Author Topic: MCT Speculation and Discussion Thread 4  (Read 621114 times)

Offline kch

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Re: MCT Speculation and Discussion Thread 4
« Reply #2100 on: 06/03/2016 01:36 PM »
After Elon's Mars schedule announcement, I was wondering about this (I don't know if this has been discussed before, I presume so but perhaps not in this specific context) :

A way to speed up the development of the first manned Mars mission (to keep up with the aggressive 2024/5 schedule) would be to bring molecular H to the Martian surface (which could also serve as a radiation shield on the way there). If the BFS must have a dV capacity of 6 km/s and has a dry mass of 200 tons, it will need about 800 tons of fuel for the return journey. Since only about 5% of a stochiometric Methane/LOX fuel is hydrogen, they could bring down about 40 tons of molecular H with each BFS, well within its payload capacity (of 100 tons). Even if we add a few percent of that for the mass of the tank, this is still very feasible.

All that the first SpaceX astronauts would then have to do after landing is react the H with the atmospheric CO2 in the Sabatier reaction - this could virtually been done without any human supervision or involvement. This is also a much simpler and cleaner (and less energy intensive) process than having the crew looking for water ice, digging it out, cleaning it, testing it for any potential chemical agents (e.g., peroxides, salts, etc.) and removing them before electrolysis, etc. This is also a technology that 1) is already in development and 2) would be reasonably easy to demonstrate with a precursor Red Dragon mission. The same cannot be said of actively digging for water ice on Mars.

While I am certain the plan is for a Mars base to eventually provide BFS's with fuel synthesized from martian water ice and atmospheric CO2, the very first landings could / should skip this step and bring the H from Earth instead.

It's been mentioned:

https://en.wikipedia.org/wiki/Mars_Direct

;)

Offline Bynaus

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Re: MCT Speculation and Discussion Thread 4
« Reply #2101 on: 06/03/2016 03:22 PM »
@kch: sure, I am aware that the idea of bringing in H is from Mars Direct (and as such I should perhaps have said so), but I mean in the specific context of the BFS and speeding up the schedule to make a 2024/5 manned SpaceX mission to Mars feasible. ISRU is (well, presumably so) an integral part of the SpaceX architecture, but some of it (like digging up water ice) has very low technological readiness and this is unlikely to change before 2024/5. Also, consider that the initial crew would have to dig up 360 tons of water ice to produce the fuel, or 60 tons each if they are 6 astronauts.... Hard even if you bring some landmoving equipment....

Envy887 made an excellent point on the volume and cooling systems this would require. This is the kind of answer and input I was going after. A tank this size would only be 3 m high at 15 diameter for the BFS. Even if cooling etc take up 10 tons or more, at 100 tons total you still have some serious payload capacity left.
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Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #2102 on: 06/03/2016 03:41 PM »
Also, consider that the initial crew would have to dig up 360 tons of water ice to produce the fuel, or 60 tons each if they are 6 astronauts.... Hard even if you bring some landmoving equipment....

Worse.  :)

Elon Musk has once mentioned that crew would only be sent when return fuel is waiting for them. Not sure if this stands. If I had to decide I would opt for producing it during their 2 year stay. And prepare for worst case with 4 year supplies if anything goes wrong with production during this time. But that's just me and I have no say fortunately.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #2103 on: 06/03/2016 03:58 PM »
@kch: sure, I am aware that the idea of bringing in H is from Mars Direct (and as such I should perhaps have said so), but I mean in the specific context of the BFS and speeding up the schedule to make a 2024/5 manned SpaceX mission to Mars feasible. ISRU is (well, presumably so) an integral part of the SpaceX architecture, but some of it (like digging up water ice) has very low technological readiness and this is unlikely to change before 2024/5. Also, consider that the initial crew would have to dig up 360 tons of water ice to produce the fuel, or 60 tons each if they are 6 astronauts.... Hard even if you bring some landmoving equipment....

Envy887 made an excellent point on the volume and cooling systems this would require. This is the kind of answer and input I was going after. A tank this size would only be 3 m high at 15 diameter for the BFS. Even if cooling etc take up 10 tons or more, at 100 tons total you still have some serious payload capacity left.

I really doubt that they won't have return an Earth return capability in place before they land (not necessarily 100% ready before they get there). So the first people going to Mars are to arrive with the capability to return to Earth already in place, or they bring it with them. To arrive to it already in place then the most likely scenario is that an automated ISRU system was sent the previous launch window and took nearly two years to produce enough propellant to return a single, occupied, MCT to Earth (one ton per day roughly). Note, I also consider that this is a back up plan only and that the arriving manned expedition plans to stay through the next return window, (though sending back as many craft as they can refuel less one kept in reserve for their return) and that more people and supplies arrive the next Earth - Mars window, and that by then there is more robust ISRU with more capacity, more habitat space and quite a bit of propellant stored up ready to send a large portion of the arriving craft back the following window, and probably some of the people from each expedition.

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.

As an aside there is an old song about a miner loading 16 tons of coal each day. I don't think they will be doing it by pick and shovel, but really they could, the power is more gating I think. Going from ISRU water and atmospheric CO2 to several hundred tons of propellant, only costs about 25% to 33% more power than going from transported H2 and atmospheric CO2 and still requires the electrolysis step on the water vapour produced in the Sabatier reaction. As well to get the proper mixture ratio of Oxygen to Methane you need to separate some oxygen from CO2 or collect local water, even if you brought hydrogen because going with the Sabatier reaction and electrolysing the water from that only gives you a stochiometric ratio.
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 #2104 on: 06/04/2016 12:24 AM »
Did Musk say humans would LAND on Mars, or just be sent TO Mars in 2024?  That later leaves open a purely orbital mission.

Offline AC in NC

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Re: MCT Speculation and Discussion Thread 4
« Reply #2105 on: 06/04/2016 01:15 AM »
Did Musk say humans would LAND on Mars, or just be sent TO Mars in 2024?  That later leaves open a purely orbital mission.

He said "to".  Arriving in 2025.  Musk doesn't mince words so suspect strongly that Mars means the planet not an orbit around the planet.  Underpromise, Overdeliver. 

Offline Bynaus

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Re: MCT Speculation and Discussion Thread 4
« Reply #2106 on: 06/04/2016 08:47 AM »
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. In any case, this would mean the very first BFS landing to be in 2023 (I can't imagine a Red Dragon producing 800 tons of fuel....).
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Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #2107 on: 06/04/2016 09:10 AM »
Assuming its a landing in 2025, ISRU water from martian ground ice has still extremely low technological readiness,

Supersonic Retropropulsion was too, until SpaceX just did it. I say with absolute confidence they will not transport H2 to Mars. That concept was always the weak spot of Mars direct by Robert Zubrin IMO. And he proposed that because at the time it was not known how much water there is on Mars.

Offline The Amazing Catstronaut

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Re: MCT Speculation and Discussion Thread 4
« Reply #2108 on: 06/04/2016 01:15 PM »
I would go as far as saying the trade-offs of transporting H2 offset the advantages of having a less complex ISRU system. It seems like a waste of volume and mass.

There's nothing inherently unproven about ISRU processes (it's well understood science after all), the problem is conducting the same familiar chemical processes on Mars, adapted to the unique conditions of the on-site martian materials. That's something surveying missions will help to answer and a role red dragon can fill.
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Offline RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #2109 on: 06/04/2016 01:22 PM »
Another issue with ISRU is reliability. Can an unmanned mission fill the tanks before the system breaks down? Will a crew be required to do repairs, can the repairs be automated, or will there be enough redundancy?

Offline Bynaus

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Re: MCT Speculation and Discussion Thread 4
« Reply #2110 on: 06/04/2016 02:00 PM »
I don't think we can speak with confidence right now (in neighter direction), except if you had some insider knowledge.

Supersonic retropropulsion is close to the core competence of SpaceX, while teleoperation of ISRU units autonomously extracting water ice from soils on another planet isn't, really. But we will see in September.

Why do you think bringing down H to the surface is a weak point of Mars Direct? The motivation is not so much that there is no H on Mars, it's that this allows you to take one big unknown (how youw get from sub-surface dirty ice to CH4 in your tanks) out of the equation.
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Offline the_other_Doug

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Re: MCT Speculation and Discussion Thread 4
« Reply #2111 on: 06/04/2016 02:29 PM »
I'd think SpaceX would have a Plan A -- if the ISRU works fine and they'e pumping out fuel for the following synod -- and Plan B, if ISRU falls short for any reason.  And Plan B may have any number of sub-plans, to cope with a variety of potential issues.

As I've said on a number of occasions, we won't be able to intelligently address SpaceX's Mars architecture, including all Plans A, B, etc., until they announce it, hopefully this coming September.  And if what Chris has hinted about it is in any way representative, I think we'll have an awful lot to discuss then.

In any event, once we know what the architecture actually is, then we can see what the various plans are for cases where ISRU doesn't work as planned, or where not all of the planned pre-landed cargo makes it through, etc., etc.

So... while SpaceX may get plenty of kudos for landing the first humans on Mars, it will pretty much kill their colonization plans if those first humans end up on a one-way trip with no hope of either survival or return.  I'm therefore awfully confident that they will have anticipated most, if not all, of the obvious common-sense precautions we're all coming up with here, and will have plans in place to cope with those situations if they arise.  :)
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Offline su27k

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Re: MCT Speculation and Discussion Thread 4
« Reply #2112 on: 06/04/2016 02:48 PM »
If ISRU didn't work for the first time, they'll just have to postpone the manned mission and try again, they don't have to make the 2024 date (and it may be delayed for other reasons anyway). The problem with LH2 is that it's a dead end for them, they don't plan to use it in the future so it would be just a waste of resources to develop it, unless someone else (ULA?) can provide a low cost turnkey solution.

I think ISRU would definitely be challenging for them, mainly because the feedback cycle is very long (2 years), they couldn't use their iterative test some/fix some approach easily. Maybe they'll need to send plan A/B/C together and test them one by one. Some capable telerobotics would also be very useful, I wonder if Elon is an investor in Boston Dynamics...

Offline The Amazing Catstronaut

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Re: MCT Speculation and Discussion Thread 4
« Reply #2113 on: 06/04/2016 03:29 PM »

 I wonder if Elon is an investor in Boston Dynamics...

That rings a bell - will do some searching and report back if it turns out to be factual.
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Offline geza

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Re: MCT Speculation and Discussion Thread 4
« Reply #2114 on: 06/04/2016 03:40 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.

Offline pobermanns

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Re: MCT Speculation and Discussion Thread 4
« Reply #2115 on: 06/04/2016 03:43 PM »
So... while SpaceX may get plenty of kudos for landing the first humans on Mars, it will pretty much kill their colonization plans if those first humans end up on a one-way trip with no hope of either survival or return.  I'm therefore awfully confident that they will have anticipated most, if not all, of the obvious common-sense precautions we're all coming up with here, and will have plans in place to cope with those situations if they arise.  :)

Dumb question - if the first people there had some really serious problem, that would force them to evacuate after the return launch window ended and before the next synod started, would they even be able to return?

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #2116 on: 06/04/2016 04:00 PM »

 I wonder if Elon is an investor in Boston Dynamics...

That rings a bell - will do some searching and report back if it turns out to be factual.

Google bought Boston Dynamics in 2013 and has put it up for sale now (and it looks like Toyota might buy)
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 #2117 on: 06/04/2016 04:06 PM »
Why do you think bringing down H to the surface is a weak point of Mars Direct? The motivation is not so much that there is no H on Mars, it's that this allows you to take one big unknown (how youw get from sub-surface dirty ice to CH4 in your tanks) out of the equation.

Because storing LH is hard. SpaceX avoids it for their propulsion for a good reason. They won't introduce it through the back door, that's my rationale.

Water ISRU is a problem that needs solving. Not only for a future colony with many people. Even NASA included it in their Mars mission architecture. And that's for a small group of astronauts. It is much more important for SpaceX because I am sure even their first group will be much bigger than NASA plans for.

Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #2118 on: 06/04/2016 04:25 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
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 Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2119 on: 06/04/2016 05:41 PM »
Check L2 and tell me that SpaceX isn't seriously looking at how to process water for ISRU on Mars.
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