Author Topic: MCT Speculation and Discussion Thread 4  (Read 504713 times)

Offline Vultur

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Re: MCT Speculation and Discussion Thread 4
« Reply #360 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...

Offline lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #361 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.

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #362 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.

Offline lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #363 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?

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #364 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.
« Last Edit: 08/15/2015 10:45 PM by Impaler »

Offline Soralin

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Re: MCT Speculation and Discussion Thread 4
« Reply #365 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)

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #366 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.

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #367 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.

Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #368 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".

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #369 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.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #370 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.
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 sghill

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Re: MCT Speculation and Discussion Thread 4
« Reply #371 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.
« Last Edit: 08/17/2015 05:11 PM by sghill »
Bring the thunder Elon!

Offline Vultur

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Re: MCT Speculation and Discussion Thread 4
« Reply #372 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.

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #373 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.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #374 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


Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #375 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.

Offline Owlon

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Re: MCT Speculation and Discussion Thread 4
« Reply #376 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

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #377 on: 08/17/2015 04:09 PM »
Wait but Why post

http://waitbutwhy.com/2015/08/how-and-why-spacex-will-colonize-mars.html

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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.

Offline Oli

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Re: MCT Speculation and Discussion Thread 4
« Reply #378 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.
« Last Edit: 08/17/2015 05:14 PM by Oli »

Offline sghill

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Re: MCT Speculation and Discussion Thread 4
« Reply #379 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...
Bring the thunder Elon!

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