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Post by jageriv on Oct 25, 2016 5:00:07 GMT
I get the impression from the backstory and base designs that Methane seems to be the backbone of the interplanetary economy, the fuel(well, I guess the fuel is uranium, so reaction mass? I think?) that makes most of the travel possible.
My question then, where does all the thousands or possibly millions of tons of methane necessary come from? From my understanding, Methane on earth is primarily a byproduct of biological processes. Off of earth though, is there any major sources of Methane besides Titian, which I understand has lakes of the stuff? Or does most of the methane have to actually be manufactured in general, which would seem to suggest it might be much more expensive to use than a more commonly available element/molecule, like water.
This is just me thinking on the economics of the universe in question.
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Post by shiolle on Oct 25, 2016 9:27:58 GMT
Methane can be produced from CO2 and hydrogen by Sabatier process. Hydrogen in turn can be acquired from water, which is one of the most common substances in the Solar System. One of the missions also features a methane depot skimming the atmosphere of Neptune to gather methane.
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Post by zuthal on Oct 25, 2016 11:43:50 GMT
The atmospheres of Uranus, Neptune and Titan all contain significant amounts of methane (2.3%, 1.5% and 1.6%, respectively). That is why in On the Surface of Giants, the propellant depot is in such a close orbit - it is skimming methane from the atmosphere. And the methane is relatively easy to distill out of the atmospheric gases that are collected, as it boils quite a bit higher than nitrogen, hydrogen and helium, and quite a bit lower than ammonia.
And you are right in your terminology, the stuff you toss out the back is propellant or reaction mass (or remass for short), the fuel is what gives the propellant the energy. Propellant and fuel are the same only for combustion rockets.
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Post by Dhan on Oct 25, 2016 17:02:20 GMT
Each ship is equipped with a few cows for constant in-situ methane production.
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Post by wafflestoo on Oct 25, 2016 17:03:44 GMT
Who needs cows when you have the pantries stocked with pork-n-beans.
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Post by jageriv on Oct 25, 2016 18:34:35 GMT
Methane can be produced from CO2 and hydrogen by Sabatier process. Hydrogen in turn can be acquired from water, which is one of the most common substances in the Solar System. One of the missions also features a methane depot skimming the atmosphere of Neptune to gather methane. Huh, looking at the process, it doesn't look like it actually uses all that much energy to make. Then again, it seems to require having hydrogen, which if you have to make it from water could be expensive. Then again, the closest thing I see to an energy cost on the page is -165 kJ/mol, and I have no idea if that is a lot of energy or not. Hm, maybe someone could answer this: our country in game seems based off Mars. It would thus make a lot of sense to have at least some native Mars based methane production. I would think this would require using the Sabatier process. So the question then would be, what all is necessary to make methane on Mars (assuming there's no large deposits of it that can be mined, which might be the case for all I know). This is what I'm able to figure out so far: 1) raw materials of CO2 plus Water. 2) Water is broken down as a source of Hydrogen. This requires some process of which I don't know the other chemical or energy needs. So the needs of this process would be the first thing you would need to know. This is of course assuming water is the best source of Hydrogen on Mars. If there's a better way to get Hydrogen, that would be good to know. 3) The Sabatier process combines that Hydrogen (wherever it comes from) with the CO2. The only major unknown for me at this point is energy requirements if any and possibly if the catalyst gets used up in this process at all. This should help generate a good idea of the inputs for Martian Methane production, and thus an idea of costs.
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Post by shiolle on Oct 25, 2016 21:01:39 GMT
Water is separated into hydrogen and oxygen via electrolysis of course. The reaction itself requires 285.83 kJ per mole of water. One mole of water produces one mole of hydrogen and a half mole of oxygen. A mole of hydrogen weighs 1.01g (see this calculator), which means that a you need at least 1000 * 285.83 / 1.01 = 283 MJ per kilogram of hydrogen thus produced. However, if your water is not 100% pure H2O there will be side reactions which will make your efficiency suffer. Additionally, you need to expend some energy to separate the gases, which depends on the method of separation, but it appears that this cost may be small compared to the energy for the reaction itself. Sabatier process itself exothermic, i.e. it produces heat, so while you need to heat up the reactor to start the reaction (yes, apparently these devices are called chemical reactors), it will then support itself. In practice the reaction also needs a catalyst and it seems that different catalysts can change Sabatier reaction efficiency though I'm not clear on how that affects energy requirements. The whole process in relation to methane production on Mars is described in this article. If you are wondering why is the delta H for electrolysis in this article is twice as large as what I cited previously, this is, as far as I understand, due to the fact they are talking about a chain of reactions, so that value is for two moles of water instead of one.
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Post by RA2lover on Oct 25, 2016 23:23:25 GMT
Each ship is equipped with a few cows for constant in-situ methane production. Have they perfected spherical cow technology?
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Post by cuddlefish on Oct 25, 2016 23:58:49 GMT
Each ship is equipped with a few cows for constant in-situ methane production. Have they perfected spherical cow technology? Yes, but you have to keep them in a vacuum.
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Post by coaxjack on Oct 26, 2016 0:38:15 GMT
/!\ Module Bovine Bioreactor is uncooled, and will be unusable.
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Post by nerd1000 on Oct 26, 2016 2:07:55 GMT
/!\ Module Bovine Bioreactor is unmilked, and will be unusable. FTFY.
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Post by coaxjack on Oct 26, 2016 2:21:36 GMT
Fresh milk on a tour of duty where you presumably live on dehydrated rations sounds pretty nice.
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Post by jageriv on Oct 26, 2016 4:28:36 GMT
So, under an ideal circumstances,
1 mole of water makes 1 mole of H2 for 285 kj. The sabatier process actually needs 4 moles of H2 per mole of CO2, so about a total of 1.14 MJ.
You then mix those 4 moles of H2 plus a mole of CO2 for 1 mole of Methane plus about 165 kj of energy, which might partially be able to offset energy costs, but probably not all that much.
So, 1 kg of Methane would be (1,000/16) 62.5 moles, which would require (62.5x4)=250 moles of H2, or close to 500 grams. But, as your link shows, that's inefficient since your actually making two water molecules for every methane molecule. By reusing the water molucules, you can reduce your need to two H2 per methane. Thus, you would only need 125 moles of H2 per Kg of Methane, about 250 grams of H2.
So, assuming you had a source of H2 available, you could make 1 kg of methane on mars using 500 g of H2 and require basically no energy, or make 1 kg out of 250g of H2 if you were willing to spend some 318 kj per mole of methane, or about 2 MJ of energy per kg. This is if you have H2 already available. If you need to produce H2 initially from water, that would seem to add some 3.6 MJ per kg if your reusing the water generated.
So, from scratch, it looks like you would need about 6 MJ of energy to make 1 kg of methane. Lets round up, somewhat arbitrarily, to 10 MJ in actual practice.
So, if you had a 4 GWatt powerplant dedicated solely to making Methane, it could theoretically make 400 kg a second. Over a day, that would be 35,000 tonnes a day at full output.
Now, the next question would be, how much production do you need?
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Post by zuthal on Oct 26, 2016 5:43:33 GMT
Have they perfected spherical cow technology? Yes, but you have to keep them in a vacuum. Don't forget to keep it frictionless, too!
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Post by cuddlefish on Oct 26, 2016 5:54:00 GMT
Yes, but you have to keep them in a vacuum. Don't forget to keep it frictionless, too! Well, the PTFE is on the materials list for a reason.
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