Author Topic: necessity of methane production on Mars  (Read 8806 times)

Offline spacenut

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Re: necessity of methane production on Mars
« Reply #20 on: 01/11/2017 02:04 PM »
I look at the Saturn V.  Kerolox first stage, hydrolox second stage.  5 engines each.  The first stage produced 7.5 million lbs thrust, while the second only produced 1 million.  It may have burned longer, but, lift off from the surface of a spacecraft will require a more dense fuel to keep the size of the spacecraft down.  Thus methane.  Mars has the ingrediants, and for simplicity, both stages of the BFR and ITS are to be methalox.  Same with the New Glenn with BO. 

Offline guckyfan

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Re: necessity of methane production on Mars
« Reply #21 on: 01/11/2017 03:27 PM »
True that it is easier to produce high thrust for takeoff with methane, but at Mars gravity LH may do it, better than on earth. It is doable even on earth, as the Delta IV Heavy proves, though at enormous cost.

I too think methane is the best overall compromise, mainly for storage. To do interplanetary travel there needs to be propellant stored until arrival, which is much  easier with methalox than LH.

Online TrevorMonty

Re: necessity of methane production on Mars
« Reply #22 on: 01/11/2017 05:19 PM »
Not sure about CO/O2 engine for lander/ascent vehicle but for Mars hopper it sounds ideal.

Offline dror

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Re: necessity of methane production on Mars
« Reply #23 on: 01/11/2017 05:47 PM »
Thanks Robotbeat, three times!

It seems to me  that harvesting water is the longest pole of their architecture, and yet it all depends on it.
If it will be half as complicated as I think it will, than it will be the limiting factor from day 0.
An option that does not depaned on it has a great advantage in the short term and is more robust in the long term.

You made an excellent argument for CO + O2.
A super-MOXIE can be brought there in a box and have much fewer unknowns compared to water harvesting.
But that fuel probably won't be optimal for earth side or even Mars escape, so,
 do you think it can be made to work in a complete architecture?

About solid carbon, that still may be feasable in the future through a hybrid engine or a future carbon-dust-gas-generator magic engine. Can you tell the ISP of C+O2 ?

Offline Oli

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Re: necessity of methane production on Mars
« Reply #24 on: 01/11/2017 05:49 PM »
As for the energy cost.

Electrolysis: 50kwh/kg.
Hydrogen Liquefaction: 10kwh/kg.

Assuming free oxygen/methane liquefaction.

50kwh+10kwh -> 1kg LH2 -> 7kg hydrolox -> 8.6kwh per kg hydrolox.

50kwh -> 2kg LCH4 -> 9kg methalox -> 5.6kwh per kg methalox.

Naturally a hydrolox stage uses less fuel for the same delta-v, but how much less depends on how much delta-v the stage must provide, so whether hydrolox wins over methalox energy-wise depends on the mission delta-v.

As for storage, the cost of that depends on the architecture, i.e. how long the fuel is being stored before it is used and where it is being stored etc. At least in space passive insulation seems to be sufficient to reduce LH2 boil-off to very low levels (if ULA is to believed).
« Last Edit: 01/11/2017 05:50 PM by Oli »

Offline Robotbeat

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Re: necessity of methane production on Mars
« Reply #25 on: 01/11/2017 06:36 PM »
Good post, Oli. For completeness:

Assuming the same efficiency of electrolysis as hydrogen (i.e. Taking about 20% more energy input than output), I get just:

2.1kWh/kg for CO/O2

...stemming from the fact that CO has lower energy. That's over twice as good per kg of propellant as methane/O2, and FOUR times as good as hydrogen...
« Last Edit: 01/11/2017 06:42 PM by Robotbeat »
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Offline llanitedave

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Re: necessity of methane production on Mars
« Reply #26 on: 01/12/2017 02:50 PM »
What about solid carbon as fuel?
Theoretically, powdered coal will burn just fine with O2 and may be tweaked to produce thrust in the right configuration. That can be produced without water mines.

Coal is an organic fossil fuel-rocks formed from living plants from hundreds of millions of years ago, metamorphed through all those years into peat, lignite, bituminous, then anthracite. None of it is pure carbon nor pure hydrocarbon. All fossil fuels are hydrocarbons, never pure carbon, and even anthracite has impurities in it. The conditions never existed on Mars for coal to be made there. The stuff isn't just organic; it's a product of biochemistry, followed by immense prolonged geological processes. Also, there is no practical way to manufacture solid carbon on Mars. Solid fuels cannot use pure oxygen as an oxidizer anyway, at least not under these circumstances. You have to mix solid fuel and solid oxidizer as liquid/paste like substance and carefully cast in a casing. Solid rockets have relatively poor ISP anyway. Liquid engines are the only real possibility, and when it comes to making fuel on Mars, methane is the only practical fuel. Sorry, but this is a real dead end.
Most of this post is missing the point and/or wrong, although I agree with the conclusion that liquid fuels are a much better way to go.

Solid carbon CAN be produced synthetically (in spite of your claim otherwise), I don't know why you brought up several sentences about fossil fuels just because he mentioned the fact that powdered coal burns well (he only used that as a supporting statement... High grade coal is almost all carbon).

And where did he mention a solid rocket? Solid fuel and liquid oxidizer is also clearly a thing. It's called a hybrid rocket, of course, and it's what Virgin Galactic is using for suborbital flights.

Why do people like to jump in quickly to say something is impossible without doing any research? Solid carbon is actually a byproduct of certain closed loop life support systems designed to pull all the oxygen out of exhaled CO2.

But I agree with the conclusion. Liquid fuels are best since you would have to manufacture a hybrid fuel grain on Mars versus just a liquid process, especially because liquid is far better suited for reuse.

In answer to dror, carbon monoxide actually makes a good enough fuel. It has lower Isp, but not THAT low. A pump-fed CO/O2 rocket could get better than 300s in vacuum and the bulk density is higher than methane/LOx. And 300s is better Isp than most first stage engines on Earth, so I'm not sure why people dismiss it so easily. Additionally, the flip side of lower specific energy (i.e. essentially related to lower Isp) is the fact that the it takes less energy to produce in the first place, AND can be done in a single step (unlike methane which needs Sabatier to combine CO2 and H2, thus introducing losses). Remember, with ISRU for a single stage vehicle we're not really limited by propellant mass, but instead by dry mass, energy required to make the propellant, and perhaps water needed to be harvested. So if you consider the ACTUAL constraints, CO/O2 looks good. Not only that, but it'll be the first ISRU technology to be tested on Mars (that we know of). The ISRU demo flying on the 2020 rover will produce not only oxygen but also carbon monoxide (which is usually discarded).

And one more thing: if you're trying to minimize energy to reach orbit in a single stage, you don't want to maximize Isp. At some point, if you have higher Isp, it'll actually take MORE energy to get to orbit. I believe the optimal exhaust velocity for a given delta-v is about 60-80% of the delta-v. So for a 4km/s delta-v needed to reach orbit, CO/O2's 3km/ exhaust velocity is pretty close to optimal.

So yeah, I do think there's something to be said of using a fuel that doesn't need water. But not solid carbon, but liquid CO.
You don't have to claim something is impossible to show that it's a very bad idea.
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Offline Robotbeat

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Re: necessity of methane production on Mars
« Reply #27 on: 01/12/2017 02:54 PM »
Of course not, but the claim was that it's basically not possible to make carbon on Mars, which is patently false as it's actually produced as a byproduct of some closed loop ECLSS designs.

There's also this false idea that fossil fuels are somehow special and oh-so-hard to replicate (hence a long shpeal about fossil fuels) . Not true at all, it's done all the time, it just isn't usually as cheap as finding it ready to go already made for you underground.
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Offline llanitedave

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Re: necessity of methane production on Mars
« Reply #28 on: 01/12/2017 03:01 PM »
Of course not, but the claim was that it's basically not possible to make carbon on Mars, which is patently false as it's actually produced as a byproduct of some closed loop ECLSS designs.

There's also this false idea that fossil fuels are somehow special and oh-so-hard to replicate (hence a long shpeal about fossil fuels) . Not true at all, it's done all the time, it just isn't usually as cheap as finding it ready to go already made for you underground.


Agreed, but per the thread topic, none of that relieves colonists/explorers of the "necessity" of producing methane.  They can in principle produce other propellants, but they have no advantage to doing so.
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Offline Robotbeat

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Re: necessity of methane production on Mars
« Reply #29 on: 01/12/2017 03:05 PM »
Elsewhere, I did show how one can avoid producing methane. Carbon monoxide is a perfectly fine fuel, its low Isp is offset by the fact it takes less than half the energy to produce (per kg of propellant), AND requires no water.

It wouldn't work well in the ITS framework, as it really works best for a dedicated surface-LMO-surface shuttle/lander, but it does indeed obviate the need for vast amounts of methane.
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Online TrevorMonty

Re: necessity of methane production on Mars
« Reply #30 on: 01/12/2017 03:48 PM »
Your production assumes all processing is done on surface. With lunar ISRU there is good case for delivering water into space and process it there. A space solar powered plant is cheaper than surface plant. Still need to produce launch fuel on surface.

With Mars the same would apply if using LH for earth return fuel.

Online TomH

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Re: necessity of methane production on Mars
« Reply #31 on: 01/12/2017 08:25 PM »
There's also this false idea that fossil fuels are somehow special and oh-so-hard to replicate (hence a long shpeal about fossil fuels)

You completely misread all of that. dror's post was not clearly written. In one sense he seemed to be asking whether extant coal on Mars could be pulverized into rocket fuel. I was actually trying to be nice in reply to what seemed a most absurd question.

Offline Robotbeat

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Re: necessity of methane production on Mars
« Reply #32 on: 01/12/2017 08:29 PM »
There's also this false idea that fossil fuels are somehow special and oh-so-hard to replicate (hence a long shpeal about fossil fuels)

You completely misread all of that. dror's post was not clearly written. In one sense he seemed to be asking whether extant coal on Mars could be pulverized into rocket fuel. I was actually trying to be nice in reply to what seemed a most absurd question.
I don't see that anywhere in his post.
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Online TomH

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Re: necessity of methane production on Mars
« Reply #33 on: 01/12/2017 09:13 PM »
I don't see that anywhere in his post.

An entire piece of writing usually has one overarching idea known as the thesis. Typically a paragraph has one single main idea stated in a topic sentence. More often than not, that topic sentence is the first sentence in the paragraph. The following sentences are detail sentences which expand on the main idea. Examine the structure of dror's paragraph:

What about solid carbon as fuel? Theoretically, powdered coal will burn just fine with O2 and may be tweaked to produce thrust in the right configuration. That can be produced without water mines.

The thesis idea already is Fuel Produced on Mars. In this paragraph dror nominates solid carbon as fuel as the main idea of his paragraph. The second sentence seems to expand on this fuel as being sourced from coal that has been powdered. dror implied something he apparently did not intend. My intent was to explain in a nonjudgemental manner why this was not possible.
« Last Edit: 01/12/2017 09:15 PM by TomH »

Offline Robotbeat

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Re: necessity of methane production on Mars
« Reply #34 on: 01/12/2017 09:28 PM »
Or, more likely, using coal as shorthand for "synthesized carbon." Seems far more likely than him claiming there are vast coal deposits on Mars.

We're woefully off-topic, but I think we'd all be far better off if we used Occam's Razor every once in a while and didn't uncharitably read-in absurd claims into other people's slight ambiguous posts.
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Offline MATTBLAK

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Re: necessity of methane production on Mars
« Reply #35 on: 01/12/2017 09:35 PM »
« Last Edit: 01/12/2017 09:37 PM by MATTBLAK »
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Online TomH

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Re: necessity of methane production on Mars
« Reply #36 on: 01/12/2017 09:38 PM »
Or, more likely, using coal as shorthand for "synthesized carbon." Seems far more likely than him claiming there are vast coal deposits on Mars.

We're woefully off-topic, but I think we'd all be far better off if we used Occam's Razor every once in a while and didn't uncharitably read-in absurd claims into other people's slight ambiguous posts.

I agree we are woefully off-topic, but it is you who is being uncharitable. I am a teacher. Through my career I have dealt with students of all backgrounds and intelligence levels. You seem to assume that I was being condescending to dror. The truth is that I took his question at what appeared to be face value and attempted to give a factual answer. I feel that you are personalizing this for some reason of which I am not aware. It is time to just let this go. I will not reply again re. this point.

MATTBLAK, Please correct me if I am wrong. Isn't the oxidizer in most hybrid engines hypergolic? Though I do see the igniter in this illustration. I think the above reference dealt with LOX as the oxidizer. I am not aware of the use of LOX in a hybrid engine. I would be interested in reading about this if I am incorrect.
« Last Edit: 01/12/2017 10:16 PM by TomH »

Offline MATTBLAK

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Re: necessity of methane production on Mars
« Reply #37 on: 01/12/2017 10:32 PM »
I don't know enough about hybrid engines to speak authoratively - they're not something I've ever paid a lot of attention to. I've got to read some papers on the subject :) Banishment or reduction of ignorance is something I'm always striving for.
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Offline Rocket Science

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Re: necessity of methane production on Mars
« Reply #38 on: 01/12/2017 11:12 PM »
I don't know enough about hybrid engines to speak authoratively - they're not something I've ever paid a lot of attention to. I've got to read some papers on the subject :) Banishment or reduction of ignorance is something I'm always striving for.
Some good reading...
http://www.spacesafetymagazine.com/aerospace-engineering/rocketry/hybrid-rocket-overview-part-2/
« Last Edit: 01/12/2017 11:16 PM by Rocket Science »
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Offline dror

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Re: necessity of methane production on Mars
« Reply #39 on: 01/13/2017 02:02 PM »
There's also this false idea that fossil fuels are somehow special and oh-so-hard to replicate (hence a long shpeal about fossil fuels)

You completely misread all of that. dror's post was not clearly written. In one sense he seemed to be asking whether extant coal on Mars could be pulverized into rocket fuel. I was actually trying to be nice in reply to what seemed a most absurd question.

Sorry for the confusion I induced, and thanks for the informative and interesting answers  :)
I didn't think coal could be found on Mars, I meant what Robotbeat wrote - artificially synthesized carbon, such as the one disscussed here:
http://forum.nasaspaceflight.com/index.php?topic=38283.msg1418010#msg1418010

My original line of thought was that maybe turning hydrolox to methalox was not necessary;
Now I believe that the Mars endeavour can be based on a process that does not depend on ice mining at all.

Attached is a pic from the "Synthesis of Carbon Nanofibers from CO2 " thread in the link above
« Last Edit: 01/13/2017 02:06 PM by dror »

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