Author Topic: MCT Speculation and Discussion Thread 4  (Read 621495 times)

Offline CuddlyRocket

Re: MCT Speculation and Discussion Thread 4
« Reply #2120 on: 06/04/2016 05:43 PM »
Assuming its a landing in 2025, ISRU water from martian ground ice has still extremely low technological readiness, much less doing it fully automated (for prepositioning)! The energy required is also much more than the one needed for electrolysis, its also the digging itself, warming up the ice to form water (in a -55C environment), cleaning and chemically purifying it (by destillation?), etc. And all that without human supervision? If we take Elons requirement of prepositioned fuel serious, I see no other way than to bring in H with an unmanned mission in 2022/3 and producing the fuel during the two years that follow.

You cane extract water from the Martian atmosphere. It requires power (you get about 1.5 kg/kW/sol, if I remember correctly), but the equipment is not particularly massive. It has the advantage of simplicity (little need for purification) and may be preferable for initial missions, switching to local mined water once it has been located and characterised etc.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2121 on: 06/04/2016 05:46 PM »
SpaceX is definitely going to do water ISRU. Here are some of the early instruments that are proposed to fly on Red Dragon:
http://digitalvideo.8m.net/SpaceX/RedDragon/karcz-red_dragon-nac-2011-10-29-1.pdf
slide 8
"Water extraction system &
propellant production system.
HEOMD funded KSC & JSC
ISRU activity at TRL 5."

And Musk has said they want robotic mining to produce propellant on Mars. You cannot get more direct than that.
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Offline Elmar Moelzer

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Re: MCT Speculation and Discussion Thread 4
« Reply #2122 on: 06/04/2016 08:16 PM »
Another interesting tidbit to take away from the RecodeDotNet interview with Musk is that the trip will (initially) take less than 90 days. We should be able to deduct how much propellant would be needed to do such a short trip time with that much payload. He also said that they want to get to shorter trips (less than 30 days) at a later time. I presume that this would require some change to the whole architecture, though.

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2123 on: 06/04/2016 09:11 PM »
Another interesting tidbit to take away from the RecodeDotNet interview with Musk is that the trip will (initially) take less than 90 days. We should be able to deduct how much propellant would be needed to do such a short trip time with that much payload. He also said that they want to get to shorter trips (less than 30 days) at a later time. I presume that this would require some change to the whole architecture, though.

If the BFS is the second stage to the BFR it needs about 5.5 - 6.5 km/s of delta-v, this is enough to give 90-120 days transit to Mars for most synods. If the BFS also carries extra tankage, so that it can act as a tanker carrying 100+ tonnes of extra propellant to LEO, then it should be able to do 90 day transits to Mars on most if not all synods. Some of these transits have high entry velocities at Mars which might be too much for the thermal protection system (but as we know little about such details it is impossible to say whether this is the limiting factor.

The journey back might be a different matter. I've tried and failed to work out a consistent set of trajectories which allow next synod reuse and allow return with 25 tonnes of payload and have 90-120 day transits. Some synods seem easy, others do not seem to allow next synod reuse without about 9 km/s delta-v and extremely high entry velocities.

Cargo flights can have relaxed delta-v requirements, but still need relatively fast transits to allow next synod reuse.

One limiting factor is how fast they can unload cargo, refuel and refly the BFS on Mars. Return is much easier if this can be a few days, rather than a few months.

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2124 on: 06/04/2016 09:16 PM »
Assuming its a landing in 2025, ISRU water from martian ground ice has still extremely low technological readiness, much less doing it fully automated (for prepositioning)! The energy required is also much more than the one needed for electrolysis, its also the digging itself, warming up the ice to form water (in a -55C environment), cleaning and chemically purifying it (by destillation?), etc. And all that without human supervision? If we take Elons requirement of prepositioned fuel serious, I see no other way than to bring in H with an unmanned mission in 2022/3 and producing the fuel during the two years that follow.

You cane extract water from the Martian atmosphere. It requires power (you get about 1.5 kg/kW/sol, if I remember correctly), but the equipment is not particularly massive. It has the advantage of simplicity (little need for purification) and may be preferable for initial missions, switching to local mined water once it has been located and characterised etc.

The equipment may not be particularly massive, but it is large as you have to process a lot of Martian atmosphere (both volume and mass as the martian atmosphere is thin and very dry).

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2125 on: 06/04/2016 09:27 PM »
The other option is to land enough propellant on Mars for the ascent of the escape vehicle. This is possible, but not nearly as economical, potentially requiring one MCT to stay in low Mars Orbit with its payload of propellant that came from Earth and 3 or 4 cargo MCTs arriving with just propellant for the emergency ascent vehicle. The complexity of this is that propellant transfer from landed craft is required. The ISRU example might be accomplished with the ISRU MCT refueling itself and it being the emergency return vehicle not just an ascent to orbit vehicle.
The emergency ascent spacecraft can be very small, like a Dragon, without the heat-shield and SDs. Launch it to reach the Earth-return MCT in low Mars orbit will not require an enormous amount of fuel. If the capsule + ascent stage is 10 t dry, then 30 t wet is enough. The ascent stage can be derived (shortened) from F9 second stage, so the ascent vechicle need not be developed from scratch. A single MCT can land the fueled ascent vechicle together with extra cargo, or even the hab modul.

Fleshing this out a little more:

First, I am happy to entertain this for the first expedition so that they can leave scale ISRU until people are there.

2nd, for this to be worth more savings than the cost of sending enough propellant for an MCT return, the development has to be truly minimal, as well the development of this becomes critical path for the Mars Mission and either has to fly with the 2024 armada or the window before.

3rd, having a single one of these limits the first expedition crew to 7 (presuming that is still the maximum complement on a D2) 2 limit it to 14.  By the time you have 2 the development cost really has to be just about zero because 3 or 4 and you just use MCTs to ferry propellant down for 1 MCT to make orbit again.

technical difficulties that may push the development from minimal to too complex to be worth doing:

1. Modifying MCT to not only accommodate and land this craft without damaging it but to support its launch
2. keeping RP-1 from freezing/gelling (doable but needs design and development work)
3. modifying D2 to have the lifespan needed for this (going from nominally 9 months or so to 4 years)
4. modifying Falcon S2 to short length required

I can't see SpaceX doing this, it is technically possible, but for an emergency ascent craft, it adds lots of new systems and complexity for something that is not likely to be used.

Much more likely in my opinion is to assume that ISRU works, assume that if it doesn't work robotically then with crew on the scene it can be made to work, if both of those fail supply enough consumables so that there is no chance of the crew dying until further missions can be sent (with improved ISRU and more provisions). A single MCT cargo flight of 100 tonnes is the equivalent of 30 Dragon cargo flights to the ISS, and would provide the initial crew with many years worth of provisions, there is no possibility of them running out of food or other essentials.

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2126 on: 06/04/2016 09:50 PM »
The schedule for 2024 is very tight.

Raptor is probably on the critical path at present.

Design and development through the equivalent of PDR and CDR.

The factory: finding a site, permitting, building it, installing and commissioning equipment. Then using it to build the BFS and BFR.

The launch site: intimately connected with the factory, permits, building it, commissioning.

ECLS: design and testing, reliability takes time to build up.

Avionics and Software: lots of flight modes for BFR, BFS tanker, BFS cargo and BFS crew. Takes time to develop.

Any or all could be on the critical path.

Then after the first BFR/BFS first flight there needs to be a period of testing in LEO and cis-lunar space. Several flights checking out refuelling, ECLS, ops, etc. while building up confidence in the launch and reuse processes.

SpaceX are going to be very busy.

Online Bynaus

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Re: MCT Speculation and Discussion Thread 4
« Reply #2127 on: 06/04/2016 10:01 PM »
@Robobeat: if you read my first post on the matter carefully, I am not suggesting they are not persueing eventual ISRU of Martian water. Bringing in H would just be an interim solution until full scale ISRU is capable of providing the necessary fuel. How exactly are they going about scraping up 100s of tons of ice robotically for each return mission, processing it and all - and without any humans supervising the process? I just don't see this happening in 9 years. You'd probably need multiple design iterations for the entire process to work, and there are only 3 transfer windows left before the process *has* to work if the 2024/5 mission date is to be met. On the other hand, the H + CO2 approach can easily be tested on Earth.

The 2011 proposal for possible payloads on Red Dragon is a NASA idea, not SpaceX. Also, it is unclear how the water extraction system mentioned there would work - drilling, or from the atmosphere? At least the former is unlikely to be scaleable to 360 tons of water....

Finally, extracting water from air (as mentioned by CuddlyRocket) might indeed be a good alternative to bringing down H. This seems much simpler than digging for  ice, but the question is whether you could produce enough fuel. At 700 sols and 1.5 kg/kW/sol, you'd need 340 kW of continous  power for extraction of 360 tons of water (!).
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Offline Bob Shaw

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Re: MCT Speculation and Discussion Thread 4
« Reply #2128 on: 06/04/2016 10:13 PM »
There are always nay-sayers regarding the business of ISRU on Mars, with the whole business of water mining being dismissed as 'too difficult'. I wonder if we're not exploiting the environmental properties of Mars sufficiently, however.

I'm thinking of an almost passive distillation water-mine, where broken-up winter temperature perchlorate-rich ice is shovelled into a large vessel, which is heated in the summer by sunshine. The ice sublimates, and the water-laden air rises into a second, insulated  chamber which is never allowed to heat beyond winter temperatures and where it freezes out as rime or snow. You harvest the output, and perhaps distill again.

My starting point for this was the thought of the traditional adiabatic atmospheric 'springs' constructed in various Earth deserts using no resources other than piles of rock and a knowledge of the local winds. Obviously, Mars is different, but low-tech solutions would be a good tradeoff, using scarce imported resources only where needed.

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2129 on: 06/04/2016 10:49 PM »
How exactly are they going about scraping up 100s of tons of ice robotically for each return mission, processing it and all - and without any humans supervising the process?

We don't know. There are 4 possible sources of water on Mars: ice (glaciers, etc.), brine aquifers, hydrated minerals (various types and concentrations) and the atmosphere. These all have various advantages and disadvantages which vary between landing sites, power supply (solar or nuclear), and things like how much water is needed, what the growth rate and potential is, other base needs (water, heat, electricity, process heat, mining).

We don't know that any water mining will be done robotically, that is an assumption based on the rather dubious proposition that SpaceX won't send a crew until there is a fully fueled return BFS waiting on the martian surface.

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #2130 on: 06/04/2016 10:54 PM »
There are always nay-sayers regarding the business of ISRU on Mars, with the whole business of water mining being dismissed as 'too difficult'. I wonder if we're not exploiting the environmental properties of Mars sufficiently, however.

I'm thinking of an almost passive distillation water-mine, where broken-up winter temperature perchlorate-rich ice is shovelled into a large vessel, which is heated in the summer by sunshine. The ice sublimates, and the water-laden air rises into a second, insulated  chamber which is never allowed to heat beyond winter temperatures and where it freezes out as rime or snow. You harvest the output, and perhaps distill again.

My starting point for this was the thought of the traditional adiabatic atmospheric 'springs' constructed in various Earth deserts using no resources other than piles of rock and a knowledge of the local winds. Obviously, Mars is different, but low-tech solutions would be a good tradeoff, using scarce imported resources only where needed.

Day/night temperature swings probably would be enough, that would allow a far greater volume of water to be collected.

Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #2131 on: 06/04/2016 11:01 PM »
We don't know that any water mining will be done robotically, that is an assumption based on the rather dubious proposition that SpaceX won't send a crew until there is a fully fueled return BFS waiting on the martian surface.
The idea (originating from Mars Direct) was to ensure the safety of the crew.

As Zubrin said in "The Case for Mars" (pg. 70-71):
"To ensure our Mars crew would not be stranded, the ERV would fly one launch opportunity, or twenty-six months, prior to the launch of the astronauts. Thus all the propellant would be made before the crew ever left Earth, and since the propellant plant was flown to Mars integrated with the ERV there was no question about landing 'within a hose length.' The plumbing that would deliver the Mars-manufactured propellant from the chemical synthesis unit into the ERV's fuel tanks would be hardwired, installed on Earth."

"if the ERV [Earth Return Vehicle] is sent first, the crew will know before they even leave Earth that they have a fully functional Mars ascent and Earth return system waiting for them on the Martian surface, one that has already survived the trauma of landing. In contrast, a crew that lands with their ascent system can only guess in what shape their Mars ascent vehicle will be after they've hit the surface."

SpaceX did test fire F9 engines after they've been through supersonic retropropulsion in conditions relevant to Mars EDL systems development, so the latter might not be a problem.
« Last Edit: 06/04/2016 11:17 PM by Pipcard »

Offline Bob Shaw

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Re: MCT Speculation and Discussion Thread 4
« Reply #2132 on: 06/04/2016 11:23 PM »
There are always nay-sayers regarding the business of ISRU on Mars, with the whole business of water mining being dismissed as 'too difficult'. I wonder if we're not exploiting the environmental properties of Mars sufficiently, however.

I'm thinking of an almost passive distillation water-mine, where broken-up winter temperature perchlorate-rich ice is shovelled into a large vessel, which is heated in the summer by sunshine. The ice sublimates, and the water-laden air rises into a second, insulated  chamber which is never allowed to heat beyond winter temperatures and where it freezes out as rime or snow. You harvest the output, and perhaps distill again.

My starting point for this was the thought of the traditional adiabatic atmospheric 'springs' constructed in various Earth deserts using no resources other than piles of rock and a knowledge of the local winds. Obviously, Mars is different, but low-tech solutions would be a good tradeoff, using scarce imported resources only where needed.

Day/night temperature swings probably would be enough, that would allow a far greater volume of water to be collected.

Very possibly. I was being as conservative as possible! The point is, where there is an energy gradient, work can be extracted in one form or another. Diurnal or seasonal, the resource is there, and simple solar heating is astonishingly cheap (black paint).

Offline CuddlyRocket

Re: MCT Speculation and Discussion Thread 4
« Reply #2133 on: 06/04/2016 11:50 PM »
We don't know that any water mining will be done robotically, that is an assumption based on the rather dubious proposition that SpaceX won't send a crew until there is a fully fueled return BFS waiting on the martian surface.
The idea (originating from Mars Direct) was to ensure the safety of the crew.

As Zubrin said in "The Case for Mars" (pg. 70-71):
"To ensure our Mars crew would not be stranded, the ERV would fly one launch opportunity, or twenty-six months, prior to the launch of the astronauts. Thus all the propellant would be made before the crew ever left Earth, and since the propellant plant was flown to Mars integrated with the ERV there was no question about landing 'within a hose length.' The plumbing that would deliver the Mars-manufactured propellant from the chemical synthesis unit into the ERV's fuel tanks would be hardwired, installed on Earth."

"if the ERV [Earth Return Vehicle] is sent first, the crew will know before they even leave Earth that they have a fully functional Mars ascent and Earth return system waiting for them on the Martian surface, one that has already survived the trauma of landing. In contrast, a crew that lands with their ascent system can only guess in what shape their Mars ascent vehicle will be after they've hit the surface."

SpaceX did test fire F9 engines after they've been through supersonic retropropulsion in conditions relevant to Mars EDL systems development, so the latter might not be a problem.

The ERV doesn't have to be fully fuelled before the crew leaves Earth. It merely needs to have landed safely and be producing propellant at a rate that means it will be fully fuelled by the time the crew needs to use it to launch back to Earth. No doubt there will be margins to take account of any possible breakdown after the crew has set off for Mars. Set against that is the possibility of the crew making repairs and the additional output of any further ISRU equipment they bring with them. If additional margins and/or redundancy is required you can always send two ERVs on the first trip, or perhaps an ERV and a dedicated ISRU propellant production lander.

Offline matthewkantar

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Re: MCT Speculation and Discussion Thread 4
« Reply #2134 on: 06/04/2016 11:57 PM »
I am pretty sure there is something very wrong with this idea, but I cannot see it. Send an early MCT with most of it's cargo as water. Include some pumps and soft insulated containers that could be set on the ground and pumped full. Design them to withstand freezing and also have the capability to electrically melt the ice. The goal for the arrivers can still be to mine the water locally, with a back up source for ISRU and consumption.

No need for cryogenic storage of H2.

Having 90 tons or so of pure water as a contingency might be worth the price of tying up an expensive space ship for two plus years. The water MCT could also be a test mission without having any expensive gear at risk, with water as a sort of a mass simulator.

Matthew

Edited for a stray 'O' and to add the bit about H2
« Last Edit: 06/04/2016 11:59 PM by matthewkantar »

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2135 on: 06/04/2016 11:57 PM »
SpaceX is definitely going to do water ISRU. Here are some of the early instruments that are proposed to fly on Red Dragon:
http://digitalvideo.8m.net/SpaceX/RedDragon/karcz-red_dragon-nac-2011-10-29-1.pdf
slide 8
"Water extraction system &
propellant production system.
HEOMD funded KSC & JSC
ISRU activity at TRL 5."

And Musk has said they want robotic mining to produce propellant on Mars. You cannot get more direct than that.

Musk will have enslaved an entirely robotic populated planet.  Without their bio-masters present don't be surprised if there isn't a revolution.  You've been warned!
« Last Edit: 06/04/2016 11:58 PM by philw1776 »
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline Bob Shaw

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Re: MCT Speculation and Discussion Thread 4
« Reply #2136 on: 06/05/2016 12:02 AM »
I am pretty sure there is something very wrong with this idea, but I cannot see it. Send an early MCT with most of it's cargo as water. Include some pumps and soft insulated containers that could be set on the ground and pumped full. Design them to withstand freezing and also have the capability to electrically melt the ice. The goal for the arrivers can still be to mine the water locally, with a back up source for ISRU and consumption.

No need for cryogenic storage of H2.

Having 90 tons or so of pure water as a contingency might be worth the price of tying up an expensive space ship for two plus years. The water MCT could also be a test mission without having any expensive gear at risk, with water as a sort of a mass simulator.

Matthew

Edited for a stray 'O' and to add the bit about H2

Indeed. The early landers might even be repurposed as water distillation vats, or as gasometers.

Offline Bob Shaw

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Re: MCT Speculation and Discussion Thread 4
« Reply #2137 on: 06/05/2016 12:04 AM »
I, for one, wish to be among the first to welcome our new overlords... ...just sayin'.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2138 on: 06/05/2016 01:13 AM »
@Robobeat: if you read my first post on the matter carefully, I am not suggesting they are not persueing eventual ISRU of Martian water. Bringing in H would just be an interim solution until full scale ISRU is capable of providing the necessary fuel. How exactly are they going about scraping up 100s of tons of ice robotically for each return mission, processing it and all - and without any humans supervising the process?
That's like a few hundred pounds a day if spread over a year. Not that bad. I could definitely see it done using scaled up versions of some mining rovers I've seen.
Quote
I just don't see this happening in 9 years. You'd probably need multiple design iterations for the entire process to work, and there are only 3 transfer windows left before the process *has* to work if the 2024/5 mission date is to be met.....
Yeah, and they're going to utilize each one. 2024/5 doesn't leave a lot of margin, but that's the "if everything goes according to plan" date. When Musk gives that kind of date, usually it's the earliest it can be done, not the "we'll definitely be able to do it by then" date. Which means you should probably expect it to slip.

But again, Musk has repeatedly said they're going to mine water. I really don't think they'll mess around with liquid hydrogen. Instead, they'll double-down on getting water extraction to work. And some of that they can test here on Earth before sending it to Mars.
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Offline the_other_Doug

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Re: MCT Speculation and Discussion Thread 4
« Reply #2139 on: 06/05/2016 03:16 PM »
SpaceX is definitely going to do water ISRU. Here are some of the early instruments that are proposed to fly on Red Dragon:
http://digitalvideo.8m.net/SpaceX/RedDragon/karcz-red_dragon-nac-2011-10-29-1.pdf
slide 8
"Water extraction system &
propellant production system.
HEOMD funded KSC & JSC
ISRU activity at TRL 5."

And Musk has said they want robotic mining to produce propellant on Mars. You cannot get more direct than that.

Musk will have enslaved an entirely robotic populated planet.  Without their bio-masters present don't be surprised if there isn't a revolution.  You've been warned!

And it now comes out -- the reason why Musk is so paranoid about AI becoming sentient and turning against us!  He's planning on creating a robotic serving class on Mars, and is afraid of the robot servitors fomenting rebellion... ;)
-Doug  (With my shield, not yet upon it)

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