NASASpaceFlight.com Forum

SpaceX Vehicles and Missions => SpaceX BFR - Earth to Deep Space => 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://www.youtube.com/watch?v=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 180º 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 fanboys/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 fanboys/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 fanboys/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/m². Calculate with 25% efficiency for low efficiency but very low weight solar foils and you get 100W/m². That's 1000m² 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 a