Author Topic: MCT Speculation and Discussion Thread 4  (Read 503329 times)

Offline Owlon

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Re: MCT Speculation and Discussion Thread 4
« Reply #420 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.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #421 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.
« Last Edit: 08/20/2015 11:20 AM by Burninate »

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #422 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.

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #423 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.

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #424 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.

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #425 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.

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #426 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.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #427 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.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #428 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.
« Last Edit: 08/20/2015 02:49 PM by Burninate »

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #429 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.
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 nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #430 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.

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 guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #431 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.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #432 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.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #433 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.
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 Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #434 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 oneís exactly sure how the transportation will work, but itíll likely be something like this: "

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #435 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 oneís exactly sure how the transportation will work, but itíll 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"
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 Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #436 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'.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #437 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.
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 MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #438 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 oneís exactly sure how the transportation will work, but itíll 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.

Offline MickQ

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Re: MCT Speculation and Discussion Thread 4
« Reply #439 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.

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