Author Topic: necessity of methane production on Mars  (Read 8754 times)

Offline dror

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necessity of methane production on Mars
« on: 01/10/2017 07:22 PM »
SpaceX plan to produce Methane on Mars but to do so, they need to harvest water and break it.

Step one - produce hydrolox
 2H2O -> 2H2 + O2

Step two - produce methalox
 2H2 + O2 + CO2  ->  CH4 + 2O2

My back of the envelope (attached) shows that using the HydroLox from stage one gives almost as much dV as the methalox of both steps, which makes me wonder, does it worth the extra effort of producing methane?
« Last Edit: 01/10/2017 07:27 PM by dror »

Offline RonM

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Re: necessity of methane production on Mars
« Reply #1 on: 01/10/2017 07:26 PM »
Long term storage of liquid hydrogen is difficult. Methane is easier to handle.

Offline philw1776

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Re: necessity of methane production on Mars
« Reply #2 on: 01/10/2017 07:28 PM »
Yes, it's worth the effort because your Raptor engines run on methalox, not hydrolox. Apologies to Gen One BO.

Methane is denser meaning smaller fuel tanks, less mass.

Methane is much, much easier to store and handle than sneaky, leaky hydrogen.  Less massive failure prone cooling.
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Offline oiorionsbelt

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Re: necessity of methane production on Mars
« Reply #3 on: 01/10/2017 07:31 PM »
In the making life multi-planetary presentation this chart was shown.

Offline dror

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Re: necessity of methane production on Mars
« Reply #4 on: 01/10/2017 07:31 PM »
Long term storage of liquid hydrogen is difficult. Methane is easier to handle.

So do you think that the extra effort in producing methane is overall better because of storage?
Do you think that that's what drives SpaceX to do so?
Looking at that table above  ::) it does seem like the biggest showstopper
« Last Edit: 01/10/2017 07:42 PM by dror »

Offline envy887

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Re: necessity of methane production on Mars
« Reply #5 on: 01/10/2017 07:55 PM »
It appears your calculations assume the same dry mass for a hydrolox rocket capable of storing the same amount of propellant and producing the same thrust as a methalox rocket: (m_dry = 0.05*m_fuel).

Since tank mass and propulsion mass both scale with bulk density, and a rocket's mass is primarily tankage and propulsion, and hydrolox bulk density is ~half of methalox, this is a poor assumption.

Offline Robotbeat

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Re: necessity of methane production on Mars
« Reply #6 on: 01/10/2017 08:35 PM »
Ignoring mass fraction is one of the biggest mistakes I see people make again and again in rocketry.
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Offline dror

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Re: necessity of methane production on Mars
« Reply #7 on: 01/10/2017 09:03 PM »
It appears your calculations assume the same dry mass for a hydrolox rocket capable of storing the same amount of propellant and producing the same thrust as a methalox rocket: (m_dry = 0.05*m_fuel).

Since tank mass and propulsion mass both scale with bulk density, and a rocket's mass is primarily tankage and propulsion, and hydrolox bulk density is ~half of methalox, this is a poor assumption.
I put it as 0.05*m_fuel which is different for LH2LO2 (36 ton in that example) and for LCH4LO2 (80 ton).
Only the payload is the same for both (10 ton). The two rockets doesn't produce the same thrust nor store the same mass.
The volume may be similar but I assumed that the tank's wheight is dominated by the propelant's mass and not by it's volume.

Offline dglow

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Re: necessity of methane production on Mars
« Reply #8 on: 01/10/2017 09:24 PM »
The volume may be similar but I assumed that the tank's wheight is dominated by the propelant's mass and not by it's volume.

That part is backwards.

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Re: necessity of methane production on Mars
« Reply #9 on: 01/10/2017 09:26 PM »
Another factor is water consumption. By using CO2 as one of your feedstocks your IMLMO is higher per litre of water consumed. We believe water to be abundant but it's not as abundant as CO2.
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Offline envy887

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Re: necessity of methane production on Mars
« Reply #10 on: 01/10/2017 09:59 PM »
It appears your calculations assume the same dry mass for a hydrolox rocket capable of storing the same amount of propellant and producing the same thrust as a methalox rocket: (m_dry = 0.05*m_fuel).

Since tank mass and propulsion mass both scale with bulk density, and a rocket's mass is primarily tankage and propulsion, and hydrolox bulk density is ~half of methalox, this is a poor assumption.
I put it as 0.05*m_fuel which is different for LH2LO2 (36 ton in that example) and for LCH4LO2 (80 ton).
Only the payload is the same for both (10 ton). The two rockets doesn't produce the same thrust nor store the same mass.
In terms of relative mass, they do. A hydrolox engine sized to loft 47.6t will mass about as much as a methalox engine sized to loft 94t. A fuel tank sized to hold 36t of hydrolox will mass about as much as a tank sized to hold 80t of methalox, because the hydrogen tank needs more insulation.
Quote
The volume may be similar but I assumed that the tank's wheight is dominated by the propelant's mass and not by it's volume.
A pressure vessel's mass scales linearly with volume, at a constant pressure... generally regardless of the density of it's contents. LH2 is particularly hard (read: mass intensive) to store long-term, since it tends to leak and boil-off much worse than LCH4 or LOX.

In short, there is no way a hydrolox rocket massing 1.6t dry will boost the same payload as a methalox rocket massing 4t dry. It simply cannot hold enough propellant. (Upper stages are different since they do not have to lift their own mass and thus can have tiny engines and tiny thrust structures. They also don't have to store LH2 for more than a few hours).

And you're still 10% short on dV, which is a big deal, despite the unrealistic mass fractions.

Offline TomH

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Re: necessity of methane production on Mars
« Reply #11 on: 01/10/2017 10:25 PM »
The volume may be similar but I assumed that the tank's wheight is dominated by the propelant's mass and not by it's volume.

That part is backwards.

It surely is. Hydrogen's ISP density would require the fuel tanks on the ITS to be multiple times larger.

Offline oiorionsbelt

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Re: necessity of methane production on Mars
« Reply #12 on: 01/11/2017 01:07 AM »
According to Elon "the energy cost on Mars, of producing and storing hydrogen is very high."

Offline dror

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Re: necessity of methane production on Mars
« Reply #13 on: 01/11/2017 04:09 AM »
According to Elon "the energy cost on Mars, of producing and storing hydrogen is very high."
My point was that hydrogen production on mars is necessary but methane production is not.
The hydrogen is turned into methane in order to get a better fuel and slightly better performance, which you all seem to belive is worth the effort.

Offline Robotbeat

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Re: necessity of methane production on Mars
« Reply #14 on: 01/11/2017 04:18 AM »
/liquid/ hydrogen production on Mars is not necessary, though. Going to methane solves that problem. And then you can use equipment that's actually easier than the oxygen liquifier.

Also, methane is a feedstock in many chemical processes, including some ways of growing single celled protein.
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Re: necessity of methane production on Mars
« Reply #15 on: 01/11/2017 04:28 AM »
Methane production is very useful on Mars. But depending on your propulsion systems; not essential. I think LOX production is equally if not more important - you can use LOX with hydrazine, kerosene, LH2, propane, LNG, etc. And even with Carbon Monoxide, too - albeit with poor specific impulse.
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Offline dror

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Re: necessity of methane production on Mars
« Reply #16 on: 01/11/2017 04:59 AM »
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.

Offline TomH

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Re: necessity of methane production on Mars
« Reply #17 on: 01/11/2017 06:02 AM »
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.
« Last Edit: 01/11/2017 07:46 AM by TomH »

Offline envy887

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Re: necessity of methane production on Mars
« Reply #18 on: 01/11/2017 12:42 PM »
Don't forget that returning from Mars requires far more than getting to LMO. The return vehicle needs storable propellants for RCS, trajectory corrections, and landing at Earth. The mass penalty for storing liquid hydrogen in space for that long is much higher than LOX or LCH4.

Offline Robotbeat

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Re: necessity of methane production on Mars
« Reply #19 on: 01/11/2017 01:22 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.
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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. 

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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.

Offline 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.
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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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Offline 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.

Offline 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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Offline 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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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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Offline 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 »

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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 »

Offline TomH

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Re: necessity of methane production on Mars
« Reply #40 on: 01/14/2017 12:59 AM »
Sorry for the confusion..

Me too. I learned something from this. Next time I will ask for clarification as a first step.

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Re: necessity of methane production on Mars
« Reply #41 on: 01/16/2017 08:02 AM »
What about much larger synthetic hydrocarbons? C12H20 / TH-dimer / tetrahydromethylcyclopentadiene / RJ-4 as an example.

Another example would be RJ-5, discussed here: https://forum.nasaspaceflight.com/index.php?topic=19457.0

More generally http://www.biofuelsdigest.com/bdigest/2014/06/18/9-advanced-molecules-that-could-revolutionize-jet-and-missile-fuel/ lists a bunch.

Are any of these appropriate targets of synthesis on Mars?
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Re: necessity of methane production on Mars
« Reply #42 on: 01/16/2017 08:31 AM »
The first step beyond methane would likely be ethylene. It is the base of many chemical products. There is also extensive research going on to transfer the production of ethylene from methane from lab status to practical application. This is driven by the fact that many remote oil production facilities still burn methane byproduct because of transport problems. If methane can be processed on site to ethylene this waste would go away. Incidentally it would be extremely useful for Mars.

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Re: necessity of methane production on Mars
« Reply #43 on: 01/16/2017 08:39 AM »
Yes but don't all the small hydrocarbons (e.g. methane, ethane, propane, butane) have fairly high vapor pressures, i.e. aren't they gasses under standard conditions? Bigger ones are liquids....
« Last Edit: 01/16/2017 08:39 AM by sdsds »
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Offline TomH

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Re: necessity of methane production on Mars
« Reply #44 on: 01/17/2017 04:57 AM »
Yes but don't all the small hydrocarbons (e.g. methane, ethane, propane, butane) have fairly high vapor pressures, i.e. aren't they gasses under standard conditions? Bigger ones are liquids....

Gasoline is a mixture of quite a few hydrocarbons and has a fairly low molar enthalpy of vaporization. #1 and #2 (diesel) fuel oils take longer. Being mixtures, they lose the lighter volatiles and thicken in viscosity. You mention "standard conditions." The 0.0059 atmospheric density on Mars allows almost any liquid to quickly evaporate. OTOH, any synthesis is going to be in closed tanks, not open vats, so I would think that tanks with the necessary strength eliminate the problem by allowing pressurization. Getting LOX cold enough on Mars is what I see as the biggest hurdle. (I am assuming methane as the fuel, not LH2.) As it is compressed, a lot of heat will have to be dumped and you have to get it to -183C (and the methane -162C or so) at STP to liquify and even colder to densify. You can do that, but I just wonder about the mass requirement for such hardware on Mars. When you look at down to 20K for LH2, how much more mass is required for the necessary hardware? Not only do you have to make the stuff, you have to make it faster than it boils off in the ITS tanks and you have to keep it cold. I do not see how you have storage tanks that are separate from the on board prop tanks. IDK, but my WAG is that the requirements for all this are well beyond simple.
« Last Edit: 01/17/2017 05:02 AM by TomH »

Offline john smith 19

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Re: necessity of methane production on Mars
« Reply #45 on: 01/17/2017 07:23 AM »
so I would think that tanks with the necessary strength eliminate the problem by allowing pressurization.
Keep in mind all tanks on Earth are "pressurized" to 1 atmosphere absolute. The fact that we breath that pressure normally means we forget about it.
Quote
Getting LOX cold enough on Mars is what I see as the biggest hurdle. (I am assuming methane as the fuel, not LH2.) As it is compressed, a lot of heat will have to be dumped and you have to get it to -183C (and the methane -162C or so) at STP to liquify and even colder to densify. You can do that, but I just wonder about the mass requirement for such hardware on Mars. When you look at down to 20K for LH2, how much more mass is required for the necessary hardware?
LH2 could be more viable on Mars. On Earth LH2 is difficult because it chills LOX out of air and creates a fire and explosion hazard. On Mars it would chill CO2 to dry ice (eventually)

In principle refrigeration is easier on Mars as the difference between outside air temperature and the target is smaller, needing less power to put a refrigerant through its compression/expansion cycle. OTOH the atmosphere is 1/160 that of Earth. Not a vacuum but I suspect actual radiation would be a bigger part of how a radiator would dump heat on Mars. A nice convenient glacier would be a useful heat sink at this point.
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Offline Norm38

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Re: necessity of methane production on Mars
« Reply #46 on: 01/17/2017 05:20 PM »
In short, there is no way a hydrolox rocket massing 1.6t dry will boost the same payload as a methalox rocket massing 4t dry. It simply cannot hold enough propellant. (Upper stages are different since they do not have to lift their own mass and thus can have tiny engines and tiny thrust structures. They also don't have to store LH2 for more than a few hours).

I don't want to derail this thread any, but has anyone ever worked up what the Space Shuttle would have looked like as methalox instead of LH2?  That would be instructive.

Offline envy887

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Re: necessity of methane production on Mars
« Reply #47 on: 01/17/2017 06:02 PM »
In short, there is no way a hydrolox rocket massing 1.6t dry will boost the same payload as a methalox rocket massing 4t dry. It simply cannot hold enough propellant. (Upper stages are different since they do not have to lift their own mass and thus can have tiny engines and tiny thrust structures. They also don't have to store LH2 for more than a few hours).

I don't want to derail this thread any, but has anyone ever worked up what the Space Shuttle would have looked like as methalox instead of LH2?  That would be instructive.

The Shuttle+ET was effectively an upper stage. Hydrolox made sense there since the SSMEs burned through almost 10 km/s of delta-v and didn't have to lift the entire stack off the pad.

Offline TomH

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Re: necessity of methane production on Mars
« Reply #48 on: 01/18/2017 02:20 AM »
Keep in mind all tanks on Earth are "pressurized" to 1 atmosphere absolute. The fact that we breath that pressure normally means we forget about it.

As a former physics teacher, I am quite aware of what you are talking about. I disagree, however, because an open container has the same pressure on the inside and outside walls, therefore the pressure differential is zero. If you boil a tiny bit of water in metal can, then screw the cap on immediately after removing it from heat, a partial vacuum will begin to form within the can as the steam condenses back to liquid water, and the outer pressure will almost completely crush the can. On Mars, you have almost no exterior pressure. To condense vaporous CH4 or O2 into liquid, the container will need to be pressurized internally, but there will be almost no compensating external pressure. Of course most containers can withstand far more internal pressure than external pressure (think COPV issues).

OTOH the atmosphere is 1/160 that of Earth. Not a vacuum but I suspect actual radiation would be a bigger part of how a radiator would dump heat on Mars.

That is exactly my point. There is almost no atmosphere to use as a heat sink nor to convect heat off of radiator fins. The thermal energy must be radiated into space. If you could afford the mass, you could drill vertical shafts into the ground and make an earth-coupled (Mars-coupled??) heat-pump with tubes full of ethylene or propylene glycol, ammonia, or some class of freon and dump the heat into the ground. If you had a trencher or backhoe you could lay out tubes in a back and forth pattern a couple of meters down. My WAG is that something like the ammonia radiators on ISS would be required.

I fear chilling and storing prop on Mars may be more complicated than many people realize due to these issues.

I personally think the ideal mission for the first Red Dragon (other than landing) would be a basic experimental exercise in making and storing LCH4 and LOX. That is the most important thing that has to happen to get back off The Red Planet.
« Last Edit: 01/18/2017 02:33 AM by TomH »

Offline Hotblack Desiato

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Re: necessity of methane production on Mars
« Reply #49 on: 01/18/2017 08:29 AM »

I fear chilling and storing prop on Mars may be more complicated than many people realize due to these issues.

Yes, storing methane and LOX for extended periods of time could be difficult.

The LOX requires constant cooling, so that the oxygens partial pressure stays low. It will form a dry ice layer on the outside (just frozen martian atmosphere). Which could be actually an advantage. It adds an extra insulation layer. Just keep it in the shadow duing the day (It will still require constant cooling).

On the fuel side, things are more interesting.

We don't know yet, if methane is the only liquid fuel the raptor engine can consume. I'm thinking about propane, butane and pentane, which have very interesting melting and boiling points. Butane melts at 139K and boils at 274K, propane EDIT pentane (my bad) melts at 144K and boils at 309K. This will shift a bit to lower temperatures due to lower temperatures due to the lower pressure on Mars, but it could still be good enough for thin walled metal tanks to store large quantities of fuel at outside temperatures.

As a nice bonus, these fuels are much more dense than methane, not requireing extensive subcooling of the fuel for densification, yet they behave similarly to methane in terms of viscosity and energy density (actually, energy density is better).

The fuel could be easily produced (requires CO and H2O via the Fischer Tropsch Process) in situ, similar to the Haber Bosch Process, which only gives methane. Actually, Fischer Tropsch would give a mix of different hydrocarbons (propane to hexane), which can be adjusted even better for the required melting and boiling points, since hydrocarbons mix very well.

EDIT: as a funny side note, wikipedia mentiones a large FT-reactor was operated from 1951 to 57 in Brownsville, TX.
« Last Edit: 01/20/2017 10:48 PM by Hotblack Desiato »

Offline Paul451

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Re: necessity of methane production on Mars
« Reply #50 on: 01/19/2017 08:40 PM »
propane melts at 144K and boils at 309K

I think you meant pentane.

Offline CuddlyRocket

Re: necessity of methane production on Mars
« Reply #51 on: 02/10/2017 11:42 PM »
SpaceX plan to produce Methane on Mars but to do so, they need to harvest water and break it.

Step one - produce hydrolox
 2H2O -> 2H2 + O2

Step two - produce methalox
 2H2 + O2 + CO2  ->  CH4 + 2O2

My back of the envelope (attached) shows that using the HydroLox from stage one gives almost as much dV as the methalox of both steps, which makes me wonder, does it worth the extra effort of producing methane?

Step two is not how it is usually proposed to produce methalox on Mars. It's generally not a good idea to conflate steps as this can lead you astray.

The Sabatier reaction is 4H2 + CO2  ->  CH4 + 2H2O. The water goes back into step one. The entire process does not produce sufficient LOX for methalox propellant so additional LOX is obtained by electrolysing CO2 directly. People tend to concentrate on the fuel component, but it's the LOX that dominates the mass of the propellant. Plus Oxygen has other uses!

Online guckyfan

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Re: necessity of methane production on Mars
« Reply #52 on: 02/11/2017 06:28 AM »
The Sabatier reaction is 4H2 + CO2  ->  CH4 + 2H2O. The water goes back into step one. The entire process does not produce sufficient LOX for methalox propellant so additional LOX is obtained by electrolysing CO2 directly. People tend to concentrate on the fuel component, but it's the LOX that dominates the mass of the propellant. Plus Oxygen has other uses!

You forgot the O2 from electrolysis. The complete process produces O2 at stochiometric value so there is an excess of oxygen because the rocket engines always run fuel rich.

Edit: You need O2 from CO2 if you assume feed H2 brought in from earth.
« Last Edit: 02/11/2017 06:35 AM by guckyfan »

Offline dror

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Re: necessity of methane production on Mars
« Reply #53 on: 02/11/2017 07:26 AM »
SpaceX plan to produce Methane on Mars but to do so, they need to harvest water and break it.

Step one - produce hydrolox
 2H2O -> 2H2 + O2

Step two - produce methalox
 2H2 + O2 + CO2  ->  CH4 + 2O2

My back of the envelope (attached) shows that using the HydroLox from stage one gives almost as much dV as the methalox of both steps, which makes me wonder, does it worth the extra effort of producing methane?

Step two is not how it is usually proposed to produce methalox on Mars. It's generally not a good idea to conflate steps as this can lead you astray.

The Sabatier reaction is 4H2 + CO2  ->  CH4 + 2H2O. The water goes back into step one. The entire process does not produce sufficient LOX for methalox propellant so additional LOX is obtained by electrolysing CO2 directly. People tend to concentrate on the fuel component, but it's the LOX that dominates the mass of the propellant. Plus Oxygen has other uses!

That's a schematic of their plan. The source of H is ISRU water ice, not H2 from earth.
http://www.spacex.com/sites/spacex/files/mars_presentation.pdf

Offline john smith 19

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Re: necessity of methane production on Mars
« Reply #54 on: 02/13/2017 07:40 AM »
OTOH the atmosphere is 1/160 that of Earth. Not a vacuum but I suspect actual radiation would be a bigger part of how a radiator would dump heat on Mars.

That is exactly my point. There is almost no atmosphere to use as a heat sink nor to convect heat off of radiator fins. The thermal energy must be radiated into space. If you could afford the mass, you could drill vertical shafts into the ground and make an earth-coupled (Mars-coupled??) heat-pump with tubes full of ethylene or propylene glycol, ammonia, or some class of freon and dump the heat into the ground. If you had a trencher or backhoe you could lay out tubes in a back and forth pattern a couple of meters down. My WAG is that something like the ammonia radiators on ISS would be required.
I'd be careful here. While roughly 640Pa is nothing by human standards that's nowhere near hard vacuum. Anyone who's tried to draught proof a house will know that even small draughts can carry a lot of heat.

On an odd physics note a pipe hanging down the side of a narrow hole should look quite a lot like an ideal black body radiator.

The balance will shift a lot on Mars but it's still a balance, unlike the Moon or LEO, where it's strictly radiation only.
Quote
I personally think the ideal mission for the first Red Dragon (other than landing) would be a basic experimental exercise in making and storing LCH4 and LOX. That is the most important thing that has to happen to get back off The Red Planet.
Yes. When someone said it'd take about 50  000 tonnes of propellant to propel ITS back to Earth I wondered if people realize just how big a system they are talking about.
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Offline R7

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Re: necessity of methane production on Mars
« Reply #55 on: 02/13/2017 02:04 PM »
That is exactly my point. There is almost no atmosphere to use as a heat sink nor to convect heat off of radiator fins. The thermal energy must be radiated into space
I'd be careful here. While roughly 640Pa is nothing by human standards that's nowhere near hard vacuum. Anyone who's tried to draught proof a house will know that even small draughts can carry a lot of heat.

Yep, heat transfer coefficient isn't linear to pressure. Martian atmosphere carries heat surprisingly well.

https://www.researchgate.net/profile/Alvaro_Soria-Salinas/publication/299600459_Convective_Heat_Transfer_Measurements_at_the_Martian_Surface/links/570361ee08aedbac126f4bc4/Convective-Heat-Transfer-Measurements-at-the-Martian-Surface.pdf

Estimates h of almost 10 W/m2K for 4m/s wind. Forced convection would increase that a lot.

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Offline john smith 19

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Re: necessity of methane production on Mars
« Reply #56 on: 02/13/2017 04:06 PM »
Yep, heat transfer coefficient isn't linear to pressure. Martian atmosphere carries heat surprisingly well.

https://www.researchgate.net/profile/Alvaro_Soria-Salinas/publication/299600459_Convective_Heat_Transfer_Measurements_at_the_Martian_Surface/links/570361ee08aedbac126f4bc4/Convective-Heat-Transfer-Measurements-at-the-Martian-Surface.pdf

Estimates h of almost 10 W/m2K for 4m/s wind. Forced convection would increase that a lot.
Something to keep in mind. ITS will need a fair bit of insulation to keep temperatures reasonable.  The upside is "radiators" will be much more efficient than in deep space and the high delta t will translate to actual useful improvements in radiator size reduction.

That still leaves you with an awful lot of water and CO2 to move to refuel.
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Offline Kaputnik

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Re: necessity of methane production on Mars
« Reply #57 on: 02/13/2017 09:16 PM »
The first step beyond methane would likely be ethylene. It is the base of many chemical products. There is also extensive research going on to transfer the production of ethylene from methane from lab status to practical application. This is driven by the fact that many remote oil production facilities still burn methane byproduct because of transport problems. If methane can be processed on site to ethylene this waste would go away. Incidentally it would be extremely useful for Mars.

It's a few years since I last read it, but didn't Zubrin make a strong case for ethylene, as a sort of footnote to Mars Direct?
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Offline Dalhousie

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Re: necessity of methane production on Mars
« Reply #58 on: 02/14/2017 12:24 AM »
Yes. When someone said it'd take about 50  000 tonnes of propellant to propel ITS back to Earth I wondered if people realize just how big a system they are talking about.

Do you have a link? Back of the envelope suggests that for a minimum energy unmanned return ~1500 tonnes should be enough.  Which is still a substantial amount to make on Mars.
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Offline envy887

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Re: necessity of methane production on Mars
« Reply #59 on: 02/14/2017 12:35 AM »
Yes. When someone said it'd take about 50  000 tonnes of propellant to propel ITS back to Earth I wondered if people realize just how big a system they are talking about.

Do you have a link? Back of the envelope suggests that for a minimum energy unmanned return ~1500 tonnes should be enough.  Which is still a substantial amount to make on Mars.

50,000 tonnes of propellant at the Earth's surface is about what it will take to land a single loaded ITS on Mars.

Getting it back empty could probably be done for only ~800 tonnes the Mars surface.

Offline Dalhousie

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Re: necessity of methane production on Mars
« Reply #60 on: 02/14/2017 04:16 AM »
Yes. When someone said it'd take about 50  000 tonnes of propellant to propel ITS back to Earth I wondered if people realize just how big a system they are talking about.

Do you have a link? Back of the envelope suggests that for a minimum energy unmanned return ~1500 tonnes should be enough.  Which is still a substantial amount to make on Mars.

50,000 tonnes of propellant at the Earth's surface is about what it will take to land a single loaded ITS on Mars.

Getting it back empty could probably be done for only ~800 tonnes the Mars surface.

Seems a bit low.  I don't see how it can go belong 1200 tonnes even assuming no back mass.  Could easily be wrong of course.
"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Offline john smith 19

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Re: necessity of methane production on Mars
« Reply #61 on: 02/14/2017 06:26 AM »
Do you have a link? Back of the envelope suggests that for a minimum energy unmanned return ~1500 tonnes should be enough.  Which is still a substantial amount to make on Mars.

50,000 tonnes of propellant at the Earth's surface is about what it will take to land a single loaded ITS on Mars.

Getting it back empty could probably be done for only ~800 tonnes the Mars surface.

Seems a bit low.  I don't see how it can go belong 1200 tonnes even assuming no back mass.  Could easily be wrong of course.
That's a lot smaller. The number came from memory of an entry on IIRC this thread.

While 1200 tonnes is much smaller it's still a lot. Doing a quick BOTE with MR of 2.3 gave Methane at 454 tonnes, needing about 113.5 tonnes of H2 from water and 340.5 tonnes of Carbon from CO2.  With a rough surface air density of 8.4g/m^3 that's a humongous amount of gas to move to extract that' Carbon.  About 148 million m^3.
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Offline jpo234

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Re: necessity of methane production on Mars
« Reply #62 on: 02/14/2017 07:02 AM »
With a rough surface air density of 8.4g/m^3 that's a humongous amount of gas to move to extract that' Carbon.  About 148 million m^3.

There is dry ice on Mars. Could it be easier to collect frozen CO2?
« Last Edit: 02/14/2017 07:08 AM by jpo234 »

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Re: necessity of methane production on Mars
« Reply #63 on: 02/14/2017 07:46 AM »

There is dry ice on Mars. Could it be easier to collect frozen CO2?

Dry ice is at the poles. Settlements and landing sites will be nearer the equator. Dry ice would need to be transported for thousands of km. Maybe feasible when there is significant industry and infrastructure. Not early.

Offline envy887

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Re: necessity of methane production on Mars
« Reply #64 on: 02/14/2017 12:35 PM »
Yes. When someone said it'd take about 50  000 tonnes of propellant to propel ITS back to Earth I wondered if people realize just how big a system they are talking about.

Do you have a link? Back of the envelope suggests that for a minimum energy unmanned return ~1500 tonnes should be enough.  Which is still a substantial amount to make on Mars.

50,000 tonnes of propellant at the Earth's surface is about what it will take to land a single loaded ITS on Mars.

Getting it back empty could probably be done for only ~800 tonnes the Mars surface.

Seems a bit low.  I don't see how it can go belong 1200 tonnes even assuming no back mass.  Could easily be wrong of course.

Mars escape is 5.0 km/s, a slow Earth return is about 1.0 km/s from escape, EDL at Earth about 0.5 km/s. Gravity losses and drag at Mars are minimal for a high TWR vehicle with no human g-limits... with 800 tonnes of fuel the ITS spaceship would have a TWR of nearly 10:1 at liftoff. So I'd figure about 0.5 km/s for drag and grav losses, and course corrections.

That means it needs 7 km/s for a slow return all the way to Earth. At a dry mass of 150t and ISP of 382, that is 972t wet or 822 tonnes of fuel.

Offline Dalhousie

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Re: necessity of methane production on Mars
« Reply #65 on: 02/14/2017 10:20 PM »

Mars escape is 5.0 km/s, a slow Earth return is about 1.0 km/s from escape, EDL at Earth about 0.5 km/s. Gravity losses and drag at Mars are minimal for a high TWR vehicle with no human g-limits... with 800 tonnes of fuel the ITS spaceship would have a TWR of nearly 10:1 at liftoff. So I'd figure about 0.5 km/s for drag and grav losses, and course corrections.

That means it needs 7 km/s for a slow return all the way to Earth. At a dry mass of 150t and ISP of 382, that is 972t wet or 822 tonnes of fuel.

Thanks!  What sort of acceleration are you thinking?
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Offline envy887

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Re: necessity of methane production on Mars
« Reply #66 on: 02/14/2017 10:39 PM »
IIRC Musk said the tanker could land at up to 20 g, so the structural limits are probably pretty high. Acceleration at liftoff could be around 4 g, and engines can be throttled/shut down as needed to avoid exceeding structural limits. I don't think aero loads are a limiting factor at all.

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Re: necessity of methane production on Mars
« Reply #67 on: 02/15/2017 04:31 AM »
IIRC Musk said the tanker could land at up to 20 g, so the structural limits are probably pretty high. Acceleration at liftoff could be around 4 g, and engines can be throttled/shut down as needed to avoid exceeding structural limits. I don't think aero loads are a limiting factor at all.

The limits in nominal flights should be what the payload or passengers can take. A vehicle that will be used many times should have much higher limits and not be used to these limits if possible. Especially the booster that is supposed to fly 1000 times. But the tanker too which is supposed to fly 100 times.

Offline Semmel

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Re: necessity of methane production on Mars
« Reply #68 on: 02/15/2017 05:49 AM »
I don't think that ITS will launch with less than full tanks. SpaceX will want to maximise the probability of successful return to Earth. That means it should have maximum margin for error, which involves a full tank. So no where near an acceleration of 4g. Or I just realised.. Did you mean 4 times Mars surface gravity?

Offline john smith 19

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Re: necessity of methane production on Mars
« Reply #69 on: 02/15/2017 06:11 AM »
With a rough surface air density of 8.4g/m^3 that's a humongous amount of gas to move to extract that' Carbon.  About 148 million m^3.

There is dry ice on Mars. Could it be easier to collect frozen CO2?
The answer is yes if it's co-located with water (liquid, ice or mud) and if you have humans to handle the collection. Building a remote managed ISRU to do so is likely more difficult as it's likely to be buried. Depends on the co-lo and wheather you can reuse most of the water extraction hardware for dry ice.
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Offline envy887

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Re: necessity of methane production on Mars
« Reply #70 on: 02/15/2017 02:21 PM »
I don't think that ITS will launch with less than full tanks. SpaceX will want to maximise the probability of successful return to Earth. That means it should have maximum margin for error, which involves a full tank. So no where near an acceleration of 4g. Or I just realised.. Did you mean 4 times Mars surface gravity?
They want to minimize cost, which probably means maximum reuse, which means getting the ship back as quickly as possible.   So a full load of fuel would probably be used to get a faster return trajectory.

But if fuel production is a constraint, they might just fill it enough to get it back empty, with margins of course.

Offline Semmel

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Re: necessity of methane production on Mars
« Reply #71 on: 02/16/2017 06:21 AM »
I would expect them to land the first ITS and not return it. It can then be used as fuel depot that gets filled up in between travel windows. An ITS coming in would be refuelled from that old one and can be good to go within a few weeks. Short enough for any reasonable one-window turn around.

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Re: necessity of methane production on Mars
« Reply #72 on: 02/16/2017 07:34 AM »
I would expect them to land the first ITS and not return it. It can then be used as fuel depot that gets filled up in between travel windows. An ITS coming in would be refuelled from that old one and can be good to go within a few weeks. Short enough for any reasonable one-window turn around.

I agree with using the first ship that way. The second ship, the first manned landing will also stay for 2 years because it will be needed as a habitat for quite a while. I always have difficulties imagining that a ship that has stayed on the surface of Mars for 2 years would fly again after that waiting period. But that's just me.

Offline meekGee

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Re: necessity of methane production on Mars
« Reply #73 on: 02/16/2017 06:29 PM »
I would expect them to land the first ITS and not return it. It can then be used as fuel depot that gets filled up in between travel windows. An ITS coming in would be refuelled from that old one and can be good to go within a few weeks. Short enough for any reasonable one-window turn around.
Agreed, and as GF says, probably more than one.
I wonder how much pre-supply they'll end up sending before crew #1 lands.
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Offline jpo234

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Re: necessity of methane production on Mars
« Reply #74 on: 02/16/2017 07:08 PM »


I always have difficulties imagining that a ship that has stayed on the surface of Mars for 2 years would fly again after that waiting period. But that's just me.

Opportunity is still reasonably healthy after more than 12 years on the surface. The martian atmosphere is close to a vacuum compared to earth and CO2 does not cause corrosion.

Why would something degrade in 2 years?

Offline Semmel

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Re: necessity of methane production on Mars
« Reply #75 on: 02/17/2017 05:14 AM »
Things might degrade due to Martian dust and movement. Opportunity is an exceptional good engineered piece of hardware. You can't rely on stuff lasting 10 times longer than anticipated.

Would it make sense to send an ITS equipped with a permanent fuel production plant inside it's belly? With permanent I mean one that is not removed from ITS after landing. If it does not come back and is used as a depot, why unpack it?

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Re: necessity of methane production on Mars
« Reply #76 on: 02/17/2017 06:20 AM »
Would it make sense to send an ITS equipped with a permanent fuel production plant inside it's belly? With permanent I mean one that is not removed from ITS after landing. If it does not come back and is used as a depot, why unpack it?

yes. i thought that was the plan...
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Offline dror

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Re: necessity of methane production on Mars
« Reply #77 on: 02/17/2017 06:49 AM »
Things might degrade due to Martian dust and movement. Opportunity is an exceptional good engineered piece of hardware. You can't rely on stuff lasting 10 times longer than anticipated.

Would it make sense to send an ITS equipped with a permanent fuel production plant inside it's belly? With permanent I mean one that is not removed from ITS after landing. If it does not come back and is used as a depot, why unpack it?
Because of water ice harvesting.
The bigger part of the effort is not related to water purifying, electrolysis, methan, liquification etc but to the water harvesting procedure itself.
I suspect thats the long pole.

Offline CuddlyRocket

Re: necessity of methane production on Mars
« Reply #78 on: 02/18/2017 01:36 AM »
I always have difficulties imagining that a ship that has stayed on the surface of Mars for 2 years would fly again after that waiting period. But that's just me.

Opportunity is still reasonably healthy after more than 12 years on the surface. The martian atmosphere is close to a vacuum compared to earth and CO2 does not cause corrosion.

Why would something degrade in 2 years?
Things might degrade due to Martian dust and movement. Opportunity is an exceptional good engineered piece of hardware. You can't rely on stuff lasting 10 times longer than anticipated.

Two things: First, the ship will be designed to meet the mission criteria, including launch after 2 years. Second, the design will take account of the fact that there will be human engineers on Mars who can implement a proper maintenance cycle etc.

Although there are differences in scale etc, there are plenty of interplanetary probes that coasted through space for more than 2 years and whose engines have still worked perfectly.

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Re: necessity of methane production on Mars
« Reply #79 on: 02/18/2017 06:13 AM »
Two things: First, the ship will be designed to meet the mission criteria, including launch after 2 years. Second, the design will take account of the fact that there will be human engineers on Mars who can implement a proper maintenance cycle etc.

Although there are differences in scale etc, there are plenty of interplanetary probes that coasted through space for more than 2 years and whose engines have still worked perfectly.

Mission criteria don't have to include launch after 2 years. ITS is designed for quick turn around with only weeks on the ground, maybe longer for some purposes but not 2 years. Giving it 2 years would be advantagous, I agree. But only if it is not too hard. I am also thinking they may want or need the first few landers on the ground on Mars and begin return flights with the cargo and crew carriers arriving in the third synod.

I think NASA mission profiles that preland assets like MAVs do assume 2 years so it probably is not too hard. I just worry a bit about it, especially for early manned missions.

Interplanetary probes are not a good comparison. They use monopropellants or ion drives. Not the most complex engine cycle ever designed.

Offline Semmel

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Re: necessity of methane production on Mars
« Reply #80 on: 03/02/2017 07:43 PM »
Here is a paper that might be relevant.

http://onlinelibrary.wiley.com/doi/10.1002/slct.201601169/full

Quote
Herein we report a common element, nanostructured catalyst for the direct electrochemical conversion of CO2 to ethanol with high Faradaic efficiency (63 % at −1.2 V vs RHE) and high selectivity (84 %) that operates in water and at ambient temperature and pressure. Lacking noble metals or other rare or expensive materials, the catalyst is comprised of Cu nanoparticles on a highly textured, N-doped carbon nanospike film. Electrochemical analysis and density functional theory (DFT) calculations suggest a preliminary mechanism in which active sites on the Cu nanoparticles and the carbon nanospikes work in tandem to control the electrochemical reduction of carbon monoxide dimer to alcohol.

Offline dror

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Re: necessity of methane production on Mars
« Reply #81 on: 03/04/2017 04:04 PM »
Here is a paper that might be relevant.

http://onlinelibrary.wiley.com/doi/10.1002/slct.201601169/full

Quote
Herein we report a common element, nanostructured catalyst for the direct electrochemical conversion of CO2 to ethanol with high Faradaic efficiency (63 % at −1.2 V vs RHE) and high selectivity (84 %) that operates in water and at ambient temperature and pressure. Lacking noble metals or other rare or expensive materials, the catalyst is comprised of Cu nanoparticles on a highly textured, N-doped carbon nanospike film. Electrochemical analysis and density functional theory (DFT) calculations suggest a preliminary mechanism in which active sites on the Cu nanoparticles and the carbon nanospikes work in tandem to control the electrochemical reduction of carbon monoxide dimer to alcohol.

Though very interesting, it looks like procucing ethanol requires a lot of hydrogen so water ice harvesting will still be necessaryon Mars.

Offline gospacex

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Re: necessity of methane production on Mars
« Reply #82 on: 03/04/2017 05:34 PM »

There is dry ice on Mars. Could it be easier to collect frozen CO2?

Dry ice is at the poles. Settlements and landing sites will be nearer the equator. Dry ice would need to be transported for thousands of km. Maybe feasible when there is significant industry and infrastructure. Not early.

Exactly.
If you need faster fuel generation, send a few more ITSes loaded with atmospheric fuel production plants and solar panels, and deploy those. There is no shortage of atmosphere and land there.

It's one-time expense, compared to constant hassle of digging up H2O/CO2 ices, hauling them around and purifying them.

Thankfully, at the moment Mars has very low population of bureaucrats, no zoning committees and no EPA. At least here, the weight of plant equipment will be substantially larger than the weight of paperwork needed to deploy it.
« Last Edit: 03/04/2017 05:35 PM by gospacex »

Offline lamontagne

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Re: necessity of methane production on Mars
« Reply #83 on: 03/05/2017 12:29 AM »

There is dry ice on Mars. Could it be easier to collect frozen CO2?

Dry ice is at the poles. Settlements and landing sites will be nearer the equator. Dry ice would need to be transported for thousands of km. Maybe feasible when there is significant industry and infrastructure. Not early.

Exactly.
If you need faster fuel generation, send a few more ITSes loaded with atmospheric fuel production plants and solar panels, and deploy those. There is no shortage of atmosphere and land there.

It's one-time expense, compared to constant hassle of digging up H2O/CO2 ices, hauling them around and purifying them.

Thankfully, at the moment Mars has very low population of bureaucrats, no zoning committees and no EPA. At least here, the weight of plant equipment will be substantially larger than the weight of paperwork needed to deploy it.
Isn't it really a question of energy?  The power required to compress the atmosphere into a usable liquid for separation, vs the power to transport CO2 for a long distance?
Clearly not a viable short term solution, but it would be interesting to calculate the cost of moving CO2 on a large Mars train vs the cost of compression, for example.

Offline lamontagne

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Re: necessity of methane production on Mars
« Reply #84 on: 03/05/2017 12:30 AM »
Do we need methane to produce ammonia by the Haber process for plant fertilizer, or is there a more direct way?

Offline Norm38

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Re: necessity of methane production on Mars
« Reply #85 on: 03/05/2017 12:58 AM »
Isn't it really a question of energy?  The power required to compress the atmosphere into a usable liquid for separation, vs the power to transport CO2 for a long distance?
Clearly not a viable short term solution, but it would be interesting to calculate the cost of moving CO2 on a large Mars train vs the cost of compression, for example.

Energy has to be stored to be used. Solar panels can dump their energy straight to chemical storage. But to haul
dry ice from the poles requires a lot more hardware. Meaning a lot more shipment from Earth and all that energy.  I bet compression wins out.

Offline gospacex

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Re: necessity of methane production on Mars
« Reply #86 on: 03/05/2017 04:49 PM »
Isn't it really a question of energy?  The power required to compress the atmosphere into a usable liquid for separation, vs the power to transport CO2 for a long distance?
Clearly not a viable short term solution, but it would be interesting to calculate the cost of moving CO2 on a large Mars train vs the cost of compression, for example.

And the cost of separation out dust and sand from that frozen CO2. And the cost of operating and maintaining earthmoving equipment at the ice mining site. And the cost of maintaining trains and rails. All that machinery is bound to break from time to time.

Offline lamontagne

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Re: necessity of methane production on Mars
« Reply #87 on: 03/05/2017 05:18 PM »
Isn't it really a question of energy?  The power required to compress the atmosphere into a usable liquid for separation, vs the power to transport CO2 for a long distance?
Clearly not a viable short term solution, but it would be interesting to calculate the cost of moving CO2 on a large Mars train vs the cost of compression, for example.

And the cost of separation out dust and sand from that frozen CO2. And the cost of operating and maintaining earthmoving equipment at the ice mining site. And the cost of maintaining trains and rails. All that machinery is bound to break from time to time.
As do compressors and other gas separation equipment.  And you need to separate the dust out of the atmosphere as well, and that can wear out.  I have no preference one way or the other, really.  Horizontal transportation on rails can be pretty cheap.  but the cost of the infrastructure needs to be proportional to the demand, and for a 5000 km run, at, 1 million per km?  That's a 5 billion dollars in rail...  won't be producing those levels of fuel before some time :-)

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Re: necessity of methane production on Mars
« Reply #88 on: 03/10/2017 06:40 PM »
Do we need methane to produce ammonia by the Haber process for plant fertilizer, or is there a more direct way?

Fish

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Re: necessity of methane production on Mars
« Reply #89 on: 03/10/2017 06:43 PM »
Isn't it really a question of energy?  The power required to compress the atmosphere into a usable liquid for separation, vs the power to transport CO2 for a long distance?
Clearly not a viable short term solution, but it would be interesting to calculate the cost of moving CO2 on a large Mars train vs the cost of compression, for example.

And the cost of separation out dust and sand from that frozen CO2. And the cost of operating and maintaining earthmoving equipment at the ice mining site. And the cost of maintaining trains and rails. All that machinery is bound to break from time to time.
As do compressors and other gas separation equipment.  And you need to separate the dust out of the atmosphere as well, and that can wear out.  I have no preference one way or the other, really.  Horizontal transportation on rails can be pretty cheap.  but the cost of the infrastructure needs to be proportional to the demand, and for a 5000 km run, at, 1 million per km?  That's a 5 billion dollars in rail...  won't be producing those levels of fuel before some time :-)


Why use rails? An autonomous tanker truck would work just as well.

Offline lamontagne

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Re: necessity of methane production on Mars
« Reply #90 on: 03/10/2017 08:50 PM »
Do we need methane to produce ammonia by the Haber process for plant fertilizer, or is there a more direct way?

Fish
Fish food?

Offline lamontagne

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Re: necessity of methane production on Mars
« Reply #91 on: 03/10/2017 09:07 PM »
Just how hard is it to separate out the CO2 in Mars' atmosphere anyway?

It seems clear that a frozen CO2 hauler would also be moving water, as the two seem to freeze out more or less together in the present atmosphere of Mars, as per the joined paper.

Perhaps the membrane or chemical way would be cheaper than compression, after all.



Offline Rei

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Re: necessity of methane production on Mars
« Reply #92 on: 03/10/2017 09:15 PM »
Do we need methane to produce ammonia by the Haber process for plant fertilizer, or is there a more direct way?

There are other processes (such as from cyanides and electric arcs), but not good ones. The discovery of the Haber process was really one of the great moments in chemistry - production of nitrates previously had been low volume and expensive, but the process created a way that works so well that the design of modern ammonia plants is little changed from the original days.  Three different Nobel prizes have been granted in relation to the process. The catalyst (iron/magnetite with various promoters) is easy to make and renew (indeed, at very high pressures you don't even need catalysts - the walls of the reactor themselves act as a catalyst).  There are a couple alternative modern catalysts, but no real huge leaps forward.

The main disadvantage of the Haber process is the need for high pressures. But that's pretty unavoidable, you have to shift the thermodynamic equilibrium to favour ammonia.

Now the Ostwald process, there's a lot more potential for improvement there... mainly reducing catalyst erosion and/or better catalyst recovery and/or cheaper catalysts.

ED: Wait, you said methane?  Methane isn't involved in the Haber process, hydrogen is. On Earth we make most hydrogen from methane, because that's the cheapest way here, but it's certainly not the cheapest way on Mars.
« Last Edit: 03/10/2017 09:17 PM by Rei »

Offline Rei

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Re: necessity of methane production on Mars
« Reply #93 on: 03/10/2017 09:21 PM »
Just how hard is it to separate out the CO2 in Mars' atmosphere anyway?

It seems clear that a frozen CO2 hauler would also be moving water, as the two seem to freeze out more or less together in the present atmosphere of Mars, as per the joined paper.

Perhaps the membrane or chemical way would be cheaper than compression, after all.

Mars's water vapour is so vanishingly sparse that it's generally not considered a practical feedstock vs. ground sources (for which the TRL is still very low).

As for how easy it is to separate, I'd recommend reading the design of MOXIE  :)  It gives an idea of the various complications that have to be handled.  Still, as far as feedstocks go, it's a relatively uncomplicated one. 

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Re: necessity of methane production on Mars
« Reply #94 on: 03/10/2017 09:56 PM »
Do we need methane to produce ammonia by the Haber process for plant fertilizer, or is there a more direct way?

Fish

Fish don't produce nitrates from nitrogen. They produce it from proteins in their food. So not a source. They can help keep it in circulation.

Offline Robotbeat

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Re: necessity of methane production on Mars
« Reply #95 on: 03/11/2017 07:53 PM »
Do we need methane to produce ammonia by the Haber process for plant fertilizer, or is there a more direct way?

Fish

Fish don't produce nitrates from nitrogen. They produce it from proteins in their food. So not a source. They can help keep it in circulation.
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