Author Topic: MCT Speculation and Discussion Thread 4  (Read 621445 times)

Offline JasonAW3

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Re: MCT Speculation and Discussion Thread 4
« Reply #20 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.
« Last Edit: 06/15/2015 03:25 PM by JasonAW3 »
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Offline oldAtlas_Eguy

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Re: MCT Speculation and Discussion Thread 4
« Reply #21 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.

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #22 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.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #23 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.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline oldAtlas_Eguy

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Re: MCT Speculation and Discussion Thread 4
« Reply #24 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.

Online lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #25 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

Online lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #26 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?

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #27 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.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #28 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.
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Online lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #29 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.

Offline spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #30 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. 

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #31 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.





Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #32 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?


Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #33 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. 

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #34 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. 


Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #35 on: 06/15/2015 11:22 PM »
Stretching probably does make sense. At least, once we're talking hundreds of MCTs per synod.
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Online lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #36 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.
« Last Edit: 06/15/2015 11:49 PM by lamontagne »

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #37 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.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #38 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?
« Last Edit: 06/16/2015 01:23 AM by Burninate »

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #39 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.

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