be accomplished with the ISRU MCT refueling itself and it being the emergency return vehicle not just an ascent to orbit vehicle.
The emergency ascent spacecraft can be very small, like a Dragon, without the heat-shield and SDs. Launch it to reach the Earth-return MCT in low Mars orbit will not require an enormous amount of fuel. If the capsule + ascent stage is 10 t dry, then 30 t wet is enough. The ascent stage can be derived (shortened) from F9 second stage, so the ascent vechicle need not be developed from scratch. A single MCT can land the fueled ascent vechicle together with extra cargo, or even the hab modul.

Fleshing this out a little more:

First, I am happy to entertain this for the first expedition so that they can leave scale ISRU until people are there.

2nd, for this to be worth more savings than the cost of sending enough propellant for an MCT return, the development has to be truly minimal, as well the development of this becomes critical path for the Mars Mission and either has to fly with the 2024 armada or the window before.

3rd, having a single one of these limits the first expedition crew to 7 (presuming that is still the maximum complement on a D2) 2 limit it to 14.  By the time you have 2 the development cost really has to be just about zero because 3 or 4 and you just use MCTs to ferry propellant down for 1 MCT to make orbit again.

technical difficulties that may push the development from minimal to too complex to be worth doing:

1. Modifying MCT to not only accommodate and land this craft without damaging it but to support its launch
2. keeping RP-1 from freezing/gelling (doable but needs design and development work)
3. modifying D2 to have the lifespan needed for this (going from nominally 9 months or so to 4 years)
4. modifying Falcon S2 to short length required

I can't see SpaceX doing this, it is technically possible, but for an emergency ascent craft, it adds lots of new systems and complexity for something that is not likely to be used.

Much more likely in my opinion is to assume that ISRU works, assume that if it doesn't work robotically then with crew on the scene it can be made to work, if both of those fail supply enough consumables so that there is no chance of the crew dying until further missions can be sent (with improved ISRU and more provisions). A single MCT cargo flight of 100 tonnes is the equivalent of 30 Dragon cargo flights to the ISS, and would provide the initial crew with many years worth of provisions, there is no possibility of them running out of food or other essentials.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/04/2016 09:50 pm
The schedule for 2024 is very tight.

Raptor is probably on the critical path at present.

Design and development through the equivalent of PDR and CDR.

The factory: finding a site, permitting, building it, installing and commissioning equipment. Then using it to build the BFS and BFR.

The launch site: intimately connected with the factory, permits, building it, commissioning.

ECLS: design and testing, reliability takes time to build up.

Avionics and Software: lots of flight modes for BFR, BFS tanker, BFS cargo and BFS crew. Takes time to develop.

Any or all could be on the critical path.

Then after the first BFR/BFS first flight there needs to be a period of testing in LEO and cis-lunar space. Several flights checking out refuelling, ECLS, ops, etc. while building up confidence in the launch and reuse processes.

SpaceX are going to be very busy.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 06/04/2016 10:01 pm
@Robobeat: if you read my first post on the matter carefully, I am not suggesting they are not persueing eventual ISRU of Martian water. Bringing in H would just be an interim solution until full scale ISRU is capable of providing the necessary fuel. How exactly are they going about scraping up 100s of tons of ice robotically for each return mission, processing it and all - and without any humans supervising the process? I just don't see this happening in 9 years. You'd probably need multiple design iterations for the entire process to work, and there are only 3 transfer windows left before the process *has* to work if the 2024/5 mission date is to be met. On the other hand, the H + CO2 approach can easily be tested on Earth.

The 2011 proposal for possible payloads on Red Dragon is a NASA idea, not SpaceX. Also, it is unclear how the water extraction system mentioned there would work - drilling, or from the atmosphere? At least the former is unlikely to be scaleable to 360 tons of water....

Finally, extracting water from air (as mentioned by CuddlyRocket) might indeed be a good alternative to bringing down H. This seems much simpler than digging for  ice, but the question is whether you could produce enough fuel. At 700 sols and 1.5 kg/kW/sol, you'd need 340 kW of continous  power for extraction of 360 tons of water (!).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bob Shaw on 06/04/2016 10:13 pm
There are always nay-sayers regarding the business of ISRU on Mars, with the whole business of water mining being dismissed as 'too difficult'. I wonder if we're not exploiting the environmental properties of Mars sufficiently, however.

I'm thinking of an almost passive distillation water-mine, where broken-up winter temperature perchlorate-rich ice is shovelled into a large vessel, which is heated in the summer by sunshine. The ice sublimates, and the water-laden air rises into a second, insulated  chamber which is never allowed to heat beyond winter temperatures and where it freezes out as rime or snow. You harvest the output, and perhaps distill again.

My starting point for this was the thought of the traditional adiabatic atmospheric 'springs' constructed in various Earth deserts using no resources other than piles of rock and a knowledge of the local winds. Obviously, Mars is different, but low-tech solutions would be a good tradeoff, using scarce imported resources only where needed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/04/2016 10:49 pm
How exactly are they going about scraping up 100s of tons of ice robotically for each return mission, processing it and all - and without any humans supervising the process?

We don't know. There are 4 possible sources of water on Mars: ice (glaciers, etc.), brine aquifers, hydrated minerals (various types and concentrations) and the atmosphere. These all have various advantages and disadvantages which vary between landing sites, power supply (solar or nuclear), and things like how much water is needed, what the growth rate and potential is, other base needs (water, heat, electricity, process heat, mining).

We don't know that any water mining will be done robotically, that is an assumption based on the rather dubious proposition that SpaceX won't send a crew until there is a fully fueled return BFS waiting on the martian surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/04/2016 10:54 pm
There are always nay-sayers regarding the business of ISRU on Mars, with the whole business of water mining being dismissed as 'too difficult'. I wonder if we're not exploiting the environmental properties of Mars sufficiently, however.

I'm thinking of an almost passive distillation water-mine, where broken-up winter temperature perchlorate-rich ice is shovelled into a large vessel, which is heated in the summer by sunshine. The ice sublimates, and the water-laden air rises into a second, insulated  chamber which is never allowed to heat beyond winter temperatures and where it freezes out as rime or snow. You harvest the output, and perhaps distill again.

My starting point for this was the thought of the traditional adiabatic atmospheric 'springs' constructed in various Earth deserts using no resources other than piles of rock and a knowledge of the local winds. Obviously, Mars is different, but low-tech solutions would be a good tradeoff, using scarce imported resources only where needed.

Day/night temperature swings probably would be enough, that would allow a far greater volume of water to be collected.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 06/04/2016 11:01 pm
We don't know that any water mining will be done robotically, that is an assumption based on the rather dubious proposition that SpaceX won't send a crew until there is a fully fueled return BFS waiting on the martian surface.
The idea (originating from Mars Direct) was to ensure the safety of the crew.

As Zubrin said in "The Case for Mars" (pg. 70-71):
"To ensure our Mars crew would not be stranded, the ERV would fly one launch opportunity, or twenty-six months, prior to the launch of the astronauts. Thus all the propellant would be made before the crew ever left Earth, and since the propellant plant was flown to Mars integrated with the ERV there was no question about landing 'within a hose length.' The plumbing that would deliver the Mars-manufactured propellant from the chemical synthesis unit into the ERV's fuel tanks would be hardwired, installed on Earth."

"if the ERV [Earth Return Vehicle] is sent first, the crew will know before they even leave Earth that they have a fully functional Mars ascent and Earth return system waiting for them on the Martian surface, one that has already survived the trauma of landing. In contrast, a crew that lands with their ascent system can only guess in what shape their Mars ascent vehicle will be after they've hit the surface."

SpaceX did test fire F9 engines after they've been through supersonic retropropulsion in conditions relevant to Mars EDL systems development, so the latter might not be a problem.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bob Shaw on 06/04/2016 11:23 pm
There are always nay-sayers regarding the business of ISRU on Mars, with the whole business of water mining being dismissed as 'too difficult'. I wonder if we're not exploiting the environmental properties of Mars sufficiently, however.

I'm thinking of an almost passive distillation water-mine, where broken-up winter temperature perchlorate-rich ice is shovelled into a large vessel, which is heated in the summer by sunshine. The ice sublimates, and the water-laden air rises into a second, insulated  chamber which is never allowed to heat beyond winter temperatures and where it freezes out as rime or snow. You harvest the output, and perhaps distill again.

My starting point for this was the thought of the traditional adiabatic atmospheric 'springs' constructed in various Earth deserts using no resources other than piles of rock and a knowledge of the local winds. Obviously, Mars is different, but low-tech solutions would be a good tradeoff, using scarce imported resources only where needed.

Day/night temperature swings probably would be enough, that would allow a far greater volume of water to be collected.

Very possibly. I was being as conservative as possible! The point is, where there is an energy gradient, work can be extracted in one form or another. Diurnal or seasonal, the resource is there, and simple solar heating is astonishingly cheap (black paint).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CuddlyRocket on 06/04/2016 11:50 pm
We don't know that any water mining will be done robotically, that is an assumption based on the rather dubious proposition that SpaceX won't send a crew until there is a fully fueled return BFS waiting on the martian surface.
The idea (originating from Mars Direct) was to ensure the safety of the crew.

As Zubrin said in "The Case for Mars" (pg. 70-71):
"To ensure our Mars crew would not be stranded, the ERV would fly one launch opportunity, or twenty-six months, prior to the launch of the astronauts. Thus all the propellant would be made before the crew ever left Earth, and since the propellant plant was flown to Mars integrated with the ERV there was no question about landing 'within a hose length.' The plumbing that would deliver the Mars-manufactured propellant from the chemical synthesis unit into the ERV's fuel tanks would be hardwired, installed on Earth."

"if the ERV [Earth Return Vehicle] is sent first, the crew will know before they even leave Earth that they have a fully functional Mars ascent and Earth return system waiting for them on the Martian surface, one that has already survived the trauma of landing. In contrast, a crew that lands with their ascent system can only guess in what shape their Mars ascent vehicle will be after they've hit the surface."

SpaceX did test fire F9 engines after they've been through supersonic retropropulsion in conditions relevant to Mars EDL systems development, so the latter might not be a problem.

The ERV doesn't have to be fully fuelled before the crew leaves Earth. It merely needs to have landed safely and be producing propellant at a rate that means it will be fully fuelled by the time the crew needs to use it to launch back to Earth. No doubt there will be margins to take account of any possible breakdown after the crew has set off for Mars. Set against that is the possibility of the crew making repairs and the additional output of any further ISRU equipment they bring with them. If additional margins and/or redundancy is required you can always send two ERVs on the first trip, or perhaps an ERV and a dedicated ISRU propellant production lander.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 06/04/2016 11:57 pm
I am pretty sure there is something very wrong with this idea, but I cannot see it. Send an early MCT with most of it's cargo as water. Include some pumps and soft insulated containers that could be set on the ground and pumped full. Design them to withstand freezing and also have the capability to electrically melt the ice. The goal for the arrivers can still be to mine the water locally, with a back up source for ISRU and consumption.

No need for cryogenic storage of H2.

Having 90 tons or so of pure water as a contingency might be worth the price of tying up an expensive space ship for two plus years. The water MCT could also be a test mission without having any expensive gear at risk, with water as a sort of a mass simulator.

Matthew

Edited for a stray 'O' and to add the bit about H2
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/04/2016 11:57 pm
SpaceX is definitely going to do water ISRU. Here are some of the early instruments that are proposed to fly on Red Dragon:
http://digitalvideo.8m.net/SpaceX/RedDragon/karcz-red_dragon-nac-2011-10-29-1.pdf
slide 8
"Water extraction system &
propellant production system.
HEOMD funded KSC & JSC
ISRU activity at TRL 5."

And Musk has said they want robotic mining to produce propellant on Mars. You cannot get more direct than that.

Musk will have enslaved an entirely robotic populated planet.  Without their bio-masters present don't be surprised if there isn't a revolution.  You've been warned!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bob Shaw on 06/05/2016 12:02 am
I am pretty sure there is something very wrong with this idea, but I cannot see it. Send an early MCT with most of it's cargo as water. Include some pumps and soft insulated containers that could be set on the ground and pumped full. Design them to withstand freezing and also have the capability to electrically melt the ice. The goal for the arrivers can still be to mine the water locally, with a back up source for ISRU and consumption.

No need for cryogenic storage of H2.

Having 90 tons or so of pure water as a contingency might be worth the price of tying up an expensive space ship for two plus years. The water MCT could also be a test mission without having any expensive gear at risk, with water as a sort of a mass simulator.

Matthew

Edited for a stray 'O' and to add the bit about H2

Indeed. The early landers might even be repurposed as water distillation vats, or as gasometers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bob Shaw on 06/05/2016 12:04 am
I, for one, wish to be among the first to welcome our new overlords... ...just sayin'.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/05/2016 01:13 am
@Robobeat: if you read my first post on the matter carefully, I am not suggesting they are not persueing eventual ISRU of Martian water. Bringing in H would just be an interim solution until full scale ISRU is capable of providing the necessary fuel. How exactly are they going about scraping up 100s of tons of ice robotically for each return mission, processing it and all - and without any humans supervising the process?
That's like a few hundred pounds a day if spread over a year. Not that bad. I could definitely see it done using scaled up versions of some mining rovers I've seen.
Quote
I just don't see this happening in 9 years. You'd probably need multiple design iterations for the entire process to work, and there are only 3 transfer windows left before the process *has* to work if the 2024/5 mission date is to be met.....
Yeah, and they're going to utilize each one. 2024/5 doesn't leave a lot of margin, but that's the "if everything goes according to plan" date. When Musk gives that kind of date, usually it's the earliest it can be done, not the "we'll definitely be able to do it by then" date. Which means you should probably expect it to slip.

But again, Musk has repeatedly said they're going to mine water. I really don't think they'll mess around with liquid hydrogen. Instead, they'll double-down on getting water extraction to work. And some of that they can test here on Earth before sending it to Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: the_other_Doug on 06/05/2016 03:16 pm
SpaceX is definitely going to do water ISRU. Here are some of the early instruments that are proposed to fly on Red Dragon:
http://digitalvideo.8m.net/SpaceX/RedDragon/karcz-red_dragon-nac-2011-10-29-1.pdf
slide 8
"Water extraction system &
propellant production system.
HEOMD funded KSC & JSC
ISRU activity at TRL 5."

And Musk has said they want robotic mining to produce propellant on Mars. You cannot get more direct than that.

Musk will have enslaved an entirely robotic populated planet.  Without their bio-masters present don't be surprised if there isn't a revolution.  You've been warned!

And it now comes out -- the reason why Musk is so paranoid about AI becoming sentient and turning against us!  He's planning on creating a robotic serving class on Mars, and is afraid of the robot servitors fomenting rebellion... ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 06/05/2016 04:24 pm
Quote
I just don't see this happening in 9 years. You'd probably need multiple design iterations for the entire process to work, and there are only 3 transfer windows left before the process *has* to work if the 2024/5 mission date is to be met.....
Yeah, and they're going to utilize each one. 2024/5 doesn't leave a lot of margin, but that's the "if everything goes according to plan" date. When Musk gives that kind of date, usually it's the earliest it can be done, not the "we'll definitely be able to do it by then" date. Which means you should probably expect it to slip.

But again, Musk has repeatedly said they're going to mine water. I really don't think they'll mess around with liquid hydrogen. Instead, they'll double-down on getting water extraction to work. And some of that they can test here on Earth before sending it to Mars.

I agree they are going to mine water - eventually. And I am sure they will bring in some equipment towards that end as soon as possible. Some of the technology to do this can indeed be tested on Earth, but the conditions on Mars (chemistry of the water ice, extent of the ice in the ground, hardness of the ground, other reactive species present etc.) are all unknown and will likely remain so up until the first (unmanned) BFS mission is sent (even if you send a Red Dragon to scout). There are so many things that can go wrong, and if the entire process is only, say, 20% slower than thought, it means you will have to skip an entire window. However, once you have humans in place, this kind of thing (scouting for new ice, testing it, adopting the technology to account for reactants in the ice, etc.) is relatively easy to do. Developing the whole process to work completely robotically, building in all the necessary margins, for a process that will, at a later date, be supervised by humans anyway, is in my view a waste of resources.

On the other hand, the capability to bring in tanked H to jump-start fuel production can be used again whenever a new site is opened on Mars (and not all sites might have readily available ground ice). The crew bringing their own return fuel is also a more conservative approach than having to rely on locally produced fuel (what happens if there is, e.g., an explosion in the fuel factory while the first manned BFS is on its way to Mars?). Sure, something might happen to the H on the way to Mars too, but usually if there is a problem with the BFS, they are in big trouble anyway.

But of course I might be wrong. I just think it would be a way to enable a landing sooner (2024/5) rather than later, because the most cumbersome part of ISRU on Mars, robotic ice mining, can be skipped and the fuel can be produced cleanly and completely with "on board" means. We will see in September. :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 06/05/2016 05:22 pm
The fleet aspect of MCT seems to be unduly neglected in this early ISRU discussion, imo.

Suggest that BFS will only do solo missions in cis-lunar.

Suggest that even the first BFS sent to Mars will be at least a couple of vessels, for example a cargo version (which is tasked with landing, unloading and getting back to orbit and then returning to Earth), and a tanker version (bigger built-in or maybe "as-cargo" tanks), which then could be left in Mars orbit (as a fuel depot for the cargo BFS before/after landing, a spare parts source and a comms relay) until ISRU fuel is available.

Obviously, a fleet of two leaves the cargo BFS for a solo voyage, which might be acceptable for early missions or when there's no people or precious cargo on board. Suggest that fleet is more than two, though...

"Land the whole thing" does not imply every "thing" lands, while "want them back" implies, imho, "for reuse", so if the "thing" can be "reused" at Mars... When the ISRU hits production scale at the surface (in a couple of synods?) there might be some use for BFS tankers, apart from getting themselves fueled and sent to Earth, that is.

How viable would be a rendezvous and docking between two spacecraft after their separate (coordinated, synchronised?) TMI / TEI burns?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 06/05/2016 05:36 pm
In line with the philosophy of reuse mfck articulated...

I could see the MCT being "partially strippable"... if you had cabins for 100, but are only returning 20 people why carry all of that back? if the fittings, panels, wiring, plumbing etc was designed to be modular and reusable it could be removed by humans and used in outfitting the base.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/05/2016 05:56 pm
We don't know that any water mining will be done robotically, that is an assumption based on the rather dubious proposition that SpaceX won't send a crew until there is a fully fueled return BFS waiting on the martian surface.
The idea (originating from Mars Direct) was to ensure the safety of the crew.

As Zubrin said in "The Case for Mars" (pg. 70-71):
"To ensure our Mars crew would not be stranded, the ERV would fly one launch opportunity, or twenty-six months, prior to the launch of the astronauts. Thus all the propellant would be made before the crew ever left Earth, and since the propellant plant was flown to Mars integrated with the ERV there was no question about landing 'within a hose length.' The plumbing that would deliver the Mars-manufactured propellant from the chemical synthesis unit into the ERV's fuel tanks would be hardwired, installed on Earth."

"if the ERV [Earth Return Vehicle] is sent first, the crew will know before they even leave Earth that they have a fully functional Mars ascent and Earth return system waiting for them on the Martian surface, one that has already survived the trauma of landing. In contrast, a crew that lands with their ascent system can only guess in what shape their Mars ascent vehicle will be after they've hit the surface."

SpaceX did test fire F9 engines after they've been through supersonic retropropulsion in conditions relevant to Mars EDL systems development, so the latter might not be a problem.

The ERV doesn't have to be fully fuelled before the crew leaves Earth. It merely needs to have landed safely and be producing propellant at a rate that means it will be fully fuelled by the time the crew needs to use it to launch back to Earth. No doubt there will be margins to take account of any possible breakdown after the crew has set off for Mars. Set against that is the possibility of the crew making repairs and the additional output of any further ISRU equipment they bring with them. If additional margins and/or redundancy is required you can always send two ERVs on the first trip, or perhaps an ERV and a dedicated ISRU propellant production lander.

I say dubious for several reasons. Firstly Zubrin's Mars Direct architecture is very different, you cannot throw out all the rest of the Mars Direct architecture and just kept the fully fuelled return vehicle (at least not without arguments based on the MCT architecture).

Secondly, Mars will be a very safe place for the crew, they will have access to several BFS (cargo and crew), hundreds of tonnes of supplies, equipment and habs, access to ISRU resources and the ability to be resupplied from Earth. In contract the return journey is likely to be relatively hazardous, the hab is relatively light at 25 tonnes, there are solar storms, Earth EDL and a BFS which has been sitting in the martian environment for a couple of years. Just having a fuelled BFS does not mean the crew can return in it, checkout before launch could turn up any number of problems.

Thirdly, the robotics is hard and is special purpose to the initial landing. It is probably at least an order of magnitude (perhaps two orders of magnitude) harder than Curiosity. The robotics would almost certainly be the long pole with a 2022 launch this would be really hard. The chances are that it would not work perfectly the first time. Correcting the robotics could easily take several attempts, each of which are hard to do before launch of the next synod. Worst case SpaceX could take a decade before they got the ISRU robotics correct, each year burning through a $1B or two.

Fourthly, it is likely that more than one FBS would be needed for the power supply (solar or nuclear), power supply deployment, mining robotics, ISRU, tanks etc. The FBS containing the return hab might be another craft. These BFS may have to land a considerable distance apart 100+ meters, due to landings (and even more take offs) throwing up rocks.

To sum up waiting for a fully fueled return FBS before sending crew is an assumption, the analysis above suggests it is a rather dubious assumption.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 06/05/2016 05:57 pm
Go back to that Max Fagin (former SpaceX intern) retropropulsion thesis defense video.

Whole vehicle lands, but only an upper portion returns to Earth. If the propulsion is in the upper portion (Dragon 2 heritage) the left behind cargo section can be used for most anything; habitation, cargo, or perhaps a dual  purpose.

How about some stripped down cargo sections hauling expandable & repurposeable tanks full of distilled water (thinking Thin Red Line's expandable tank tech.) AKA, 'how to ship hydrogen and oxygen without cryocoolers', and the cargo bay volume could be repurposed for colony use later.

http://m.youtube.com/watch?v=GQueObsIRfI
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/05/2016 06:03 pm
Go back to that Max Fagin (former SpaceX intern) retropropulsion thesis defense video.

Whole vehicle lands, but only an upper portion returns to Earth. If the propulsion is in the upper portion (Dragon 2 heritage) the left behind cargo section can be used for most anything; habitation, cargo, or perhaps a dual  purpose.

How about some cargo sections hauling expandable & repurposeable tanks full of distilled water (thinking Thin Red Line's expandable tank tech.) AKA, 'how to ship hydrogen and oxygen without cryocollers', and the cargo bay volume vould be repurposed for colony use later.

Maybe, but his thesis will probably be deliberately different from the MCT architecture so as to not appropriate SpaceX IPR.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 06/05/2016 06:04 pm
Thirdly, the robotics is hard and is special purpose to the initial landing. It is probably at least an order of magnitude (perhaps two orders of magnitude) harder than Curiosity. The robotics would almost certainly be the long pole with a 2022 launch this would be really hard. The chances are that it would not work perfectly the first time. Correcting the robotics could easily take several attempts, each of which are hard to do before launch of the next synod. Worst case SpaceX could take a decade before they got the ISRU robotics correct, each year burning through a $1B or two.
I think this is a valid concern but I am expecting Musk thinks he can hack this in time. Asked about driving AI he called it a "solved problem" and said widespread class 4 (handless, not requiring attention) driving was 2 years away technically.  So maybe he thinks ISRU robotics won't be that hard? You'd expect a lot more visible precursor work but if there is work going already, SpaceX is very tightlipped about it!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/05/2016 06:15 pm
Thirdly, the robotics is hard and is special purpose to the initial landing. It is probably at least an order of magnitude (perhaps two orders of magnitude) harder than Curiosity. The robotics would almost certainly be the long pole with a 2022 launch this would be really hard. The chances are that it would not work perfectly the first time. Correcting the robotics could easily take several attempts, each of which are hard to do before launch of the next synod. Worst case SpaceX could take a decade before they got the ISRU robotics correct, each year burning through a $1B or two.
I think this is a valid concern but I am expecting Musk thinks he can hack this in time. Asked about driving AI he called it a "solved problem" and said widespread class 4 (handless, not requiring attention) driving was 2 years away technically.  So maybe he thinks ISRU robotics won't be that hard? You'd expect a lot more visible precursor work but if there is work going already, SpaceX is very tightlipped about it!

Autonomous driving is one of the easier ISRU robotics problems, unlike Earth the environment is very static, however Tesla are gathering 1M miles of driving data every 10 hours to use for training, spotting corner cases, etc. there is hardly any equivalent data for Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 06/05/2016 06:46 pm
Why would one complicate ISRU with driving robots, excuse me my bluntness? Wouldn't it be more prudent to plan for ISRU capability be as plain and as independent of anything as possible?

Something along the lines of a self-contained chemical plant, that melts into a glacier, at landing point, brought as is by a BFS. Maybe two, one for the nuclear reactor to power it. Once you got that thing going, you can drive around all you want ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/05/2016 06:59 pm
It's not as if no thought has gone into mining regolith before. There are sthudent regolith mining competitions held every year (I visited one a few weeks ago). NASA has built a bunch of prototype rovers to test mining techniques (I saw some at Glenn Research Center). Even private companies like Astrobotic have developed and tested rovers for mining regolith.

And of course, there's the entire terrestrial mining community which has put billions into autonomous and remote mining tech.

We're not starting from scratch, here, it's just there hasn't been a good cheap ride to Mars before Red Dragon.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 06/05/2016 07:21 pm
The point about driving AI is not driving per se, although that's a useful part of the overall problem... it's that they implemented something that learns.

IF SpaceX end up needing to dig for water, rather than just being able to drill into something and tap enough water via in situ heating or whatever, then I'd predict they use the learning part of the Tesla SW, but adapted to also handle things like bucket load operations, drilling, dumping, etc. Whenever a unit gets stuck or stuck on how to proceed (two different things) and phones home for help, the moves used to unstick things get high weight in learnings, but all moves even those the system comes up with, are evaluated and feed back into the routines. maybe randomize choices a bit and evaluate how well that choice did. Simulated annealing writ large.

with two years of learning time the units might be better than when they arrived...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/06/2016 01:27 am
If they simply install a large (but very lightweight) crane somewhere with lots of water in the soil, the crane base wouldn't need to move but could still mine thousands of tons of water. This would be pretty easy to automate.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/06/2016 02:39 am
Remember Mars has a atmosphere and has water cycles (water vapor and water ice, does not have liquid phase). So to mine all the water you need, you compress the air and liquefy the water vapor in the atmosphere. Admittedly you would have to compress a lot of atmosphere for a little bit of water but the advantage is you do not have to go out and dig it up! Once the quantities needed become very high then comes the mining of water. But for the initial methalox manufacture for the return trip this method would be an easy one to implement and would not require complex equipment just plenty of power. Compressing gas takes a great deal of energy. But you need the atmosphere compressed for other parts of the methalox manufacture as well.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/06/2016 12:54 pm
In line with the philosophy of reuse mfck articulated...

I could see the MCT being "partially strippable"... if you had cabins for 100, but are only returning 20 people why carry all of that back? if the fittings, panels, wiring, plumbing etc was designed to be modular and reusable it could be removed by humans and used in outfitting the base.

Or just have a cargo hold with multiple hab modules inside, and pull most of the modules out at Mars to live in.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 06/06/2016 01:15 pm
If they simply install a large (but very lightweight) crane

You presumably mean a power-shovel or dragline. A crane isn't mining equipment.

This would be pretty easy to automate.

It really isn't. It takes a lot of finesse to run a bucket at the end of a flexible line. Even a basic bucket excavator would be better. But a bucket-wheel might the best option for robotic operation.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 06/06/2016 01:29 pm
As Zubrin said in "The Case for Mars" (pg. 70-71):
"the ERV would fly one launch opportunity, or twenty-six months, prior to the launch of the astronauts.
[...]
the crew will know before they even leave Earth that they have a fully functional Mars ascent and Earth return system waiting for them on the Martian surface [...]"

...Which has been sitting idle and exposed on the surface for over a year. Fully-fuelled does not mean "fully functional". Zubrin's plan was just exchanging one risk for another.

(And the idea that pre-landing the ERV means it's somehow more "proven" than landing the ERV with the crew was always just silly.)

Thirdly, the robotics is hard

EVAs are also hard, and expensive. (And risky.)

And not on the development path that SpaceX is currently on. Unlike their rocket development, there's no synergies between the intermediate steps to MCT and lowering the cost/complexity/risk of EVAs. Whereas there are some synergies between robotic science missions via Red Dragon, and subsequent robotic ISRU missions.

{shrug} September.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/06/2016 01:58 pm
Remember Mars has a atmosphere and has water cycles (water vapor and water ice, does not have liquid phase). So to mine all the water you need, you compress the air and liquefy the water vapor in the atmosphere. Admittedly you would have to compress a lot of atmosphere for a little bit of water but the advantage is you do not have to go out and dig it up! Once the quantities needed become very high then comes the mining of water. But for the initial methalox manufacture for the return trip this method would be an easy one to implement and would not require complex equipment just plenty of power. Compressing gas takes a great deal of energy. But you need the atmosphere compressed for other parts of the methalox manufacture as well.

Not really possible to get water by compression. Water vapour is about 0.03%, so for every kg of water you would need to compress and liquefy 3 tonnes of water air.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/06/2016 02:15 pm
The point about driving AI is not driving per se, although that's a useful part of the overall problem... it's that they implemented something that learns.

...

with two years of learning time the units might be better than when they arrived...

The way that most successful AI learning works is that they use large amounts of data for training. For instance Tesla collections 1 million miles of driving data every 10 hours. This data is used to train the algorithms, but also used to evaluate how the AI does on real world data, it is also used to detect real world corner cases and allows humans to tweek the AI to handle these unusual situations better. Tesla also runs autopilot in shadow mode on customers cars, comparing what new algorithms do with what the human driver does.

For rover driving on Mars we have none of that, no large data sets, no real world data around the landing site, no ability to look at corner cases and no ability to compare AI results with what a human would do. This applies not only to driving but also to many other tasks the mining system would have to perform.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/06/2016 02:15 pm
Remember Mars has a atmosphere and has water cycles (water vapor and water ice, does not have liquid phase). So to mine all the water you need, you compress the air and liquefy the water vapor in the atmosphere. Admittedly you would have to compress a lot of atmosphere for a little bit of water but the advantage is you do not have to go out and dig it up! Once the quantities needed become very high then comes the mining of water. But for the initial methalox manufacture for the return trip this method would be an easy one to implement and would not require complex equipment just plenty of power. Compressing gas takes a great deal of energy. But you need the atmosphere compressed for other parts of the methalox manufacture as well.

Not really possible to get water by compression. Water vapour is about 0.03%, so for every kg of water you would need to compress and liquefy 3 tonnes of water <air>.
Compression requires much too much work.  It should be fairly simple to use dessicants to dry out the air, then extract the water by heating the dessicant.  This is one of the most common technologies today to dry compressed air or indoor ice rinks (and was part of the original Mars direct proposal).  alternatively you can compress a refrigerant, and use that to create a cold surface on which the water in the air will condense out.  Any of these solutions will require a minimum of about 1000 btu/lb or 2300 kJ/kg of water, the phase change energy of water.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/06/2016 03:32 pm
If they simply install a large (but very lightweight) crane

You presumably mean a power-shovel or dragline. A crane isn't mining equipment.
...on Earth. But sure, power-shovel or bucketwheel would work, too.

Quote
This would be pretty easy to automate.

It really isn't. It takes a lot of finesse to run a bucket at the end of a flexible line. Even a basic bucket excavator would be better. But a bucket-wheel might the best option for robotic operation.
I never said you'd use a bucket-line, you're the one who mentioned that. :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 06/06/2016 04:09 pm
The point about driving AI is not driving per se, although that's a useful part of the overall problem... it's that they implemented something that learns.

...

with two years of learning time the units might be better than when they arrived...

The way that most successful AI learning works is that they use large amounts of data for training. For instance Tesla collections 1 million miles of driving data every 10 hours. This data is used to train the algorithms, but also used to evaluate how the AI does on real world data, it is also used to detect real world corner cases and allows humans to tweek the AI to handle these unusual situations better. Tesla also runs autopilot in shadow mode on customers cars, comparing what new algorithms do with what the human driver does.

For rover driving on Mars we have none of that, no large data sets, no real world data around the landing site, no ability to look at corner cases and no ability to compare AI results with what a human would do. This applies not only to driving but also to many other tasks the mining system would have to perform.

Read up on simulated annealing, please.

Also, I realise that there won't be large datasets,  but every time an excavator moves its bucket, there is a chance for improvement in routines for bucket motion by evaluating how the motion went.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/07/2016 01:29 am
Robotic deployment of thin-solar panels to power an atmospheric water adsorption system is the most practical means to refuel an initial landing vehicle, it requires the least knowledge about the martian subsurface and is the most reliable due to minimal moving parts and minimal contact with abrasive regolith.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 06/07/2016 02:01 am
Robotic deployment of thin-solar panels to power an atmospheric water adsorption system is the most practical means to refuel an initial landing vehicle, it requires the least knowledge about the martian subsurface and is the most reliable due to minimal moving parts and minimal contact with abrasive regolith.
Absolutely, given what we know now. But a Red Dragon or two could inform more efficient techniques, if conditions supported it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 06/07/2016 05:12 am
If they simply install a large (but very lightweight) crane
A crane isn't mining equipment.
...on Earth.
[...]
I never said you'd use a bucket-line

Okay, in all seriousness, how did you envision using a crane to do mining, without a bucket or scoop?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/07/2016 05:11 pm
If they simply install a large (but very lightweight) crane
A crane isn't mining equipment.
...on Earth.
[...]
I never said you'd use a bucket-line

Okay, in all seriousness, how did you envision using a crane to do mining, without a bucket or scoop?
A dragline is a specific type of machine. You can have a bucket or a scoop without having a dragline. (I accidentally said "bucket line," but we were talking about a dragline... sometimes it's better NOT to trim quotes.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/08/2016 12:42 am
Robotic deployment of thin-solar panels to power an atmospheric water adsorption system is the most practical means to refuel an initial landing vehicle, it requires the least knowledge about the martian subsurface and is the most reliable due to minimal moving parts and minimal contact with abrasive regolith.
Absolutely, given what we know now. But a Red Dragon or two could inform more efficient techniques, if conditions supported it.

It is unlikely that even insitu observation alone can validate a complex mining system, at best it can tell us that their is something worth mining (prospecting) and that certain techniques will NOT work. 

A mining system would need to actually RUN and be closely observed by engineers to see what is and isn't working and how it will need to be refined or scaled up. 

Atmospheric water on the other hand can be fully validated by small scale demonstrators and then scaled up with far fewer issues due to the non-contact and uniformity of input principles.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 06/08/2016 04:49 am

You still haven't said how you can use a crane to do mining. (Let alone how this could be automated.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/08/2016 02:16 pm
From the FH discussion speculating on Raptor upper stage for FH


Raptor with a 4 m nozzle loses about 1% of ISP compared to a 4.8 m nozzle: 376 s vs 380 s.

This is based on sim in RPA lite using: Methane/LOX at:
9.7 MPa chamber pressure (same as Merlin)
2.8 O/F ratio (optimum for methalox at 9.7 MPa)
165 expansion ratio for the 4.8 m nozzle (same as Merlin Vac)
115 expansion ratio for the 4 m nozzle (assuming same throat diameter as the 4.8 m nozzle)

IF Rvac does have a 4.8m diameter, what does this say about max # of Rvac engines for the hypothetical 2nd stage BFS @ a given stage diameter?  Makes the case for >10m with even 15m having issues with # of Rvacs.

10m is out for > 3 engines
12m only fits 4 engines
15m seems OK for a ring of 6 engines, or 5 engines and a center engine.  Maybe too little swivel clearance for CE.

My guess is 15m BFS with slightly under 4.8m Rvac diameter bell, say ~4.5m such that a center engine is feasible.
4.5m also allows a 12m BFS to hold 5 engines in a ring.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/08/2016 04:02 pm
From the FH discussion speculating on Raptor upper stage for FH


Raptor with a 4 m nozzle loses about 1% of ISP compared to a 4.8 m nozzle: 376 s vs 380 s.

This is based on sim in RPA lite using: Methane/LOX at:
9.7 MPa chamber pressure (same as Merlin)
2.8 O/F ratio (optimum for methalox at 9.7 MPa)
165 expansion ratio for the 4.8 m nozzle (same as Merlin Vac)
115 expansion ratio for the 4 m nozzle (assuming same throat diameter as the 4.8 m nozzle)

IF Rvac does have a 4.8m diameter, what does this say about max # of Rvac engines for the hypothetical 2nd stage BFS @ a given stage diameter?  Makes the case for >10m with even 15m having issues with # of Rvacs.

10m is out for > 3 engines
12m only fits 4 engines
15m seems OK for a ring of 6 engines, or 5 engines and a center engine.  Maybe too little swivel clearance for CE.

My guess is 15m BFS with slightly under 4.8m Rvac diameter bell, say ~4.5m such that a center engine is feasible.
4.5m also allows a 12m BFS to hold 5 engines in a ring.

4 engines matches the expected values best IMO. BFR thrust levels (15mlbf) indicate a 10x scaling from F9, which would put the total US thrust at 900t. Musk said optimization was indicating 230t per engine which gives 920t thrust for 4 engines.

4 engines precludes a center engine landing, but I don't think a center engine landing is optimal anyway for orbital or interplanetary reentry velocities. Side engines firing at an outward angle is a requirement for increasing drag during Mars retropropulsive reentry, and they can be far enough forward to gimbal behind a heatshield for Earth entry (or at least far enough to stay inside the bow shock and keep heat load manageable).

With four 4.8m engines, the interstage needs to be 12m at it's widest point for clearance... but it doesn't necessarily have to be cylindrical since it's not pressurized and supports mostly axial and bending loads. If a 10m vehicle is desirable the interstage could have engine cowlings like the Falcon 9 v1.0 did for the tic-tac-toe engine arrangement.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/08/2016 04:11 pm
Good points but I don't see the BFR/BFS as a direct scale up extrapolation.  Stage 2 will be heavier because (1) it's fully recoverable/re-useable and (2) from models I've run I think it's also going to need to be heavier for propellant needed for delta V for escape LEO to Mars xfer & Mars to Earth return. 
So, I get 5 engines estimated and even with that the ignition T/W < 1 for LEO launch, which is OK.  Plus I assume Rvac thrust > Raptor sea level thrust.

Of course we're assuming that raptors still have the actual thrust levels similar to Musk's 18 months ago statement.  I doubt this will be so as actual design always makes changes from early design calculations.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/08/2016 04:35 pm
You're right, it's not a direct extrapolation. However, Falcon can put over 26 metric tons in LEO (22,500 kg of payload plus a 4,000+ kg upper stage). If BFR/BFS is scaled ~10x it would put over 250!!!! metric tons in orbit. It only needs to take 100t of payload to Mars, so they can dedicate ~100 tons to a reuseable US. Even with booster RTLS.

It really doesn't need more dV than the Falcon US, because it will be refueled in LEO and at Mars surface. Even at really poor mass fractions (about 10:1 vs Falcon's 27:1) it can still to a 3-month Mars injection almost every synod, and a 6-7 month direct return from Mars surface with a 25t payload.

So the thrust requirement is pretty much fixed, and the only reason to add engines is if they are a little smaller. 5 engines with a 4 to 4.5m nozzle and 180-200t thrust would make sense.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/08/2016 04:59 pm
By more US DV I mean (1) less performance needed from 1st stage BFR making the big boy's re-use environ slightly more benign and lowering cost {My unsubstantiated assumption}, (2) when you re-fuel in LEO you still need the tankage structure mass for propellant for the BFS's DV needed for fast transfer to Mars, say 90-120 days whatever, possible or maybe not propulsive breaking, aerobraking and powered landing.

Using today's F9 as a model, the Rvac would have ~ 110% the thrust of the assumed 230mT Elon referred to.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/08/2016 06:22 pm
By more US DV I mean (1) less performance needed from 1st stage BFR making the big boy's re-use environ slightly more benign and lowering cost {My unsubstantiated assumption}, (2) when you re-fuel in LEO you still need the tankage structure mass for propellant for the BFS's DV needed for fast transfer to Mars, say 90-120 days whatever, possible or maybe not propulsive breaking, aerobraking and powered landing.

Using today's F9 as a model, the Rvac would have ~ 110% the thrust of the assumed 230mT Elon referred to.

Falcon with 10-15t of LEO payload stages quite low and slow. A 15m lbf BFR should have little problem putting 100t and a reusable US up while still doing a comfy RTLS.

Transfers as fast as 80 days and never longer than 120 days aren't all that difficult if you have LEO refueling capability; they requires 4.5 to 4.9 km/s from LEO. The EDL maneuver burns another ~1.5 km/s, for a total of ~6.0 to ~6.4 km/s so there's no need for tanks that are much bigger than Falcon's (relative to payload, of course).

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/08/2016 06:26 pm

You still haven't said how you can use a crane to do mining. (Let alone how this could be automated.)
Honestly, you can't figure it out? Different requirements from Earth mining. Don't need nearly the throughput. You're talking like a factor of 1000-100,000x less than large mining equipment on Earth, like a few tons of soil per day to fuel up an MCT in a synod (even less for a subscale MCT). So if you can pick up and drop some weight, you can mine with it. If it takes 15 minutes to move 100kg of soil, that's fine. That would, of course, be a joke on Earth. And yeah, you could outperform it with a hand shovel. But that's irrelevant.

But fine, I'll posit something /intentionally/ non-optimal just to show you can do it.
On the end of the crane, you'd have a clamshell bucket or orange-peel grabs or something like a blend between the two. It'd be awkward and slow (and could be enhanced by dragging it with another cable), but it still could work. Randomly grabbing scoops of soil within reach would be effective enough to get a few tons of material per day.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/08/2016 06:42 pm
...
4 engines precludes a center engine landing...
Not true. An axi-symmetrical "Y" shape with 4 engines would allow it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/08/2016 07:38 pm
...
4 engines precludes a center engine landing...
Not true. An axi-symmetrical "Y" shape with 4 engines would allow it.
Sure, but that takes up as much space as 7 engines. I suppose if you're pointing a central engine in the direction of reentry, you want a very wide, very light stage anyway. Optimize for reentry ballistic coefficient, and just live with the drag on the way up.

Besides aerodynamics, which factors really optimize stage diameter? Road transport isn't a consideration.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/09/2016 03:39 am
A central landing engine wouldn't need a vacuum bell nozzle on it, it would be simple to use 4 vac engines and a central sea-level engine tucked in between them, at landing just gimbal the large nozzles outward to give the central engine plume as much clearance as possible.

On Mars your going to be firing all 4 vac engines in a hover-slam and only firing the central engine in an emergency that requires a shutdown of a pair of outer engines.

I'm betting on 12.5 m diameter 4v1s (4 vacuum, 1 sea-level) for the second stage.  And ~30 engines first stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/09/2016 05:50 am
The nozzle extensions of vac engines will need protection to survive reentry at least on earth. So they will probably be retractable for that reason. Can the remaining nozzle part formed like first stage engines and work as such in retracted state?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/09/2016 01:28 pm
The nozzle extensions of vac engines will need protection to survive reentry at least on earth. So they will probably be retractable for that reason. Can the remaining nozzle part formed like first stage engines and work as such in retracted state?

It won't be formed like a SL nozzle, because to get optimal vacuum expansion it needs a rapid increase in area immediately after the throat. In this area, the gas is expanding radially, so the velocity component is reduced in the thrust direction. Just look up a picture of the Mvac compared to the SL Merlin, and see how much fatter it is at the same distance from the throat. In theory still work, just at a lower efficiency and thrust. At sea level the flow would separate about 1/3 the way down the nozzle anyway, so it's not really less efficient than running a vac engine at SL.

Based on some more simulations with varying nozzle efficiency, the unextended nozzle should get 70 to 90% of the impulse and thrust of a SL optimized engine at SL, depending on how overexpanded it is. But it will separate a lot earlier in the throttle band, which might cause control issues.

Also of interest: in a vacuum it gets 92 to 96 % of the performance fully expanded vac nozzle. If the mission requires that last 4-8% of performance, then an extension failure would cause LoM.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/09/2016 03:36 pm
...

Also of interest: in a vacuum it gets 92 to 96 % of the performance fully expanded vac nozzle. If the mission requires that last 4-8% of performance, then an extension failure would cause LoM.
...for a LOT of missions, success isn't entirely binary. I can point to several times when RL-10-based upper stages had a significantly early shutdown for one reason or another but the performance was still made up for, perhaps by the payload. This may lead to lower on-orbit fuel, which is annoying and can shorten the life of the payload, but this isn't LoM.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 06/09/2016 05:08 pm
On the end of the crane, you'd have a clamshell bucket or orange-peel grabs or something like a blend between the two.

I said a bucket on a cable requires human finesse to control, something that can't be automated yet (certainly not "easily"). You specifically said you weren't talking about that.

and could be enhanced by dragging it with another cable

So now you're describing a dragline, which you specifically said you weren't.

You're shocked at my confusion when you completely contradict yourself?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/09/2016 05:42 pm
On the end of the crane, you'd have a clamshell bucket or orange-peel grabs or something like a blend between the two.

I said a bucket on a cable requires human finesse to control, something that can't be automated yet (certainly not "easily"). You specifically said you weren't talking about that....
I thought you were referring to a dragline. Anyway, I've seen these mechanisms in action. Very little finesse is necessary to grab material if you're not concerned with exactly what spot of dirt you're grabbing or if you're getting a whole bunch of dirt or not. This is not an especially hard problem.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/09/2016 05:43 pm
...
and could be enhanced by dragging it with another cable

So now you're describing a dragline, which you specifically said you weren't.

You're shocked at my confusion when you completely contradict yourself?
I WASN'T talking about a dragline, I was simply acknowledging there that you COULD use one.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 06/09/2016 05:57 pm
I've operated a dragline[1]. It's pretty hard to get a good load and raise it successfully. Especially repeatably. So I think it's not exactly something I'd call "very little finesse".

1 - It was a LEGO model, but it was built by someone whose job it is to spec draglines for coal mines and he said the real thing operates the same way. Very finicky in operation, and taking a very deft hand on the controls with situational awareness of exactly what kinds of lumps and irregularities face you.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/09/2016 06:00 pm
I've operated a dragline[1]. It's pretty hard to get a good load and raise it successfully. Especially repeatably. So I think it's not exactly something I'd call "very little finesse".

1 - It was a LEGO model, but it was built by someone whose job it is to spec draglines for coal mines and he said the real thing operates the same way. Very finicky in operation, and taking a very deft hand on the controls with situational awareness of exactly what kinds of lumps and irregularities face you.
A) Getting a good load is not at all a requirement. We're talking about a very small amount of material, relatively speaking.
B) The dragline comment was an aside, an acknowledgement of a possible improvement. Not my actual point. I was talking about this: https://en.wikipedia.org/wiki/Bucket_(machine_part)#/media/File:Coal_loading_shell_grabs,_Cardiff.jpg
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 06/09/2016 06:26 pm
I've operated a dragline[1]. It's pretty hard to get a good load and raise it successfully. Especially repeatably. So I think it's not exactly something I'd call "very little finesse".

1 - It was a LEGO model, but it was built by someone whose job it is to spec draglines for coal mines and he said the real thing operates the same way. Very finicky in operation, and taking a very deft hand on the controls with situational awareness of exactly what kinds of lumps and irregularities face you.
A) Getting a good load is not at all a requirement. We're talking about a very small amount of material, relatively speaking.
B) The dragline comment was an aside, an acknowledgement of a possible improvement. Not my actual point. I was talking about this: https://en.wikipedia.org/wiki/Bucket_(machine_part)#/media/File:Coal_loading_shell_grabs,_Cardiff.jpg
A lot will depend on the condition of the soil/regolith.  If it is solidly frozen, rather like permafrost, then shovels and draglines will not be much use, it'll be too tough to penetrate.  If it's loose with boulders or large 'rocks' of sand and ice, then it's a lot simpler.  If it's a cliff face, then it's relatively easy to bore into.  A few kg of well placed explosives might do wonders in loosening up the soil. That's a well known procedure!
Some kind of scrapper tool, rather like an ice rink Zamboni, but tougher, might work in certain conditions as well.  If it's a layer cake of sand and ice, and the sand layer is not solidly frozen, then you might just want to saw out layers of ice. Very site specific is my guess.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/09/2016 06:51 pm
Drop a weight on it to break it up. Then scoop up the broken up soil. Could be done very inefficiently and still be acceptable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 06/09/2016 07:02 pm
Having some trouble with the notion that you can do this "inefficiently" and actually get any useful material before you wear out your equipment.

Those coal loader scoops only work when dropped pretty much straight down. So now you need a boom of some sort to position the scoop where you want it (which you did with a dragline too).

Why are we arguing about this? And why here? I've lost how this is related to the MCT per se. It's related to how to do ISRU, for sure but not MCT design...

Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 06/09/2016 07:14 pm
Well, something will have to be able to prepare propellent for the first crewed MCT, probably a robotic MCT.

One possibility is to use a modified version of a solar still. Making a solar still are one of the things taught in survival training. Instead of digging a hole in the ground, a box can be lowered to the surface. The idea is that solar energy would create enough heat to cause ice to sublimate. The trick would be how to collect the moisture. Should be a lot easier than mechanical systems. Once a crew arrives, an ice mining system can be setup.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/09/2016 07:37 pm
Having some trouble with the notion that you can do this "inefficiently" and actually get any useful material before you wear out your equipment.
Go back and read the orders of magnitude point I made. We can get just 1/1000th the material that you'd get with typical mining equipment and still have sufficient material. Our intuitions are screaming about stuff that is not relevant at this scale.

Quote
Those coal loader scoops only work when dropped pretty much straight down. So now you need a boom of some sort to position the scoop where you want it (which you did with a dragline too).
Yeah, that's what the crane is for.

Quote
Why are we arguing about this? And why here? I've lost how this is related to the MCT per se. It's related to how to do ISRU, for sure but not MCT design...
Because I threw out the fact that something simple, even something as dumb as a crane, could be used instead of a rover. And the throw of a crane would be enough that it wouldn't even need to move its base to capture enough material. It was a throwaway comment that someone couldn't resist challenging with their intuitions honed on Earth but misled because the intuition is trained with orders of magnitude more throughput requirements.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/09/2016 08:33 pm
...

Also of interest: in a vacuum it gets 92 to 96 % of the performance fully expanded vac nozzle. If the mission requires that last 4-8% of performance, then an extension failure would cause LoM.
...for a LOT of missions, success isn't entirely binary. I can point to several times when RL-10-based upper stages had a significantly early shutdown for one reason or another but the performance was still made up for, perhaps by the payload. This may lead to lower on-orbit fuel, which is annoying and can shorten the life of the payload, but this isn't LoM.

If you think of the nozzle as retractable rather than extendable ( i.e. their purpose is to permit supersonic retropropulsion without blasting the extension bell, rather than to save length), then LoM isn't very likely even if 100% performance is needed.

In this case the nozzles could be extended before committing to launch from either Earth or Mars surface, and would be retracted after transfer injection. With 4 or more engines, landing should still be feasible even if one fails to retract and can't be fixed during transfer.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 06/10/2016 07:26 am
Very site specific is my guess.

Most mining/tunnelling/clearing work is. That's why handwaving it as "easily automated" gets my attention.

Existing mining "automation" is limited to already prepared sites, and it isn't automated. The overwhelming majority is merely remotely driven by humans. The few things that people hope to automate are generally things like on-site transport. Moving material between set locations along prepared and marked (robot-friendly) paths.

They are also massively overbuilt, heavy, and still high-maintenance. And the usual engineering rule of thumb is that every time you halve the mass, you drop the work-life by an order of magnitude.

[I recall as a kid, every fortnight or so, having to help Dad change out the hardened steel teeth on the trenching machine. This was for something that spent 90% of its working life digging through clay and clean compacted fill, not mining, hardly a rock in sight.]
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/10/2016 07:30 am
It wouldn't be worth automating on Mars if sending people out to do the work were as easy to do as it is on Earth. The required soil could be shoveled manually at sufficient rates. We wouldn't automate such a task, we'd just give them a backhoe or something. The only reason to automate it is because it's on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 06/10/2016 09:12 am
For Lar's sake I'll let it drop, but assume my right eye is twitching and my fingers are clawing at the screen.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mme on 06/10/2016 04:56 pm
a few more teasers before the september reveal:

https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/

1 red dragon in 2018, 'at least 2' in 2020, then first flight of MCT in 2022...
Bold mine.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/10/2016 05:03 pm
a few more teasers before the september reveal:

https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/

1 red dragon in 2018, 'at least 2' in 2020, then first flight of MCT in 2022...
Bold mine.

That is first fight of MCT to Mars in 2022, which likely means that BFR/BFS first flight would need to be in 2021.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/10/2016 05:23 pm
This thread hasn't been updated for a while (so there may be some public details that have been missed), but here's something new:

a few more teasers before the september reveal:

https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/

1 red dragon in 2018, 'at least 2' in 2020, then first flight of MCT in 2022...

This statement was in the timeline of mars missions, so implies MCT to Mars in 2022 and likely first flight of BFR/BFS in 2021.

Also something we already suspected but now have added confirmation:
Quote from: musk
“the first mission wouldn’t have a huge number of people on it because if something goes wrong, we want to risk the fewest number of lives as possible.”
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/10/2016 06:01 pm
a few more teasers before the september reveal:

https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/

1 red dragon in 2018, 'at least 2' in 2020, then first flight of MCT in 2022...
Bold mine.

That is first fight of MCT to Mars in 2022, which likely means that BFR/BFS first flight would need to be in 2021.

"Then in 2022, Musk said he hoped to launch what the company now sometimes refers to as the Mars Colonial Transporter, designed to bring a colony to Mars."

Says to me, first launch of MCT in 2022, NOT specifically TO Mars, just launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/10/2016 06:06 pm
Says to me, first launch of MCT in 2022, NOT specifically TO Mars, just launch.

Not at all. That timetable was explicitly for Mars launches. And first landing on Mars with MCT is an obvious necessity. Not only to install ISRU. They need successful Mars landings with MCT before they can send people.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/10/2016 06:45 pm
I think they may be sending significant ISRU equipment in 2020, even before MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TheTraveller on 06/10/2016 06:49 pm
a few more teasers before the september reveal:

https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/

1 red dragon in 2018, 'at least 2' in 2020, then first flight of MCT in 2022...
Bold mine.

That is first fight of MCT to Mars in 2022, which likely means that BFR/BFS first flight would need to be in 2021.

"Then in 2022, Musk said he hoped to launch what the company now sometimes refers to as the Mars Colonial Transporter, designed to bring a colony to Mars."

Says to me, first launch of MCT in 2022, NOT specifically TO Mars, just launch.

Launch 1st BFS into LEO, do heaps of checks, put in a bit of fuel, do a lunar loop & propulsive land on Earth.

Maybe next check flight is to land on Luna and rtn Earth.

No need to wait for Mars synods to do these and other pre TMI burn checkouts of the 1st BFS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/10/2016 06:55 pm
Mars EDL is different enough from Earth EDL that you're going to have to do a test of MCT on Mars before you send people.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TheTraveller on 06/10/2016 07:06 pm
Mars EDL is different enough from Earth EDL that you're going to have to do a test of MCT on Mars before you send people.

Well an landed and not refueled crewless BFS / MCT would make an excellent hab and start of a Mars base.

Imagine the workshops, repair and other facilities, heavy earth movers, cranes, rovers, power & ISRU plants etc that could be built into and delivered by a crewless BFS that never returned to Earth but became SpX Mars Base 1.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/10/2016 07:07 pm
Mars EDL is different enough from Earth EDL that you're going to have to do a test of MCT on Mars before you send people.

Well an landed and not refueled crewless BFS / MCT would make an excellent hab and start of a Mars base.

Imagine the workshops, repair and other facilities, heavy earth movers, cranes, rovers, etc that could be built into and delivered by a crewless BFS that never returned to Earth but became SpX Mars Base 1.
Maybe they'll send 2 BFSes the first time, one to return and one to stay.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TheTraveller on 06/10/2016 07:09 pm
Mars EDL is different enough from Earth EDL that you're going to have to do a test of MCT on Mars before you send people.

Well an landed and not refueled crewless BFS / MCT would make an excellent hab and start of a Mars base.

Imagine the workshops, repair and other facilities, heavy earth movers, cranes, rovers, etc that could be built into and delivered by a crewless BFS that never returned to Earth but became SpX Mars Base 1.
Maybe they'll send 2 BFSes the first time, one to return and one to stay.

That would generate excellent backup as the best could return. Much better than driving several thousand kms across Mars to get to a Ares 4 ascent module.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 06/10/2016 08:15 pm
2022 is planned MCT flight to Mars, because he was talking about Spacex Mars sorties starting 2018 one dragon, 2020 2 dragons and 2022 MCT.
I am sure MCT will be test before on LEO, Luna orbit and luna Surface. My guess first BFR and MCT flight has to be 2020, be ready for 2022 Mars flight.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: llanitedave on 06/10/2016 08:51 pm
I'm extremely curious about what kind of site selection process they'll be going through.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 06/10/2016 08:57 pm
Think about this my friends. We're discussing unmanned MCT to Mars in 2022 and testing before that. We're halfway through 2016. First flight in 4 to 5 years! Wow.

How are they going to be able to build a pad, factory, and MCT in such a short time? MCT must be similar to F9 and Dragon 2 just to cut down on development and testing time. Can't wait until September when we find out what is really going on.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: IntoTheVoid on 06/10/2016 09:00 pm
Launch 1st BFS into LEO, do heaps of checks, put in a bit of fuel, do a lunar loop & propulsive land on Earth.

Maybe next check flight is to land on Luna and rtn Earth.

No need to wait for Mars synods to do these and other pre TMI burn checkouts of the 1st BFS.
If this is the 1st BFS you don't have anything to put in a bit of fuel.

Perhaps Mission 2a & 2b:
  Relauch BFS 1; Launch BFS 2
  BFS 1 refuels BFS 2, or vice versa.
  BFS 1 lands; BFS 2 goes to moon, possibly landing if fuel levels permit return.
  BFS 2 returns and lands.

But certainly agree this is not tied to Mars synods, other than to be done beforehand.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Coastal Ron on 06/10/2016 09:10 pm
Musk quoted in the Washington Times article (https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/):

"At another point he said, “I’m so tempted to talk more about the details of it. But I have to restrain myself.”"

First a bit of irony is that Musk is talking about his plans in a publication that Jeff Bezos owns.

What caught my eye in the article also was this:

"Then in 2022, Musk said he hoped to launch what the company now sometimes refers to as the Mars Colonial Transporter, designed to bring a colony to Mars."

Being a product scheduling professional, my mind started backing off that date all of the physical tasks that needed to happen in just 6 short years.  Including:

- Launch and manufacturing site selection, development, and building and staffing of the factory (assumed to be co-located).

- Production of the first test vehicle, which may not go to Mars but is used only for test purposes.

- Production and testing of the first vehicle to go to Mars in 2022, with test flights to validate it's ready.

- Sources of funding, i.e. money, and lots of it.  Sure SpaceX and Musk will be supplying some part of that, but I would imagine that Musk is working on getting BOMC's (Believers Of Mars Colonization) to contribute too.

And if we're talking MCT, we have to assume the BFR will also be under development.  That is a lot.  I would imagine we'll get a sense of the schedule of events when Musk unveils more details in September, and as he says in the article:

"And he acknowledged that the company would have to “get lucky and things go according to plan” to hit a launch window for manned flight in late 2024, with a landing in 2025."

I'm already crossing my fingers for luck...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TheTraveller on 06/10/2016 09:30 pm
Launch 1st BFS into LEO, do heaps of checks, put in a bit of fuel, do a lunar loop & propulsive land on Earth.

Maybe next check flight is to land on Luna and rtn Earth.

No need to wait for Mars synods to do these and other pre TMI burn checkouts of the 1st BFS.
If this is the 1st BFS you don't have anything to put in a bit of fuel.

Perhaps Mission 2a & 2b:
  Relauch BFS 1; Launch BFS 2
  BFS 1 refuels BFS 2, or vice versa.
  BFS 1 lands; BFS 2 goes to moon, possibly landing if fuel levels permit return.
  BFS 2 returns and lands.

But certainly agree this is not tied to Mars synods, other than to be done beforehand.

BFR, without a BFS load can put a lot of fuel into LEO. So launch BFS on BFR which lands, is refueled and launch into LEO, then transfers fuel to BFS for moon loop around or later Luna landing and return (will need to be a very light BFS or maybe put a BFR tanker in LLO)

For sure SpX will have solved how to maintain methlox in space for a very long time or Mars landing of BFS using methlox Raptors will never happen.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: IntoTheVoid on 06/10/2016 09:39 pm
Launch 1st BFS into LEO, do heaps of checks, put in a bit of fuel, do a lunar loop & propulsive land on Earth.

Maybe next check flight is to land on Luna and rtn Earth.

No need to wait for Mars synods to do these and other pre TMI burn checkouts of the 1st BFS.
If this is the 1st BFS you don't have anything to put in a bit of fuel.

Perhaps Mission 2a & 2b:
  Relauch BFS 1; Launch BFS 2
  BFS 1 refuels BFS 2, or vice versa.
  BFS 1 lands; BFS 2 goes to moon, possibly landing if fuel levels permit return.
  BFS 2 returns and lands.

But certainly agree this is not tied to Mars synods, other than to be done beforehand.

BFR, without a BFS load can put a lot of fuel into LEO. So launch BFS on BFR which lands, is refueled and launch into LEO, then transfers fuel to BFS for moon loop around or later Luna landing and return (will need to be a very light BFS or maybe put a BFR tanker in LLO)

For sure SpX will have solved how to maintain methlox in space for a very long time or Mars landing of BFS using methlox Raptors will never happen.

BFR doesn't go to orbit; it stages low and slow by all estimations of the professionals on this forum. The only thing conceived that would potentially be able to refuel BFS 1, is a raptor upper stage for FH, but a refueling capability on that, would have a very short product lifetime if you're already launching BFS which will be vastly larger.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/10/2016 09:49 pm
It will need two orbiting vehicles. One that gets refuelled and one that does the fuelling run. An ability that needs to be tested early. The tanker may not qualify as MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: IntoTheVoid on 06/10/2016 10:07 pm
It will need two orbiting vehicles. One that gets refuelled and one that does the fuelling run. An ability that needs to be tested early. The tanker may not qualify as MCT.

Well, util the recent article the MCT term had seemed to be in retirement, replaced by the BFR/BFS terminology, and purposefully or not Elon seems to keep the terms 'muddy'.
My point was/is that the first space vehicle boosted to orbit by a raptor powered first stage is highly unlikely to be refueled by anything. It is far more likely that that space vehicle will be the thing expected to do the refueling in the future. If there is a specific tanker version, I would expect it to be the first version launched because none of the others go too far without it. It's also likely to be the simplest version (if in fact there are different versions).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/10/2016 10:34 pm
I'm extremely curious about what kind of site selection process they'll be going through.

It will be ISRU driven.  Access to subsurface water if the site selection is for the putative Mars colony.
It will differ from NASA interests to find evidence of past or present Mars biology.
Of course as a transportation company, SX will be happy to sell seats & tonnage to Mars for NASA's quest.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/10/2016 10:54 pm
Musk quoted in the Washington Times article (https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/):

"At another point he said, “I’m so tempted to talk more about the details of it. But I have to restrain myself.”"

First a bit of irony is that Musk is talking about his plans in a publication that Jeff Bezos owns.

What caught my eye in the article also was this:

"Then in 2022, Musk said he hoped to launch what the company now sometimes refers to as the Mars Colonial Transporter, designed to bring a colony to Mars."

Being a product scheduling professional, my mind started backing off that date all of the physical tasks that needed to happen in just 6 short years.  Including:

- Launch and manufacturing site selection, development, and building and staffing of the factory (assumed to be co-located).

- Production of the first test vehicle, which may not go to Mars but is used only for test purposes.

- Production and testing of the first vehicle to go to Mars in 2022, with test flights to validate it's ready.

- Sources of funding, i.e. money, and lots of it.  Sure SpaceX and Musk will be supplying some part of that, but I would imagine that Musk is working on getting BOMC's (Believers Of Mars Colonization) to contribute too.

And if we're talking MCT, we have to assume the BFR will also be under development.  That is a lot.  I would imagine we'll get a sense of the schedule of events when Musk unveils more details in September, and as he says in the article:

"And he acknowledged that the company would have to “get lucky and things go according to plan” to hit a launch window for manned flight in late 2024, with a landing in 2025."

I'm already crossing my fingers for luck...

Great post.
My career was hardware/software systems new next state of the art telecom product development. 
When I enumerate the myriad serious steps and when I look at the cash needed, I am very skeptical of Musk's admitted "everything goes right" schedule. But unlike myself as a former VP Engineering/CTO, he won't fire himself when he seriously misses the best case schedule.
When you own the whole thing you can set best case schedules and not suffer the consequences of missing them....unless you run out of cash!  I also have an MBA in finance and do worry about sufficient cash to fund all this.  On top of everything SX is doing, they gotta fund BFR/BFS development, a BFR/BFS factory, a launch complex, a likely off shore launch complex... the list goes on. 
As someone who had to nickel & dime product cost as well as product performance to be competitive, I have industry experience based respect for Elon's product cost management and life cycle cost management.  The guy is a true polymath.
Bottom Line: even if he's years late as I believe he will be, it is civilization changing.
Good health, Elon!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: a_langwich on 06/10/2016 11:32 pm
Can't wait until September when we find out what is really going on.

Surely the most anticipated speech about space this year, maybe in quite a few years.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Coastal Ron on 06/11/2016 12:47 am
When I enumerate the myriad serious steps and when I look at the cash needed, I am very skeptical of Musk's admitted "everything goes right" schedule. But unlike myself as a former VP Engineering/CTO, he won't fire himself when he seriously misses the best case schedule.

It's hard to know when he makes schedule proclamations how much detailed work has been done vs gut feel.

Quote
When you own the whole thing you can set best case schedules and not suffer the consequences of missing them....unless you run out of cash!  I also have an MBA in finance and do worry about sufficient cash to fund all this.

I share your concerns.  Certainly he can leverage the SpaceX organization as it exists today, and just add onto it, but there is a lot to do.

Quote
On top of everything SX is doing, they gotta fund BFR/BFS development, a BFR/BFS factory, a launch complex, a likely off shore launch complex... the list goes on.

I've always been on the scheduling side, and haven't had to worry about the money going out (I was responsible for money coming back in through shipping product).  And even with the capabilities that SpaceX has developed, I see schedule challenges.

Quote
As someone who had to nickel & dime product cost as well as product performance to be competitive, I have industry experience based respect for Elon's product cost management and life cycle cost management.  The guy is a true polymath.
Bottom Line: even if he's years late as I believe he will be, it is civilization changing.
Good health, Elon!

Yeah, if he's later than he planned he's still far earlier than anyone else.  I won't complain.  And the entertainment value of it all...   :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 06/11/2016 01:25 am
It will need two orbiting vehicles. One that gets refuelled and one that does the fuelling run. An ability that needs to be tested early. The tanker may not qualify as MCT.

Well, util the recent article the MCT term had seemed to be in retirement, replaced by the BFR/BFS terminology, and purposefully or not Elon seems to keep the terms 'muddy'.
My point was/is that the first space vehicle boosted to orbit by a raptor powered first stage is highly unlikely to be refueled by anything. It is far more likely that that space vehicle will be the thing expected to do the refueling in the future. If there is a specific tanker version, I would expect it to be the first version launched because none of the others go too far without it. It's also likely to be the simplest version (if in fact there are different versions).

I believe Elon called MCT a system. So BFR, BFS, a tanker, etc. would be part of the MCT system.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/11/2016 03:33 am
BFS without refueling should able to a free return circumlunar mission with a small payload. No need for a tanker version or even a second spacecraft for that.

I think BFS will only have a payload adapter (passenger hab or cargo hold integrated as needed), so a tanker would only differ in tank size and might not be necessary at all.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 06/11/2016 01:06 pm
BFS without refueling should able to a free return circumlunar mission with a small payload. No need for a tanker version or even a second spacecraft for that.

I think BFS will only have a payload adapter (passenger hab or cargo hold integrated as needed), so a tanker would only differ in tank size and might not be necessary at all.

BFS is likely designed to reach LEO with little fuel remaining.  Refueling is essential.
This is not one-shot rocketry.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/11/2016 01:16 pm
BFS without refueling should able to a free return circumlunar mission with a small payload. No need for a tanker version or even a second spacecraft for that.

I think BFS will only have a payload adapter (passenger hab or cargo hold integrated as needed), so a tanker would only differ in tank size and might not be necessary at all.

BFS is likely designed to reach LEO with little fuel remaining.  Refueling is essential.
This is not one-shot rocketry.
BFS would necessarily be able to reach LEO with lots of fuel, just not also with a maximum payload. So the point stands.

But refueling will be needed early on.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: linxiaoyi on 06/11/2016 01:47 pm
BFS without refueling should able to a free return circumlunar mission with a small payload. No need for a tanker version or even a second spacecraft for that.

I think BFS will only have a payload adapter (passenger hab or cargo hold integrated as needed), so a tanker would only differ in tank size and might not be necessary at all.

BFS is likely designed to reach LEO with little fuel remaining.  Refueling is essential.
This is not one-shot rocketry.
I think a BFS with only main rocket systems(tanks, engines, control, etc),can reach a TMI and land on Mars surface by a single launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 06/11/2016 01:47 pm
BFS without refueling should able to a free return circumlunar mission with a small payload. No need for a tanker version or even a second spacecraft for that.

I think BFS will only have a payload adapter (passenger hab or cargo hold integrated as needed), so a tanker would only differ in tank size and might not be necessary at all.

BFS is likely designed to reach LEO with little fuel remaining.  Refueling is essential.
This is not one-shot rocketry.
BFS would necessarily be able to reach LEO with lots of fuel, just not also with a maximum payload. So the point stands.

But refueling will be needed early on.

If payload is 100-200 tonnes, and dry mass is comparable, replacing a large fraction of payload mass with propellant still provides a very low payload mass fraction.  That said, there could easily be conventional second stages and payloads designed for delivering significant Lunar payloads (10-15m fairing?) on BFR.  Just haven't heard any hints taking us in that direction.

Still don't see BFS going much of anywhere without refueling.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/11/2016 01:59 pm
Dry mass likely to be much less than the payload. At least for cargo configuration.

There's one area where SpaceX has proven the ability to advance performance WELL beyond the current state of the art, and that's mass fraction.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: linxiaoyi on 06/11/2016 02:44 pm
BFS without refueling should able to a free return circumlunar mission with a small payload. No need for a tanker version or even a second spacecraft for that.

I think BFS will only have a payload adapter (passenger hab or cargo hold integrated as needed), so a tanker would only differ in tank size and might not be necessary at all.
A BFS with only main rocket systems can reach LLO and back without refueling.But it's not worth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/11/2016 03:18 pm
Dry mass likely to be much less than the payload. ...

Doesn't need to be that much less, a 1:1.35 ratio of dry mass to payload saves enough propellent for TLI. In this case, a 100t ship and nominal 135t payload, for 235t IMLEO.

Forego 99% of the payload and it should reach orbit with enough remaining prop for a 3200m/s burn.

However, that only tests deep space flight and low-mass re-entry. In order to really test interplanetary re-entry it needs an interplanetary payload, so refueling will be implemented quite quickly.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/11/2016 04:13 pm
I ran the #s in my spreadsheet simulator and yes, a lightly loaded BFS can reach LEO with more than enough tons of propellant to do a lunar free return and Earth landing.  Apollo 8 redux!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 06/11/2016 04:32 pm
As large as its likely to be, and with baked in habitation, could a BFS be considered a lunar "base" if left in place? Guessing it depends on ease of egress/ingress, crew rotation landers and power generation, but still.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Mongo62 on 06/11/2016 04:51 pm
IAC Congress schedule (https://www.iac2016.org/Congress.html#congress) (scroll down):

Friday, September 30 at 8:30 to 10:30 -- Late Breaking News: Elon Musk Space X Title to Be Confirm - Mars

So two hours on the final morning of the congress.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/11/2016 04:53 pm
Newer refined model for BFR/BFS. Spreadsheet attached.

   BFR & BFS MODELS: MCT as 2nd Stage with 100  Metric Tons CARGO   
      BLUE: Enter parameter variable
S1 Avg ISP Sea L to MECO   335   
S2 vac ISP   380   
Raptor sea level thrust KLB & mT   518   235
Rvac thrust KLB & mT   559   254
S1 Dry Wt %    4.5%   
      
   BFR 1   
BFR DIA   15.0   m
MCT BFS Dry Wt & Cargo   225   mT
S2 Dry Mass   125   mT
Propellant for S2 BFS Landing   30   mT
Total Mass to LEO   255   mT
1st Stage Propellant Tank Length   18.0   m
S1 Propellant Volume   3179   m3
Propellant Mass   3371   mT
S1 Dry Wt %    4.5%   
S1 DRY Weight   159   mT
S1 Total Weight mT   3529   mT
S! Dry Wt Delta V (No 2nd stage)   10.2   Km/sec Rocket Equation
Stage One Full Load Delta V    3.35   Km/sec Rocket Equation
RTxx Propellant   70   mT
RTxx Delta V @Minimum Load   1.20   Km/sec Rocket Equation
Est S1 Gravity Loss    0.9   Km/sec
Est S1 Velocity @ Burnout   2.45   Km/sec
2nd Stage Propellant Tank Length   7.5   m
Propellant Volume   1,325   m3
Propellant Mass   1,404   mT
S2 Mass w/MCT   1,629   mT
S2 Mass w/MCT   3.6   Million LBS
Calc # Rvac Raptor Eng   5.01   0.78
Stage 2 Thrust mT   1271   
Stage 2 Thrust   2.8   Million LBS
Stage 2 Km/sec    6.91   Km/sec Rocket Equation
Stage 2 Wet to Dry Mass Ratio   12.2   
S1 + S2  Total Delta V   9.4   Km/sec
TOTAL WT mT   5,159   mT
TOTAL WT LBS   11.4   Million LBS
THRUST Needed LBS   14.0   Million LBS
THRUST Needed mT   6345   
THRUST Needed MegaNewtons   62   
1st Stage T/W @ Takeoff   1.23   
1st STAGE # ENG    27   
LEO Mass Fract   4.4%    %
LEO Wet to Dry Mass Ratio   23    F9 v1.1 25/1 Musk
MCT Cargo Hold length   10   m
MCT Cargo Vol m3   1766   m3
   Eng 16+8+3=27   
   Outer Ring, Inner Ring, Central Engs   
   NOTE 1:   S1 Km/sec + S2 Km/sec must ~9Km/sec for LEO with grav losses
   NOTE 2:   Rocket Equation   
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/11/2016 05:40 pm
As large as its likely to be, and with baked in habitation, could a BFS be considered a lunar "base" if left in place? Guessing it depends on ease of egress/ingress, crew rotation landers and power generation, but still.
If Tiangong can be considered a space station, then sure, why the heck not?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/11/2016 06:06 pm
As large as its likely to be, and with baked in habitation, could a BFS be considered a lunar "base" if left in place? Guessing it depends on ease of egress/ingress, crew rotation landers and power generation, but still.
If Tiangong can be considered a space station, then sure, why the heck not?
I doubt the hab will be baked in, which probably helps. Thermal control during the month long day/night cycle is an issue though.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/11/2016 06:27 pm
As large as its likely to be, and with baked in habitation, could a BFS be considered a lunar "base" if left in place? Guessing it depends on ease of egress/ingress, crew rotation landers and power generation, but still.
If Tiangong can be considered a space station, then sure, why the heck not?
I doubt the hab will be baked in, which probably helps. Thermal control during the month long day/night cycle is an issue though.
According to Musk, it will be.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/11/2016 06:55 pm
Musk said the life support will have to be very light, and that everything would be reused with nothing discarded. That's not incompatible with the hab being modular. Nor is it incompatible with the hab being left somewhere to be reused.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: pobermanns on 06/11/2016 06:56 pm
Musk quoted in the Washington Times article (https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/):

"Being a product scheduling professional, my mind started backing off that date all of the physical tasks that needed to happen in just 6 short years.  …...

And if we're talking MCT, we have to assume the BFR will also be under development.  That is a lot.  I would imagine we'll get a sense of the schedule of events when Musk unveils more details in September, and as he says in the article:

I think that lots of guys have shared your skepticism about the timeline. But do you think that slippage of one synod would not be OK for this grand plan? Meaning, that he's shooting for the 2022 synod but expects the next one to be achievable.

From a leadership standpoint, it seems that this plan might be very effective to motivate the "true believers" to put in their 100%. He's got a real strong cadre with world-class skills, but they need a clear goal. If he sets a goal for 2022, they'll bust their a**es to make it happen. If that comes to pass, GREAT, but if it slips for whatever technical reasons, won't this still be a winning situation? All of them will understand why thy didn't *quite* make it for that synod, and they'll be stoked to make it happen for the next  one.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/11/2016 07:00 pm
I would definitely bet that SpaceX is unlikely to meet the 2025 window for crew. Musk said 2025 is the date if everything went according to plan. You and I and Musk know that not everything goes according to plan. So yeah, I'd say 2027 is more likely for crew. But yeah, they'll probably have to be working on MCT realsoonnow. Break ground on launch site by 2018/2019.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/11/2016 07:12 pm
Break ground on launch site by 2018/2019.

Which would require start of a EIS tomorrow I would guess. Unless there is a site with a special deal for EIS, is there? At the cape, anywhere?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Coastal Ron on 06/11/2016 07:25 pm
I think that lots of guys have shared your skepticism about the timeline. But do you think that slippage of one synod would not be OK for this grand plan? Meaning, that he's shooting for the 2022 synod but expects the next one to be achievable.

I will cheer them on regardless, since despite any inevitable slips to their schedule they will likely be far ahead of anyone else, and it won't be costing me any of my tax dollars.  This is free entertainment as far as I'm concerned.

Quote
From a leadership standpoint, it seems that this plan might be very effective to motivate the "true believers" to put in their 100%. He's got a real strong cadre with world-class skills, but they need a clear goal. If he sets a goal for 2022, they'll bust their a**es to make it happen. If that comes to pass, GREAT, but if it slips for whatever technical reasons, won't this still be a winning situation? All of them will understand why thy didn't *quite* make it for that synod, and they'll be stoked to make it happen for the next  one.

I think Musk is very good at keeping his employees and followers motivated, and no doubt setting challenging goals is part of that.  Doable, but challenging.

Also, there are other aspects to his plan that we don't see yet, and I think part of that is assembling funding partners.  And according to the plan he's announced, they will need a lot money upfront to do everything he wants to do, so I think he's announcing these dates as part of his fundraising efforts.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/11/2016 09:05 pm
Newer refined model for BFR/BFS. Spreadsheet attached.

   BFR & BFS MODELS: MCT as 2nd Stage with 100  Metric Tons CARGO   
      BLUE: Enter parameter variable
S1 Avg ISP Sea L to MECO   335   
S2 vac ISP   380   
Raptor sea level thrust KLB & mT   518   235
Rvac thrust KLB & mT   559   254
S1 Dry Wt %    4.5%   
      
   BFR 1   
BFR DIA   15.0   m
MCT BFS Dry Wt & Cargo   225   mT
S2 Dry Mass   125   mT
Propellant for S2 BFS Landing   30   mT
Total Mass to LEO   255   mT
1st Stage Propellant Tank Length   18.0   m
S1 Propellant Volume   3179   m3
Propellant Mass   3371   mT
S1 Dry Wt %    4.5%   
S1 DRY Weight   159   mT
S1 Total Weight mT   3529   mT
S! Dry Wt Delta V (No 2nd stage)   10.2   Km/sec Rocket Equation
Stage One Full Load Delta V    3.35   Km/sec Rocket Equation
RTxx Propellant   70   mT
RTxx Delta V @Minimum Load   1.20   Km/sec Rocket Equation
Est S1 Gravity Loss    0.9   Km/sec
Est S1 Velocity @ Burnout   2.45   Km/sec
2nd Stage Propellant Tank Length   7.5   m
Propellant Volume   1,325   m3
Propellant Mass   1,404   mT
S2 Mass w/MCT   1,629   mT
S2 Mass w/MCT   3.6   Million LBS
Calc # Rvac Raptor Eng   5.01   0.78
Stage 2 Thrust mT   1271   
Stage 2 Thrust   2.8   Million LBS
Stage 2 Km/sec    6.91   Km/sec Rocket Equation
Stage 2 Wet to Dry Mass Ratio   12.2   
S1 + S2  Total Delta V   9.4   Km/sec
TOTAL WT mT   5,159   mT
TOTAL WT LBS   11.4   Million LBS
THRUST Needed LBS   14.0   Million LBS
THRUST Needed mT   6345   
THRUST Needed MegaNewtons   62   
1st Stage T/W @ Takeoff   1.23   
1st STAGE # ENG    27   
LEO Mass Fract   4.4%    %
LEO Wet to Dry Mass Ratio   23    F9 v1.1 25/1 Musk
MCT Cargo Hold length   10   m
MCT Cargo Vol m3   1766   m3
   Eng 16+8+3=27   
   Outer Ring, Inner Ring, Central Engs   
   NOTE 1:   S1 Km/sec + S2 Km/sec must ~9Km/sec for LEO with grav losses
   NOTE 2:   Rocket Equation

Pretty much what I think the the BFS/MCT will be, with a few minor changes:
1. larger (longer) cargo hold.
2. slightly better mass fractions (but maybe not on the first MCT).
3. slightly less delta-v required to reach orbit, difference from your figures gives margin.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/11/2016 09:16 pm
As large as its likely to be, and with baked in habitation, could a BFS be considered a lunar "base" if left in place? Guessing it depends on ease of egress/ingress, crew rotation landers and power generation, but still.
If Tiangong can be considered a space station, then sure, why the heck not?
I doubt the hab will be baked in, which probably helps. Thermal control during the month long day/night cycle is an issue though.
According to Musk, it will be.

We know that return payload is 25 tonnes. If the hab were integrated into the BFS (and it is still counted as payload) then it is likely yo be too heavy to be returned. But if it isn't returned then how can crew return.

Return from Mars is a strong constraint on the architecture, there are lots of potential architectures that can "land the whole thing" with 100 tonnes of payload, but very few that can return 25 tonnes within one synod. About the only one I can see working is a modular habitat of 25 tonnes (wet fully provisioned), able to carry 25 crew, which may be left on Mars or returned within 1-4 BFS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 06/11/2016 09:25 pm
We know that return payload is 25 tonnes. If the hab were integrated into the BFS (and it is still counted as payload) then it is likely yo be too heavy to be returned. But if it isn't returned then how can crew return.

Return from Mars is a strong constraint on the architecture, there are lots of potential architectures that can "land the whole thing" with 100 tonnes of payload, but very few that can return 25 tonnes within one synod. About the only one I can see working is a modular habitat of 25 tonnes (wet fully provisioned), able to carry 25 crew, which may be left on Mars or returned within 1-4 BFS.

If we go back to the Max Fagin presentation only a fraction of the BFS returns to Earth, leaving (for lack of a better term) a large logistics module on Mars and the ERV much lighter. Fagin shows an "über-Dragon" style configuration with integrated sidewall engines (tiltable?) If these are only enough get it to LMO (easier on the ISRU needs) a pre-positioned depot could provide the deltaV home. The interstage between "über-Dragon" and the logistics module protects the formers heat shield inbound. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/11/2016 09:44 pm
We know that return payload is 25 tonnes. If the hab were integrated into the BFS (and it is still counted as payload) then it is likely yo be too heavy to be returned. But if it isn't returned then how can crew return.

Return from Mars is a strong constraint on the architecture, there are lots of potential architectures that can "land the whole thing" with 100 tonnes of payload, but very few that can return 25 tonnes within one synod. About the only one I can see working is a modular habitat of 25 tonnes (wet fully provisioned), able to carry 25 crew, which may be left on Mars or returned within 1-4 BFS.

If we go back to the Max Fagin presentation only a fraction of the BFS returns to Earth, leaving (for lack of a better term) a large logistics module on Mars. Fagin shows an "über-Dragon" style configuration with integrated sidewall engines. If these are only enough get it to LMO (easier on the ISRU needs) a pre-positioned depot could provide the deltaV home. The interstage between "über-Dragon" and the logistics module protects the formers heat shield inbound.

It is very unlikely that the Max Fagin presentation is the MCT architecture, he would have been prevented by non-disclosure agreement from using SpaceX IPR.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 06/11/2016 09:45 pm
IP protections don't cover obviousness. See rocket landings on barges. See here for another split vehicle config,

http://forum.nasaspaceflight.com/index.php?topic=33224.0

Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/11/2016 10:20 pm
IP protections don't cover obviousness. See rocket landings on barges. See here for another split vehicle config,

I'm not talking about patents, I'm talking about trade secrets. It might be obvious, but there are several other "obvious" ways of doing the MCT. Saying which of these "obvious" ways SpaceX has chosen is a trade secret and would be covered under the non-disclosure terms of standard contracts of employment
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 06/11/2016 11:12 pm
In most jurisdictions a trade secret is 'not generally known or reasonably ascertainable by others.' We also don't know if his slide was approved or not under an NDA. They do seem to like leaving bread crumbs. Keeps the chatter level up.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/11/2016 11:40 pm
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/11/2016 11:54 pm
We know that return payload is 25 tonnes. If the hab were integrated into the BFS (and it is still counted as payload) then it is likely yo be too heavy to be returned. But if it isn't returned then how can crew return.

Return from Mars is a strong constraint on the architecture, there are lots of potential architectures that can "land the whole thing" with 100 tonnes of payload, but very few that can return 25 tonnes within one synod. About the only one I can see working is a modular habitat of 25 tonnes (wet fully provisioned), able to carry 25 crew, which may be left on Mars or returned within 1-4 BFS.

If we go back to the Max Fagin presentation only a fraction of the BFS returns to Earth, leaving (for lack of a better term) a large logistics module on Mars. Fagin shows an "über-Dragon" style configuration with integrated sidewall engines. If these are only enough get it to LMO (easier on the ISRU needs) a pre-positioned depot could provide the deltaV home. The interstage between "über-Dragon" and the logistics module protects the formers heat shield inbound.

It is very unlikely that the Max Fagin presentation is the MCT architecture, he would have been prevented by non-disclosure agreement from using SpaceX IPR.

I agree with Mike, no integrated Hab, rather 4 Hab modules 25 mt a piece placed inside BFS, 3 are left behind on Mars, 1 is returned.  This minimizes return mass and maximizes useful buildup of infrastructure on Mars.

It also makes moving the habs much easier then the Fagin single-massive block concept which dose not look to be intended for movement at all.  Modular habs allow a single common BFS to handle cargo and crew and for crew to return on a different BFS then they arrive in just exchanging habs, this means a faulty BFS doesn't strand the crew on Mars and allows all cargo delivery BFS landings to act ac backups for the crew.

The BFS shape I see is one with the cargo hold at the bottom, Propellant above and engines on the size in 2 pairs with only a slight canting of the engines similar to Dragon capsule.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/12/2016 12:25 am

Pretty much what I think the the BFS/MCT will be, with a few minor changes:
1. larger (longer) cargo hold.
2. slightly better mass fractions (but maybe not on the first MCT).
3. slightly less delta-v required to reach orbit, difference from your figures gives margin.

I'm OK with all that.
I expect to receive some shocks in September
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/12/2016 12:37 am
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.

2 good observations.

First, the tanks.  You're on target.  What I did was simply compute volume and weight of cylinders to estimate the mass of the rocket, etc.  I do NOT mean that the propellant tank is really18m for example,  My bad. There is a big O2 tank and a separate methane tank.  They have rounded ends in reality, making them longer.  A 15m wide rocket does not really have a 15m wide tank.  Again the simplification is used to estimate mass, thrust, etc. and not length of rocket which however I believe will still be squat under 100m.  Engines, interstage, whatever.  I needed to add prose to be clear on that.

Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bob Shaw on 06/12/2016 12:54 am
In line with the philosophy of reuse mfck articulated...

I could see the MCT being "partially strippable"... if you had cabins for 100, but are only returning 20 people why carry all of that back? if the fittings, panels, wiring, plumbing etc was designed to be modular and reusable it could be removed by humans and used in outfitting the base.

Or just stacked up outside under Mylar sheets, ready for use sometime soon. Every last screw and panel should be recovered - nothing should return to Earth which has a value on Mars!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bob Shaw on 06/12/2016 12:59 am
Remember Mars has a atmosphere and has water cycles (water vapor and water ice, does not have liquid phase). So to mine all the water you need, you compress the air and liquefy the water vapor in the atmosphere. Admittedly you would have to compress a lot of atmosphere for a little bit of water but the advantage is you do not have to go out and dig it up! Once the quantities needed become very high then comes the mining of water. But for the initial methalox manufacture for the return trip this method would be an easy one to implement and would not require complex equipment just plenty of power. Compressing gas takes a great deal of energy. But you need the atmosphere compressed for other parts of the methalox manufacture as well.

Not really possible to get water by compression. Water vapour is about 0.03%, so for every kg of water you would need to compress and liquefy 3 tonnes of water <air>.
Compression requires much too much work.  It should be fairly simple to use dessicants to dry out the air, then extract the water by heating the dessicant.  This is one of the most common technologies today to dry compressed air or indoor ice rinks (and was part of the original Mars direct proposal).  alternatively you can compress a refrigerant, and use that to create a cold surface on which the water in the air will condense out.  Any of these solutions will require a minimum of about 1000 btu/lb or 2300 kJ/kg of water, the phase change energy of water.

Basically, you need an energy gradient to extract work - in this case, 'work' equates to water. Some energy can be stored, but the beauty of energy is that it can also be *transformed*.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/12/2016 03:13 am
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.

2 good observations.

First, the tanks.  You're on target.  What I did was simply compute volume and weight of cylinders to estimate the mass of the rocket, etc.  I do NOT mean that the propellant tank is really18m for example,  My bad. There is a big O2 tank and a separate methane tank.  They have rounded ends in reality, making them longer.  A 15m wide rocket does not really have a 15m wide tank.  Again the simplification is used to estimate mass, thrust, etc. and not length of rocket which however I believe will still be squat under 100m.  Engines, interstage, whatever.  I needed to add prose to be clear on that.

Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.
Your dry mass is too high.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/12/2016 05:19 am
Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.

When I did similar calculations (what seems like an age ago) I got 7 - 9 refuelling flights.

I think that brute force is the method they will choose, at least initially.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/12/2016 01:00 pm
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.

2 good observations.

First, the tanks.  You're on target.  What I did was simply compute volume and weight of cylinders to estimate the mass of the rocket, etc.  I do NOT mean that the propellant tank is really18m for example,  My bad. There is a big O2 tank and a separate methane tank.  They have rounded ends in reality, making them longer.  A 15m wide rocket does not really have a 15m wide tank.  Again the simplification is used to estimate mass, thrust, etc. and not length of rocket which however I believe will still be squat under 100m.  Engines, interstage, whatever.  I needed to add prose to be clear on that.

Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.
Your dry mass is too high.

4.5% for 1st stage may be high.  I'm in the camp of those who say minimum 6 legs.  I hope it's high, but I think the BFR has to be more robust, read heavier, if it really is a quick turn around, only very minor refurbishment vehicle.  I think today's F9 has unresolved issues there.

As to the BFS, with all the exotica of engines placed high for Mars landing & takeoff, cargo arrangement complications and robust TPS that lasts many re-entries at interplanetary velocities, I don't buy the dry mass under 100mT thinking for such a complex, lightly serviced vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Mark S on 06/12/2016 02:48 pm
a few more teasers before the september reveal:

https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/

1 red dragon in 2018, 'at least 2' in 2020, then first flight of MCT in 2022...
Bold mine.

From the article:

Quote
Then in 2022, Musk said he hoped to launch what the company now sometimes refers to as the Mars Colonial Transporter, designed to bring a colony to Mars.

I'm sorry, but this is nuts  somewhat optimistic. You all realize that 2022 is only six years away, right? Regardless of the fact that Dragon v2 hasn't flown yet, and regardless of the fact that FH hasn't flown yet; NOTHING concrete about BFR/MCT has even been released, and Musk is talking about launching one in six years. Six. Years.

Six years to get BFR off the ground, literally. To build a factory on the scale of Michoud (only bigger) for fabrication and assembly of BFR and MCT. To build a huge HIF to handle the 12.5m or 15m cores, or heck even to lease one of the VAB high bays and get it fitted out for BFR. To build all of the ground support infrastructure and ground transportation. To get the entire Raptor engine (not just components) off of the drawing board and into the test stands and validated.

Heck, you guys are still arguing over where the thing will be built and launched from. Do you think that would really be the case if they were going to be rolling off the assembly line in less than six years?

I like SpaceX and they are doing amazing things. But come on. Please apply a little common sense when these kinds of pronouncements are made. Two days after the article was published and three pages on in this thread, I would expect to see some kind of discussion about how that would even be possible.

Cheers!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/12/2016 03:40 pm
So basically you're saying that Musk is deliberately lying about his plan date then since none of these activities you cite have happened yet.  I do not believe this to be so.
I am extremely skeptical about the 2022 etc. dates but I believe that Musk has a plan, a plan that requires everything meets aggressive dates and goes right, but a plan that if this miracle happened would be feasible.

I think humans land on Mars in 2033.  2029 best case.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/12/2016 04:25 pm
We don't know the development status of MCT. It could be anywhere from a few powerpoints which seem to hang together as an architecture, to having passed PDR (or the SpaceX equivalent) several months ago. About the only thing known in public is that the Raptor has had component level tests which have gone quite well.

It is now 8 months since Chris Bergin made that tweet https://forum.nasaspaceflight.com/index.php?topic=38593.0 and things will have moved on a lot since then. Chris has shared some of the information that he received in L2, I cannot say what that is, but just given the fact that things were far enough advanced for Chris to be shown data means that they were far enough advanced for the basic factory and launch site specs to be determined (not the detailed ones, but such things as floor area, overhead crane height, access requirements, thrust levels and landing pad requirements). These are enough to start looking for a factory and launch site, and if they have been at it for 8 months SpaceX probably have a pretty good idea about the possibilities.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: the_other_Doug on 06/12/2016 05:39 pm
We don't know the development status of MCT. It could be anywhere from a few powerpoints which seem to hang together as an architecture, to having passed PDR (or the SpaceX equivalent) several months ago. About the only thing known in public is that the Raptor has had component level tests which have gone quite well.

It is now 8 months since Chris Bergin made that tweet https://forum.nasaspaceflight.com/index.php?topic=38593.0 and things will have moved on a lot since then. Chris has shared some of the information that he received in L2, I cannot say what that is, but just given the fact that things were far enough advanced for Chris to be shown data means that they were far enough advanced for the basic factory and launch site specs to be determined (not the detailed ones, but such things as floor area, overhead crane height, access requirements, thrust levels and landing pad requirements). These are enough to start looking for a factory and launch site, and if they have been at it for 8 months SpaceX probably have a pretty good idea about the possibilities.

And to tie it together to other "signs and indicators," for those who have been following the "Where will BFR launch from?" thread, if you look at SpaceX planning on building and launching BFRs in six years, the only place where they are currently beginning construction on new facilities is Boca Chica.

If y'all are saying that SpaceX needs to be building the BFR factory and launch facilities right now, well -- maybe they are.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/12/2016 05:58 pm
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.

2 good observations.

First, the tanks.  You're on target.  What I did was simply compute volume and weight of cylinders to estimate the mass of the rocket, etc.  I do NOT mean that the propellant tank is really18m for example,  My bad. There is a big O2 tank and a separate methane tank.  They have rounded ends in reality, making them longer.  A 15m wide rocket does not really have a 15m wide tank.  Again the simplification is used to estimate mass, thrust, etc. and not length of rocket which however I believe will still be squat under 100m.  Engines, interstage, whatever.  I needed to add prose to be clear on that.

Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.
Your dry mass is too high.

4.5% for 1st stage may be high.  I'm in the camp of those who say minimum 6 legs.  I hope it's high, but I think the BFR has to be more robust, read heavier, if it really is a quick turn around, only very minor refurbishment vehicle.  I think today's F9 has unresolved issues there.

As to the BFS, with all the exotica of engines placed high for Mars landing & takeoff, cargo arrangement complications and robust TPS that lasts many re-entries at interplanetary velocities, I don't buy the dry mass under 100mT thinking for such a complex, lightly serviced vehicle.
And so you have 14 refuelings. That's not going to happen. That is definitely not what SpaceX is planning. Your dry masses are too high.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/12/2016 06:04 pm
We don't know the development status of MCT. It could be anywhere from a few powerpoints which seem to hang together as an architecture, to having passed PDR (or the SpaceX equivalent) several months ago. About the only thing known in public is that the Raptor has had component level tests which have gone quite well.

It is now 8 months since Chris Bergin made that tweet https://forum.nasaspaceflight.com/index.php?topic=38593.0 and things will have moved on a lot since then. Chris has shared some of the information that he received in L2, I cannot say what that is, but just given the fact that things were far enough advanced for Chris to be shown data means that they were far enough advanced for the basic factory and launch site specs to be determined (not the detailed ones, but such things as floor area, overhead crane height, access requirements, thrust levels and landing pad requirements). These are enough to start looking for a factory and launch site, and if they have been at it for 8 months SpaceX probably have a pretty good idea about the possibilities.

And to tie it together to other "signs and indicators," for those who have been following the "Where will BFR launch from?" thread, if you look at SpaceX planning on building and launching BFRs in six years, the only place where they are currently beginning construction on new facilities is Boca Chica.

If y'all are saying that SpaceX needs to be building the BFR factory and launch facilities right now, well -- maybe they are.

In my opinion Boca Chica is not suitable for the MCT manufacturing site. Other places in the Brownsville area maybe. That we have not seen an environmental impact statement is perhaps an indication that SpaceX have found a site that does not need one (existing large factory or facility?) or that they think an environmental impact statement will be a formality (contaminated land, brownfield site?).

If Musk thinks 2024 MCT is possible, then he must see a way forward, but I have no clue about what that path is.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/12/2016 06:05 pm
We don't know the development status of MCT. It could be anywhere from a few powerpoints which seem to hang together as an architecture, to having passed PDR (or the SpaceX equivalent) several months ago. About the only thing known in public is that the Raptor has had component level tests which have gone quite well.

It is now 8 months since Chris Bergin made that tweet https://forum.nasaspaceflight.com/index.php?topic=38593.0 and things will have moved on a lot since then. Chris has shared some of the information that he received in L2, I cannot say what that is, but just given the fact that things were far enough advanced for Chris to be shown data means that they were far enough advanced for the basic factory and launch site specs to be determined (not the detailed ones, but such things as floor area, overhead crane height, access requirements, thrust levels and landing pad requirements). These are enough to start looking for a factory and launch site, and if they have been at it for 8 months SpaceX probably have a pretty good idea about the possibilities.

And to tie it together to other "signs and indicators," for those who have been following the "Where will BFR launch from?" thread, if you look at SpaceX planning on building and launching BFRs in six years, the only place where they are currently beginning construction on new facilities is Boca Chica.

If y'all are saying that SpaceX needs to be building the BFR factory and launch facilities right now, well -- maybe they are.
Yeah, that's certainly a possibility. Boca Chica isn't perfect for daily launches, but for the first decade or two, when the launch rate is more modest, it could certainly function as the first BFR launch site. SpaceX seems to not have a problem with multiple launch sites nor with solutions that only are going to work for a few years or a decade or so.

And SpaceX knows how to make big structures quickly and cheaply. Look at the HIF at LC-39A. I'm not worried about the buildings.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/12/2016 06:06 pm
We don't know the development status of MCT. It could be anywhere from a few powerpoints which seem to hang together as an architecture, to having passed PDR (or the SpaceX equivalent) several months ago. About the only thing known in public is that the Raptor has had component level tests which have gone quite well.

It is now 8 months since Chris Bergin made that tweet https://forum.nasaspaceflight.com/index.php?topic=38593.0 and things will have moved on a lot since then. Chris has shared some of the information that he received in L2, I cannot say what that is, but just given the fact that things were far enough advanced for Chris to be shown data means that they were far enough advanced for the basic factory and launch site specs to be determined (not the detailed ones, but such things as floor area, overhead crane height, access requirements, thrust levels and landing pad requirements). These are enough to start looking for a factory and launch site, and if they have been at it for 8 months SpaceX probably have a pretty good idea about the possibilities.

And to tie it together to other "signs and indicators," for those who have been following the "Where will BFR launch from?" thread, if you look at SpaceX planning on building and launching BFRs in six years, the only place where they are currently beginning construction on new facilities is Boca Chica.

If y'all are saying that SpaceX needs to be building the BFR factory and launch facilities right now, well -- maybe they are.

In my opinion Boca Chica is not suitable for the MCT manufacturing site. Other places in the Brownsville area maybe. That we have not seen an environmental impact statement is perhaps an indication that SpaceX have found a site that does not need one (existing large factory or facility?) or that they think an environmental impact statement will be a formality (contaminated land, brownfield site?).

If Musk thinks 2024 MCT is possible, then he must see a way forward, but I have no clue about what that path is.
Boca Chica doesn't have to be the manufacturing site, it just has to be nearby so that transporting a large structure isn't too hard.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: the_other_Doug on 06/12/2016 06:28 pm
Also, the "local manufacturing site" is likely going to be at least partially an assembly site.  They likely won't want to truck BFR stages around -- too large -- but I bet the engines and whatever serves as an octaweb (the thrust and plumbing structures) could still be made at one primary site, like Hawthorne, and shipped out to the tank manufacture/stage assembly sites.

It's not like there would be no manufacturing happening near the BFR launch sites, but the only things that, it would seem, are required to be built near the launch site are the tanks/stage structures.  A lot of pieces will be sub-assemblies that are manufactured elsewhere and shipped to the BFR sites in by conventional means...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/12/2016 06:44 pm
Also, the "local manufacturing site" is likely going to be at least partially an assembly site.  They likely won't want to truck BFR stages around -- too large -- but I bet the engines and whatever serves as an octaweb (the thrust and plumbing structures) could still be made at one primary site, like Hawthorne, and shipped out to the tank manufacture/stage assembly sites.

It's not like there would be no manufacturing happening near the BFR launch sites, but the only things that, it would seem, are required to be built near the launch site are the tanks/stage structures.  A lot of pieces will be sub-assemblies that are manufactured elsewhere and shipped to the BFR sites in by conventional means...

Possibly, but Hawthorne will be at or near capacity with F9/FH, as reusability reduces the need for first stages, an increased flight rate would increase second stage production*. It is much easier to build on a greenfield site than trying to cram production for completely different (and bigger elements). That said the avionics is probably going to be similar so could be produced at Hawthorne with little difficulty.

[*] in future a reusable raptor based second stage might reduce Hawthorne production requirements, but probably not until the early 2020's.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/12/2016 07:44 pm
Also, the "local manufacturing site" is likely going to be at least partially an assembly site.  They likely won't want to truck BFR stages around -- too large -- but I bet the engines and whatever serves as an octaweb (the thrust and plumbing structures) could still be made at one primary site, like Hawthorne, and shipped out to the tank manufacture/stage assembly sites.

It's not like there would be no manufacturing happening near the BFR launch sites, but the only things that, it would seem, are required to be built near the launch site are the tanks/stage structures.  A lot of pieces will be sub-assemblies that are manufactured elsewhere and shipped to the BFR sites in by conventional means...

Possibly, but Hawthorne will be at or near capacity with F9/FH, as reusability reduces the need for first stages, an increased flight rate would increase second stage production*. It is much easier to build on a greenfield site than trying to cram production for completely different (and bigger elements). That said the avionics is probably going to be similar so could be produced at Hawthorne with little difficulty.

[*] in future a reusable raptor based second stage might reduce Hawthorne production requirements, but probably not until the early 2020's.
...could happen in late 2010s, too. I've suspected they'd start with a Raptor upper stage before MCT. I'm unsure if they will or not, but it's certainly a possibility, since a Raptor upper stage for Falcon 9 and Heavy is mentioned in the USAF contract for Raptor.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/12/2016 07:59 pm
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.

2 good observations.

First, the tanks.  You're on target.  What I did was simply compute volume and weight of cylinders to estimate the mass of the rocket, etc.  I do NOT mean that the propellant tank is really18m for example,  My bad. There is a big O2 tank and a separate methane tank.  They have rounded ends in reality, making them longer.  A 15m wide rocket does not really have a 15m wide tank.  Again the simplification is used to estimate mass, thrust, etc. and not length of rocket which however I believe will still be squat under 100m.  Engines, interstage, whatever.  I needed to add prose to be clear on that.

Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.
Your dry mass is too high.

4.5% for 1st stage may be high.  I'm in the camp of those who say minimum 6 legs.  I hope it's high, but I think the BFR has to be more robust, read heavier, if it really is a quick turn around, only very minor refurbishment vehicle.  I think today's F9 has unresolved issues there.

As to the BFS, with all the exotica of engines placed high for Mars landing & takeoff, cargo arrangement complications and robust TPS that lasts many re-entries at interplanetary velocities, I don't buy the dry mass under 100mT thinking for such a complex, lightly serviced vehicle.
And so you have 14 refuelings. That's not going to happen. That is definitely not what SpaceX is planning. Your dry masses are too high.

I don't get 14 refuelings as there is excess capacity in the Km/sec budget which as I responded above to another poster translates into propellant to LEO.
The dry mass listed for the BFS is for the Mars transport vehicle.  I assume a lesser dry mass for the stripped down tanker to LEO version.  I ran the numbers again and get 6-7 tanker trips which I agree is too many for a cost effective campaign.  SX will do better.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Mark S on 06/12/2016 08:15 pm
If y'all are saying that SpaceX needs to be building the BFR factory and launch facilities right now, well -- maybe they are.

Yes, I am saying that SpaceX would have to be building the production facilities and launch site right now, and much much more. I don't think there is any evidence of that, and it would all be much too large to keep secret. The factory will have to have a welding tool that is twice the diameter of the vertical welding facility for SLS, and probably much taller. The launch site will have to be qualified for launching a vehicle with twice the thrust of the Saturn-V. The transporter/tilt-up gantry will have to be the length of a football field. The MCT itself will dwarf anything launched to space except for ISS, how could it possibly be far enough along (in total secrecy) to be ready to launch in six years?

I'm not saying all of this is impossible. I'm saying that I do think it would be impossible for it all to be ready for launch in six years, with no one hearing a peep of any such activity already under way.

I would love to be proven wrong, though. :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/12/2016 10:18 pm
philw1776:  It seems that your design would require 14 refueling flights to be ready for TMI, and then at Mars a staggering amount of propellant to return.  I'm incredibly doubtful of these fast LEO departures and direct returns because the launch count necessary to do a mission will run up costs and the Mars surface refueling will stress ISPP too far.

Also the vehicle dimensions seem incredibly squat, with tanks that are nearly hockey-pucks in shape, whats the total stack height at launch, it seems like it would be shorter then F9 given the numbers your providing.  I don't see the motivation for such squatness unless you believe Raptor has terrible thrust density, but Russian staged combustion hydrocarbon engines (our best analogs for Raptor) have great thrust density which should easily support a vehicle of 80-100 m of height at liftoff.

2 good observations.

First, the tanks.  You're on target.  What I did was simply compute volume and weight of cylinders to estimate the mass of the rocket, etc.  I do NOT mean that the propellant tank is really18m for example,  My bad. There is a big O2 tank and a separate methane tank.  They have rounded ends in reality, making them longer.  A 15m wide rocket does not really have a 15m wide tank.  Again the simplification is used to estimate mass, thrust, etc. and not length of rocket which however I believe will still be squat under 100m.  Engines, interstage, whatever.  I needed to add prose to be clear on that.

Mike A observed that there is excess Km/sec capacity in that the craft can arrive in LEO with extra tons of fuel.  I believe there will be an upper stage BFS configuration used as a fuel truck with less dry mass.  I get 8-10 refueling trips for one 120 day or less transit.  I think that's too many refueling trips.

Rest assured SX has a much better solution as I'm just a EE and not an aerospace engineer.

One final point.  This is a brute force all chemical approach.  SX will be more imaginative.
Your dry mass is too high.

4.5% for 1st stage may be high.  I'm in the camp of those who say minimum 6 legs.  I hope it's high, but I think the BFR has to be more robust, read heavier, if it really is a quick turn around, only very minor refurbishment vehicle.  I think today's F9 has unresolved issues there.

As to the BFS, with all the exotica of engines placed high for Mars landing & takeoff, cargo arrangement complications and robust TPS that lasts many re-entries at interplanetary velocities, I don't buy the dry mass under 100mT thinking for such a complex, lightly serviced vehicle.
And so you have 14 refuelings. That's not going to happen. That is definitely not what SpaceX is planning. Your dry masses are too high.

I don't get 14 refuelings as there is excess capacity in the Km/sec budget which as I responded above to another poster translates into propellant to LEO.
The dry mass listed for the BFS is for the Mars transport vehicle.  I assume a lesser dry mass for the stripped down tanker to LEO version.  I ran the numbers again and get 6-7 tanker trips which I agree is too many for a cost effective campaign.  SX will do better.

Can I get the numbers for your Tanker dry mass and the expected propellant delivery per trip, I don't see how it can get the BFS vehicle full in the 7 trips your proposing as it would need to offload ~200 mt per flight.  Between landing propellant reserves and the dry mass of something that is basically just a 2nd stage I don't think you have that much propellant offload capacity, 10 flights seems more reasonable.

All that said I agree even 6-7 refueling flights is not viable, and no amount of Dry mass shaving on RB's part is going to make it work.  This is why I belive the only viable architecture is a SEP tug based system in which propellant is pre-placed into high Earth orbit and Mars orbit.  The BFS is radically smaller and goes from LEO to EML-2, refuels, goes to Mars, refuels, launches to LMO, refuels and then returns to Earth, all the DeltaV legs are ~4 km/s and allow fast transit times and only requires a vehicle carry around 300 mt of propellant.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 06/12/2016 10:41 pm
Yes, I am saying that SpaceX would have to be building the production facilities and launch site right now, and much much more. I don't think there is any evidence of that, and it would all be much too large to keep secret. The factory will have to have a welding tool that is twice the diameter of the vertical welding facility for SLS, and probably much taller. The launch site will have to be qualified for launching a vehicle with twice the thrust of the Saturn-V. The transporter/tilt-up gantry will have to be the length of a football field. The MCT itself will dwarf anything launched to space except for ISS, how could it possibly be far enough along (in total secrecy) to be ready to launch in six years?

I'm not saying all of this is impossible. I'm saying that I do think it would be impossible for it all to be ready for launch in six years, with no one hearing a peep of any such activity already under way.

I would love to be proven wrong, though. :)

The Saturn V was designed and launched in five years or so, with all of its launch infrastructure. The money for it was off the charts, but computing power, rocketry, and manufacturing have come a long way since the 1960s. 2024 is 8 years away. It an audacious plan, but who know what resources Mr Musk might be able to tap push this thing forward.

Matthew

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/12/2016 11:11 pm
Any attempt to throw 'computing power' and 'manufacturing' into the same improvement over time comparison is insane and shreds your credibility, the differences are astronomical.  Concrete cures at the same speed now as it did in 1950, if anything launch pads and related construction is slower now.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 06/12/2016 11:59 pm
Any attempt to throw 'computing power' and 'manufacturing' into the same improvement over time comparison is insane and shreds your credibility, the differences are astronomical.  Concrete cures at the same speed now as it did in 1950, if anything launch pads and related construction is slower now.

Easy there. I made no attempt equate those improvements, the commas are there to number them into a list. I am fairly sure the speed at which concrete dries will not determine the schedule. Are you sure you want to describe me as an 'insane?' Hyperbole like that is more unhinged than anything I wrote.

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 06/13/2016 12:01 am
Civil engineering hasn't got a lot faster (from when you break ground, because concrete doesn't cure any faster), but design times can be far less, since you have less empirical and grinding manual calculation, and more simulation. So the pad construction, even if a bit faster, certainly is a long lead time item. 

That said ...The closer you get to compute-ish things, the faster cycles are getting...  circuit board designs for new phones certainly are a lot faster than they were. Look up how long the first Princess phone was in development, perhaps. Then think about how many features it had. Not even a built in calculator, much less the ability to shoot cat videos. Then think about the cycle time to go from the Galaxy S5 to S6...

So I expect that if the resources and will are there, MCT is **barely** doable to have a first launch in 2022. If you claim it's impossible, you're wrong, it's not impossible. (show your work if you disagree!!). If you claim it's improbable, you're probably right.

The Musk way is to set crazy impossible deadlines that rely on everything going perfectly perfect, and expect people to do their best to deliver.  I'll be delighted if MCT only slips one synod...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/13/2016 01:46 am

Can I get the numbers for your Tanker dry mass and the expected propellant delivery per trip, I don't see how it can get the BFS vehicle full in the 7 trips your proposing as it would need to offload ~200 mt per flight.  Between landing propellant reserves and the dry mass of something that is basically just a 2nd stage I don't think you have that much propellant offload capacity, 10 flights seems more reasonable.

All that said I agree even 6-7 refueling flights is not viable, and no amount of Dry mass shaving on RB's part is going to make it work.  This is why I belive the only viable architecture is a SEP tug based system in which propellant is pre-placed into high Earth orbit and Mars orbit.  The BFS is radically smaller and goes from LEO to EML-2, refuels, goes to Mars, refuels, launches to LMO, refuels and then returns to Earth, all the DeltaV legs are ~4 km/s and allow fast transit times and only requires a vehicle carry around 300 mt of propellant.

Yes, you may...

VLEO   8.7   
V  needed by S2 for LEO only   6300   V=VLEO-DeltaV Stage1
TOTAL Mass to LEO   300   m1=m0/(EXP(V/Ve)
BFS Propellant excess mT   75   
Tanker Mass Saving   25   
Tanker Propellant to LEO   200   
# of Tanker Flights for Mars   6.9   

Translation to English...
Excess delta V meant excess propellant to LEO; I had reserved landing propellent in spreadsheet
Tanker dry mass at 100mT, a savings of 25mT
~7 refueling flights needed
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/13/2016 04:59 am
Your only allowing 900 m/s for all drag and gravity losses which looks to be too low by around 300 m/s as I can't find any vehicle with total losses of less then around 1200 m/s.  That would drop your mass in LEO by about 25 mt and put the flight total at an even 8 which is roughly meeting in the middle of our earlier estimates.  Alternatively stretching your vehicle will likely make up the difference.

I'm willing to accept 8 as the best estimate for refueling flights needed to perform this all-chemical brute-force mission architecture when performing a fast crew transfer.  Do you have an estimate for what could be sent on a slow cargo flight?

P.S.  Oops, 300 m/s is what you get from Earth rotation so looks good.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 06/13/2016 05:24 am
-Raptor engine I think is going to production very soon. They work  on it for 6 years.
-BFR is probably ready for building, I am just curious what design changes return stages give them:
 they will use heat shield for BRF
or during atmosphere heating  keeping slightly under power , to shield engine compartment?
-I am almost sure, that first crew to Mars will not have rocket ready with fuel for return trip, but Spacex guarantee them every 2 years, provide provision and supply for finishing ISRU and start return to Earth business.
I think we are not ready to have robotic facility to finish it without human presence and ability to fix, modify and adjust plan and build the plant.
-ISRU will have energy  enormous requirement, will solar be enough to provided?
-They will also need lot heat just to keep habs temperature up, without radioisotope thermoelectric generator at least as backup energy source, will be not wise in my opinion.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 06/13/2016 05:37 am
I think they choosed diameter 15 meters because:
-MCT will have same diameter to have better characteristic during braking in Mars atmosphere, will be similar to shape of  Dragon 2 and have interesting lifting attributes, maybe even side engine for landing maneuvers, Raptor thrust will be not necessary.
-BFR will have better characteristic during braking in Mars atmosphere and safe more fuel for landing
-whole rocket will be under 100m height.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: geza on 06/13/2016 05:53 am
So I expect that if the resources and will are there, MCT is **barely** doable to have a first launch in 2022. If you claim it's impossible, you're wrong, it's not impossible. (show your work if you disagree!!). If you claim it's improbable, you're probably right.
It is good to discuss the optimal, albeit improbable, case. We can trust Elon that he has a timeline in his mind. I am more troubled with the payload for this launch. Developing surface systems is not considered trivial. Neither mining operaations. Especially troubled if robotic fuel production for MCT return is assumed before the first crewed lauch in '24. You need to understand soil properties at the chosen location to design mining and oxigen extraction. The '18 Dragon lander is said to be only a landing test. Then the Dragons launched in '20 have to study the soil and to do mining and O2 extraction experiments. Then, you have a little more than a single year to develop the equipment. Maybe, the '18 lander should be more than a landing experiment. Maybe, it will include drilling and analysis of the samples. (Some of you say that it  would be impossible to develop such payload for '18.) Then, the '20 landers can validate the mining/extraction methods developed on an informed basis. Maybe, the '20 landers include sample return...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 06/13/2016 07:33 am
a few more teasers before the september reveal:

https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/

1 red dragon in 2018, 'at least 2' in 2020, then first flight of MCT in 2022...
Bold mine.

From the article:

Quote
Then in 2022, Musk said he hoped to launch what the company now sometimes refers to as the Mars Colonial Transporter, designed to bring a colony to Mars.

I'm sorry, but this is nuts  somewhat optimistic. You all realize that 2022 is only six years away, right? Regardless of the fact that Dragon v2 hasn't flown yet, and regardless of the fact that FH hasn't flown yet; NOTHING concrete about BFR/MCT has even been released, and Musk is talking about launching one in six years. Six. Years.

Six years to get BFR off the ground, literally. To build a factory on the scale of Michoud (only bigger) for fabrication and assembly of BFR and MCT. To build a huge HIF to handle the 12.5m or 15m cores, or heck even to lease one of the VAB high bays and get it fitted out for BFR. To build all of the ground support infrastructure and ground transportation. To get the entire Raptor engine (not just components) off of the drawing board and into the test stands and validated.

Heck, you guys are still arguing over where the thing will be built and launched from. Do you think that would really be the case if they were going to be rolling off the assembly line in less than six years?

I like SpaceX and they are doing amazing things. But come on. Please apply a little common sense when these kinds of pronouncements are made. Two days after the article was published and three pages on in this thread, I would expect to see some kind of discussion about how that would even be possible.

Cheers!

To be honest?  "What could you possibly do in six years" is kind of ridiculous.  Many of the largest megaprojects of industrial humanity have been done on this sort of timescale.  In modern politics, a leader announcing a megaproject that won't be completed (or worse, have construction spending even ramp up) within his term has become an antipattern that costs us inordinately;  The successor predictably cancels it so they can announce their own, or never mentions it again.  "We'll do this by $time+20years" means very nearly nothing at all.  If you think that kind of timespan is genuinely required, it's usually a sign that you're not being a audacious enough to get anything whatsoever done - you don't want to commit the resources, don't care about the end goal, and aim to cruise on some political impetus gained by the initial announcement, which was essentially a lie.

I don't completely see the point of a privately run for-profit enterprise racing to Mars,  but I see even less point in them aiming to do so *slowly*.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/13/2016 11:27 am
Your only allowing 900 m/s for all drag and gravity losses which looks to be too low by around 300 m/s as I can't find any vehicle with total losses of less then around 1200 m/s.  That would drop your mass in LEO by about 25 mt and put the flight total at an even 8 which is roughly meeting in the middle of our earlier estimates.  Alternatively stretching your vehicle will likely make up the difference.

I'm willing to accept 8 as the best estimate for refueling flights needed to perform this all-chemical brute-force mission architecture when performing a fast crew transfer.  Do you have an estimate for what could be sent on a slow cargo flight?

P.S.  Oops, 300 m/s is what you get from Earth rotation so looks good.

No cargo estimate but as you can probably infer I made the 2nd stage ~ 7Km/sec capable so trading off Km/sec for payload & using trajectory browser you can get increased cargo for transit.  However it means a few tonnes more propellant in the Mars landing burn. 

Thanks for the informed critiques, people.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: geza on 06/13/2016 11:55 am
How much is 6 or 8 years?

Kennedy challenge: May 25, 1961
Announcement of Saturn 5: Jan 10, 1962
Mode decision: Nov 7, 1962
First flight of Saturn 5: Nov 9, 1967
Moon landing: Jul 20, 1969
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 06/13/2016 12:05 pm
Split out part thread on mini-BFR speculation:

Building a smaller BFR would require almost the same up front cost as the full thing. The factory, tooling, workforce, launch infrastructure, etc are at best slightly cheaper for a mini version but not by much. The cost of doing it twice (mini+full BFR) seems so prohibitive that investing only in the full size BFR seems much better in comparison. The length of BFR might change over time because it does not require a retooling of the factory.  I don't think the diameter will change once it is set though.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 12:56 pm
Your only allowing 900 m/s for all drag and gravity losses which looks to be too low by around 300 m/s as I can't find any vehicle with total losses of less then around 1200 m/s.  That would drop your mass in LEO by about 25 mt and put the flight total at an even 8 which is roughly meeting in the middle of our earlier estimates.  Alternatively stretching your vehicle will likely make up the difference.

I'm willing to accept 8 as the best estimate for refueling flights needed to perform this all-chemical brute-force mission architecture when performing a fast crew transfer.  Do you have an estimate for what could be sent on a slow cargo flight?

P.S.  Oops, 300 m/s is what you get from Earth rotation so looks good.
8 is too many.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/13/2016 02:40 pm
Phil, if I might ask, why do you have so much performance spec'ed into the upper stage?

A fast (80-120 day) transfer to Mars rarely requires more than 4.5 to 5 km/s from LEO, but your numbers (1604t wet, 225t dry, 380 ISP) give 7.32 km/s of total performance with a 100t payload. Mars EDL will add somewhere in the 1.2 to 1.5 km/s range (I don't see an estimate in your spreadsheet), but even with that requirement your margins run from 12.6% to 28.4%. Since it can do a fast transfer and Mars EDL while only partly fueled, I get 4 to 5.5 refueling launches per fast Mars transfer.

Earth return definitely can use that performance, but you don't include any numbers for that. By my estimates the poor alignments in the 2020's prevent even a 1604t wet, 125t dry vehicle from returning before the next synod's optimal launch window.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 02:49 pm
1.2-1.5km/s is on the high end for EDL except if you decide to do a braking burn before entry.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/13/2016 03:02 pm
1.2-1.5km/s is on the high end for EDL except if you decide to do a braking burn before entry.

That would indicate 30t of fuel is excessive for Earth EDL, as that's 0.85 to 1.0 km/s for a 100t tanker depending on the altitude/ISP. I don't anticipate anything with an orbital re-entry heatshield will do an entry burn (it's rather pointless in Earth's dense atmosphere), and terminal velocity on Earth will be under 200 m/s for a very large, relatively light vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 03:03 pm
1.2-1.5km/s is on the high end for EDL except if you decide to do a braking burn before entry.

That would indicate 30t of fuel is excessive for Earth EDL, as that's 0.85 to 1.0 km/s for a 100t tanker depending on the altitude/ISP. I don't anticipate anything with an orbital re-entry heatshield will do an entry burn (it's rather pointless in Earth's dense atmosphere), and terminal velocity on Earth will be under 200 m/s for a very large, relatively light vehicle.
Right. And you'll have enough thrust to do a high-thrust landing, which means low gravity losses.

Also, 100t tanker is much too small.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/13/2016 03:08 pm
1.2-1.5km/s is on the high end for EDL except if you decide to do a braking burn before entry.

That would indicate 30t of fuel is excessive for Earth EDL, as that's 0.85 to 1.0 km/s for a 100t tanker depending on the altitude/ISP. I don't anticipate anything with an orbital re-entry heatshield will do an entry burn (it's rather pointless in Earth's dense atmosphere), and terminal velocity on Earth will be under 200 m/s for a very large, relatively light vehicle.
Right. And you'll have enough thrust to do a high-thrust landing, which means low gravity losses.

Also, 100t tanker is much too small.

That's 100t dry. Would be 1200t or 1500t at launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 03:10 pm
1.2-1.5km/s is on the high end for EDL except if you decide to do a braking burn before entry.

That would indicate 30t of fuel is excessive for Earth EDL, as that's 0.85 to 1.0 km/s for a 100t tanker depending on the altitude/ISP. I don't anticipate anything with an orbital re-entry heatshield will do an entry burn (it's rather pointless in Earth's dense atmosphere), and terminal velocity on Earth will be under 200 m/s for a very large, relatively light vehicle.
Right. And you'll have enough thrust to do a high-thrust landing, which means low gravity losses.

Also, 100t tanker is much too small.

That's 100t dry. Would be 1200t or 1500t at launch.
100t dry is too high for a tanker, I think. And maybe try 1000t instead. And greater payload.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 03:17 pm
SpaceX can do dry masses of about 25:1 (and I think they can do better, actually). Take away 10% for using methane (due to lower density), 10% for TPS (this is what a TPS expert told me), 10% for landing legs (that's very conservative for an optimized design, by the way), 10% for landing thrust (assumes 300m/s landing delta-v, so 200m/s terminal velocity with 50% gravity losses), you're left with a mass ratio of ~18.

18 mass ratio with 1000t is 56t on-orbit (with enough propellant to land) and about 50t totally dry.

And I think SpaceX can do much better using better materials. If you look at how good the later versions of the Shuttle external tank were, combined with SpaceX's T/W=200, and further materials improvements (by using state of the art composites instead of just al-li alloys), I can definitely see it being improved further, and not just incrementally but dramatically. Like 30-40t dry.

But assuming 100t dry is about twice as heavy as what I think is realistic for SpaceX to achieve. That's sandbagging, IMO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/13/2016 04:01 pm
100t dry is too high for a tanker, I think. And maybe try 1000t instead. And greater payload.
For a dedicated tanker which does not share the outer mould line of the BFS then 100 tonnes is too high (I reckon something like 70 tonnes, but SpaceX might be able to reduce that even more). However, the first tanker flights may not be a dedicated design, instead just standard BFS with extra fuel in their tanks and perhaps long duration equipment removed. Then 100 tonnes dry is probably a bit too little.

Although a dedicated tanker design with all the excess mass removed would be cheaper in the long run, during BFR/BFS development it would be another craft competing for development funds and effort.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/13/2016 04:40 pm
Phil, if I might ask, why do you have so much performance spec'ed into the upper stage?

A fast (80-120 day) transfer to Mars rarely requires more than 4.5 to 5 km/s from LEO, but your numbers (1604t wet, 225t dry, 380 ISP) give 7.32 km/s of total performance with a 100t payload. Mars EDL will add somewhere in the 1.2 to 1.5 km/s range (I don't see an estimate in your spreadsheet), but even with that requirement your margins run from 12.6% to 28.4%. Since it can do a fast transfer and Mars EDL while only partly fueled, I get 4 to 5.5 refueling launches per fast Mars transfer.

Earth return definitely can use that performance, but you don't include any numbers for that. By my estimates the poor alignments in the 2020's prevent even a 1604t wet, 125t dry vehicle from returning before the next synod's optimal launch window.

Nit, I used 1629 wet, but that's beside your point.

Here's what I was using for Mars transit...
"LEO esc 3.2Km/s + Fast transit ~1.7 Km/s + aerocapture + Mars landing 2Km/s ~ 7 Km/sec Delta V for 2nd stage MCT"  Since I was sloppy and forgot to include the URL on my spreadsheet I'm not sure of the source.  I was trying for the 7Km/sec to Mars and propellant tank volume for 8 something Km/sec for return from Mars with reduced payload, 25t, not 100t.
Hopefully I erroneously over required Km/sec for transit, which would lower the # of tanker flights needed.
I solicit better estimates of the delta V needed to go all chemical from LEO to Mars surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 04:42 pm
100t dry is too high for a tanker, I think. And maybe try 1000t instead. And greater payload.
For a dedicated tanker which does not share the outer mould line of the BFS then 100 tonnes is too high (I reckon something like 70 tonnes, but SpaceX might be able to reduce that even more). However, the first tanker flights may not be a dedicated design, instead just standard BFS with extra fuel in their tanks and perhaps long duration equipment removed. Then 100 tonnes dry is probably a bit too little.

Although a dedicated tanker design with all the excess mass removed would be cheaper in the long run, during BFR/BFS development it would be another craft competing for development funds and effort.
I think the initial BFSes will be on the order of 80-120 tons dry, even with crew equipment.

At first, they won't need much equipment due to a small crew. I mean,  the entire Salyut 6 module was 20 tons and was not anywhere NEAR mass-optimized but still was enough for 2 crew for 100 days. So yeah, I think another 30-50 tons dry over the tanker mass would be more than enough (actually, overkill) for a small crew.

But there's tons of room for mass optimization. How lightweight can things really get? Incredibly lightweight. Think backpacking, but with materials and manufacturing capabilities available in the 2030s. Already, you can easily halve the mass of many living quarters-related items with cleverness. So you can start supporting larger crews, like 50 passengers, in that original 30-50 tons. I could even see 100 passengers in 50 tons, plus consumables (many of which could be recycled or available in ultra-dense forms, like 300-500 grams of low-glycemic food per day, just 3-5 tons for the transit). It might take decades to get to that level of optimization, but they have decades before they will be sending that many people at once.

So I think we should make the assumption that SpaceX will start with fairly low dry masses. Like perhaps as low as 80 tons dry for the initial crew vehicle. To support larger crews, the dry mass may increase slightly over time, but they'll likely be aggressively optimizing and reducing the dry mass per passenger, so it may not change too much.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 04:59 pm
http://www.defense.gov/News/Contracts/Contract-View/Article/642983

Quote
This other transaction agreement requires shared cost investment with SpaceX for the development of a prototype of the Raptor engine for the upper stage of the Falcon 9 and Falcon Heavy launch vehicles.

Considering:
1) the MCT (or BFS) is essentially a big reusable upper stage
2) Raptor is being built primarily for MCT/BFS
3) It's doubtful SpaceX would be building a new /expendable/ upper stage based on Raptor when they have plenty of performance with Falcon Heavy for any commercial payloads

...this info suggests that SpaceX is considering building an almost-certainly-reusable upper stage based on Raptor. Since all info suggests such a stage would be VTVL, it'd essentially already BE a lander, and Earth-lander. Such a stage could also be used on Mars (especially if the upper stage has the sort of long-lifetime modifications you might want for direct GSO insertion), just like Red Dragon is.

So it's false to say there's "zero reason to suspect that a mini-MCT may exist." The USAF contract suggests it could be an option, so that's non-zero reason.

...doesn't have to be a terribly CONVINCING reason, but it's reason nonetheless, so your statement is false.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 05:01 pm
Note: Elon's recent announcement of a first possible flight to Mars of MCT in 2022 reduces the odds that SpaceX will be using a Raptor-based upper stage in that manner.

I wouldn't bet any money that SpaceX is developing the mini-MCT, but it still remains a possibility.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/13/2016 05:26 pm
...
"LEO esc 3.2Km/s + Fast transit ~1.7 Km/s + aerocapture + Mars landing 2Km/s ~ 7 Km/sec Delta V for 2nd stage MCT"  Since I was sloppy and forgot to include the URL on my spreadsheet I'm not sure of the source.  I was trying for the 7Km/sec to Mars and propellant tank volume for 8 something Km/sec for return from Mars with reduced payload, 25t, not 100t.
...
Thanks. Terminal velocity should be in the range of 500 to 1,250 m/s at Mars, depending on atmospheric density, drag coefficient, etc. 2 km/s for EDL is very conservative.
128 day transits require 3.75 to 4.87 km/s from 200km LEO for TMI (80 days can be done under 5 km/s sometimes):
Edit (other link was rather long) See NASA's trajectory browser: http://goo.gl/yHCwzE
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 06/13/2016 05:46 pm
Or, this stage is a SpaceX long duration stage for bidding on the same contracts as Vulcan ACES.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 06:11 pm
Or, this stage is a SpaceX long duration stage for bidding on the same contracts as Vulcan ACES.
Right, but that could be done with their current kerolox stage as well, you just need more batteries.

Musk said they decided to put off second stage reuse because it's not quite worth it yet with kerolox (and to high energy orbits). But he left open the use of methane/LOx.

This would be the PERFECT opportunity to develop a reusable upper stage, and I cannot imagine them spending so much money on a new upper stage with a new propellant combination and a new engine and likely much, much higher performance that was not intended to be reusable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 06/13/2016 06:23 pm
How about the reusable RaptorVac S2 first, likely 5+ meters, with a later Falcon-Raptor high performance S1 to replace the F9 Merlin cores? That eliminates duplicious ground systems and possibly having 2 launchers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 07:08 pm
2km/s is ridiculously high for EDL unless you're doing a large braking burn.

Sandbagging stuff is not helpful and will mislead you.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: baldusi on 06/13/2016 07:17 pm
Upto now SpaceX modus operandi has been to under deliver initially and over deliver after a few iterations. Dragon is not a scaled down MCT. So they will probably start with something small to validate it and learn and only later do the huge stuff when everything else closes.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/13/2016 07:26 pm
2km/s is ridiculously high for EDL unless you're doing a large braking burn.

Sandbagging stuff is not helpful and will mislead you.

...and reasonable Km/sec budget ranges from LEO to Mars surface are...?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 07:38 pm
2km/s is ridiculously high for EDL unless you're doing a large braking burn.

Sandbagging stuff is not helpful and will mislead you.

...and reasonable Km/sec budget ranges from LEO to Mars surface are...?
7km/s is reasonable for like 90-100 day transits and /especially/ bad transit opportunities. But I think 6km/s is enough for nominal mission.

...a big question is Mars to Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/13/2016 08:02 pm
7km/s is reasonable for like 90-100 day transits and /especially/ bad transit opportunities. But I think 6km/s is enough for nominal mission.

...a big question is Mars to Earth.
If you budget 6.3 km/s (5.0 km/s for TMI and 1.3 km/s for EDL), you will typically be able to make a ~100-day transit with plenty of margin. Fast TMI is typically 4.5 to 4.9 km/s:

Edit: fuel loads and payloads can always be tweaked for faster or slower transits, so tank size isn't really a limiting design factor. Design for a standard case, then optimize for other factors.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/13/2016 08:10 pm
7km/s is reasonable for like 90-100 day transits and /especially/ bad transit opportunities. But I think 6km/s is enough for nominal mission.

...a big question is Mars to Earth.
If you budget 6.3 km/s (5.0 km/s for TMI and 1.3 km/s for EDL), you will typically be able to make a ~100-day transit with plenty of margin. Fast TMI is typically 4.5 to 4.9 km/s:

Edit: fuel loads and payloads can always be tweaked for faster or slower transits, so tank size isn't really a limiting design factor. Design for a standard case, then optimize for other factors.
Right.

I think 6km/s is enough for LEO to Mars surface (I think 1km/s is more than enough for EDL, provided you can handle that fast of a reentry for gee-load reasons), but I wonder also about Mars to Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/13/2016 08:20 pm
2km/s is ridiculously high for EDL unless you're doing a large braking burn.

Sandbagging stuff is not helpful and will mislead you.

...and reasonable Km/sec budget ranges from LEO to Mars surface are...?
7km/s is reasonable for like 90-100 day transits and /especially/ bad transit opportunities. But I think 6km/s is enough for nominal mission.

...a big question is Mars to Earth.

Yes, Mars to Earth is harder, especially with 25 tonnes of payload.

It would be instructive for someone to put together a table like that above showing transits in both directions.

I think it is not particularly easy to do, it needs to give a reasonable length of time on Mars (at least a week, more like a month, to allow cargo transfer/refueling/processing of multiple BFS) and also a reasonable length of time on Earth so that it can enable relaunched and refueling of the BFS fleet.

Some of these return transits may use longer, lower delta-v orbits, but at each synod there should also be a fast transit for crew (even if that transit does not allow one synod reuse).

I think returns in the 3-4 month duration are only possible if higher delta-v off-optimum Earth to Mars transits are made. It would be nice to have this confirmed. I've tried to do this with the data from NASA's trajectory browser, but have failed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mlindner on 06/13/2016 09:27 pm
Upto now SpaceX modus operandi has been to under deliver initially and over deliver after a few iterations.

Since when?

Quote
Dragon is not a scaled down MCT. So they will probably start with something small to validate it and learn and only later do the huge stuff when everything else closes.

And Dragon is a scaled up version of nothing.

Why would they build something else when they've explicitly stated that they are not? The explicit statement is MCT first test launch in 2022. The only reason they've built anything smaller in the past is when they've been unable to build what they intended. Falcon 9 only happened because Falcon 5 wasn't big enough to carry Dragon and they'd already substantially designed Falcon 5. The rocket only got bigger because they found optimizations they could make to the architecture and the engines.

A mini-MCT would happen if they build the Raptor and then found it was underperforming and needed to scale back the MCT and it wouldn't be that much smaller and the goal wouldn't be the mini-MCT. I can't understand why an engineer would consider a mini-MCT as being preferable to a full-up MCT if the intention was ultimately to build an MCT. You should build the MCT first as you intend and then compromise if you have to and then work on fixing the bugs and refine your design over time. As it is, MCT is likely to scale up even further as they refine Raptor engine design.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 06/13/2016 09:42 pm
But there's tons of room for mass optimization. How lightweight can things really get? Incredibly lightweight. Think backpacking, but with materials and manufacturing capabilities available in the 2030s.

We need to look no further than the ISS living quarters. Just little 'cocoons' with velcroed flaps. That should be just fine for intrepid spacefarers going to Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/13/2016 10:23 pm
2km/s is ridiculously high for EDL unless you're doing a large braking burn.

Sandbagging stuff is not helpful and will mislead you.

...and reasonable Km/sec budget ranges from LEO to Mars surface are...?

I estimate 800 m/s for Mars EDL which is consistent with Red Dragons simulations.  A decelerator in excess of 15m in diameter such as ADEPT or HIAD could lower this but at the cost of higher dry mass.

Departing Earth from EML1 with a lunar and Earth swing-buy can send you to a fast Mars transit can be around 1 km/s.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/13/2016 11:31 pm
EML1 is 3.77 km/s from 200 km LEO, so the total budget via that route is about the same as direct TMI from LEO. It's just broken into smaller steps.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/14/2016 01:19 am
I think he's talking about starting at EML1, dropping to ~LEO and doing an Oberth burn
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/14/2016 03:17 am
I think he's talking about starting at EML1, dropping to ~LEO and doing an Oberth burn
Indeed. And if you had a full propellant load at EML1/2, you could do even faster transits, though you'd have to reserve some of the propellant for slowing down. You're hitting diminishing returns if you have to use a lot of propellant to slow down, but it's still interesting to consider.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RobLynn on 06/14/2016 03:03 pm
MCT booster design height:

An optimally over-expanded rocket (eg RD193) produces 56 tonnes thrust per square meter of nozzle area at sea level, won't be much difference between various hydrocarbon rockets as all have similar pressures and velocities at nozzle exit.

Packing of multiple nozzles will only cover about 60% of the rocket base area at best, probably more like 50% given allowances for gimballing.

Need about 1.3g acceleration at liftoff (or more for higher ISP)

So 56*.5/1.3= ~20-25 tonnes of mass per square meter of base area that can be supported by a rocket.  For LOX/CH4 bulk density of ~800kg/m that means that rockets can only support a column of fuel about 25-30m high in a prismatic form factor.

There are of course advantages to being thin for reduced aero losses - so maximum fuel column height within this constraint is likely to be the design chosen.

There will of course be substantial height taken by domed tank ends, 1st and 2nd stage engines, and finally cargo bay, but assuming a common bulkhead between LOX and CH4 and a single stick design I think could safely assume that will only be 30m+~1.4 stage diameter (4x domed ends for 2 stacked stages) + engine lengths (perhaps 4m per stage).

So overall I think 1st+2nd stage very unlikely to be taller than 50-60m.  Though payload might add 30m in some cases.  Ie rocket portion is pretty damned similar heights to Falcon9.  It will just be substantially bigger diameter.

100M+ tall rockets only make sense for LH2.

Given Musk's suggestions of 2-3MN thrust to weight optimum for SC engines, I think that the design starts to look quite constrained.  with perhaps the big choice being 2 rings (7-9 engines, 2000-3000 tonne GTOW) or 3 rings, 21-25 engines and 6-9000 tonne GTOW, and given development costs, launch site costs, and market it will almost certainly be the former.

Assuming 9x2.5MN engines each 4m long , that is about 9m diameter and total 50m tall (without cargo)
Assuming 25x2.5MN engines each 4m long, that is about 14m diameter and 58m tall (without cargo)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/14/2016 05:01 pm
Given Musk's suggestions of 2-3MN thrust to weight optimum for SC engines, I think that the design starts to look quite constrained.  with perhaps the big choice being 2 rings (7-9 engines, 2000-3000 tonne GTOW) or 3 rings, 21-25 engines and 6-9000 tonne GTOW, and given development costs, launch site costs, and market it will almost certainly be the former.

Given that it needs to put 200-300 metric tons in orbit, it will almost certainly be the latter. SpaceX's goal is Mars in the 2020's, and a 9-Raptor booster that's only marginally more powerful than Falcon Heavy doesn't get them there.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 06/14/2016 05:16 pm
In addition, it needs to put 100 metric tons of payload, not just spacecraft mass, onto the Martian surface. It's it's go ginormous or go home.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 06/14/2016 05:16 pm
Musk has stated 15,000,000 lbf of takeoff thrust, so take it from there. Go long or go home.

Edit: GMTA :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 06/14/2016 05:41 pm
MCT booster design height:

An optimally over-expanded rocket (eg RD193) produces 56 tonnes thrust per square meter of nozzle area at sea level, won't be much difference between various hydrocarbon rockets as all have similar pressures and velocities at nozzle exit.

Packing of multiple nozzles will only cover about 60% of the rocket base area at best, probably more like 50% given allowances for gimballing.

Need about 1.3g acceleration at liftoff (or more for higher ISP)

So 56*.5/1.3= ~20-25 tonnes of mass per square meter of base area that can be supported by a rocket.  For LOX/CH4 bulk density of ~800kg/m that means that rockets can only support a column of fuel about 25-30m high in a prismatic form factor.

There are of course advantages to being thin for reduced aero losses - so maximum fuel column height within this constraint is likely to be the design chosen.

There will of course be substantial height taken by domed tank ends, 1st and 2nd stage engines, and finally cargo bay, but assuming a common bulkhead between LOX and CH4 and a single stick design I think could safely assume that will only be 30m+~1.4 stage diameter (4x domed ends for 2 stacked stages) + engine lengths (perhaps 4m per stage).

So overall I think 1st+2nd stage very unlikely to be taller than 50-60m.  Though payload might add 30m in some cases.  Ie rocket portion is pretty damned similar heights to Falcon9.  It will just be substantially bigger diameter.

100M+ tall rockets only make sense for LH2.

Given Musk's suggestions of 2-3MN thrust to weight optimum for SC engines, I think that the design starts to look quite constrained.  with perhaps the big choice being 2 rings (7-9 engines, 2000-3000 tonne GTOW) or 3 rings, 21-25 engines and 6-9000 tonne GTOW, and given development costs, launch site costs, and market it will almost certainly be the former.

Assuming 9x2.5MN engines each 4m long , that is about 9m diameter and total 50m tall (without cargo)
Assuming 25x2.5MN engines each 4m long, that is about 14m diameter and 58m tall (without cargo)

Well, your numbers differ astoundingly from Musk's numbers. And HE is the one building the rocket.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/14/2016 06:43 pm
We know from public info that BFR is supposed to be about 15 million lbf of thrust. That implies a mass of around 12E6lbm or 6000tons.

It's quite true that there's a limit to the height of the fueled portion of a rocket of constant diameter just simply due to what an efficient rocket engine can achieve.

But there will be space for plumbing and for an interstage and the payload (the cabin portion of the BFS) may be quite low density, so you could definitely imagine around 100m or more for the whole shebang.

...interestingly, try doing a similar calculation for Falcon 9, and you'll see that it should be much shorter than its 70m height.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Mongo62 on 06/14/2016 09:49 pm
IAC 2016 PLENARIES AND HIGHLIGHT LECTURES (http://www.iafastro.org/events/iac/iac2016/plenary-programme/)

Tuesday September 27
13:30-14:30 CDT = 14:30-15:30 EDT
Colonizing Mars -- A deep technical presentation on the space transport architecture needed to colonize Mars (SpaceX late breaking)

Is this in addition to the previously known Friday 8:30-10:30 CDT = 9:30-11:30 EDT session?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/15/2016 04:20 pm
How about the reusable RaptorVac S2 first, likely 5+ meters, with a later Falcon-Raptor high performance S1 to replace the F9 Merlin cores? That eliminates duplicious ground systems and possibly having 2 launchers.

Musk is saying MCT will launch for Mars in 2022 if everything works right. I don't see any time to develop a ~5 meter Raptor booster before that, or any real reason to have it at all after BFR is flying. BFR will eventually service the common orbits (GTO, ISS, synchronous LEO, and all BEO), and other orbits will be serviced by Falcon, SEP from a BFR launch orbit, buying a whole BFR launch, or another launch provider.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/15/2016 04:55 pm
How about the reusable RaptorVac S2 first, likely 5+ meters, with a later Falcon-Raptor high performance S1 to replace the F9 Merlin cores? That eliminates duplicious ground systems and possibly having 2 launchers.

Musk is saying MCT will launch for Mars in 2022 if everything works right. I don't see any time to develop a ~5 meter Raptor booster before that...
Unless they've already started building it.

But I agree the 2022 date for MCT (which we assume is basically the full MCT, right?) does make such a stage less likely (ESPECIALLY a booster).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/16/2016 01:15 pm
I think it's pretty clear that they have started building Raptor. They might have started building a ~5m upper stage for it since that could go on FH pretty easily and maybe even on F9.

But building a Falcon Heavy replacement booster, before FH even flies? I don't think so. MCT has a pretty clearly defined set of goals including super heavy lift, and building another heavy lift booster doesn't help achieve those in the very tight timeframe Musk is shooting for.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 06/16/2016 01:51 pm
I think it's pretty clear that they have started building Raptor. They might have started building a ~5m upper stage for it since that could go on FH pretty easily and maybe even on F9.

But building a Falcon Heavy replacement booster, before FH even flies? I don't think so. MCT has a pretty clearly defined set of goals including super heavy lift, and building another heavy lift booster doesn't help achieve those in the very tight timeframe Musk is shooting for.

It's quite common to be designing and test building your next version of <whatever> before the current version hits the market...Especially true of things that have a long development time.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 06/16/2016 02:31 pm
IAC 2016 PLENARIES AND HIGHLIGHT LECTURES (http://www.iafastro.org/events/iac/iac2016/plenary-programme/)

Tuesday September 27
13:30-14:30 CDT = 14:30-15:30 EDT
Colonizing Mars -- A deep technical presentation on the space transport architecture needed to colonize Mars (SpaceX late breaking)

Is this in addition to the previously known Friday 8:30-10:30 CDT = 9:30-11:30 EDT session?

Looks like they have a session on "The Saturn system as a natural laboratory to investigate the emergence of biology" from 8:30 - 9:30 Friday now.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/16/2016 02:34 pm
I'm not so sure the engines can't be protruding through a heatshield (more or less like a Falcon 9 first stage), assuming they have sufficient propellent to run at least some of the engines with enough power to use the supersonic retropropulsion effect to push the shock wave far enough out to reduce aero heating. For Mars decent that is probably easier since the atmosphere is thinner in the first place (less need for a heat shield), for Earth this may be more difficult.

Even if you cant the engines around the heatshield (more like Crew Dragon than Falcon 9 first stage), if you drop off the cargo as one giant module, you still have a problem, since you just dropped your (Mars) heat shield you need a second, more massive (at least you could save mass on the Martian one) Earth heat shield, which is above your engine nacelles. Alternatively you might put your engines far up the side of the vehicle to be above the Earth return heat shield, but now you need to shield the sides of the cargo from the engine exhaust and so on.

Vacuum nozzles cannot take the heat loads or the aero loads to do this during interplanetary entries. I don't think Falcon stage 1 nozzles could either. Falcon reenters at Mach 5. MCT will enter at Mach 25, with 25 times the energy dispersion and 125 times the heat load. Even if you push the shockwave away the plasma prevents any real radiative cooling. Retracting the vac bells can help with aero loads, but I don't believe they will survive the heat loads without an ablative shield.

SpaceX's approach with Dragon is to poke the engines around the heatshield and use very underexpanded but short and sturdy nozzles. That's good for reentry and landing, but terrible for high ISP in vacuum. The only way I can see to get high ISP with engines that can perform EDL is to move the engines behind the heatshield (or the shield in front of the engines). That gets complex in a hurry, many times more so than RL-10B nozzle extension, and I can't wait to see how they plan to solve all the movement-related issues.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/16/2016 02:53 pm
I think it's pretty clear that they have started building Raptor. They might have started building a ~5m upper stage for it since that could go on FH pretty easily and maybe even on F9.

But building a Falcon Heavy replacement booster, before FH even flies? I don't think so. MCT has a pretty clearly defined set of goals including super heavy lift, and building another heavy lift booster doesn't help achieve those in the very tight timeframe Musk is shooting for.

It's quite common to be designing and test building your next version of <whatever> before the current version hits the market...Especially true of things that have a long development time.

This would be developing and testing TWO versions ahead, since they have clearly been working on BFR for a while also. I don't see any reason to build a booster that will at best marginally outperform Heavy and will be superseded by BFR within ~2 years unless they plan to fly it concurrently with BFR... which seems unlikely.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/16/2016 03:15 pm
This would be developing and testing TWO versions ahead, since they have clearly been working on BFR for a while also. I don't see any reason to build a booster that will at best marginally outperform Heavy and will be superseded by BFR within ~2 years unless they plan to fly it concurrently with BFR... which seems unlikely.

They may want to fly BFR only to equatorial destinations. Which is most but not all of Falcon payloads. They will want to go fully reusable on all their flights. They may want to switch to all methane and Raptor. That would need a new first stage replacing Falcon. Not a priority but in the pipeline, I suspect. Especially if they build a wider upper stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/16/2016 06:29 pm
On MCT speculation, I'm sure I read quotes by Musk saying he advocates fast transit times 102 or 100 days or something.  Anyone know a source of such statement(s) or do I have a false memory?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/16/2016 06:38 pm
On MCT speculation, I'm sure I read quotes by Musk saying he advocates fast transit times 102 or 100 days or something.  Anyone know a source of such statement(s) or do I have a false memory?

I think he mentions 3-month transits in this recent interview:
https://youtu.be/wsixsRI-Sz4
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/16/2016 06:55 pm
Is that supposed to be a drawing of Musk, because it looks terrible if it is.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/16/2016 07:02 pm
They may want to fly BFR only to equatorial destinations. Which is most but not all of Falcon payloads.

If they only launch out of Boca Chica, perhaps. If they hit anywhere near their reusability and cost targets for BFR/BFS it should be cheaper to launch (over the life of the vehicle) than Falcon is now, with 10x the performance. I think all GTO and BEO payloads will fly on BFR/BFS. Virtually all other payloads are small enough for Falcon 9 to easily RTLS, up to 15 to 20t to LEO with a reusable Raptor US. The slice of market that a 9-Raptor booster fits is very small and is firmly wedged between F9 and BFR.

Quote
They will want to go fully reusable on all their flights.
Which would be possible with a Raptor upper stage on F9 or FH, although Raptor might be easier to reuse than Merlin since methane burns cleaner. The only real case for a ~5m booster that I can see is if kerolox turns out to be a significant pain to reuse compared to methalox, or if its a USEFUL part of the MCT architecture.

Quote
They may want to switch to all methane and Raptor. That would need a new first stage replacing Falcon. Not a priority but in the pipeline, I suspect. Especially if they build a wider upper stage.
Flying a mix of kerolox and methalox is entirely viable long term IMO. Almost every launch provider has used higher energy fuels for upper stages for years, so these aren't new problems. Handling RP-1 is probably easier than LCH4.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/16/2016 07:58 pm
They may want to switch to all methane and Raptor. That would need a new first stage replacing Falcon. Not a priority but in the pipeline, I suspect. Especially if they build a wider upper stage.
Flying a mix of kerolox and methalox is entirely viable long term IMO. Almost every launch provider has used higher energy fuels for upper stages for years, so these aren't new problems. Handling RP-1 is probably easier than LCH4.

I agree that a mix of kerolox and methanlox is viable. But building only one type of main engine, the Raptor, has its advantages. It is possible they want to switch completely, especially now that Raptor is not that huge.

If they want to serve all orbits, they would need a west coast launch pad.

If a competitor like ULA or Blue Origin builds a fully reusable system that has a lower launch cost than BFR/MCT they may need that methane first stage too.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/16/2016 08:40 pm
A switch to only producing Raptor is possible if Falcon is switched to using 5 Raptor engines on first stage AND the Raptor has a very deep throttle capability allowing it to land on the center engine.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/16/2016 08:46 pm
A switch to only producing Raptor is possible if Falcon is switched to using 5 Raptor engines on first stage AND the Raptor has a very deep throttle capability allowing it to land on the center engine.
But you really might as well use a wider tank and go for more engines, like 7 or 9, to get at least FH performance. Still substantially less work than BFR to turnaround, but also allows full RTLS (no droneship needed) for almost all commercial payloads.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Doesitfloat on 06/16/2016 08:50 pm
If they keep the Merlin based Falcon family of rockets. and they add the raptor based completely reusable rocket.
 Spacex would have 2 independent rocket systems.
Then all launches (US) could be Spacex. ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/16/2016 09:03 pm
But you really might as well use a wider tank and go for more engines, like 7 or 9, to get at least FH performance. Still substantially less work than BFR to turnaround, but also allows full RTLS (no droneship needed) for almost all commercial payloads.

I always liked the idea of 7. It allows an equal spacing of all engines. It may not reach full Falcon Heavy capacity but for everything too big there would be BFR.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/16/2016 10:08 pm
5 Raptors won't fit under a 3.7m Falcon (need about 4.5m), and anything bigger won't be able to use all the Falcon infrastructure. Unlike a 5m US, a 5m booster would be rather hard to transport except via ship. In a lot of ways, it would have BFR heritage instead of Falcon's.

It's certainly a possibility, but I just don't see the need when F9 (or FH) can RTLS anything not worth launching BFR for.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 06/18/2016 01:52 am
Just wondering, how hard is methalox propellant transfer in microgravity compared to hypergolic or hydrolox refueling?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/18/2016 03:01 pm
Just wondering, how hard is methalox propellant transfer in microgravity compared to hypergolic or hydrolox refueling?

Unknown as nobody has done any.  {EDIT: see refutations in following posts}
Hydrolox would be the toughest mainly because of hydrogen's tiny atoms finding leaks really well and its need for really low temperature.
Hypergolic might be the easiest...until you accidentally started it up.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 06/18/2016 03:13 pm
Just wondering, how hard is methalox propellant transfer in microgravity compared to hypergolic or hydrolox refueling?

Unknown as nobody has done any.
Hydrolox would be the toughest mainly because of hydrogen's tiny atoms finding leaks really well and its need for really low temperature.
Hypergolic might be the easiest...until you accidentally started it up.

ISS is refueled by Progress.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 06/18/2016 03:24 pm
Just wondering, how hard is methalox propellant transfer in microgravity compared to hypergolic or hydrolox refueling?

Unknown as nobody has done any.
Hydrolox would be the toughest mainly because of hydrogen's tiny atoms finding leaks really well and its need for really low temperature.
Hypergolic might be the easiest...until you accidentally started it up.

ISS is refueled by Progress.
ULA did a LOX transfer test on a Centaur several years ago. The result was that cryo transfer was simple. Just need a pressure differential between tanks and a constant ulage motor firing to keep the cryo settled. The rest is just isolation valves opening and closing and pressures of the tanks control.

Added: BTW: The key difference is that for the cryo is that there are no tank bladders but on Progress the storeable prop tanks have bladders so that no ulage motor is required.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 06/18/2016 03:45 pm
Thin Red Line Aerospace has expandable cryo tank tech which sounds good for Progress style tanker/depot bladders.

Space News link... (http://spacenews.com/41009spotlight-thin-red-line-aerospace/)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: mvpel on 06/19/2016 10:30 pm
I'm saying that I do think it would be impossible for it all to be ready for launch in six years, with no one hearing a peep of any such activity already under way.

I would love to be proven wrong, though. :)

Suffice it to say that you'd be amazed what kind of development work takes place without anyone hearing a peep of any such activity already under way. And I, from my own perspective, would love to be proven right.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/23/2016 02:45 pm
Actually, retractable nozzles usually have an expansion ratio of ~50:1, but an extendable nozzle with the retraction split pulled back to about 15% of the nozzle length gets the retracted expansion ratio down to ~20:1 so the SL ISP goes up to ~300s and the thrust to ~2000 kN if they run the chamber at 12MPa. That ISP increase is enough to reduce fuel requirements to ~650t so that a very lightweight (~42t) 4-engine vehicle could put itself in a low parking orbit for refueling.

I don't think anyone has flown a engine like that, and it has it own set of engineering difficulties. But that certainly doesn't mean SpaceX wouldn't try.
They may want an engine like that for the center landing engine in any case.

Pulling this over from the BFR launch pad thread, since it's really BFS/MCT speculation.

Some estimates at what a Raptor flying on Falcon Heavy would look like (in the FH thread) put a different light on BFS as a potential self-SSTO. The ISP numbers Tom Mueller quoted for the SL Raptor engine (321s SL, 363s vacuum) are only achievable at much higher chamber pressures than Merlin, around 20-25 MPa. At those chamber pressures a RL10-B style engine becomes considerably more feasible for SSTO operation, with a retracted average ISP of 330 to 340s. Whether rapid reusability and long life are possible at those chamber pressures is questionable, but SpaceX clearly intends to try.

Specifically at 25 MPa, 3.45 O/F, 55:1 expansion (retracted), it would get 220 tonnes thrust at a 316s SL and 359s vac ISP, increasing to 265t and 380s when the vac bell is extended. 4 of those could theoretically put a 51t ship in low parking orbit, with a liftoff mass of 700t.

The other interesting factor is that a 4 to 5 meter vac bell is unnecessary at these chamber pressures. A 25 Mpa engine can realistically get 265t of thrust at 380s ISP with only a 3.15m nozzle - only slightly larger than Mvac.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 06/23/2016 08:18 pm
Actually, retractable nozzles usually have an expansion ratio of ~50:1, but an extendable nozzle with the retraction split pulled back to about 15% of the nozzle length gets the retracted expansion ratio down to ~20:1 so the SL ISP goes up to ~300s and the thrust to ~2000 kN if they run the chamber at 12MPa. That ISP increase is enough to reduce fuel requirements to ~650t so that a very lightweight (~42t) 4-engine vehicle could put itself in a low parking orbit for refueling.

I don't think anyone has flown a engine like that, and it has it own set of engineering difficulties. But that certainly doesn't mean SpaceX wouldn't try.
They may want an engine like that for the center landing engine in any case.

Pulling this over from the BFR launch pad thread, since it's really BFS/MCT speculation.

Some estimates at what a Raptor flying on Falcon Heavy would look like (in the FH thread) put a different light on BFS as a potential self-SSTO. The ISP numbers Tom Mueller quoted for the SL Raptor engine (321s SL, 363s vacuum) are only achievable at much higher chamber pressures than Merlin, around 20-25 MPa. At those chamber pressures a RL10-B style engine becomes considerably more feasible for SSTO operation, with a retracted average ISP of 330 to 340s. Whether rapid reusability and long life are possible at those chamber pressures is questionable, but SpaceX clearly intends to try.

Specifically at 25 MPa, 3.45 O/F, 55:1 expansion (retracted), it would get 220 tonnes thrust at a 316s SL and 359s vac ISP, increasing to 265t and 380s when the vac bell is extended. 4 of those could theoretically put a 51t ship in low parking orbit, with a liftoff mass of 700t.

The other interesting factor is that a 4 to 5 meter vac bell is unnecessary at these chamber pressures. A 25 Mpa engine can realistically get 265t of thrust at 380s ISP with only a 3.15m nozzle - only slightly larger than Mvac.

On that note, pulling this over from the FH thread, because Raptor speculation has direct import on MCT's mission architecture:

That's interesting. So the best way to increase the payload of the Falcon Heavy is a bigger upper stage. If such a need existed, I would guess space X would choose to stretch the second stage, and add two more vaccum Merlins to the stage. Easier than integating a second fuel type into the launch infrastructure to allow for the use of the Raptor engine.
No need to add an engine, the Merlin has plenty of thrust for a larger upper stage, especially if that stage is only used with the FH so it will be further along than the current F9 upper stage is at ignition.

The reason to go Raptor is to get improved ISP and more balanced fuel/oxidizer temperatures (which may make long life easier without adding extra mass).

Plus the Merlin Vacuum engine is gigantic, there is no way to fit 3 of them on any remotely Falcon-sized stage. You'd need a 8m diameter interstage at minimum.

To re-iterate that point.

(http://i.imgur.com/FRszulq.png)

MVac pushes 95 tonnes. By the time the fuel runs out, the engine has to throttle below 40% so as to not kill the payload with high g-forces.
The feasible way is to have a wider upper stage and interstage.
This probably is what they will do if they go wider. But I think it will take some careful thought, since the widest part of the nozzle is at the bottom. And the bottom is where the narrowest part of the interstage would be, since that is where it starts flaring out... so there may need to be a gap of some size to get it to work.
...or have an extendible nozzle like the part that you trimmed from my post.

The last bit of the conversation is great.

Extendible nozzle helps with interstage length, doesn't nothing for width. 

A 4.8 meter nozzle is 4.8 meters whether in 1, 2 or more pieces.  As we've seen from on board footage the separation events are not that smooth.

A rocket with a 500,000 lbf upper stage is going to need good clearances and some creative problem solving.

Of course maybe there is a smaller Raptor in the works and this discussion changes.

How much ISP would Raptor lose when it has a nozzle diameter of only 4m?
Does it have to make the same thrust as the 4.8m nozzle? Because ISP isn't solely dictated by nozzle size - for the same fuels it is a function of pressure ratios... and there are other ways to change pressure ratios (e.g. change mass flow and/or throat diameter) at the expense of thrust.

Obviously I don't even know enough to ask the right question. For arguments sake assume the same engine, just a smaller nozzle.

Though what we know does not rule out that a dedicated smaller version of Raptor might be built.
Raptor with a 4 m nozzle loses about 1% of ISP compared to a 4.8 m nozzle: 376 s vs 380 s.

This is based on sim in RPA lite using: Methane/LOX at:
9.7 MPa chamber pressure (same as Merlin)
2.8 O/F ratio (optimum for methalox at 9.7 MPa)
165 expansion ratio for the 4.8 m nozzle (same as Merlin Vac)
115 expansion ratio for the 4 m nozzle (assuming same throat diameter as the 4.8 m nozzle)

O/F ratio was supposed to be 3.8.  Chamber pressure seems like the big unknown - if the M1D gas generator produces 9.7MPa, what should we expect in a FFSC Raptor?

Musk: "The critical elements of the solution are rocket reusability and low cost propellant (CH4 and O2 at an O/F ratio of ~ 3.8 ). And, of course, making the return propellant on Mars, which has a handy CO2 atmosphere and lots of H2O frozen in the soil." - http://waitbutwhy.com/2015/08/how-and-why-spacex-will-colonize-mars.html/4


Neither of those particularly affect the relative differences between the 4 meter and 4.8 meter nozzle; the benefit of having extra expansion is about the same for a higher pressure engine.

I just grabbed that 2.8:1 O/F number off a chart, and according to RPA it is actually a bit low for a 165:1 expansion vacuum engine. At 10 MPa the O/F for optimal ISP is 3.4:1, and at 15 MPa it optimizes at 3.45:1. However, 3.8:1 is rather high and actually loses a second or two of ISP (although you get a bit better thrust due to higher massflow).


How are real numbers likely to come in, in relation to the figures provided by RPA Lite?  Would the RPA numbers represent a theoretical maximum or perhaps a plausible best-guess at the exact values?

RPA calculates both the theoretical best possible performance, and a best guess at the actual performance after accounting for combustion and nozzle inefficiencies. I have no idea how accurate it is in reality. And we don't have a ton of known parameters to put in.
From the O/F and the two isp points I had estimated 20.5MPa as Pc. Can't recall the expansion.
The four datapoints we have are 321s (sealevel small-nozzle?) , 363s (vacuum small-nozzle?), and 380s (vacuum big-nozzle?), with an O:F ratio of 3.8.  I had 14.5MPa working for theoretical numbers ("Express thermodynamic analysis") at expansion ratios of 32.5 and 75.

Changing it to "Extended analysis" and examining chamber performance given the estimated reaction and nozzle efficiencies, I end up losing 14s off of each number.
I used actual vs theoretical. And modified a bit the freeze chemistry since the ch4/lox combustion, while appears simple, has a lot of steps.
Punch it up to the RD-180 chamber pressure - 26.7MPa
Using the listed estimates for 3.8:1 inefficiencies rather than theoretical maxima in RPA Lite:
With an expansion ratio of 59, you get 321s at sealevel and 363s in vacuum.
With an expansion ratio of 164, you get 380s in vacuum.

Sidenote: Do we have a higher chamber pressure liquid rocket engine in existence than the RD-180?

That's very interesting. Do you really think they will try to run at 26.7 MPa? For comparison, the RD-191 and RD-180 run at 26.7 MPa, and the SSME ran up to 21 MPa. I think that's the highest pressure ever flown in a reusable engine. A 100% length bell nozzle gets the same performance at 25 MPa and 55:1 expansion (155:1 for the vac nozzle).

The nice thing about higher chamber pressures is the engine gets much smaller (but not lighter) for the same thrust. At 25 MPa the SL Raptor only needs a 1.88m diameter nozzle to get Musk's estimated 500klbf of thrust, and the vac version gets 591klbf with only a 3.16m dia nozzle.

To bring this entire conversation back to Falcon Heavy (we were wandering OT for a bit there), that would mean it's possible a 25 MPa Raptor Vac could fly in the current Falcon interstage. Even with the nozzle trimmed back to 70% (which would put it very nearly in the Mvac envelope), it could realistically get 265 tonnes of thrust at 377s ISP. That's a healthy upgrade over Mvac's 95 tonnes thrust and 348 ISP.

I have no idea.  I was about to ask you, and everybody else.

What chamber pressures should we expect out of Raptor?  Do we have any evidence or reasoning one way or the other? (other than the previously mentioned 321s, 363s, 380s, and 3.8:1, and "FFSC should permit higher chamber pressures" notion)
Sidenote: Do we have a higher chamber pressure liquid rocket engine in existence than the RD-180?
RD-191, 262.6kg/cm˛ vs 261.7kg/cm˛. RD-270 was 266.1.  I know of nothing bigger than this. But some military RCS engines (like the one in MIRVs) probably have higher Pc.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/23/2016 08:43 pm
Thanks for collecting those. As far as the expected chamber pressure, that really depends on the performance and design requirements. Increasing the pressure requires a bigger or faster turbopump... and a lost more strength to keep everything from going kabloomy.

However, the 321s SL and 363s vacuum ISP numbers do put some hard limits on how low chamber pressure can be. Getting 363s in vacuum requires at least 50:1 expansion even with a very efficient nozzle design... but getting 321s with 50:1 expansion agasint SL backpressure requires at least 22.5 MPa chamber pressure. So a pressure in the 22-25 MPa range looks pretty likely based on that info.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/23/2016 10:14 pm
I had always though the estimates of nozzle diameter for the Raptor were WAY too high, if were looking at vac nozzles only around 3 m across then a hexagonal 6 engine arrangement can easily fit in an upper-stage of around 12.5 m in diameter.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/24/2016 01:49 am
We really need a Raptor speculation thread  ::)

If Raptor follows a development arc somewhat like Merlin, the first versions will probably operate at lower pressure/thrust/impulse than later versions, as SpaceX figures out methane, staged combustion, high pressure engines, etc. I could see a MVac-sized version flying on Falcon Heavy with a stretched or bigger upper stage, maybe on Falcon 9 as well.

BFS won't have the packaging constraints or the need to throttle as deep to avoid excessive acceleration.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Andy USA on 06/25/2016 03:24 am
Thread trimmed as it was taken off topic by a completely false statement that was removed from another thread and then reposted here. I will be reviewing the members in question.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/27/2016 06:42 pm
I had always though the estimates of nozzle diameter for the Raptor were WAY too high, if were looking at vac nozzles only around 3 m across then a hexagonal 6 engine arrangement can easily fit in an upper-stage of around 12.5 m in diameter.

You don't think 6 engines is a bit much, even for engine-out operation? It looks like Raptor vac should make 265 tonnes thrust each, if the SL version makes 230. That would be a total vacuum thrust of 1600 tonnes with 6 engines. If it's designed to TWR=1 at 1.5 kms staging with a 92% PMF, that puts 300t total in LEO (and fully refueled in about eight 175t tanker trips would put 300t total through fast TMI and to the Mars surface).

A 4-engine design with 92% PMF and TWR=1 at 1.5 kms staging would lift 100t of payload to a 500km parking orbit with 5% margins, even with 2 engines out. It would still be capable of pulling a 3g Mars landing burn even with 2 engines out (530t thrust, 180t mass at burnout), and more than 4g at Earth landing even accounting for SL backpressure. And it would have a 1.47:1 TWR at Mars liftoff with a full 770t prop load.

While it would be nice to get to LEO with 100t payload and 50-80t of prop left, I just don't see that being worthwhile if it means the spacecraft is grossly oversized for everything else.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/27/2016 06:49 pm
I doubt that more than 5 Raptors are required.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: biosehnsucht on 06/27/2016 10:02 pm
Wouldn't depending on which engines are 'out', fewer number of engines could potentially require greater gimball and/or throttle ranges to compensate - i.e. if you have 4 engines and capable of 2-out but the 2 you lose are next to each other, you're gonna want some Shuttle-esque gimbal? With 6 engines, you can probably get away with lower gimbal ranges, etc.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/27/2016 11:21 pm
My main point was that you can get all the thrust you could want in a 12.5 m diameter upper stage and engine thrust density is not a driver for any higher diameter.

Having an engine out capability on a 2nd stage would be a first and very desirable as the intent is to reuse them.  I am very doubtful that gimbaling on remaining engines will be adequate to compensate for any engine out because the vehicle is too short, that puts the center of mass closer to the engines and the thrust vector MUST go through the center of mass of the vehicle, that is MUCH easier on a long thin first stage.  Thus I conclude that a symmetrical shutdown is the only viable means to get engine out, the remaining 4 engines of a 6 engine configuration would be sufficient to reach orbit.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/28/2016 03:21 am
I was implying symmetrical shutdown in the two engine out scenario. With 2 of 4 engines out as described it still has plenty of margin to orbit. It would be pretty unlikely to lose opposite pairs simultaneously, IMO. I think the numbers still work out better for the 4 engine case, unless Raptor vac turns out to be a lot smaller than expected.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/28/2016 08:24 am
Your payload is too small at 100 mt, I'm thinking payload to LEO of around 200 mt even after engine loss, so that would require 4 functional engines and 6 total.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/28/2016 02:00 pm
Your payload is too small at 100 mt, I'm thinking payload to LEO of around 200 mt even after engine loss, so that would require 4 functional engines and 6 total.

But why would you want that? Staging to LEO and LEO to Mars surface have almost exactly the same DV requirements, so the vehicle should be optimized to deliver the same payload to both. A typical fast transit and EDL only requires ~6 kms. Launching 200t payload and 100t ship into LEO requires about 1400t of propellant in the US, but transit and EDL of 100t payload and 100t ship only require about 800t. You're shipping an extra 20% to 30% of useless dry mass (engines and tankage) to Mars and back.

For LEO tanker runs the 200t payload is useful, but that can be accomplished with larger tanks that the Mars transit ship doesn't need. And it still doesn't really need 6 engines for high-thrust engine out capability, because a tanker won't be carrying people and it can always use some of it's extra fuel load for margin. An off-nominal LEO launch has a lot of options for abort, particularly if a rapid launch cadence, on-orbit refueling, and LEO rendezvous are SOP.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/28/2016 02:42 pm
Yeah, I'm fairly certain that the BFS will go straight to Earth from the surface of Mars (at least for the early missions), in which case you'll want the BFS fully fueled with 1000-1400 tons of propellant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/28/2016 04:26 pm
How much dV are you estimating for return, and how fast a transit? A typical 6-month return is only about 6.5 to 7 km/s from Mars surface to Earth surface (5.25 for launch to escape, 1 to 1.5 for transfer injection, 0.35 for EDL).

Increasing return DV reduces the total mission duration by allowing a earlier launch, but I don't see any solutions in the trajectory browser for reducing the actual return transit time below about 5 months. If you have computed such solutions I'd love to see them.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/28/2016 05:10 pm
How much dV are you estimating for return, and how fast a transit? A typical 6-month return is only about 6.5 to 7 km/s from Mars surface to Earth surface (5.25 for launch to escape, 1 to 1.5 for transfer injection, 0.35 for EDL).

Increasing return DV reduces the total mission duration by allowing a earlier launch, but I don't see any solutions in the trajectory browser for reducing the actual return transit time below about 5 months. If you have computed such solutions I'd love to see them.
6.5-7km/s sounds about right. I expect return trips to be much longer than 100 days.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/28/2016 06:05 pm
How much dV are you estimating for return, and how fast a transit? A typical 6-month return is only about 6.5 to 7 km/s from Mars surface to Earth surface (5.25 for launch to escape, 1 to 1.5 for transfer injection, 0.35 for EDL).

Increasing return DV reduces the total mission duration by allowing a earlier launch, but I don't see any solutions in the trajectory browser for reducing the actual return transit time below about 5 months. If you have computed such solutions I'd love to see them.
6.5-7km/s sounds about right. I expect return trips to be much longer than 100 days.

Then your dry mass or return payload is too high if it needs 1000-1400t of prop for direct return. A 80t dry, 380s ISP vehicle with 25t return payload gets 7 km/s with less than 600t of prop, and can do 6.5 km/s with only 500t. Even a 100t vehicle with a 50t return payload only needs 725t to 825t of prop.

I can't see a real need to ever have more than ~800t of methalox in a crewed version of the BFS, as long as the dry mass is reasonable. That does all three legs of the trip (BFR staging to LEO; LEO to Mars surface; Mars surface to Earth surface) with a lot more than the expected payload for each leg.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/28/2016 06:07 pm
The return flight will not likely be in the exact optimum window. Also, it'll likely be less than 6 months.

Remember, SpaceX wants the vehicle back each time.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Elmar Moelzer on 06/28/2016 07:29 pm
A typical 6-month return is only about 6.5 to 7 km/s from Mars surface to Earth surface (5.25 for launch to escape, 1 to 1.5 for transfer injection, 0.35 for EDL).
We had already established that the trip would be 3 months?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/28/2016 07:30 pm
A typical 6-month return is only about 6.5 to 7 km/s from Mars surface to Earth surface (5.25 for launch to escape, 1 to 1.5 for transfer injection, 0.35 for EDL).
We had already established that the trip would be 3 months?
Who said the return trip must be the same length of time as the trip to Mars?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 06/28/2016 07:30 pm
Why rush faster than 6 months on return?  Take 3-4 months Earth to Mars with humans.  One month or less on Mars. 6 months return, some little cargo and a few possible humans.  Plenty of time to get the BFS ready for the next synod which is the goal.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: stoker5432 on 06/28/2016 07:34 pm
Maybe to optimize crew health for further missions if there is a crew coming back.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/28/2016 07:41 pm
The return flight will not likely be in the exact optimum window. Also, it'll likely be less than 6 months.

Remember, SpaceX wants the vehicle back each time.

I don't think it's feasible or necessary for early missions to return the vehicle for launch the next synod. IMO that won't happen until LMO refueling is possible and all the kinks/upgrades are worked out of the system. Probably 2030's. That requires a lot of pre-positioned assets to support fast ground unloading/refueling and LMO refueling.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/28/2016 08:06 pm
Why rush faster than 6 months on return?  Take 3-4 months Earth to Mars with humans.  One month or less on Mars. 6 months return, some little cargo and a few possible humans.  Plenty of time to get the BFS ready for the next synod which is the goal.

You're describing an opposition class mission. That's feasible with LMO refueling and hot reentries, but requires one leg of the trajectory dip inside the orbit of Venus which puts a lot of constraints on the spacecraft to handle different thermal and radiation environments. And 10 months in zero-gee isn't ideal for humans.

Orbital mechanics generally preclude having both short stays and fast transits.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/28/2016 08:13 pm
The return flight will not likely be in the exact optimum window. Also, it'll likely be less than 6 months.

Remember, SpaceX wants the vehicle back each time.

I don't think it's feasible or necessary for early missions to return the vehicle for launch the next synod. IMO that won't happen until LMO refueling is possible and all the kinks/upgrades are worked out of the system. Probably 2030's. That requires a lot of pre-positioned assets to support fast ground unloading/refueling and LMO refueling.
LMO refueling isn't required.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/28/2016 08:32 pm
...

Orbital mechanics generally preclude having both short stays and fast transits.
That changes if you're using massive amounts of ISRU propellants.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 06/28/2016 08:36 pm
...

Orbital mechanics generally preclude having both short stays and fast transits.
That changes if you're using massive amounts of ISRU propellants.

You are right that in orbit refuelling is not necessary. It would make using massive amounts of propellants much easier though. Especially if there were in orbit ressources for fuel available.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 06/28/2016 08:45 pm
...

Orbital mechanics generally preclude having both short stays and fast transits.
That changes if you're using massive amounts of ISRU propellants.

You are right that in orbit refuelling is not necessary. It would make using massive amounts of propellants much easier though. Especially if there were in orbit ressources for fuel available.
Or you just develop a lightweight vehicle with lots of room for propellant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/28/2016 08:54 pm
...

Orbital mechanics generally preclude having both short stays and fast transits.
That changes if you're using massive amounts of ISRU propellants.

You are right that in orbit refuelling is not necessary. It would make using massive amounts of propellants much easier though. Especially if there were in orbit ressources for fuel available.

The need for orbital refueling is highly dependent on the planetary alignment. On poor alignments same-synod return takes 10 km/s just to get from the surface through TEI, and Earth reentry is over 20 km/s. On others it takes less than 7 km/s to get through injection and reentry is under 14 km/s.

The mid to late 2020's are relatively poor alignments, and I doubt the infrastructure will be in place to allow rapid return and reuse. But the early 2030's are quite good, good enough to allow same-synod reuse without orbital refueling. By the late 2030's when the alignments shift again, that infrastructure might be in place and the campaign of launches with rapid reuse can continue.

MCT might have grown in capacity by then, however.... it wouldn't surprise me to see a couple versions with improved performance after the early 2020's missions.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 06/29/2016 11:28 pm
Your payload is too small at 100 mt, I'm thinking payload to LEO of around 200 mt even after engine loss, so that would require 4 functional engines and 6 total.

But why would you want that? Staging to LEO and LEO to Mars surface have almost exactly the same DV requirements, so the vehicle should be optimized to deliver the same payload to both. A typical fast transit and EDL only requires ~6 kms. Launching 200t payload and 100t ship into LEO requires about 1400t of propellant in the US, but transit and EDL of 100t payload and 100t ship only require about 800t. You're shipping an extra 20% to 30% of useless dry mass (engines and tankage) to Mars and back.

For LEO tanker runs the 200t payload is useful, but that can be accomplished with larger tanks that the Mars transit ship doesn't need. And it still doesn't really need 6 engines for high-thrust engine out capability, because a tanker won't be carrying people and it can always use some of it's extra fuel load for margin. An off-nominal LEO launch has a lot of options for abort, particularly if a rapid launch cadence, on-orbit refueling, and LEO rendezvous are SOP.

You misunderstand, I foresee at F9 like configuration with a rather plain 2nd stage that is just reusable (much like the original F9 video) the 200 mt is the total payload atop that 2nd stage and needs to be that large in order to carry the BFS and it's payload and small amount of propellant for emergency landing needs in case of an abort.

I do not believe the 1 synod round-trip plan is remotely viable and Musk is wishing when he expressed it, but it will not come to pass because it requires both too much propellant and has too high of a entry velocity particularly at Earth.  Finally it is a terribly inefficient cargo delivery method, as cargo will dominate by at least 10:1 over crew the optimum vehicle would be optimized for cargo and then sped-up to accommodate crew.

The whole premise of 1 synod cycles is more frequent trips and better amortization of the vehicle.  But the difference is between terrible and abysmal amortization because 1 synod is 780 days which means your looking at 7 uses of a vehicle or 14 over it's entire 30 year lifespan (and that's assuming it last that long).  A fundamentally different strategy is needed to make amortization work and it is simple, keep the earth launch vehicle and mars landing vehicle at Earth and Mars for a long as possible doing many surface to orbit shuttle flights bringing cargo up and down respectively.  A much simpler freight vehicle goes between Earth and Mars and it suffers the poor amortization hit but it carries large amounts of cargo externally to compensate.  The ideal Earth launch vehicle is thus a simple 2nd stage with a payload fairing which can launch any cargo imaginable, and the ideal mars lander is a modest size capsule that can fit on top of it as a 3rd stage.

Departure from Earth would be from a high orbit like EML1, departure from Mars will be from LMO, refueling at both locations makes for a vehicle vastly smaller with only ~4 km/s needed to perform any one leg which is the Mars assent, a leg which can not be sub-divided and is the long pole.  The constant harping on a similar DeltaV between LEO->Mars and Mars surface->Earth is a false prophet because correct strategy is to create the smallest single DeltaV leg possible between viable rendezvous points so as to defeat the rocket equation piece meal.  Vehicle Rendezvouses, fuel transfer and multiple restart engines are all baseline assumptions we have with regard to SpaceX technology, once you have thouse capabilities it's crazy not to use them throughout the whole mission architecture to get more leverage out of your IMLEO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 06/30/2016 04:07 pm
...  The ideal Earth launch vehicle is thus a simple 2nd stage with a payload fairing which can launch any cargo imaginable, and the ideal mars lander is a modest size capsule that can fit on top of it as a 3rd stage.
...

So assuming that the 2020's missions will be entirely methalox propulsion (SEP can't be a long pole), this is basically a non-integrated large Dragon architecture? It does free up a lot of design constraints, but it adds some additional issues. As I see them:

Pros:
a) Tankage volume in the capsule is around 1/3 as large (~360 m^3 vs ~975 m^3).
b) The capsule can be probably around 40% lighter for the same landed payload.
c) Might be able to do direct return if it doesn't need to carry payload.
d) The capsule does far less deep-space propulsion (mostly EDL and launch), no gigantic, fragile vac nozzles needed.
e) The vac-optimized 2nd stage can do most of the heavy lifting in vacuum (to within 1 km/s of TMI), and with a low ballistic coefficient and good heatshield doesn't need to do hypersonic retroprop at Earth entry.
f) The constraints around LAS are much easier for a ~150t unfueled capsule than a ~1000t fueled capsule.
g) The capsule doesn't need a dispenser system to be useful for satellite launches. Multi-sat deployment from 2nd stage is more proven technology.
h) 2nd stage needs some endurance but doesn't have to fly beyond GTO.
i) 2nd stage doesn't need any abort capabilities.
j) Capsule and 2nd stage can basically be scaled-up Dragon and Falcon, reducing development costs and major risks.
k) The 2nd stage is a potential lower-cost path to a minimum viable sat-launch product, since second stage recovery experiments can still fly profitable payloads even if they end up expending the stage.

Cons:
i) Mars Orbital Rendezvous is required before trans-Earth injection if returning any payload.
ii) There always has to be 2 capsules at Mars in order to send one home, even on very early missions.
iii) Capsules have to perform 2 (or more) Mars decents and ascents on average before being serviced at Earth.
iv) Integrating 3 vehicles for every capsule launch slows launch cadence and adds expense.
v) Capsule and 2nd stage don't share a lot of development or manufacturing costs with each other, requiring 2 full dev programs and 2 manufacturing lines (and maybe a 3rd for BFR, depending how similar it is to 2nd stage).
vi) The second stage needs a unique reentry and landing architecture with a lot of potential development risks.
vii) Developing 3 codependent vehicles presents a larger potential for delays and perhaps higher bar for minimum viable Mars transport product.
viii) Doesn't reduce the number of launches required for an early Mars mission, and might increase them since 2 capsules need to be at Mars for the first crewed mission.

Edit: clarity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jpo234 on 07/11/2016 12:10 pm
Richard Heidmann (Snecma and Ariane) about the MCT (http://planete-mars.com/mars-colonization-transport-rumeurs-avant-revelation-du-projet/).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/11/2016 01:48 pm
Richard Heidmann (Snecma and Ariane) about the MCT (http://planete-mars.com/mars-colonization-transport-rumeurs-avant-revelation-du-projet/).

A year ago he wrote a more in depth article on the same concept with an English translation:
http://planete-mars.com/what-could-the-mars-colonization-transport-mct-spacex-project-look-like-continued/

None of it makes any sense to me. A 10,000 tonne GLOW stack with 120 mN (27 mlbf) of total thrust? 700 tonne-thrust Raptors? A winged belly-landing super-shuttle? Integrated habitats?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jpo234 on 07/11/2016 01:59 pm
A winged belly-landing super-shuttle?

In the latest article the "super-shuttle" is not really a shuttle. It's more about maximizing the surface available for aerobraking. This is at least how I interpret the renders.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/11/2016 02:11 pm
A winged belly-landing super-shuttle?

In the latest article the "super-shuttle" is not really a shuttle. It's more about maximizing the surface available for aerobraking. This is at least how I interpret the renders.

It's maximizing the surface available for aerobraking by entering with the ventral side forward, like the shuttle. That's great for increasing ballistic drag, but not great for optimizing structural mass. And the horizontal take-off/landing is interesting.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jpo234 on 07/11/2016 02:22 pm
A winged belly-landing super-shuttle?

In the latest article the "super-shuttle" is not really a shuttle. It's more about maximizing the surface available for aerobraking. This is at least how I interpret the renders.

It's maximizing the surface available for aerobraking by entering with the ventral side forward, like the shuttle. That's great for increasing ballistic drag, but not great for optimizing structural mass. And the horizontal take-off/landing is interesting.

That image is from the older article. The article from 07/09/2016 shows a different BFS: just small winglets. IMHO this one is meant to actually land vertically.

EDIT: Of course it will enter "with the ventral side forward", but later on reorient for a vertical landing. I don't know whether this is actually possible.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/11/2016 02:34 pm
That image is from the older article. The article from 07/09/2016 shows a different BFS: just small winglets. IMHO this one is meant to actually land vertically.

EDIT: Of course it will enter "with the ventral side forward", but later on reorient for a vertical landing. I don't know whether this is actually possible.

Where does it show a vertical landing? He seems rather stuck on the horizontal landing, and there are no engines in the rear of that thing in the illustrations.

Which makes me wonder... how does it get to orbit? Horizontally?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jpo234 on 07/11/2016 02:43 pm
Where does it show a vertical landing? He seems rather stuck on the horizontal landing, and there are no engines in the rear of that thing in the illustrations.

It doesn't show a vertical landing. But since it doesn't have anything but a big heat shield on the side I'm assuming a vertical landing. I might be wrong, happened before.

Which makes me wonder... how does it get to orbit? Horizontally?

No. See
(http://planete-mars.com/wp-content/uploads/2016/07/PressingToLEO.jpg)
(http://planete-mars.com/wp-content/uploads/2016/07/MCT4_15m.jpg)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: slavvy on 07/11/2016 03:04 pm
It does land horizontal, see pictures at the bottom of this page
http://planete-mars.com/mars-colonization-transport-main-findings-of-our-analysis/ (http://planete-mars.com/mars-colonization-transport-main-findings-of-our-analysis/)

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/11/2016 03:11 pm
Landing horizontally seems like a terrible idea, not at all SpaceX-y.

DC-X demonstrated swan dive maneuver already. We don't need this horizontal landing nonsense.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/11/2016 03:13 pm
The booster doesn't go to orbit, and there's no second stage so the shuttle must be it's own 2nd stage (confirmed by the trajectory graphic). At staging it's clearly pointed nose-downrange, but there are apparently no engines in the tail... so does it point it's dorsal side downrange and use belly engines? That seems questionable as there are still considerable aero loads at staging. Or do the engines pivot out and point back enough to continue vertically? There's no mechanism described for that.

The booster clearly lands vertically, but I don't see any indication that the shuttle does.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/11/2016 04:24 pm
The booster doesn't go to orbit, and there's no second stage so the shuttle must be it's own 2nd stage (confirmed by the trajectory graphic). At staging it's clearly pointed nose-downrange, but there are apparently no engines in the tail... so does it point it's dorsal side downrange and use belly engines? That seems questionable as there are still considerable aero loads at staging. Or do the engines pivot out and point back enough to continue vertically? There's no mechanism described for that.

The booster clearly lands vertically, but I don't see any indication that the shuttle does.

See SpaceX's old reuse video. Shows the upper stage reentering on its belly, then at some point it transitions and in the end it lands vertically:
https://www.youtube.com/watch?v=OX2-qEC7P_I

That counts as some indication (hint), although we do not have any actual source info that says it will land vertically (and it could be that they were or are still trading how to land). So while horizontal landing can't be ruled out, it does indeed seem unlikely to me.

Note also that the Delta Clipper (a vehicle somewhat analogous to what BFS /might/ be) was supposed to land vertically but reentry belly-first, like is shown in the Falcon 9 reuse video. The transition from belly to vertical landing was tested by DC-X in the swan dive test, so it can be done with just engines on the tail (although some thrusters or aerosurfaces/gridfins to assist turning like the booster seems likely):
https://www.youtube.com/watch?v=wv9n9Casp1o
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 07/11/2016 04:35 pm
The image of the "shuttle" in the new article is consistent with the horizontal image from the April article. And Heidmann is tagged as the artist for both. So I doubt he's changed his mind.

From the July article:

(http://planete-mars.com/wp-content/uploads/2016/07/ArtifGrav2.jpg) (http://planete-mars.com/wp-content/uploads/2016/07/ArtifGrav2.jpg)

Note that there are no engines at the rear, it's more like the Dragon trunk, with doors.

This is consistent with the April article:

(http://planete-mars.com/wp-content/uploads/2016/04/MCTLanded.jpg) (http://planete-mars.com/wp-content/uploads/2016/04/MCTLanded.jpg)

And the four belly engines is consistent with the description in the July article.

So clearly when acting as its own second stage, Heidmann is imagining it firing sideways after staging. (Yes, we joked about this earlier in the thread. I even made a little picture. But we were joking.)



Heidmann is also in the "escape module" school. Having the passenger compartment separate upon launch abort. Debated here earlier (and apparently adopted in L2).

(http://planete-mars.com/wp-content/uploads/2016/04/MCTShuttle.jpg) (http://planete-mars.com/wp-content/uploads/2016/04/MCTShuttle.jpg)

...which never made any sense to me. For starters, look how complex that ejection process would have to be, given that most of the escape vehicle is inside the main "shuttle". Are the nose and surround panels ejectable shrouds? Or are they a structural part of the "shuttle", with the escape pod pushing out of a cylindrical slot? If the former, must the shrouds jettison before the LAS engines fire, or (in both cases) are the LAS engines firing inside the "shuttle"? The whole thing is bonkers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/11/2016 04:36 pm
Vertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 07/11/2016 05:00 pm
(Also insert my obligatory objection to the completely arbitrary 2RPM limit for AG, necessitating a long tether.

At 5RPM, the two "shuttles" could just dock tail-to-tail and the forward passenger compartment would be at 1g. Moreso, given that Musk's plan is permanent colonisation, he obviously believes that Mars gravity is sufficient for humans permanently. Two "shuttles" docked directly tail-to-tail could provide Mars gravity in the passenger compartment at just 3RPM. And depending on internal mass distribution, a single "shuttle" rotating end-over-end (tumbling pigeon) could provide Mars gravity at 4RPM. No docking and certainly no tether.  Hell, at 7RPM (which recent experiments suggest is tolerable), a 15m "shuttle" can provide Mars gravity by rotating around it's own long axis.

(Of course, in reality, I can't see Musk even looking at AG.))
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/11/2016 05:04 pm
Vertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings.
...
Do we need a new thread for Heidmann's design? Because this thread is supposed to be about MCT, and it may get confusing if we're talking about a /specific/ (and fairly fleshed-out) speculation of someone's own imagining in a thread that's supposed to be about SpaceX's actual MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/11/2016 05:53 pm
Seems like many of the major architecture points match known MCT plans: TSTO with VTVL booster, all methalox propulsion, LEO refueling, fully reusable booster and orbiter/lander.

While horizontal entry and/or landing seems very backwards to me, I don't know know of any official information that precludes such speculation. There are a lot of speculative biconic designs in this thread.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DanielW on 07/11/2016 06:36 pm
Vertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 

The trade off is that you move your flip maneuver from just before landing to just after booster separation. That gives you one flip event rather than two. Though I am not sure it is inherently risky enough to matter. I know that as a passenger I would rather perform it once at altitude.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 07/11/2016 06:51 pm
Vertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 

The trade off is that you move your flip maneuver from just before landing to just after booster separation. That gives you one flip event rather than two. Though I am not sure it is inherently risky enough to matter. I know that as a passenger I would rather perform it once at altitude.

I'm pretty much of the opinion that the way that he illustrates the side mounted engines for landing simply is too mass heavy to really be accurate.

     I have seen no indications from SpaceX of them even considering development of a vehicle like he describes.

     Overall, I suspect that SpaceX will likely create a large scale version of the Dragon 2 craft as the actual MCT lander.

     Perfecting the landing capability of both the first stage of the F9FT as well as the Dragon 2, would give them practical experience with a similar, but much larger payload structure.  No other type of designs have been even hinted at as yet.

     Development of a completely new design, rather than basing the design on an existing vehicle would be a very expensive and time consuming endeavor that would tend to delay Elon's ambition to get to Mars by at least a half decade, if not longer, and, patient as he is, I doubt very much he'd want to add more delays into the equation than he has to.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/11/2016 07:01 pm
Vertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 
...
Who said you'd have side mounted engines for supersonic retropropulsion?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DanielW on 07/11/2016 07:12 pm
Vertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 
...
Who said you'd have side mounted engines for supersonic retropropulsion?

That falls under the speculation part of the threads title. Side entry to maximize drag, and thus to simplify, point the engines that way too. By "simplify" I mean just taking the mars entry / landing piece separately.  If you were only designing a craft that had to land at mars you would make it wide and squat with engines in that direction. Of course you do have to take launch from earth into account but that only means you need to be thin in one plan view. There is no need to put engines on one end. Like you argue with landing, I propose that you can just rotate the craft once out of the atmosphere.

This is not necessarily what I think they will do, but it does not contradict any evidence either and it seems a way to optimize for the hard part of EDL at mars. I admit that it would make structures a bit more complex but if you are going to aeroload from the side anyway you still have to take that mass penalty.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/11/2016 07:20 pm
It seems very unlikely that SpaceX would launch horizontally from Mars. Nor does horizontal engines on an upper stage make sense.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: pobermanns on 07/11/2016 07:22 pm
Vertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 
...
Who said you'd have side mounted engines for supersonic retropropulsion?
In that video from Max Fagin, he strongly advocated side-mounted engines to increase the drag. OFC, he was only an intern at SpX, so that doesn't mean that his opinion represents corporate plans.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DanielW on 07/11/2016 07:27 pm
It seems very unlikely that SpaceX would launch horizontally from Mars. Nor does horizontal engines on an upper stage make sense.

You will have to help me on the basis for those assertions. With a thin martian atmosphere there would not be much penalty. Throttling would certainly have to be more responsive than vertical launching but that is not a known show stopper.

You don't have horizontal engines on an upper stage. You have an upper stage that you are launching sideways. You just light the engines on one side of it slightly before the other and it rotates 90 degs. It makes as much sense as a swan dive maneuver on a landing craft.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/11/2016 07:30 pm
It seems very unlikely that SpaceX would launch horizontally from Mars. Nor does horizontal engines on an upper stage make sense.

You will have to help me on the basis for those assertions. With a thin martian atmosphere there would not be much penalty. Throttling would certainly have to be more responsive than vertical launching but that is not a known show stopper.

You don't have horizontal engines on an upper stage. You have an upper stage that you are launching sideways. You just light the engines on one side of it slightly before the other and it rotates 90 degs. It makes as much sense as a swan dive maneuver on a landing craft.
Except there's still a lot of drag for a second stage, especially one like the BFS (which probably stages fairly early).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/11/2016 07:34 pm
Vertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings.

I was really wondering how it goes up, since all the visible engines are pointed to the side during launch.

This is something that I have wondered about. In most phases of the mission a horizontal orientation is better. EDL at both mars and earth, and surface operations. In transit does not care about the orientation. The only part that "wants" to be vertical is the few minutes it takes to leave earth's atmosphere. If you are going to have side mounted engines for super sonic retro propulsion you might as well use them for ascent. 
...
Who said you'd have side mounted engines for supersonic retropropulsion?
In that video from Max Fagin, he strongly advocated side-mounted engines to increase the drag. OFC, he was only an intern at SpX, so that doesn't mean that his opinion represents corporate plans.

You will have to define what you mean by side-mounted engines. Dragon's engines are side-mounted but face downward... they cannot be used for a horizontal take-off or horizontal landing. Fagin's proposal is very much like a Dragon in terms of engine setup (he actually used SuperDraco parameters in his simulations).

Side-mounted engines that point perpendicular to the vehicles' long axis are needed for HTHL. The only similar vehicles I can think of are VTVL jets like F-35 and Harrier. Like those jets' ducted exhausts, this think would need to be able to point its rockets backwards at staging... unless it did something weird like go to orbit dorsal side first.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DanielW on 07/11/2016 07:38 pm
It seems very unlikely that SpaceX would launch horizontally from Mars. Nor does horizontal engines on an upper stage make sense.

You will have to help me on the basis for those assertions. With a thin martian atmosphere there would not be much penalty. Throttling would certainly have to be more responsive than vertical launching but that is not a known show stopper.

You don't have horizontal engines on an upper stage. You have an upper stage that you are launching sideways. You just light the engines on one side of it slightly before the other and it rotates 90 degs. It makes as much sense as a swan dive maneuver on a landing craft.
Except there's still a lot of drag for a second stage, especially one like the BFS (which probably stages fairly early).

I will admit to not having specific knowlege there. But I assumed a more lofted trajectory for ease of RTLS as opposed to simply low and slow. The question becomes is the drag significant enough at 100 + km, or wherever they decide to stage, to make it a bad trade. I don't know. But you could fudge your staging higher in the trades if it were an issue. I simply assumed that if you can dump you fairing on a comm sat at that altitude you can probably fly with triple the crossection.

Edit: Also note that the falcon 9 boosters already perform twice the rotation that I am proposing at that altitude so SpaceX does have some experience in that regime.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/11/2016 07:41 pm
It seems very unlikely that SpaceX would launch horizontally from Mars. Nor does horizontal engines on an upper stage make sense.

You will have to help me on the basis for those assertions. With a thin martian atmosphere there would not be much penalty. Throttling would certainly have to be more responsive than vertical launching but that is not a known show stopper.

You don't have horizontal engines on an upper stage. You have an upper stage that you are launching sideways. You just light the engines on one side of it slightly before the other and it rotates 90 degs. It makes as much sense as a swan dive maneuver on a landing craft.
Except there's still a lot of drag for a second stage, especially one like the BFS (which probably stages fairly early).

The shuttle shape is going to be most aerodynamically stable in the reentry configuration, so launching from Mars (or after staging) horizontally would be like trying to fly a jet airplane backwards. Possible, perhaps, but definitely not ideal. Especially with those winglets.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DanielW on 07/11/2016 07:44 pm
It seems very unlikely that SpaceX would launch horizontally from Mars. Nor does horizontal engines on an upper stage make sense.

You will have to help me on the basis for those assertions. With a thin martian atmosphere there would not be much penalty. Throttling would certainly have to be more responsive than vertical launching but that is not a known show stopper.

You don't have horizontal engines on an upper stage. You have an upper stage that you are launching sideways. You just light the engines on one side of it slightly before the other and it rotates 90 degs. It makes as much sense as a swan dive maneuver on a landing craft.
Except there's still a lot of drag for a second stage, especially one like the BFS (which probably stages fairly early).

The shuttle shape is going to be most aerodynamically stable in the reentry configuration, so launching from Mars (or after staging) horizontally would be like trying to fly a jet airplane backwards. Possible, perhaps, but definitely not ideal. Especially with those winglets.

I don't propose the winglets though. It is also possible to have shapes that are bi-stable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 07/11/2016 10:29 pm
Landing horizontally seems like a terrible idea, not at all SpaceX-y.

DC-X demonstrated swan dive maneuver already. We don't need this horizontal landing nonsense.

Agreed. 

Not to mention there's additional issues with horizontal thrusting (which it'd have to do also for TMI, EDL, take off, TEI, and Earth EDL.)  Primarily those being bid doors in the heat shield that need to not just pop open once (like the Space Shuttle or X-37B), but open and close multiple times during a mission.  If one doesn't open or close just right, then you have a problem.

Plus you probably can't use cylindrical tanks, and would have to use spherical tanks, since the propellant will have to drain from the ventral side which would be a problem with a long cylindrical tank, unlike vertical propellant feeding for vertical thrusting.
I think this concept does use spherical, or some odd shape to allow propellant to drain down the ventral side in order to feed the engines.

There's probably a few other issues I'm not thinking of right now. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 07/11/2016 10:35 pm
The booster doesn't go to orbit, and there's no second stage so the shuttle must be it's own 2nd stage (confirmed by the trajectory graphic). At staging it's clearly pointed nose-downrange, but there are apparently no engines in the tail... so does it point it's dorsal side downrange and use belly engines? That seems questionable as there are still considerable aero loads at staging. Or do the engines pivot out and point back enough to continue vertically? There's no mechanism described for that.

The booster clearly lands vertically, but I don't see any indication that the shuttle does.

Yes, at booster staging, the ship would need to pitch 90 degrees, open it's belly engine doors (which would need to be closed during launch for aerodynamics) and then begin thrusting up to LEO.  Would probably need to be high enough so that any aerodynamic issues would be minimal for that.  At that point it can keep the doors open for TMI.  It would need to close them for Mars atmospheric entry, and then open them up again at terminal velocity to propulsively brake and then land.  .  They could stay open on the surface until launch, and stay open for TEI.  They'd need to close again for Earth atmospheric entry, and then open again at terminal velocity for propulsive landing and braking.

It also provides a pretty un-aerodynamic surface for Mars Launch like that.  But maybe that's not too much of a problem in the thin Mars atmosphere?  Not sure.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 07/11/2016 11:54 pm
The booster doesn't go to orbit, and there's no second stage so the shuttle must be it's own 2nd stage (confirmed by the trajectory graphic). At staging it's clearly pointed nose-downrange, but there are apparently no engines in the tail... so does it point it's dorsal side downrange and use belly engines? That seems questionable as there are still considerable aero loads at staging. Or do the engines pivot out and point back enough to continue vertically? There's no mechanism described for that.

The booster clearly lands vertically, but I don't see any indication that the shuttle does.

Yes, at booster staging, the ship would need to pitch 90 degrees, open it's belly engine doors (which would need to be closed during launch for aerodynamics) and then begin thrusting up to LEO.  Would probably need to be high enough so that any aerodynamic issues would be minimal for that.  At that point it can keep the doors open for TMI.  It would need to close them for Mars atmospheric entry, and then open them up again at terminal velocity to propulsively brake and then land.  .  They could stay open on the surface until launch, and stay open for TEI.  They'd need to close again for Earth atmospheric entry, and then open again at terminal velocity for propulsive landing and braking.

It also provides a pretty un-aerodynamic surface for Mars Launch like that.  But maybe that's not too much of a problem in the thin Mars atmosphere?  Not sure.
I've looked up the original article of version II of Heidmann's design.  The ship flies up after separation in the horizontal position using the belly landing nozzles.  The back doors stay closed.  There are no additional thrusters.
The author proposes that aerodynamic drag at separation altitude is low enough to allow this, as is the drag at Take-off from Mars.
So it also takes off from Mars with the ship in the horizontal position, as per the picture.
The authors admits the additional doors required for the engine bays might be a serious design problem, but sees this as a details to be worked out in time.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/12/2016 12:19 am
Vertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings.
...
Do we need a new thread for Heidmann's design? Because this thread is supposed to be about MCT, and it may get confusing if we're talking about a /specific/ (and fairly fleshed-out) speculation of someone's own imagining in a thread that's supposed to be about SpaceX's actual MCT.

???  Have you read the title of the thread, it is indeed a SPECULATION thread, their will not be an 'actual' MCT thread until Musk spills the beans publicly and we can comment on the plan, even then most comments will be speculation as to the unknown details and which details will be changed in the course of production.  Commenting on the Heidmann speculation is perfectly on topic.

That said I find this Richard Heidmann speculation line very weak in it's use of horizontal landing, vertical is almost certainly the path SpaceX will choose given their growing expertise in the area and the mechanical efficiency of cylinders under axial compression.

Their are some elements I like, notably the recognition that large cargo-holds are necessary and they need to be close to the ground to be unloaded safely and efficiently (and such cargo-holds are compatible with vertical landing).  Also the use of a reasonable 12.5 m diameter second stage, though I foresee the first stage being the same diameter rather then the N-1 colossus he foresees.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 07/12/2016 07:18 am
Have you read the title of the thread, it is indeed a SPECULATION thread,

It is supposed to be a MCT speculation thread. Not a generic speculation thread on just any Mars architecture. We have the Mars section for that. Things here should be based on what was said by SpaceX about MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 07/12/2016 08:19 am
Have you read the title of the thread, it is indeed a SPECULATION thread,

It is supposed to be a MCT speculation thread. Not a generic speculation thread on just any Mars architecture. We have the Mars section for that. Things here should be based on what was said by SpaceX about MCT.

Which is practically nothing. So, generic speculation would appear to be a valid approach.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: kch on 07/12/2016 08:20 am
Vertical landing after a ventral entry certainly seems feasible, that's not what I was questioning. I don't see any indication that Heidmann considered a vertical landing at all for this spaceship: all his articles show horizontal landings.
...

Do we need a new thread for Heidmann's design? Because this thread is supposed to be about MCT, and it may get confusing if we're talking about a /specific/ (and fairly fleshed-out) speculation of someone's own imagining in a thread that's supposed to be about SpaceX's actual MCT.

Yes, please!  :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 07/12/2016 09:37 am
ISTM that accommodating two main load axis (for a 100 mT to Mars surface vehicle) that are perpendicular one to another is in severe conflict with SX known optimizations for PMF and cost. That alone seems to make the Heidmann (HCT) design off-topic for any MCT discussion, before even counting L2 info available (which further invalidates HCT as possible SX design). YMMV
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DanielW on 07/12/2016 01:13 pm
ISTM that accommodating two main load axis (for a 100 mT to Mars surface vehicle) that are perpendicular one to another is in severe conflict with SX known optimizations for PMF and cost. That alone seems to make the Heidmann (HCT) design off-topic for any MCT discussion, before even counting L2 info available (which further invalidates HCT as possible SX design). YMMV

Heidmann aside, There is nothing off-topic about an architecture that lands and flies "horizontally." Unless you are proposing basically a massive dragon capsule with the heatshield on the bottom you need to support side load paths for 4-5gs anyway. I don't see anyway that a super-dragon style capsule will get enough drag to slow down enough. It almost has to be side entry. Thus your assertion that there is some SX way of doing things that precludes any discussion of a two load path structure is not based on physics.

I am also in L2, you are welcome to pm me any L2 info that contradicts such an architecture. There simply isn't any that I have seen.

I am not saying that a side flying / landing craft is my preferred architecture. I think a big pancake of a capsule would be better for all phases of the mission other than earth ascent. Just not sure how you could ever get such a thing into space.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/12/2016 01:36 pm
I was simply suggesting that if we're starting to talk for several pages about one person's specific vision for what MCT is like, and if it's highly fleshed out, then it's probably best to have a dedicated thread. That doesn't mean it's off-topic here, but that it might be better in its own thread. Geez y'all.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DanielW on 07/12/2016 02:12 pm
I was simply suggesting that if we're starting to talk for several pages about one person's specific vision for what MCT is like, and if it's highly fleshed out, then it's probably best to have a dedicated thread. That doesn't mean it's off-topic here, but that it might be better in its own thread. Geez y'all.

Agreed. I just want to clarify that some aspects of his architecture are things I have been thinking independently without any knowledge that someone else proposed launching into LEO sideways. If we are going to discuss specifics of his plan then yes another thread is appropriate. But I am not terribly interested in his over-all plan. We need to divorce the idea of a horizontally laid-out craft from any specific person or proposal. I honestly think it addresses many issues, not without draw-backs of its own. But I do think we have collectively let the earth ascent part of the mission drive what we think a proper space-ship should look like.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/12/2016 02:30 pm
...
I don't see anyway that a super-dragon style capsule will get enough drag to slow down enough.
...

If Red Dragon works, a larger vehicle with the same entry velocity, lift/drag ratio, ballistic coefficient, propellant mass fraction, and engine efficiency should work just as well. Because of the cube-square law it will have to be less dense, but since it's largely made of nearly empty propellant tanks that shouldn't be a major issue.

Trading propellant mass for engine efficiency (Raptor 380s vs. SuperDraco 240s) also helps hit the required density reduction.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 07/12/2016 03:23 pm
I was simply suggesting that if we're starting to talk for several pages about one person's specific vision for what MCT is like, and if it's highly fleshed out, then it's probably best to have a dedicated thread. That doesn't mean it's off-topic here, but that it might be better in its own thread.

This thread has quietened down lately, so a few pages of renewed activity will hardly kill us. (And judging by the last time people discussed Heidmann's articles, it won't go much beyond a few pages.)

OTOH, a separate thread will die out within a couple of weeks and drop off the first page within a month, then it won't be here with the rest of the MCT speculation - where it belongs.

OTGH, discussion of Heidmann's design has already peaked and is moving onto a generic discussion about landing strategies. So a new thread would be redundant unless you can convince a admin-privileged mod to move the last couple of pages to the new thread; at which point that thread would go off-topic as people spin off into generic discussion as they are doing here.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: the_other_Doug on 07/12/2016 03:29 pm
...
I don't see anyway that a super-dragon style capsule will get enough drag to slow down enough.
...

If Red Dragon works, a larger vehicle with the same entry velocity, lift/drag ratio, ballistic coefficient, propellant mass fraction, and engine efficiency should work just as well. Because of the cube-square law it will have to be less dense, but since it's largely made of nearly empty propellant tanks that shouldn't be a major issue.

Trading propellant mass for engine efficiency (Raptor 380s vs. SuperDraco 240s) also helps hit the required density reduction.

Yes, but -- how wide would such a scaled-up Dragon capsule be at the base, if it's got to be designed to carry at least 100 people, along with all the stuff (like food, water and life support) they will need for three to six months?

I think simply scaling up the dimensions of a Dragon to where it has the interior space available for the actual stated mission requirements would make the base diameter in the hundreds of meters.  How ya gonna fit that on any booster, much less one with the most-commonly-speculated (see L2) width of the BFR?

And if you change the basic shape, you inevitably have to go through a lot of design work to achieve similar lift/drag characteristics, etc.  In other words, BFS is gonna have to be designed from scratch, it won't take advantage of Dragon's shape or flying characteristics as a starting point.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 07/12/2016 03:34 pm
I was simply suggesting that if we're starting to talk for several pages about one person's specific vision for what MCT is like, and if it's highly fleshed out, then it's probably best to have a dedicated thread. That doesn't mean it's off-topic here, but that it might be better in its own thread. Geez y'all.
Yes.

If there are enough posts any mod would be happy to fork it off for you. Not sure there were or if it has legs but... PM any mod if you think so.  In case you can't tell I tend to agree with Paul451 regarding forking... not warranted. And all this meta discussion is meta.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/12/2016 04:24 pm
Yes, but -- how wide would such a scaled-up Dragon capsule be at the base, if it's got to be designed to carry at least 100 people, along with all the stuff (like food, water and life support) they will need for three to six months?

I think simply scaling up the dimensions of a Dragon to where it has the interior space available for the actual stated mission requirements would make the base diameter in the hundreds of meters.  How ya gonna fit that on any booster, much less one with the most-commonly-speculated (see L2) width of the BFR?

And if you change the basic shape, you inevitably have to go through a lot of design work to achieve similar lift/drag characteristics, etc.  In other words, BFS is gonna have to be designed from scratch, it won't take advantage of Dragon's shape or flying characteristics as a starting point.

Let's do at least a first order pass at actually calculating this. If BFR's diameter is 15m, BFS can easily be at least 15 to 16m.  Dragon's OML including the nose but not the trunk encloses about 25 m^3 with a major radius of 1.85 meters. Volume increases with size as r^3, so a 15 meter Dragon would enclose about 1,875 m^3 and a 16m version about 2,050 m^2

Estimates of necessary volume per person and propellant mass vary, but usually range somewhere from 5 to 15 m^2 per person and 300-1200 tonnes of propellant. Averaging those gets 10 m^3 per person and 750t propellant, or 1000 m^2 habitable volume and 915 m^3 tank volume (100 people, 820 kg/m^3 methalox). That totals 1915 m^3, or pretty close to what a 15 to 16m Dragon would enclose.

Obviously, that's only enclosed volume and not all the space can be utilized efficiently, and engines etc. all take up volume. But volume shouldn't be a show-stopper considering that it's probably feasible to launch up to a 20m diameter (4,500 m^3 volume) object on top of BFR.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 07/12/2016 04:34 pm
I believe this is first available translation of recent French article:

Quote
Mars Colonisation Transportation: Project Revelation Before Rumours

https://medium.com/@YawLife/mars-colonisation-transportation-project-revelation-before-rumours-ac7c33fcd40a#.d8140tfsh

Translation isn't great...

One interesting tidbit, though:
Quote
But a noise is that SpaceX would work on a Raptor 700 Tf !

Not sure of rumor source for an F-1 class engine, but certainly would simplify first stage design if nine 1.5-1.6Mlbf engines were used on booster.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DanielW on 07/12/2016 04:46 pm
One interesting tidbit, though:
Quote
But a noise is that SpaceX would work on a Raptor 700 Tf !

Not sure of rumor source for an F-1 class engine, but certainly would simplify first stage design if nine 1.5-1.6Mlbf engines were used on booster.

Not sure how this jives with the news that the AirForce is paying for a raptor based upper for F9 and FH. 2 engines or rumor wrong?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/12/2016 05:00 pm
This is just a guy's opinion, not actual new information. In case that wasn't clear already (the article seems a bit misleading that way).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 07/12/2016 05:10 pm
One interesting tidbit, though:
Quote
But a noise is that SpaceX would work on a Raptor 700 Tf !

Not sure of rumor source for an F-1 class engine, but certainly would simplify first stage design if nine 1.5-1.6Mlbf engines were used on booster.

Not sure how this jives with the news that the AirForce is paying for a raptor based upper for F9 and FH. 2 engines or rumor wrong?

Don't think 'rumor' applies to USAF paying for F9/FH upper stage raptor -- that one is fact, at least for a prototype Raptor.  When the upper stage development effort hit the press, there were many speculations about more than one size of Raptor.  Don't think a definitive answer that there will only be one size is in hand yet.

Some of the number-of-engine dots we're trying to connect:
F9/FH upper stage engine might call for smaller engine than BFR booster.
SpaceX has declared the engine quite scaleable. 
Optimum efficiency (maybe thrust-to-weight ratio?) was pronounced by EM to be 550klbf, and result would be 'lots of them.'  (15Mlbf BFR requires 27 at this size.)
Landing engines on Mars would require deep throttling of 550klbf engine.
Nine engines has some heritage (my personal dot).

So, it wouldn't surprise me if September reveal shows more than one engine size.  (Three is my guess.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DanielW on 07/12/2016 05:18 pm
So, it wouldn't surprise me if September reveal shows more than one engine size.  (Three is my guess.)

Booster, upper / MCT, and Orbital maneuvering?

I would personally like to see an electrically pumped methalox orbital maneuvering / attitude engine.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/12/2016 05:25 pm
...
Landing engines on Mars would require deep throttling of 550klbf engine.
...

Just to address this point: Merlin throttles to 40%, and MVac to 30%. That's more than deep enough to land 100t payload on Mars even using two 550 klbf engines.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 07/12/2016 06:44 pm
Yes, but -- how wide would such a scaled-up Dragon capsule be at the base, if it's got to be designed to carry at least 100 people, along with all the stuff (like food, water and life support) they will need for three to six months?

I think simply scaling up the dimensions of a Dragon to where it has the interior space available for the actual stated mission requirements would make the base diameter in the hundreds of meters.  How ya gonna fit that on any booster, much less one with the most-commonly-speculated (see L2) width of the BFR?

And if you change the basic shape, you inevitably have to go through a lot of design work to achieve similar lift/drag characteristics, etc.  In other words, BFS is gonna have to be designed from scratch, it won't take advantage of Dragon's shape or flying characteristics as a starting point.

Let's do at least a first order pass at actually calculating this. If BFR's diameter is 15m, BFS can easily be at least 15 to 16m.  Dragon's OML including the nose but not the trunk encloses about 25 m^3 with a major radius of 1.85 meters. Volume increases with size as r^3, so a 15 meter Dragon would enclose about 1,875 m^3 and a 16m version about 2,050 m^2

Estimates of necessary volume per person and propellant mass vary, but usually range somewhere from 5 to 15 m^2 per person and 300-1200 tonnes of propellant. Averaging those gets 10 m^3 per person and 750t propellant, or 1000 m^2 habitable volume and 915 m^3 tank volume (100 people, 820 kg/m^3 methalox). That totals 1915 m^3, or pretty close to what a 15 to 16m Dragon would enclose.

Obviously, that's only enclosed volume and not all the space can be utilized efficiently, and engines etc. all take up volume. But volume shouldn't be a show-stopper considering that it's probably feasible to launch up to a 20m diameter (4,500 m^3 volume) object on top of BFR.

Nit: I get ~1,000 Kg/m3 for methalox at a 3.7:1 oxygen ratio.  Maybe ~7% higher with superchilling.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 07/12/2016 09:30 pm
...
Landing engines on Mars would require deep throttling of 550klbf engine.
...

Just to address this point: Merlin throttles to 40%, and MVac to 30%. That's more than deep enough to land 100t payload on Mars even using two 550 klbf engines.

How's that?
100tonne payload would  'weigh' 37tonnes on Mars.
550,000lbf (250tf) at 40% is 100tonnes... T/W=2.7 (major hoverslam required)
Two 550klbf engines at 40%... T/W=5.4
Even if spacecraft dry weight is same as payload, T/W is still greater than 1 with a single engine.

Single engine would also have to be directed straight downward, digging a crater and ejecting debris back up toward the descending stage.

To answer DanielW's question above, my three would be booster engines at 1.5-1.6Mlbf, an MCT/BFS engines at 550klbf each, and landing (or second stage F9/FH) at 150-200klbf.  Note: Purely speculating -- we don't have a definitive answer yet...  But this is a speculation thread.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 07/12/2016 09:41 pm
Even if spacecraft dry weight is same as payload, T/W is still greater than 1 with a single engine.

There is the all important difference between weight and mass. It is the weight that would need to be countered for a hover. But they don't want to hover. It is the mass that needs to be decelerated. That's mostly the same effort as on earth for landing, just with less gravity losses.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/13/2016 12:38 am
My expectation is that the main propulsion will 'hover slam' to a full stop at a height of a few dozen meters above the ground and then cut out.  Then the vehicle will touch down on orbital maneuvering engines located higher on the vehicle and canted outward, where they will not impinge on the ground, this will only require the equivalent of a dozen Super Draco engines.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Adriano on 07/13/2016 03:35 am
It is clear Spacex is mastering first stage usability, but they indicated they are not finding practical bringing the second stages down to earth. ULA on their part are toying with ACES, a second stage spending extended time in orbit, but they have not been explaining how they plan to bring supplies to orbit without creating a glut of second stages up there... If it is not practical to bring back to earth the second stage, the only remaining solution for a reusable second stage is to park it in orbit and perform a suborbital load transfer from the first stage carrying the load and a second stage descending from orbit to pick up the load. Unquestionable the maneuver is tricky and must be performed quickly... Have you seen discussions on this topic somewhere?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/13/2016 03:51 am
It is clear Spacex is mastering first stage usability, but they indicated they are not finding practical bringing the second stages down to earth. ULA on their part are toying with ACES, a second stage spending extended time in orbit, but they have not been explaining how they plan to bring supplies to orbit without creating a glut of second stages up there... If it is not practical to bring back to earth the second stage, the only remaining solution for a reusable second stage is to park it in orbit and perform a suborbital load transfer from the first stage carrying the load and a second stage descending from orbit to pick up the load. Unquestionable the maneuver is tricky and must be performed quickly... Have you seen discussions on this topic somewhere?
SpaceX didn't think reuse of the second stage was practical when both these conditions are true:
1) high energy, GTO style missions (majority of commercial payloads)
2) kerolox propellants

But other than that, they are fully supportive of 2nd stage reuse, provided at least one of the two above conditions are not met.

They are developing Raptor, which is a methane/LOx engine (higher performance) and thus would potentially allow reuse of a Falcon 9 or Falcon Heavy upper stage built around Raptor. Or, BFR/BFS will have a reusable upper stage as well (BFS).


SpaceX doesn't think 2nd stage reuse is impractical, they just haven't developed a vehicle where it makes sense to attempt it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/13/2016 04:37 pm
... If it is not practical to bring back to earth the second stage, the only remaining solution for a reusable second stage is to park it in orbit and perform a suborbital load transfer from the first stage carrying the load and a second stage descending from orbit to pick up the load. Unquestionable the maneuver is tricky and must be performed quickly... Have you seen discussions on this topic somewhere?

This is off-topic in this thread, try the General Q&A thread:
http://forum.nasaspaceflight.com/index.php?topic=13543.0
It's also not possible with current technology as the orbiting second stage is travelling about 15,000 miles per hour (24,000 km/hr) faster than the first stage ever goes. It's a problem of speed, not altitude.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 07/13/2016 09:07 pm
Even if spacecraft dry weight is same as payload, T/W is still greater than 1 with a single engine.

There is the all important difference between weight and mass. It is the weight that would need to be countered for a hover. But they don't want to hover. It is the mass that needs to be decelerated. That's mostly the same effort as on earth for landing, just with less gravity losses.

Good point.  High-G deceleration can be accomplished with two engines or more reasonable decelaration with one for 100 tonnes (mass).  I was considering the terminal phase of landing where they won't be able to handle the payload (crew, for instance) as roughly as they do an inanimate booster during a hover slam -- 10-ish Gs on three engine ASDS landings from GTO launches.   Landing the BFS, as they are practicing with Dragon 2, will require hover or near hovering and gentle touchdown, requiring T/W<1 on a 37tonne (weight) payload.  There may also be a need to do last minute obstacle avoidance which would require lateral translation near the surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 07/13/2016 09:20 pm
My expectation is that the main propulsion will 'hover slam' to a full stop at a height of a few dozen meters above the ground and then cut out.  Then the vehicle will touch down on orbital maneuvering engines located higher on the vehicle and canted outward, where they will not impinge on the ground, this will only require the equivalent of a dozen Super Draco engines.

This was my conjectured solution to the landing pad problem, at least for the many missions required before a hard-pad is constructed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/13/2016 10:51 pm
BFS will likely mass some 50 to 100 tonnes dry, so reasonable acceleration on two Raptors burnout is certainly possible. At 30% throttle that's 80t thrust per engine and an acceleration of about 1g (for 80t ship+100t payload). Even at WOT two Raptors would only get 3 gees at burnout, which is nowhere near the limit for transient acceleration even with crew.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/14/2016 06:17 am
I like 4 raptors on BFS to allow an engine out capability.  With two pairings of engines on the sides of the vehicle you can run on either diagonal pair of engines in case of failure.  With the engines not in the vehicles center their is room for an extensive cargo-bay at ground level, Propellant is in the nose above the cargo.  Deceleration drag area can be increased with some form of mechanical expandable shield on the nose which folds down umbrella like over the vehicle and forms its conical outer mold line when not in use, entry would be nose first followed by a flip over for landing burn.  The bottom of the vehicle would have landing gear and systems used in orbit such as radiators and solar panels which likewise fold when not in use.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lobo on 07/14/2016 06:50 pm
My expectation is that the main propulsion will 'hover slam' to a full stop at a height of a few dozen meters above the ground and then cut out.  Then the vehicle will touch down on orbital maneuvering engines located higher on the vehicle and canted outward, where they will not impinge on the ground, this will only require the equivalent of a dozen Super Draco engines.

This is certainly a possibility, and something that has been speculated on before.  To have "landing thrusters", likely pressure fed, for more precise throttle response as well as engine out capability, like superdracos and D2.

However, if Raptor has adequate throttle response, and if there are 5 engines in a cross pattern under the BFS, and if Raptor can throttle down to where two Raptors are not over powered to hover and land, and if you plan to land on an area that's level and rocky rather than with deep regolith that would be excavated during a landing....then they could potentially still land on Raptors, and still have engine-out capability and not have issues with the engines kicking up too much debris.
That advantage of this is then you don't need to have a separate propulsion system in addition to your main propulsion, which simplifies things. 
But there are some technical hurdles to overcome.
If MCT masses 100mt, and has 100mt of cargo on it, and maybe 20mt (guess) of residual propellants at touchdown, then that's 220mt total mass.  On Mars that would weigh about 184,300lbs.  So one 550klbs enigne would need to throttle down to about 33.5%...which is very plausible given Merlin-Vac throttle and RD-180 is about that.  But with 5 engines, you want redundancy if you loose your center engine.  So you really need to be able to land on either of the two outer pairs of engines.  That means about 17% throttle.  That's pretty low.  So I think that'd be the primary hurdle to land on the primary engines.
If you can do that, then you have not one, but two engine-out during EDL backup scenarios.  During EDL, once BFS is at terminal velocity and ready to do retro propulsion, it lights all 5 engines briefly.  That way all 5 can be tested to see if there is a failure after the long cruise to Mars.  If all are nominal, then the 4 outer engines are shut down and landing is done on the central engine like the F9 booster.  If there is a failure in the center engine, then all but one of the outer pairs of engines are shut down, and landing is done on that.  If the center engine plus one outer engine fails, then landing is done on the other outer pair. 

Ascent should also be possible with one engine failure, as depending on the weight of the fueled MCT, it should be able to lift off on 3 engines. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/14/2016 07:06 pm
I like Impaler's idea. I arrived at the same thing independently.

There's an opportunity to allow some abort capability, too, if the terminal landing thrusters are located on a relatively small, separable module on top that the crew is smushed into for launches and/or landings. Could allow aborts for launches on either planet (requires propulsive landing on Mars, of course, not parachute) and landings on either planet.

Of course, there's no actual evidence for such an idea from SpaceX, that's just something I think needn't add much mass and could significantly reduce loss of crew probability.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/14/2016 11:32 pm
Some form of orbital maneuvering engine is a must, you can't use the main propulsion system for thouse kinds of maneuvers.  Draco (not super) might do the very fine maneuvers for docking and such but you will still want something stronger for a de-orbit burn.

Lets compare to shuttle, it massed around 75 mt on orbit and had OMS with 53 kN thrust.  Scale up to a likely 200+ mt mass in orbit and your looking at the thrust of 2 Super Draco engines for a de-orbit burn.  A Raptor engine would need to throttle down to 6% to give that thrust. 

Still we would be looking at about a 6 fold increase over a reasonable orbital maneuvering system so it's not free.  Their may be additional benefits to these engines, their position high on the vehicle gives them huge leverage on the vehicle useful in EDL if a flip over is needed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 07/14/2016 11:42 pm
I agree there will need to be some sort of maneuvering system, but if what Elon has said holds up, there will be no need for a deorbit burn, MCT will be designed to hit Earth's or Mars' atmosphere at interplanetary velocity. A number of distributed Draco sized engines may suffice.

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/15/2016 12:01 am
Apollo used a 90 kN engine for orbital maneuvers of a 30 tonne CSM  ::) that would work pretty well at hovering on Mars.

And yes, BFS will need deorbit maneuvers. That how it gets out of orbit... not every mission will be to escape or free-return.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/15/2016 03:43 am
Another concept I just considered, with a small BFS and a larger second stage without using SEP.  Launch with just cargo in the BFS and all propellant in the 2nd stage, the two stay together and reach orbit much like a Dragon capsule and it's trunk. 

Then both are refueled to full, TMI is conducted by firing the 2nd stage for ~2 km/s of acceleration then the BFS separates and performs the remaining boost.  This leaves the 2nd stage far short of Earth escape and it will be in an elliptical orbit which can easily allow it to land again.

Another 2nd stage without a BFS attached is also placed in orbit and refueled to make a TMI on it's own with a propulsive insertion at Mars, by utilizing a slow hohoman transfer the propellant delivery is much more efficient.  BFS then rendezvouses with it in orbit and takes on the necessary propellant for TEI.  The 2nd stage now very light now returns to Earth via a slow transfer and aero-captures at Earth. 

The 2nd stage would be capable of this kind of total DeltaV because it is almost nothing but tank so a 4-5% dry mass fraction is reasonable for it (far lower then what the BFS could achieve).  The main challenge is endurance and maintaining propellants against boil-off for that length of time, but any vehicle that waits in LEO while it is being filled up will need considerable insulation so this 2nd stage can perform the job of tanker to LEO, depot in LEO, tanker to Mars and heavy lifter to LEO for the BFS and other payloads.

I see this stage being around 60 mt in dry mass with 1200 mt of propellant capacity and equipped with solar and radiators on the surface as on the Dragon 2 capsule.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 07/15/2016 09:09 pm
Some form of orbital maneuvering engine is a must, you can't use the main propulsion system for thouse kinds of maneuvers.  Draco (not super) might do the very fine maneuvers for docking and such but you will still want something stronger for a de-orbit burn.

Lets compare to shuttle, it massed around 75 mt on orbit and had OMS with 53 kN thrust.  Scale up to a likely 200+ mt mass in orbit and your looking at the thrust of 2 Super Draco engines for a de-orbit burn.  A Raptor engine would need to throttle down to 6% to give that thrust. 

Still we would be looking at about a 6 fold increase over a reasonable orbital maneuvering system so it's not free.  Their may be additional benefits to these engines, their position high on the vehicle gives them huge leverage on the vehicle useful in EDL if a flip over is needed.

Couldn't you just use a single Raptor and fire it for a shorter time period?  What type of delta V is needed for a de-orbit burn typically?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 07/15/2016 11:24 pm
Some form of orbital maneuvering engine is a must, you can't use the main propulsion system for thouse kinds of maneuvers.  Draco (not super) might do the very fine maneuvers for docking and such but you will still want something stronger for a de-orbit burn.

Lets compare to shuttle, it massed around 75 mt on orbit and had OMS with 53 kN thrust.  Scale up to a likely 200+ mt mass in orbit and your looking at the thrust of 2 Super Draco engines for a de-orbit burn.  A Raptor engine would need to throttle down to 6% to give that thrust. 

Still we would be looking at about a 6 fold increase over a reasonable orbital maneuvering system so it's not free.  Their may be additional benefits to these engines, their position high on the vehicle gives them huge leverage on the vehicle useful in EDL if a flip over is needed.

Couldn't you just use a single Raptor and fire it for a shorter time period?  What type of delta V is needed for a de-orbit burn typically?

~100 Km/sec from LEO.  Less from low Mars orbit.

EDIT:  100 METERS/sec!!!!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 07/16/2016 01:18 am
Some form of orbital maneuvering engine is a must, you can't use the main propulsion system for thouse kinds of maneuvers.  Draco (not super) might do the very fine maneuvers for docking and such but you will still want something stronger for a de-orbit burn.

Lets compare to shuttle, it massed around 75 mt on orbit and had OMS with 53 kN thrust.  Scale up to a likely 200+ mt mass in orbit and your looking at the thrust of 2 Super Draco engines for a de-orbit burn.  A Raptor engine would need to throttle down to 6% to give that thrust. 

Still we would be looking at about a 6 fold increase over a reasonable orbital maneuvering system so it's not free.  Their may be additional benefits to these engines, their position high on the vehicle gives them huge leverage on the vehicle useful in EDL if a flip over is needed.

Couldn't you just use a single Raptor and fire it for a shorter time period?  What type of delta V is needed for a de-orbit burn typically?

I was thinking the same thing. De-orbit burns have typically been low thrust and moderate duration from small engines because that was sufficient; in this situation you don't need a large engine to fight gravity losses. Also, typically, larger engines and tankage have already jettisoned. If, however, you already have a larger engine on the vehicle (e.g. BFS) which can do a burn that gives accurate ∆V, and you have fuel and oxidizer available (STS couldn't de-orbit with RS-25 as prop tanks were gone), use of the larger engine seems possible.

I am not suggesting a high-G burst that lasts a fraction of a second, as you are more unlikely to get the precision ∆V required for precision landing. If, however, the burn is long enough and the engine controllable enough to give precise ∆V, it seems that option is possible.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/16/2016 02:41 am
Perhaps a shorter burn can do the job for de-orbit but that is the heaviest demand placed on an OMS, I'm sure their will be needs that are too fine and delicate for a Raptor engine and a set of maneuvering engines will exist. 

The question is will they be very small jets that are of no use in landing or would they be intentionally oversized to act as touchdown engines, I favor that approach as it solves a major issue during touchdown while allowing another system to serve double duty.

Note that the thrust from these small engines because they would have the thrust to just hover at landing with cargo could allow the vehicle when empty to make short hops like the Grasshopper test vehicle which might be an excellent means of moving the vehicle around the surface and landing it adjacent to fueling, servicing or repair infrastructure without endangering these places with a strong rocket exhaust.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Nilof on 07/16/2016 06:52 pm
One thing worth keeping in mind is that since Mars has a very low atmospheric pressure, the throttle range is essentially the vacuum throttle range, not the sea level one. So I wouldn't be surprised if the Raptor could have very deep throttling for a Mars landing, significantly deeper than the Merlin for Earth landings.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/16/2016 07:33 pm
Whats the Vac throttle range on comparable Russian staged combustion hydro-carbon engines?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: KelvinZero on 07/16/2016 10:48 pm
btw, would the weight of these small low-ISP engines reduce overall performance to orbit, or could they pay for themselves with a bit more oomph at the very beginning of liftoff?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/17/2016 12:25 am
Insignificant at launch from either Earth or Mars, their mass is a performance loss but the comparison is not just will the same vehicle minus these engines, if your trying to land directly on Raptor engines the vehicle might need to be strengthened or have more mass in other places. 

I've estimated 1 mt for these engines and they would draw from the vehicles main Methane/LoX tanks, though they may require a pressurization tank and a tertiary pressurizing gas supply.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/18/2016 03:40 pm
Another concept I just considered, with a small BFS and a larger second stage without using SEP.  Launch with just cargo in the BFS and all propellant in the 2nd stage, the two stay together and reach orbit much like a Dragon capsule and it's trunk. 

Then both are refueled to full, TMI is conducted by firing the 2nd stage for ~2 km/s of acceleration then the BFS separates and performs the remaining boost.  This leaves the 2nd stage far short of Earth escape and it will be in an elliptical orbit which can easily allow it to land again.

Another 2nd stage without a BFS attached is also placed in orbit and refueled to make a TMI on it's own with a propulsive insertion at Mars, by utilizing a slow hohoman transfer the propellant delivery is much more efficient.  BFS then rendezvouses with it in orbit and takes on the necessary propellant for TEI.  The 2nd stage now very light now returns to Earth via a slow transfer and aero-captures at Earth. 

The 2nd stage would be capable of this kind of total DeltaV because it is almost nothing but tank so a 4-5% dry mass fraction is reasonable for it (far lower then what the BFS could achieve).  The main challenge is endurance and maintaining propellants against boil-off for that length of time, but any vehicle that waits in LEO while it is being filled up will need considerable insulation so this 2nd stage can perform the job of tanker to LEO, depot in LEO, tanker to Mars and heavy lifter to LEO for the BFS and other payloads.

I see this stage being around 60 mt in dry mass with 1200 mt of propellant capacity and equipped with solar and radiators on the surface as on the Dragon 2 capsule.

I think SpaceX is likely to build a tanker stage similar to what you're suggesting. They are going to be launching a LOT of fuel, and a lightweight stage can put more payload up. And since it would never carry significant downmass, its very low ballistic coefficient makes nose-first entry from LEO much easier. No need for hypersonic retropropulsion, just float down to a low terminal velocity, and swan-dive to land.

But, sending it to Mars seems pretty inefficient long term. They are going to want that stage at Earth paying for itself by ferrying up payloads. The prop tanks on BFS will also be in the 4% mass fraction range, so having tanks big enough for 6km/s isn't a major mass penalty. Massive ISRU refueling is a significant long pole in the architecture anyway, sending TEI fuel from Earth might somewhat reduce that short-term but adds a lot of cost and complexity. And the BFS needs to be big enough to shuttle a significant fuel payload to LMO if it's to be used as a LMO shuttle eventually.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/19/2016 02:43 am
BFS will certainly cost more then the 2nd stage I'm suggesting, so any job that can be performed by the cheaper stage should be given to it rather then the BFS.  And remember everything is predicated on propellant depots which occupy vehicle time too.  Sending one 2nd stage off to Mars for a synod to do a refueling in order to bring back a crew is not that significant in the course of the many many launches necessary to make the whole mission work.

The difference in ISPP needed between these scenario is quite massive, direct return will likely require around 8 km/s because the vehicle needs to go fast and have propellant for Earth landing.  Which means 2-3x as much propellant on Mars surface vs the minimal trip to LMO.  If massive ISRU is the long pole then we want an architecture that makes that pole as short as possible, not one that simply assumes that is will be done and makes no attempt to conserve.

Lastly the known 25 mt launch capability of the BFS from Mars means that it can do the future job of surface to orbit tanker by substituting propellant in place of that cargo.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/19/2016 07:54 pm
Sending prop from Earth to LMO reduces ISPP by 2x to 3x, but increases launch requirements from Earth by the same 2x to 3x (by my calculations ISPP goes down from 500t to 200t, but Earth launches increase from 4 to 9). And there's a mission-critical Mars orbital rendezvous, and lot more separation events and LEO rendezvous.

So you're retiring some risk from one part of the architecture (ISRU) by imposing more risk on other parts (mission complexity). Granted, LEO rendezvous and Earth launch are at a much higher TRL than ISRU. Until ISRU is proven it certainly makes sense to send as much fuel as possible from Earth, but not in the long term.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/19/2016 09:30 pm
Yes this 2nd stage to Mars orbit for refueling is only intended as an early mission enabler when the ISPP surface production is first being established and presents a significant constraint on return capability and an untested element.  All ISPP infrastructure is going to remain in place once deployed so their will be an infrastructure build up that allows a gradual transition to more and more earth return propellant being sourced at Mars.

In the long term I favor rapid mars surface to orbit cycling of the BFS, bringing down cargo from orbit and dropping off a small propellant surplus in a Mars depot each time.  Then when at conjunction the Mars propellant depot is drained to allow a fast return for crew.  The 10:1 cargo:crew ratio means just a small propellant offload on each cargo retrieval (25 mt) can supply a generous return burn.

Note that all of the rendezvous at Mars involve the same vehicle and the same propellant transfer task that is part of the Earth side orbital fueling process which is expected to be as common as launch as most launches are tankers.  Rendezvous is completely routine today and is one of the the safest most reliable parts of space travel, to date I believe the one instance of Soyuz striking Mir is the only anomaly EVER to occur in the history of rendezvous.  I see no reason why we should consider Mars orbital rendezvous even remotely dangerous considering the other far more dangerous elements in the mission like EDL and launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 07/19/2016 10:12 pm
It is not "considered dangerous",  it elevates the risks for mission success. It's a statistics and systems analysis thing and prior performance of the general principle of docking is probably only marginally relevant to a specific system, in this context. Three docking events present more risk than two identical docking events, even if you eventually manage to pull both flawlessly, 100 times each.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: the_other_Doug on 07/19/2016 10:18 pm
It is not "considered dangerous",  it elevates the risks for mission success. It's a statistics and systems analysis thing and prior performance of the general principle of docking is probably only marginally relevant to a specific system, in this context. Three docking events present more risk than two identical docking events, even if you eventually manage to pull both flawlessly, 100 times each.

Yes, but you have to also evaluate, and weight, each of your events to see if increasing their number actually significantly increases the risk of mission failure (or worse).

For example, if adding a third docking event means you can eliminate an extendable-pipe refueling event that is considered inherently riskier than the docking event, well, you weight each option and determine which one actually reduces overall risk more.

Sometimes, increasing events of low to moderate risk, even a lot, to reduce or eliminate events of much higher risk, or of much greater impact to the mission or crew safety, leads you to increase some events, and increasing risk of those events failing, to gain redundant capability and avoid single-point failures that can ensure not just mission failure, but loss of crew as well...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 07/19/2016 10:25 pm
Agreed, it's all trades. Impaler made it sound like there's an irrational phobia of docking events :) I just don't think there is one.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/20/2016 02:31 am
mfck you had it right, I am saying their is an irrational fear of rendezvouses in mission planning.  I think this goes back to the Apollo's fight over Lunar Orbital Rendezvous (LOR) architecture which was massively resisted and only done when it became obvious that the NOVA rocket and direct assent was impossible. 

Their was good reason to be worried about LOR durring the design of Apollo because Gemini had not even flown yet, but after the numerous Gemini-Agena missions most of the risk had been retired before Apollo left the pad, other parts of the mission were far more dangerous and likely to kill the crew then a failure to rendezvous.  But people have internalized this notion that each rendezvous event has a high failure probability but this is clearly falsified by experience.

Their have been ZERO failures of American vehicles to dock and were getting more experienced on every ISS mission.  In a fuel transfer scenario the challenges are reduced because you don't have to create an air-tight seal between habitable spaces, you just need to connect hoses which can easily have redundant ports, redundant hoses and be manipulated via EVA if any automation fails.  The true failure risk is only if ALL the contingency options fail and the mission is marooned in LMO unable to make TEI.

NASA assesses the chance of a crewed Orion capsule with a contingency EVA option failing to dock with a lunar assent vehicle at just 1 in 546.  https://www.nasa.gov/pdf/140639main_ESAS_08.pdf (Page 13)

The BFS will have even more resources to bring to the docking, particularly TIME because the crew is already IN the habitat that will return to Earth they have months on the consumables clock, the only timeline is making Earth departure which is flexible due to the ~1 month that Earth and Mars are at conjunction, a few weeks delay in departure would be accommodated by lengthening the time of flight of return.  You can even launch from Mars surface a few weeks early on purpose to provide ample time for rendezvous while still making TEI as scheduled.

So I would estimate a failure chance of the BFS to achieve refueling in Mars orbit at around 1:1000 and not at all something worth of concern.  Nor is it even a development cost driver because BFS and tankers will have propellant transfer as a BASELINE capability.  Their is cost in extra launch in sending a tanker from Earth but that should be weighed against the ISPP leverage ratio and risk of failure.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 07/20/2016 12:15 pm
Impaler, I'm probably being dense here, but I fail to see the rationale in doing Mars orbit refueling for the BFS return, versus just fully fueling the BFS on Mars surface for a direct return to Earth.  ISRU fuel production is already needed to leave Mars surface, so why not just fully fuel the beast while it's on the surface and launch back to Earth.  I think delta V wise a direct return is actually somewhat better than first going to Mars orbit then doing a TEI burn, right?

Is the thrust of your position that it is not feasible to have a vehicle do direct return from Mars surface to the Earth?  I thought I'd seen that the delta V for this is only on the order of 5-6 kms, so that should be well within modern capabilities, yes?  If so, this would seem to be the much simpler way to go compared to refueling in Mars orbit, with fuel sent form Earth surface.  (Note, I don't dispute at all your points about the well established feasibility of docking events.) 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/20/2016 01:27 pm
Mars surface to Earth surface is a minimum of about 5.8 km/s, for optimal launch alignments and 8+ month transits. 6.5 to 7.0 km/s is more realistic for real launch sites, average Earth-Mars alignments, and faster transits.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 07/20/2016 01:48 pm
So even at the upper 7 kms figure, that still implies just a 6.5 mass ratio, right?  I'd think this is quite do-able with present technology.

It's just easier for me to wrap my mind around this, versus the dozens of required BFR launches to get some return fuel prepositioned in LMO.  And until direct return is shown to be unworkable, I'd think it should be the default assumption for return mode (Occam's razor and all that).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/21/2016 02:24 am
I estimate a direct return requires 3x the propellant at Mars surface, which is nothing to sneeze at when we know so little about how hard that propellant will be to acquire.  Note that envy887 just gave us the TEI numbers not the TOTAL the vehicle would need because he didn't include the DeltaV for propulsive landing on Earth, that's going to add around another 500 m/s, that along with a safety margin reserves means your looking at 8 km/s to do the direct return which starts to look prohibitive.

Also no one seems to be taking into account how tripling the propellant capacity of the BFS affects it's design and adds to it's dry mass which has multiplicative penalties not just at return but through the entire mission.  You can not simply take the marginal propellant mass multiply by a tankage fraction of 4% and call that the added dry mass, the larger vehicle needs more thermal protection, stronger landing gear to support it's mass at launch, more thrust to liftoff and land, more systems to chill and hold the propellants.

The DeltaV number I'm targeting is slightly above that required just for launch to mars orbit because I see potential for a surface-orbit-surface cycle and returning a completely empty vehicle to Earth via a slow transfer.  I estimate a vehicle mass of 75 mt and thus a propellant capacity of 300 mt gets both of these capabilities, having 6 km/s when empty and 5.1 km/s when carrying the 25 mt return cargo spec which allows 4.1 km/s to orbit and and 800 m/s on landing with cargo (taking on cargo in orbit means it dose not sum to 5.1 km/s).

A direct return vehicle would have a higher mass, 25 tons more for a total of 100 mt and would require a 900 mt propellant capacity and that is JUST the 4% tank fraction of the marginal propellant as 600 * .04 = 24 so the vehicle could be considerably heavier.  Take off dry mass at Mars would then be 125 (100 dry + 25 cargo) rather then 100.  Now consider total initial mass in LEO that this system would need to do the TMI with it's outbound 100 mt cargo would be 1125 mt.

A smaller BFS using a 2nd stage massing 50 mt for assist in TMI is almost identical at 1151 mt IMLEO for the same trajectory which is split between the 2nd stage and the BFS, with a reserve for the 2nd stage to do a full propulsive reversal and return to LEO.  So

Now how much mass is needed for the refueling tanker.  The smaller BFS has the DeltaV to go to very near the 5 km/s Mars Escape from the surface so the refueling tanker can be placed in a high Martian orbit. The BFS would then need 3 km/s after the refueling to archive a comparable fast transit to Earth as the 8 km/s direct launch.  To do that it needs to take on 125 mt of Propellant.  If the tanker masses 50 mt and will need to return to Earth on a hohmann after the fuel transfer it needs to retain about 13 mt for that, so mass in high Mars orbit is 187 mt and that means an initial mass in LEO of 936 mt, an 80% increase in total IMLEO.

While 936 might seem prohibitive, it is substituting for 600 mt of propellant MADE on the surface of Mars, so the ratio of substitution is ~3:2 when propellant is delivered to a high Mars orbit.  This is quite different then the traditional view that Mars ISPP will have a IMLEO reduction factor of 10x - 20x but thouse estimates are based on taking all propellant down to the Martian surface which is an additional 10 km/s DeltaV, this scenario puts the refueling at the optimum point for efficient delivery.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/21/2016 02:33 am
We don't know isn't a valid reason. Same line of reasoning would give us Apollo-like hypergols.

SpaceX is going to find out. So make a first-try estimate. You'll see that a ton of water per day isn't unreasonable to harvest since you need to harvest at least hundreds of kilograms per day anyway. Better than tripling the required number of launches and the complexity of the architecture.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 07/21/2016 06:48 am
mfck you had it right, I am saying their is an irrational fear of rendezvouses in mission planning. 
....

NASA assesses the chance of a crewed Orion capsule with a contingency EVA option failing to dock with a lunar assent vehicle at just 1 in 546.  https://www.nasa.gov/pdf/140639main_ESAS_08.pdf (Page 13)
...

So I would estimate a failure chance of the BFS to achieve refueling in Mars orbit at around 1:1000 and not at all something worth of concern. 
....

I am not an engineer, but those risk figures seem odd. 1:546 might be considered OK for Orion, a craft that will hardly (imo) fly 100 missions combined, but a 1:1000, for a mass transportation architecture that MCT is, seems unacceptable. What am I missing? What are the comparable risks in, say, aviation?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/21/2016 09:05 am
mfck you had it right, I am saying their is an irrational fear of rendezvouses in mission planning. 
....

NASA assesses the chance of a crewed Orion capsule with a contingency EVA option failing to dock with a lunar assent vehicle at just 1 in 546.  https://www.nasa.gov/pdf/140639main_ESAS_08.pdf (Page 13)
...

So I would estimate a failure chance of the BFS to achieve refueling in Mars orbit at around 1:1000 and not at all something worth of concern. 
....

I am not an engineer, but those risk figures seem odd. 1:546 might be considered OK for Orion, a craft that will hardly (imo) fly 100 missions combined, but a 1:1000, for a mass transportation architecture that MCT is, seems unacceptable. What am I missing? What are the comparable risks in, say, aviation?

Maybe you misunderstood, 1 in 546 is the chance of failure PER attempt, the number of missions an individual vehicle makes isn't relevant to that figure. 

A refueling failing on the first few missions when their is only ONE BFS at Mars and no assistance available could result in a loss of crew.  But when whole fleets of vehicles are operating continually then their is no more danger from a refueling failure then when an airplane flight gets canceled, people are just transferred to another vehicle for Earth return.

No one has any concern about loss of life from a failure to fill up propellant depots at Earth because we have all our resources available here to render aid to any stricken vessel, the lack of that aid chance is WHY distant exploration is dangerous.  If Mars gets a functioning base and a propellant depot in orbit then the rescue contingencies become more robust and mechanical failures that are not 'kinetic' aka don't cause immediate destruction or lose of life become lower impact and thus lower risk because risk = probability * impact.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/21/2016 09:24 am
We don't know isn't a valid reason. Same line of reasoning would give us Apollo-like hypergols.

SpaceX is going to find out. So make a first-try estimate. You'll see that a ton of water per day isn't unreasonable to harvest since you need to harvest at least hundreds of kilograms per day anyway. Better than tripling the required number of launches and the complexity of the architecture.

At least quote my numbers correctly when you give a rebuttal, it was an 80% increase in IMLEO in exchange for a 66% reduction in propellant produced at Mars.

And while we don't know the efficiency of water collection yet this shows what the bar is in performance needed to make it attractive.  Basically propellant production at Mars has a marginal utility that drops as you produce more of it and burn it farther away from Mars due to both the rocket equation and the closer supply from Earth.  The most efficient use is assent to LMO, then rising to high Mars orbit, then TEI, then Earth landing.

Lastly it's quite clear that the vehicles I'm proposing are no more complex then your larger vehicle alternative, they are very likely much simpler to produce due to lower mass.  Likewise the mission profile though it is more costly due to IMLEO and launch increases isn't doing anything that isn't already expected, you have BFS and Tankers and propellant transfer, something we always knew would exist, it's just repeated more times.  And in exchange the longest pole of the whole system the ISPP is cut by 2/3rds
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 07/21/2016 09:40 am
While 936 might seem prohibitive, it is substituting for 600 mt of propellant MADE on the surface of Mars, so the ratio of substitution is ~3:2 when propellant is delivered to a high Mars orbit.  This is quite different then the traditional view that Mars ISPP will have a IMLEO reduction factor of 10x - 20x but thouse estimates are based on taking all propellant down to the Martian surface which is an additional 10 km/s DeltaV, this scenario puts the refueling at the optimum point for efficient delivery.

The 2nd stage is not just substituting for propellant made on Mars. It is a whole new reusable long duration spacecraft which needs to be designed and manufactured. It will have heatshield, landing legs (and engines?), deep space avionics, solar panels (+ radiators?), propellant cooling loop, docking (berthing?) adapter, etc. While not quite as complex as a do-it-all BFS, it is still a major project, costing lots of up-front development effort and testing.

The BFS might be a bit simpler using a second stage, but not by much, all major subsystems would still be present, the only advantage is that it would need a lower propellant mass fraction. An do-it-all BFS has as far as we can tell a reasonably high, but not exceptional propellant mass fraction.

Using a hohmann transfer for the 2nd stage reduces its reuse to every 2 synods (it might be every 3 synods because I think that refuelling the BFS in Mars orbit occurs after the hohmann transfer window closes - I haven't checked this).

Adding in a 2nd stage and refuelling in Mars orbit adds in complexity and a lot of extra failure modes, this is not just docking, but failures in aerocapture, propellant transfer, BFS engine restarts, etc. These failure modes then drive extra abort scenarios.

In my opinion these extra up-front costs and complexity mean that a design like this with a 2nd stage is not optimum in the short term. In the long term the higher IMLEO and longer reuse cycle (2-3 synods) would mean it is likely more costly as well. It really only makes sense if the do-it-all BFS becomes difficult or impossible because of its extra propellant mass requirements.

Edit:

The 2nd stage (burn out) + BFS + cargo would mass more in LEO than a do-it-all BFS (burn out) + cargo, I estimate about 20% more. Which would mean that the BFR would need to be 20% larger, and cost more. This extra cost is mostly offset by the 2nd stage in tanker mode carrying more propellant.

Turning the rocket into 3 stages (BFR + 2nd stage + BFS)  with the 2nd stage not reaching orbit and landing downrange, could lead to a smaller BFS. Even with the expense of downrange recovery this might end up cheaper.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/21/2016 10:21 pm
A stage with all of the capabilities I've described for the 2nd stage is a necessity under any architecture, others have simply been calling it a 'BFS-Tanker' as it is clear that the cargo carrying BFS vehicle would not be an efficient tanker to LEO and something specialized for that purpose is necessary.

The 2nd stage would need longer duration thus solar panels and radiators but these can be put directly on the surface of the cylindrical body as in the Dragon2 trunk.  It needs to be able to re-enter and land but only at Earth onto a concrete pad and without any cargo meaning it would land nearly empty of propellant, it would have a dry mass about twice that of the F9 first stage and can use a similar set of fold down legs which are nothing compared to the legs systems that the BFS needs to be able to land on rough ground.  Sending the tanker off to Mars is just 2 engine restarts, the rest of the duration it's just free floating in space in a thermal environment much cooler then remaining near the Earth.

As for synod cycle times we already have a terrible rate on the BFS, the one synod cycle Musk has speculated about require insane DeltaV levels and In my opinion they will never happen, not least of which is the fact that the BFS will have nothing to do in Earth space until the next Mars transit window opens.

Your comment on long and short term costs seems to be based on a false premise, that the refueling plan I described is intended for long term usage.  If you had read my comments fully it would be clear that I intended this as just a bootstrapping technique for early missions.

This is one of the more annoying aspects of most discussion on this thread, most commentators are seemingly incapable of conceiving of a MCT SYSTEM which evolves or grows over time in any capacity other then sending larger and larger numbers of the same vessels.  Every proposal is evaluated as if that system MUST satisfy all transport needs from the first human landing to the 10 millionth colonist.  Nothing could be farther from reality, Musk looks for the minimum viable product and then improves and adds to it, a Mars transport system will also expand with additional components that act as force multipliers on the whole system.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/27/2016 07:03 pm
A stage with all of the capabilities I've described for the 2nd stage is a necessity under any architecture, others have simply been calling it a 'BFS-Tanker' as it is clear that the cargo carrying BFS vehicle would not be an efficient tanker to LEO and something specialized for that purpose is necessary.
...

Musk said that (paraphrasing) "he's tempted to pursue stage 2 reuse on FH, but it's probably better to focus on Mars architecture".

Since a reusable upper stage on FH is a natural iterative development towards any potential reusable S2 on BFR, I think it's highly probable based on this statement that the Mars architecture won't include a S2 at all. If BFR did have a S2 on it, any focus on developing a smaller version would help (not detract from) focus on the larger one.

So I think the Falcon upper stage is an architectural dead end, and BFR/BFS will derive from the vehicles SpaceX is currently reusing: Falcon Stage 1, and Dragon. That wouldn't mean that specialized (e.g. Tanker) version wouldn't exist, just that they would share heritage with Dragon and not with the F9 S2.

Most of the specializations (lightweight legs, insulation, cryocoolers, extra PV arrays, bigger tanks) will fit just as well in a similar outer mold line to BFS, even though internal and structural components would differ. It would be more like the relation between FH center and side boosters than between F9 S2 and Dragon: looks very much the same, but a bit different inside.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/27/2016 10:04 pm
BFS will not be anything like Dragon except in the broadest terms. The delta-v will be nearly an order of magnitude different. About as similar as a jellyfish and a rat. "Derive" is not the right word.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/27/2016 11:58 pm
To be clear, I'm referring to Crew Dragon, most specifically Red Dragon. And I think there will certainly be more than superficial parallels: both will be interplanetary spacecraft capable of using hypersonic retropropulsion for high-precision EDL optimized for Mars and Earth - but potentially on a variety of Solar System bodies. If SpaceX thinks they have found good Earth and Mars EDL profiles after landing Crew and Red Dragon, they will probably try to keep similar EDL profiles for BFS to minimize risk from new variables.

Of course that doesn't mean the spacecraft will be at all internally similar or have at all similar performance in all respects. They will have different dry mass fractions, payload capabilities, prop mass fractions, very different structures, fuels, pressure vessels, engines, Isp, materials, manufacturing methods, etc. Delta v is just a function of Isp and PMF, and clearly those will be very different.

But that doesn't mean the EDL profiles cannot be similar. The outer mold lines and engine position/orientation can be roughly similar (yes, I know, cosine losses and vac bells, etc... but those are definitely not complete showstoppers). As long as the AOA vs. L/D curves, L/D ratios, COG and COP locations, drag coefficients, mass/area ratios, ballistic coefficients, etc. are similar, they can retire a lot of risk by flying Red/Crew Dragon as a subscale model and applying scale factors.

If you're looking for a animal analogue, try honeybee vs hummingbird: very different scales, structures and physiology, but the aerodynamics scale to allow similar flight profiles.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/28/2016 01:44 am
Outer mold line similarities are n8ot en8ough t8o c8onsider 8one vehic2le derived
A stage with all of the capabilities I've described for the 2nd stage is a necessity under any architecture, others have simply been calling it a 'BFS-Tanker' as it is clear that the cargo carrying BFS vehicle would not be an efficient tanker to LEO and something specialized for that purpose is necessary.
...

Musk said that (paraphrasing) "he's tempted to pursue stage 2 reuse on FH, but it's probably better to focus on Mars architecture".

Since a reusable upper stage on FH is a natural iterative development towards any potential reusable S2 on BFR, I think it's highly probable based on this statement that the Mars architecture won't include a S2 at all. If BFR did have a S2 on it, any focus on developing a smaller version would help (not detract from) focus on the larger one.

So I think the Falcon upper stage is an architectural dead end, and BFR/BFS will derive from the vehicles SpaceX is currently reusing: Falcon Stage 1, and Dragon. That wouldn't mean that specialized (e.g. Tanker) version wouldn't exist, just that they would share heritage with Dragon and not with the F9 S2.

Most of the specializations (lightweight legs, insulation, cryocoolers, extra PV arrays, bigger tanks) will fit just as well in a similar outer mold line to BFS, even though internal and structural components would differ. It would be more like the relation between FH center and side boosters than between F9 S2 and Dragon: looks very much the same, but a bit different inside.

Not a sound basis for speculation.  No reusable 2nd stage for F9 has always been stated to be an economic choice due to lack of margin and most customers wanting GTO launches. 

But we now know that a Raptor upper stage is being made, which IS exactly what would make sense as a for runner to a reusable BFS upper stage, the new F9 upper stage can do controlled re-entry burn tests  while still being disposed of, just as the F9 first stage was splashed into the ocean several times before even trying to put legs on it.  The new upper stage lets SpaceX do it's tests at customer expense, which is how they like to do all their testing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 07/28/2016 08:35 am
...
But we now know that a Raptor upper stage is being made, which IS exactly what would make sense as a for runner to a reusable BFS upper stage, the new F9 upper stage can do controlled re-entry burn tests  while still being disposed of, just as the F9 first stage was splashed into the ocean several times before even trying to put legs on it.  The new upper stage lets SpaceX do it's tests at customer expense, which is how they like to do all their testing.

Err, how exactly do we now know that a Raptor upper stage is being made?  I thought the only things we know are (1) The Air Force has thrown some money SpaceX's way to develop a Raptor vac engine, and (2) Musk has recently said that doing a new, reusable upper stage for Falcon is tempting, but SpaceX will be concentrating on developing the 'Mars rocket' instead.  This would imply to me that (sadly) there is no effort underway to do a new upper stage for Falcon, and likely won't be in the future.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 07/28/2016 12:03 pm
Err, how exactly do we now know that a Raptor upper stage is being made?  I thought the only things we know are (1) The Air Force has thrown some money SpaceX's way to develop a Raptor vac engine, and (2) Musk has recently said that doing a new, reusable upper stage for Falcon is tempting, but SpaceX will be concentrating on developing the 'Mars rocket' instead.  This would imply to me that (sadly) there is no effort underway to do a new upper stage for Falcon, and likely won't be in the future.

The Air Force said specifically that the engine is for F9.

Quote
This other transaction agreement requires shared cost investment with SpaceX for the development of a prototype of the Raptor engine for the upper stage of the Falcon 9 and Falcon Heavy launch vehicles.

http://www.defense.gov/News/Contracts/Contract-View/Article/642983
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/28/2016 01:35 pm
There is a whole thread for the Raptor on F9/FH discussion: http://forum.nasaspaceflight.com/index.php?topic=39314.msg1563987#msg1563987

It's important to distinguish a couple things here:
1) the AF is paying for ENGINE technology development; I doubt they care much what vehicle it flies on;
2) there is a difference between a "new" Raptor stage and a "new, reusable" Raptor stage. The minimum viable product for recovering a Raptor upper stage is appreciably more complex than the minimum viable product for launching it.
3) Raptor expendable on F9 might be commercially viable if it allows them to compete with Ariane on 5300+ kg to GTO with booster reuse.

Quote from: Impaler
Outer mold line similarities are n8ot en8ough t8o c8onsider 8one vehic2le derived
I listed several other similarities; whether "derived" is a good descriptor of their relation is semantic.

Quote from: Impaler
...the new F9 upper stage can do controlled re-entry burn tests while still being disposed of...
I don't think it can at all. It will break up from heat load on reentry unless heavily shielded - at which point it's basically a reusable upper stage, which Musk specifically said they aren't working on. The velocity change for a orbital reentry is about 4 to 5x greater, and the max heating rate 20 to 25x greater than what the F9 S1 sees on entry. Even if it's possible to orbit enough fuel retroburn through the peak heating phase (and I STRONGLY doubt that it is), why would they? The stage has a low ballistic coefficient, lots of area to dissipate heat, and slow terminal velocity: shield the front and part of one side, enter nose-first, and keep all the sensitive, expensive parts out of the hypersonic flow and well away from the bow shock. This is exactly how SpaceX envisioned S2 reuse... and they aren't pursuing it.

The same goes for BFR. I'm extremely doubtful that orbital reentry using primarily retropropulsion for shock standoff and cooling is possible and more optimal than nose-first entry for a S2 type vehicle. If there's any evidence to the contrary please point it out.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 07/28/2016 01:44 pm
Err, how exactly do we now know that a Raptor upper stage is being made?  I thought the only things we know are (1) The Air Force has thrown some money SpaceX's way to develop a Raptor vac engine, and (2) Musk has recently said that doing a new, reusable upper stage for Falcon is tempting, but SpaceX will be concentrating on developing the 'Mars rocket' instead.  This would imply to me that (sadly) there is no effort underway to do a new upper stage for Falcon, and likely won't be in the future.

The Air Force said specifically that the engine is for F9.

Quote
This other transaction agreement requires shared cost investment with SpaceX for the development of a prototype of the Raptor engine for the upper stage of the Falcon 9 and Falcon Heavy launch vehicles.

http://www.defense.gov/News/Contracts/Contract-View/Article/642983

Picky, but that statement does not say anything about actually making a Rapter equipped  U/S, just a Rapter proto ENGINE for a U/S. One could argue why do one without the other, but it may just be a proof of principle. Find out whether a Rapter VAC could be use on an F9 U/S
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/28/2016 01:53 pm
... Find out whether a Rapter VAC could be use on an F9 U/S

Almost certainly yes. Read the last few pages of the Raptor on F9/FH discussion: http://forum.nasaspaceflight.com/index.php?topic=39314
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 07/28/2016 03:44 pm
... Find out whether a Rapter VAC could be use on an F9 U/S

Almost certainly yes. Read the last few pages of the Raptor on F9/FH discussion: http://forum.nasaspaceflight.com/index.php?topic=39314

"Almost certainly" is "almost certainly" not good enough for the US DoD!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/28/2016 04:26 pm
It could be, but it's not going to. At least not before MCT flies.

I started at least one thread speculating about a Raptor-based reusable upper stage for Falcon 9/FH, given that hint from the Air Force (which is not new, we've known about that for a quite long while). But now we know from Musk that they're not going to pursue that right now.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/28/2016 04:41 pm
"Almost certainly" is "almost certainly" not good enough for the US DoD!

Again, the AF is paying for ENGINE technology development and demonstration; I doubt that what vehicle the engine will fly on (if any at all) is contractually obligated in any way.

If SpaceX prefers to fly Raptor on a 250t to LEO vehicle instead of a 25t to LEO vehicle, all the better for the AF.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 07/28/2016 07:27 pm
It could be, but it's not going to. At least not before MCT flies.

I started at least one thread speculating about a Raptor-based reusable upper stage for Falcon 9/FH, given that hint from the Air Force (which is not new, we've known about that for a quite long while). But now we know from Musk that they're not going to pursue that right now.

That leaves the questions of if and when wide open...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/28/2016 07:34 pm
It could be, but it's not going to. At least not before MCT flies.

I started at least one thread speculating about a Raptor-based reusable upper stage for Falcon 9/FH, given that hint from the Air Force (which is not new, we've known about that for a quite long while). But now we know from Musk that they're not going to pursue that right now.

That leaves the questions of if and when wide open...
Sure, the future is wide open. But a post-MCT world is going to be weird and difficult to analyze before we see MCT and how well it flies.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 07/29/2016 02:18 am

I don't think it can at all. It will break up from heat load on reentry unless heavily shielded - at which point it's basically a reusable upper stage, which Musk specifically said they aren't working on. The velocity change for a orbital reentry is about 4 to 5x greater, and the max heating rate 20 to 25x greater than what the F9 S1 sees on entry. Even if it's possible to orbit enough fuel retroburn through the peak heating phase (and I STRONGLY doubt that it is), why would they? The stage has a low ballistic coefficient, lots of area to dissipate heat, and slow terminal velocity: shield the front and part of one side, enter nose-first, and keep all the sensitive, expensive parts out of the hypersonic flow and well away from the bow shock. This is exactly how SpaceX envisioned S2 reuse... and they aren't pursuing it.

The same goes for BFR. I'm extremely doubtful that orbital reentry using primarily retropropulsion for shock standoff and cooling is possible and more optimal than nose-first entry for a S2 type vehicle. If there's any evidence to the contrary please point it out.

First SpaceX and Must throw out ideas without being slavishly committed too them, they generally stop talking about them once they find out they don't work.  They though 1st stages would land on parachutes so any notion that first choice methods are the ONLY options and if they fail the whole effort will fail is flat nonsense. 

Second even at the time of the release of that infamous video it was obvious that the 2nd stage recovery shown was Holly Wood nonsense and nothing more then a placeholder, nose first re-entry is impossible because it is totally unstable, the engine is most massive part of a 2nd stage and this will dictate an engine first entry.  Second it was clear that the nose of a second stage can't do the basic job of attaching a payload if it is a smooth heat shield.

The only feasible entry is engine first, which means either a shield that moves to cover the engine or a retro propulsive burn during entry can push the shock front away from the engine and keep it safe.  Entry can be short and at high G because it is an unmanned vehicle.

What I'm proposing is basically a Test bed, it gets valuable mid-air ignition experience on the Raptor (impossible to replicate on the ground) while delivering higher payloads and then gets some test data.  No actual modifications for re-use are required beyond developing a Raptor upper stage for F9, it's just plunges into the atmosphere to see how long it takes to disintegrate, the data is all that matters, none would ever be recovered.  Just as Grasshopper did not go to space but gathered valuable data.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/29/2016 03:29 am
There are two feasible reentry positions, not just one. Side and engines-first. Both have been tested to varying degrees by SpaceX, Shuttle, DC-X, Blue Origin, as well as simulated.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 07/29/2016 09:28 am
Isn't the mVac nozzle much too flimsy to withstand an engine first re-rentry? Or even a relatively low altitude/low speed (100's kmh) environment?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Crispy on 07/29/2016 09:30 am
Isn't the mVac nozzle much too flimsy to withstand an engine first re-rentry? Or even a relatively low altitude/low speed (100's kmh) environment?
Yes, it would be torn to shreds. You'd either have to stow it, or have most of it be disposable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 07/29/2016 12:47 pm
Isn't the mVac nozzle much too flimsy to withstand an engine first re-rentry? Or even a relatively low altitude/low speed (100's kmh) environment?
Yes, it would be torn to shreds. You'd either have to stow it, or have most of it be disposable.

So amy S2 powered recovery will require either an engine that can cope with its nozzle being discarded, or have alternative propulsion/navigation.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/29/2016 01:00 pm
Or retractable nozzle. Am I the only one who remembers the Falcon 9 reuse video?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 07/29/2016 03:10 pm
Or, re-enter horizontally like a biconic then either rotate or land on minimalist skids. Perhaps small flush folding winglets. Like an elongated version of the early Kliper or Blues SV.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 07/29/2016 06:10 pm
There are two feasible reentry positions, not just one. Side and engines-first. Both have been tested to varying degrees by SpaceX, Shuttle, DC-X, Blue Origin, as well as simulated.

Is there not a third? Reenter top first, and then do a swoop maneuver to land engine side down, propulsive, on legs? Or maybe a fourth, unlikly because of CG issues, Reenter top first and land upside down, propulsive, on legs?

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/29/2016 06:21 pm
There are two feasible reentry positions, not just one. Side and engines-first. Both have been tested to varying degrees by SpaceX, Shuttle, DC-X, Blue Origin, as well as simulated.

None of those vehicles reenter engines-first from orbital velocity. They are either side/nose first from orbit (Shuttle, DC-X) or engine-first from sub-orbital velocity (SpaceX, BO).

Retracting or discarding the radiatively cooled nozzle extension is an absolute must for engine-first retro-propulsive entry from orbit for both aerodynamic and cooling issues.

But the biggest issue is orbiting enough propellent to run an engine during reentry. To get from orbit to a safe heating speed in atmosphere (below Mach 5) requires losing 6500 m/s of velocity: even at 10 g average deacceleration that's 65 seconds of retro burn, during which a Merlin will consume up to 17.5t of propellent and a Raptor would consume some 3x that. Even with throttling that's a massive payload reduction.

Retropropulsion decreases drag, so getting as high as 10g of deceleration is not all that likely. And fast entries increase the heating rate along with the structural loads, since the total dissipated energy remains constant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/29/2016 07:11 pm
Retropropulsion often reduces drag, actually. But that's fine because the thrust of retropropulsion may be much greater than the thrust.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 07/29/2016 08:41 pm
If second stages are going to be reused and deliver worthwhile payloads, I think most of the braking will need to be done with friction and not propulsion.

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BobHk on 07/29/2016 08:56 pm
So can anyone make a 2nd stage with a clamshell fairing that opens, delivers payload to orbit, closes [and acts as a heatshield for reentry (if it even needs to)]...then the stage flips, the bell retracts its vulnerable bit and that single engine lands the stage on some legs attached to the side?

Added bits (what kind of uphill penalty will this incur?):
 Landing legs
 X-Wing gridfins
 Actuators for clamshell payload fairing
 Fuel for re-entry

SpaceX seems to have chewed this through and come up with? nothing yet.

Can you design a fairing that can act like a seed wing in atmosphere to bleed velocity and take pressure off the engine to slow the thing down?    You people are a lot smarter than me.  Why no epiphanies?



Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 07/30/2016 12:31 am
Sure, but SpaceX isn't going to take that approach. There are also several reasons that is suboptimal.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 07/30/2016 05:08 am
If second stages are going to be reused and deliver worthwhile payloads, I think most of the braking will need to be done with friction and not propulsion.

Matthew

How about like this?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 07/30/2016 08:45 am
...
Second even at the time of the release of that infamous video it was obvious that the 2nd stage recovery shown was Holly Wood nonsense and nothing more then a placeholder, nose first re-entry is impossible because it is totally unstable, the engine is most massive part of a 2nd stage and this will dictate an engine first entry.  Second it was clear that the nose of a second stage can't do the basic job of attaching a payload if it is a smooth heat shield.
...

Impaler, could/would nose first reentry be stable if there were grid fins near the engine?  I think they could be configured to provide significant drag at that end, right?  And stability would be helped if there were a (fairly heavy) TPS up at the nose of the 2nd stage.

And I think attaching a stage with a smooth heat shield to something else is a solved problem.  Else how does the Dragon capsule mate to the current 2nd stage?

Seems like a reusable Raptor 2nd stage could be done if it entered and landed nose first.  Add upside down landing legs near the top of the stage, TPS around the 'nose' (perhaps even a bit oversized diameter, to protect the body of the stage), some Super Dracos for landing assist, and grid fins near the engine.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/30/2016 02:45 pm
...
 it is totally unstable, the engine is most massive part of a 2nd stage and this will dictate an engine first entry.
...

False. On a Dragon to ISS mission the residual propellent outweighs the entire second stage, and it only takes 1% of the initial 100 tonne propellent load to outweigh a Merlin.

At atmospheric drag will settle the remaining propellent in the nose long before it's significant enough to overpower the RCA thrusters, resulting in a quasi-stable configuration that cold be controlled by either RCS or small active aerodynamic surfaces during re-entry.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 07/30/2016 03:08 pm
...it was clear that the nose of a second stage can't do the basic job of attaching a payload if it is a smooth heat shield.

The only feasible entry is engine first, which means either a shield that moves to cover the engine...

These two statements are entirely inconsistent. Either it's possible to have a moveable heatshield to cover either the engine or the payload adapter, or it's not possible to have either. More likely, both are possible but both are too complicated and heavy to be feasible.

Bot attachment through the headshield isn't necessary. Dragon already attaches around the perimeter of the heatshield. The second stage - interstage interface is also completely around the perimeter of the stage. Attaching the payload adapter and fairing in a similar manner would likely require the least development work and mass penalty, and allow a smooth continuous heatshield on the stage 2.

The payload adapter would have to be discarded before re-entry.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 07/31/2016 12:48 pm
Seems like a reusable Raptor 2nd stage could be done if it entered and landed nose first.  Add upside down landing legs near the top of the stage, TPS around the 'nose' (perhaps even a bit oversized diameter, to protect the body of the stage), some Super Dracos for landing assist, and grid fins near the engine.

I agree that a second stage could enter and land nose first. However, given the difficulty of accurately predicting the landing zone of a GEO second stage, the odds are that it would land in the ocean. Why not design for this eventuality? If the drag coefficient was made sufficiently high, perhaps using a HIAD, retro propulsion for EDL would not be necessary, hence eliminating the need for extra fuel. The TPS around the nose could also be an inflatable, simplifying staging, and reducing mass. Grid fins would also not be required.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 07/31/2016 03:53 pm
A reusable second stage would be actively guided it its landing zone, just like the first stage. No need to drop it in the ocean. It could land back at the launch site or on a barge.

BTW, this is the MCT speculation thread, so why are we having what seems to be a F9/FH discussion?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Elmar Moelzer on 07/31/2016 09:15 pm
I would assume that the DC-X or subsequently the Delta Clipper would have had the same problem with nose first entry. IIRC, the DC-X demonstrated it to work just fine.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 07/31/2016 09:30 pm
A reusable second stage would be actively guided it its landing zone, just like the first stage. No need to drop it in the ocean. It could land back at the launch site or on a barge.

BTW, this is the MCT speculation thread, so why are we having what seems to be a F9/FH discussion?

Agreed, it's in the wrong thread, I suspect it spun off the Raptor powered upper stage discussion. It should probably be moved.

Whilst the stage could be actively guided in the landing zone, for a GEO launch, the zone itself would be determined by the highly elliptical orbit after launching the satellite, and how quickly that orbit decayed. It can take years for that to happen, so there probably wouldn't be any fuel left for landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 08/01/2016 12:02 am
A reusable second stage would be actively guided it its landing zone, just like the first stage. No need to drop it in the ocean. It could land back at the launch site or on a barge.

BTW, this is the MCT speculation thread, so why are we having what seems to be a F9/FH discussion?

Agreed, it's in the wrong thread, I suspect it spun off the Raptor powered upper stage discussion. It should probably be moved.

Whilst the stage could be actively guided in the landing zone, for a GEO launch, the zone itself would be determined by the highly elliptical orbit after launching the satellite, and how quickly that orbit decayed. It can take years for that to happen, so there probably wouldn't be any fuel left for landing.

If it is designed as a reusable stage then it would have enough fuel to deorbit and land. It's a tall order to have that much fuel and a usable payload, so that's where a cargo version of the MCT system could come in handy.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/01/2016 06:14 am
...
 it is totally unstable, the engine is most massive part of a 2nd stage and this will dictate an engine first entry.
...

False. On a Dragon to ISS mission the residual propellent outweighs the entire second stage, and it only takes 1% of the initial 100 tonne propellent load to outweigh a Merlin.

At atmospheric drag will settle the remaining propellent in the nose long before it's significant enough to overpower the RCA thrusters, resulting in a quasi-stable configuration that cold be controlled by either RCS or small active aerodynamic surfaces during re-entry.

ISS missions have literal tons of unused margin, if your going to re-enter nose first with a heat shield then your not using propulsion until terminal landing so their is no reason for the vehicle to have tons of excess propellant unless you have intentionally kept it for ballast.

In an engine first re-entry your burning propellant during entry and losing mass and you have to remain stable all the way through that burn which means you need to be stable with your burnout quantity of propellant, not just the initial propellant.

Lastly the engine mass here is going to be a Raptor which is certainly going to have a higher mass then a Merlin, also propellant is at a minimum in two tanks so propellant center of mass can never be fully up at the nose.  Propellant tanks structures and engine intakes are designed for propellant at the bottom of the tank, if its gone to the nose the engine will not be able to start.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 08/04/2016 04:43 am
Here is my idea of BFR and MCT. The major idea is I am predicting that MCT will not have heat shield, except MCT Escape module for emergency situation.
MCT will shield engine compartment using low thrust to create buble and push heated air from engine compartment.
it will avoid to build 15 m heat shield, or complicated maneuver during landing using MCT Escape module heat shield and then turn around for braking and landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Crispy on 08/04/2016 09:37 am
Does the mass of the heat shield exceed the mass of the fuel required to create a sufficiently large "bubble" ?
Please show your working :D
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/04/2016 10:52 am
Does the mass of the heat shield exceed the mass of the fuel required to create a sufficiently large "bubble" ?
Please show your working :D

That idea comes from the concept of entering engines first. I am sure the mass of propellant would dwarf the weight of a heat shield, but a heatshield protecting the engines is tricky, especially if like on Mars you need to fire them supersonic.

To me it means you cannot enter engines first and have to find a solution to the stability and other problems, when entering nose first.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 08/04/2016 06:00 pm
Does the mass of the heat shield exceed the mass of the fuel required to create a sufficiently large "bubble" ?
Please show your working :D
Not but it will technologically and operation less complicated.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 08/04/2016 06:27 pm
MCT without heat shield for MCT Booster
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/04/2016 06:41 pm
Is this a SSTO?  How do you get enough Km/sec to reach LEO, etc?
How do humans get from the living area to/from escape pod with heat shield in between?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Elmar Moelzer on 08/04/2016 07:44 pm
Is this a SSTO?  How do you get enough Km/sec to reach LEO, etc?
How do humans get from the living area to/from escape pod with heat shield in between?
The MCT is currently assumed to be the second stage of a two stage LV. It will (probably) launch from mars as an SSTO, though.
They would get through the heat shield with a door.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 08/04/2016 07:50 pm
If second stages are going to be reused and deliver worthwhile payloads, I think most of the braking will need to be done with friction and not propulsion.

Matthew

How about like this?

It has to turn around for landing, I think retro propulsive braking test give them numbers that propulsion is good enough to build shield.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 08/04/2016 08:52 pm
Is this a SSTO?  How do you get enough Km/sec to reach LEO, etc?
How do humans get from the living area to/from escape pod with heat shield in between?
Just showing MCT. BFR is not part of this picture, but BFR still need it. By the way BFR will be use together with MCT just 0.0000019% MCT Mars flight.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/04/2016 10:18 pm
If second stages are going to be reused and deliver worthwhile payloads, I think most of the braking will need to be done with friction and not propulsion.

Matthew

How about like this?

It has to turn around for landing, I think retro propulsive braking test give them numbers that propulsion is good enough to build shield.

The S2 doesn't have to turn around for landing. It could land on the inflatable, which would incidentally absorb some shock loading, as would the ocean.

SRP is only intended for the range from Ma5 to Ma1.5. The mass of fuel required to burn retro-propulsively for the entire EDL sequence would be vastly greater than the mass of a heatshield, and would severely limit the landed payload, if not eliminate it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/05/2016 09:39 am
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/05/2016 12:05 pm
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

Sorry, I should have been clearer. I suspect there are (at least) two scenarios being discussed concurrently on the thread. One is the Earth EDL of a Raptor engined Falcon S2, possibly from a highly elliptical orbit after delivering a geosynchronous satellite, and the other is raketa's proposal for a BFS performing Mars EDL without a heatshield.

For the S2 I was suggesting a HIAD could remove the EDL fuel requirement entirely. For the BFS, which could be manned, I was suggesting that to achieve the ΔV for Mars EDL purely propulsively would require too much fuel for it to have any useful payload.

I hope this helps.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Danny Dot on 08/05/2016 01:42 pm
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

The crew can tolerate a 20G entry.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 08/05/2016 03:26 pm
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

The crew can tolerate a 20G entry.

Yeah, maybe, but they ain't gonna like it!

     Seriously though, the G tolerance will vary from person to person.  Assuming the average group of people, up to half of these people will likely be knocked unconscious, Some may have breathing issues, and a few may have heart issues due to the G load.  This is not even taking into account three to nine months of deconditioning from microgravity.

     Even with current exercise, drugs and therapy, there will be health issues that have to be compensated for during the descent.  25Gs may be the normal max that people can take, with minimal deconditioning, but I don't think we've ever had anybody come back to Earth after more than three months of microgravity at a 20G reentry.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/05/2016 04:29 pm
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

It still has to be shielded; it will be exposed to at least 60 seconds of plasma blast hotter than Raptor exhaust temps. It's going to be WAY hotter than a Falcon 9 S1 entry, which is already pretty toasty.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/05/2016 05:52 pm
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

The crew can tolerate a 20G entry.
No, frankly.  They can't.  Check your sources.  We're talking about sustained G-loading that lasts tens of seconds at near-peak intensity, presumably with considerable additional vibration from the turbulence.  Per Wikipedia, "Only the most motivated volunteers were capable" of reaching this 20G level in testing for 10s duration with a steady centrifuge, and more than that is suggested to result in injury and/or LOC.

Call it 10G peak eyeballs-in and assume some of the crew will black out or come down with concussions.  For existing spacecraft like Soyuz, 8.2G is an emergency condition encountered only during a ballistic reentry, after something goes wrong with separation, and the Shuttle gets more like 3G.

Eyeballs-in may not always be perfectly achievable either.  A reusable lander has to decelerate at a variety of orientations, and it may not be weight-feasible to have a pivoting chair.  20G's applied for a very short time at a slight angle to eyeballs-in will cause a red-out or a black-out by pushing enough G's at a person in the wrong direction, where they have low tolerance.

I'm not even trying to take into account deconditioning;  A known unknown.  But there's too many reasons to be conservative with G-loading already.  If your mission needs 20G reentry, redesign your mission.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 08/05/2016 06:00 pm
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

The crew can tolerate a 20G entry.
No, frankly.  They can't.  Check your sources.  We're talking about sustained G-loading that lasts tens of seconds at near-peak intensity, presumably with considerable additional vibration from the turbulence.  Per Wikipedia, "Only the most motivated volunteers were capable" of reaching this 20G level in testing for 10s duration with a steady centrifuge, and more than that is suggested to result in injury and/or LOC.

Call it 10G peak eyeballs-in and assume some of the crew will black out or come down with concussions.  For existing spacecraft like Soyuz, 8.2G is an emergency condition encountered only during a ballistic reentry, after something goes wrong with separation, and the Shuttle gets more like 3G.

Eyeballs-in may not always be perfectly achievable either.  A reusable lander has to decelerate at a variety of orientations, and it may not be weight-feasible to have a pivoting chair.  20G's applied for a very short time at a slight angle to eyeballs-in will cause a red-out or a black-out by pushing enough G's at a person in the wrong direction, where they have low tolerance.

I'm not even trying to take into account deconditioning;  A known unknown.  But there's too many reasons to be conservative with G-loading already.  If your mission needs 20G reentry, redesign your mission.

Thanks for the update!  I'd forgotten that the 20g load limit was for short durations myself!

     Overall, I think what I said still holds up pretty well.  With the possible exceptions and additions of broken bones during sustained 20g reentries...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/05/2016 06:07 pm
10G is marginal but probably safely achievable assuming you screen/test passengers on the ground before missions.  If there's lots of vibration or not a lot of weight to spend on anti-G accommodations or deconditioning is a major stressor, even that's chancy.

In cases where we're reentering from high orbit (definitely Mars fast transits, maybe also Mars slow transits and GTO) without advanced techniques like MAC, it may be advantageous (the additional radiation and uncertainty may be outweighed by the advantages in spacecraft design tradespace) to do a two-stage entry, with an aerocapture to an intermediate elliptical orbit near LEO (or a suborbit with one end below LEO), then a control burn to target the landing zone, then a final entry the rest of the way.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oiorionsbelt on 08/05/2016 07:05 pm

Eyeballs-in may not always be perfectly achievable either.  A reusable lander has to decelerate at a variety of orientations, and it may not be weight-feasible to have a pivoting chair.  20G's applied for a very short time at a slight angle to eyeballs-in will cause a red-out or a black-out by pushing enough G's at a person in the wrong direction, where they have low tolerance.

The forums HMXHMX may not agree with you.
 Here's t/Space's CVX pivoting seat, weighing less than 20% of the shuttle seat.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 08/05/2016 07:47 pm
10G is marginal but probably safely achievable assuming you screen/test passengers on the ground before missions.  If there's lots of vibration or not a lot of weight to spend on anti-G accommodations or deconditioning is a major stressor, even that's chancy.

In cases where we're reentering from high orbit (definitely Mars fast transits, maybe also Mars slow transits and GTO) without advanced techniques like MAC, it may be advantageous (the additional radiation and uncertainty may be outweighed by the advantages in spacecraft design tradespace) to do a two-stage entry, with an aerocapture to an intermediate elliptical orbit near LEO (or a suborbit with one end below LEO), then a control burn to target the landing zone, then a final entry the rest of the way.

I considered the possibility of a craft design that in some ways, is similar to a tractor trailer system.

A separate cargo module attached to the main MCT craft that would have a heavy, "single use" TPS shield for the aerocapture, which is afterwards detached and either automatically landed at the primary landing site, or remote piloted down.  (Single use would actually be twice use in this case. Once for Aerocapture then again for final descent)  The main craft would then descend and land nearby the cargo module.

     The advantage here is that a cargo module could take higher G loads and more punishment than the fragile human cargo.

     The alternative idea I had was to Aerocapture, then reenter with both craft and cargo module through the "7 minutes of hell" then detach the two, cargo module coming down via parachute with a Russian style retrorocket cushioning in the final few meters, and the main craft descending via retropropulsion.  This latter idea keeps both craft and cargo near to each other, while protecting the main craft's TPS for the reentry at Earth.

     I doubt something quite like this has ever been tried, but it doesn't really seem too far fetched.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 08/05/2016 07:59 pm
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

It still has to be shielded; it will be exposed to at least 60 seconds of plasma blast hotter than Raptor exhaust temps. It's going to be WAY hotter than a Falcon 9 S1 entry, which is already pretty toasty.
My understanding is, that proper rocket thrust could cause that heated and compressed air is  moved from engine compartment in front of the vehicle and plasma slide around vehicle, this what I try describe on picture.
I think, this is what Spacex found out during his retropropulsion events.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/05/2016 08:24 pm
I assume you are talking about Mars EDL here. There are a lot of discussions going on here and it's getting confusing, so stating something like: "for Mars EDL" or "Earth EDL from interplanetary trajectories" would help.

A separate cargo module attached to the main MCT craft that would have a heavy, "single use" TPS shield for the aerocapture, which is afterwards detached and either automatically landed at the primary landing site, or remote piloted down...
The main craft would then descend and land nearby the cargo module. The advantage here is that a cargo module could take higher G loads and more punishment than the fragile human cargo.

This requires duplicating all the avionics, power, thermal control, retro-propulsion engines and tanks, landing legs, TPS, etc from the main module to the cargo module, essentially making it a complete spacecraft. ALL of those elements would be single use, which contradicts SpaceX philosophy.

Quote
The alternative idea I had was to Aerocapture, then reenter with both craft and cargo module through the "7 minutes of hell" then detach the two, cargo module coming down via parachute with a Russian style retrorocket cushioning in the final few meters, and the main craft descending via retropropulsion.  This latter idea keeps both craft and cargo near to each other, while protecting the main craft's TPS for the reentry at Earth.

Terminal velocity for a 15 meter, 100 tonne object on Mars is around 1 km/s, much too fast for "parachutes and retrorockets". Also, they won't land near each other if one pops chutes and the other uses retropropulsion, those are very different trajectories.

Retropropulsion is required on Mars for large, dense objects that want to achieve precision landing locations. Like a heavy cargo shipment that's going somewhere specific.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/05/2016 08:25 pm
Taking a look at the Libelle G-Multiplus suit, which uses a liquid-immersion-mimicking system.  Seems to be a drastic upgrade over the pneumatic G-suits they've used in air forces, shifting manual dexterity, communication, and lastly consciousness up 3 or 4 G's.  Short-duration testing capped out at 12G fully conscious, with talking at 9G and (as a stunt) eating candy at 6G, using a trained pilot in their self-contained suit.  Their marketing graphs portray a doubling of usable acceleration in fighter aircraft, from ~7G to ~14G.

I guess high-G suits/couches are something we can work on Earthside without a ton of money.  I'm just mystified that we haven't already, given the importance of fighter aircraft.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/05/2016 09:02 pm
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

It still has to be shielded; it will be exposed to at least 60 seconds of plasma blast hotter than Raptor exhaust temps. It's going to be WAY hotter than a Falcon 9 S1 entry, which is already pretty toasty.
My understanding is, that proper rocket thrust could cause that heated and compressed air is  moved from engine compartment in front of the vehicle and plasma slide around vehicle, this what I try describe on picture.
I think, this is what Spacex found out during his retropropulsion events.
Yes, but... it's still really hot and still heats up the vehicle through radiative transfer. Compression heating goes up with the velocity^3, so orbital entry at Mach 25 has the heating rate is 30 times more than a hot F9 S1 at Mach 8. It also takes a lot longer to slow down to Mach 3 from Mach 25 than it does from Mach 8, so the vehicle is soaking heat for at least 60 seconds (and can be 10x that) instead of around 20 seconds for an F9 S1.

Plus, it doesn't save any orbited mass with hypersonic retropropulsion. A single Raptor can easily burn 60 tonnes of fuel during a 10 G orbital entry, so the expended fuel to keep the engines running, plus the TPS needed to keep the engines from torching the vehicle, almost always add up to a lot more mass than a modern heatshield.

Bottom line: SpaceX has proposed and actually flown a number of methods for suborbital and orbital entry, but orbital retropropulsion isn't one of them based on any evidence I've ever seen.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/06/2016 01:23 am
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

It still has to be shielded; it will be exposed to at least 60 seconds of plasma blast hotter than Raptor exhaust temps. It's going to be WAY hotter than a Falcon 9 S1 entry, which is already pretty toasty.

The exhaust IS the shield, run the engine fuel rich or inject some kerosene into the nozzle and you would get a sooty exhaust.  The dark soot absorbs the intense radiation coming off of the shock front and keeps it from actually reaching the ship, ablative carbon rich heat shields already exploit this principle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/06/2016 01:44 am
Interesting idea. Is there any evidence that they run the F9 S1 fuel rich during entry?

Are you proposing that this would work for manned interplanetary entries as well? How much fuel would have to be burned for a 13 km/s entry, and what decelerations are reasonable for manned entries? How many engines are what throttle settings?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Vultur on 08/06/2016 01:53 am
I'd imagine MCT would land automatically rather than human-piloted, so blackouts from G-forces may not be relevant. You'd need to keep below the level where any lasting harm is done, of course, but brief unconsciousness itself might not matter.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 08/06/2016 03:57 am
I'd imagine MCT would land automatically rather than human-piloted, so blackouts from G-forces may not be relevant. You'd need to keep below the level where any lasting harm is done, of course, but brief unconsciousness itself might not matter.

      OK, while computers and software have advanced a lot since Apollo 11, I'm still not quite sure I'd want to put my complete faith and my life in the trust of a machine that could easily glitch out because of a stray cosmic ray.

      Murphy's in the details, and I'd just as soon avoid giving him the chance of really messing up the day we land people on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/06/2016 05:10 am

      OK, while computers and software have advanced a lot since Apollo 11, I'm still not quite sure I'd want to put my complete faith and my life in the trust of a machine that could easily glitch out because of a stray cosmic ray.

I think I would not want to sit in a vertically landing spacecraft when there is the possibility of a pilot messing up.

Yes I am aware of Apollo 11. But BFR is not going to be like the moon lander.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/06/2016 05:24 am
Interesting idea. Is there any evidence that they run the F9 S1 fuel rich during entry?

Are you proposing that this would work for manned interplanetary entries as well? How much fuel would have to be burned for a 13 km/s entry, and what decelerations are reasonable for manned entries? How many engines are what throttle settings?

I'm not proposing it for manned or interplanetary entries, just for re-entry of a conventional 2nd stage from LEO, possibly from a GTO trajectory as well.  The intent is not to be maximally efficient in propellant but to be operationally simple and be a maneuver that can be attempted on a 2nd stage with the minimum possible modifications.

I see a BFR as a 2 stage vehicle like F9, the 2nd stage carrying ~1200 mt of propellant and having 6 Raptor Vac engines and one central sea-level engine, fire 3 of the Raptors at low thrust outward and the center engine too.  At 10 G's your looking at around 1 minute for peak entry heating.

Current F9 first stages will fire 3 engines for boost-back for 50 seconds, then 3 engines again for 20 seconds during entry, then the single central engine for 30 seconds at landing, a total equivalent to 27 seconds worth of full thrust.  The whole initially launch up to MECO is 141 seconds, so all these re-entry maneuvers are using ~1/6th of the total propellant available at launch.  So something of comparable propellant cost should be a viable.

Note that the scenario I foresee is for the 2nd stage to do one orbit of the Earth and then re-enter, that means the boost back burn is eliminated and all propellant is available to entry followed by the very small  landing burn.  If the stage experiences twice the deceleration rate of the F9 from LEO orbital velocity and reaches the same speed at the end of the burn (250 m/s) then it should take 70 seconds, assuming half power that's equal to 35 seconds of full thrust which compares very well to the current burn time of 372 seconds on the current 2nd stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/06/2016 02:27 pm
Propellent cost in orbit is significantly different than propellent cost at stage 1 separation; and propellent cost to GTO or escape is even more. Even the largest estimates for BFR only have a GTO payload in the 50t range, and on a second stage the entry propellent trades for payload at a 1:1 ratio.

4 Raptors will burn through over 1000 kg/s of propellent, even when throttled to 40%. A 10G orbital entry needs about 60 seconds to lose 6000 m/s and thus needs about 60 tonnes of fuel for that maneuver; an entry from GTO needs to lose almost 9000 m/s over 90 second, and needs nearly 90 tonnes of fuel; and entry from 12+ km/s interplanetary velocities needs over 120t of fuel for a burn of more than 120 seconds.

When an ablative heatshield for return from GTO or interplanetary velocities is only about 15% of dry mass, why would it possibly make sense to carry more than 100% of the vehicle's dry mass (and more than its payload capacity to GTO) in fuel for the same purpose?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: the_other_Doug on 08/06/2016 07:05 pm
Also recall what Elon tweeted a short while back (I'm pretty sure it was an Elon tweet), that when the BFS arrives at Mars it will need to shed about 13 km/sec of speed, and propulsion will only be able to take out 1 km/sec of that.  The remainder will need to be taken out via aerodynamic braking.

It won't be possible for BFS to do the entire entry propulsively, is my take-away on that...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/06/2016 07:34 pm
and propulsion will only be able to take out 1 km/sec of that. 

I have been wondering what that exactly means. Is that 1km/s the landing burn or do they need to brake 1km/s before they can enter the atmosphere and the landing burn will be separate? I had anticipated at the time he means the latter but may be completely wrong.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/06/2016 09:35 pm
and propulsion will only be able to take out 1 km/sec of that. 

I have been wondering what that exactly means. Is that 1km/s the landing burn or do they need to brake 1km/s before they can enter the atmosphere and the landing burn will be separate? I had anticipated at the time he means the latter but may be completely wrong.

13 km/s is consistent with Earth entry after a 6-month Earth return or a Mars entry after a 3 month transit. 1 km/s is about the terminal velocity of a 15m 100t object in Mars atmosphere. I don't see any reason to spend fuel slowing down before hitting the atmosphere, so I absolutely agree with the interpretation that the 1 km/s has to be the landing burn.

Perhaps a better way to phrase it would be "the atmosphere can brake all but 1 km/s of that".
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/07/2016 12:34 am
Propellent cost in orbit is significantly different than propellent cost at stage 1 separation; and propellent cost to GTO or escape is even more. Even the largest estimates for BFR only have a GTO payload in the 50t range, and on a second stage the entry propellent trades for payload at a 1:1 ratio.

4 Raptors will burn through over 1000 kg/s of propellent, even when throttled to 40%. A 10G orbital entry needs about 60 seconds to lose 6000 m/s and thus needs about 60 tonnes of fuel for that maneuver; an entry from GTO needs to lose almost 9000 m/s over 90 second, and needs nearly 90 tonnes of fuel; and entry from 12+ km/s interplanetary velocities needs over 120t of fuel for a burn of more than 120 seconds.

When an ablative heatshield for return from GTO or interplanetary velocities is only about 15% of dry mass, why would it possibly make sense to carry more than 100% of the vehicle's dry mass (and more than its payload capacity to GTO) in fuel for the same purpose?

Same reason the F9 first stage uses propulsion rather then heat-shields to re-enter, orientation demands base first entry and it is simpler to both engineer and operate which means minimal cost.

Also how do you calculate mass flow rate for Raptor?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/07/2016 02:36 am
When an ablative heatshield for return from GTO or interplanetary velocities is only about 15% of dry mass, why would it possibly make sense to carry more than 100% of the vehicle's dry mass (and more than its payload capacity to GTO) in fuel for the same purpose?

Same reason the F9 first stage uses propulsion rather then heat-shields to re-enter, orientation demands base first entry and it is simpler to both engineer and operate which means minimal cost.

Are you sure you are comparing apples here?

The fastest F9S1 sub-orbital entry is about 2.2km/s. A super-synchronous GTO transfer orbit could re-enter as fast as 10.3km/s. Assuming the same altitude, the difference in heating would be 10.3/2.2^3 = 102.6, or two orders of magnitude higher.

If JCSAT-14 took "max damage" at 2.2km/s, then what sort of damage would F9S2 take at 10.3 km/s? Would it not require major (total?) redesign to mitigate that damage?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/07/2016 03:47 am
Also how do you calculate mass flow rate for Raptor?

Conservation of momentum. Mass flow (kg/s) is thrust (kg-m/s2) divided by exhaust velocity (m/s). SpaceX has indicated that the thrust is about 2.5x106 N and the exhaust velocity is some 3700 m/s, yielding a massflow of 675 kg/s per engine. At 40% throttle that's 270 kg/s per engine, so 4 engines would burn over 1000 kg/s.

Mass flow is also proportional to thrust and inversely proportional to ISP; since we know Raptor will have thrust around 300% of Merlin, and ISP around 120% of Merlin, and Merlin has a mass flow of 270 kg/s, then Raptor should have a 40% throttled mass flow of around 270*300%/120%*40%=270 kg/s.

Both calculation methods indicate that 40% throttled mass flow for Raptor should be very similar to 100% mass flow for Merlin. Running 4 of those for 60 to 120 seconds is a LOT of fuel to put in orbit, ESPECIALLY to GTO or escape trajectories. Maybe they don't need to run 4, and maybe they can throttle lower, but please show your math for how big the rocket needs to be just to launch EDL fuel before stating it's simpler to engineer and launch than a heatshield.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/07/2016 08:51 am
Your asking me to prove it is more EFFICIENT, that is completely different from saying it is SIMPLER.  I have NEVER claimed it is more efficient, but you keep confusing the thouse concepts.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/07/2016 10:56 am
Your asking me to prove it is more EFFICIENT, that is completely different from saying it is SIMPLER.  I have NEVER claimed it is more efficient, but you keep confusing the thouse concepts.

It is not an either/or question.  The optimal design will balance simple and efficient.  A heat shield has many benefits, and will be employed to maximize those obvious benefits (without adding complexity and risk to the design such as an inflatable HAID) and retro-propulsion will do the rest*. 

Generous up-mass is one of the features of the architecture being proposed -- another is refueling on orbit.
This design will not throw away what has been learned about atmospheric deceleration with heat shields, but will add to that a total destruction of the mass-constrained designs of the past.

This reminds me of the argument between the small rocket plus depot versus big rocket without refueling.  If you are going to have a significant Mars campaign, you need both... big rocket plus depots/refueling.  SpaceX is proposing the largest rocket by a factor of two and refueling it (the spaceship) as soon as it is in orbit.

* Note: F9 uses exactly this approach... it decelerates with a re-entry burn to the velocity that the engine end of the booster can handle, and then allows the atmosphere to decelerate to terminal velocity, and finally does a propulsive landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/07/2016 11:28 am
Another simple versus efficient issue is the use of gravitational assist...  This 'free lunch' won't be ignored.  Departure will likely use it -- Oberth burns, starting from high orbit, which are efficient, instead of direct departure burns from LEO which are simpler.  Gravitational capture (assisted by retro-propulsion) may also be employed at the Mars end instead of direct entry.  Passive/'free' benefits such as this -- which are accepted spaceflight methods  (e.g., launching to the east) -- will be in the parameter space for the Mars architecture.

We'll have to wait until September 27th to see which are chosen.  My money will be on d. All of the above.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/07/2016 12:11 pm
A heat shield has many benefits, and will be employed to maximize those obvious benefits (without adding complexity and risk to the design such as an inflatable HAID) and retro-propulsion will do the rest*. 

A HIAD is just a more efficient heatshield. It is a simple concept and it has been shown to work. This NASA video shows the application of a HIAD for the safe return of a cargo spaceship from the ISS. It is not a great leap to imagine the same technology being used for the return of an F9S2.

https://www.nasa.gov/directorates/spacetech/game_changing_development/HIAD/HEART-Desig-Concept.html
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/07/2016 12:24 pm
A heat shield has many benefits, and will be employed to maximize those obvious benefits (without adding complexity and risk to the design such as an inflatable HAID) and retro-propulsion will do the rest*. 

A HIAD is just a more efficient heatshield. It is a simple concept and it has been shown to work. This NASA video shows the application of a HIAD for the safe return of a cargo spaceship from the ISS. It is not a great leap to imagine the same technology being used for the return of an F9S2.

https://www.nasa.gov/directorates/spacetech/game_changing_development/HIAD/HEART-Desig-Concept.html

Adding a HAID to the flamey end of a F9 is not simple.  It has to deploy from the engine compartment/octaweb over hot engines between burns and then get out of the way for the landing burn. 

Efficient, maybe. Simple, NOT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/07/2016 12:29 pm
Adding a HAID to the flamey end of a F9 is not simple.  It has to deploy from the engine compartment/octaweb over hot engines between burns and then get out of the way for the landing burn. 

Efficient, maybe. Simple, NOT.

Who said to add it to the flamey end?

https://forum.nasaspaceflight.com/index.php?topic=37808.msg1565000#msg1565000

Just pack it in the interstage with some nitrogen bottles.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/07/2016 12:53 pm
Adding a HAID to the flamey end of a F9 is not simple.  It has to deploy from the engine compartment/octaweb over hot engines between burns and then get out of the way for the landing burn. 

Efficient, maybe. Simple, NOT.

Who said to add it to the flamey end?

https://forum.nasaspaceflight.com/index.php?topic=37808.msg1565000#msg1565000

Just pack it in the interstage with some nitrogen bottles.

Oops. Sorry, did not see your application to F9S2.


A HIAD is just a more efficient heatshield. It is a simple concept and it has been shown to work. This NASA video shows the application of a HIAD for the safe return of a cargo spaceship from the ISS. It is not a great leap to imagine the same technology being used for the return of an F9S2.

https://www.nasa.gov/directorates/spacetech/game_changing_development/HIAD/HEART-Desig-Concept.html

How many of the cargo return proposals/designs are using HIADs?  Why is that?
How much cargo is NASA itself returning from the ISS?  Why is that?
NASA PowerPoint/video does not an operating system make.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/07/2016 01:09 pm
How many of the cargo return proposals/designs are using HIADs?
NASA PowerPoint/video does not an operating system make.

HIAD is way beyond PowerPoint presentations. Google is of course your friend, but there have been successful tests of the technology, and it's potential applications also extend to super heavy Mars landers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/07/2016 01:13 pm
How many of the cargo return proposals/designs are using HIADs?
NASA PowerPoint/video does not an operating system make.

HIAD is way beyond PowerPoint presentations. Google is of course your friend, but there have been successful tests of the technology, and it's potential applications also extend to super heavy Mars landers.

How many super heavy Mars landers have used HIADs?  Why is that?

Google "If a hammer is the only tool"
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/07/2016 01:27 pm
How many of the cargo return proposals/designs are using HIADs?
NASA PowerPoint/video does not an operating system make.

HIAD is way beyond PowerPoint presentations. Google is of course your friend, but there have been successful tests of the technology, and it's potential applications also extend to super heavy Mars landers.

How many super heavy Mars landers have used HIADs?  Why is that?

Google "If a hammer is the only tool"

Err, either because it's a potential application, or because there haven't been any super heavy Mars landings yet, take your pick.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/07/2016 03:03 pm
NASA has been flying to Mars for over 50 years, and landing there for 40+.
The heaviest payload so far has been under 1t.  None used HIADs.  Mars 2020 and ExoMars won't either.

One of the next landings there (most likely) will be a spacecraft that was designed (and is being built) for human transportation to/from LEO by a company that has been flying to space for under 10 years.  It will be their first trip to Mars.  Landed mass will be about 10t, and use a fixed heat shield and supersonic retro-propulsion.  Several more such spacecraft (or their derivatives) will follow in early 2020s.

Another round of Lunar landings is in the making... no HIADs there for certain.  Landing on Europa... no HIAD.

Every spacecraft that has returned 10t or more from space to date has used heat shields and/or supersonic retro-propulsion.  Retro-propulsion alone has returned five 20+ tonne vehicles with another 70 or so planned for the immediate future.  Plans will soon be released for returning 100t vehicles from space near Earth using supersonic retro-propulsion only and delivering >>100t to Mars' surface using heat shields and supersonic retro-propulsion.

I'm not seeing a lot of real applications in the next decade or two for HIADs.  I suspect they will go the way of supersonic parachutes for applications that require tens of tonnes of landed mass.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/07/2016 05:24 pm
2020 and exomars aren't going to be significantly larger than MSL.

This is a dumb way to argue. Please bring better game.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/07/2016 05:50 pm
2020 and exomars aren't going to be significantly larger than MSL.

This is a dumb way to argue. Please bring better game.

Fine. 
What evidence is there that MCT will use a HIAD?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/07/2016 05:56 pm
2020 and exomars aren't going to be significantly larger than MSL.

This is a dumb way to argue. Please bring better game.

Fine. 
What evidence is there that MCT will use a HIAD?
There's some indirect evidence that it may be one of several options they'll consider.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/07/2016 07:11 pm
2020 and exomars aren't going to be significantly larger than MSL.

This is a dumb way to argue. Please bring better game.

Fine. 
What evidence is there that MCT will use a HIAD?
There's some indirect evidence that it may be one of several options they'll consider.

I don't disagree that it will be or already was considered; there are many possibilities that will be discarded as not optimum or unworkable.
Certainly no evidence that it will be used on Red Dragon, which would be the obvious opportunity to test it...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: lamontagne on 08/07/2016 07:17 pm
I thought supersonic retropropulsion was particularly useful for Mars, as there was a 'hole' in the flight path between aerodynamic braking and retropropulsive landing since the atmosphere is not thick enough.
Perhaps this in not required for the Earth, with its thicker atmosphere?  Aerodynamic braking might be enough, with retropropulsion reserved for the landing?



Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/07/2016 07:31 pm
Your asking me to prove it is more EFFICIENT, that is completely different from saying it is SIMPLER.  I have NEVER claimed it is more efficient, but you keep confusing the thouse concepts.

I'm merely asking for evidence that's it's physically possible, not proof that it's optimal. It does appear possible for a stage that only enters from LEO or suborbital trajectories.

GTO and BLEO orbits would require a 3rd stage with a lot of Delta V, but I suppose that's not an issue is you assume BFS is a third stage and SEP tugs will fill some of those roles eventually.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/07/2016 07:49 pm
Your asking me to prove it is more EFFICIENT, that is completely different from saying it is SIMPLER.  I have NEVER claimed it is more efficient, but you keep confusing the thouse concepts.

I'm merely asking for evidence that's it's physically possible, not proof that it's optimal. It does appear possible for a stage that only enters from LEO or suborbital trajectories.

GTO and BLEO orbits would require a 3rd stage with a lot of Delta V, but I suppose that's not an issue is you assume BFS is a third stage and SEP tugs will fill some of those roles eventually.

Or refueling of a second stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/07/2016 08:07 pm
Refueling is fine for BLEO, particularly human launches, but seems like a lot of work for a GTO commsat launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/07/2016 08:26 pm
2020 and exomars aren't going to be significantly larger than MSL.

This is a dumb way to argue. Please bring better game.

Fine. 
What evidence is there that MCT will use a HIAD?
There's some indirect evidence that it may be one of several options they'll consider.

I don't disagree that it will be or already was considered; there are many possibilities that will be discarded as not optimum or unworkable.
Certainly no evidence that it will be used on Red Dragon, which would be the obvious opportunity to test it...
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT. None will be used on Red Dragon, which is not at all a reason to think it won't be used on MCT.

I don't have any particular belief that SpaceX will use something like HIAD. I don't envision they will. But you dismiss the possibility far too easily.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/07/2016 10:40 pm
The HIAD appears to be an unambiguous advancement on the static heatshield for landing arbitrary low-complexity payloads.  Funding for its development is sparse.  A few tens of millions thrown its way would establish some of the engineering as mature.

The problem is the same chicken-and-egg stuff as other human spaceflight engineering: We do not have a solid economic rationale to develop it yet.  Downmass requirements from the Space Station are tiny, and fully satisfied by most attempts at a reusable spacecraft.  New technology that shaves a few percent off of necessary upmass is not worth developing if it's only going to be used half a dozen times (and this is how far the planning forecast engages) and it is not guaranteed to work every time.  Absent economic rationale, it's a matter of the whimsy of whoever's funding advanced projects.

IRVE-3 -> IRVE-4 -> HEART -> routine use on Cygnus capsules... assuming funding and interest sustains, the papers suggest we could have completed this progression by now.  The roadmaps for this stuff portray it as not-very-far-out, but there are always "And then wait for more funding" points in the actual process.

I think there's a reasonable chance no such device will be used for MCT, for the sole reason that reusable controlled reliable powered landing is neither fully compatible nor fully benefitted by HIAD;  from landing control precision to plume impingement to a question of orientation, a full working rocketship capable of taking off again is the last thing you would put behind such a drag device (still a possible net benefit, but less of one than any other return payload).  A gliding orientation with heatshields can fill a similar niche, particularly if there is a large degree of change in hypersonic aerodynamics using weight-shift or control-surfaces, between the capture/reentry and low-hypersonic regimes.  On top of that, as far as we can tell SpaceX has advanced the thermal capability of lightweight rigid heatshield design *considerably* during their tenure, though the specific progress is a trade secret.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Torbjorn Larsson, OM on 08/07/2016 10:59 pm
I think there's a reasonable chance no such device will be used for MCT, for the sole reason that reusable controlled reliable powered landing is neither fully compatible nor fully benefitted by HIAD;

I thought HIAD was a technology for relatively small scale EDL (NASA@Mars)? Here we are talking about ships that are as large as projected HIAD brake area, so why waste mass?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/07/2016 11:08 pm
I think there's a reasonable chance no such device will be used for MCT, for the sole reason that reusable controlled reliable powered landing is neither fully compatible nor fully benefitted by HIAD;

I thought HIAD was a technology for relatively small scale EDL (NASA@Mars)? Here we are talking about ships that are as large as projected HIAD brake area, so why waste mass?

It is unclear to me which or whether various bits of engineering (the fabric, the support, the air pressure) would limit the scale of a HIAD to a certain window or make it less mass-efficient than a rigid aeroshell at a given size.  I imagine some of the guys developing it could project various materials/mass limits out way beyond the planned development sizes that are testable on routine presentday launches, but I can't.

It was certainly investigated in part (if not in whole) because it might be used for manned missions to Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/08/2016 12:34 am
I think there's a reasonable chance no such device will be used for MCT, for the sole reason that reusable controlled reliable powered landing is neither fully compatible nor fully benefitted by HIAD;

I thought HIAD was a technology for relatively small scale EDL (NASA@Mars)? Here we are talking about ships that are as large as projected HIAD brake area, so why waste mass?
HIAD is scalable to enormous sizes. It's not just for small scale EDL.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/08/2016 06:35 am
HIAD is scalable to enormous sizes. It's not just for small scale EDL.

Developed by NASA in that way? I only see them developing HIAD as a stage before using parachutes and parachutes limiting the downmass to Mars severely. Combining HIAD with SRP seems a serious headache.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/08/2016 09:25 am
HIAD is scalable to enormous sizes. It's not just for small scale EDL.

Developed by NASA in that way? I only see them developing HIAD as a stage before using parachutes and parachutes limiting the downmass to Mars severely. Combining HIAD with SRP seems a serious headache.

From http://gameon.nasa.gov/projects/hypersonic-inflatable-aerodynamic-decelerator-hiad-2/

The Hypersonic Inflatable Aerodynamic Decelerator (HIAD) project is a disruptive technology that will accommodate the atmospheric entry of heavy payloads to planetary bodies such as Mars. HIAD overcomes size and weight limitations of current rigid systems by utilizing inflatable softgood materials that can be packed into a small volume and deployed to form a large aeroshell before atmospheric entry.

And from Langley's Game Changing Development Industry Day Presentation there is an interesting rendering of a Mars lander that combines a HIAD and retropropulsion. It even repacks the HIAD after landing.

http://www.nasa.gov/sites/default/files/atoms/files/gcd_industryday_hiad.pdf

Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/08/2016 09:36 am
Yes, I am fully aware of that. But how much more than the 1t limit they have reached with Curiosity? No word on that in there. Will it support manned ERV MAV?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/08/2016 10:13 am
Yes, I am fully aware of that. But how much more than the 1t limit they have reached with Curiosity? No word on that in there. Will it support manned ERV MAV?

If you were fully aware of it, then why did you 'only see them developing HIAD as a stage before using parachutes'? As Robotbeat suggested, HIAD scales to enormous sizes, certainly hundreds of tonnes. In other words 'heavy payloads'. If you examine the rendering closely, you will see that the lander has windows and a hatch. It is obviously intended to be manned crewed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/08/2016 12:31 pm
NASA considers SRP to be used for EVERY Mars EDL concept big enough for humans.
It's now baselined. And HIAD is also used. There's no reason they can't both be used, and that is, in fact, NASA current preferred plan.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/08/2016 12:46 pm
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT.

IMO deployables will be limited to control surfaces much smaller than the heatshield. I tend to doubt that they will use inflatables, just because it's unnecessary complexity if they are willing to spend 1 km/s of delta-v on EDL.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/08/2016 01:13 pm
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT.

IMO deployables will be limited to control surfaces much smaller than the heatshield. I tend to doubt that they will use inflatables, just because it's unnecessary complexity if they are willing to spend 1 km/s of delta-v on EDL.

The trade is that to reduce the maximum g forces, you need to increase the available negative lift. If you have more negative lift, you can decelerate more gradually, higher in the Martian atmosphere. It will be interesting to see what SpaceX deem the maximum acceptable g forces. I suspect that will determine the size of any enhancements.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Torbjorn Larsson, OM on 08/08/2016 11:29 pm
I think there's a reasonable chance no such device will be used for MCT, for the sole reason that reusable controlled reliable powered landing is neither fully compatible nor fully benefitted by HIAD;

I thought HIAD was a technology for relatively small scale EDL (NASA@Mars)? Here we are talking about ships that are as large as projected HIAD brake area, so why waste mass?
HIAD is scalable to enormous sizes. It's not just for small scale EDL.

Ah, good to know! Extrapolating NASA's usually approach, they develop unique solutions for every mass scale to - ironically at high cost - fit their minimal budget. So now we have two scalable EDL techniques for Mars.

I would guess retrorockets is the far easier, cheaper method to scale tough. Just add engines as the craft diameter goes up. After all, that is how Flash Gordon did it! (Lots of engines looked good ...) And you need the engines for re-launch anyway.

Questions that popped up:

How far can NASA's current HIAD scale? Looks to me from artist conceptual sketches they want to re-engineer between prototypes for testing and their first use at, what, 10 m? What then if SpaceX needs a 15 m wide brake surface with tested technology?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Torbjorn Larsson, OM on 08/08/2016 11:40 pm
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT.

IMO deployables will be limited to control surfaces much smaller than the heatshield. I tend to doubt that they will use inflatables, just because it's unnecessary complexity if they are willing to spend 1 km/s of delta-v on EDL.

The trade is that to reduce the maximum g forces, you need to increase the available negative lift. If you have more negative lift, you can decelerate more gradually, higher in the Martian atmosphere. It will be interesting to see what SpaceX deem the maximum acceptable g forces. I suspect that will determine the size of any enhancements.

'It's bones, Jim, but now as we know it.' [Referring to the state of bodies of newly arrived martian colonists.]

Yes, I can't see a company invest in added mass and (fragile) complexity unless it is really necessary. By the way, wouldn't the side of a large craft offer a lot of negative lift? [Not an aerodynamist ... obviously.]

EDIT: Typo.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/09/2016 01:27 am
....
I would guess retrorockets is the far easier, cheaper method to scale tough.

As I said before:

HIAD and supersonic retropropulsion are complementary, not competing, technologies.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/09/2016 10:12 am
How far can NASA's current HIAD scale?

There are plenty of studies that consider HIADs up to 50m in diameter. They scale extremely well, and there is no reason they could not be made even larger.

It may be of interest that there are simulations of the phases of various MCT mission profiles in the L2 SpaceX Mars Discussion and Envisioning  (https://forum.nasaspaceflight.com/index.php?topic=40127.0) thread. Many of the simulations utilise HIADs of various sizes.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ionmars on 08/09/2016 11:59 am
..
...
...
Yes, I can't see a company invest in added mass and (fragile) complexity unless it is really necessary. By the way, wouldn't the side of a large craft offer a lot of negative lift? [Not an aerodynamist ... obviously.]
Perhaps the trade may include the mass of PICA-X running down one side of the vehicle versus the mass of HIAD to perform the same EDL.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 08/09/2016 04:07 pm
A very thorough presentation of ideas for BFR/MCT from "coborop" at Reddit:
https://www.reddit.com/r/spacex/comments/4wks2h/fanmade_mct_and_bfr_architecture_cad_and_math/

Beautiful renders!:
https://imgur.com/a/2k10I
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/09/2016 05:10 pm
A very thorough presentation of ideas for BFR/MCT from "coborop" at Reddit:
https://www.reddit.com/r/spacex/comments/4wks2h/fanmade_mct_and_bfr_architecture_cad_and_math/

Beautiful renders!:
https://imgur.com/a/2k10I

Interesting. Has the upper stage co-fire @ takeoff to increase T/W. Problem with Rvacs there.
What I like is someone not showing some BFR/BFS that is some ridiculous height like past Reddit posts I've seen elsewhere.  A >10m wide BFR gets very heavy quickly with propellant.  I'm confident that the reveal will be short and stout.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DanielW on 08/09/2016 05:11 pm
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT.

IMO deployables will be limited to control surfaces much smaller than the heatshield. I tend to doubt that they will use inflatables, just because it's unnecessary complexity if they are willing to spend 1 km/s of delta-v on EDL.

The trade is that to reduce the maximum g forces, you need to increase the available negative lift. If you have more negative lift, you can decelerate more gradually, higher in the Martian atmosphere. It will be interesting to see what SpaceX deem the maximum acceptable g forces. I suspect that will determine the size of any enhancements.

Is there any benefit in using your engines as your "negative lift" component? Supersonic Perpendicular Propulsion SPP. Or do you get more deceleration from retro propulsion? How many G's of negative lift do you need to stay in the atmosphere?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 08/09/2016 06:01 pm
FYI - This may interest people here - first MCT related hardware now exists in pre-production form:  Raptor :D

https://twitter.com/RocketScient1st/status/763063393745940481

Quote
C. G. Niederstrasser ‏@RocketScient1st
Shotwell - just shipped first Raptor engine to Texas last night. #SpaceX #smallsat

No pictures are available yet, but this probably means that Musk will show pictures of real hardware in his September presentation.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 08/09/2016 06:59 pm
FYI - This may interest people here - first MCT related hardware now exists in pre-production form:  Raptor :D

https://twitter.com/RocketScient1st/status/763063393745940481

Quote
C. G. Niederstrasser ‏@RocketScient1st
Shotwell - just shipped first Raptor engine to Texas last night. #SpaceX #smallsat

No pictures are available yet, but this probably means that Musk will show pictures of real hardware in his September presentation.
As I mentioned on another thread this is 1 year earlier than we have assumed for such engine and tests. This makes our estimates for NET BFR first launch test conservative by as much as 1 year moving the possibility of  a BFR to exist as early as 2019/2020.

SpaceX is moving faster than we expect. This is surprise number 2 for this year in relation to Mars after the RD mission date.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 08/09/2016 07:14 pm
FYI - This may interest people here - first MCT related hardware now exists in pre-production form:  Raptor :D

https://twitter.com/RocketScient1st/status/763063393745940481

Quote
C. G. Niederstrasser ‏@RocketScient1st
Shotwell - just shipped first Raptor engine to Texas last night. #SpaceX #smallsat

No pictures are available yet, but this probably means that Musk will show pictures of real hardware in his September presentation.
As I mentioned on another thread this is 1 year earlier than we have assumed for such engine and tests. This makes our estimates for NET BFR first launch test conservative by as much as 1 year moving the possibility of  a BFR to exist as early as 2019/2020.

SpaceX is moving faster than we expect. This is surprise number 2 for this year in relation to Mars after the RD mission date.

One of the advantages of a privately held company is the ability to keep projects secret. No SEC paperwork giving away what's going on.

I bet MCT and Red Dragon are further along than we imagined.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 08/09/2016 07:15 pm
A very thorough presentation of ideas for BFR/MCT from "coborop" at Reddit:
https://www.reddit.com/r/spacex/comments/4wks2h/fanmade_mct_and_bfr_architecture_cad_and_math/

Beautiful renders!:
https://imgur.com/a/2k10I

Interesting. Has the upper stage co-fire @ takeoff to increase T/W. Problem with Rvacs there.
What I like is someone not showing some BFR/BFS that is some ridiculous height like past Reddit posts I've seen elsewhere.  A >10m wide BFR gets very heavy quickly with propellant.  I'm confident that the reveal will be short and stout.

Also of interest: N-1-like spherical tanks in the MCT. Nested methalox tanks actually! http://imgur.com/a/pvAh8

In the discussion thread it appears that MCT co-fire may not be necessary, since his concept has a first stage which delivers enough power to give the whole stack a thrust-to-weight similar to Saturn 5/Apollo (around 1:1.15).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/09/2016 07:20 pm
Sea Level ISP 350 seconds seems too high so the BFR will not perform to that level assumed.
On the other hand you don't need the same Km/sec to RTLS as you launched because some of the launch velocity vector is vertical. It's not pure horizontal velocity.  Yes, you need some additional -X delta V to actually fly back.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/10/2016 12:58 am
2020 and exomars aren't going to be significantly larger than MSL.

This is a dumb way to argue. Please bring better game.

Fine. 
What evidence is there that MCT will use a HIAD?
There's some indirect evidence that it may be one of several options they'll consider.

I don't disagree that it will be or already was considered; there are many possibilities that will be discarded as not optimum or unworkable.
Certainly no evidence that it will be used on Red Dragon, which would be the obvious opportunity to test it...
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT. None will be used on Red Dragon, which is not at all a reason to think it won't be used on MCT.

I don't have any particular belief that SpaceX will use something like HIAD. I don't envision they will. But you dismiss the possibility far too easily.

GS:
Quote
Figuring out how to do this on Mars is going to be a challenge, part of why we need retro-propulsion on Mars, more predictable than aerodynamics.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Norm38 on 08/10/2016 01:37 am

Beautiful renders!:
https://imgur.com/a/2k10I

The shuttlecock style interstage is quite interesting. How close do you all feel this is to what we will see in Sept?
Also, is it possible to build control surfaces into that?  How does it give control authority like grid fins?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 08/10/2016 11:04 am
Maybe coborop believes that all the control authority needed can come from the main engines and a couple of cold thrusters. I however think that they haven't invested in know-how of grid fins without also using them for the MCT. As I see it they deliver much better targeting ability than the shuttle cock, even though the shuttle cock probably ensures better passive stability.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/10/2016 11:18 am
Could grid fins (or flaps of some sort) be used forward and aft to control a belly first EDL?
Would give control authority during pop-up maneuver to prepare for landing burn, too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/10/2016 01:09 pm
Sea Level ISP 350 seconds seems too high so the BFR will not perform to that level assumed.
On the other hand you don't need the same Km/sec to RTLS as you launched because some of the launch velocity vector is vertical. It's not pure horizontal velocity.  Yes, you need some additional -X delta V to actually fly back.

I think that's 350s for the SL engine operating in vacuum (e.g. booster stage near MECO). SpaceX is proposing 321s at SL and 363s in vacuum for the SL engine, so 350s is probably conservative.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oldAtlas_Eguy on 08/10/2016 03:31 pm
With a prototype Raptor engine going into test the preliminary (concepts/requirements/definition) phase is drawing to a close with the detail design phase starting now. With a good model of what the Raptor will be able to achieve (ISP, thrust, engine bell size, T/W, etc) the specific capabilities of the two elements BFR and BFS will be set by the Sept reveal. Think of that as the PDR for those familiar with US government development program milestones. Although this is a pure commercial development it still has the same phases in its development:
- preliminary (concept/specifications),
- critical (detail design, manufacture "drawings", prototypes, tooling, etc for all elements of the vehicles),
- production of test articles, and
- finally production of flight articles.

And with the drawing of this preliminary design phase to a close so dose this thread's speculation about concepts and capabilities. It will then refocus on the details not revealed in Sept.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/10/2016 03:43 pm
Sea Level ISP 350 seconds seems too high so the BFR will not perform to that level assumed.
On the other hand you don't need the same Km/sec to RTLS as you launched because some of the launch velocity vector is vertical. It's not pure horizontal velocity.  Yes, you need some additional -X delta V to actually fly back.

I think that's 350s for the SL engine operating in vacuum (e.g. booster stage near MECO). SpaceX is proposing 321s at SL and 363s in vacuum for the SL engine, so 350s is probably conservative.

Yes, we know that. 
His calculations use 350seconds ISP for the 1st stage BFR, so as I said his BFR model over performs what we know about a SL methalox engine.  The "average" ISP for stage one is most likely under 350s.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/10/2016 08:08 pm
Ugh, not looking forward to half a dozen pages of naming speculation. THE most boring aspect of this whole endeavor.

Does any of the info from Shotwell belong in the MCT source information update thread?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: oiorionsbelt on 08/10/2016 11:47 pm
2020 and exomars aren't going to be significantly larger than MSL.

This is a dumb way to argue. Please bring better game.

Fine. 
What evidence is there that MCT will use a HIAD?
There's some indirect evidence that it may be one of several options they'll consider.

I don't disagree that it will be or already was considered; there are many possibilities that will be discarded as not optimum or unworkable.
Certainly no evidence that it will be used on Red Dragon, which would be the obvious opportunity to test it...
It's nearly certain that some sort of deployable drag enhancement device will be used for MCT. None will be used on Red Dragon, which is not at all a reason to think it won't be used on MCT.

I don't have any particular belief that SpaceX will use something like HIAD. I don't envision they will. But you dismiss the possibility far too easily.

Are HIADs considered to be a ballute?
 At the 46:00 in the Small Sat keynote address by Qwynne Shotwell, she's says "Retropropulsion is really the answer. As opposed to parachutes, aero foils, ballutes and those things. Atmospheres are much too dynamic. Retroprpulsion really is the answer. In addition it will scale."
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/11/2016 12:28 pm
Are HIADs considered to be a ballute?

They probably shouldn't be. Although ballutes are capable of generating drag, they are not capable of generating negative lift. Also they, and parachutes aerofoils only appear to be intended for supersonic and subsonic flight regimes, rather than hypersonic.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/11/2016 02:21 pm
Are HIADs considered to be a ballute?

They probably shouldn't be. Although ballutes are capable of generating drag, they are not capable of generating negative lift. Also they, parachutes and aerofoils only appear to be intended for supersonic and subsonic flight regimes, rather than hypersonic.

HIADs are none of the above, but they do suffer from the same issues when it comes to precision landing.

Also, some airfoils are quite capable of hypersonic flight. The Shuttle, Buran, and a number of lifting body designs were airfoils designed/tested and/or flown at hypersonic reentry speeds.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 08/11/2016 04:21 pm
Naming is off topic here. I've splitmerged to the naming thread https://forum.nasaspaceflight.com/index.php?topic=35208

Props to Burninate for a heroic copypasta...  which got moved over here https://forum.nasaspaceflight.com/index.php?topic=35208.msg1567939#msg1567939

Wrong idea though, just report to mod (as someone did) and we'll sort it out eventually.

If you think I moved your post incorrectly, PM me. Whether you know my name or not.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/16/2016 08:08 pm
Carbon fiber bodies/stages instead of aluminum... Advances the state-of-the-art in rocketry.
Helps mass reduction and secondary radiation effects simultaneously.

Quote
SpaceX is switching to carbon fibers from aluminum as it develops heavy rockets for carrying people and large quantities of material. A lighter body would allow more cargo to be loaded, which would cut transport costs.
http://asia.nikkei.com/Business/Deals/Toray-carbon-fiber-to-carry-SpaceX-s-Mars-ambitions

Combined with fast transits, rad problem could be largely mitigated.
PMF could (will) be best ever by far...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BobHk on 08/17/2016 04:11 pm
Carbon fiber bodies/stages instead of aluminum... Advances the state-of-the-art in rocketry.
Helps mass reduction and secondary radiation effects simultaneously.

Quote
SpaceX is switching to carbon fibers from aluminum as it develops heavy rockets for carrying people and large quantities of material. A lighter body would allow more cargo to be loaded, which would cut transport costs.
http://asia.nikkei.com/Business/Deals/Toray-carbon-fiber-to-carry-SpaceX-s-Mars-ambitions

Combined with fast transits, rad problem could be largely mitigated.
PMF could (will) be best ever by far...

Quote
Update: On Tuesday evening SpaceX would not confirm that a large deal had been reached. "Toray is one of a number of suppliers we work with to meet our carbon fiber needs for Falcon rocket and Dragon spacecraft production, and we haven’t announced any new agreements at this time," a company spokesman told Ars. "As our business continues to grow, the amount of carbon fiber we use may continue to grow."

http://arstechnica.com/science/2016/08/spacex-reportedly-signs-multibillion-deal-for-carbon-fiber-composites/

meh harrumph
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 08/19/2016 01:26 am
Sliced out some posts that weren't really MCT to a new thread. When proposing new ideas let's stay focused on what is within the bounds of what we know already... if your idea doesn't fit what has already been said it probably doesn't belong here.

http://forum.nasaspaceflight.com/index.php?topic=40953.0 in SpaceX general ...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/22/2016 07:37 pm
Does all-composite construction favor any particular architecture choices? SpaceX seems to put quite a bit of effort into TPS on the composite Falcon interstage compared to the Al-Li tanks. I wonder if they will need TPS basically everywhere on a composite booster and especially on an orbiter.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/22/2016 08:15 pm
Does all-composite construction favor any particular architecture choices? SpaceX seems to put quite a bit of effort into TPS on the composite Falcon interstage compared to the Al-Li tanks. I wonder if they will need TPS basically everywhere on a composite booster and especially on an orbiter.
Al-Li hates heat basically just as much, the difference is the interstage gets full blast from the upper stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 08/22/2016 08:33 pm
Does all-composite construction favor any particular architecture choices? SpaceX seems to put quite a bit of effort into TPS on the composite Falcon interstage compared to the Al-Li tanks. I wonder if they will need TPS basically everywhere on a composite booster and especially on an orbiter.

Al-Li favours bi-conic fairing like shapes while composites could enable a much wider range of shapes. I've long thought that the BFS could have a semi-lifting body shape, one without winglets, but a non-circular cross section.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/22/2016 11:30 pm
Does all-composite construction favor any particular architecture choices? SpaceX seems to put quite a bit of effort into TPS on the composite Falcon interstage compared to the Al-Li tanks. I wonder if they will need TPS basically everywhere on a composite booster and especially on an orbiter.

The lower mass may allow double hulled designs on BFS (or fuel depots to limit boiloff), where the propellant tankage is surrounded by a vacuum space to the outer mold line.  Tank reinforcements and/or MLI could then be in the interstitial space between the shells.  Something like this is needed because CO2 (and H2O, of course) freezes out at lox/liquid methane temps, so the vehicle cannot sit on the Martian surface with fuel in the tanks for very long.  Design would be functionally similar to an LN2 storage Dewar.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 08/23/2016 01:31 am
Does all-composite construction favor any particular architecture choices? SpaceX seems to put quite a bit of effort into TPS on the composite Falcon interstage compared to the Al-Li tanks. I wonder if they will need TPS basically everywhere on a composite booster and especially on an orbiter.

Al-Li favours bi-conic fairing like shapes while composites could enable a much wider range of shapes. I've long thought that the BFS could have a semi-lifting body shape, one without winglets, but a non-circular cross section.

Richard Heidmann,

Bio.... (http://www.futura-sciences.com/magazines/espace/infos/personnalites/d/astronautique-richard-heidmann-6/)

French Mars Society

MCT concept.... (http://planete-mars.com/what-could-the-mars-colonization-transport-mct-spacex-project-look-like-continued/)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/23/2016 01:34 am
It's not going to have wings or land horizontally like that. I'd put a lot of money on that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 08/23/2016 01:54 am
It's not going to have wings or land horizontally like that. I'd put a lot of money on that.

I'm more interested in the broad profile with a large TPS area than the engine placement and wings, which ISTM are of questionable utility in a thin atmosphere.

Think Max Fagin's retropropulsion thesis defense...

Horizontal entry, tail-landed (low c/g) uber-Dragon-ish split vehicle, with SD like pods in the upper 1/3-1/2 serving as LAS/ERV thrusters with the bottom, which contains the cargo, staying?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/23/2016 02:05 am
Maybe. I think side entry is the most probable. I just don't think they'll use wings. I wonder if grid fins will make an appearance? May help a lot with the transition.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/23/2016 02:11 am
Simply entering an atmosphere sideways as opposed to vertically is only going to approximately double the area at best and it requires the vehicle to be load bearing in a second direction, which is a significant mass penalty for a vehicle this large.

I suspect we will see the vehicle equipped with some form of radial expansion mechanism that give it a much larger cross sectional area and entry will be in a vertical orientation either base first or nose first to keep the forces of entry on the single strong vertical axis that is used during launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/23/2016 02:26 am
Simply entering an atmosphere sideways as opposed to vertically is only going to approximately double the area at best and it requires the vehicle to be load bearing in a second direction, which is a significant mass penalty for a vehicle this large.

I suspect we will see the vehicle equipped with some form of radial expansion mechanism that give it a much larger cross sectional area and entry will be in a vertical orientation either base first or nose first to keep the forces of entry on the single strong vertical axis that is used during launch.
That's plausible as well. But a doubling or tripling of the area is not insignificant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/23/2016 03:36 am
Simply entering an atmosphere sideways as opposed to vertically is only going to approximately double the area at best and it requires the vehicle to be load bearing in a second direction, which is a significant mass penalty for a vehicle this large.

I suspect we will see the vehicle equipped with some form of radial expansion mechanism that give it a much larger cross sectional area and entry will be in a vertical orientation either base first or nose first to keep the forces of entry on the single strong vertical axis that is used during launch.

Plausible, certainly. But that's just trading structural mass for mechanism mass and additional complexity. They could also trade that mass for fuel and start SRP at a higher velocity.

Each approach has advantages that show in other parts of the mission, and it's hard to optimize without knowing the full mission profile. Particularly since more than one could be used.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/23/2016 05:54 am
First, frictional dissipation of velocity using heat-shields, parachutes, HIAD, you name it, Always comes out more mass efficient then propellant, we would always choose to trade landing propellant for structural mass in the vehicle because the ratio is likely to be in excess of 10 to 1 in favor of the structural element over propellant.  Complexity is a downside, yes but if it means not having to be loaded with large amounts of propellant on atmospheric entry that is a big deal because that saves mass twice in two high delta v maneuvers, departure from Earth and departure from Mars.

Second SRP is only usable in the later parts of EDL after most velocity has already been lost through friction.  The problem is that the vehicle is going to have so high of a ballistic coefficient that it would strike the ground on mars before even reaching the speed with sufficient remaining altitude that SRP can handle, their must be something to lower the coefficient.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/23/2016 08:51 am
I suspect we will see the vehicle equipped with some form of radial expansion mechanism that give it a much larger cross sectional area and entry will be in a vertical orientation either base first or nose first to keep the forces of entry on the single strong vertical axis that is used during launch.

Sure, increasing Cd will help enormously with fuel conservation, but more is required. For the sake of argument assume your spaceship is travelling horizontally in the upper Martian atmosphere at 13km/s. Orbital velocity is 3.3km/s, so just to stay in the atmosphere, the ship needs to generate 3 Martian gs of negative lift.

So, it is not enough to expand the cross section radially, some sort of asymmetry needs to be introduced in order to create lift. What would be especially helpful would be if the Cl could be modulated. It will be extremely interesting to see how SpaceX solve this problem.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/23/2016 12:40 pm
First, frictional dissipation of velocity using heat-shields, parachutes, HIAD, you name it, Always comes out more mass efficient then propellant, we would always choose to trade landing propellant for structural mass in the vehicle because the ratio is likely to be in excess of 10 to 1 in favor of the structural element over propellant.  Complexity is a downside, yes but if it means not having to be loaded with large amounts of propellant on atmospheric entry that is a big deal because that saves mass twice in two high delta v maneuvers, departure from Earth and departure from Mars.
It's not entirely necessary to increase drag or ballistic coefficient for Earth return, so un-deploying a deployable drag device on Mars and then dragging it back to Earth is actually less efficient. The extra propellant capacity is actually useful for the return transit burns.

Quote
Second SRP is only usable in the later parts of EDL after most velocity has already been lost through friction.  The problem is that the vehicle is going to have so high of a ballistic coefficient that it would strike the ground on mars before even reaching the speed with sufficient remaining altitude that SRP can handle, their must be something to lower the coefficient.

Red Dragon will (try) to baseline a low Lift/Drag, high ballistic coefficient Mars entry. Assuming that succeeds in getting to the SRP regime with an appreciable amount of payload (i.e. it doesn't go "splat" first), than a larger vehicle with similar aerodynamic characteristics should be feasible.

That's where carbon fiber allows some architectural choices. With a lower density and much higher strength to weight ratio, it might be able to help get around the cube-square issues of scaling a vehicle up. If there are any mass savings, that translates directly to both a better L/D ratio and a better ballistic coefficient.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 08/23/2016 01:13 pm
Simply entering an atmosphere sideways as opposed to vertically is only going to approximately double the area at best ...

If the info in L2 is to believed (and I do not believe this bit of info), it is more like four times.

Drag is approximately proportional to area, but lift should be much higher for a (semi-)lifting body (i.e. one without wings/winglets) so the lift/drag should be better.

If my understanding of EDL is correct higher lift/drag can lead to both lower peak acceleration and lower speed before transition to retro-propulsion. Both very desirable characteristics.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 08/23/2016 01:20 pm
Second SRP is only usable in the later parts of EDL after most velocity has already been lost through friction.  The problem is that the vehicle is going to have so high of a ballistic coefficient that it would strike the ground on mars before even reaching the speed with sufficient remaining altitude that SRP can handle, their must be something to lower the coefficient.

Red Dragon will (try) to baseline a low Lift/Drag, high ballistic coefficient Mars entry. Assuming that succeeds in getting to the SRP regime with an appreciable amount of payload (i.e. it doesn't go "splat" first), than a larger vehicle with similar aerodynamic characteristics should be feasible.

My understanding is that Red Dragon will have g-forces which are too high for humans (especially those that have spent 3+ months in zero-g). So it is not just possible to scale up Red Dragon (to about 22 m in diameter).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/23/2016 05:04 pm
Red Dragon's gee forces are not too high. Compare a Soyuz ballistic entry after 6 months in orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/24/2016 06:47 am
Red Dragon's gee forces are not too high. Compare a Soyuz ballistic entry after 6 months in orbit.

Those forces are not nominal and are routinely cause the cosmonauts to black out, your always siting superlatives and extremes as if they are usable as nominal conditions but that is flawed because their would be no margin left for any off nominal event.

A radial area expansion system dose not rule out lift generation, in fact it makes it easier to control the asymmetry of the vehicle and control the amount of lift generated which is highly advantageous given the variable density of mars atmosphere.  A lifting body or bi-conic will generated high lift but at the cost of reducing drag as these bodies to not enter fully horizontally and while the lift is needed for g-force reduction from what I've read you lose too much drag which raises the ballistic coefficient back into dangerous territory.  A fairly simple radial expansion in the form of fold down petals and connecting carbon fiber webbing between them could easily triple the vehicle radius to 40 meters which would give a comparable ballistic coefficient to the MSL.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/24/2016 01:01 pm
I suspect we will see the vehicle equipped with some form of radial expansion mechanism that give it a much larger cross sectional area and entry will be in a vertical orientation either base first or nose first to keep the forces of entry on the single strong vertical axis that is used during launch.

Regarding lift generation, I had assumed from this post that you expected the entry to be in a purely vertical orientation. I agree that a radial area expansion system could generate lift, but to do so, the ship would need to pitch off axis by some amount. Still, the stress on a blunt body shape would be significantly less than that experienced by a biconic or lifting body, or indeed any shape that would be dynamically modelled by a pinned beam.

Red Dragon's gee forces are not too high. Compare a Soyuz ballistic entry after 6 months in orbit.

Those forces are not nominal and are routinely cause the cosmonauts to black out, your always siting superlatives and extremes as if they are usable as nominal conditions but that is flawed because their would be no margin left for any off nominal event.

A radial area expansion system dose not rule out lift generation, in fact it makes it easier to control the asymmetry of the vehicle and control the amount of lift generated which is highly advantageous given the variable density of mars atmosphere.  A lifting body or bi-conic will generated high lift but at the cost of reducing drag as these bodies to not enter fully horizontally and while the lift is needed for g-force reduction from what I've read you lose too much drag which raises the ballistic coefficient back into dangerous territory.  A fairly simple radial expansion in the form of fold down petals and connecting carbon fiber webbing between them could easily triple the vehicle radius to 40 meters which would give a comparable ballistic coefficient to the MSL.

Regarding ballistic coefficients, I've attached a table that compares several designs, including a hypothetical BFS with the same ballistic coefficient as Red Dragon.

SpacecraftDiameter mArea m^2Volume m^3Mass mTBallistic coefficientSidewall angle °Peak gsEntry velocity km/s
MSL4.515.21?3.314840155.8
Soyuz2.23.843789747.6
Cargo dragon3.710.75107.2515154.57.6
Red dragon3.710.751010715157.49.6
BFS22380.13400035771530?412

Firstly, MSL is the only spacecraft in the list that has actually landed on Mars. For me, the standout difference is its ballistic coefficient, at least 3 times less than all the others. Of course Soyuz and Cargo Dragon only need to perform EDL on Earth, so a higher β makes sense. I've simulated the Red Dragon EDL profile, and I believe that on a good day it will work. The problem is the day to day variation in the density of the upper Martian atmosphere. On a bad day, the density might be halved, making EDL much more difficult and dangerous. As a risk mitigation strategy, I'd suggest increasing the BFS Cd and Cl, giving greater control authority, and minimising peak g forces.

The other standout difference is entry velocity. Heating increases as the cube of velocity, so, for the same β, the thermal difference between MSL and BFR is a factor of 9. Again, lowering the β of the BFR to perhaps 400kg/m^2 would help. A higher entry velocity also magnifies any trajectory deviation, and hence landing positional error, so maximising control authority is critical.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/24/2016 01:30 pm
...easily triple the vehicle radius to 40 meters which would give a comparable ballistic coefficient to the MSL.

How much mass are you figuring at EI? MSL had 3300 kg at EI behind a 10.75 m2 heatshield, or 307 kg/m2, and it slowed to below 450 m/s before deploying chutes.

If BFS masses 240,000 kg at EI (100t payload, 80t vehicle, 60t EDL propellant), then it only needs a 15.8m radius to match MSL's ballistic coefficient.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/24/2016 01:55 pm
MSL had 3300 kg at EI behind a 10.75 m2 heatshield, or 307 kg/m2, and it slowed to below 450 m/s before deploying chutes.

Are you sure? Wikipedia quotes 2,401 kg for the EDL system, and a 4.5m diameter heatshield, giving an area of 15.21 m^2. That's a β of 158 kg/m^2, although I've seen 110 kg/m^2 quoted elsewhere.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/24/2016 04:31 pm
MSL had 3300 kg at EI behind a 10.75 m2 heatshield, or 307 kg/m2, and it slowed to below 450 m/s before deploying chutes.

Are you sure? Wikipedia quotes 2,401 kg for the EDL system, and a 4.5m diameter heatshield, giving an area of 15.21 m^2. That's a β of 158 kg/m^2, although I've seen 110 kg/m^2 quoted elsewhere.

You're right about the 4.5m MSL shield, I was thinking of the Viking shields.

But the 2.4t mass is for the EDL system ONLY (skycrane, fuel, chutes, shield, backshell), and doesn't include the 900 kg rover itself. 3300 kg over 15.2 m2 gives a beta of 217 kg/m2

Edit: here's the link to JPL's listed masses for MSL... http://mars.jpl.nasa.gov/msl/mission/spacecraft/
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/24/2016 05:03 pm
SpacecraftDiameter mArea m^2Volume m^3Mass mTBallistic coefficientSidewall angle °Peak gsEntry velocity km/s
BFS22380.13400035793030?412
Can you list the assumptions behind these values? The volume and mass seem rather high to me.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/24/2016 09:54 pm
Can you list the assumptions behind these values? The volume and mass seem rather high to me.

I just took MikeAtkinson's suggestion of a 22m diameter, and worked back from the Red Dragon β and shape to derive the hypothetical mass and volume. There is a much more detailed analysis in L2.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/25/2016 01:20 am
I don't find 22 m diameter to be plausible, it's far wider then even the widest speculated size of the BFR, but a vehicle 15 m in diameter with fold down flaps the same size as the current F9 landing legs which are 18 m long would give a 51 m diameter, and the legs only mass 2,500 kg on the F9R so this looks eminently practical and it far exceeds the diameter that a monolithic vehicle could be launched as. 

I'm also operating under the assumption of a 200 mt entry mass and a much more modest propellant quantity sufficient for 800 m/s.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/25/2016 04:40 am
MSL had 3300 kg at EI behind a 10.75 m2 heatshield, or 307 kg/m2, and it slowed to below 450 m/s before deploying chutes.

Are you sure? Wikipedia quotes 2,401 kg for the EDL system, and a 4.5m diameter heatshield, giving an area of 15.21 m^2. That's a β of 158 kg/m^2, although I've seen 110 kg/m^2 quoted elsewhere.

You're right about the 4.5m MSL shield, I was thinking of the Viking shields.

But the 2.4t mass is for the EDL system ONLY (skycrane, fuel, chutes, shield, backshell), and doesn't include the 900 kg rover itself. 3300 kg over 15.2 m2 gives a beta of 217 kg/m2

Edit: here's the link to JPL's listed masses for MSL... http://mars.jpl.nasa.gov/msl/mission/spacecraft/

I think I see the problem. β = mass / area * Cd, so we've both forgotten to divide by the drag coefficient, which for MSL is 1.4, giving 148 kg/m2. I've updated my table.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/25/2016 02:38 pm
I don't find 22 m diameter to be plausible, it's far wider then even the widest speculated size of the BFR, but a vehicle 15 m in diameter with fold down flaps the same size as the current F9 landing legs which are 18 m long would give a 51 m diameter, and the legs only mass 2,500 kg on the F9R so this looks eminently practical and it far exceeds the diameter that a monolithic vehicle could be launched as. 

I'm also operating under the assumption of a 200 mt entry mass and a much more modest propellant quantity sufficient for 800 m/s.

I think they could use shorter flaps as deployable drag and as variable lift control surfaces. Webbing has a lot of challenges, but interleaved rigid deployable flaps could easily double the diameter, say from 16m to 32m. That would only require flaps some 8m long.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Xentry on 08/25/2016 03:04 pm
Regarding ballistic coefficients, I've attached a table that compares several designs, including a hypothetical BFS with the same ballistic coefficient as Red Dragon.

SpacecraftDiameter mArea m^2Volume m^3Mass mTBallistic coefficientSidewall angle °Peak gsEntry velocity km/s
MSL4.515.21?3.314840155.8
Soyuz2.23.843789747.6
Cargo dragon3.710.75107.2515154.57.6
Red dragon3.710.751010715157.49.6
BFS22380.13400035771530?412

Is there any particular reason why Mars atmospheric entry velocities would be as high as 9-12km/s for the Red Dragon and BFS? I would expect them to be on the same order of past Mars missions (that is, 5-7km/s)...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/25/2016 03:18 pm
Regarding ballistic coefficients, I've attached a table that compares several designs, including a hypothetical BFS with the same ballistic coefficient as Red Dragon.

SpacecraftDiameter mArea m^2Volume m^3Mass mTBallistic coefficientSidewall angle °Peak gsEntry velocity km/s
MSL4.515.21?3.314840155.8
Soyuz2.23.843789747.6
Cargo dragon3.710.75107.2515154.57.6
Red dragon3.710.751010715157.49.6
BFS22380.13400035771530?412

Is there any particular reason why Mars atmospheric entry velocities would be as high as 9-12km/s for the Red Dragon and BFS? I would expect them to be on the same order of past Mars missions (that is, 5-7km/s)...

As to BFS Musk has said that he wants shorter trip times, so shorter trip times equates to higher Km/sec entry velocity
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 08/25/2016 03:44 pm
Regarding ballistic coefficients, I've attached a table that compares several designs, including a hypothetical BFS with the same ballistic coefficient as Red Dragon.

SpacecraftDiameter mArea m^2Volume m^3Mass mTBallistic coefficientSidewall angle °Peak gsEntry velocity km/s
MSL4.515.21?3.314840155.8
Soyuz2.23.843789747.6
Cargo dragon3.710.75107.2515154.57.6
Red dragon3.710.751010715157.49.6
BFS22380.13400035771530?412

Is there any particular reason why Mars atmospheric entry velocities would be as high as 9-12km/s for the Red Dragon and BFS? I would expect them to be on the same order of past Mars missions (that is, 5-7km/s)...

As to BFS Musk has said that he wants shorter trip times, so shorter trip times equates to higher Km/sec entry velocity

Not necessarily. You just need more fuel to slow down before you get to entry.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jimmy Murdok on 08/25/2016 04:30 pm
I suspect we will see the vehicle equipped with some form of radial expansion mechanism that give it a much larger cross sectional area and entry will be in a vertical orientation either base first or nose first to keep the forces of entry on the single strong vertical axis that is used during launch.
I agree with you and when I saw the "Battlestar Galactica" french design... :o Should be much more simple.

What if the actual configuration of F9 is already testing many parts of the final design:

- Landing a 9 motor configuration. Or at least vertical landing similar to what they are mastering.
- During launch, the abort unit is a "Super Dragon" with similar shape to the V2. The trunk include the living quarters and services.
- In case of main stage issues during EDL, the "Super Dragon" could detach and follow similar trajectory of Red Dragon. Survival in the capsule until new ascent spaceship arrives.
- The legs have double function: semi expanded work as a frame for a deceleration fabric that increase the surface. (If active hydraulics can also provide control).
- The legs do provide enough clearance for relaunch: no need to move the rocket to vertical position. Just land on top of a leveled clean pad.
- The plan in September would not look that crazy (except for the scale). We have seen landings and the dragon abort.
- The deceleration system can be scale tested in F9 with practical output: reduce landing fuel and stress of the engines. 

See the graphics attached. Need much more development but tomorrow I work early.
I´m happy to modify if good suggestions and/or share the models.

Edit:typo
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/25/2016 05:15 pm
Overall, some really cool ideas, but you could work on how they are configured. Do you have any masses for any of the vehicles, or required fuel masses calculated?

- Landing a 9 motor configuration. Or at least vertical landing similar to what they are mastering.
How does this monster get to LEO? 9 Raptors are VERY underpowered for Earth launch at sea level, but rather overpowered for anything else.
Are you planning on having those 9 engines facing into the orbital reentry blast? They won't like that, unless they are firing the whole time... and firing the whole time uses too much fuel.
That lower section should have more engines, and just be a stage 1 booster. It only does sub-orbital EDL and doesn't need much shielding. Move the deployable heat shield up the the Super Dragon Trunk. The Trunk and Super Dragon are the unit that then would go to orbit, and with the deployable shield for reentry at Mars and Earth.
Move the "SuperDraco" pods down to the trunk sidewall and fire them nearly straight back, between the landing legs. They have to be able to fire with the shield folded or deployed. That's how it will get from staging to orbit/TMI (with the shield folded) and that's how it will do supersonic retro-propulsion (with the shield open).

Quote
- During launch, the abort unit is a "Super Dragon" with similar shape to the V2. The trunk include the living quarters and services.
How much mass are you putting through abort? What engines would be used for abort? IFAIK SpaceX is not working on a engine that would be suitable to abort that large a capsule from Earth launch.
Also, why do you need to abort the whole thing? MCT can easily carry a 7 man Dragon 2 (or later a hypothetical ~25 passenger, ~6 meter Dragon 3) on top, which can abort on SuperDracos and shuttle back to Earth immediately. Since ~4 refueling launches are needed per Mars injection, just send 1/4 of the people up on every launch.

Quote
- In case of main stage issues during EDL, the "Super Dragon" could detach and follow similar trajectory of Red Dragon. Survival in the capsule until new ascent spaceship arrives.
I can see where EDL abort capability would be nice, but I can't see any way it's practical. No Earth return craft has ever had that, for good reasons. Any EDL failure that's not survivable on a spacecraft probably isn't survivable in the abort capsule either. There's really no reason to separate the Super Dragon from it's Trunk. Land them together, launch them together, and abort them together if needed.

Quote
- The legs have double function: semi expanded work as a frame for a deceleration fabric that increase the surface. (If active hydraulics can also provide control).
You don't need grid fins for Mars, and behind a heatshield they won't do anything useful on Earth, so move teh heatshield up to the Trunk. Where does the fabric go when the legs are folded up? Is it stowed? Can it be re-stowed automatically on Mars for relaunch?


Quote
- The legs do provide enough clearance for relaunch: no need to move the rocket to vertical position. Just land on top of a leveled clean pad.
A separate "cargo bay" isn't practical; the cargo bay and hab should be the same size and shape to fit in the same mold lines. Almost everything will need to be shipped pressurized, and the pressure vessel should to be removed at Mars to serve as storage/habitat. There's no point in returning your shipping container to Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/25/2016 06:16 pm
Regarding ballistic coefficients, I've attached a table that compares several designs, including a hypothetical BFS with the same ballistic coefficient as Red Dragon.

SpacecraftDiameter mArea m^2Volume m^3Mass mTBallistic coefficientSidewall angle °Peak gsEntry velocity km/s
MSL4.515.21?3.314840155.8
Soyuz2.23.843789747.6
Cargo dragon3.710.75107.2515154.57.6
Red dragon3.710.751010715157.49.6
BFS22380.13400035771530?412

Is there any particular reason why Mars atmospheric entry velocities would be as high as 9-12km/s for the Red Dragon and BFS? I would expect them to be on the same order of past Mars missions (that is, 5-7km/s)...

As to BFS Musk has said that he wants shorter trip times, so shorter trip times equates to higher Km/sec entry velocity

Not necessarily. You just need more fuel to slow down before you get to entry.

Not a great mission profile wasting valuable rocket equation exponential propellant when the atmosphere gives the delta V to you if you are very clever in your spacecraft design and guidance.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Jimmy Murdok on 08/25/2016 06:37 pm
Overall, some really cool ideas, but you could work on how they are configured. Do you have any masses for any of the vehicles, or required fuel masses calculated?
The main objective of the post was to get feedback about the concept of decelerator deployed with legs. Done all the design after work. Many artistic licenses.  If you want to feed with data, I´m happy to modify and improve. Everything is parametric.

Quote
How does this monster get to LEO? 9 Raptors are VERY underpowered for Earth launch at sea level, but rather overpowered for anything else.
It´s a second stage BFS. And one stage to orbit form Mars + earth injection.

Quote
Are you planning on having those 9 engines facing into the orbital reentry blast? They won't like that, unless they are firing the whole time... and firing the whole time uses too much fuel. ´
Was thinking on extensions on the low part of the legs that cover the external engines when deployed. Depends on how many engines are needed in total and how many only for the EDL?  9 were random to visualize the concept (an octaweb would simplify their design).

Quote
That lower section should have more engines, and just be a stage 1 booster. It only does sub-orbital EDL and doesn't need much shielding. Move the deployable heat shield up the the Super Dragon Trunk. The Trunk and Super Dragon are the unit that then would go to orbit, and with the deployable shield for reentry at Mars and Earth.
Move the "SuperDraco" pods down to the trunk sidewall and fire them nearly straight back, between the landing legs. They have to be able to fire with the shield folded or deployed. That's how it will get from staging to orbit/TMI (with the shield folded) and that's how it will do supersonic retro-propulsion (with the shield open).
Need to analyze this input

Quote
How much mass are you putting through abort? What engines would be used for abort? IFAIK SpaceX is not working on a engine that would be suitable to abort that large a capsule from Earth launch.
Also, why do you need to abort the whole thing? MCT can easily carry a 7 man Dragon 2 (or later a hypothetical ~25 passenger, ~6 meter Dragon 3) on top, which can abort on SuperDracos and shuttle back to Earth immediately. Since ~4 refueling launches are needed per Mars injection, just send 1/4 of the people up on every launch.
Those huge super dracos are artistic. Could be a much smaller capsule powered by SD like your 6m Dragon 3. But I expect there will be an abort function during launch and EDL.
 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/25/2016 07:44 pm
The main objective of the post was to get feedback about the concept of decelerator deployed with legs. Done all the design after work. Many artistic licenses.  If you want to feed with data, I´m happy to modify and improve. Everything is parametric.
I can certainly provide some calculations. It would be helpful to know some of the dimensions you have modeled, such the main diameter of the stage.

The deployable decelerator is a great idea, although I would suggest you decouple it from the landing legs, for a couple reasons: 1) a Mars lander will be rather short and squat, so it's legs can be mostly under it (look at the leg concepts for Red Dragon). 2) you want to be able to stow the decelerator while keeping the legs out... can't have that thing hanging out when you launch from Mars, since it will make a great drag device going the other direction as well 8) The frames used for deployment can still look a lot like the F9 legs, but don't need to rotate all the way to the ground.

Quote
It´s a second stage BFS. And one stage to orbit form Mars + earth injection.
That good, but it's quite over sized for that. A 15m diameter subcooled methalox tank holds about 180 tonnes of propellant per meter of length, so for the 1000t or so of propellant it takes to put 100t of payload through TMI and EDL, you only need some 5 to 6 meter long tanks. The tanks on BFS are going to be pretty close to spherical and 10 to 12m diameter, not a long cylinder as you show. The long cylinder is exactly what the booster stage will look like.

Quote
Was thinking on extensions on the low part of the legs that cover the external engines when deployed. Depends on how many engines are needed in total and how many only for the EDL?  9 were random to visualize the concept (an octaweb would simplify their design).
Depending on how massive it is, it will need somewhere between 2 to 6 vacuum Raptors on the second stage. Retropropulsion requires that the engines be as far outboard as possible, and if they are set back from the heatshield around the edges they don't need a cover - the bow shock will carry the hot plasma out and around them. Look at the SuperDracos on Dragon 2. That's exactly where you want to put your engines for EDL... or pretty much like this:

Quote from: envy887
Move the "SuperDraco" pods down to the trunk sidewall and fire them nearly straight back, between the landing legs. They have to be able to fire with the shield folded or deployed. That's how it will get to orbit/TMI (with the shield folded) and that's how it will do supersonic retro-propulsion (with the shield open).

Quote
But I expect there will be an abort function during launch and EDL.
Launch? Yes. EDL? I don't think there are a lot of scenarios where that's survivable with any form of abort. Maybe on early missions where you can fit the crew in a Dragon on top, but certainly not at the colonization level. Some risks are just inherent with no practical means for abort, and EDL has always been one of those. By the time they get past the "3.7m or 6m Dragon on top" type of missions, the architecture will have flown thousands of entries and have a very high confidence in reliability, 99.9% or greater.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Nilof on 08/25/2016 10:02 pm
I'm not sure about the whole super-dragon thing and some of the other details, but that leg + decelerator combined design is really clever.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 08/25/2016 10:38 pm
My first memory of a deployable decelerator like that was the TGV  MICHELLE 2 Ansari X-Prize entrant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/26/2016 01:38 am
Yes something like that, though I expect a much shorter vehicle then that depiction or the one Murdock mocked up, the fundamentals of the deployment are what I was envisioning.  A base first entry is the most likely entry orientation but I'm not  entirely ruling out nose first entry.  In the base first configuration I would expect a heat-shield to cover most of the vehicle base with immovable engines nozzles flush to the heat-shield and located around the perimeter. 

Using the ribs as landing legs is not something I'm comfortable endorsing, the leg system needs to absorb shock which is a very different function from the ribs of a decelerator which need to be stiff, if the system were only used once some kind of crumple system might work but reusability is a must and bringing the ribs down in contact with the surface presents a danger to the fabric as well as complicates unloading and launch.  A more likely leg configuration is like that on Dragon v2, telescoping out from heat shield with a segment of the shield forming the foot.

Lastly I should note that I see the whole side of the vehicle folding down like a petal not just a set of singular ribs that are visible on the outside of the vessel, when the system is stowed it is all under a smooth shell which covers the whole vehicle.  This allows delicate systems intended for use in space to be stowed under the petals, such as radiators and solar panels, I see solar being on the underside of the petals and radiators on the sides of the vehicle body, this allows the vehicle to fly through space with the nose pointing sun-ward which will illuminate the panels and shade the radiators.

Lastly some estimates on mass, as noted earlier the leg system on F9 masses 2500 kg, carbon fiber fabric 5 layers thick totaling 1 kg/m^2 and covering the space between a 15 m base and a 51 m total diameter would be 1800 m and kg bringing total mass to 4.3 mt, a very modest amount that would be far lighter then carrying extra propellant.  The propellant needed for just the last bit of deceleration and up to landing is going to need to do around 800 m/s based on extrapolation from Red Dragon, and that's going to come out to around 20 percent propellant fraction minimum.  I'm estimating 200 mt at entry and 40 mt of landing propellant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 08/26/2016 08:39 am
Regarding ballistic coefficients, I've attached a table that compares several designs, including a hypothetical BFS with the same ballistic coefficient as Red Dragon.

SpacecraftDiameter mArea m^2Volume m^3Mass mTBallistic coefficientSidewall angle °Peak gsEntry velocity km/s
MSL4.515.21?3.314840155.8
Soyuz2.23.843789747.6
Cargo dragon3.710.75107.2515154.57.6
Red dragon3.710.751010715157.49.6
BFS22380.13400035771530?412

Is there any particular reason why Mars atmospheric entry velocities would be as high as 9-12km/s for the Red Dragon and BFS? I would expect them to be on the same order of past Mars missions (that is, 5-7km/s)...

As to BFS Musk has said that he wants shorter trip times, so shorter trip times equates to higher Km/sec entry velocity

Not necessarily. You just need more fuel to slow down before you get to entry.

Not a great mission profile wasting valuable rocket equation exponential propellant when the atmosphere gives the delta V to you if you are very clever in your spacecraft design and guidance.

Never said it was a good idea, just that it was a possible idea, as the previous post needed correction. Although depending on how good your craft design is, you MIGHT need to slow down to get to a survivable entry speed, if you want fast transit times.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 08/26/2016 11:27 am
Lastly some estimates on mass, as noted earlier the leg system on F9 masses 2500 kg, carbon fiber fabric 5 layers thick totaling 1 kg/m^2 and covering the space between a 15 m base and a 51 m total diameter would be 1800 m and kg bringing total mass to 4.3 mt, a very modest amount that would be far lighter then carrying extra propellant.  The propellant needed for just the last bit of deceleration and up to landing is going to need to do around 800 m/s based on extrapolation from Red Dragon, and that's going to come out to around 20 percent propellant fraction minimum.  I'm estimating 200 mt at entry and 40 mt of landing propellant.

Reducing dry mass will have priority since the architecture is constrained by the return leg. The main benefit of something like HIAD would be its lower mass compared to a mid L/D aeroshell.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Eerie on 08/26/2016 02:57 pm
I have a totally crazy idea, feel free to shoot it down.

The idea is a Tri-propellant (but not really) MCT.

Assuming that:
1. Methalox engines are required for utilizing Mars-side ISRU.
2. Most payload mass will only go one way: Earth to Mars.

How much sense would it make to use Hydrolox engines for the Mars-bound half of the trip?
Basically, you use highly efficient Hydrolox engines to get to Mars, use ISRU there to fill the hydrogen tank with methane, and use Raptors to go back home (and I know, the tank volume ratios are problematic).

You may say, but SpaceX doesn't have Hydrolox engines. True, but Blue Origin does. One good enough to land, too. :-)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/26/2016 02:58 pm
I have a totally crazy idea, feel free to shoot it down.

The idea is a Tri-propellant (but not really) MCT.

Assuming that:
1. Methalox engines are required for Mars-side ISRU.
2. Most payload mass will only go one way: Earth to Mars.

How much sense would it make to use Hydrolox engines for the Mars-bound half of the trip?
Basically, you use highly efficient Hydrolox engines to get to Mars, use ISRU there to fill the hydrogen tank with methane, and use Raptors to go back home (and I know, the tank volume ratios are problematic).

You may say, but SpaceX doesn't have Hydrolox engines. True, but Blue Origin does. :-)
You'd actually get much more performance by filling the tanks with methane than with hydrogen.

Hydrogen has terrible density, so you could fit a LOT more methane in there than hydrogen.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Eerie on 08/26/2016 03:16 pm
You'd actually get much more performance by filling the tanks with methane than with hydrogen.

Hydrogen has terrible density, so you could fit a LOT more methane in there than hydrogen.

This doesn't make sense. There is a reason Saturn 5, STS, SLS and the Centaur all use hydrolox...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/26/2016 03:18 pm
Hydrogen already has a lot of negative design trades, and if you add in the requirement that the system also has to burn methane equally well, there's no good reason to use hydrogen at all.

And the tank volume ratios are more than slightly problematic. The hydrogen tank to put 180 tonnes through TMI and EDL would be more than 7 times larger in volume than the methane tank needed to return a 80 tonne vehicle from Mars surface to Earth's surface. It would be larger in volume than most estimates for the entire BFR booster.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/26/2016 03:21 pm
You'd actually get much more performance by filling the tanks with methane than with hydrogen.

Hydrogen has terrible density, so you could fit a LOT more methane in there than hydrogen.

This doesn't make sense. There is a reason Saturn 5, STS, SLS and the Centaur all use hydrolox...

The main reason is that obscene costs weren't a deal-breaker for those programs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Eerie on 08/26/2016 03:24 pm
Hydrogen already has a lot of negative design trades, and if you add in the requirement that the system also has to burn methane equally well, there's no good reason to use hydrogen at all.

And the tank volume ratios are more than slightly problematic. The hydrogen tank to put 180 tonnes through TMI and EDL would be more than 7 times larger in volume than the methane tank needed to return a 80 tonne vehicle from Mars surface to Earth's surface. It would be larger in volume than most estimates for the entire BFR booster.

...on the positive side, a huge MCT means a great ballistic coefficient for Mars aerobraking/landing. :-)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/26/2016 03:38 pm
You'd actually get much more performance by filling the tanks with methane than with hydrogen.

Hydrogen has terrible density, so you could fit a LOT more methane in there than hydrogen.

This doesn't make sense. There is a reason Saturn 5, STS, SLS and the Centaur all use hydrolox...
And if you switched those stages over to methane with the same total tank volume, the stages would weigh more, but they'd give you a much higher performance. More payload to higher delta-v, GIVEN the same starting point.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: IntoTheVoid on 08/26/2016 03:40 pm
Assuming that:
1. Methalox engines are required for utilizing Mars-side ISRU.
2. Most payload mass will only go one way: Earth to Mars.
False assumption.
Mars ISRU is not capturing existing methane as we do on earth. Mars ISRU envisions building the methane from water derived H2 and atmospheric CO2. If the system had H2 engines and tanks you'd refill them with H2 and skip the methane altogether.

In other words, if the trades worked in hydrogen's favor, there's nothing preventing them from building a hydrogen rocket without the methane. Since they have chosen to build a methane rocket, one might presume that the trades did not work in hydrogen's favor. Quite possibly for some of the reasons mentioned above.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/26/2016 03:42 pm
Assuming that:
1. Methalox engines are required for utilizing Mars-side ISRU.
2. Most payload mass will only go one way: Earth to Mars.
False assumption.
Mars ISRU is not capturing existing methane as we do on earth. Mars ISRU envisions building the methane from water derived H2 and atmospheric CO2. If the system had H2 engines and tanks you'd refill them with H2 and skip the methane altogether.

In other words, if the trades worked in hydrogen's favor, there's nothing preventing them from building a hydrogen rocket without the methane. Since they have chosen to build a methane rocket, one might presume that the trades did not work in hydrogen's favor. Quite possibly for some of the reasons mentioned above.

Good point, however remember that hydrogen is terrible for storing on Mars. And for the same mass of propellant, if you used hydrogen on Mars, it'd require much more water to be mined than if you used methane.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 08/26/2016 05:28 pm
You'd actually get much more performance by filling the tanks with methane than with hydrogen.

Hydrogen has terrible density, so you could fit a LOT more methane in there than hydrogen.

This doesn't make sense. There is a reason Saturn 5, STS, SLS and the Centaur all use hydrolox...

It makes complete and perfect sense. The tanks are volume constrained. Hydrogen has high ISP but very low ISP Density. Given equal masses of H2 vs CH4, the H2 has more energy. However, you need around five or more times the volume to contain that Hydrogen. Given equal volumes of H2 and CH4, there is far more impulse energy packed into the methane. If you fly to Mars on H2, you need fuel tanks roughly 5 times the size that BFS currently has. Once you put CH4 into them on Mars, you only fill them 20% full for equal amount of needed energy. Now you have a whole bunch of wasted mass in the form of the oversized fuel tank.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Eerie on 08/26/2016 06:29 pm
Thanks for demolishing my proposal. :-)

So, I am correct to understand that the increased mass of the tanks would eat all the performance gains from using Hydrolox?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/26/2016 06:43 pm
Thanks for demolishing my proposal. :-)

So, I am correct to understand that the increased mass of the tanks would eat all the performance gains from using Hydrolox?
It depends. If your initial mass isn't a constraint, then for the same tanks, you're better off with methane.

If your initial mass is your greatest constraint (and you're able to vary tank size), then hydrogen provides better performance.

If neither are really constraints, and you're just asking what the burn-out mass of an empty stage would be using either technology (and a very small payload), then it's kind of a toss-up.

With ISRU on Mars, initial mass of the stage is not such a concern. Maybe ISRU power is the greatest constraint, in which case methane may be the better option (though this depends on how fast you intend to launch the ascent vehicle back to Earth).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/26/2016 07:27 pm
Approaching 30 days from what (we hope) is the big reveal, I thought it a good time to revisit and post revised BFR/MCT speculation before any info leaks out.  Trying to stay within the parameters of what Musk has said as I best understand.  A TSTO vehicle launched by a re-useable, single core BFR that puts the BFS a.k.a. the MCT into LEO where it is re-fueled, travels to and lands on Mars where it is again refueled for the journey back to Earth carrying a quarter of the outbound “cargo” mass.  The outbound cargo masses 100 tonnes which I assume means either cargo or people or a combination thereof.  BFS/MCT mass not included in the 100T.

Myriad unknowns led by the dry mass of the BFS.  Rocket equation dictates various mass assumptions here can produce wildly different answers.

My predictions, metric unless otherwise stated:
1.   Entire launch vehicle BFR+BFS masses under 5,000T.  Guestimate ~4,500T.
2.   BFS dry mass < 100T, my pick is 85T carbon composites BUT heavier than some predictions because ruggedized to allow for minimal maintenance.
3.   BFR absolutely > 10m diameter to fit enough engines. Likely between 12.5 and 15m.  My guess 15m.  Allows addition of more engines in the future.
4.   My guestimate BFR+BFS stack <100m height.  Certainly <125m.
5.   Sticking with the “over 230T” Raptor thrust Elon mentioned, I get 25-27 engines.  My guestimate is 26 with “over 230T” as 235T in my spreadsheet.  Around 13.5 million Lbs force.
Engine # most likely wrong because…
6.   Predict that Raptor engine design goal thrust changed to higher than 230T previously stated, but only by several 10s of tonnes, not hundreds.
7.   BFS with 5 Rvac engines
8.   RTLS minimizes cost, turnaround time, effort.  Changed my opinion from max payload ASDS for those reasons.  Just make the BFR bigger. Stages low and slow ~2.2 Km/sec.  “Easy” recovery & re-flight vs F9 GTO flights.
9.   Initial BFR test flights likely equipped with less engines and less payload.
10.   Large crew volume design >2,000m3.  Initial flights with less people & people space but more cargo space.
11.   Initial crewed Mars mission will carry 6-12 people.  10 is my latest #. Why?
NASA & other nations will buy seats. 
http://forum.nasaspaceflight.com/index.php?topic=40683.msg1557261#msg1557261
12.   SEP still under development awaits later opposition cargo transits
13.   BFS will have “exotic” upper mounted engines for rough terrain Mars landing &takeoff (just echoing others’ analysis here)
14.   BFS will be a lifting body for EDL, but not a scaled up Dragon capsule shape.  It will look badass.

You know we’re totally screwed trying to predict Musk because he already warned us,
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

I’ve attached a spreadsheet showing different assumptions, BFS mass, etc.

Anyone else want to update their speculations?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/26/2016 08:32 pm
Lastly some estimates on mass, as noted earlier the leg system on F9 masses 2500 kg, carbon fiber fabric 5 layers thick totaling 1 kg/m^2 and covering the space between a 15 m base and a 51 m total diameter would be 1800 m and kg bringing total mass to 4.3 mt, a very modest amount that would be far lighter then carrying extra propellant.  The propellant needed for just the last bit of deceleration and up to landing is going to need to do around 800 m/s based on extrapolation from Red Dragon, and that's going to come out to around 20 percent propellant fraction minimum.  I'm estimating 200 mt at entry and 40 mt of landing propellant.

Reducing dry mass will have priority since the architecture is constrained by the return leg. The main benefit of something like HIAD would be its lower mass compared to a mid L/D aeroshell.

That is very shortsighted their are important trades to be made for each unit of dry mass, simply aiming for the lowest possible dry mass would give us an expendable centaur stage.  A decelerator is clearly going to save mass at Mars entry, I'd even argue that entry is impossible without it.  And given the entry speed that will be experienced at Earth return it will be useful their as well by allowing lower peak g-forces during entry and a lower terminal velocity in the lower atmosphere which means less propellant needed at landing and more safety margin.  If the decelerator can cut the deceleration needs of the terminal landing burn by just 150 m/s it's more efficient then it's mass in propellant.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 08/26/2016 11:10 pm
Regarding decelerator devices...
Isn't it somewhat counter-intuitive to put them at the front of the vehicle? Wouldn't such a vehicle normally flip around to have the area of maximum resistance at the back?
I am thinking that any large-scale decelerators should be deployed at the rear of the vehicle, as a form of drogue chute. That would give a heatshield of vehicle diameter at the front and a large-diameter deployable decelerator trailing behind, to create a stable configuration. And no, I am not just talking about a parachute, because I think of a much more robust device, be it with fins or petals or whatever the aerodynamicists can come up with.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/27/2016 12:41 am
Regarding decelerator devices...
Isn't it somewhat counter-intuitive to put them at the front of the vehicle? Wouldn't such a vehicle normally flip around to have the area of maximum resistance at the back?
I am thinking that any large-scale decelerators should be deployed at the rear of the vehicle, as a form of drogue chute. That would give a heatshield of vehicle diameter at the front and a large-diameter deployable decelerator trailing behind, to create a stable configuration. And no, I am not just talking about a parachute, because I think of a much more robust device, be it with fins or petals or whatever the aerodynamicists can come up with.

The decelerator designs are generally inherently stable in either direction once they have commenced their descent into the atmosphere. The hypersonic heating rate is proportional to velocity cubed, and to the inverse of the square root of the atmospheric density divided by the leading edge radius.

HeatingRate = 1.83e-4 * Math.Pow(speed, 3) * Math.Sqrt(atmosphericDensity / HeatingRadius());

So, the larger the leading edge radius (i.e. the blunter the body), the lower the heating rate. Although perhaps counter-intuitive, this is why the decelerator is best positioned at the front of the vehicle. I've attached a few design alternatives below.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CyclerPilot on 08/27/2016 01:23 am


Approaching 30 days from what (we hope) is the big reveal, I thought it a good time to revisit and post revised BFR/MCT speculation before any info leaks out.  Trying to stay within the parameters of what Musk has said as I best understand.  A TSTO vehicle launched by a re-useable, single core BFR that puts the BFS a.k.a. the MCT into LEO where it is re-fueled, travels to and lands on Mars where it is again refueled for the journey back to Earth carrying a quarter of the outbound “cargo” mass.  The outbound cargo masses 100 tonnes which I assume means either cargo or people or a combination thereof.  BFS/MCT mass not included in the 100T.

Myriad unknowns led by the dry mass of the BFS.  Rocket equation dictates various mass assumptions here can produce wildly different answers.

My predictions, metric unless otherwise stated:
1.Entire launch vehicle BFR+BFS masses under 5,000T.  Guestimate ~4,500T.
2.BFS dry mass < 100T, my pick is 85T carbon composites BUT heavier than some predictions because ruggedized to allow for minimal maintenance.
3.BFR absolutely > 10m diameter to fit enough engines. Likely between 12.5 and 15m.  My guess 15m.  Allows addition of more engines in the future.
4.My guestimate BFR+BFS stack <100m height.  Certainly <125m.
5.Sticking with the “over 230T” Raptor thrust Elon mentioned, I get 25-27 engines.  My guestimate is 26 with “over 230T” as 235T in my spreadsheet.  Around 13.5 million Lbs force.
Engine # most likely wrong because…
6.Predict that Raptor engine design goal thrust changed to higher than 230T previously stated, but only by several 10s of tonnes, not hundreds.
7.BFS with 5 Rvac engines
8.RTLS minimizes cost, turnaround time, effort.  Changed my opinion from max payload ASDS for those reasons.  Just make the BFR bigger. Stages low and slow ~2.2 Km/sec.  “Easy” recovery & re-flight vs F9 GTO flights.
9.Initial BFR test flights likely equipped with less engines and less payload.
10.Large crew volume design >2,000m3.  Initial flights with less people & people space but more cargo space.
11.Initial crewed Mars mission will carry 6-12 people.  10 is my latest #. Why?
NASA & other nations will buy seats. 
http://forum.nasaspaceflight.com/index.php?topic=40683.msg1557261#msg1557261
12.SEP still under development awaits later opposition cargo transits
13.BFS will have “exotic” upper mounted engines for rough terrain Mars landing &takeoff (just echoing others’ analysis here)
14.BFS will be a lifting body for EDL, but not a scaled up Dragon capsule shape.  It will look badass.

You know we’re totally screwed trying to predict Musk because he already warned us,
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

I’ve attached a spreadsheet showing different assumptions, BFS mass, etc.

Anyone else want to update their speculations?

Wow.   Time flies.  September is almost here.  Great list.  I agree with most of what you have but had a few differences.

I think the dry mass needs to be 70k or less.  This mass has to be accelerated so many times, there is immense financial and archetecture-feasibility pressure to trim dry mass. The return leg is a killer and the return cargo mass quickly falls to zero for some synodes if the dry mass is too high.

For BFS engines, I think 4 or 5 is a good number.  4 around the perimeter could allow for any one engine to be out and maintain a symmetric thrust.  With 5, having one central engine helps obviously,  but I think adding a 5th eats up dry mass budget.  Having a 5th raptor helps with gravity losses at earth launch, but is mostly dead weight the rest of the trip.

I think if the raptor was slightly less powerful, 5 would be perfect.  I think the raptor will actually start with lower thrust than has been publicly shared.  They will increase chamber pressure on later iterations to increase thrust and isp.

As for exotic upper mounted engines, I used to think they were required, but now I think terminal landing will be done on raptors alone (again to save dry mass).  For this to be possible from the first BFS landing will require scouting an appropriate flat solid rock surface and a dragon placed rover to sweep away any rocks/pebbles and place beacons to allow for guidance to the landing pad within a few meters.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 08/27/2016 02:28 am
Regarding decelerator devices...
Isn't it somewhat counter-intuitive to put them at the front of the vehicle? Wouldn't such a vehicle normally flip around to have the area of maximum resistance at the back?
I am thinking that any large-scale decelerators should be deployed at the rear of the vehicle, as a form of drogue chute. That would give a heatshield of vehicle diameter at the front and a large-diameter deployable decelerator trailing behind, to create a stable configuration. And no, I am not just talking about a parachute, because I think of a much more robust device, be it with fins or petals or whatever the aerodynamicists can come up with.
That's an option, but would have lower drag and wouldn't protect the rest of the vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/27/2016 03:20 am
As for exotic upper mounted engines, I used to think they were required, but now I think terminal landing will be done on raptors alone (again to save dry mass).  For this to be possible from the first BFS landing will require scouting an appropriate flat solid rock surface and a dragon placed rover to sweep away any rocks/pebbles and place beacons to allow for guidance to the landing pad within a few meters.

Whilst I agree that Raptors alone would save dry mass, as well as removing the dependency on two successfully serialised miracles, if a Red Dragon could safely land on an unprepared Martian surface, why couldn't a BFS, especially if it resembles a scaled up Dragon?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Chris_Pi on 08/27/2016 03:57 am
Whilst I agree that Raptors alone would save dry mass, as well as removing the dependency on two successfully serialised miracles, if a Red Dragon could safely land on an unprepared Martian surface, why couldn't a BFS, especially if it resembles a scaled up Dragon?

A Red Dragon's heat shield and motors don't need to survive past touchdown. Safe for it is no destructive motor failures. Gouging up the heatshield and throwing rocks up into motors is fine as long as it can land once. A vehicle that has to take off again and do another re-entry needs an intact heatshield and motors for Earth return.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/27/2016 04:15 am
Whilst I agree that Raptors alone would save dry mass, as well as removing the dependency on two successfully serialised miracles, if a Red Dragon could safely land on an unprepared Martian surface, why couldn't a BFS, especially if it resembles a scaled up Dragon?

A Red Dragon's heat shield and motors don't need to survive past touchdown. Safe for it is no destructive motor failures. Gouging up the heatshield and throwing rocks up into motors is fine as long as it can land once. A vehicle that has to take off again and do another re-entry needs an intact heatshield and motors for Earth return.

Sure, the BFS has to take off again, but why are you so sure rocks would be thrown up into the motors? If the Raptors were sufficiently canted, wouldn't they direct ejecta away from the spaceship?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/27/2016 04:26 am
I would hardly consider a set of pressure fed engines firing on touch-down to be a 'miracle', it's a normal and standard part of the Soyuz capsule landing after all.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 08/27/2016 04:29 am
If the Raptors were sufficiently canted, wouldn't they direct ejecta away from the spaceship?

Launching directly back to Earth is the highest demanding part of the missioną, those first moments of take-off from the Martian surface will have the highest fuel load and hence require maximum thrust. You can't afford cosine losses of canted engines. Otherwise the stage is overpowered for every other part of the missions, and hence wasting mass.˛

ą Unless Musk has something extra up his sleeve, like Mars orbital refuelling.
˛ Unless the BFS is built entirely around SuperDraco-like side-mount engines; hence is sized for cosign losses at all stages.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 08/27/2016 04:38 am
Approaching 30 days from what (we hope) is the big reveal, I thought it a good time to revisit and post revised BFR/MCT speculation before any info leaks out. [...]
Anyone else want to update their speculations?

Shotwell dropped the name Falcon 20 for the BFR. Either a play on Falcon XX (from the early Great-Chart-Of-SpaceX), or signifying the number of Raptor engines. (Or perhaps the first-stage diameter in metres ...what?)

So I'll speculate that we're gonna have to get used to another set of names for both BFR and BFS.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/27/2016 05:52 am
I would hardly consider a set of pressure fed engines firing on touch-down to be a 'miracle', it's a normal and standard part of the Soyuz capsule landing after all.

Every time a mission critical event in deep space succeeds, it is a (tongue firmly in cheek) 'miracle'. To paraphrase Elon, part of good spaceship design is minimising the number of serialised miracles that need to occur.

If the Raptors were sufficiently canted, wouldn't they direct ejecta away from the spaceship?

Launching directly back to Earth is the highest demanding part of the missioną, those first moments of take-off from the Martian surface will have the highest fuel load and hence require maximum thrust. You can't afford cosine losses of canted engines. Otherwise the stage is overpowered for every other part of the missions, and hence wasting mass.˛

Please bear in mind, I don't expect the engines to be canted for the entire mission. However, it would help optimise SRP if the ability to cant existed, and it would also help for Mars landing and re-launch. If there are five Raptors, as most people seem to believe, then available thrust will greatly exceed the weight of the spaceship in Martian gravity, so you could certainly afford large cosine losses at that point. The real challenge is the ΔV requirement back to Earth. As you suggest, LMO refuelling could help with that.

From the simulations I've done, the point at which maximum thrust is most required is the ascent from Earth to LEO, immediately after BFR MECO, when BFS thrust to weight is less than 1 for a short period. For the rest of the mission, 4 or even 3 Raptors are sufficient, but having 5 provides redundancy.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 08/27/2016 06:21 am

Shotwell dropped the name Falcon 20 for the BFR. >

Source?

Or, she could be talking a Dassault Falcon 20 business jet. SpaceX has used Falcon jets in the past.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 08/27/2016 06:23 am
Regarding decelerator devices...
Isn't it somewhat counter-intuitive to put them at the front of the vehicle? Wouldn't such a vehicle normally flip around to have the area of maximum resistance at the back?

With HIAD the center of gravity must be sufficiently low and offset to create lift. It's really no different from a capsule in that respect.

Some of the concepts here which show a long cylinder on a small inflatable aren't realistic IMO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/27/2016 06:45 am
Regarding decelerator devices...
Isn't it somewhat counter-intuitive to put them at the front of the vehicle? Wouldn't such a vehicle normally flip around to have the area of maximum resistance at the back?

With HIAD the center of gravity must be sufficiently low and offset to create lift. It's really no different from a capsule in that respect.

Some of the concepts here which show a long cylinder on a small inflatable aren't realistic IMO.

For high velocity Mars EDL, yes, I agree. However, for Earth entry, especially from LEO, lift is less of a requirement. For example IRVE-3, which is quite a long cylinder, has been successfully demonstrated.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/27/2016 07:19 am
I would hardly consider a set of pressure fed engines firing on touch-down to be a 'miracle', it's a normal and standard part of the Soyuz capsule landing after all.

Every time a mission critical event in deep space succeeds, it is a (tongue firmly in cheek) 'miracle'. To paraphrase Elon, part of good spaceship design is minimising the number of serialised miracles that need to occur.


No neither Musk nor any other engineer ever said that every event is a miracle, a real engineer understands the difficulty and likely-hood for success of every event so that an intelligent optimum between cost, safety and performance can be found. 

Pressure fed engines involve valves opening and closing and are orders of magnitude more reliable then a turbo-pump engines like Raptor which we know have to fire several times in mission critical situations.  Protecting thouse big delicate engines is the reason for having touchdown engines, so your trading one risk for another and if you did your homework you reduced total risk. 

Simply saying that less systems and less events is safer is a gross mutilation of the point Musk is trying to make which is about DEVELOPMENT risk not flight risk, but because SpaceX already has an excellent pressure fed engine the development risk is minimal.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 08/27/2016 07:57 am
Regarding decelerator devices...
Isn't it somewhat counter-intuitive to put them at the front of the vehicle? Wouldn't such a vehicle normally flip around to have the area of maximum resistance at the back?

With HIAD the center of gravity must be sufficiently low and offset to create lift. It's really no different from a capsule in that respect.

Some of the concepts here which show a long cylinder on a small inflatable aren't realistic IMO.

For high velocity Mars EDL, yes, I agree. However, for Earth entry, especially from LEO, lift is less of a requirement. For example IRVE-3, which is quite a long cylinder, has been successfully demonstrated.

The CG offset is needed to create lift, but even if you do not need lift the center of gravity must be sufficiently low. The shape of the payload doesn't really matter, as long as the CG is low relative to the cone of the inflatable (to be more precise: There must be sufficient distance between center of gravity and center of pressure for stability).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Semmel on 08/27/2016 08:58 am
Ok, I have not posted many speculations in the past, but here it is:

1. Diameter of BFR ~15 m. The shorter and wider it is, the easier it is to land. Also, I assume that the dV of BFR before staging is around the same as for dragon flights to allow for RTLS in all launches.

2. The BFS will be its own second stage and will be designed to maximize vehicle volume rather than utilize HIAD or other deployables for EDL. This has two advantages: Less failure modes and higher Habitat volume once landed. It has the disadvantages of more dry mass and more difficult landing on Mars and Earth. I assume for that reason that the thrust structure of BFS will have 5 to 6 vacuum Raptors. First to minimize gravity losses on Earth assent due to early staging and for redundancy during transit and return.

3. The first version of BFS will be designed to service LEO and GTO missions. Maybe also a trip around the moon for fun (not a serious suggestion). That has many advantages vs. going directly to Mars: Faster turn around time for testing hardware and procedures; no deep space communications; no deep space navigation; no long term propellant storage; no Mars EDL on the first few flights; can generate revenue for GTO and LEO missions. Eventually all above mentioned things have to be solved but this way, some of the near earth problems can be solved before going to Mars.

4. The first BFS/MCT mission to Mars will be a technology demonstrator. It will carry an atmosphere scrabber and maybe able to extract water from the atmosphere for slow fuel production. It might carry some equipment to test the soil for water but no water mining from the ground. I expect that they will concentrate on demonstrate Methane production with the little water from the atmosphere without the goal of filling the tank. LOX production will be on large scale though, with the intent to fill the tank by the time the second BFS/MCT launches from Earth. The energy will come from solar panels. The BFS/MCT will contain enough food and water to supply the crew of the next mission for redundancy. This BFS/MCT will stay on Mars.

5. The second BFS/MCT mission to Mars will have crew of approx 10, one synod after the first successful demonstrator BFS/MCT. The crew BFS/MCT will be the base, no habitat will be brought along. The mission for the first crew will be to return safely one synod later. The task will be to mine the soil for water and execute large scale methane production. The LOX from the first mission will be transferred to the returning BFS/MCT, so no LOX mining equipment will be present. The first landed BFS/MCT will supply any spare parts required for the second BFS, also the food and other consumables transported in the first BFR/MCT are there in case the crew can not leave and has to stay an other synod. The majority of Marstronauts will probably not be SpaceX employees but come from NASA, Roscosmos, ESA, JAXA, India, China, etc. Musk is advertising competition but I think he will not reject the opportunity to sell a seat for ~200 Million a peace to who ever wants to pay.

6. There will be no tanker version of BFR at first. The BFS will be refuelled using a FH Raptor upper stage tanker. The reason for this is, that they dont have rapid re-usability of the BFR just yet. This will be replaced in due time by a tanker BFS but not for the first missions. This has the advantage to supply a Raptor upper stage for FH as the contract with the AF sais and it allows SpaceX to develop a reusable second stage for the Falcon family as well as boost their F9 performance to GTO to allow for RTLS even for GTO F9 missions.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/27/2016 09:07 am
There must be sufficient distance between center of gravity and center of pressure for stability.

Agreed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 08/27/2016 01:45 pm
Please bear in mind, I don't expect the engines to be canted for the entire mission.

That was my point. At a time when the vehicle is maximally loaded, needing high thrust, you are deliberately tilting the engines away.

Therefore you need more thrust for this moment, therefore when the engines aren't canted, they are overpowered (oversized) for every other part of the mission.

(As I said in my addendum, it only makes sense if they are perma-canted. I mean, you still get the wasted engine mass, but presumably it is being paid off by some other aspect, such as a simpler re-entry shape.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/27/2016 04:52 pm
Staging requires more thrust than any other point in the BFS mission. It's in a bigger gravity well, with a full fuel load and a full payload.

A vehicle that can stage during Earth launch with 100t payload can easily liftoff from Mars with a 25t payload.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Chris_Pi on 08/27/2016 06:09 pm
Whilst I agree that Raptors alone would save dry mass, as well as removing the dependency on two successfully serialised miracles, if a Red Dragon could safely land on an unprepared Martian surface, why couldn't a BFS, especially if it resembles a scaled up Dragon?

A Red Dragon's heat shield and motors don't need to survive past touchdown. Safe for it is no destructive motor failures. Gouging up the heatshield and throwing rocks up into motors is fine as long as it can land once. A vehicle that has to take off again and do another re-entry needs an intact heatshield and motors for Earth return.

Sure, the BFS has to take off again, but why are you so sure rocks would be thrown up into the motors? If the Raptors were sufficiently canted, wouldn't they direct ejecta away from the spaceship?

I'm pretty sure there's a link to the article around here somewhere - I do vaguely remember reading it, But I can't find it right now. Very short version is high-thrust motors close to the surface dig really deep holes that throw junk back at the motors. Either have a prepared pad, keep the motors far away, or build something that can take the beating. The Curiosity rover ended up with quite a lot of big gravel all over the top and visible gouges in the ground from the skycrane motors. And those were at the top end of 25 feet of cable and canted somewhat.

I'm wondering about a rover with a solar concentrator to melt a thin layer of surface material in place as a solidified layer.  Presuming this layer didn't crack too badly it should make a good surface for a landing pad or road.
Don't know but intuition says anything less than one m thick under MCT will be flying FOD.

###

ADDED: Your question deserves a better answer so I looked up what NASA scientists have found in their studies. The following statement is a verbatim copy of a summary that addresses the problem. It was a section of the Mars Design Reference Architecture, Addendum A,  published in 2009:

"5.9.1 Summary and recommendations
The predictions and recommendations for a 40-t spacecraft on Mars are described in summary in this section. The next section of the report will then explain in detail how these predictions were obtained.
The engine exhaust plume from a 40-t lander on Mars will blow dust, sand, gravel, and even rocks up to about 7 cm in diameter at high velocity. These ejecta will cause significant damage to any hardware that is already placed on the martian surface within the blast radius. However, the blast radius is modest, extending out to approximately 1 km. The largest debris is accelerated by the plume to lower velocities and, thus, falls closer to the landing site; and the smallest particles are attenuated by the martian atmosphere, also falling closer to the landing. Thus, maintaining the distance of about 1 km between the landing site and any existing surface assets will completely solve this problem for all sizes of debris.
A second concern arises because the exhaust from the large engines will form deep, narrow craters that are directly beneath each of their nozzles, and these craters will redirect the supersonic jet of gas with sand and rocks up toward the landing spacecraft. This has been demonstrated in large-scale engine tests in sand and clay (Alexander, et al, 1966) 25, small-scale experiments (Metzger, 2007) 26, numerical simulations (Liever, et al, 2007) 27, and soil dynamics analysis (see section 5.10.2.3), so there is no question that this will occur. It did not occur in the Apollo and Viking missions because the thrust was lower and/or because the lunar regolith had higher shear strength and less permeability than martian soil. These variables have been taken into consideration in this report. An example of a small-scale test is provided in figure 5-55. The impact of debris striking the lander will be sufficient to cause damage to the lander, possibly resulting in LOM and LOC, and therefore must be prevented. Of special concern is damage to the engine nozzles, because with a multiple-engine lander the debris that is ejected by one engine will be aimed directly at the other engines. One mitigation approach is to add shielding to the spacecraft to block the debris. This will increase the mass of the lander and, therefore, reduce the mass of the payload by approximately 1 t."
Title: Re: MCT Speculation and Discussion Thread 4
Post by: the_other_Doug on 08/27/2016 07:07 pm
Someone suggested the possibility that MCT/BFS is just a massively scaled-up Crew Dragon.  While I'm sure other things are happening than that, it did get me to thinking that arranging BFS's Raptors in the same "covered dugout" configuration that Crew Dragon uses for its Super Draco's might be the winning guess.

First, you could just fill the space between the outer and inner hulls with your fuel and oxidizer, inside big bladders.  This might also be one of the boil-off and radiation remediation strategies.  Locating the engines in pods around the circumference also lets you cant them out or swivel them in to the true plus-X direction, as needed.  It lets you have TPS flaps over the Raptor dugouts that let you enter from orbital and super-orbital speeds without damaging the engines, and that can be deployed down to clear the engines for retro-propulsion.  And it lets you have a bottom-end cargo hatch that opens up from the base heat shielding.

It wouldn't surprise me to see such a design.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/28/2016 03:57 am
I'm pretty sure there's a link to the article around here somewhere - I do vaguely remember reading it, But I can't find it right now. Very short version is high-thrust motors close to the surface dig really deep holes that throw junk back at the motors. Either have a prepared pad, keep the motors far away, or build something that can take the beating. The Curiosity rover ended up with quite a lot of big gravel all over the top and visible gouges in the ground from the skycrane motors. And those were at the top end of 25 feet of cable and canted somewhat.

Yes, they dig deep holes if the plume is vertical. You can test this for yourself with a high pressure water hose on dirt. As you increase the 'cant' of the hose there comes a point at which a trench rather than a hole is created, and no ejecta comes back towards you. The MSL skycrane was only canted at about 20°, and that was obviously not sufficient to prevent damage to the lander. The plume from a rocket on Mars is surprisingly long and narrow at low altitude, so even though the skycrane engines were at an altitude of 7.5m, four fairly tight craters were formed. So, even if you are prepared to accept the additional mass and complexity, it is not enough to have a secondary set of rocket engines high up on the BFS, the key is how canted they are. For efficient SRP, BFS should be able to cant the engines to at least 45°, which may or may not be sufficient to prevent damage.

An additional concern is the operational risk associated with the creation of a dependency on a second propulsion system. At the point that you might transition to the second system, the Raptors are already running. The chances that they will continue to run until touchdown are extremely good. To shut them down and start a second system at that point sounds to me like the higher risk option. I'd only attempt it if there was no other choice. Anyway, we'll all know what SpaceX have decided in a month, I can't wait.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 08/28/2016 05:29 am
... but why are you so sure rocks would be thrown up into the motors? If the Raptors were sufficiently canted, wouldn't they direct ejecta away from the spaceship?

Fluid dynamics is extremely complex. Gasses swirl in ways that are sometimes impossible to model even on supercomputers. Ever shake one of those lava lamp jars? The variables involved are almost infinite and landing on a surface whose characteristics are not completely known is not something to take lightly.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 08/28/2016 05:51 am
Someone asked me about my "Shotwell called BFR 'Falcon 20'" comment. I've been trying to find where I read about it, but I didn't keep it, and I can't find it in my browser history. It was a recent, no more than a month ago. But... No sauce means no meat.

Quote
"5.9.1 Summary and recommendations
[...] It did not occur in the Apollo and Viking missions because the thrust was lower and/or because the lunar regolith had higher shear strength and less permeability than martian soil. [...] "

Also the Viking didn't relaunch, and the Apollo LM's had two stages, so the descent stage protected the ascent engine. And neither of them had to protect a heat shield for Earth re-entry.

Staging requires more thrust than any other point in the BFS mission. It's in a bigger gravity well, with a full fuel load and a full payload.

We don't know the final delta-v of the first stage at separation. If it works anything like conventional launches, then the delta-v for a second stage to LEO is much less than the delta-v from Mars surface to direct Earth return.

Of course, the BFS has to land on Earth as well, so who knows what work-around they have for that. Second set of engines? 1atm nozzles? Side-mount canted nozzles?

Someone suggested the possibility that MCT/BFS is just a massively scaled-up Crew Dragon.  While I'm sure other things are happening than that, it did get me to thinking that arranging BFS's Raptors in the same "covered dugout" configuration that Crew Dragon uses for its Super Draco's might be the winning guess.

For example,
(https://i.imgur.com/pZmuel6.png) (https://i.imgur.com/pZmuel6.png)

(Thirty engine BFR booster, that load-lattice at the top serves as a supersonic brake/stabiliser, while allowing a wider base for the "Roc" heatshield. The "Roc" is shown with cargo hatches open. [Shouldn't the hatches fold down? To become ramps?])

Full image set: https://imgur.com/a/2k10I (https://imgur.com/a/2k10I)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/28/2016 06:38 am
Staging requires more thrust than any other point in the BFS mission. It's in a bigger gravity well, with a full fuel load and a full payload.

We don't know the final delta-v of the first stage at separation. If it works anything like conventional launches, then the delta-v for a second stage to LEO is much less than the delta-v from Mars surface to direct Earth return.

Actually we do. Elon said in an interview that the BFR is just there to compensate for the difference in the two longest poles of the mission. The ΔV to LEO is about 9.5 km/s, including gravity and aerodynamic losses. Mars-Earth is about 7km/s. BFR will provide about 3.5km/s, so if the BFS can generate 7.5 km/s, the remainders are the payloads.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 08/28/2016 07:41 am
Actually we do. Elon said in an interview that the BFR is just there to compensate for the difference in the two longest poles of the mission. The ΔV to LEO is about 9.5 km/s, including gravity and aerodynamic losses. Mars-Earth is about 7km/s. BFR will provide about 3.5km/s, so if the BFS can generate 7.5 km/s, the remainders are the payloads.

But then we get back to loaded vs empty.

However, that just reiterates my point. If the BFR is designed to exactly balance the difference between Mars-Earth and Earth-LEO, then if you make the Mars launch less efficient, you need more fuel, bigger tanks, different volume trades, then you are also changing every other part of the equation.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/28/2016 08:36 am
I expect that BFR will stage even slower than Falcon 9  for efficient RTLS. Which requires BFS to do even more than the F9 upper stage. I don't see the engines of BFS fire at any angle. They do everything to improve efficiency, light weight, highly optimized engines with high ISP. They won't give any of that away for canted engines.

Which of course makes the methods of EDL and avoiding debris hurled up more interesting. If not prepared too much in advance, find a hard flat surface. Such was mentioned as a requirement for a landing site in the NASA workshop on potential landing sites on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/28/2016 09:13 am
However, that just reiterates my point. If the BFR is designed to exactly balance the difference between Mars-Earth and Earth-LEO, then if you make the Mars launch less efficient, you need more fuel, bigger tanks, different volume trades, then you are also changing every other part of the equation.

There are only cosine losses for the first few seconds of the Mars launch, and never for launch to LEO. The canting is adjustable.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/28/2016 09:34 am
Rocket engine gimbal is only on the order of 10 degrees, nothing like the kind of 45 degree plus that's being proposed here has ever been done and would complicate the engines thrust structure and plumping hugely.

A secondary set of touch down engines would be ignited BEFORE shutting down the Raptor engines and in the event that they don't start you would ride the Raptor thrust all the way to the ground in a hover-slam and risk what ever damage may come as that's preferable to crashing.  To suggest that one engines is just shut off before any validation of the next engines is to practice in straw-man engineering, Musk even went into detail about how Dragon v2 will test it's engines first before diverting from a splash-down trajectory so a parachute landing can be executed in case of any engine failure and I am sure they will not forget this concept on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 08/28/2016 01:15 pm
I expect that BFR will stage even slower than Falcon 9  for efficient RTLS. Which requires BFS to do even more than the F9 upper stage. I don't see the engines of BFS fire at any angle. They do everything to improve efficiency, light weight, highly optimized engines with high ISP. They won't give any of that away for canted engines.

Which of course makes the methods of EDL and avoiding debris hurled up more interesting. If not prepared too much in advance, find a hard flat surface. Such was mentioned as a requirement for a landing site in the NASA workshop on potential landing sites on Mars.

Exactly.

Simple models with the rocket equation show that there's a sweet spot where a low & slow BFR and a high delta V 2nd stage BFS works out well for (1) launch to LEO delta V (2) refueled, TMI and EDL delta V and (3) reduced payload return to the green hills of Earth delta V.

The reduced payload from Mars makes the 3 delta Vs @ payload mass required close.  The difficult engineering is going to be mostly in the BFS with conflicting requirements for exotic Mars terrain landing techniques, high speed EDL and extreme mass savings.

The BFR is a robust (for RTLS) heavy thrust augmenter likely netting <2Km/sec after gravity losses towards LEO.  It will be engineered with all the lessons SX is in process of learning from returned F9 cores so that checkout and reliable re-flight is a minimal cost operation.  A few kilos here and there to improve safety and rapid re-use hurts less on the 1st stage. 

Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/28/2016 03:35 pm
Agree with the low and slow staging. 
The 'few extra kilos' will be more like a few extra tens of tonnes of fuel to guarantee RTLS, paying the performance hit so that relaunch can be expeditious.
BFS will achieve low Earth orbit, but with fuel mostly exhausted -- supplying something like 7.5km/s delta-v.
Refueling those huge tanks on orbit is the genius #2* here... topping off tanks again in high orbit** before a departure burn will maximize payload or minimize transit time if crewed.

* #1 was low and slow staging, then RTLS.
** hat trick
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 08/28/2016 05:40 pm
There are only cosine losses for the first few seconds of the Mars launch, and never for launch to LEO. The canting is adjustable.

CITATION NEEDED!!!  What is your epistemology?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 08/28/2016 06:54 pm
There are only cosine losses for the first few seconds of the Mars launch, and never for launch to LEO. The canting is adjustable.

CITATION NEEDED!!!  What is your epistemology?

It was his theory, so his post IS the citation.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/28/2016 10:24 pm
Rocket engine gimbal is only on the order of 10 degrees, nothing like the kind of 45 degree plus that's being proposed here has ever been done and would complicate the engines thrust structure and plumping hugely.

A secondary set of touch down engines would be ignited BEFORE shutting down the Raptor engines and in the event that they don't start you would ride the Raptor thrust all the way to the ground in a hover-slam and risk what ever damage may come as that's preferable to crashing.  To suggest that one engines is just shut off before any validation of the next engines is to practice in straw-man engineering, Musk even went into detail about how Dragon v2 will test it's engines first before diverting from a splash-down trajectory so a parachute landing can be executed in case of any engine failure and I am sure they will not forget this concept on Mars.

While I tend to agree with your reasoning for the most part, the numbers aren't quite so bad.  The Space Shuttle Orbiter's main engines were IIRC offset from each other's center of thrust line by 10 or 15 degrees, and had an additional +-10.5 degree gimbal range on top of that, to deal with the very large changes in center of mass and the aerodynamic asymmetry during the ascent of the Shuttle system.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 08/28/2016 11:43 pm
The decelerator designs are generally inherently stable in either direction once they have commenced their descent into the atmosphere. The hypersonic heating rate is proportional to velocity cubed, and to the inverse of the square root of the atmospheric density divided by the leading edge radius.

HeatingRate = 1.83e-4 * Math.Pow(speed, 3) * Math.Sqrt(atmosphericDensity / HeatingRadius());

So, the larger the leading edge radius (i.e. the blunter the body), the lower the heating rate. Although perhaps counter-intuitive, this is why the decelerator is best positioned at the front of the vehicle. I've attached a few design alternatives below.

Thank you, OneSpeed, for your very informative reply!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 08/28/2016 11:55 pm
I would hardly consider a set of pressure fed engines firing on touch-down to be a 'miracle', it's a normal and standard part of the Soyuz capsule landing after all.

Soyuz uses small solid-fuel retro rockets. More like explosives, actually.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 08/29/2016 01:08 am
I expect that BFR will stage even slower than Falcon 9  for efficient RTLS. Which requires BFS to do even more than the F9 upper stage. I don't see the engines of BFS fire at any angle. They do everything to improve efficiency, light weight, highly optimized engines with high ISP. They won't give any of that away for canted engines.

Which of course makes the methods of EDL and avoiding debris hurled up more interesting. If not prepared too much in advance, find a hard flat surface. Such was mentioned as a requirement for a landing site in the NASA workshop on potential landing sites on Mars.
I think you are right BFS will give same or less staging speed then Falcon 9.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/29/2016 03:56 am
There are only cosine losses for the first few seconds of the Mars launch, and never for launch to LEO. The canting is adjustable.

CITATION NEEDED!!!  What is your epistemology?

My last response was one of several in a chain, and some of those responses did include brief discussion of the issues. If you would like to know more about why extreme canting could be useful for SRP, you could do a whole lot worse than start with the attached Parametric Study of Peripheral Nozzle Configurations for Supersonic Retropropulsion by Bakhtian and Aftosmis.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CuddlyRocket on 08/29/2016 05:37 am
Rocket engine gimbal is only on the order of 10 degrees, nothing like the kind of 45 degree plus that's being proposed here has ever been done ...

There's always a first time!

Quote
... and would complicate the engines thrust structure and plumping hugely.

But has to be compared with complications etc of having a separate set of engines for landing etc.

SpaceX needs to make an assessment of what exactly are the dangers of landing, and especially taking off again, on a natural Mars surface. Perhaps it may be worth their while doing some experiments on those lines? If the dangers are too great, then they'll need another solution.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/29/2016 10:53 am
Ok lets make that comparison, touch down engines would be as simple as a dozen super draco engines around the nose of the vehicle.  That is sufficient thrust to hover the likely landing mass of around 100 tons after the main propulsion system brings the vehicle to zero ground velocity at some safe height.  These engines would mass less then a ton and consume just slightly more propellant then the Raptor engines would to do the same job, the lower touch down speed should allow for a much lighter landing gear system as well which is nothing to sneeze at as landing gear is historically 10 percent of landed mass.

Making an engine gimbal a huge amount will basically require a completely second thrust structure to keep the inward thrust vectors from crushing the vehicle, thrust structures are usually more massive then the actual engines they hold.  Propellant lines need to use bellows to allow them to flex but they are like springs, the bend radius is large so to get a greater deflection the engine needs to be at the end of a longer and wider thrust structure, the mass of all this would quickly become prohibitive.

And as for the shuttle main engine achieving 10 degrees of movement please look at some cut-aways and see how deeply all the mess of plumbing goes in the vehicle just to do that much.  The shuttle engine had to be designed with that level of gimbaling, so unless SpaceX had the whole mars EDL system figured out before starting engine development it's very unlikely that Raptor would ever be capable of more then the typical single digit gimbaling of a standard rocket engine.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 08/29/2016 11:12 am
Ok lets make that comparison, touch down engines would be as simple as a dozen super draco engines around the nose of the vehicle. [...]

None of which helps for the re-launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/29/2016 01:13 pm
That is sufficient thrust to hover the likely landing mass of around 100 tons after the main propulsion system brings the vehicle to zero ground velocity at some safe height.

I assume you mean weight, the mass would be at least 250mT, and much higher if the ship was to carry enough fuel to return directly to LMO or Earth. MCT is a fuel rich architecture, allowing for many mission profiles.

These engines would mass less then a ton and consume just slightly more propellant then the Raptor engines would to do the same job, the lower touch down speed should allow for a much lighter landing gear system as well which is nothing to sneeze at as landing gear is historically 10 percent of landed mass.

The landing velocity would be close to zero in either scenario.

Making an engine gimbal a huge amount will basically require a completely second thrust structure to keep the inward thrust vectors from crushing the vehicle, thrust structures are usually more massive then the actual engines they hold.  Propellant lines need to use bellows to allow them to flex but they are like springs, the bend radius is large so to get a greater deflection the engine needs to be at the end of a longer and wider thrust structure, the mass of all this would quickly become prohibitive.
And as for the shuttle main engine achieving 10 degrees of movement please look at some cut-aways and see how deeply all the mess of plumbing goes in the vehicle just to do that much.  The shuttle engine had to be designed with that level of gimbaling, so unless SpaceX had the whole mars EDL system figured out before starting engine development it's very unlikely that Raptor would ever be capable of more then the typical single digit gimbaling of a standard rocket engine.

Who said anything about gimbaling more than a few degrees? The idea is to allow the canting of the entire engine mount in a single degree of freedom. Canting is required anyway by SRP, so there is no extra engineering required for landing.

MCT missions will require landing a mass more than two orders of magnitude greater than any Mars mission so far. It amazes me that you assume that everything about MCT will be something that has been done before. SpaceX starts with what works, then iterates to improve the state of the art. When no solution exists, it innovates brilliantly. I expect no less from the MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/29/2016 01:14 pm
Ok lets make that comparison, touch down engines would be as simple as a dozen super draco engines around the nose of the vehicle. [...]

None of which helps for the re-launch.

And would be unnecessary mass once a hard concrete landing/launching pad is in place, which will probably be ASAP.

Would deployable thrust deflectors make sense? Rather than gimballing the engines, just redirect the exhaust away from the vehicle at 30 or 45 degrees. I'm thinking an ablative-coated panel set just below the engines (which I think will be mounded on the sidewalls), that pops out into the exhaust stream.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/29/2016 01:28 pm
...The idea is to allow the canting of the entire engine mount in a single degree of freedom.
...

I think you're drawing unnecessary distinctions between multiple static engine positions (e.g. 0 degrees +/- 5 degrees and 45 degrees +/- 5 degrees) and a large variable dynamic range (e.g. -5 to 50 degrees) of engine positions.

If you have 2 (nearly) static positions, you still have to feed pressurized propellant to the turbopumps at both of them, which requires incredibly flexible plumbing. And you still require a thrust structure that can take the load of the engines in VERY different directions.

Both of these are sizable engineering problems with either multiple near-static positions, or with a very wide dynamic range.

Quote
Canting is required anyway by SRP, so there is no extra engineering required for landing.

The minimum feasible solution for landing is certainly different than the minimum feasible solution for SRP, so there will definitely be "extra" engineering required to bridge the gap between those two requirements. As I understand, SRP is viable at around 15 to 20 degrees of canting, while landing/relaunching on unprepared soil is not.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Arb on 08/29/2016 01:40 pm
It could be that one of the roles of the Red Dragon missions is ground confirmation of a flat clear area of rock to use as an initial BFS landing site.

Someone mentioned that such an area was one of the requirements of the recent NASA landing site selection conference. So they are known to exist.

Would make this discussion moot.

Legs need to be very strong, don't they. What's the weight on Mars of the fuel needed to launch direct to Earth?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/29/2016 02:00 pm
Legs need to be very strong, don't they. What's the weight on Mars of the fuel needed to launch direct to Earth?

In a ideal scenario (empty 65t mass vehicle, slow 6 km/s return) about 120t of weight.

More realistic scenario (75t mass vehicle, 25t mass payload, 7 km/s return) about 250t of weight.

Even in a worst case scenario (100t mass vehicle, 25t mass payload, 8 km/s fast return) about 400t of weight.

However, I'm not sure this is the primary design constraint on the legs, since they have to decelerate some 160 to 200 tonnes of mass from some small velocity (~2  m/s?) during landing. It's entirely possible that the landing "impact", if at dynamic acceleration of 1 to 2 gees, will generate more leg loading than the static weight of the return fuel under Mars gravitational acceleration of .38 gees.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 08/29/2016 02:09 pm
Would deployable thrust deflectors make sense? Rather than gimballing the engines, just redirect the exhaust away from the vehicle at 30 or 45 degrees. I'm thinking an ablative-coated panel set just below the engines (which I think will be mounded on the sidewalls), that pops out into the exhaust stream.

If you mean the deflectors would be attached to the vehicle itself, then at 45°, the vertical thrust would push down on the panels (and hence the ship) exactly as much as it pushes up; resulting in zero vertical net force. The sideways thrust would presumably be balanced in each horizontal direction by ensuring the panels point in different direction, so you wouldn't get any horizontal movement either. Essentially is would be a very elaborate scheme to stop the rockets from doing anything at all. It would just sit there, burning away, until something gave out.

If you mean to mount the deflectors on the surface, you are essentially talking about a flame-trench. Which means a large concrete construction, along with some way of suspending the vehicle over it, so a launch platform/gantry of some kind. Which wouldn't be a good place to land (too much stuff in the way), so you'd need a vehicle capable of hoisting and transporting the BFR.... basically you've added an awful lot of hardware.

[edit: typo]
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/29/2016 03:36 pm
Would deployable thrust deflectors make sense? Rather than gimballing the engines, just redirect the exhaust away from the vehicle at 30 or 45 degrees. I'm thinking an ablative-coated panel set just below the engines (which I think will be mounded on the sidewalls), that pops out into the exhaust stream.

If you mean the deflectors would be attached to the vehicle itself, then at 45°, the vertical thrust would push down of the panels (and hence the ship) exactly as much as it pushes up; resulting in zero vertical net force. The sideways thrust would presumably be balanced in each horizontal direction by ensuring the panels point in different direction, so you wouldn't get any horizontal movement either. Essentially is would be a very elaborate scheme to stop the rockets from doing anything at all. It would just sit there, burning away, until something gave out.

If you mean to mount the deflectors on the surface, you are essentially talking about a flame-trench. Which means a large concrete construction, along with some way of suspending the vehicle over it, so a launch platform/gantry of some kind. Which wouldn't be a good place to land (too much stuff in the way), so you'd need a vehicle capable of hoisting and transporting the BFR.... basically you've added an awful lot of hardware.

The deflectors would be attached to the vehicle.

And Newton says that the only way to get zero net vertical thrust is to redirect the net flux EXACTLY horizontally, which is neither the object, or realistically feasible. If the panels deployed to 45 degrees, the exhaust would be travelling at nearly 45 degrees after deflection, because exhaust particles hitting an impenetrable surface is not an elastic collision, and the pressure from the rest of the exhaust flux will keep the flow moving as much as possible in the direction it started.

If you do the FBD on this system, the down-force on the panels is equal to the net loss of exhaust massflow*velocity in that direction, which is any friction forces, plus the cosine loss of the redirection. The up-force however doesn't have cosine losses, so the net effect on thrust is no different than canting the engines. Picture the variable thrust vectoring nozzles on modern fighter jets for a similar concept: high-temp control surfaces redirecting hot exhaust gas to give more control authority. The V-2 rocket did something similar with graphite vanes in the exhaust nozzle, instead of gimballing the whole engine.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/30/2016 05:20 am
Ok lets make that comparison, touch down engines would be as simple as a dozen super draco engines around the nose of the vehicle. [...]

None of which helps for the re-launch.

Actually you could fire them at take off for a small additional thrust but that's not the point, you take off with your main propulsion system which is pointed strait down for maximum efficiency.  The comparison here is between having your main engines be able to gimbal out by huge amounts to avoid having the thrust crater the ground under you on landing, or just having second set of small canted engines at the top of the vehicle for landing.

Taking off again is going to be a whole other problem and will require a surface under the engine that won't be destroyed at liftoff because angling the engines isn't an option because you can't afford cosine loss at takeoff.


I assume you mean weight, the mass would be at least 250mT, and much higher if the ship was to carry enough fuel to return directly to LMO or Earth. MCT is a fuel rich architecture, allowing for many mission profiles.

First the vehicle is not going to be full of propellant at landing, that is nonsense.

The mass I wrote was wrong because I just wrote the cargo mass without including dry vehicle mass which I estimate at around 75 mt.  So a total of 175, add another 10 for residual propellants, at Mars that's a weight of 703 kN.  Super Draco produces 73 kN so 10 would hover the vehicle if pointed strait down, with cosine losses from 40 degree canting that brings the total to 12, for deeper angles like 60 degrees the number of engines would go up to 20 which is still quite reasonable if that angle proves necessary, by placing the engines at the nose of the vehicle they are far from the ground, farther then the MSL decent engines were from the ground, though admittedly their thrust was just 3 kN each.


The landing velocity would be close to zero in either scenario.

It would be targeted at zero, yes but the range of actual touchdown velocity that the landing gear must handle has to be higher when you have only huge raptor engines to slow down with.  The deceleration has to be high all the way to the ground and large turbo-pump engines are far less responsive then small pressure fed engines.  All that put together means a different touch down speed and a different landing gear design driven by thouse speeds.


Who said anything about gimbaling more than a few degrees? The idea is to allow the canting of the entire engine mount in a single degree of freedom. Canting is required anyway by SRP, so there is no extra engineering required for landing.

All of the issues I raised about propellant lines, thrust structures and the like are going to be problems even if your only trying to move in one axis.  I'd already assumed that would be the mode of action as it is obviously simpler then moving in two axis, to gimbal in one axis you need 1 gimbal, to gimbal in 2 axes you need 2 gimbals, canting simply means something being at an angle in this case an angle pointing off from vertical.

To launch you can't be canting, you need vertical thrust or your engine efficiency is ruinous.  So if you want the same engine to be used for landing without the plume cratering the ground and throw rock ejecta back at the engine and underside of the vehicle it would need to be pointed nearly sideways at the moment of touchdown, I've been saying 45 degrees as a conservative estimate, maybe rocks will all fly away from the vehicle at that kind of angle but in reality it would likely need to be even more, that's where I get a 45 degree rotation range from.  SRP dose not require anywhere near this level of rotation as we know it will work with just a 20 degrees canting which is at the upper limit of what has been done before.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 08/30/2016 10:01 am
Making an engine gimbal a huge amount will basically require a completely second thrust structure to keep the inward thrust vectors from crushing the vehicle, thrust structures are usually more massive then the actual engines they hold.  Propellant lines need to use bellows to allow them to flex but they are like springs, the bend radius is large so to get a greater deflection the engine needs to be at the end of a longer and wider thrust structure, the mass of all this would quickly become prohibitive.

Your alternative, canted Super-Dracos, would presumably also require a second thrust structure. So, in any case, gimballing the main engines or using separate thusters, a truss structure would presumably be needed. You could even say, perhaps, that a main engine truss structure for gimballing engines would probably perform dual use to some extent.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/30/2016 01:24 pm
To launch you can't be canting, you need vertical thrust or your engine efficiency is ruinous.

You can't be canting for the entire LMO and TEI burns, but what if it was just for the first few seconds, enough to avoid the risk of ejecta impacting the ship?

The heaviest estimate I've seen for BFS dry mass + payload from Mars to Earth is about 160mT. Assuming 7.5 km/s of ΔV is required, that is a takeoff mass of about 1280mT. If there are 5 Raptors, each having around 270mT of thrust, that is 1360mT of thrust at takeoff. For Mars gravity (0.38g), that is a thrust to weight ratio of 1360 / 1280 * 0.38 = 2.8, far more than necessary to achieve liftoff. Allowing a worst case T/W of 1.15, cos^-1(1.15/2.8) = 65.7°, probably more than enough to mitigate the ejecta risk. After a few seconds of flight, the cant could be reduced to zero, and the flight continue with no further cosine losses to TEI.

First the vehicle is not going to be full of propellant at landing, that is nonsense.

As shown above, the ship wouldn't need to be completely full of propellant to relaunch, and it certainly wouldn't be necessary once ISRU is established, but why is it a nonsense? Do you have any supporting calculations?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/30/2016 02:29 pm
Why would a lander want to land with enough propellant to relaunch? Landing prop for earth return is prohibitive, so where would it go with landed prop, and what would it do when it got there?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JamesH65 on 08/30/2016 06:08 pm
Why would a lander want to land with enough propellant to relaunch? Landing prop for earth return is prohibitive, so where would it go with landed prop, and what would it do when it got there?

To reduce the time taken to generate enough for relaunch? Use as a raw material?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 08/30/2016 06:52 pm
Why would a lander want to land with enough propellant to relaunch? Landing prop for earth return is prohibitive, so where would it go with landed prop, and what would it do when it got there?

To reduce the time taken to generate enough for relaunch? Use as a raw material?

It doesn't make sense to land some propellant unless it's coming out of your long-term payload baseline, which as we understand it is 100 tonnes. Eventually ISRU will be fully established and then payload can rise to the baseline, but until then there's no reason to spec margin for prop. Just count the propellant mass as a fraction of the 100t of generic payload delivered to the surface, or more likely as 100 tonne batches of fuel delivered as payload.

I don't think landing propellant (CH4 or more likely jsut LH2) is necessarily a bad idea until IRSU is fully established, but designing an architecture around what would be a short-term crutch is definitely a bad idea.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 08/30/2016 07:09 pm
I've tried to fit landing some methalox in, but even for a small portion of the vehicle (an 'escape pod'), the math doesn't work for return to orbit (much less return to Earth), it swamps other payload.  If you could wring 4.5km/s out of an escape pod, you could return to MLO and a waiting lifeboat there for return to Earth.  But that's too much.  Landing mostly dry just works a lot better.  Every kilogram of propellant landed reduces the ISRU gear landed by 1kg, which reduces the propellant generated by many kilograms per synod.

Now...  that's not to say landing *completely* dry is the preferred option.  Liquid propellants are useful for a number of things other than full-on Mars ascent.  Solar storm shielding, EDL mass redistribution maneuvers, and high-thrust RCS landing maneuvers are all made considerably easier if you pack a sizable quantity of, say, monomethyl hydrazine on board.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/30/2016 07:34 pm
To launch you can't be canting, you need vertical thrust or your engine efficiency is ruinous.

You can't be canting for the entire LMO and TEI burns, but what if it was just for the first few seconds, enough to avoid the risk of ejecta impacting the ship?

The heaviest estimate I've seen for BFS dry mass + payload from Mars to Earth is about 160mT. Assuming 7.5 km/s of ΔV is required, that is a takeoff mass of about 1280mT. If there are 5 Raptors, each having around 270mT of thrust, that is 1360mT of thrust at takeoff. For Mars gravity (0.38g), that is a thrust to weight ratio of 1360 / 1280 * 0.38 = 2.8, far more than necessary to achieve liftoff. Allowing a worst case T/W of 1.15, cos^-1(1.15/2.8) = 65.7°, probably more than enough to mitigate the ejecta risk. After a few seconds of flight, the cant could be reduced to zero, and the flight continue with no further cosine losses to TEI.

First the vehicle is not going to be full of propellant at landing, that is nonsense.

As shown above, the ship wouldn't need to be completely full of propellant to relaunch, and it certainly wouldn't be necessary once ISRU is established, but why is it a nonsense? Do you have any supporting calculations?

Your not seriously trying to equate a thrust structure that hold 4 or more Raptor engines which produce 2,300 kN EACH with a structure that is going to handle around 900 kN TOTAL.  Even throttled to 40 percent and canted 45 degrees out 4 Raptor engines will be putting 2600 kN of inward crushing force on the vehicle, all that force has to be resisted with higher dry mass.

As for not landing with propellant, landed cargo mass on mars is one of the most expensive things in the whole architecture, it will take something like 10 kg IMLEO for each kg of cargo delivered to surface.  Taking propellant with you for return is very very expensive and avoiding that has always been the point of ISRU.  But even if for some reason this were to be done the propellants would come out of the 100 mt cargo capacity because the vehicles EDL profile would be completely ruined if it were over it's normal mass.

So the whole point of that tangent which was to claim that touchdown mass might be crazy high is moot.  Touch down mass will just be 100 mt cargo be it in the cargo hold or in tanks plus vehicle dry mass and a small propellant residuals for safe landing.  This is the only thing that makes any sense.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 08/31/2016 10:55 am
Impaler, I'm drawn to your suggestion re smaller, more responsive engines for Mars landing.  But I think Super Dracos aren't the answer for a couple of reasons. 

First, you still need the Raptors for Mars ascent (unless you are arguing that the Dracos will be able to lift a fully fueled BFS from Mars surface).  And the Raptors will have to be canted, so as to avoid backsplash during ascent.  This is exactly the same problem as on descent.  So if you have to solve it for ascent, why include a separate method for descent?

Second, the hypergolic fuel used on the Super Dracos is not easily made via ISRU.  That means that the fuel used for Earth landing must be carried from Earth to Mars, then back to Earth again.  This would really cut into the available payload landed on Mars (given the dictatorship of the rocket equation).  Right?

I think ideally a 1/2 to 1/3 scale Raptor would be ideal for the BFS, but I think SpaceX has indicated they are going to only develop one size of this guy.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 08/31/2016 12:13 pm
I think ideally a 1/2 to 1/3 scale Raptor would be ideal for the BFS, but I think SpaceX has indicated they are going to only develop one size of this guy.

Interesting that you should say that. In Noël Bakhtian's thesis 'Drag Augmentation via Supersonic Retropropulsion for Atmospheric Deceleration' she finds that the optimum number of engines for Mars SRP is actually 15 engines in a peripheral array, canted outboard. 15 1/3 scale Raptors would give the same thrust as 5 full scale.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 08/31/2016 12:38 pm
Didn't really read it I admit. Looks interesting and I hope it will be discussed more. But interesting theme for a doctorate in philosphy.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 08/31/2016 02:09 pm
"Doctorate in philosophy" = PhD. Doctorates in the natural and engineering sciences are typically all "doctorates in philosophy".
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AncientU on 08/31/2016 02:11 pm
I think ideally a 1/2 to 1/3 scale Raptor would be ideal for the BFS, but I think SpaceX has indicated they are going to only develop one size of this guy.

Interesting that you should say that. In Noël Bakhtian's thesis 'Drag Augmentation via Supersonic Retropropulsion for Atmospheric Deceleration' she finds that the optimum number of engines for Mars SRP is actually 15 engines in a peripheral array, canted outboard. 15 1/3 scale Raptors would give the same thrust as 5 full scale.

Nice find!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 08/31/2016 10:13 pm
Impaler, I'm drawn to your suggestion re smaller, more responsive engines for Mars landing.  But I think Super Dracos aren't the answer for a couple of reasons. 

First, you still need the Raptors for Mars ascent (unless you are arguing that the Dracos will be able to lift a fully fueled BFS from Mars surface).  And the Raptors will have to be canted, so as to avoid backsplash during ascent.  This is exactly the same problem as on descent.  So if you have to solve it for ascent, why include a separate method for descent?

Second, the hypergolic fuel used on the Super Dracos is not easily made via ISRU.  That means that the fuel used for Earth landing must be carried from Earth to Mars, then back to Earth again.  This would really cut into the available payload landed on Mars (given the dictatorship of the rocket equation).  Right?

I think ideally a 1/2 to 1/3 scale Raptor would be ideal for the BFS, but I think SpaceX has indicated they are going to only develop one size of this guy.

I think your misunderstanding what I'm saying, I've never said you don't have Raptor engines.  The only questions is you ALSO have smaller engines.

I'm proposing the vehicle would have a cluster of small canted engines at the nose AND a set of vertical Raptor engines on the bottom.  The small canted engines are used just for the final touch down at landing, any SRP higher in the atmosphere is done via Raptor engines.  And the Raptor engines also do most of the landing burn, they bring the vehicle to a standstill just above the height where they would impinge and the ground, then the smaller engines take over and do a slow decent for the final few hundred meters to touchdown.  Lastly their might be some use small engines in orbital maneuvering or to steer during decent but these are secondary functions.

While I'm siting the super-Draco numbers for thrust and engine count necessary to do the job I do suspect that a modified version running on Metho-Lox might be preferable and I've speculated on such an engine myself in the past, allowing it to use ISRU propellants is a big advantage on Earth return as you pointed out.  The point was just to demonstrate the size of the system with a reasonable approximation engine rather then to down select to a specific engine.  I think a methane-Lox version of super-Draco is more likely to be developed then small version of Raptor because pressure fed engines are so much simpler.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 08/31/2016 10:47 pm
Got it.

But I think you're ignoring the problem of take off from Mars surface.

The Dracos (or their methalox equivalents) are not going to lift you off the surface.  So you're left with using the Raptors.  If they are bottom mounted and can't cant much, you have the same problem with liftoff as you've just solved for touchdown.  So whatever you do to the Raptors to avoid backwash of regolith on ascent, you could have used for descent.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/01/2016 02:44 am
No we have many more options once we are landed on the surface that we don't have when doing an initial landing, namely to modify the surface directly under the engines to make them resilient enough for take off.

Some kind of wire mesh screen can be put down, or even an inflatable 'kidi pool' which can be filled with water and fiber then allowed to freeze into a pykrete pad, the fiber is usually sawdust and by treating it with chemicals that produce and endothermic reaction so the water can be made to freeze almost immediately. 

Along with some stakes to keep it in place his should be strong enough to take the full force of the Raptor engine without breaking as pykrete has physical properties comparable to concrete and is an excellent insulator so it won't melt under the exhaust and it would take a long time to sublimate to so launch windows are not too tight.  It will obviously take a good deal of water but if we don't have that available the vehicle isn't getting filled with propellant anyway.  With say 1 ton of fiber and 10 tons of water you could create 4 pads each 6 meters across and 10 cm thick.  Package each one as a plastic pouch with fiber already inside and just roll it out and fill with water.

It is even possible that an automated means of deploying simple under engine pads like this can be developed, they only need to work once and for a few initial missions until more permanent pads are created.  This is far better then compromising the vehicle itself with under-powered engines on assent or trying to do crazy degrees of movement on the engines.  And far better then the wand-waving some engage in that say the vehicle will only land on naturally occurring bed rock.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jpo234 on 09/01/2016 06:55 am
Isn't the simplest solution to foreign object damage an engine that is robust enough to survive the odd pebble? And maybe some redundancy in case one engine breaks?
I have a really hard time to imagine how something could enter an active combustion chamber against the flow of the combusted fuel.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 09/01/2016 10:29 am
Isn't the simplest solution to foreign object damage an engine that is robust enough to survive the odd pebble? And maybe some redundancy in case one engine breaks?
I have a really hard time to imagine how something could enter an active combustion chamber against the flow of the combusted fuel.

Not all engines are active on landing. But probably all are required for launch when fully fuelled. At least when engine out capability on launch is to be maintained.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 09/01/2016 12:04 pm
I think the answer to this issue is landing on bedrock or somewhere else deemed reasonably safe. Extra engines will just be dead weight which you can't afford under the constraints of the mission profile. Spacex have shown with Dragon 2 what I think will be the probable approximate configuration for the MCT. We'll all be much wiser in a few days...

Title: Re: MCT Speculation and Discussion Thread 4
Post by: jpo234 on 09/01/2016 12:22 pm
I think the answer to this issue is landing on bedrock or somewhere else deemed reasonably safe.

Is "landing on bedrock" compatible with ISRU, e.g. would you have access to water?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 09/01/2016 12:45 pm
I think the answer to this issue is landing on bedrock or somewhere else deemed reasonably safe.

Is "landing on bedrock" compatible with ISRU, e.g. would you have access to water?

All 40 potential landing sites, considered during the NASA workshop, had both water, some of them huge amounts of glacial water and hard flat surfaces for landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 09/02/2016 08:07 am
Isn't the simplest solution to foreign object damage an engine that is robust enough to survive the odd pebble? And maybe some redundancy in case one engine breaks?

The odd pebble?

https://www.youtube.com/watch?v=SZQY902xQcw (https://www.youtube.com/watch?v=SZQY902xQcw)

9 Merlins, roughly the same force generated as three Raptors. People are anticipating up to five Raptors on the lander.

So picture something with 2/3rd more power than what is depicted here, sitting on landing legs, a metre or two above hard flat surface. Even bedrock would spall. And it's not just damage to the engines, you also can't damage that heat-shield either, because you'll need it to get the ship back to Earth.

In NASA's proposals (DRA 5.0), the Earth return vehicle is vastly smaller, and launched from a "launch platform" made from its own landing system. Similar to the two-stage ascent/descent modules on the Apollo LM.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 09/02/2016 08:19 am
Aside: No engine retesting on Mars before relaunch back to Earth. Three months in deep space, slammed into Mars-entry, supersonic retropropulsion, landing on - at best - a rock surface. Sitting in a dusty, cold, semi-vacuum during refuelling for however long that takes, and where the atmosphere freezes out at the temperatures you are using for the fuel. Plus there might be repair/refurb performed by the crew, "Sensors say valve four was sticky during landing".

But you can't test your engines before a launch into a direct Earth return trajectory, because there's no infrastructure that can withstand the test (or hold down the vehicle.)

Or would you perform a short vertical (sub-orbital) hop to test the engines before final fuel and re-launch?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 09/02/2016 08:21 am
Perhaps this is better. Low-powered Merlin 1a testing nozzle ablative.

https://www.youtube.com/watch?v=JOHp0YMdfa0 (https://www.youtube.com/watch?v=JOHp0YMdfa0)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/03/2016 12:17 am
Isn't the simplest solution to foreign object damage an engine that is robust enough to survive the odd pebble? And maybe some redundancy in case one engine breaks?

The odd pebble?....
So picture something with 2/3rd more power than what is depicted here, sitting on landing legs, a metre or two above hard flat surface. Even bedrock would spall. ...
They did this above concrete, which spalls. Short turnaround time.
https://www.youtube.com/watch?v=DgLBIdVg3EM
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 09/03/2016 12:27 am
But you can't test your engines before a launch into a direct Earth return trajectory, because there's no infrastructure that can withstand the test (or hold down the vehicle.)

Actually you could test the engines if they were sufficiently canted, and the ship was fully fuelled. For a T/W of 1 at launch, cos^-1(1/2.8) = 69.1°, so set the cant at 70° or more, and you could perform a short full thrust static fire.
Admittedly, I have some trepidation regarding static fires at the moment.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/03/2016 12:30 am
But you can't test your engines before a launch into a direct Earth return trajectory, because there's no infrastructure that can withstand the test (or hold down the vehicle.)

Actually you could test the engines if they were sufficiently canted, and the ship was fully fuelled. For a T/W of 1 at launch, cos^-1(1/2.8) = 69.1°, so set the cant at 70° or more, and you could perform a short full thrust static fire.
Admittedly, I have some trepidation regarding static fires at the moment.
Static fires are fine (if maybe expensive), provided you don't put your payload on top.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 09/03/2016 01:06 am
Making the vehicle strong enough for a static fire in two different directions is a somewhat questionable design choice, even if we were to assume that the gimbals for canting posed no weight issues or technical unknowns.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/03/2016 01:22 am
Making the vehicle strong enough for a static fire in two different directions is a somewhat questionable design choice, even if we were to assume that the gimbals for canting posed no weight issues or technical unknowns.
I wasn't suggesting that, by the way. I don't yet believe in the idea of extreme canting for MCT.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 09/03/2016 01:28 am
Making the vehicle strong enough for a static fire in two different directions is a somewhat questionable design choice, even if we were to assume that the gimbals for canting posed no weight issues or technical unknowns.

Perhaps it would help to consider the idea of 15 1/3 scale Raptors, arranged in a circle. Their 'dance floor' would also be circular and made strong enough to support full inline thrust. The engineering required to make a such a structure also support a radial load is a solved problem. In fact, a circular structure is ideal for bearing radial loads, e.g. the wheel.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Patchouli on 09/03/2016 04:09 am
I've tried to fit landing some methalox in, but even for a small portion of the vehicle (an 'escape pod'), the math doesn't work for return to orbit (much less return to Earth), it swamps other payload.  If you could wring 4.5km/s out of an escape pod, you could return to MLO and a waiting lifeboat there for return to Earth.  But that's too much.  Landing mostly dry just works a lot better.  Every kilogram of propellant landed reduces the ISRU gear landed by 1kg, which reduces the propellant generated by many kilograms per synod.

Now...  that's not to say landing *completely* dry is the preferred option.  Liquid propellants are useful for a number of things other than full-on Mars ascent.  Solar storm shielding, EDL mass redistribution maneuvers, and high-thrust RCS landing maneuvers are all made considerably easier if you pack a sizable quantity of, say, monomethyl hydrazine on board.

Why not put the first habs in place before sending crew so you can just abort to the Martian surface vs MLO?

Once there are assets on Mars it be a safe haven as well.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/03/2016 05:09 pm
Who here still believes that some new pad at Cape Canaveral or some future pad at Boca Chica is still viable for BFR launches?  Given the recent pad anomaly, I believe that more stringent safety zones will force the BFR to be launched off shore, assuming any US based launch site, which I do because of ITAR.

There are shallow seas offshore from both SX launch sites.  At first a platform could be anchored to the sea floor and serviced by barges and hydrofoils while launch rates remained low.  A very expensive causeway could later be constructed to support higher flight rates.

I do not feel that on shore launch remains an option assuming the BFR is really ~2x Saturn V size or more.

The noise dB problem remains as RTLS sonic booms propagate tens of miles with little attenuation.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 09/03/2016 05:57 pm
Who here still believes that some new pad at Cape Canaveral or some future pad at Boca Chica is still viable for BFR launches?  Given the recent pad anomaly, I believe that more stringent safety zones will force the BFR to be launched off shore, assuming any US based launch site, which I do because of ITAR.

There are shallow seas offshore from both SX launch sites.  At first a platform could be anchored to the sea floor and serviced by barges and hydrofoils while launch rates remained low.  A very expensive causeway could later be constructed to support higher flight rates.

I do not feel that on shore launch remains an option assuming the BFR is really ~2x Saturn V size or more.

The noise dB problem remains as RTLS sonic booms propagate tens of miles with little attenuation.

I agree an offshore platform is the best option for the BFR we've been discussing. But with the schedule Elon mentioned there really isn't enough time to build a pad or platform before initial BFR testing. Maybe the BFR isn't going to be as big as we think. Perhaps the first generation BFS will be 50 tonnes cargo to Mars instead of 100 tonnes, requiring a BFR about the size of a Saturn V. That's still impressive. Pad 39A can handle that. We'll find out in a few weeks.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/03/2016 07:00 pm
Who here still believes that some new pad at Cape Canaveral or some future pad at Boca Chica is still viable for BFR launches?  Given the recent pad anomaly, I believe that more stringent safety zones will force the BFR to be launched off shore, assuming any US based launch site, which I do because of ITAR....
This has no bearing on BFR.

Explosions on pads are not new. If it wasn't feasible to have BFR some place after this accident, it wouldn't have been feasible before.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/03/2016 10:49 pm
I tend to agree, the possibility of pad detonation had to already be present and evaluated in sizing the BFR before the recent incident.  Also consider that NASA had plans for rockets considerably larger then Saturn V, such as NOVA which they must have considered possible to launch from land at the cape.

Also we know BFR is to have approximately twice the Saturn V thrust but that doesn't mean it carries twice the propellant load, the considerably greater efficiency of Raptor engines may make for a rocket that is smaller then expected.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: zubenelgenubi on 09/03/2016 11:53 pm
A side note:
IIRC, the Advanced Saturn and/or NOVA pads would have been constructed on land originally purchased for the center to the north of the current boundary--including what is now Canaveral National Seashore.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 09/04/2016 06:24 am
...
I do not feel that on shore launch remains an option assuming the BFR is really ~2x Saturn V size or more.
...

I agree an offshore platform is the best option for the BFR we've been discussing. But with the schedule Elon mentioned there really isn't enough time to build a pad or platform before initial BFR testing. Maybe the BFR isn't going to be as big as we think. Perhaps the first generation BFS will be 50 tonnes cargo to Mars instead of 100 tonnes, requiring a BFR about the size of a Saturn V. That's still impressive. Pad 39A can handle that. We'll find out in a few weeks.

Maybe a shipyard somewhere is already slated to work on floating BFR launch platform of some sort already designed.

Could be a converted semi-submersible oil production platform.

A more radical approach is to convert a VLCC (aka supertanker) as a launch platform and LV hangar. Pour some concrete as semi-ablative coating over the ship's top surface. Installed a flame trench section on the ship with the usual water suppression system. Build a reinforced hangar to stored the complete BFR/BFS stack. Voila a fast mobile autonomous sea going launch facility. There is a lot of candidate surplus VLCC available currently. Before anyone ask, the LV launch crew is taken off the ship in helicopter to support ship prior to launch. The Royal Navy convert the RFA Argus (A135) aviation training/hospital ship from a container ship by in part adding 1800 tons of concrete.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 09/09/2016 04:06 am
[Keep in mind, I am still both excited and skeptical at the same time about MCT. But I am talking about theoretical plans here.]

I know that Musk wants to do a Mars round trip within a Earth/Mars synodic period (26 months or 780 days) for easy reuse. This would necessitate a short-stay, high delta-v opposition class travel profile, as opposed to a long-stay conjunction class profile.

But for the first mission, the MCT is supposed to be inhabited for the entire journey (presumably, with pre-landed cargo MCTs for in-situ propellant production), unlike the fully operational phase in which MCT is primarily used for one-way colonization (it seems to be designed that way).

An opposition-class first mission would require astronauts to stay in microgravity (if artificial gravity is not involved) and completely exposed to cosmic radiation (unlike the Martian surface which at least offers some protection) for the return trip (which would last about a year, unlike the 100-day trip to Mars). So might the first mission be conjunction-class?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/10/2016 11:42 pm
My predictions are still going against the grain, I think we will see mostly BFR details with only modest information on the actual mars transit and landing and what ever details are revealed of that phase of the mission will be subject to change as SpaceX actually gets landing experience on Mars, it's too soon to completely commit to the mode or design of the mars landing vehicles at this time.

BFR will be narrower then the 15m diameter many have speculated, I think closer to 12m diameter as the thrust density of the Raptor engine will be high and a narrower vehicle makes for a lighter more efficient thrust structure to transmit the thrust of many engines to the tank side walls and makes for lower air resistance on assent as well.  The first stage will be recovered right from the first orbital flight and will be well tested on it's own in sub-orbital flights with a mass-simulating 2nd stage used for testing.

A recoverable second stage with vacuum raptor engines, probably 6 so it has engine out capability, will be used along with a conventional payload fairing to launch large payloads of high volume and make the BFR a direct competitor to SLS.  This 2nd stage will also act as the LEO propellant tanker with just the attachment of a minimal nosecone.  Recovery of the 2nd stage still be slightly experimental at the time the first orbital launches and the fist few launches will be refine the recovery process for the 2nd stage and several may be lost in the process.  The 2nd stage will orbit the Earth one or more times before recovery and might not land at the launch site.

Overall vehicle height is be over 200 ft at the top of the 2nd stage, with payload fairing around 300 ft.  Any mars bound spacecraft will be introduced several years after BFR itself is flying and will not fly the super-direct flight plan of departing from LEO directly to mars surface and then from Mars surface directly back to Earth surface, this requires too much delta-V and propellant production on Mars, rather their will be a refueling step somewhere between likely in a high Earth orbit and/or high Mars orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/11/2016 03:18 pm
My predictions are still going against the grain, I think we will see mostly BFR details with only modest information on the actual mars transit and landing and what ever details are revealed of that phase of the mission will be subject to change as SpaceX actually gets landing experience on Mars, it's too soon to completely commit to the mode or design of the mars landing vehicles at this time.

Agree completely.  MCT/BFS will be more conceptual and under development than big 1st stage.

BFR will be narrower then the 15m diameter many have speculated, I think closer to 12m diameter as the thrust density of the Raptor engine will be high and a narrower vehicle makes for a lighter more efficient thrust structure to transmit the thrust of many engines to the tank side walls and makes for lower air resistance on assent as well.  The first stage will be recovered right from the first orbital flight and will be well tested on it's own in sub-orbital flights with a mass-simulating 2nd stage used for testing.

Believe that # engines and room for architectural growth makes > 12m more likely.  I say closer to 15m than 12m.
Do the tooling expense once and use it "forever".

Stage one will be recovered from the get go and may actually fly with less than the standard # of engines for 1st test flights.

A recoverable second stage with vacuum raptor engines, probably 6 so it has engine out capability, will be used along with a conventional payload fairing to launch large payloads of high volume and make the BFR a direct competitor to SLS.  This 2nd stage will also act as the LEO propellant tanker with just the attachment of a minimal nosecone.  Recovery of the 2nd stage still be slightly experimental at the time the first orbital launches and the fist few launches will be refine the recovery process for the 2nd stage and several may be lost in the process.  The 2nd stage will orbit the Earth one or more times before recovery and might not land at the launch site.

Good case for 6th engine for engine out capability.  Mostly needed on launch to LEO.

If not landing @ launch site which is certainly possible, it will have to be someplace where water transport can move this expensive 12m+ asset back to the launch site.  Launch site will be the preferred landing site.

Overall vehicle height is be over 200 ft at the top of the 2nd stage, with payload fairing around 300 ft.  Any mars bound spacecraft will be introduced several years after BFR itself is flying and will not fly the super-direct flight plan of departing from LEO directly to mars surface and then from Mars surface directly back to Earth surface, this requires too much delta-V and propellant production on Mars, rather their will be a refueling step somewhere between likely in a high Earth orbit and/or high Mars orbit.

Reasonable height.  Still under 100m.

Agree couple years of BFR flights before 2nd stage ready for Mars transit.

Although the big risk/problem is making sufficient qty of propellant on Mars, sending "tanker" flights to Mars orbit is very resource consuming (read expensive) and leaves you with empty tanker(s) stuck in Mars orbit.  Sure they could be landed IF they had heat shielding and some propellant left, but then they too need surface and orbital refueling.  I think tankers would not have propellant expensive wasted mass heat shielding, so landing these near empty tankers on Mars is a moot point.

Glad to read good specific predictions before the IAC talk.
Anyone else have predictions/updates?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/11/2016 10:03 pm
Thx 4 reply philw1776 I have a few counter and clarifying points.


Planning for future upgrades to BFR is interesting, but I'm doubtful that a vehicles diameter is made larger then necessary to allow for the insertion of extra engines at a later date.  First the extra engines and thrust would require a complete redesign of the plumbing structures and thrust structures which is a significant part of the first stages total design.

Second the traditional means to add more engines is with boosters and I could see the addition of say 6 Falcon boosters much like thouse from FH each running 4 Raptors each, for a total of 24 additional engines as a more straightforward way to make a super powerful version of BFR.  I expect the falcon family to eventually be converted to Raptors, plus a small landing engine, for it's own reasons so this booster will be available to BFR as the path of least resistance.

For 2nd stage landing, the launch site is certainly the preferred location but because the 2nd stage can not possibly boost back to the launch site and must instead do at least one Earth orbit the ground track may be several hundred miles away from the launch site.  So the vehicle either needs to have a lot of cross-range when doing a once around entry like the shuttle, or it needs to remain in orbit until ground track intersects the launch site again, that requires a longer on orbit life-span.  Which will be simpler I'm not sure and as I expect the 2nd stage to be getting developed while in service some transition may occur during development.  If the landing is not at the launch site then your right it had better be coastal so the stage can be put on a barge for transport back to the launch site.

Lastly I believe it may be possible to send tankers from Earth to a high mars orbit, have them offload propellants and still return to Earth orbit either via chemical propulsion or SEP so all vehicles are recovered.  This would allow the Mars landing and relaunch vehicles to be much lighter at liftoff from Mars, using something like 1/3rd as much propellant, then refill in orbit and make a fast return to Earth. 

The exact details of how and where refueling occurs aren't clear yet but what I'm sure of is that the direct return approach is not viable, the fixation many have with it is analogous to the fixation on direct earth return in the early days of Apollo, it's attractive for it's simplicity but it a bridge too far in a lot of engineering areas.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: KelvinZero on 09/12/2016 03:57 am
Agree completely.  MCT/BFS will be more conceptual and under development than big 1st stage.
...
Anyone else have predictions/updates?
My totally uninformed and unsubstantiated pet hope is a sudden plan for a falcon heavy replacement:
How short could you plausibly make the full-diameter BFR? Im just thinking a lot shorter and symmetrically remove some engines.
If it is only needs 12 meter diameter instead of 15 that is great. However dumb my idea was at 15m, it is probably a bit less dumb at 12m :)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 09/12/2016 06:46 am
Agree completely.  MCT/BFS will be more conceptual and under development than big 1st stage.
...
Anyone else have predictions/updates?
My totally uninformed and unsubstantiated pet hope is a sudden plan for a falcon heavy replacement:
How short could you plausibly make the full-diameter BFR? Im just thinking a lot shorter and symmetrically remove some engines.
If it is only needs 12 meter diameter instead of 15 that is great. However dumb my idea was at 15m, it is probably a bit less dumb at 12m :)
I'm not sure how valid this is, but the tanks have to be some shape.  And that shape will probably have hemispherical endcaps for mass efficiency.   You can't make a tank with hemispherical endcaps smaller than a sphere, and it is far easier to build a cylinder than other shapes.  If this is a crippling constraint, it seems like you probably have to use multiple smaller subscale tanks.

For monolithic common-wall tankage, though, a synergy shows up at approximately:
~4000 ton S1 mass
3.8kg LOX to 1kg LNG
7.5m radius spherical LNG tank, sharing a wall with a
7.5m radius, 15m height cylindrical-with-hemispherical-endcap LOX tank (volume calcs are cylindrical)

~2000 ton S2 mass
3.8kg LOX to 1kg LNG
6m radius spherical LNG tank, sharing a wall with a
6m radius, 12m height cylindrical-with-hemispherical-endcap LOX tank (volume calcs are cylindrical)
51.2% the volume of S1 based on simple geometry

Problems unresolved:
* In a common thermal environment, a LOX tank will be higher pressure than an LNG tank.  Will this work with the common wall under compressive stress, or is the common wall on the wrong way around?
* Are multiple tanks (probably 2.5m radius tanks) going to be easier than a monolithic tank?
* Does the thin-wall pressure vessel approximation (Ideal pressure vessel mass scales directly with mass contained at the same pressure) hold at either scale, or are the walls instead dictated by a minimum gauge or some other constraint?  Does it hold at one third scale (2.5m radius)?  If it did we would be dealing with seven long cylinders of the same mass as a monolithic tank.
* Will the slosh on a 7.5m radius tank, especially a 7.5m radius spherical tank, be manageable through a fairly high-rotation 'swan dive' maneuver?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/12/2016 08:51 am
I think it is likely that the first stage tank bottom will be flattened or perhaps be a Diffuser head https://en.wikipedia.org/wiki/Head_(vessel), aka concave like the bottom of a soda can.

This would provide room for plumbing between the thrust structure and tank as well as allowing the thrust structure to be very close to the tanks bottom rim again minimizing it's size and mass.

The second stage would likely just have the normal tank shape because it's smaller engine count would mean the engines are basically all along the periphery and the thrust structure can just be a ring.

 In any case perfect hemispheres aren't the only option for tank bottoms or tops, modified ellipsoids are common.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/12/2016 05:20 pm
Thx 4 reply philw1776 I have a few counter and clarifying points.

Lastly I believe it may be possible to send tankers from Earth to a high mars orbit, have them offload propellants and still return to Earth orbit either via chemical propulsion or SEP so all vehicles are recovered.  This would allow the Mars landing and relaunch vehicles to be much lighter at liftoff from Mars, using something like 1/3rd as much propellant, then refill in orbit and make a fast return to Earth. 

The exact details of how and where refueling occurs aren't clear yet but what I'm sure of is that the direct return approach is not viable, the fixation many have with it is analogous to the fixation on direct earth return in the early days of Apollo, it's attractive for it's simplicity but it a bridge too far in a lot of engineering areas.

Gwynne has said, "We're looking at SEP" so this is a possibility.
On the downside if it's SEP, it is yet another vehicle to be developed and tested.

I haven't looked deeply at delta Vs, masses and run the rocket equation to comment cogently on the feasibility of SEP, etc. tankers to HMO & back.  I'm certain that SX has done so in their architectural bakeoffs.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 09/12/2016 06:32 pm
As the Big Reveal is nearly upon us (hopefully!), I think that someone (not me) should generate an official Mars MCT Architecture Prediction contest.  This would be composed of a list of questions with multiple choice answers, with a fixed value for each question.  Prizes TBD.

One problem is that L2 members may have 'insider information' on this topic.  So I guess they will have to be just guided by their own conscience as to their level of participation.

Anyway, I'll kick it off with a few suggested questions (but will be happy for someone else to officially take this over and come up with the canonical list, as well as being judge, jury, etc.)

1) Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft
     b)  Boost phase consists of 2 stages, which put the BFS into orbit
     c)  Other: 3rd stage, 'half' stages, drop tanks, etc.

2) Number of Raptor Engines on BFR (1st stage)

3) Diameter of BFR (1st stage)

4) Total Raptor 1st stage thrust (sl)

5) LAS Architecture
     a) No LAS - BFS is the escape mechanism
     b) Traditional LAS - above BFS and is nominally jettisoned during launch phase
     c) BFS contains smaller 'ejection pod' where humans reside during launch
     d) Other, non-traditional LAS design

6) Shape and Landing Mode of BFS
     a) Capsule (perhaps elongated), w/ TPS on base
     b) Cylindrical or biconic - horizontal landing
     c) Cylindrical or biconic - vertical landing
     d) Other

7) Mars and Earth return
     a) BFS does direct entry into Mars and Earth atmosphere
     b) BFS does orbital capture before performing entry burn and landing
     c) Same as b, but upon Earth return, stays in orbit for next synod

8)  Use of non-chemical thrust
     a) Not part of the plan
     b) Will use SEP for some/all of the big transits
     c) All chemical for now, but plans to incorporate SEP down the road


Can anyone think of more/better questions?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bob Shaw on 09/12/2016 06:40 pm
Thx 4 reply philw1776 I have a few counter and clarifying points.


Planning for future upgrades to BFR is interesting, but I'm doubtful that a vehicles diameter is made larger then necessary to allow for the insertion of extra engines at a later date.  First the extra engines and thrust would require a complete redesign of the plumbing structures and thrust structures which is a significant part of the first stages total design.

Actually, that is *exactly* the approach taken with the S-1C in the days of Saturn development!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DJPledger on 09/12/2016 07:06 pm
As the Big Reveal is nearly upon us (hopefully!), I think that someone (not me) should generate an official Mars MCT Architecture Prediction contest.  This would be composed of a list of questions with multiple choice answers, with a fixed value for each question.  Prizes TBD.

One problem is that L2 members may have 'insider information' on this topic.  So I guess they will have to be just guided by their own conscience as to their level of participation.

Anyway, I'll kick it off with a few suggested questions (but will be happy for someone else to officially take this over and come up with the canonical list, as well as being judge, jury, etc.)

1) Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft
     b)  Boost phase consists of 2 stages, which put the BFS into orbit
     c)  Other: 3rd stage, 'half' stages, drop tanks, etc.

2) Number of Raptor Engines on BFR (1st stage)

3) Diameter of BFR (1st stage)

4) Total Raptor 1st stage thrust (sl)

5) LAS Architecture
     a) No LAS - BFS is the escape mechanism
     b) Traditional LAS - above BFS and is nominally jettisoned during launch phase
     c) BFS contains smaller 'ejection pod' where humans reside during launch
     d) Other, non-traditional LAS design

6) Shape and Landing Mode of BFS
     a) Capsule (perhaps elongated), w/ TPS on base
     b) Cylindrical or biconic - horizontal landing
     c) Cylindrical or biconic - vertical landing
     d) Other

7) Mars and Earth return
     a) BFS does direct entry into Mars and Earth atmosphere
     b) BFS does orbital capture before performing entry burn and landing
     c) Same as b, but upon Earth return, stays in orbit for next synod

8)  Use of non-chemical thrust
     a) Not part of the plan
     b) Will use SEP for some/all of the big transits
     c) All chemical for now, but plans to incorporate SEP down the road


Can anyone think of more/better questions?
SL thrust of each Raptor on BFR.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/12/2016 09:01 pm
Thx 4 reply philw1776 I have a few counter and clarifying points.

Lastly I believe it may be possible to send tankers from Earth to a high mars orbit, have them offload propellants and still return to Earth orbit either via chemical propulsion or SEP so all vehicles are recovered.  This would allow the Mars landing and relaunch vehicles to be much lighter at liftoff from Mars, using something like 1/3rd as much propellant, then refill in orbit and make a fast return to Earth. 

The exact details of how and where refueling occurs aren't clear yet but what I'm sure of is that the direct return approach is not viable, the fixation many have with it is analogous to the fixation on direct earth return in the early days of Apollo, it's attractive for it's simplicity but it a bridge too far in a lot of engineering areas.

Gwynne has said, "We're looking at SEP" so this is a possibility.
On the downside if it's SEP, it is yet another vehicle to be developed and tested.

I haven't looked deeply at delta Vs, masses and run the rocket equation to comment cogently on the feasibility of SEP, etc. tankers to HMO & back.  I'm certain that SX has done so in their architectural bakeoffs.

First I find focusing on vehicle count as a measure of difficulty is a poor metric which I think has led many people astray, when the mission requires a high performance in a number of conflicting areas trying to achieve all these performance values out of one vehicle is usually far more difficult then breaking up the problem using specialized vehicle. 

That has been the lesson of all space travel, it's why rockets have stages, it's why the LEM rather then the command module landed on the moon and it's why I consistently foresee more complex mission modalities then the majority.

Second It's more likely that for retrieving tankers we would be looking at a SEP engine section carried on top of the 2nd stage like a payload and which remains attached to it for the duration of the mission.  Effectively creating a bi-modal-propulsion tanker.  The SEP propellants can used to return the tanker to LEO after it's offloaded all of the chemical propellants in the vicinity of Mars, the low dry mass at that point and the fact their is no propellant to chill means all power can be directed to the engines so the SEP unit dose not need to be very large at all. 

Alternatively if your willing to just throw chemical propellant at the problem, two tankers full in LEO should be able to go to high mars orbit and offload propellant to a manned return and then themselves return, though they would face high entry velocities.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 09/13/2016 10:24 am
As the Big Reveal is nearly upon us (hopefully!), I think that someone (not me) should generate an official Mars MCT Architecture Prediction contest.  This would be composed of a list of questions with multiple choice answers, with a fixed value for each question.  Prizes TBD.

One problem is that L2 members may have 'insider information' on this topic.  So I guess they will have to be just guided by their own conscience as to their level of participation.

Anyway, I'll kick it off with a few suggested questions (but will be happy for someone else to officially take this over and come up with the canonical list, as well as being judge, jury, etc.)

1) Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft
     b)  Boost phase consists of 2 stages, which put the BFS into orbit
     c)  Other: 3rd stage, 'half' stages, drop tanks, etc.

2) Number of Raptor Engines on BFR (1st stage)

3) Diameter of BFR (1st stage)

4) Total Raptor 1st stage thrust (sl)

5) LAS Architecture
     a) No LAS - BFS is the escape mechanism
     b) Traditional LAS - above BFS and is nominally jettisoned during launch phase
     c) BFS contains smaller 'ejection pod' where humans reside during launch
     d) Other, non-traditional LAS design

6) Shape and Landing Mode of BFS
     a) Capsule (perhaps elongated), w/ TPS on base
     b) Cylindrical or biconic - horizontal landing
     c) Cylindrical or biconic - vertical landing
     d) Other

7) Mars and Earth return
     a) BFS does direct entry into Mars and Earth atmosphere
     b) BFS does orbital capture before performing entry burn and landing
     c) Same as b, but upon Earth return, stays in orbit for next synod

8)  Use of non-chemical thrust
     a) Not part of the plan
     b) Will use SEP for some/all of the big transits
     c) All chemical for now, but plans to incorporate SEP down the road


Can anyone think of more/better questions?
SL thrust of each Raptor on BFR.

Implied by the combination of questions 2 and 4.  But maybe this would be a better question than #4.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 09/13/2016 06:24 pm
First I find focusing on vehicle count as a measure of difficulty is a poor metric which I think has led many people astray, when the mission requires a high performance in a number of conflicting areas trying to achieve all these performance values out of one vehicle is usually far more difficult then breaking up the problem using specialized vehicle. 

That has been the lesson of all space travel, it's why rockets have stages, it's why the LEM rather then the command module landed on the moon and it's why I consistently foresee more complex mission modalities then the majority.
I thought this too, and you still have a point about conflicting performance requirements, but the reason why Apollo was broken up into separate spacecraft instead of a direct ascent architecture was because expensive expendable rockets forced constraints on mass, so there were compromises.

The difference is that MCT speculators assume that a fully reusable launcher would reduce costs such that
IMLEO is no longer the primary constraint

The idea (with an all-chemical MCT) is that only a single monolithic vehicle needs to be developed, refueled by tankers (of mostly the same design) in Earth orbit before going to Mars (where it gets refueled by pre-placed ISRU before going back to Earth).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: KelvinZero on 09/15/2016 09:23 am
Gwynne has said, "We're looking at SEP" so this is a possibility.
On the downside if it's SEP, it is yet another vehicle to be developed and tested.
Random thought: What about a vehicle that can do missions with small crews without SEP, but you have a plan to add SEP later (as a stage, cycler or L2 propellant tug, whatever) when you have multiple flights to spread the costs over and want closer to that 500k/passenger goal, and also to achieve that fast return to earth for immediate reuse?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/15/2016 01:57 pm
Gwynne has said, "We're looking at SEP" so this is a possibility.
On the downside if it's SEP, it is yet another vehicle to be developed and tested.
Random thought: What about a vehicle that can do missions with small crews without SEP, but you have a plan to add SEP later (as a stage, cycler or L2 propellant tug, whatever) when you have multiple flights to spread the costs over and want closer to that 500k/passenger goal, and also to achieve that fast return to earth for immediate reuse?
Sure, just change how many tankers are used to refuel (& where) the BFS in orbit. SEP can be to push the fuel to a higher energy orbit before refueling.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 09/15/2016 08:36 pm
Gwynne has said, "We're looking at SEP" so this is a possibility.
On the downside if it's SEP, it is yet another vehicle to be developed and tested.
Random thought: What about a vehicle that can do missions with small crews without SEP, but you have a plan to add SEP later (as a stage, cycler or L2 propellant tug, whatever) when you have multiple flights to spread the costs over and want closer to that 500k/passenger goal, and also to achieve that fast return to earth for immediate reuse?
Sure, just change how many tankers are used to refuel (& where) the BFS in orbit. SEP can be to push the fuel to a higher energy orbit before refueling.

Staging fuel at EML1/2 or similar HEO with SEP would cut refueling launches from Earth by about 50% for crewed flights.

SEP tugs could also put cargo landers directly into TMI from LEO, and then quickly return to LEO. That would cut refueling Earth launches for cargo flights by 65% to 80%. And there will be a lot more cargo flights than crew flights.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/15/2016 10:00 pm
Gwynne has said, "We're looking at SEP" so this is a possibility.
On the downside if it's SEP, it is yet another vehicle to be developed and tested.
Random thought: What about a vehicle that can do missions with small crews without SEP, but you have a plan to add SEP later (as a stage, cycler or L2 propellant tug, whatever) when you have multiple flights to spread the costs over and want closer to that 500k/passenger goal, and also to achieve that fast return to earth for immediate reuse?
Sure, just change how many tankers are used to refuel (& where) the BFS in orbit. SEP can be to push the fuel to a higher energy orbit before refueling.

Staging fuel at EML1/2 or similar HEO with SEP would cut refueling launches from Earth by about 50% for crewed flights.

SEP tugs could also put cargo landers directly into TMI from LEO, and then quickly return to LEO. That would cut refueling Earth launches for cargo flights by 65% to 80%. And there will be a lot more cargo flights than crew flights.

I think that the Mars transport system will evolve considerably over time by the addition of new vehicles and operations that augment and multiply the effectiveness of the initial vehicle.

The BFR as the primary LEO launch vehicle and the vehicle that lands on mars will likely remain as they are in form and function as the constraints imposed during launch and landing force these vehicles to be very dedicated to these roles. 

But the entire middle of the transit will be subject to upgrading by adding one or more vehicles dedicated to that role as well as more complex rendezvouses, propellant transfers and cargo-handling operations.  So while initial missions are likely to see the mars lander just depart from LEO using large amounts of propellant the ultimate goal would be to keep the lander at Mars permanently and use an in-space only transfer vehicle. 

This is another reason that I reject the direct return modality, in creating a vehicle system designed for direct flight and completely independent operation it makes upgrading nearly impossible.  It is better to have the initial role out of the system be more flexible even if it makes for a more complex mission modality and higher IMLEO because it provides a smooth transition into expanded capacity and lower eventual prices.


Lastly SEP can not perform a TMI and then rapidly return to Earth.  If a SEP tug took a payload to the very edge of Earths gravity well and then accelerated to just above escape velocity and released the cargo the heliocentric orbit would still be very Earthlike and would not intersect Mars, the SEP tug has to push the payload a good deal beyond Earth escape to actually give a Mars intersecting trajectory to the payload, and this would take time, a few weeks at least even using a very high acceleration, low ISP SEP system, by that time the tug would be well away from the Earth with considerable velocity and return would take quite a long time via retro propulsion, it might be better to just let the tug fly on to mars and try to slingshot around mars back towards Earth as this would require virtually no propellant until your back in the Earths gravity well when you can try to decelerate and capture into an elliptical orbit.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/17/2016 12:42 am
Elon Musk ✔ @elonmusk
Turns out MCT can go well beyond Mars, so will need a new name…
8:22 PM - 16 Sep 2016
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Chris Bergin on 09/17/2016 12:55 am
Elon Musk ✔ @elonmusk
Turns out MCT can go well beyond Mars, so will need a new name…
8:22 PM - 16 Sep 2016

*Sirens* Elon has begun talking about MCT *Sirens* ;D

I just hope there aren't any stupid name suggestion tweets in the replies.......oh ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/17/2016 12:59 am
Enterprise, Defiant, Voyager, Discovery (new CBS show)....or how about Serenity?

Sent from my 9020A using Tapatalk

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/17/2016 01:37 am
Kazunori Makino ‏12 minutes ago
https://twitter.com/kzmakino/status/776954933820002305
Quote from: @kzmakino
Hi Mr. Musk,
how about "Interplanetary Colonial Transporter" ?
Quote from: Elon Musk
Turns out MCT can go well beyond Mars, so will need a new name…

 
https://twitter.com/elonmusk/status/776956202936782850
Quote from: Elon Musk

@kzmakino sounds about right
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/17/2016 05:44 am
Is he talking about the asteroid belt or something, I can't see the landing vehicle with it's normal atmospheric EDL profile being appropriate on any other planetary body in the solar system other then Venus. 

While it could retro-propulsive land on an airless body it would be complete overkill to do that on an asteroid with a vehicle with so much thrust and when something like RCS would be able to land and take off.  If he thinks the system will be this flexible it strongly suggests an in space transit vehicle is being used.

From what I can find the Delta V to get to main belt asteroids is around 4.5 km/s burn at LEO and another 4.5 km/s to direct land because their is no significant gravity well or anything to brake against.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/17/2016 05:56 am
Is he talking about the asteroid belt or something, I can't see the landing vehicle with it's normal atmospheric EDL profile being appropriate on any other planetary body in the solar system other then Venus. 
>

Ceres, Vesta....
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Zed_Noir on 09/17/2016 06:05 am
Is he talking about the asteroid belt or something, I can't see the landing vehicle with it's normal atmospheric EDL profile being appropriate on any other planetary body in the solar system other then Venus. 

While it could retro-propulsive land on an airless body it would be complete overkill to do that on an asteroid with a vehicle with so much thrust and when something like RCS would be able to land and take off.  If he thinks the system will be this flexible it strongly suggests an in space transit vehicle is being used.

From what I can find the Delta V to get to main belt asteroids is around 4.5 km/s burn at LEO and another 4.5 km/s to direct land because their is no significant gravity well or anything to brake against.
Maybe for Asteroid missions long duration SEP burns as orbital matching delta-V.

Ohh, don't forget the Moon. SpaceX might not have any cis-Lunar plans. Doesn't mean they will not provide transportation services to that region if someone is willing to pay.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: cebri on 09/17/2016 08:41 am
Kazunori Makino ‏12 minutes ago
https://twitter.com/kzmakino/status/776954933820002305
Quote from: @kzmakino
Hi Mr. Musk,
how about "Interplanetary Colonial Transporter" ?
Quote from: Elon Musk
Turns out MCT can go well beyond Mars, so will need a new name…

 
https://twitter.com/elonmusk/status/776956202936782850
Quote from: Elon Musk

@kzmakino sounds about right

ICT - Columbia Would be very nice.

Back on topic, going doesn't mean it'll be able to land. They are going to be bound to the capacity of manufacturing methane for fueling their ship.  I'm a bit skeptical that MCT is going to go anywhere is not Mars or even the Moon. But hey, amazing we are even having this conversation. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/17/2016 11:37 am
I'd think pre-positioned tankers at the destination make such trips a matter of stowed consumables, solar array efficiency etc. A crew of 10 with 50-100t of consumables could stay away from home for quite some time.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/17/2016 12:33 pm
Kazunori Makino ‏12 minutes ago
https://twitter.com/kzmakino/status/776954933820002305
Quote from: @kzmakino
Hi Mr. Musk,
how about "Interplanetary Colonial Transporter" ?
Quote from: Elon Musk
Turns out MCT can go well beyond Mars, so will need a new name…

 
https://twitter.com/elonmusk/status/776956202936782850
Quote from: Elon Musk

@kzmakino sounds about right

ICT - Columbia Would be very nice.

Back on topic, going doesn't mean it'll be able to land. They are going to be bound to the capacity of manufacturing methane for fueling their ship.  I'm a bit skeptical that MCT is going to go anywhere is not Mars or even the Moon. But hey, amazing we are even having this conversation.
Takes some cleverness. Maybe use tankers or SEP to get further. MCT should be able to do Ceres just fine. Maybe Callisto, too. Europa is doable but requires more radiation hardening.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/17/2016 03:23 pm
If it can get to Callisto and land it may be able to get to Titan aerobrake and land using far less landing delta V.  On Titan ISRU methane would be easy.  I believe Titan also has water ice on some parts of its surface.  If not, the other Saturnian moons are covered with ice. 

Callisto has water ice but no methane I know of.  Maybe Bezos sends a hydrolox tug with onboard nuclear reactor electricity generator to refuel itself and bring her back.  :)

Kidding aside, we need Bezos et. al. to get NASA to spend energy (Heh!) on a space qualified nuclear electric generator, needed for any trips beyond Ceres or so.  JUNO at Jupiter shows the limits of solar electric at 5AU.

I expect Musk to ask for cooperation and outside development of nukes for colonization at IAC.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Thorny on 09/17/2016 09:48 pm
Enterprise, Defiant, Voyager, Discovery (new CBS show)....or how about Serenity?

Pioneer
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/17/2016 10:03 pm
Is he talking about the asteroid belt or something, I can't see the landing vehicle with it's normal atmospheric EDL profile being appropriate on any other planetary body in the solar system other then Venus. 

While it could retro-propulsive land on an airless body it would be complete overkill to do that on an asteroid with a vehicle with so much thrust and when something like RCS would be able to land and take off. If he thinks the system will be this flexible it strongly suggests an in space transit vehicle is being used.

From what I can find the Delta V to get to main belt asteroids is around 4.5 km/s burn at LEO and another 4.5 km/s to direct land because their is no significant gravity well or anything to brake against.

I think your delta V budget is too high.
Just read a paper on NTP for a Jupiter flyby that used a Zubrin # of 4.19 Km/sec (edited) to get to Jupiter in 4.1 years.  My MCT model has ~6.5 Km/sec delta V capability fully fueled so I think most asteroids close to the ecliptic, and Saturn's moon Titan with aerobraking are in the cards.  Drop the 100 tonnes cargo to 50 tonnes or whatever and pick up almost another Km/sec.  Then again add in an onboard nuclear electric power source that weighs, what 25 tonnes net after dropping the solar panel array.  Whatever, back of the spreadsheet calcs say that a vehicle with MCT capability to Mars surface can get most anywhere, especially when you drop the cargo # a bit.

EDIT: I agree with your implication in bold, just not strongly, perhaps
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 09/18/2016 12:49 am
I think new Spacex MCT(ICT) could do excursion trips to Jupiter and Saturn moons, when Mars transportation will become regular service. It will be able to deliver small crew to  this moons for scientific trips.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Helodriver on 09/18/2016 01:10 am
In the days of sail and early transoceanic flight it was the Clipper that traversed the great spans bringing passenger and cargo to distant lands. So should the Interplanetary Clipper cross the expanses of space in the solar system. The names Clipper Asimov, Clipper Heinlein, Clipper Roddenberry, Clipper Bonestell have a nice ring to them.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/18/2016 02:05 am
https://twitter.com/elonmusk/status/777325549442232320

@elonmusk
Preview of the @SpaceX interplanetary transport system at @IAC2016
https://t.co/Rz4XmeAoRw

(Rocket scene from Lego Movie, but the name....)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Mongo62 on 09/18/2016 02:20 am
"Interplanetary Transport System" is kind of bland, but descriptive. "Mars Colonial Transport" had a definite Bladerunner vibe to me, while this seems more like a municipal rapid transit system.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/18/2016 02:27 am
I think that's the idea - a 21st century transcontinental railroad - in space.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: biosehnsucht on 09/18/2016 03:29 am
I was hoping for perhaps Multibody Cononial Transporter, to keep the MCT acronym. I'm used to it and it has a nice sound to it ... ITS not so much.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/18/2016 04:30 am
Is he talking about the asteroid belt or something, I can't see the landing vehicle with it's normal atmospheric EDL profile being appropriate on any other planetary body in the solar system other then Venus. 

While it could retro-propulsive land on an airless body it would be complete overkill to do that on an asteroid with a vehicle with so much thrust and when something like RCS would be able to land and take off.  If he thinks the system will be this flexible it strongly suggests an in space transit vehicle is being used.

From what I can find the Delta V to get to main belt asteroids is around 4.5 km/s burn at LEO and another 4.5 km/s to direct land because their is no significant gravity well or anything to brake against.
Maybe for Asteroid missions long duration SEP burns as orbital matching delta-V.

Ohh, don't forget the Moon. SpaceX might not have any cis-Lunar plans. Doesn't mean they will not provide transportation services to that region if someone is willing to pay.

SEP has always made more sense on a transfer vehicle then on a lander, that's my point that the mars landing vehicle is probably not what is going out to the asteroid belt.  As for the moon, we have always known the MCT was to be capable of landing their, that's not 'beyond Mars' and dose not explain this new statement in any way.

The idea of an in-space transit vehicle, propellant tanker and SEP are things that I've been talking about for at least a year as the most likely means to accomplish the Mars transport goals and this has been in stark contrast to a direct-all-chemical integrated 2nd stage architecture that's been the preferred mode of most other commentators.  So the lack of crow eating seems odd as that architecture should be ruled out entirely if this statement is taken literally, at best one might argue for a family of vehicles of which one might do the mars flight and other which go further.

I'm incredibly doubtful of traveling to any of the moons of gas-giants within any near term vehicle, that requires huge delta V, many years of transit time and lots of radiation mitigation.



I think your delta V budget is way too high.
Just read a paper on NTP for a Jupiter flyby that used a Zubrin # of 4.19 Km/sec (edited) to get to Jupiter in 4.1 years.  My MCT model has ~6.5 Km/sec delta V capability fully fueled so I think most asteroids close to the ecliptic, and Saturn's moon Titan with aerobraking are in the cards.  Drop the 100 tonnes cargo to 50 tonnes or whatever and pick up almost another Km/sec.  Then again add in an onboard nuclear electric power source that weighs, what 25 tonnes net after dropping the solar panel array.  Whatever, back of the spreadsheet calcs say that a vehicle with MCT capability to Mars surface can get most anywhere, especially when you drop the cargo # a bit.

EDIT: I agree with your implication in bold, just not strongly, perhaps

That can't possibly be right, 4.19 km/s is barely a decent speed Mars bound injection, Wikipedia lists a trans Jovian injection on slow Hohmann transfer from LEO as 6.3 km/s.  The study your reading must have assumed the launch vehicle was contributing significantly the Earth escape delta V,  this is an instance where a simply sanity check should have been done on a number that sounded too good to be true.  So the high delta-V MCT design in question would arrive in the Jovian system with only about 1.2 km/s remaining, not enough to land on any any moon or likely even capture into the Jovian gravity-well, and the transit time of 4 years is a show stopper even if you had that much propellant.

Note that we can't aero-capture or even approach Jupiter the radiation intensity right at the planet in it's equivalent of the van-Allen belts is unbelievable, some of the outer most moons might be approachable but the core of the Jovian system is basically a no-go zone for manned spacecraft and that makes orbital mechanics much more difficult because you lose much of the Oberth benefits that we take for granted.  You would be looking at low efficiency purely propulsive braking at the outer edge of the system to capture into an orbit close to that of the moon you want to land on, with Callisto being the easiest to reach.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Eric Hedman on 09/18/2016 05:05 am
"Interplanetary Transport System" is kind of bland, but descriptive. "Mars Colonial Transport" had a definite Bladerunner vibe to me, while this seems more like a municipal rapid transit system.
If "Interplanetary Transport System" is kind of bland, how about Intrastellar Colonial Transport since it would stay within the our stellar system?  Plus it wouldn't sound limited to going to planets.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MATTBLAK on 09/18/2016 05:57 am
if they called it 'Intrasteller', there will always be someone in the media mis-pronouncing it as 'Interstellar' :(
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 09/18/2016 08:43 pm
Re using MCT (or ICT...) for Ceres, Europa, etc.:  Shouldn't we be basing delta Vs on leaving from Mars orbit rather than from LEO?  And refueled in LMO from Mars sourced ISRU propellants?  How much does this extend the ICT's reach?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/18/2016 09:17 pm
It worsens it, LEO is around 4 km/s faster the LMO and your deeper in the suns gravity well too, all of that makes for a higher Oberth effect and higher velocity at infinity.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 09/18/2016 11:29 pm
It worsens it, LEO is around 4 km/s faster the LMO and your deeper in the suns gravity well too, all of that makes for a higher Oberth effect and higher velocity at infinity.

However, refuelling in Mars orbit changes these assumptions. Launch into LEO (or HEO), refuel in LEO (or HEO), launch to Mars, aerobrake into Mars orbit (not surface), refuel from Mars ISRU prop launched into LMO (or HMO) by tugs...

Creating fuelling stations at each stepping stone breaks the rocket equation and changes our normal assumptions of spaceflight "efficiency".
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/19/2016 12:17 am
Why go through the monkey motion in LMO  vs just landing and refuelling from a Tesla tanker truck? Fewer pieces, fewer steps.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 09/19/2016 12:54 am
Fewer pieces, fewer steps.

...Less delta-v available after re-launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/19/2016 01:07 am
If the vehicle is split, Fagin-esque, it's also much light because the lower cargo section stays on Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/19/2016 07:45 am
It worsens it, LEO is around 4 km/s faster the LMO and your deeper in the suns gravity well too, all of that makes for a higher Oberth effect and higher velocity at infinity.

However, refuelling in Mars orbit changes these assumptions. Launch into LEO (or HEO), refuel in LEO (or HEO), launch to Mars, aerobrake into Mars orbit (not surface), refuel from Mars ISRU prop launched into LMO (or HMO) by tugs...

Creating fuelling stations at each stepping stone breaks the rocket equation and changes our normal assumptions of spaceflight "efficiency".

That sounds very inefficient, your scrubbing speed at mars that you then have to regain via propellant picked up at mars.  Having any kind of braking necessary to reach your next propellant fill up, even if it is frictional braking is going to be really bad.  But lets stop spit balling and crunch some numbers, lets say the destination is the Jovian system.  Based on this table http://www.projectrho.com/public_html/rocket/appmissiontable.php I can deduce the mars to Jupiter deltaV.

Direct from LEO we need 6.3 km/s

If we go to mars first  we can depart with just 3.6 km/s to mars and if we capture fictionally all the way to LMO, then from LMO a burn of 4.3 km/s is needed to send you on to Jupiter.  High mars orbit is 1.44 km/s above LMO so the Jupiter burn their would be 2.9 km/s from there.

That's still a total of 7.9 km/s but it is admittedly broken up into two legs which are considerably less then the single burn from LEO.  To convert that into propellant fraction at 380 ISP, at Earth you need 4.4:1 propellant to dry ratio to go to Jupiter, but to go to mars you need 1.6:1 and then at mars you need 2.1:1 to complete the journey.

So total propellant is very similar with the direct from Earth method need 19 percent more total.  The question is really one of the trades between availability of propellant at Earth and Mars, as I think propellant in mars orbit is going to be significantly more expensive then propellant in earth orbit so I think the direct approach wins.

If you think 6.3 km/s is too much for one vehicle to handle then simply depart from a high Earth orbit which will split the deltaV very nicely into 3.2 and 3.1 which gets you virtually the same departure burn that you would have needed from high mars orbit, which proves my point their is no advantage to falling into the mars gravity well if your destination is an outer planet.

But the whole idea is really moot anyway cause it would take lots more delta v then is viable upon arrival to just land on a moon like Callisto, Titan would be do able with aero-braking and direct decent but we are not going to send people out that far in any kind of conceivable time frame.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/19/2016 11:24 am

That sounds very inefficient, your scrubbing speed at mars that you then have to regain via propellant picked up at mars.  Having any kind of braking necessary to reach your next propellant fill up, even if it is frictional braking is going to be really bad.  But lets stop spit balling and crunch some numbers, lets say the destination is the Jovian system.  Based on this table http://www.projectrho.com/public_html/rocket/appmissiontable.php I can deduce the mars to Jupiter deltaV.

Direct from LEO we need 6.3 km/s

If we go to mars first  we can depart with just 3.6 km/s to mars and if we capture fictionally all the way to LMO, then from LMO a burn of 4.3 km/s is needed to send you on to Jupiter.  High mars orbit is 1.44 km/s above LMO so the Jupiter burn their would be 2.9 km/s from there.

That's still a total of 7.9 km/s but it is admittedly broken up into two legs which are considerably less then the single burn from LEO.  To convert that into propellant fraction at 380 ISP, at Earth you need 4.4:1 propellant to dry ratio to go to Jupiter, but to go to mars you need 1.6:1 and then at mars you need 2.1:1 to complete the journey.

So total propellant is very similar with the direct from Earth method need 19 percent more total.  The question is really one of the trades between availability of propellant at Earth and Mars, as I think propellant in mars orbit is going to be significantly more expensive then propellant in earth orbit so I think the direct approach wins.

If you think 6.3 km/s is too much for one vehicle to handle then simply depart from a high Earth orbit which will split the deltaV very nicely into 3.2 and 3.1 which gets you virtually the same departure burn that you would have needed from high mars orbit, which proves my point their is no advantage to falling into the mars gravity well if your destination is an outer planet.

But the whole idea is really moot anyway cause it would take lots more delta v then is viable upon arrival to just land on a moon like Callisto, Titan would be do able with aero-braking and direct decent but we are not going to send people out that far in any kind of conceivable time frame.

The spacecraft formerly known as MCT could be purchased by some future billionaire or government space agency to land a large cargo payload on Titan's surface or just aerobrake at Titan and land on say, Enceladus.  Various combinations thereof, possibly dropping off small landing vehicle payloads of several tons. Expensive but clearly matching the name of ITS.  Would need a nuclear power source that far out but ITS should have the cargo hold space to fit one.  Cut the nominal 100T cargo payload to some lower # to pick up delta V.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 09/19/2016 02:38 pm
Is he talking about the asteroid belt or something, I can't see the landing vehicle with it's normal atmospheric EDL profile being appropriate on any other planetary body in the solar system other then Venus. 

Venus it is then. It's the easiest place to colonize anyway.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/19/2016 03:10 pm
Land on Ceres or the Moon. Musk had earlier made reference to landing MCT on the Moon. Ceres would be similar.

The landing thrust is not necessarily a big problem. You can do a burn above the surface and cut off thrust at just the right moment and fall the rest of the way, perhaps using RCS thrusters to finetune the landing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 09/19/2016 04:17 pm
Land on Ceres or the Moon. Musk had earlier made reference to landing MCT on the Moon. Ceres would be similar.

The landing thrust is not necessarily a big problem. You can do a burn above the surface and cut off thrust at just the right moment and fall the rest of the way, perhaps using RCS thrusters to finetune the landing.

Ceres? With chemical propulsion?

The moon is certainly possible, though lunar ISRU (water ice) would clearly favor hydrolox (from what I remember).

The spacecraft formerly known as MCT could be purchased by some future billionaire or government space agency to land a large cargo payload on Titan's surface or just aerobrake at Titan and land on say, Enceladus.

Sending cargo one-way doesn't require a vehicle like MCT. There's no need to land the entire Earth departure stage and the heat shield if they're not needed to get back. That said, an aeroshell of similar size is still required. For Venus colonization for example, I would expect payloads to go one way with expendable aeroshells.
 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/19/2016 05:49 pm
Who said purely chemical propulsion? It could be done (I could show you if you like), but I'm not going to say SpaceX has ruled it out yet!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/19/2016 06:36 pm
Land on Ceres or the Moon. Musk had earlier made reference to landing MCT on the Moon. Ceres would be similar.

The landing thrust is not necessarily a big problem. You can do a burn above the surface and cut off thrust at just the right moment and fall the rest of the way, perhaps using RCS thrusters to finetune the landing.

Ceres? With chemical propulsion?

The moon is certainly possible, though lunar ISRU (water ice) would clearly favor hydrolox (from what I remember).

The spacecraft formerly known as MCT could be purchased by some future billionaire or government space agency to land a large cargo payload on Titan's surface or just aerobrake at Titan and land on say, Enceladus.

Sending cargo one-way doesn't require a vehicle like MCT. There's no need to land the entire Earth departure stage and the heat shield if they're not needed to get back. That said, an aeroshell of similar size is still required. For Venus colonization for example, I would expect payloads to go one way with expendable aeroshells.

Of course it doesn't.
Just showing that the spacecraft formerly known as MCT or BFS has the capability.  It meets the "ITS" claim.
Certainly not optimal or purpose built for such missions as far as we know.

Think about this. 
What other craft claimed to be under development could actually get 10s of tonnes to the aforementioned destinations in its claimed configuration?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/19/2016 06:41 pm
The problem with Ceres is the extra delta V for out of plane xfer.  However, slowing down @Ceres does not need delta V again for plane change.  I have not run the #s myself to see what a cargo tonnes reduction offers in increased delta V in a Ceres scenario.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/19/2016 09:45 pm

The spacecraft formerly known as MCT could be purchased by some future billionaire or government space agency to land a large cargo payload on Titan's surface or just aerobrake at Titan and land on say, Enceladus.  Various combinations thereof, possibly dropping off small landing vehicle payloads of several tons. Expensive but clearly matching the name of ITS.  Would need a nuclear power source that far out but ITS should have the cargo hold space to fit one.  Cut the nominal 100T cargo payload to some lower # to pick up delta V.

While a one way unmanned expendable landing on Titan seems technologically plausible, I don't think it fulfills the 'C' keyword colonial anymore.  Of course the transit time to Saturn blows any hope of amortization away so their is little point in getting the vehicle back if it is unmanned.


Is he talking about the asteroid belt or something, I can't see the landing vehicle with it's normal atmospheric EDL profile being appropriate on any other planetary body in the solar system other then Venus. 

Venus it is then. It's the easiest place to colonize anyway.

I am one that believes is unfairly overlooked to do to 'surfacism' and I find concepts like Landis2land and HAVOC plausible, deploying large balloons to float in the Venusian atmosphere at an altitude with a hospitable temperature and sunlight.  But it is likely better to just drop a full functional habitats directly into the atmosphere rather then employ a vehicle to carry it.

The problem with Ceres is the extra delta V for out of plane xfer.  However, slowing down @Ceres does not need delta V again for plane change.  I have not run the #s myself to see what a cargo tonnes reduction offers in increased delta V in a Ceres scenario.

The plane change is just icing on the cake, the real problem is that the tiny gravity wells give you almost no Oberth benefit when capturing.  The DeltaV to land on Vesta from LEO is 8.7 km/s, from LMO it's considerably better at 4 km/s.  The other large asteroids are slightly harder to reach as Vesta is one of the easier ones. 

So going from mars out to an asteroid is just barely plausible if you have the ability to fill up in mars orbit, and can tolerate a 500 day transit.  Return would likely be directly to Earth.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CuddlyRocket on 09/19/2016 10:55 pm
I am one that believes is unfairly overlooked to do to 'surfacism' and I find concepts like Landis2land and HAVOC plausible, deploying large balloons to float in the Venusian atmosphere at an altitude with a hospitable temperature and sunlight.

Plausible? Theoretically, perhaps. Practical? In the light of today's engineering knowledge and industrial infrastructure, very questionable! The same goes for Lunar water-ice mining; Martian orbital propellant depots; O'Neill habitats etc. One day, we might see some or all of these things - though by 'we', I mean humanity; I don't expect to see many, if any, of these in my lifetime.

What's the strategy for bringing any of these things into existence; other than a Kennedy-esque program involving the spending of large amounts of public money - a plan fraught with potential political pitfalls! (One of Musk's strengths is his ability to see the practical, profitable steps between the here and now and his future goals.)

In any event, none of these things seem to be within the ambit of SpaceX's activities or plans, so should be discussed in other, more appropriate parts of the forum!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: ciscosdad on 09/20/2016 12:10 am
In my view, the MCT system (or whatever its to be called) will initially perform refuelling in low earth orbit. '
Later if demand requires it or the performance is needed, then a depot at L1, L2 or somewhere else at the edge of our gravity well.
The decision will be based on infrastructure cost. Fuel depots are relatively simple, but will be costly, as is all space based devices.
Given the amazing usefulness of this system, I expect rapid expansion of the fleet and its capabilities. Missions to Ceres, Vesta or anywhere beyond Mars will increasingly demand the higher performance

my 2c

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/20/2016 12:15 am
I love how Venus is viewed as somehow easier to colonize by people fond of contrarian theories. It might be POSSIBLE to colonize, but no way in heck is it easier. Please try, though. May a thousand flowers bloom!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/20/2016 01:16 am
I wouldn't say it is easy, I'd say that mars colonization difficulty is just massively under-estimated. 

Their is a belief that planetary surfaces are easy source of resources but I contend that mining and processing solid surfaces is the least desirable means of acquiring resources.  Atmospheric processing is preferable both for propellant production and producing chemical feed stocks for life-support and manufacturing.  So my low assessment of the value of surfaces puts Mars and Venus on roughly equal footing as the Venusian gravity well dose present significant difficulty in return to Earth which balance it's higher solar flux, radiation protection, temperature, pressure and more frequent launch opportunities and lower transit times.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 09/20/2016 05:18 am
MCT, including all the technologies necessary to get to Mars and back, is a starting point for serious planetary exploration.  There are only very limited things you get to think about with planetary exploration if you're confined to existing launch vehicles and no propellant depots.   A fully reusable MCT that gets fully refueled in LEO permits you to bring a payload somewhere in the 300-1000 ton class to Earth escape velocity.  If that payload is itself a multi-stage rocket, it opens up the possibility to send sizable probes to a great number of places on (high-thrust chemical) mission timeframes that fit within a principal investigator's career length, and low-thrust missions that send massive quantities of hardware on longer journeys.

Refuel fully in high Earth orbit with an expendable MCT, and you can start thinking about things like Main Belt, Jupiter Moon, and Saturn Moon sample returns.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DaveH62 on 09/20/2016 05:32 am
Wouldn't it make more sense to refuel in lunar orbit and use earth gravity for a kick on your way out?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 09/20/2016 06:42 am
How about this?

Fully fuel MCT and a tanker in LEO. Launch them in tandem to a highly elliptic orbit, chosing the orbit so that the tanker has enough fuel left to fully fuel the MCT again. The tanker returns to earth on that orbit. The MCT does its earth departure burn at perigee with max. efficiency. How much delta-v would that gain over starting in LEO? Close to 3km/s?

It is operationally less complex than a depot. A depot may become more efficient when many flights go beyond Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 09/20/2016 07:18 am
It looks like MCT (ITS, BFS) can reach  433 Eros (http://trajbrowser.arc.nasa.gov/traj_browser.php?NEOs=on&NEAs=on&chk_maxMag=on&maxMag=12&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=&mission_class=roundtrip&mission_type=rendezvous&LD1=2015&LD2=2035&maxDT=15&DTunit=yrs&maxDV=20&min=DV&wdw_width=-1&submit=Search#a_load_results)

and here are the one way best trajectories to Vesta, Ceres, Hygiea and Juno (http://trajbrowser.arc.nasa.gov/traj_browser.php?maxMag=18&maxOCC=4&chk_target_list=on&target_list=Vesta%0D%0ACeres%0D%0APallas%0D%0AJuno%0D%0AAstraea%0D%0AHebe%0D%0AIris%0D%0AFlora%0D%0AMetis%0D%0AHygiea&mission_class=oneway&mission_type=rendezvous&LD1=2025&LD2=2040&maxDT=5&DTunit=yrs&maxDV=10&min=DV&wdw_width=0&submit=Search#a_load_results) which maybe possible for it with a reduced payload.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 09/20/2016 07:36 am
Wouldn't it make more sense to refuel in lunar orbit

Both HEO(at about GEO height) and lunar orbit are problematic, it would take about  4 km/s from LEO to get to either. If the craft starts from suborbital 2-3km/s velocity after staging(cannot stage much later if first stage is recovered, or needs enourmous first stage), this means about 9-10km/s total delta-v. This is just way too much, payload fraction gets very bad. You would need to refuel at both LEO and lunar orbit if you want to refuel at HEO or lunar orbit.

From delta-v point of view some highly elliptical earth orbit would make much more sense, but then there may be the problem of crossing the van allen belts multiple times.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 09/20/2016 07:47 am
How about this?

Fully fuel MCT and a tanker in LEO. Launch them in tandem to a highly elliptic orbit, chosing the orbit so that the tanker has enough fuel left to fully fuel the MCT again. The tanker returns to earth on that orbit. The MCT does its earth departure burn at perigee with max. efficiency. How much delta-v would that gain over starting in LEO? Close to 3km/s?

It is operationally less complex than a depot. A depot may become more efficient when many flights go beyond Mars.

This seems like it could work and 3km/s is in the correct ballpark.

Though, the question is that could a single tanker refuel the MCT/ITS after it has already spent 3km/s impulse for acccelerating itself(and the fuel), or would multiple tankers be needed/would the tankers need to be much bigger than the MCT/ITS?

When the tanker is returning to LEO it does not need much fuel because it can do aerobraking. Or it could return directly to earth instead of returning to LEO.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 09/20/2016 08:40 am

Though, the question is that could a single tanker refuel the MCT/ITS after it has already spent 3km/s impulse for acccelerating itself(and the fuel), or would multiple tankers be needed/would the tankers need to be much bigger than the MCT/ITS?

When the tanker is returning to LEO it does not need much fuel because it can do aerobraking. Or it could return directly to earth instead of returning to LEO.

Without calculation it seems to me that one tanker could be enough or nearly enough to give the max advantage. The tanker is much lighter than MCT, at least by the 100t payload, probably a lot more. With a delta-v of much more than 12km/s it should have more than half its propellant load left to transfer after spending 3km/s delta-v.

My assumption, the tanker is purely the propulsion unit of an MCT and should have a dry weight at ~40t 60t, compared to  160t or more of MCT including payload.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: OneSpeed on 09/20/2016 09:33 am
Without calculation it seems to me that one tanker could be enough or nearly enough to give the max advantage.

A simulation and analysis of this concept has been in L2 for some time.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/20/2016 04:17 pm
It's OK to post an L2 link here as non-members simply can't access it
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 09/20/2016 05:19 pm
It's OK to post an L2 link here as non-members simply can't access it

The header of the quote is the link.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: rakaydos on 09/20/2016 05:28 pm
Would a BFR first stage be able to single-stage-to-orbit without the BFS?

I'm wondering how hard it would be to get a BFR into orbit, fuel it, send it to Titan, propulsively land, and use ISRU to use it repeatedly as a Titan launch vehical.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 09/20/2016 05:44 pm
BFR is never going beyond suborbital Earth trajectories.

If you want a vehicle to launch of other solar system bodies, why not use BFS, which will be designed to do exactly that?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/20/2016 05:54 pm
Would a BFR first stage be able to single-stage-to-orbit without the BFS?

I'm wondering how hard it would be to get a BFR into orbit, fuel it, send it to Titan, propulsively land, and use ISRU to use it repeatedly as a Titan launch vehical.
Without any payload? Quite possibly.

Your idea is impractical (BFR is not designed itself for interplanetary travel) but still very interesting. Should be capable of putting hundreds of tons into Titan orbit IF (big if!!!) fueled up on the surface.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 09/20/2016 07:13 pm
BFR as a system comprises the booster, the pad and the "refurb street".  Having only the booster landed on Titan gives you nothing, usability wise.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/21/2016 05:31 pm
Would a BFR first stage be able to single-stage-to-orbit without the BFS?

I'm wondering how hard it would be to get a BFR into orbit, fuel it, send it to Titan, propulsively land, and use ISRU to use it repeatedly as a Titan launch vehical.
Without any payload? Quite possibly.

Your idea is impractical (BFR is not designed itself for interplanetary travel) but still very interesting. Should be capable of putting hundreds of tons into Titan orbit IF (big if!!!) fueled up on the surface.
That should be thousands of tons into Titan orbit, not just hundreds. Could also land thousands of tons.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/21/2016 05:39 pm
BFR as a system comprises the booster, the pad and the "refurb street".  Having only the booster landed on Titan gives you nothing, usability wise.
Well, sure. Kind of is assumed you're landing a bunch of ISRU equipment first.

Anyway, not sure it's worth it this century. Titan is VERY far away. Ceres, on the other hand, is very near. And due to the very low gravity, a rocket like BFR or BFS should be able to launch ~5 its own mass in payload to orbit. It'd look weird doing that. Heck, you could make a space elevator really easily on Ceres, and it'd even be worth it, too, since it wouldn't have to be very long (so you could make like a round-trip every day on it) and the cable would be able to lift like a dozen times its own mass, and it should be able to sling stuff back to Earth fairly easily.

But anyway, yeah, BFS would be interesting for all kinds of destinations, not just Mars.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CuddlyRocket on 09/21/2016 07:22 pm
Heck, you could make a space elevator really easily on Ceres...

I make the Clarke orbit for Ceres to be ~1,200 km from the centre, or about 740 km above the surface. So, a lot easier to build a space elevator for Ceres than Earth!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: JasonAW3 on 09/21/2016 07:50 pm
It occurs to me to wonder if the whole MCT concept actually comprises two segments that are effectively considered one craft.

     The top section, the actual lander, would be based upon an enlarged version of the Dragon 2 space craft, while the transfer vehicle, (Essentially, the habitat section and Mars transfer section and fuel) are designed in much the same manner as the old Pilgrim Observer concept.

     On launch and landing, all the passengers and crew would be strapped into seats in the lander, but upon orbit, the Lander would detach, turn about and dock with the actual transfer craft.  They would fully fuel the transfer craft in orbit, as well as the lander.  Once fueling is complete, and after the initial TMI burn, the three arms would be extended, and crew and passengers would transfer to the habitats.  Rotation would then be started kept to approximately that of Mars.

     As the craft approached Mars, the spin would be discontinued, and arms retracted.  Either some form of aerobraking or direct thrust deceleration would be used to achieve orbit.  The crew and passengers would then transfer to the lander and descend to Mars, leaving the Mars Transfer Vehicle in orbit.

     As the lander would be largely empty of passengers for the return flight, much of the room, both passenger and cargo space, would be given over to fuel tankage to refuel the MTV and lander for the Earth return trip.

     Point of note, SpaceX has repeatedly stated that what they have in mind for the MCT was a Mars Colonial Transport SYSTEM not simply a stage and lander.

      I could be off base about this, but it does seem to make sense, and would provide a substantial infrastructure for continuous use as a colonizing system.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/21/2016 09:35 pm
Reaching main belt asteroids via chemical propulsion is a no go.  It would take around 5 km/s burn at LEO to start the transfer and ANOTHER 5 km/s to land.  That mean SSTO propellant fractions.  Plus the transit time is a full year and their is no atmosphere to make propellant from for return.

Reaching Titan is actually easier then that, it would be 7.3 km/s burn at LEO but you can use friction to do all the deceleration at Titan.  Taking off again on Titan would be a nightmare because of the atmospheric thickness, per unit of surface area a column of Titans atmosphere is 7.3 times more massive then Earths and has huge scale height so the launch vehicle must spend a lot of time at low speed plowing through this atmosphere which adds to gravity losses too, finally the density of the atmosphere means rocket engines would yield less then sea-level ISP due to under-expansion in nozzles.

So don't expect to get a vehicle back from Titan, the transit times alone means their is little point anyway as the vehicle can't get amortized over enough missions to make reuse attractive.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: rakaydos on 09/21/2016 11:46 pm
Reaching Titan is actually easier then that, it would be 7.3 km/s burn at LEO but you can use friction to do all the deceleration at Titan.  Taking off again on Titan would be a nightmare because of the atmospheric thickness, per unit of surface area a column of Titans atmosphere is 7.3 times more massive then Earths and has huge scale height so the launch vehicle must spend a lot of time at low speed plowing through this atmosphere which adds to gravity losses too, finally the density of the atmosphere means rocket engines would yield less then sea-level ISP due to under-expansion in nozzles.

So don't expect to get a vehicle back from Titan, the transit times alone means their is little point anyway as the vehicle can't get amortized over enough missions to make reuse attractive.
That's actually why I proposed the reusable Titan BFR-varient idea- because even if it requires some performace-penalizing modifications to make the trip, the core problems of lift through a thick atmosphere are solved for Earth, and many of the same solutions would be equally viable for Titan.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 09/21/2016 11:52 pm
Point of note, SpaceX has repeatedly stated that what they have in mind for the MCT was a Mars Colonial Transport SYSTEM not simply a stage and lander.

However, Musk has explicitly described the system as BFR + BFS. With BFR being a giant booster, and BFS being the upper-stage cum Mars transport cum Mars lander cum Earth return vehicle.

He may have changed his mind, and we'll hopefully find out soon, but there's nothing announced yet by SpaceX that implies he has.

Heck, you could make a space elevator really easily on Ceres...
I make the Clarke orbit for Ceres to be ~1,200 km from the centre, or about 740 km above the surface. So, a lot easier to build a space elevator for Ceres than Earth!

A ground-based, horizontally rotating, launch-sling tower would be even easier. (But that may be somewhat off-topic for an MCT thread.)

But since I'm going off-topic...

Taking off again on Titan would be a nightmare because of the atmospheric thickness

Titan seems like the only place where supersonic/hypersonic air-breathing hybrid SSTO makes sense. You only need small wings/lifting-body-effect to get off a runway (or lose very little from VTOL), making an optimised supersonic (or even hypersonic) airframe more compatible with the slow sub-sonic flight regime, reducing the need to trade.

I doubt there's enough hydrocarbon in the atmosphere to actually fuel the turbines/ramjets (via on-board LOx), I'm just assuming the atmosphere serves as bulk inert mass for a turbofan powered by a stored-fuel/LOx jet engine. Hell, even electric ducted-fans for subsonic flight (and landing) might be useful to get to and from high altitudes.

(Titan might also be the only place other novel/barely-workable/downright-silly ideas make sense. Like balloon launch. Air-launch. VTHL flyback boosters. Etc.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/22/2016 12:29 am

However, Musk has explicitly described the system as BFR + BFS. With BFR being a giant booster, and BFS being the upper-stage cum Mars transport cum Mars lander cum Earth return vehicle.

He may have changed his mind, and we'll hopefully find out soon, but there's nothing announced yet by SpaceX that implies he has.


Musk has never said BFS is an upper stage or that it is a lander or that it is even a monolithic vehicle rather then a vehicle stack.  That's what many people have chosen to interpret it as.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/22/2016 01:22 am

However, Musk has explicitly described the system as BFR + BFS. With BFR being a giant booster, and BFS being the upper-stage cum Mars transport cum Mars lander cum Earth return vehicle.

He may have changed his mind, and we'll hopefully find out soon, but there's nothing announced yet by SpaceX that implies he has.


Musk has never said BFS is an upper stage or that it is a lander or that it is even a monolithic vehicle rather then a vehicle stack.  That's what many people have chosen to interpret it as.
He has said "land the whole thing", which is not just "interpretation."
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/22/2016 02:35 am
Yes that is an interpretation, your interpreting 'thing' to refer to the entire space craft that transits between Earth and Mars and not simply the lander at atmospheric entry, every other mars lander to date has been a Matryoshka doll that disassembles during EDL, so Musk may simply be expressing their EDL plan rather then talking about the entire mars bound vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 09/22/2016 03:50 am
Seems obvious to me that he was saying everything to be thrown as Mars was going to land on Mars. Weather that worked out when they dug into the design, we will find that out in a week.

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/22/2016 04:39 am
First off the quote is "I think you just land the entire thing." indicating he is far from decided.  The followup question was exactly to get him to clarify what 'thing' was and if it meant the giant reusable rocket then called the MCT, he said  "Maybe." 

So their is absolutely no justification for interpreting this as a set in stone architecture, the monolithic rocket lander is certainly on the table given what Musk says but it's not singled out as the only configuration being considered.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 09/22/2016 05:31 am
Musk definetly said (sometimes repeatedly):

1) There's a booster (BFR) and there's a spaceship (BFS). No further elements (e.g. upper stages, transfer habitats etc.) mentioned.

2) "Land the whole thing" in response to a question on the architecture in the vicinity of Mars. Also, approach fully reusable otherwise cannot aford it, sothere will be no matrioshkas.

3) A figure shown by a user on twitter showing essentially the BFR-boosted BFS flying to Mars, refueling there and flying back to Earth entry was commented by him to be the best representation of the MCT to date.

So I think the basic architecture is very clear.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Geron on 09/22/2016 06:10 am
I'm worried because the topic has changed to "Elon musk will discuss technologies and challenges that need to be tackled by governments and companies to create colony on Mars."

The topic used to be "SpaceX mars architecture."

Seems like confidence may have been shaken?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: AbuSimbel on 09/22/2016 09:21 am
I think they are talking about building the colony when they say "architectures in which others can partecipate". They want to provide an apt means of transportation but arguably they've  always known that building a colony can't be done on themselves. It's not only a financial matter: such an endeavor requires fine engineering in almost every field, from the kitchen equipment to the toilets to planning the whole hab architecture. A colony can't be done by a single company, neither SpaceX wants to do that: Elon envisions an international effort to create an environment on Mars in which people from all around the world can come and expand. I reckon this speech will be the beginning of an effort to seek collaboration on that, to spread the word that "building a colony on Mars is not sci-fy anymore, we are providing ITS/BFR to make it possible, are you on board?" And that's why they've chosen IAC and not a webcast from Hawthorne. Anyways we'll see in 5 days.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TomH on 09/22/2016 03:57 pm
...A figure shown by a user on twitter showing essentially the BFR-boosted BFS flying to Mars, refueling there and flying back to Earth entry was commented by him to be the best representation of the MCT to date...

Anyone have that image or a link to it? That's something I would like to see!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: TheTraveller on 09/22/2016 06:02 pm
...A figure shown by a user on twitter showing essentially the BFR-boosted BFS flying to Mars, refueling there and flying back to Earth entry was commented by him to be the best representation of the MCT to date...

Anyone have that image or a link to it? That's something I would like to see!

Was this the video?

https://m.youtube.com/playlist?list=PLBU9UJfqaRooKnHY8QtQ399qqRwBqU6W3
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/22/2016 10:44 pm
Hi Everyone, this is a concept of a monolithic BFS: http://imgur.com/gallery/fGzkH

And a previous modular concept: http://imgur.com/a/15fO2
 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 09/22/2016 11:17 pm


Hi Everyone, this is a concept of a monolithic BFS: http://imgur.com/gallery/fGzkH

And a previous modular concept: http://imgur.com/a/15fO2

What are the legs made of?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/22/2016 11:23 pm
Not specified, they look thin but ithis concept is more about the layout of the components and the general idea.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 09/22/2016 11:30 pm


...A figure shown by a user on twitter showing essentially the BFR-boosted BFS flying to Mars, refueling there and flying back to Earth entry was commented by him to be the best representation of the MCT to date...

Anyone have that image or a link to it? That's something I would like to see!

Was this the video?

https://m.youtube.com/playlist?list=PLBU9UJfqaRooKnHY8QtQ399qqRwBqU6W3

This seems like pre or early NSF MCT Team (of which Michel Lamontange is a memeber, iirc) design of a SuperDragon type. IIRC, they settled on the biconic type later. It also does not comply with the "land the whole thing" quote as interpreted around here. Moreover, the SC in this video refuels at Earth, contrary to what Bynaus describes. I don't think it's the video he saw.

I too would like to see the video and the comment
Title: Re: MCT Speculation and Discussion Thread 4
Post by: 2552 on 09/23/2016 12:34 am
...A figure shown by a user on twitter showing essentially the BFR-boosted BFS flying to Mars, refueling there and flying back to Earth entry was commented by him to be the best representation of the MCT to date...

Anyone have that image or a link to it? That's something I would like to see!

I remember seeing this (https://twitter.com/John_Gardi/status/356823217299664896), was this it? It looks like Elon's comment about it being the closest guess he's seen so far is above the linked tweet and is actually about a diagram of a Hyperloop track. I don't see a reply from Elon about the MCT diagram.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/23/2016 12:37 am


Hi Everyone, this is a concept of a monolithic BFS: http://imgur.com/gallery/fGzkH

And a previous modular concept: http://imgur.com/a/15fO2

What are the legs made of?

Apparently the same stuff the surface of Mars seems to be made of, seriously the single monolithic direct vehicle is an absurd interpretation of Musks incredibly vague hints and musings, any actual study of physics involved rules it out.

This particular concept is just too big, its what 15 m diameter and what 200 m tall, heck the lander at the top alone looks like it would mass 200 mt dry, the thrust ranges that Shotwell gave don't allow a vehicle this massive, I don't even think it could take off as their isn't enough thrust density at the base to lift it off the launchpad.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 09/23/2016 01:28 am
Not specified, they look thin but ithis concept is more about the layout of the components and the general idea.
Landing legs for such a rig would be a major component and the general idea (of anything spaceflight, let alone an ITS) would be to comply with laws of physics and waltz your design around the constraints they impose.

Do you know why people find rockets beautiful?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/23/2016 01:58 am
Not specified, they look thin but ithis concept is more about the layout of the components and the general idea.
Landing legs for such a rig would be a major component and the general idea (of anything spaceflight, let alone an ITS) would be to comply with laws of physics and waltz your design around the constraints they impose.

Do you know why people find rockets beautiful?

I've done this prevously, I thought a little about the system, but I simply didn't mind to put on the final renderings.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/23/2016 02:19 am
I'm sorry but you really haven't put much thought into the legs, they far too small, have nothing for foot pads and would immediately sink into the surface.  The spread of the legs combined with the height of the vehicle and a total lack of control authority at landing means it would tip over immediately even on a concrete landing pad.

Furthermore their is no means to get cargo onto or off of the vehicle and no description of the interior at all which is where most of the important layout would actually be. 

I really recommend you work to someone with some engineering knowledge and work to illustrate the designs they come up with because your just making very soft science fiction pictures right now.  Their are lots of folks on the forum that would be happy to collaborate with you.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 09/23/2016 02:34 am
Not specified, they look thin but ithis concept is more about the layout of the components and the general idea.
Landing legs for such a rig would be a major component and the general idea (of anything spaceflight, let alone an ITS) would be to comply with laws of physics and waltz your design around the constraints they impose.

Do you know why people find rockets beautiful?

I've done this prevously, I thought a little about the system, but I simply didn't mind to put on the final renderings.
Uh... it's better, but only marginally... I suggest you try to thoughtfully brake some things in your spare time. All kinds of things, of different materials, sizes and shapes. Also, try to be creative with how you apply the force needed to brake a thing - fast, slow, point, area, etc. While you are at it, remember that force has a vector and try to visualize it.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 09/23/2016 08:24 am
...A figure shown by a user on twitter showing essentially the BFR-boosted BFS flying to Mars, refueling there and flying back to Earth entry was commented by him to be the best representation of the MCT to date...

Anyone have that image or a link to it? That's something I would like to see!

I remember seeing this (https://twitter.com/John_Gardi/status/356823217299664896), was this it? It looks like Elon's comment about it being the closest guess he's seen so far is above the linked tweet and is actually about a diagram of a Hyperloop track. I don't see a reply from Elon about the MCT diagram.

That is definetly the image I was thinking of. but I can't find Elon's tweet/comment on it. Perhaps it was deleted. The best I can come up with is a blog entry repeating what the tweet said (including the picture):

https://rocketry.wordpress.com/2013/07/15/spacex-f9-next-generation-booster-gets-full-duration-burn/

"Pretty close to what I have in mind". So its not the Hyperloop tweet, although the content is similar.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 09/23/2016 12:30 pm
Hi Everyone, this is a concept of a monolithic BFS: http://imgur.com/gallery/fGzkH

Nice one, wouldn't be surprised if the final thing looked a lot like this, but landing this thing vertically doesn't look practical.
It's just a hunch, but I think it's gonna land horizontally, using a separate set of smaller engines. I don't think the MCT/ITS/whatever will have more than 2-3 Raptors and they will be used for orbital stuff, not landing. Oh, and deployable skids on the sides of the thermal shielding would be more robust than current F9 legs for the same mass.

Well, only 4 days left until, hopefully, we know more.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/23/2016 02:05 pm
Not specified, they look thin but ithis concept is more about the layout of the components and the general idea.
Landing legs for such a rig would be a major component and the general idea (of anything spaceflight, let alone an ITS) would be to comply with laws of physics and waltz your design around the constraints they impose.

Do you know why people find rockets beautiful?
I've done this prevously, I thought a little about the system, but I simply didn't mind to put on the final renderings.
Uh... it's better, but only marginally... I suggest you try to thoughtfully brake some things in your spare time. All kinds of things, of different materials, sizes and shapes. Also, try to be creative with how you apply the force needed to brake a thing - fast, slow, point, area, etc. While you are at it, remember that force has a vector and try to visualize it.



Of course is science fiction. I took more time on these first concepts, before the "put the entire thing on the surface of mars" rumour, I guess.

http://imgur.com/a/EtH8F

http://imgur.com/a/15fO2

As long I have no STEM background, the only part I could seriously work is on the cabin accommodations. Please look it just as a layout, not a engineering proposal.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 09/23/2016 02:05 pm
Hi Everyone, this is a concept of a monolithic BFS: http://imgur.com/gallery/fGzkH

Nice one, wouldn't be surprised if the final thing looked a lot like this, but landing this thing vertically doesn't look practical.
It's just a hunch, but I think it's gonna land horizontally, using a separate set of smaller engines. I don't think the MCT/ITS/whatever will have more than 2-3 Raptors and they will be used for orbital stuff, not landing. Oh, and deployable skids on the sides of the thermal shielding would be more robust than current F9 legs for the same mass.

Well, only 4 days left until, hopefully, we know more.
While a horizontal lander would be better for cargo access, the MCT/ITS would need to launch from the surface of Mars, so the main thrust would need to be along the longitudinal axis for better aerodynamics during ascent, and there would be extra weight and complexity to support the loads of the vehicle landing on its side in addition to the loads along the vehicle's longitudinal axis.

But I would guess that the MCT/ITS would be a lifting body like in BSenna's link (see also: HYFLEX (http://global.jaxa.jp/projects/rockets/hyflex/index.html)) and enter Mars's atmosphere on its side in order to take advantage of aerobraking a huge mass with a larger surface area before switching to hypersonic retropropulsion for the final descent sequence.

(Mars EDL becomes harder with larger masses because of the square-cube law in relation to the surface area exposed during entry into the thin atmosphere.)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/23/2016 02:13 pm
Hi Everyone, this is a concept of a monolithic BFS: http://imgur.com/gallery/fGzkH

Nice one, wouldn't be surprised if the final thing looked a lot like this, but landing this thing vertically doesn't look practical.
It's just a hunch, but I think it's gonna land horizontally, using a separate set of smaller engines. I don't think the MCT/ITS/whatever will have more than 2-3 Raptors and they will be used for orbital stuff, not landing. Oh, and deployable skids on the sides of the thermal shielding would be more robust than current F9 legs for the same mass.

Well, only 4 days left until, hopefully, we know more.

Its really puzzling. If you ask me I would think about a 20 years test programme with SEP, expandable disposable habitats, etc. But the rumour mill quasi-consensus point other way. On the Mars landing field, I agree, but other engines would add mass just for landing, and there is the coming back problem, the need to reorient the ship for take-off.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 09/23/2016 02:15 pm
While a horizontal lander would be better for cargo access, the MCT/ITS would need to launch from the surface of Mars, and there would be extra weight and complexity to support the loads of the vehicle landing on its side in addition to the loads generated by the main engine's thrust along the vehicle's longitudinal axis.

Your objections are quite reasonable, but the operational advantages when you need to operate without ground infrastructure should not be underestimated. Anyway, as I said, just a hunch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jsgirald on 09/23/2016 02:31 pm
Its really puzzling. If you ask me I would think about a 20 years test programme with SEP, expandable disposable habitats, etc. But the rumour mill quasi-consensus point other way. On the Mars landing field, I agree, but other engines would add mass just for landing, and there is the coming back problem, the need to reorient the ship for take-off.

Think of smallish engines in nacelles placed high on both sides of the ship. You could use the side engines for take off and fire the big ones (Raptors) high in the atmosphere. The mass argument is reasonable, but this alternative provides for a more flexible design. Also, smaller engines far from the ground would prevent damage from dust or rocks blasted off. Several small motors provide redundancy, so a single damaged engine would not risk the whole mission. Add a detachable nose and a ramp like some cargo planes or ferries and you get an easy to operate roll-on roll-of ship.

Just a thought anyway.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/23/2016 03:10 pm
Its really puzzling. If you ask me I would think about a 20 years test programme with SEP, expandable disposable habitats, etc. But the rumour mill quasi-consensus point other way. On the Mars landing field, I agree, but other engines would add mass just for landing, and there is the coming back problem, the need to reorient the ship for take-off.

Think of smallish engines in nacelles placed high on both sides of the ship. You could use the side engines for take off and fire the big ones (Raptors) high in the atmosphere. The mass argument is reasonable, but this alternative provides for a more flexible design. Also, smaller engines far from the ground would prevent damage from dust or rocks blasted off. Several small motors provide redundancy, so a single damaged engine would not risk the whole mission. Add a detachable nose and a ramp like some cargo planes or ferries and you get an easy to operate roll-on roll-of ship.

Just a thought anyway.

My approach was to reduce the number of moving parts for risk reduction. The 6 raptors and 6 legs are also redundancy.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: 2552 on 09/23/2016 04:55 pm
...A figure shown by a user on twitter showing essentially the BFR-boosted BFS flying to Mars, refueling there and flying back to Earth entry was commented by him to be the best representation of the MCT to date...

Anyone have that image or a link to it? That's something I would like to see!

I remember seeing this (https://twitter.com/John_Gardi/status/356823217299664896), was this it? It looks like Elon's comment about it being the closest guess he's seen so far is above the linked tweet and is actually about a diagram of a Hyperloop track. I don't see a reply from Elon about the MCT diagram.

That is definetly the image I was thinking of. but I can't find Elon's tweet/comment on it. Perhaps it was deleted. The best I can come up with is a blog entry repeating what the tweet said (including the picture):

https://rocketry.wordpress.com/2013/07/15/spacex-f9-next-generation-booster-gets-full-duration-burn/

"Pretty close to what I have in mind". So its not the Hyperloop tweet, although the content is similar.

Maybe it actually was deleted, I just found this reddit comment (https://www.reddit.com/r/spacex/comments/2mi22w/im_writing_a_website_about_spacex_and_i_want/cm6jytv) that has a screenshot (https://pbs.twimg.com/media/BahB8qnCAAAaer5.jpg:large) of John Gardi's MCT diagram and Elon's reply to it saying it's "pretty close to what I have in mind."

Also, this Google+ post (https://plus.google.com/117039636053462680924/posts/asyj9Udoeyz) has a direct link (https://twitter.com/elonmusk/status/356826725805588482) to Elon's tweet, but the tweet doesn't exist anymore.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 09/23/2016 07:22 pm
...A figure shown by a user on twitter showing essentially the BFR-boosted BFS flying to Mars, refueling there and flying back to Earth entry was commented by him to be the best representation of the MCT to date...

Anyone have that image or a link to it? That's something I would like to see!

I remember seeing this (https://twitter.com/John_Gardi/status/356823217299664896), was this it? It looks like Elon's comment about it being the closest guess he's seen so far is above the linked tweet and is actually about a diagram of a Hyperloop track. I don't see a reply from Elon about the MCT diagram.

That is definetly the image I was thinking of. but I can't find Elon's tweet/comment on it. Perhaps it was deleted. The best I can come up with is a blog entry repeating what the tweet said (including the picture):

https://rocketry.wordpress.com/2013/07/15/spacex-f9-next-generation-booster-gets-full-duration-burn/

"Pretty close to what I have in mind". So its not the Hyperloop tweet, although the content is similar.

Maybe it actually was deleted, I just found this reddit comment (https://www.reddit.com/r/spacex/comments/2mi22w/im_writing_a_website_about_spacex_and_i_want/cm6jytv) that has a screenshot (https://pbs.twimg.com/media/BahB8qnCAAAaer5.jpg:large) of John Gardi's MCT diagram and Elon's reply to it saying it's "pretty close to what I have in mind."

Also, this Google+ post (https://plus.google.com/117039636053462680924/posts/asyj9Udoeyz) has a direct link (https://twitter.com/elonmusk/status/356826725805588482) to Elon's tweet, but the tweet doesn't exist anymore.
The overall idea behind that makes sense if the goal is simple reusability operations. However, "no refueling" in Earth orbit is not an option unless you want the second stage to require SSTO-like delta-v performance or have extremely low mass margins. There will probably be MCTs/ITSs acting as tankers in the plan.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 09/23/2016 07:35 pm
...A figure shown by a user on twitter showing essentially the BFR-boosted BFS flying to Mars, refueling there and flying back to Earth entry was commented by him to be the best representation of the MCT to date...

Anyone have that image or a link to it? That's something I would like to see!

I remember seeing this (https://twitter.com/John_Gardi/status/356823217299664896), was this it? It looks like Elon's comment about it being the closest guess he's seen so far is above the linked tweet and is actually about a diagram of a Hyperloop track. I don't see a reply from Elon about the MCT diagram.

That is definetly the image I was thinking of. but I can't find Elon's tweet/comment on it. Perhaps it was deleted. The best I can come up with is a blog entry repeating what the tweet said (including the picture):

https://rocketry.wordpress.com/2013/07/15/spacex-f9-next-generation-booster-gets-full-duration-burn/

"Pretty close to what I have in mind". So its not the Hyperloop tweet, although the content is similar.

Maybe it actually was deleted, I just found this reddit comment (https://www.reddit.com/r/spacex/comments/2mi22w/im_writing_a_website_about_spacex_and_i_want/cm6jytv) that has a screenshot (https://pbs.twimg.com/media/BahB8qnCAAAaer5.jpg:large) of John Gardi's MCT diagram and Elon's reply to it saying it's "pretty close to what I have in mind."

Also, this Google+ post (https://plus.google.com/117039636053462680924/posts/asyj9Udoeyz) has a direct link (https://twitter.com/elonmusk/status/356826725805588482) to Elon's tweet, but the tweet doesn't exist anymore.
The overall idea behind that makes sense if the goal is simple reusability operations. However, "no refueling" in Earth orbit is not an option unless you want the second stage to require SSTO-like delta-v performance or have extremely low mass margins. There will probably be MCTs/ITSs acting as tankers in the plan.

Well, the "no refueling" part is actually the only point that is contradicted by something Elon said himself (that there will be re-fueling before departure). So its a safe bet that this point is (among others, perhaps) why he said "pretty close" and not "spot on".
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 09/23/2016 07:39 pm
Well, the "no refueling" part is actually the only point that is contradicted by something Elon said himself (that there will be re-fueling before departure). So its a safe bet that this point is (among others, perhaps) why he said "pretty close" and not "spot on".
Oh yeah, he did say that. (http://shitelonsays.com/transcript/elon-musk-at-mits-aeroastro-centennial-part-2-of-6-2014-10-24) (9:40 in video)

Quote from: Elon Musk
I mean, if you do a densified liquid methalox rocket with on-orbit refueling, so like you load the spacecraft into orbit and then you send a whole bunch of refueling missions to fill up the tanks and you have the Mars colonial fleet - essentially - that gets built up during the time between Earth-Mars synchronizations, which occur every 26 months, then the fleet all departs at the optimal transfer point.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Chris_Pi on 09/24/2016 03:28 am
Of course is science fiction. I took more time on these first concepts, before the "put the entire thing on the surface of mars" rumour, I guess.

AE-35 unit? I'm Sorry Dave, They won't let you fly that. :D

I don't have anything else to add, Just couldn't pass that one up.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 09/24/2016 01:03 pm
Well, this didn't get the traction that I'd hoped, but I'm still wondering if anyone would like to 'put their money where their mouth is' and declare their positions on the (hopefully) upcoming reveal details.  Only a few days left!  I'll start with my guesses:

1-a, 2-31, 3-15m, 4-17.5Mlbs, 5a, 6a, 7a, 8c



1) Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft (only)
     b)  Boost phase consists of 2 stages, which put the BFS into orbit
     c)  Other: 3rd stage, 'half' stages, drop tanks, etc.

2) Number of Raptor Engines on BFR (1st stage)

3) Diameter of BFR (1st stage)

4) Total Raptor 1st stage thrust (sl)

5) LAS Architecture
     a) No LAS - BFS is the escape mechanism
     b) Traditional LAS - above BFS and is nominally jettisoned during launch phase
     c) BFS contains smaller 'ejection pod' where humans reside during launch
     d) Other, non-traditional LAS design

6) Shape and Landing Mode of BFS
     a) Capsule (perhaps elongated), w/ TPS on base
     b) Cylindrical or biconic - horizontal landing
     c) Cylindrical or biconic - vertical landing
     d) Other

7) Mars and Earth return
     a) BFS does direct entry into Mars and Earth atmosphere
     b) BFS does orbital capture before performing entry burn and landing
     c) Same as b, but upon Earth return, stays in orbit for next synod

8)  Use of non-chemical thrust
     a) Not part of the plan
     b) Will use SEP for some/all of the big transits
     c) All chemical for now, but plans to incorporate SEP down the road

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Snake on 09/24/2016 01:38 pm
Re: GORDAP's Poll

1) a
2) 36
3) 15 m
4) 36 x 2,300 kN = 82,800 kN  (18.6 Mlbs)
5) c
6) a
7) b
8) c

Also:

6 Raptors and 16 SuperDragons on BFS.
BFS revealed as being Benjamin Franklin Class Ship.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/24/2016 07:31 pm
Re: GORDAP's Poll

1- C, drop tanks on BFS
2- 33 Raptors
3- 15m
4- 75,900 kN  (17.1 Mlbs)
5- A, BFS escape is like Dragon 2
6- C, Biconic, vertical landing
7- B, Orbital capture, then landing.
8- C, Chemical, soon SEP.

BFS will be called Master Cylinder type. (Mars bound only).


Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 09/24/2016 08:38 pm
Fun exercise. I don't know the numbers that well so just gave ranges. These ideas all seem like well received ones in the threads.

1- C - Mostly option A, in that BFS is the second stage and comes in three variants: Tanker, cargo and crew, but for special purpose missions there will be a tanker variant that can fling an expendable third stage and fairly light payload on a high energy, possibly even interstellar, trajectory, and return to a rendezvous point with dry tanks. This may be just hinted at.
2- 30-36 Raptors
3- 15m
4- 17-20 Mlbs
5- A, ala Dragon 2
6- C, Biconic, vertical landing
7- D, all of the above are possible but A (direct return) and C (stay in orbit) are primary variants, crew return usually A but sometimes cargo or tanker may stay in orbit after capture (C) instead of landing. B rarely executed because pointless compared to A if returning. Some Cs turn into Bs (vessel completes orbital transfers and then deorbits for maintenance or downmass). Use of C will grow over time. Especially cargo, long term, may transfer to other vessels for different destinations, and as on orbit capability grows there may be more and more transshipment. Again, this may be just hinted at. Everything may be A initially.
8- C, Chemical, soon SEP. Cyclers are not ruled out eventually, but won't be used initially.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 09/24/2016 09:00 pm

1) a
2) 9-12 engines
3) 8.5-10 m diameter
4)
5)c) BFS contains smaller 'ejection pod' where humans reside during launch
6)
7) a)direct entry
8.) c) All chemical for now, but plans to incorporate SEP down the road

I hope it will be called Bender 8)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: knowles2 on 09/24/2016 10:59 pm
Lot of talk here seem to be about a single vehicle that will launch from earth, land on mars, and then return to earth.

Musk isn't one to waste things, surely he will be using Red Dragon vehicle to handle the Mars orbit to ground bit and the IST will just handle the Earth to Mars bit?

It seems a bit risky to me to design a vehicle capable of being launch from earth with dozens of passengers and all their supplies sent to land to Mars and expect the same vehicle to do the reverse again.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: knowles2 on 09/24/2016 11:10 pm
Well, this didn't get the traction that I'd hoped, but I'm still wondering if anyone would like to 'put their money where their mouth is' and declare their positions on the (hopefully) upcoming reveal details.  Only a few days left!  I'll start with my guesses:

1-a, 2-31, 3-15m, 4-17.5Mlbs, 5a, 6a, 7a, 8c

Quote

1) Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft (only)
     b)  Boost phase consists of 2 stages, which put the BFS into orbit
     c)  Other: 3rd stage, 'half' stages, drop tanks, etc.
   a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft (only)


Quote
2) Number of Raptor Engines on BFR (1st stage)

27 engines.


Quote
3) Diameter of BFR (1st stage)

15-20 meters

Quote
4) Total Raptor 1st stage thrust (sl)
Don't know.


Quote
5) LAS Architecture
     a) No LAS - BFS is the escape mechanism
     b) Traditional LAS - above BFS and is nominally jettisoned during launch phase
     c) BFS contains smaller 'ejection pod' where humans reside during launch
   d) Other, non-traditional LAS design

   d) Other, non-traditional LAS design

Quote
6)

Shape and Landing Mode of BFS
     a) Capsule (perhaps elongated), w/ TPS on base
     b) Cylindrical or biconic - horizontal landing
     c) Cylindrical or biconic - vertical landing
     d) Other

Capsule, will probably be a human rated Red Dragon.

Quote
7) Mars and Earth return
     a) BFS does direct entry into Mars and Earth atmosphere
     b) BFS does orbital capture before performing entry burn and landing
     c) Same as b, but upon Earth return, stays in orbit for next synod
 

c) Same as b, but upon Earth return, stays in orbit for next synod


Quote
8)  Use of non-chemical thrust
     a) Not part of the plan
     b) Will use SEP for some/all of the big transits
     c) All chemical for now, but plans to incorporate SEP down the road


C, all chemical for now, but will probably look into electrical engines once the technology has developed.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: RonM on 09/24/2016 11:40 pm
Lot of talk here seem to be about a single vehicle that will launch from earth, land on mars, and then return to earth.

That's the conventional wisdom around here. We'll find out Tuesday if it is correct.

Musk isn't one to waste things, surely he will be using Red Dragon vehicle to handle the Mars orbit to ground bit and the IST will just handle the Earth to Mars bit?

Dragon is far too small to handle the amount of cargo/passengers mentioned, about 100 tonnes. It also can't takeoff from Mars and get back in orbit.

It seems a bit risky to me to design a vehicle capable of being launch from earth with dozens of passengers and all their supplies sent to land to Mars and expect the same vehicle to do the reverse again.

It's up to the engineers to figure out how to do the mission at an acceptable level of risk. The first generation ITS could launch without its small crew. They could dock later with a Dragon. Of course, that doesn't help for the return trip.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bob Shaw on 09/25/2016 12:13 am
Dragons might make excellent Star Wars style escape pods for the MCT, lifeboats able to save the human cargo...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Owlon on 09/25/2016 01:24 am
Dragons are heavy and carry a bunch of nasty, toxic hypergolic fuel. They're on the order of 1 ton per passenger fully fueled, which eats your entire payload budget with 100 passengers. Much more efficient to have a monolithic escape pod for the whole crew if you're going to have one at all.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 09/25/2016 02:13 am

1- Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft (only)

With a modified version of BFS serving as cargo ships. And a modified version of the cargo-ships serving as the fuel-tugs. And a modified version of the fuel-tugs serving as the fuel-depot(s).

[And upon Musk mentioning this, we'll spend every day until the damn thing flies arguing angrily over whether they are standalone designs manufactured separately, or merely exchangeable modules (passenger/cargo/fuel) that fit into a single standard BFS. "Musk clearly said..." "No, read his actual..." For years. With half our comments getting deleted and a few of us getting banned. It's gonna be awesome.]

2- Number of Raptor Engines on BFR (1st stage)
     20 < N < 30.

3- Diameter of BFR (1st stage)
     12m (if BFS is cylindrical/biconic)
     15m (if BFS is elongated capsule)
...because they'll want to simplify manufacturing by using common tank tooling for everything, hence the Mars EDL method sets the diameter of the BFS, which sets the maximum diameter of the fuel-tug BFS, which sets the maximum diameter of the BFR tanks, which is the diameter of the BFR.

5- LAS Architecture
     a) No LAS - BFS is the escape mechanism

A very small chance of...
     c) BFS contains smaller 'ejection pod' where humans reside during launch
...but I doubt it. If you design an ejection pod capable of carrying 100 people away from a BFR launch, then you've created an entirely separate manned "capsule" which can be used for launching crew/passengers into orbit separately from the BFS. In which case, you'd change the whole architecture of the mission and probably look at orbital assembly, SEP, blah blah blah. But I'm hardly going to complain if they come up with something obvious-in-hindsight clever.

6- Shape and Landing Mode of BFS
     c) Cylindrical or biconic - vertical landing

Although I prefer...
     a) Capsule (perhaps elongated), w/ TPS on base
...with the Raptors arranged above the base, a la Superdracos, accepting the cosine losses in return for a much simpler design that works both on Mars and for Earth landing without any extra engines. But the required length of the fuel tanks may exclude a capsule-like design.

7- Mars and Earth return
     a) BFS does direct entry into Mars and Earth atmosphere

8-  Use of non-chemical thrust
     a) Not part of the plan

9-BONUS ROUND
     a) Once BFR is proven, it will replace all F9 derived vehicles for SpaceX's commercial satellite launches.

A cargo version of BFS could carry 5-10 GEOsats like a freakin' cubesat ejector on F9. Or GEOsats could fly as secondary payloads on SpaceX's fuel launches. (Get someone else to pay for your fuel launches for future Mars flights.) An affordable, fully reusable HLV changes the rules of the game.

10-DOUBLE BONUS ROUND
     d) None of the above.

Musk tones his presentation way, way down, speaking only in generalities, out of concern that providing too much detail about a future plan, immediately after the loss of another F9, will create a negative impression on existing customers and provide fodder to anti-SpaceX lobbyists ("they're distracted by their Mars obsession and that's why... therefore we shouldn't...") and hence we won't get definitive answers to any of GORDAP's questions except (4), Raptor details (which I skipped.)

Dragons might make excellent Star Wars style escape pods for the MCT, lifeboats able to save the human cargo...

The image amuses me immensely. (As long as I don't think about the details.)

[edit: "could will", might did.]
Title: Re: MCT Speculation and Discussion Thread 4
Post by: raketa on 09/25/2016 06:17 am
1/MCT bassic  architecture
a/BFR 1 stage
b/BFS 2 stage:
Mars version
Tanker version
Cargo version for LEO, GEO ,Moon,Mars and beyond delivery

2/Engine number
At least 30 Report engine

3/LAS for Earth and Mars emergency launch and landing
Just to make system survivable for bad day
On Mars it will land back on surface and team in rovers will come to rescue departing party

4/BFS Shape
Engine in bottom shielded by engine thrust, very similar to Dragon 2, just bigger and more space for fuel.


5/Electric propulsion
 for offseason emergency trips to Mars and from Mars,  using Dragon 2 or small version BFS

6/BFS will launch directly to Mars

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 09/25/2016 07:03 am
An affordable, fully reusable HLV changes the rules of the game.
To think that several years ago, this would have been considered an oxymoron. That reusability would have to be designed for existing markets, that they would have small payload capacities because they would need very high flight rates to be economically viable.

If there was a demand of 100-200mT/yr propellant in LEO, then a very small RLV could be profitable. No sufficiently large markets seem likely for Falcon 9 sized payloads in the near future.

The need for high flight rates still applies now for fully reusable rockets, but this time SpaceX and Blue Origin are expecting to expand the market. I'm not sure whether to consider "build it and they will come" as a viable business strategy or just wishful thinking. There's still a possibility that launchers such as BFR and New Glenn might not pan out. But if they do, space will open up like never before.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DJPledger on 09/25/2016 08:13 am
SpaceX may decide to bite the bullet and dev. an F-1 class version of Raptor for BFR to avoid an N-1 type design and to carry over the octaweb design heritage of F9. Raptor is said to be highly scalable so there is no reason whatsoever that several sizes of it for different tasks can be dev. maybe except for dev. cost.

EM did say the plan do use only one size of Raptor throughout the BFR/MCT architecture may change during his AMA in January 2015.

I am sure EM knows what happened to the N-1 and I can't imagine him being that stupid.

Edited to correct tense regarding N-1.

We will find out on Tuesday.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 09/25/2016 10:13 am
SpaceX may decide to bite the bullet and dev. an F-1 class version of Raptor for BFR to avoid an N-1 type design and to carry over the octaweb design heritage of F9. Raptor is said to be highly scalable so there is no reason whatsoever that several sizes of it for different tasks can be dev. maybe except for dev. cost.

EM did say the plan do use only one size of Raptor throughout the BFR/MCT architecture may change during his AMA in January 2015.

I am sure EM knows what happening to the N-1 and I can't imagine him being that stupid.

We will find out on Tuesday.
Not to disagree with your point, but to nitpick on the phrasing:

Nothing is "happening" to the N-1 for decades

Even if someone, for whatever mystical reason, tried to recreate the N-1 today, for the purpose of producing the same failure, one would have failed miserably.

You'd need the Soviet industrial base, as it were at the time of N-1 production, the Soviet political augmentation of the design process and aerospace engineers with fraction of the knowledge they have today, all of which are pure unobtanium, hopefully, forever.

Edited for clarity
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Hauerg on 09/25/2016 11:06 am
SpaceX may decide to bite the bullet and dev. an F-1 class version of Raptor for BFR to avoid an N-1 type design and to carry over the octaweb design heritage of F9. Raptor is said to be highly scalable so there is no reason whatsoever that several sizes of it for different tasks can be dev. maybe except for dev. cost.

EM did say the plan do use only one size of Raptor throughout the BFR/MCT architecture may change during his AMA in January 2015.

I am sure EM knows what happening to the N-1 and I can't imagine him being that stupid.

We will find out on Tuesday.

If you want/need to go for extreme reusability you might have to go to high number of engines anyway. Engine out & containing engine failures have to be designed as something that WILL be happening during the lifetime of every single stage. And to keep a reasonable production rate for the engines.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 09/25/2016 11:12 am
http://m.imgur.com/a/87OOT
- Was this proposal, by 'Coborop' on Reddit, ever discussed in this thread?

Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 09/25/2016 11:49 am
SpaceX may decide to bite the bullet and dev. an F-1 class version of Raptor for BFR to avoid an N-1 type design and to carry over the octaweb design heritage of F9. Raptor is said to be highly scalable so there is no reason whatsoever that several sizes of it for different tasks can be dev. maybe except for dev. cost.

EM did say the plan do use only one size of Raptor throughout the BFR/MCT architecture may change during his AMA in January 2015.

I am sure EM knows what happening to the N-1 and I can't imagine him being that stupid.

We will find out on Tuesday.

N-1 failed due to fuel system problems that would not exist under present engineering conventions.

Number of engines does not increase risk. Indeed, there's an argument that a high number of engines reduces risk.

It's usually safe to assume that SpaceX isn't "stupid", they're better informed and acting under better data.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oli on 09/25/2016 01:24 pm
http://m.imgur.com/a/87OOT
- Was this proposal, by 'Coborop' on Reddit, ever discussed in this thread?

Looks really cool but...

The sidewall angle of that thing is ~15°, which results in cosine losses of ~3.4%. Too much. In addition, the upper stage engines are used at launch, i.e. at sea level pressure, which would limit their efficiency even further.

Then there's the issue of the center of gravity of the BFS. For a capsule the CoG must be very low, I don't think that's compatible with having most of the payload at the top. The fuel for landing won't make up for that. In a capsule design I would put the tanks at the top and the payload at the bottom, probably with separate tanks at the bottom for the landing fuel.

Edit: Maybe you have seen the Mars ferry design in the attached picture.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DJPledger on 09/25/2016 01:24 pm
SpaceX may decide to bite the bullet and dev. an F-1 class version of Raptor for BFR to avoid an N-1 type design and to carry over the octaweb design heritage of F9. Raptor is said to be highly scalable so there is no reason whatsoever that several sizes of it for different tasks can be dev. maybe except for dev. cost.

EM did say the plan do use only one size of Raptor throughout the BFR/MCT architecture may change during his AMA in January 2015.

I am sure EM knows what happening to the N-1 and I can't imagine him being that stupid.

We will find out on Tuesday.

N-1 failed due to fuel system problems that would not exist under present engineering conventions.

Number of engines does not increase risk. Indeed, there's an argument that a high number of engines reduces risk.

It's usually safe to assume that SpaceX isn't "stupid", they're better informed and acting under better data.
It only takes one engine to explode out of 30 to bring down an LV. I believe this happened to at least one of the N-1's. Anyone including SpaceX even attempting something like the N-1 beggars belief. The more engines you have the greater the risk of one of them exploding causing catastrophic LV failure. 5-9 engines is the optimum no. on a 1st stage to strike a balance between the risk of engine explosion and good engine out capability for benign engine failures. Lets hope that SpaceX have learned the N-1 lesson and the BFR design we should see on Tuesday will have much less than 30 engines on it.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/25/2016 01:29 pm

1) Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft
     b)  Boost phase consists of 2 stages, which put the BFS into orbit
     c)  Other: 3rd stage, 'half' stages, drop tanks, etc.

Going with (a)

2) Number of Raptor Engines on BFR (1st stage)

< 30, my best estimate is 25-27 if thrust stays close to 230 tonnes range

3) Diameter of BFR (1st stage)

Range 12.5m-15m, best estimate 15m 1st stage

4) Total Raptor 1st stage thrust (sl)

60 Meganewtons and T/W > 1.3

5) LAS Architecture
     a) No LAS - BFS is the escape mechanism
     b) Traditional LAS - above BFS and is nominally jettisoned during launch phase
     c) BFS contains smaller 'ejection pod' where humans reside during launch
     d) Other, non-traditional LAS design

Best guess is (a)

6) Shape and Landing Mode of BFS
     a) Capsule (perhaps elongated), w/ TPS on base
     b) Cylindrical or biconic - horizontal landing
     c) Cylindrical or biconic - vertical landing
     d) Other

Going with (c), definitely no horizontal landing

7) Mars and Earth return
    a) BFS does direct entry into Mars and Earth atmosphere
     b) BFS does orbital capture before performing entry burn and landing
     c) Same as b, but upon Earth return, stays in orbit for next synod

(a)

8)  Use of non-chemical thrust
     a) Not part of the plan
     b) Will use SEP for some/all of the big transits
     c) All chemical for now, but plans to incorporate SEP down the road

(c) strongly favor

Can anyone think of more/better questions?

Predict Musk will miss 1st crewed landing by >= 3 synods

5-6 Rvacs on BFS stage 2

Raptor sea level will have 10s of tonnes thrust more than the 230 tonnes mentioned by Elon

Entire BFR/BFS GLOW masses under 5.000 tonnes; my estimate ~4,500

Height of BFR/BFS stack under 120m; my estimate <100m

Cargo version, tanker version, crewed version of BFS

1st crewed landing on Mars 8-12 humans planned

Just over 48 hours until Musk makes fools of us

Title: Re: MCT Speculation and Discussion Thread 4
Post by: DJPledger on 09/25/2016 01:32 pm

1) Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft
     b)  Boost phase consists of 2 stages, which put the BFS into orbit
     c)  Other: 3rd stage, 'half' stages, drop tanks, etc.

Going with (a)

2) Number of Raptor Engines on BFR (1st stage)

< 30, my best estimate is 25-27

3) Diameter of BFR (1st stage)

Range 12.5m-15m, best estimate 15m 1st stage

4) Total Raptor 1st stage thrust (sl)

60 Meganewtons and T/W > 1.3

5) LAS Architecture
     a) No LAS - BFS is the escape mechanism
     b) Traditional LAS - above BFS and is nominally jettisoned during launch phase
     c) BFS contains smaller 'ejection pod' where humans reside during launch
     d) Other, non-traditional LAS design

Best guess is (a)

6) Shape and Landing Mode of BFS
     a) Capsule (perhaps elongated), w/ TPS on base
     b) Cylindrical or biconic - horizontal landing
     c) Cylindrical or biconic - vertical landing
     d) Other

Going with (c), definitely no horizontal landing

7) Mars and Earth return
    a) BFS does direct entry into Mars and Earth atmosphere
     b) BFS does orbital capture before performing entry burn and landing
     c) Same as b, but upon Earth return, stays in orbit for next synod

(a)

8)  Use of non-chemical thrust
     a) Not part of the plan
     b) Will use SEP for some/all of the big transits
     c) All chemical for now, but plans to incorporate SEP down the road

(c) strongly favor

Can anyone think of more/better questions?

Predict Musk will miss 1st crewed landing by >= 3 synods

5-6 Rvacs on BFS stage 2

Raptor sea level will have 10s of tonnes thrust more than the 230 tonnes mentioned by Elon

Entire BFR/BFS GLOW masses under 5.000 tonnes; my estimate ~4,500

Height of BFR/BFS stack under 120m; my estimate <100m

Cargo version, tanker version, crewed version of BFS

1st crewed landing on Mars 8-12 humans planned

Just over 48 hours until Musk makes fools of us
And announces a >F-1 thrust version of Raptor to keep no. of engines on BFR to no more than 9.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/25/2016 01:36 pm
http://m.imgur.com/a/87OOT
- Was this proposal, by 'Coborop' on Reddit, ever discussed in this thread?

Up-feed plumbing of propellant to Roc makes this way too complex & heavy.  Cosine losses and reduced engine performance by running stage 2 Roc at sea level for Earth launch a bad tradeoff.   Just add engines on 1st stage Sling until it's big enough to launch upper stage. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: rakaydos on 09/25/2016 01:47 pm
It only takes one engine to explode out of 30 to bring down an LV. I believe this happened to at least one of the N-1's. Anyone including SpaceX even attempting something like the N-1 beggars belief. The more engines you have the greater the risk of one of them exploding causing catastrophic LV failure. 5-9 engines is the optimum no. on a 1st stage to strike a balance between the risk of engine explosion and good engine out capability for benign engine failures. Lets hope that SpaceX have learned the N-1 lesson and the BFR design we should see on Tuesday will have much less than 30 engines on it.
SpaceX has been there and done that.

https://en.wikipedia.org/wiki/SpaceX_CRS-1#Falcon_9_engine_anomaly
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 09/25/2016 02:06 pm
Up-feed plumbing of propellant to Roc makes this way too complex & heavy.  Cosine losses and reduced engine performance by running stage 2 Roc at sea level for Earth launch a bad tradeoff.   Just add engines on 1st stage Sling until it's big enough to launch upper stage. 

I agree. It looks to me like he just dimensioned the "Sling" too small. Also not too convinced about the weather-vane (or shuttlecock) design. I think SpaceX will go with their tried and tested grid fins. Placed at the top of the first stage, obviously.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 09/25/2016 02:31 pm
I'm not sure, but would having 30+ engines (even if they are on a single core instead of three) result in greater operational complexity? (such as in maintenance, inspection, turnaround time, etc.)

Now, I understand that if the second stage engines need to have a high enough thrust range between getting to LEO without too much gravity losses and landing almost empty (except for payload) in the 38% gravity of Mars (by having a fraction of the engines activated), and have commonalities with the first stage, there would need to be a lot of first stage engines.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 09/25/2016 04:58 pm
I want to point out that the difference in gravity is not as important for landing as some people may think. Gravity is important if you want to hover. For braking to zero speed however the mass is the important metric and that is still the same. Just gravity losses during braking are smaller.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/25/2016 05:06 pm
It only takes one engine to explode out of 30 to bring down an LV. I believe this happened to at least one of the N-1's. Anyone including SpaceX even attempting something like the N-1 beggars belief.
>

F9 CRS-1 had an engine fuel dome fail, but unlike N1 Falcon has armor around its engines to protect neighboring engines  from engine failures. The perimeter engine cells also have blowout panels.

CRS-1's avionics shut down the propellant flow to that engine and Dragon continued on its way to ISS. IIRC, it arrived a tad early.

No doubt BFR will get the same engine out capability as it's served them well.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dror on 09/25/2016 07:52 pm
My unaducated daydream is that the Benjamin Franklin System will be very much like a scaled up Falcon 9:

9 Raptor engines at the ~10m core,
1 Raptor vac seconed stage,
1 XL Dragon2 for the crew variant or payload bay or tanker for cargo and fuel.

The big difference is that the capsule will remain attached to the second stage through the whole flight_refuel_flight_land_refuel_flight_land cycle.
The combined due will EDL at mars retropropulsivly, tail first, like the Falcon 9 core does.
The capsule allows abort throughout the whole cycle, but otherwise remains attached.

I know the stack has a high CG and that it keeps the little people high above the surface, but I try not to think about it too much.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: The Amazing Catstronaut on 09/25/2016 07:55 pm

And announces a >F-1 thrust version of Raptor to keep no. of engines on BFR to no more than 9.

Why do you assume early Sixties engine logic still applies? The base principles of rocketry do indeed move that slowly. The engineering, materials science, and practically everything else, do not.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Melanchthon on 09/25/2016 11:11 pm
...

1) a) MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft (only)
2) 30 Raptor Engines on BFR (1st stage)
3) 15m Diameter of BFR (1st stage)
4) ~20 Mlbf SL thrust (~2.5x Saturn V)
5) c) BFS contains smaller 'ejection pod' where humans reside during launch
6) c) Cylindrical or biconic - vertical landing
7) a) BFS does direct entry into Mars and Earth atmosphere
8) c) All chemical for now, but plans to incorporate SEP down the road
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/26/2016 02:31 am
1. b)  Boost phase consists of 2 stages, a BFR booster and integrated S2/BFS
     
2. 30 engines

3. 15 meter BFR, 50% possibility BFS is 16+ meters

4.18 mlbf

5. c) BFS contains upper LAS pod where crew/passengers reside during launch or landing.

6. d) a mix of capsule (LAS pod) and cylindrical which includes a drop cargo section. Side entry & rotation to vertical for landings. LAS pod has its own capsule mode entry heat shield just in case.

7. a) BFS does direct entry into Mars and Earth atmosphere
 
8.  c) All chemical for now, but plans to incorporate SEP/NEP down the road. NEP for beyond Mars: Callisto etc.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 09/26/2016 02:54 am
But really though, does the number of engines on a stage have any effect on rapid reusability?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 09/26/2016 02:59 am
If you want to scale up production and flight rate as much as Musk envisions, it is a great boon to have maximum commonality between engines, both on the first and second stage. Also for purposes of reliability and repair. 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 09/26/2016 03:29 am
Also for purposes of reliability and repair.
That's what I meant, wouldn't it take longer to repair/inspect 30 engines on one stage compared to 9 or 20? Extra person-hours required for turnaround, etc.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MichaelBlackbourn on 09/26/2016 05:25 am
Here she is!

Musk via twitter:

SpaceX propulsion just achieved first firing of the Raptor interplanetary transport engine https://t.co/vRleyJvBkx

Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/26/2016 06:04 am
@elonmusk
Production Raptor goal is specific impulse of 382 seconds and thrust of 3 MN (~310 metric tons) at 300 bar

310t = 694,400 lbf.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: malu5531 on 09/26/2016 06:05 am
Raptor design targets;
Quote
Production Raptor goal is specific impulse of 382 seconds and thrust of 3 MN (~310 metric tons) at 300 bar

Will help in modelling MCT if we assume they reach these goal.

Second tweet;
Quote
Chamber pressure is almost 3X Merlin, so engine is about the same size for a given area ratio

Some quick calculations show it's possible to achieve 333s SL Isp in ~same size as Merlin (1.08m diameter) and same area ratio as Merlin, if exhaust pressure is high (1.7x atmosphere) @ 587 klbf and 800 kg/s fuel. (673 klbf @ 382s Isp with Vac nozzle @ 4m diameter). Would improve Isp to go with a bit higher nozzle diameter for exhaust pressure < 1 at SL.

Edit: SL version would be ~334s Isp at 1 atm exhaust pressure with 1.32m diameter nozzle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/26/2016 07:10 am
1 - B, second stage of BFR has 6 engines and will become reusable through repeated trial and error, acts as tanker, propellant depot, TMI booster and sat-launch workhorse.

2 - 31 engines in honeycomb pattern around central landing engine, some engines ungimbaled or on single axis

3 -  10 to 12 m tank manufactured at Mchoud, nearly all carbon fiber, with some wider cowlings around peripheral 1st stage engines similar to Saturn V.

4 - 71MN, 16 million pounds

5 - A, BFS carries minimal propellant at launch and small fast pressure fed or solid boosters give initial push followed by Raptor engines as they come up to full thrust, RTLS for pad abort, water landing for late aborts.

6 - A, BFS will be generally Dragon capsule like in shape and flight plan and employ a radially expanding decelerator at mars to augment it's base heat-shield.  4 Raptor engines peripherally located, low central roll-on-roll-off cargo-hold, tanks above and in flanks.

7 - B, in the sense that the vehicle will be capable of aerocapture if necessary, though direct entry may be nominal flight plan.

8 - C, technically only the BFR design is finalized and when BFS is revealed eventually its mission will use SEP likely as an add on to the BFR 2nd stage tanker which moves it into position for refueling beyond LEO as Earth return will not be direct.



Title: Re: MCT Speculation and Discussion Thread 4
Post by: DJPledger on 09/26/2016 11:42 am

And announces a >F-1 thrust version of Raptor to keep no. of engines on BFR to no more than 9.

Why do you assume early Sixties engine logic still applies? The base principles of rocketry do indeed move that slowly. The engineering, materials science, and practically everything else, do not.
Looks like crazy EM is going for an N-1 type design for BFR after all judging from the announced Raptor thrust. Lets hope the 1st 4 BFR's don't explode on or just after launch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: malu5531 on 09/26/2016 11:59 am


My best guess

1 - a (BFS 2nd stage is MCT)
2 - 46x raptor on 1st stage, multiple used for landing, for redundancy
3 - 15m
4 - 120 MN SL thrust
5 - Redundant raptors on MCT for LAS / no LAS needed
6 - c
7 - a (or combination with b where there is more than one pass through atmosphere before landing)
8 - a / c
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DJPledger on 09/26/2016 12:02 pm


My best guess

1 - a (BFS 2nd stage is MCT)
2 - 46x raptor on 1st stage, multiple used for landing, for redundancy
3 - 15m
4 - 120 MN SL thrust
5 - Redundant raptors on MCT for LAS / no LAS needed
6 - c
7 - a (or combination with b where there is more than one pass through atmosphere before landing)
8 - a / c
Target BFR thrust stated by EM and Raptor announced thrust seems to indicate 25-27 Raptors which is still too many for my liking.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Darkseraph on 09/26/2016 12:10 pm
I'm guessing:

1) The booster stage will have more than 9 engines but less than 22.
2) It will be a fully reusable two stage system not including the ICT spacecraft
3) A variant of the second stage functions as a tanker
4) Booster stage will be 10-12 meters in diameter
5) The Spacecraft itself may be slightly wider than this.
6) Initial crews will be sent to the ICT in orbit, on Dragon2 flights. ICT won't have an escape system.
7) Raptor will first be tested out on an upper-stage for Falcon 9/Heavy.
8 ) This upper stage will be used for scaled tests of docking and refueling in space.
9) Falcon 9 will be eventually phased out and replaced by a raptor based reusable vehicle scaled closer to New Glenn.
10) SEP Barges for cargo are a future growth path for the Mars architecture.
11) The ICT will have an unusual configuration to both protect from radiation and allow easy and safe access to Martian surface.


*This will all be probably horribly wrong when they announce their plans tomorrow. Whatever it is, I hope it is surprising!
 
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/26/2016 01:20 pm

1) Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft
     b)  Boost phase consists of 2 stages, which put the BFS into orbit
     c)  Other: 3rd stage, 'half' stages, drop tanks, etc.

Going with (a)

2) Number of Raptor Engines on BFR (1st stage)

< 30, my best estimate is 25-27 if thrust stays close to 230 tonnes range

3) Diameter of BFR (1st stage)

Range 12.5m-15m, best estimate 15m 1st stage

4) Total Raptor 1st stage thrust (sl)

60 Meganewtons and T/W > 1.3

5) LAS Architecture
     a) No LAS - BFS is the escape mechanism
     b) Traditional LAS - above BFS and is nominally jettisoned during launch phase
     c) BFS contains smaller 'ejection pod' where humans reside during launch
     d) Other, non-traditional LAS design

Best guess is (a)

6) Shape and Landing Mode of BFS
     a) Capsule (perhaps elongated), w/ TPS on base
     b) Cylindrical or biconic - horizontal landing
     c) Cylindrical or biconic - vertical landing
     d) Other

Going with (c), definitely no horizontal landing

7) Mars and Earth return
    a) BFS does direct entry into Mars and Earth atmosphere
     b) BFS does orbital capture before performing entry burn and landing
     c) Same as b, but upon Earth return, stays in orbit for next synod

(a)

8)  Use of non-chemical thrust
     a) Not part of the plan
     b) Will use SEP for some/all of the big transits
     c) All chemical for now, but plans to incorporate SEP down the road

(c) strongly favor

Can anyone think of more/better questions?

Predict Musk will miss 1st crewed landing by >= 3 synods

5-6 Rvacs on BFS stage 2

Raptor sea level will have 10s of tonnes thrust more than the 230 tonnes mentioned by Elon

Entire BFR/BFS GLOW masses under 5.000 tonnes; my estimate ~4,500

Height of BFR/BFS stack under 120m; my estimate <100m

Cargo version, tanker version, crewed version of BFS

1st crewed landing on Mars 8-12 humans planned

Just over 48 hours until Musk makes fools of us

May have got one right with Elon's announcement of 310 tonnes thrust for Raptor. 
Not sure if Rvac or Rsea level, believe Rvac with sea level having less thrust.

If this be so, BFR may have ~19-21 engines.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 09/26/2016 02:08 pm
Also for purposes of reliability and repair.
That's what I meant, wouldn't it take longer to repair/inspect 30 engines on one stage compared to 9 or 20? Extra person-hours required for turnaround, etc.
I'm guessing now that this won't be a very huge problem (or will it?), because when Falcon 9's first stage has 9 engines, people aren't talking about how this is harder to maintain than one big engine + at least 2 small engines on the sides for landing; people instead talk about how it is more expensive to maintain production of multiple engine types instead.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Mike_1179 on 09/26/2016 03:25 pm
Also for purposes of reliability and repair.
That's what I meant, wouldn't it take longer to repair/inspect 30 engines on one stage compared to 9 or 20? Extra person-hours required for turnaround, etc.
I'm guessing now that this won't be a very huge problem (or will it?), because when Falcon 9's first stage has 9 engines, people aren't talking about how this is harder to maintain than one big engine + at least 2 small engines on the sides for landing; people instead talk about how it is more expensive to maintain production of multiple engine types instead.

Like most things that are complicated, the answer is probably "it depends".

If you have fewer engines and you're running chamber temperatures and pressures as high as the materials in the turbo-machinery will allow, you might be a situation where individual components have lower margins or safety factors. This could necessitate higher levels of support to get something in shape to run.

A less powerful engine may have a less extreme environment for its various components, meaning tolerances for some aspects can be larger and require less work.

While not directly applicable to man-hours required, the RS-68 was designed as a less expensive engine than the RS-25. The RS-68 has thrust-to-weight almost 20% lower than the RS-25 and a 10% lower Isp. While the two engines aren't directly comparable because many other design features makes the RS-68 cheaper, you can't assume that because a vehicle has 4x the number of engines, it will take 4x as many hours to get ready for flight.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 09/26/2016 04:36 pm
O.K. I want to change my guess for number of engines from 31 to 27.

And this isn't just because Musk informed us that the thrust is going to be higher than previously hinted at. ;)

It's also because I realized that, while 31 gives a very nice, minimum diameter packing pattern with a single center engine (like the F9), having a single center (landing) engine is probably not appropriate or desired here.  It's unlikely that the BFR could land on a single engine - just too heavy.  3 centralized engines would probably be appropriate.  And the nice symetrical, minimum pattern for 3 center engines comes out to be 27.

We'll know in just over a day (I hope).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 09/26/2016 07:02 pm
I think Musk's talk tomorrow will follow more or less the following logic:

0) Some remarks on AMOS-6
1) Need to make humans multiplanetary (some new twist or variant on the common theme)
2) How? Self-sufficient colony on Mars is best bet, but will not stop there. Other places just a bit harder and further.
3) How to build a colony? In steps. Argues 100 t payload per step ist best. Methalox ist best because ISRU.
4) "It all follows logically from there" -> takes us from 100 t to surface to required specs of BFR, BFS.
5) Unveils design (15 m, all that). Shows Raptor video.
6) Unveils hilariously optimistic ;) timeline to first landing:
- 2018 first BFR booster ready for initial testflights (at Spaceport America)
- 2019 first BFS ready for initial testflights.
- 2020 first orbital flight of BFR+BFS stack. First BFS-Tanker built.
- 2021 orbital refueling of BFS with tanker, lunar orbital shakedown cruise of BFS, perhaps lunar landing
- 2022 launch of first BFS (unmanned) towards Mars. First manned flight of BFS in Earth orbit, later lunar orbit (and surface?).
- 2024 launch of first BFS (manned) towards Mars.
- 2025 Landing day.
7) Makes case for public-private partnerships. "Cannot do this without NASA. But NASA might not be able to do this without us." Presents clever funding scheme which will keep them running with a small fraction of what NASA invests in SLS every year. "NASA should diversify", not only SLS but also alternatives in case rocket grounded after mishap. Multiple plans, "also Blue Origin", should keep us on track to Mars.
8 ) A bit more on the long-term plans, reiterates 500k$/pP. "Everybody who can afford a house today will be able to go." Might pool funding from wealthier passengers to enable even more people to go.

Can't wait! :D
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 09/26/2016 07:32 pm
The Falcon Heavy will lift off with 27 Merlins. I don't think it is too crazy to imagine a similar number of Raptors on this baby for lift-off.

Robustness and reliability are all-important for the engines that will act as the work-horses of this space system architecture. Commonality between the first and second stage dictates a reduced maximum size of the engine.

Many smaller engines instead of five huge ones also means that SpaceX will quickly accumulate very many hours of operation. This will help improve reliability. Running the engines to "destruction" won't necessarily result in mission failure during the first years of operations, as was proven in the F9 CRS-1 launch.

A further consideration is that if they need to swap out a Raptor on Mars (bringing along a spare) the engine can't be too big.

Many factors speak in favour of using many engines, like the N-1, rather than just a few, like the Saturn V.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Pipcard on 09/26/2016 07:41 pm
I agree with you, but N1 isn't something that "speaks in favour" of having many smaller engines instead of few big engines, though.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: docmordrid on 09/26/2016 08:01 pm
I agree with you, but N1 isn't something that "speaks in favour" of having many smaller engines instead of few big engines, though.

ISTM it's worked quite well for Falcon 9, with engine-out saving CRS-1's bacon. So long as there continues to be armored engine cells to prevent fratricde, why not?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Mike_1179 on 09/26/2016 08:03 pm
I agree with you, but N1 isn't something that "speaks in favour" of having many smaller engines instead of few big engines, though.

The B-52 uses 8 engines (TF-33) that make 76kN each. Total thrust 608 kN. It's been flying that way since the 50's

The Boeing 787 uses 2 engines (one variant uses GEnx-1B64) which make 284 kN each. Total thrust 568 kN.

It works both ways - you define the requirements of the system (cost, performance, maintenance, reliability) and design the system from there.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Oersted on 09/26/2016 08:18 pm
The Raptors are designed for missions lasting several years away from maintenance services. Reliability of the system under such circumstances is a crucial requirement.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dglow on 09/26/2016 08:50 pm
I think Musk's talk tomorrow will follow more or less the following logic:

...

7) Makes case for public-private partnerships. "Cannot do this without NASA. But NASA might not be able to do this without us." Presents clever funding scheme which will keep them running with a small fraction of what NASA invests in SLS every year. "NASA should diversify", not only SLS but also alternatives in case rocket grounded after mishap. Multiple plans, "also Blue Origin", should keep us on track to Mars.

I like your thinking save for #7. Musk will, as usual, praise NASA as an excellent partner. But he will be wise to avoid any mention of SLS or NASA 'needing' SpaceX. I can think of many a Senator and Congressperson who will already feel threatened by the reveal of BFR.

Musk's best bet is to avoid either-or comparisons between The US Govt.'s Rocket and his own. Rather, emphasize that SpaceX's system will be yet another tool available in the public/private toolbox of US Space Exploration over the years to come.

Finally, I would add one to your list:

2.5) Red Dragon in ~2018; emphasize SX-NASA cooperation, demonstration of ISRU on-planet.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: DJPledger on 09/26/2016 09:03 pm
O.K. I want to change my guess for number of engines from 31 to 27.

And this isn't just because Musk informed us that the thrust is going to be higher than previously hinted at. ;)

It's also because I realized that, while 31 gives a very nice, minimum diameter packing pattern with a single center engine (like the F9), having a single center (landing) engine is probably not appropriate or desired here.  It's unlikely that the BFR could land on a single engine - just too heavy.  3 centralized engines would probably be appropriate.  And the nice symetrical, minimum pattern for 3 center engines comes out to be 27.

We'll know in just over a day (I hope).
You can have 27 engines with a single center engine. The configuration for BFR would be a single center engine surrounded by rings of 8 and 18 engines.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Bynaus on 09/26/2016 09:14 pm
I think Musk's talk tomorrow will follow more or less the following logic:

...

7) Makes case for public-private partnerships. "Cannot do this without NASA. But NASA might not be able to do this without us." Presents clever funding scheme which will keep them running with a small fraction of what NASA invests in SLS every year. "NASA should diversify", not only SLS but also alternatives in case rocket grounded after mishap. Multiple plans, "also Blue Origin", should keep us on track to Mars.

I like your thinking save for #7. Musk will, as usual, praise NASA as an excellent partner. But he will be wise to avoid any mention of SLS or NASA 'needing' SpaceX. I can think of many a Senator and Congressperson who will already feel threatened by the reveal of BFR.

Musk's best bet is to avoid either-or comparisons between The US Govt.'s Rocket and his own. Rather, emphasize that SpaceX's system will be yet another tool available in the public/private toolbox of US Space Exploration over the years to come.

Finally, I would add one to your list:

2.5) Red Dragon in ~2018; emphasize SX-NASA cooperation, demonstration of ISRU on-planet.

You are certainly right that he will praise NASA, and you are probably right that its perhaps be better if he would not mention NASA needing SpaceX - but then, if they cannot do it on their own, he has to make the case why it would be a good thing for NASA to invest some money in the SpaceX plan: and that is difficult to do if SpaceX don't have anything to offer that NASA wants/needs. Although, thinking of it, redundancy might be that thing...

I didn't want to imply he would do an "either-or" comparison with SLS, more like you said, another tool in the box (hence the "NASA should diversify").

There is one more thing I forgot to list, somewhere around 5) : badass video of the BFR/BFS-architecture. :D
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/26/2016 09:24 pm
I'm revising BFR diameter down to a range of 10 - 12 m based on Musk comment on raptor being comparable to Merlin size but carrying 3x thrust.

That completely rules out 15 m diameters, a vehicle that size is approximately 9x the base area of F9, with triple thrust density of Raptor would lead to 27x the thrust of F9 or something close to 45 million pounds of thrust, 3x times what Musk has aimed for.

Fundamentally the 15 m speculation was nothing more then a crude attempt to multiply the thrust of F9 by a factor of 9 while completely ignoring the thrust density improvements that come from the full-flow staged combustion cycle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 09/26/2016 09:28 pm
I think Musk's talk tomorrow will follow more or less the following logic:

...

7) Makes case for public-private partnerships. "Cannot do this without NASA. But NASA might not be able to do this without us." Presents clever funding scheme which will keep them running with a small fraction of what NASA invests in SLS every year. "NASA should diversify", not only SLS but also alternatives in case rocket grounded after mishap. Multiple plans, "also Blue Origin", should keep us on track to Mars.


I like your thinking save for #7. Musk will, as usual, praise NASA as an excellent partner. But he will be wise to avoid any mention of SLS or NASA 'needing' SpaceX. I can think of many a Senator and Congressperson who will already feel threatened by the reveal of BFR.

Musk's best bet is to avoid either-or comparisons between The US Govt.'s Rocket and his own. Rather, emphasize that SpaceX's system will be yet another tool available in the public/private toolbox of US Space Exploration over the years to come.

Finally, I would add one to your list:

2.5) Red Dragon in ~2018; emphasize SX-NASA cooperation, demonstration of ISRU on-planet.

Mostly agree with 1-6, but 7 doesn't sound like Elon.

I think he will talk about Mars ground systems (habs, pressurized and unpressurized rovers, power, ISRU other than for fuel, research, mining, etc. ) and how there is a need for partners to implement them. I think the fact that Elon is presenting at IAC means that he hopes some of those partners will be international.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 09/26/2016 09:43 pm
I'm revising BFR diameter down to a range of 10 - 12 m based on Musk comment on raptor being comparable to Merlin size but carrying 3x thrust.

That completely rules out 15 m diameters, a vehicle that size is approximately 9x the base area of F9, with triple thrust density of Raptor would lead to 27x the thrust of F9 or something close to 45 million pounds of thrust, 3x times what Musk has aimed for.

Fundamentally the 15 m speculation was nothing more then a crude attempt to multiply the thrust of F9 by a factor of 9 while completely ignoring the thrust density improvements that come from the full-flow staged combustion cycle.

The 15 m diameter speculation had little to do with individual engine thrust.

1. Various attempts have been made to optimise the BFR mass, these give least tank mass for a 13-15 m stage.

2. The BFS has been said by Musk to be very large, a scaled Dragon capsule design might have to be over 23 m, which would fit much more easily on a 15 m stage. Biconic or semi-lifting body BFS designs would seem to need 12-15 m diameter to enclose the inidcated volume.

3. L2 info and various leaks on reddit
Title: Re: MCT Speculation and Discussion Thread 4
Post by: mfck on 09/26/2016 09:46 pm

...



SpaceX has what NASA needs. SX are being paid 1.6B for it. And then there's CRS-2. That's quite some money invested by NASA into the SpaceX plan
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 09/26/2016 10:22 pm
There are a few things that have stopped me from publishing my full plan other than poor time management.

Not wanting to assume an unprecedented chamber pressure was one of them, despite hints that FFSC was aimed at that.  I couldn't get RPa Lite to spit out the right numbers at ~20MPa;  While 360-370s is easy at lower pressures with realistic combustion inefficiencies, 380s is not.  I guess that's out of the way.  I'll see how much I can write tonight, before it is completely technically obsolete.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 09/26/2016 10:33 pm
I'm revising BFR diameter down to a range of 10 - 12 m based on Musk comment on raptor being comparable to Merlin size but carrying 3x thrust.

That completely rules out 15 m diameters, a vehicle that size is approximately 9x the base area of F9, with triple thrust density of Raptor would lead to 27x the thrust of F9 or something close to 45 million pounds of thrust, 3x times what Musk has aimed for.

Fundamentally the 15 m speculation was nothing more then a crude attempt to multiply the thrust of F9 by a factor of 9 while completely ignoring the thrust density improvements that come from the full-flow staged combustion cycle.
Raptor could be tiny and still obtain 3x as much thrust if you're willing to tolerate low Isp.  Nozzles get exponentially larger as you raise Isp closer to its maximum possible figure;  That max figure itself scales with chamber pressure (though not only chamber pressure, and not linearly).  The base area of F9 is 3.66m, so a 15m BFR would be a factor 16.8x as large.

Think about the problem of sealevel overexpansion, which bounds the upper end of the nozzle size range for a first stage engine;  The overexpansion threshold will occur at the same nozzle thrust density, so you have strong specific impulse incentive to make nozzles bigger if you had a hypothetical "Merlin-sized but 3x as thrust-dense".
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/27/2016 12:15 am
I'm revising BFR diameter down to a range of 10 - 12 m based on Musk comment on raptor being comparable to Merlin size but carrying 3x thrust.

That completely rules out 15 m diameters, a vehicle that size is approximately 9x the base area of F9, with triple thrust density of Raptor would lead to 27x the thrust of F9 or something close to 45 million pounds of thrust, 3x times what Musk has aimed for.

Fundamentally the 15 m speculation was nothing more then a crude attempt to multiply the thrust of F9 by a factor of 9 while completely ignoring the thrust density improvements that come from the full-flow staged combustion cycle.

The 15 m diameter speculation had little to do with individual engine thrust.

1. Various attempts have been made to optimise the BFR mass, these give least tank mass for a 13-15 m stage.

2. The BFS has been said by Musk to be very large, a scaled Dragon capsule design might have to be over 23 m, which would fit much more easily on a 15 m stage. Biconic or semi-lifting body BFS designs would seem to need 12-15 m diameter to enclose the inidcated volume.

3. L2 info and various leaks on reddit

Thrust density not individual engine thrust is the problem, people have been assuming Merlin thrust density which was never going to be the case.  Tank mass is not sole consideration in deciding a rockets width, minimizing thrust structure mass and air resistance makes the thinnest possible rocket the optimum shape.

Large dose not mean wide, the vehicle is quoted at twice the Saturn V thrust, that fulfills any 'large' descriptor independent of diameter.  Their is no need for the booster to match the width of it's payload either, all rockets routinely fly with payload fairings wider then the rockets core.  Estimates of huge BFS diameters sound like attempts to retroactively justify the 15 m diameter booster and are not credible in my opinion.

I'm saying these reddit and L2 'leaks' were nothing more then poor speculations and rumors based on naive extrapolations of F9 thrust density.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Paul451 on 09/27/2016 08:10 am
but then, if they cannot do it on their own, he has to make the case why it would be a good thing for NASA to invest some money in the SpaceX plan

There's no need for him to publicly try to "sell" MCT and his Mars architecture to NASA at the first presentation. There's already plenty of interest and there's years of development ahead, with plenty of opportunity to sell NASA on the idea of investing in some aspect of the capacity. (Similar to getting USAF interested in a Raptor-based upper-stage for FH. Gives USAF redundancy for heavy-lift/high-orbit, gives SpaceX extra funding for Raptor development and access to more USAF payloads.)

But using this presentation to, in essence, publicly mock NASA's flagship program merely creates unnecessary enemies and hence unnecessary resistance to later cooperation.

{shrug} 10 hours.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 09/27/2016 08:18 am
SpaceX has what NASA needs. SX are being paid 1.6B for it. And then there's CRS-2. That's quite some money invested by NASA into the SpaceX plan

That's NASA purchasing services at a very good price.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Robotbeat on 09/27/2016 02:57 pm
SpaceX has what NASA needs. SX are being paid 1.6B for it. And then there's CRS-2. That's quite some money invested by NASA into the SpaceX plan

That's NASA purchasing services at a very good price.
Heck, even if it was just NASA giving SpaceX money, NASA will be paid back in spades just Red Dragon succeeds.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Snake on 09/27/2016 03:39 pm
My final design. All numbers are metric.

                             TOTAL      BFR      BFS   LAS

Total Dry Mass (t)   408+100   266   142+100   21.5
Total Wet Mass (t)   5,522   3,722   1,800   29.8
Height (m)                56.6   23.0   33.6   10.2
Raptors                           36   30   6   16 (SuperDracos)
Raptor Thrust (t)      ---       252 (SL)   310 (Vac)   7.3 (SuperDraco)
Thrust (t)                 ---    7,560   1,860   117
TWR                           ---    1.37   1.03   3.9

                                                                   RTLS
Burn Time (m:s)      2:05+17   5:29   24.6   17
DeltaV (m/s)         11,000   3,500   7,500      0
DeltaV with RTLS   10,250   2,750   7,500      750
---------------------------------------------------------------------------------------------
            
Observed Velocity at MECO (m/s)   1,385
Observed Height at MECO (km)      42
Time to MECO (sec)                  2:05

BFS can make it to orbit with 2 opposing engines out with extra gravity losses of ~400 m/s.

LAS Capsule is twice the size (8 times the volume) of Dragon 2.
So can seat at least 8 x 7 = 56 crew.

SuperDracos *could* be used for final descent (200 m) to Mars Surface.

BFR looks too short. Probably because I haven't adjusted fuel density to be accurate.

Images of similar ship reaching orbit of a 6.4x Kerbin. http://imgur.com/a/hKOpG

Benjamin Franklin Class Ship
Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 09/27/2016 03:46 pm
O.K. I want to change my guess for number of engines from 31 to 27.

And this isn't just because Musk informed us that the thrust is going to be higher than previously hinted at. ;)

It's also because I realized that, while 31 gives a very nice, minimum diameter packing pattern with a single center engine (like the F9), having a single center (landing) engine is probably not appropriate or desired here.  It's unlikely that the BFR could land on a single engine - just too heavy.  3 centralized engines would probably be appropriate.  And the nice symetrical, minimum pattern for 3 center engines comes out to be 27.

3 center engines is much worse than 1.

If any of those 3 center engines fail, then it's crash and burn.

But with many more engines, the landing burn can be done with center engine + ANY two engines that are on oppisite sides of the craft.



Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 09/27/2016 04:26 pm
O.K. I want to change my guess for number of engines from 31 to 27.

And this isn't just because Musk informed us that the thrust is going to be higher than previously hinted at. ;)

It's also because I realized that, while 31 gives a very nice, minimum diameter packing pattern with a single center engine (like the F9), having a single center (landing) engine is probably not appropriate or desired here.  It's unlikely that the BFR could land on a single engine - just too heavy.  3 centralized engines would probably be appropriate.  And the nice symetrical, minimum pattern for 3 center engines comes out to be 27.

3 center engines is much worse than 1.

If any of those 3 center engines fail, then it's crash and burn.

But with many more engines, the landing burn can be done with center engine + ANY two engines that are on oppisite sides of the craft.





I think the nearly empty BFR (with some landing propellent) would be too massive for a single Raptor.  And I think if any of the 3 central engines fail, there would be a backup engine in line with the failing engine and the center of the vehicle which could be called into service.  Throttling and gimballing employed to null out any resultant moments.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: guckyfan on 09/27/2016 05:17 pm
One engine should be enough. The empty first stage does not weigh that much. I hope for a configuration with 3 central engines. The 3 fire but if one fails two are enough for braking and stability by gimballing. For the final approach any one of the three engines will do. Engines 2m from center with a 12-15 m stage should be able to land.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/27/2016 05:18 pm
Last try:
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Hauerg on 09/27/2016 05:31 pm
I'm revising BFR diameter down to a range of 10 - 12 m based on Musk comment on raptor being comparable to Merlin size but carrying 3x thrust.

That completely rules out 15 m diameters, a vehicle that size is approximately 9x the base area of F9, with triple thrust density of Raptor would lead to 27x the thrust of F9 or something close to 45 million pounds of thrust, 3x times what Musk has aimed for.

Fundamentally the 15 m speculation was nothing more then a crude attempt to multiply the thrust of F9 by a factor of 9 while completely ignoring the thrust density improvements that come from the full-flow staged combustion cycle.

We wil know within 90 minutes. But iirc there was indeed a quote from elon, or second hand reports of it, regarding 15m tank tooling or something like that.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: malu5531 on 09/27/2016 05:43 pm
Target BFR thrust stated by EM and Raptor announced thrust seems to indicate 25-27 Raptors which is still too many for my liking.

Looks like my guess was closer.  :D
Title: Re: MCT Speculation and Discussion Thread 4
Post by: dasmoth on 09/27/2016 05:45 pm
Those who didn't want it to be like the N1 have got their wish.

I make that 42 engines!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: vandersons on 09/27/2016 05:54 pm
So, if I got that right the MCT is a VTOL lifting body spacecraft. Very impressive!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: ZachF on 09/27/2016 05:57 pm
42 engines!!!! good god!

That will be like 25 million pounds of thrust at liftoff!!!!  :o 8)  ;D
Title: Re: MCT Speculation and Discussion Thread 4
Post by: inventodoc on 09/27/2016 06:00 pm
Yup 42.  Going full N1 on this thing.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: ZachF on 09/27/2016 06:01 pm
Just noticed the video says 28,730,000 pounds of thrust (127,800kN)

That rocket will be putting out more power than entire large nations when lit off!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 09/27/2016 06:08 pm
Showing my cards before they're technically obsolete:
https://docs.google.com/spreadsheets/d/1CGSeJCfWXDO9wWFW6DmuluSWdhvvkiES6XkJiJHyxaI/edit?usp=sharing
https://docs.google.com/document/d/1SJyYrgMfc1baz28EXOUPBfdBGKvXaWwLyv4stwxTZ_M/edit?usp=sharing

Illustrations were a rush-job, but they work as a diagram, and my figures are vetted against pressure, temperature, tank-volume, propellant-mass, thrust-threshold, Isp, delta-V, and some components of dry mass.

The capsule tip didn't get much elaboration because I didn't have time to finish the math, but it's important to the architecture and I'm convinced you could fit it into 150mT dry mass provided enough carbon fiber.  The legs also got left out of the document (six of them for redundancy, rather spidery and shock-absorbing).

This thing fits a token amount of reliable hypergols for each trip to maneuver.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 09/27/2016 06:44 pm
42 engines!!!! good god!

That will be like 25 million pounds of thrust at liftoff!!!!  :o 8)  ;D

Yup.  Glad I revised my engine count downwards just in time!  :o
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 09/27/2016 07:22 pm
1000 ships!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/27/2016 07:46 pm
12 meter diameter. This one was considering 15m.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 09/27/2016 08:58 pm
So, 3 SL engines and  6 fixed-mount vacuum engines.

So the 3 SL engines handle landing back to earth. And also for liftoff from mars and after staging when ging from earth the extra thrust of these is needed.

Interplanetary transport burns can be done with just the fixed vacuum engines, if differential thrusting and manouvering thrusters give enough control authority.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 09/27/2016 09:05 pm
3 center engines is much worse than 1.

If any of those 3 center engines fail, then it's crash and burn.

But with many more engines, the landing burn can be done with center engine + ANY two engines that are on oppisite sides of the craft.

You need to tell SpaceX right away.

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 09/27/2016 11:07 pm
Musk just finished a press conference, and was asked about abort capabilities:

https://twitter.com/jeff_foust/status/780896313676148737
Quote
Musk: spaceship can serve as own abort system from booster, but on Mars, either you’re taking off or you’re not. #IAC2016

https://twitter.com/NASAWatch/status/780896600294064128
Quote
Asked about abort modes for launcher @elonmusk said "make it very reliable ... you do not have parachutes for commercial airliners" #IAC2016

I have argued exactly this on these MCT threads many times, I'm glad he shares the same point of view. At this scale such systems are impractical.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/27/2016 11:09 pm
Looks like a got closest on the booster,

12 m diameter, check
tall and skinny, not short and wide, contrary to consensus
carbon fiber, check but obvious
some engines fixed rather then gimbaling, only person to predict that
possible manufacturing a Mchoud, check
landing directly on launch pad with 2nd stage put on by crane, speculated on that about a month ago
engine count undershot by 11 and thrust by about half, but did anyone predict this much thrust

Almost everything above the booster I got wrong, and I'm very skeptical of that part of the vehicle.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 09/27/2016 11:31 pm
I guessed 36 engines, did not see anybody guessing more, so if we use The Price Is Right rules....

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: malu5531 on 09/27/2016 11:33 pm
I guessed 36 engines, did not see anybody guessing more, so if we use The Price Is Right rules....

Matthew

My guess was 46
Title: Re: MCT Speculation and Discussion Thread 4
Post by: matthewkantar on 09/27/2016 11:41 pm
I guessed 36 engines, did not see anybody guessing more, so if we use The Price Is Right rules....

Matthew

My guess was 46

Must have missed that. Are you familiar with The Price Is Right over there in Sweden?

Matthew
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/28/2016 12:03 am
I grew up watching the Price is Right, it's an American produced show or at least my version was, did you have a locally produced version in Sweden as it seems that you would have to use local prices and currency for the audience to be able to have a sense of the prices.  On the other hand if I could watch the show at 8 years old with no idea what anything costs then I guess it could be watched internationally so long as it was dubbed.

Still I'm inclined to give malu5531 the engine count trophy via being only 4 engines off rather then 6 engines off, I think the default assumption is closest with both over and under being equal rather then Price is Right rules as GORDAP didn't specify any rules.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: malu5531 on 09/28/2016 12:13 am
I guessed 36 engines, did not see anybody guessing more, so if we use The Price Is Right rules....

Matthew

My guess was 46

Must have missed that. Are you familiar with The Price Is Right over there in Sweden?


I'm sorry, I'm not familiar with that.

I also did quite good on S1 thrust:


My best guess

4 - 120 MN SL thrust


Actual was 127.8 MN SL thrust
Title: Re: MCT Speculation and Discussion Thread 4
Post by: malu5531 on 09/28/2016 12:20 am
For those with L2, my guess was based on these calculations (http://forum.nasaspaceflight.com/index.php?topic=40127.msg1470042#msg1470042) I did a while ago, with the goal of figuring out what design it would take to build an MCT according to rumoured specs at that time.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: CJ on 09/28/2016 01:02 am
I'm thrilled by the Musk presentation. However, I'm worried by what I didn't see.

Two MCT concerns in particular I have; heat and power. How, exactly, will they preserve the subcooled LOX and methane needed for landing during interplanetary cruise (80 to 115 days)? And also, how will they handle the heat generated on MCT by the 100 people aboard, plus life support, plus lighting, etc? On ISS, cooling is very complex, and if I'm remembering correctly, the cooling system (ammonia based) outmasses the solar arrays.

Also, regarding solar arrays for power... what we see in the demo looks like an area on par with the ISS arrays, so how does one get sufficient power from that area to handle life support, etc, for 100 people? And that's without considering the diminished sunlight at Mars.

One guess I have regarding mass fractions, etc, is that refueling won't be done in LEO, but in an elliptical orbit - lower delta/v needed for the TMI burn that way, thus reducing the mass fraction issue. 

Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 09/28/2016 01:09 am
I'm thrilled by the Musk presentation. However, I'm worried by what I didn't see.

Two MCT concerns in particular I have; heat and power. How, exactly, will they preserve the subcooled LOX and methane needed for landing during interplanetary cruise (80 to 115 days)? And also, how will they handle the heat generated on MCT by the 100 people aboard, plus life support, plus lighting, etc? On ISS, cooling is very complex, and if I'm remembering correctly, the cooling system (ammonia based) outmasses the solar arrays.

Also, regarding solar arrays for power... what we see in the demo looks like an area on par with the ISS arrays, so how does one get sufficient power from that area to handle life support, etc, for 100 people? And that's without considering the diminished sunlight at Mars.

One guess I have regarding mass fractions, etc, is that refueling won't be done in LEO, but in an elliptical orbit - lower delta/v needed for the TMI burn that way, thus reducing the mass fraction issue.

If you expected *that* level of engineering detail, you were never going to be satisfied.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 09/28/2016 01:12 am
...
One guess I have regarding mass fractions, etc, is that refueling won't be done in LEO, but in an elliptical orbit - lower delta/v needed for the TMI burn that way, thus reducing the mass fraction issue.

What mass fraction issue? The number quoted was 450 tonnes to the Mars surface, assuming LEO transfer. The mass fraction through TMI appears to be no issue at all.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: launchwatcher on 09/28/2016 02:04 am
Must have missed that. Are you familiar with The Price Is Right over there in Sweden?
I'm sorry, I'm not familiar with that.
The phrase used on the show was "closest without going over" (in other words, the largest guess which is equal to or below the target value).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lar on 09/28/2016 02:37 am
Might be fun for folks to go back and edit their prediction lists to show how they did (me? not that great)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 09/28/2016 02:45 am
My prediction was almost exactly half the size and performance, I thought the 15 mlfb designs were oversized. 8)

I did correctly predict that the Raptor vacuum nozzle would be under 4m in diameter though (it's 3.85).
Title: Re: MCT Speculation and Discussion Thread 4
Post by: ZachF on 09/28/2016 03:03 am
Here is my rough MSPaint size comparison between the ICT and some space stations/craft.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Stan-1967 on 09/28/2016 03:21 am
Here is my rough MSPaint size comparison between the ICT and some space stations/craft.

Can you do the IST/MCT sitting on the deck of the ASDS?   :o
Title: Re: MCT Speculation and Discussion Thread 4
Post by: envy887 on 09/28/2016 03:27 am
Here is my rough MSPaint size comparison between the ICT and some space stations/craft.

Can you do the IST/MCT sitting on the deck of the ASDS?   :o

Footprint should be just about as big as the F9 S1.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 09/28/2016 03:44 am
Might be fun for folks to go back and edit their prediction lists to show how they did (me? not that great)

I don't know if I ever made real "prediction checkbox list", but I have made several posts with the following predictions that came true:
 - spacecraft as integrated 2nd stage
 - biconic/side entry
 - powered by multiple raptors instead of a single one (although I was off on the count, I expected 5)
 - no launch abort capsule (abort the whole thing)

The booster was roughly what I expected, but bigger and lacking landing gear.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: watermod on 09/28/2016 04:08 am
I would like to see the first ITS going to MARs with both a ground side fuel/oxidizer plant, 10 or 12 GPS stats and a large number of Elon's internet communications sats.   (Just like those in the planned 4000 node system for Earth) A few observation sats like Digital Globe uses too would be nice in the payload.
That way when the actual astronauts and colonists come there would be fuel, communication, accurate ground positioning and accurate imaging that could be down loaded to folks on Mars or provided to those orbiting Mars.

Another nice addition on another craft would be a nice sized spaced power system to broadcast power to the colony site on the ground.   If not that then a large mylar film mirror to concentrate sunlight for the ground based solar system.   It could provide localized heating for melting ice too.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Ludus on 09/28/2016 04:21 am
Any idea how cargo gets loaded/unloaded?

If it's going to deliver 450T of cargo some of it will have to be loaded in orbit just like it has to take on propellant, that's a lot more than it can take to NEO reusable.

I'm curious about the pure cargo variant which I'd assume would have big bay doors a bit like the shuttle.
I'd expect more to be built of that than either the Heart of Gold class or the Tanker based on the notions that there will be 10X the need for cargo over passengers and a Tanker has such a fast potential turn around by comparison that you don't need too many.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Helodriver on 09/28/2016 04:22 am
My one BFR speculation was dead on.  Helodriver predicts the future (again)   ;)



A good look at those enormous rainbirds in that photo. Assuming the yellow railing is 4' high, I get a quick-and dirty estimate of the rainbirds at 57'. :o That seems ridiculously big.

Could they be backed off from the rocket far enough that that actually makes sense? Or am I way off on the height?

Pure speculation - These are  oversized for an F9 family vehicle but are right sized for a larger follow on vehicle. 39A is the eventual BFR launch site.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/28/2016 04:31 am
Might be fun for folks to go back and edit their prediction lists to show how they did (me? not that great)

I don't know if I ever made real "prediction checkbox list", but I have made several posts with the following predictions that came true:
 - spacecraft as integrated 2nd stage
 - biconic/side entry
 - powered by multiple raptors instead of a single one (although I was off on the count, I expected 5)
 - no launch abort capsule (abort the whole thing)

The booster was roughly what I expected, but bigger and lacking landing gear.

To be precise the BFS we were shown is cylindrical with a rounded nose and thick fins that look to hold the landing gear, not bi-conic which would involve the vehicle widening all the way down to the base, the fins can give a false sense that's whats happening but the cut-away is clear the central body is cylindrical.

That said both cylindrical and bi-conic were combined on the questionnaire and the entry profile is indeed horizontal which was the more important distinction.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: ZachF on 09/28/2016 04:41 am
The ITS concept video is pretty popular on Facebook, already has over 1m views...

(at least 15 of those are mine, lol  :D )
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 09/28/2016 05:01 am
Might be fun for folks to go back and edit their prediction lists to show how they did (me? not that great)

I don't know if I ever made real "prediction checkbox list", but I have made several posts with the following predictions that came true:
 - spacecraft as integrated 2nd stage
 - biconic/side entry
 - powered by multiple raptors instead of a single one (although I was off on the count, I expected 5)
 - no launch abort capsule (abort the whole thing)

The booster was roughly what I expected, but bigger and lacking landing gear.

To be precise the BFS we were shown is cylindrical with a rounded nose and thick fins that look to hold the landing gear, not bi-conic which would involve the vehicle widening all the way down to the base, the fins can give a false sense that's whats happening but the cut-away is clear the central body is cylindrical.

That said both cylindrical and bi-conic were combined on the questionnaire and the entry profile is indeed horizontal which was the more important distinction.

Really, you of all people nitpicking me on the 'spaceship' predictions?  ;) Cylindrical is indeed what all my previously posted MCT drawings showed... Here are two old sketches of a side re-entering cylindrical MCT, pretty close in the end. (other than size, flipping the propellant and crew/cargo, and engine count)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: the_other_Doug on 09/28/2016 05:18 am
I think perhaps we will need a separate thread shortly on "Launching the ITS from LC-39A", but there is something that is a huge challenge to my understanding, here.

It sounded to me like Elon stated that LC-39A was going to be used to launch F9, FH and ITS.  Not that it would launch F9 and FH until ITS comes on line, and that the pad would then be converted for ITS launches.  No, what I heard Elon say is that all three would be able to launch out of LC-39A.

I understand how LC-39A (and SLC-4 at Vandenberg) can be configured for either Falcon 9 or Falcon Heavy launches; you have three flame holes in the launcher deck, with a set of hold-downs for FH center core/F9 and a set of hold-downs for the FH outer cores.  You just don't engage the outer hold-downs on an F9 flight, since there will be no outer cores over the outer flame holes.  The variations in servicing equipment between F9 and FH are managed within the TEL design for Vandenberg and KSC.

However, you need a much, MUCH larger flame hole for the ITS booster, and much, MUCH larger hold-downs.  The total mass of the ITS on the pad will be huge -- the hold-downs are not big in order to keep 28 million lbs of thrust from tearing them off, they are big in order to not snap at the forces of a 20-million-pound-plus rocket shifting as it lifts off.

Even assuming that ITS will somehow use the existing permanent tower for its servicing equipment (propellant feed lines, etc. -- the stuff the TEL does for the Falcons), will there somehow be an ITS-sized flame hole, launch mounts, hold-downs, etc., and then a "plug" containing the three Falcon flame holes, the Falcon launch mounts, etc., that will be plugged into the ITS flame hole when they wish to launch Falcons?  Or will each type of vehicle have its own "real estate" on the launcher, with the Falcon launch holes (and its hold-downs, etc.) on one side and the ITS launch hole (with all of its associated claptrap) on the other?

I'd have to think the launch pad would be out of commission for weeks, if not months, while converting from one launcher family to another, if a 400-square-meter (or more) slab of launcher deck, complete with launch mounts, hold-downs, electrical, data and fluid connections, etc., etc., has to be removed from the pad every time you need to literally "clear the deck" for a series of ITS launches.  By the same token, I wouldn't think the launcher deck is big enough to have flame holes, launch mounts, hold-downs, etc., for both vehicle families.

Is the talk of launching Falcons and ITS boosters from the same pad more of Elon's off-the-cuff, not-playing-it-out-in-his-head musings, or am I missing something?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 09/28/2016 05:32 am
This really belongs in the '39A' thread in the general SpaceX forum, but I see no major problem. FH fits well within the 12 m diameter 'hole' of a BFR launch/landing mount, so a launch mount could be temporarily mounted on top of a BFR launch mount. Plumbing would be an concern, but we should move talk of it to the proper forum.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Impaler on 09/28/2016 06:02 am

Really, you of all people nitpicking me on the 'spaceship' predictions?  ;) Cylindrical is indeed what all my previously posted MCT drawings showed... Here are two old sketches of a side re-entering cylindrical MCT, pretty close in the end. (other than size, flipping the propellant and crew/cargo, and engine count)

I've seen some other posts claiming the presented vehicle was bi-conic and wanted to clarify, your perdition was indeed for a cylindrical vehicle which is why I though it odd that you wrote bi-conic and that you might have been misinformed by people throwing that word around.

Also I don't see why 'I' of all people should be considered an invalid source of nitpicking even in jest, I did correctly predict nearly everything about the booster in the face of a strong opposing consensus and while I was wrong about the 2nd stage everyone else was basing their prediction on rumors and L2 information that I don't have access too.  And I stick by my opinion that the massive BFS isn't workable and think the design as presented will go the way to the reusable F9 2nd stage.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Lars-J on 09/28/2016 06:17 am

Really, you of all people nitpicking me on the 'spaceship' predictions?  ;) Cylindrical is indeed what all my previously posted MCT drawings showed... Here are two old sketches of a side re-entering cylindrical MCT, pretty close in the end. (other than size, flipping the propellant and crew/cargo, and engine count)

I've seen some other posts claiming the presented vehicle was bi-conic and wanted to clarify, your perdition was indeed for a cylindrical vehicle which is why I though it odd that you wrote bi-conic and that you might have been misinformed by people throwing that word around.

Yes, I meant cylindrical. Although the three "fins" do alter the shape slightly, so I wonder if they have seen some aerodynamic benefit of stretching them so far forward.

Also I don't see why 'I' of all people should be considered an invalid source of nitpicking even in jest, I did correctly predict nearly everything about the booster in the face of a strong opposing consensus and while I was wrong about the 2nd stage everyone else was basing their prediction on rumors and L2 information that I don't have access too.  And I stick by my opinion that the massive BFS isn't workable and think the design as presented will go the way to the reusable F9 2nd stage.

Just to be clear, I'm not an L2 member either.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: meekGee on 09/28/2016 06:23 am
My one BFR speculation was dead on.  Helodriver predicts the future (again)   ;)



A good look at those enormous rainbirds in that photo. Assuming the yellow railing is 4' high, I get a quick-and dirty estimate of the rainbirds at 57'. :o That seems ridiculously big.

Could they be backed off from the rocket far enough that that actually makes sense? Or am I way off on the height?

Pure speculation - These are  oversized for an F9 family vehicle but are right sized for a larger follow on vehicle. 39A is the eventual BFR launch site.

Come on.  You couldn't even predict that you yourself will be at the Grand Mars Reveal.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 09/28/2016 11:52 am
Well my predictions were a real mixed bag.  Missed on the engine count (27 versus 42) and booster diameter (15 versus 12).  Also really thought BFS would still end up being 'capsule' shaped.

But 'mission profile' was as clean and simple as I'd thought it would be:  No LAS, orbital refueling, BFS goes from Earth orbit, direct entry and lands on Mars, then Mars takeoff and direct entry back at Earth.

Those who insisted (pretty strenuously as I recall) on additional stages, 'pusher stages' for LEO departure, aerocapture (at Mars or Earth), early transition to SEP, and especially Mars orbit refueling were pretty much out to lunch.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: jpo234 on 09/28/2016 11:58 am
Those who insisted (pretty strenuously as I recall) on additional stages, 'pusher stages' for LEO departure, aerocapture (at Mars or Earth), early transition to SEP, and especially Mars orbit refueling were pretty much out to lunch.

The aerocapture is on the table (see slide 38 of the presentation):
Quote
From interplanetary space, the ship enters the atmosphere, either capturing into orbit or proceeding directly to landing
Title: Re: MCT Speculation and Discussion Thread 4
Post by: GORDAP on 09/28/2016 12:08 pm
Those who insisted (pretty strenuously as I recall) on additional stages, 'pusher stages' for LEO departure, aerocapture (at Mars or Earth), early transition to SEP, and especially Mars orbit refueling were pretty much out to lunch.

The aerocapture is on the table (see slide 38 of the presentation):
Quote
From interplanetary space, the ship enters the atmosphere, either capturing into orbit or proceeding directly to landing

Ah, missed this.  Does anyone recall, did Musk's remarks indicate they're leaning one way or another on this?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Helodriver on 09/28/2016 01:16 pm
My one BFR speculation was dead on.  Helodriver predicts the future (again)   ;)



A good look at those enormous rainbirds in that photo. Assuming the yellow railing is 4' high, I get a quick-and dirty estimate of the rainbirds at 57'. :o That seems ridiculously big.

Could they be backed off from the rocket far enough that that actually makes sense? Or am I way off on the height?

Pure speculation - These are  oversized for an F9 family vehicle but are right sized for a larger follow on vehicle. 39A is the eventual BFR launch site.

Come on.  You couldn't even predict that you yourself will be at the Grand Mars Reveal.

Who says I revealed all my predictions in public? ;)
Title: Re: MCT Speculation and Discussion Thread 4
Post by: hkultala on 09/28/2016 01:25 pm
a few more teasers before the september reveal:

https://www.washingtonpost.com/news/the-switch/wp/2016/06/10/elon-musk-provides-new-details-on-his-mind-blowing-mission-to-mars/

1 red dragon in 2018, 'at least 2' in 2020, then first flight of MCT in 2022...
Bold mine.

From the article:

Quote
Then in 2022, Musk said he hoped to launch what the company now sometimes refers to as the Mars Colonial Transporter, designed to bring a colony to Mars.

I'm sorry, but this is nuts  somewhat optimistic. You all realize that 2022 is only six years away, right? Regardless of the fact that Dragon v2 hasn't flown yet

Dragon v2 has flown, though not yet to orbit.

https://www.youtube.com/watch?v=1_FXVjf46T8

Quote
, and regardless of the fact that FH hasn't flown yet; NOTHING concrete about BFR/MCT has even been released, and Musk is talking about launching one in six years. Six. Years.

.. and now after 3 months they have CAD models of their crafts and detailed information of the engine has been released. And it's still 5 years, 10 and half monts until the 2022 launch window.

Quote
Six years to get BFR off the ground, literally. To build a factory on the scale of Michoud (only bigger) for fabrication and assembly of BFR and MCT. To build a huge HIF to handle the 12.5m or 15m cores, or heck even to lease one of the VAB high bays and get it fitted out for BFR. To build all of the ground support infrastructure and ground transportation.

Bigger projects have bene done on shorter timeframe.

Quote
To get the entire Raptor engine (not just components) off of the drawing board and into the test stands and validated.

It's now 3 monts after your post and now an entire raptor engine has gone through it's first test.

Quote

Heck, you guys are still arguing over where the thing will be built and launched from. Do you think that would really be the case if they were going to be rolling off the assembly line in less than six years?


Guys in this forum were arguing but Elon did know that it's going to be launchd from LC-39A.

(lack of) public knowledge on forum is completely different thing than (lack of) detailed plans by Elon/SpaceX.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/28/2016 02:57 pm
As requested, scoring my mostly way too small predictions. Comments BOLD

Approaching 30 days from what (we hope) is the big reveal, I thought it a good time to revisit and post revised BFR/MCT speculation before any info leaks out.  Trying to stay within the parameters of what Musk has said as I best understand.  A TSTO vehicle launched by a re-useable, single core BFR that puts the BFS a.k.a. the MCT into LEO where it is re-fueled, travels to and lands on Mars where it is again refueled for the journey back to Earth carrying a quarter of the outbound “cargo” mass.  The outbound cargo masses 100 tonnes which I assume means either cargo or people or a combination thereof.  BFS/MCT mass not included in the 100T.

Correct mission profile.  Most here with a few notable exceptions agreed with this, so no great insight.

Myriad unknowns led by the dry mass of the BFS.  Rocket equation dictates various mass assumptions here can produce wildly different answers.

My predictions, metric unless otherwise stated:
1.   Entire launch vehicle BFR+BFS masses under 5,000T.  Guestimate ~4,500T.
WAY off!
2.   BFS dry mass < 100T, my pick is 85T carbon composites BUT heavier than some predictions because ruggedized to allow for minimal maintenance.
WAY off
3.   BFR absolutely > 10m diameter to fit enough engines. Likely between 12.5 and 15m.  My guess 15m.  Allows addition of more engines in the future.
Another miss as I was confident of 12.5m or greater.  Not counting 17m flare outs on ITS craft.
4.   My guestimate BFR+BFS stack <100m height.  Certainly <125m.
Barely made my "certainly under 125m but missed on 15m.  Skinny rocket 12m increased height.
5.   Sticking with the “over 230T” Raptor thrust Elon mentioned, I get 25-27 engines.  My guestimate is 26 with “over 230T” as 235T in my spreadsheet.  Around 13.5 million Lbs force.
Engine # most likely wrong because…
I was right that I was wrong :)
6.   Predict that Raptor engine design goal thrust changed to higher than 230T previously stated, but only by several 10s of tonnes, not hundreds.
Hit! I was confident that more detailed design would increase Raptor SL thrust by several 10s of tonnes. 
It helped that Bezos BE-4 thrust was higher than Elon's earlier 230T for Raptor.  That shall not stand! :)

7.   BFS with 5 Rvac engines
Close but no cigar.
8.   RTLS minimizes cost, turnaround time, effort.  Changed my opinion from max payload ASDS for those reasons.  Just make the BFR bigger. Stages low and slow ~2.2 Km/sec.  “Easy” recovery & re-flight vs F9 GTO flights.
Hit!
9.   Initial BFR test flights likely equipped with less engines and less payload.
Unknown
10.   Large crew volume design >2,000m3.  Initial flights with less people & people space but more cargo space.
I believe crew volume is ~3,000 m3 so this is a hit.  Felt that nuclear sub range 20 something m3 was the goal. Never agreed with those in the 10m3 and under range.  You know who you are.
11.   Initial crewed Mars mission will carry 6-12 people.  10 is my latest #. Why?
NASA & other nations will buy seats. 
http://forum.nasaspaceflight.com/index.php?topic=40683.msg1557261#msg1557261
Unknown
12.   SEP still under development awaits later opposition cargo transits
Scoring as a miss in that not mentioned
13.   BFS will have “exotic” upper mounted engines for rough terrain Mars landing &takeoff (just echoing others’ analysis here)
Big miss.  I am concerned about SX's approach here.
14.   BFS will be a lifting body for EDL, but not a scaled up Dragon capsule shape.  It will look badass.
HIT!
You know we’re totally screwed trying to predict Musk because he already warned us,
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

I’ve attached a spreadsheet showing different assumptions, BFS mass, etc.

Anyone else want to update their speculations?
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/28/2016 03:04 pm
The same specs from Life's Man and Space's mars rocket:
lift-off 10.000 t
LEO cargo 500 t

Arthur C Clarke always choose the numbers.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/28/2016 03:06 pm
Additional predictions scoring BOLD

1) Overall Launch Architecture
     a)  MCT is composed simply of a BFR 1st stage and BFS 2nd stage/spacecraft
     b)  Boost phase consists of 2 stages, which put the BFS into orbit
     c)  Other: 3rd stage, 'half' stages, drop tanks, etc.

Going with (a)


Hit

2) Number of Raptor Engines on BFR (1st stage)

< 30, my best estimate is 25-27 if thrust stays close to 230 tonnes range

Miss

3) Diameter of BFR (1st stage)

Range 12.5m-15m, best estimate 15m 1st stage

Miss


4) Total Raptor 1st stage thrust (sl)

60 Meganewtons and T/W > 1.3

Miss

5) LAS Architecture
     a) No LAS - BFS is the escape mechanism
     b) Traditional LAS - above BFS and is nominally jettisoned during launch phase
     c) BFS contains smaller 'ejection pod' where humans reside during launch
     d) Other, non-traditional LAS design

Best guess is (a)

HIT!!!

6) Shape and Landing Mode of BFS
     a) Capsule (perhaps elongated), w/ TPS on base
     b) Cylindrical or biconic - horizontal landing
     c) Cylindrical or biconic - vertical landing
     d) Other

Going with (c), definitely no horizontal landing

HIT!!!

7) Mars and Earth return
    a) BFS does direct entry into Mars and Earth atmosphere
     b) BFS does orbital capture before performing entry burn and landing
     c) Same as b, but upon Earth return, stays in orbit for next synod

(a)

HIT

8)  Use of non-chemical thrust
     a) Not part of the plan
     b) Will use SEP for some/all of the big transits
     c) All chemical for now, but plans to incorporate SEP down the road

(c) strongly favor

a seems more correct

Can anyone think of more/better questions?

Predict Musk will miss 1st crewed landing by >= 3 synods
UNKNOWN but too easy
5-6 Rvacs on BFS stage 2
HIT sort of.  Missed on R SL engines.  frakked at self for not seeing that.

Raptor sea level will have 10s of tonnes thrust more than the 230 tonnes mentioned by Elon
HIT!!!
Entire BFR/BFS GLOW masses under 5.000 tonnes; my estimate ~4,500
BIG miss!
Height of BFR/BFS stack under 120m; my estimate <100m
MISS
Cargo version, tanker version, crewed version of BFS
HIT
1st crewed landing on Mars 8-12 humans planned
UNKNOWN
Just over 48 hours until Musk makes fools of us
Got that right!
Title: Re: MCT Speculation and Discussion Thread 4
Post by: philw1776 on 09/28/2016 03:09 pm
everyone else was basing their prediction on rumors and L2 information that I don't have access too. 

Not so.  Not at all.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: MikeAtkinson on 09/28/2016 05:36 pm
Yes, I meant cylindrical. Although the three "fins" do alter the shape slightly, so I wonder if they have seen some aerodynamic benefit of stretching them so far forward.

Although I never came out and specifically said so, I've favoured what I called a "semi-lifting body", that is something that gets some lift from its body shape and maybe has small fins but is not a traditional lifting body shape.

It looks like the Ship qualifies as a semi-lifting body.

I was wrong on payload size, I thought a total mass in LEO Ship + payload of about 300 tonnes in expendable mode and about 240 tonnes with a reusable booster.

I guessed at about 140 tonnes dry mass for the Ship and about 90 tonnes for the Tanker variant, close but not a bulls-eye.

Basic mode of operation I got correct, pretty obvious from Elon's original comments I thought. Refuel in LEO, land it all on Mars, then refuel on Mars and do a direct return. I thought aero-capture into LEO was a possibility which would have saved a launch and needed reduced heat shield capability, this looks like it might be the case as the graph showing delta-v does not show landing fuel for the low payloads typical of return flights.

I never expected a LAS.

I underestimated the Tanker fuel load so expected 5-8 Tanker flights to refuel the Ship.

I've seen estimates of crew+cargo space are about 2,200 m3, although I haven't checked that yet. I estimated about 2,100 m3 which would be for crew, cargo or a mixture.

Being miss led by L2 info I upped the diameter from 10-12m to 15m, which meant that my estimates for height were out. I thought about 30 engines, so the larger take-off mass that 42 engines allows also meant that my height estimates were too low.

Musk has several times mentioned 100 tonnes to Mars so a max payload of 450 tonnes was a complete shock.

With full number of crew and full payload I expected a delta-v of 6.5km/s or a bit above, it seems that this is more like 6km/s, but the delta-v of the Ship with 100 tonnes cargo is about 7km/s. I expected the delta-v for return with 25 tonnes cargo to be 9km/s or a bit more, this seems about correct as long as no fuel is reserved for landing.

Like most people I slightly underestimated Raptor, thinking vac Raptor Isp of 380, and sea level Raptor Isp of 330 (SL) and 350 (vac) and a greater mass and size than it appears to be.

I completely missed having only the centre engines on the booster gimbal.

I also considered and discarded having centre SL Raptors on the Ship for landing, instead I thought that they would have mini-Raptors which would also serve for a methane equivalent F9. I never thought that having engines on the sides were a good idea, due to control-ability, cosine losses and vehicle strength issues. It does mean that prepared surfaces will have to be used on Mars after the first few landings.

Electric propulsion was not mentioned so is presumably not included in the architecture, I expected this as it is almost impossible to get SEL to work with short transit times.

Elon has talked about 10 cargo flights for each crew flight, but that was when the payload capacity was 100 tonnes, now it looks like 2-3 cargo flight per crew flight is more likely.

The launch costs were about what I expected for a mature heavily used system. Payload to Mars cost is much better than I expected due to the larger payload capacity. The per person cost to Mars (Musk said under $200,000
at one point) is lower than I expected. At that price both myself and my wife could easily go (about $500k from selling the house), but we would be too old by then.

The optimistic timeline was much as I expected, as is the current number of people working on it. They will almost certainly slip, but the successful Raptor firing and full size Lox tank are indications that the program is so far going well.

The beyond Mars bit was a surprise. Instead I expected to hear about the Moon, LEO's and cis-lunar space which are better prospects for near term revenue and are much easier as well. Nothing was said about Mars' moons either.

The bit about sub-orbital transport I found strange - yes theoretically possible, but immense difficulties in making the system work.

Using the Tanker as a SSTO was also a surprise, payload would be reasonable, but in $/kg would be beaten by the Booster+Ship combination.

I also expected to hear more about Mars surface elements, possibly as a request for others to supply them.

Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/28/2016 06:21 pm
Quote
Although I never came out and specifically said so, I've favoured what I called a "semi-lifting body", that is something that gets some lift from its body shape and maybe has small fins but is not a traditional lifting body shape.

It looks like the Ship qualifies as a semi-lifting body.

The shape of the vehicle is related to development, weight and manufacturing costs. I think the actual design is strongly considering this, this bullet looks easier and cheaper to build than a real lifting body.

Other important factors that relate to SpaceX's philosophy are the scaleable design and simplicity - to reduce the number of moving parts and phases of operation to a minimum.

If they show something that looks like a rocket in ten years they will have Deep Space Industries, Google and Facebook's money. Little after, Japan, Europe and tourists paying US$10 million per person for a week in the  moon, just name the first BFS Hilton.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Burninate on 09/28/2016 06:53 pm

I underestimated the Tanker fuel load so expected 5-8 Tanker flights to refuel the Ship.


Even if dry mass has gone to zero with magical carbon negafiber and infinite TWR - 300 tons of payload can only be accelerated through 2596m/s dV by 300 tons of propellant at 382s.  You're going to require more like 6-10km/s dV for the first half of the mission described.

The video was notional, and chose not to show repetition.
Title: Re: MCT Speculation and Discussion Thread 4
Post by: BSenna on 09/28/2016 07:48 pm
Hummm...
Title: Re: MCT Speculation and Discussion Thread 4
Post by: Chris Bergin on 09/28/2016 09:25 pm
Farewell MCT, hello ITS:

Locked.

Several threads to choose from - Menu:
http://forum.nasaspaceflight.com/index.php?board=72.0