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SpaceX is currently dealing with a lot of environmental regulation issues with Starship. One issue they have is the amount of CO2 Starship produces. Their falcon 9 produces 440 tons of CO2 each flight, Starship will produce even more.

One solution to that problem would be to collect the methane needed as a fuel from the atmosphere. Since 1 kg of methane traps much more heat than 1 kg of CO2, it would actually help the environment if they used the methane from the air. Currently they probably get the methane they use as fuel from Natural gas and then that releases new CO2 into the atmosphere. When burning the methane already in the atmosphere and turning it into CO2, it would help decrease the greenhouse gases instead of increasing them.

When SpaceX flies to Mars, they will want to refuel their Starship rocket, so using the technology to capture methane in the air and use it as fuel would help with future missions to Mars too.

My question: What would it take to collect the methane in the air and use it as rocket fuel?

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    $\begingroup$ Since there are less than 2 ppm Methane in earths atmosphere, it would be more likely to collect CO2 (~400 ppm) and Water and process it to Methane. $\endgroup$
    – CallMeTom
    Sep 6 at 11:09
  • $\begingroup$ @CallMeTom that is also a cool idea $\endgroup$
    – The Rocket fan
    Sep 6 at 11:09
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    $\begingroup$ Also: Much the same reason that we don't get methane that way at surface level - the amount of power required is "excessive" $\endgroup$
    – MikeB
    Sep 6 at 12:12
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    $\begingroup$ @MikeB even though the power level might be "excessive" the question is asking what would it take to do so. $\endgroup$
    – The Rocket fan
    Sep 6 at 12:14
  • $\begingroup$ Aside from the fact that all of orbital launch taken together accounts for a negligible fraction of CO2 emissions: Starship eliminates solid boosters and heavy hydrocarbon fuels, and recovers all hardware for reuse instead of disposing of it in the ocean after a single flight, making it vastly more environmentally friendly than competing vehicles. The notion that it's somehow worse environmentally is FUD. And there is no significant methane to capture in the atmosphere of Mars. ISRU plans involve producing it from CO2 and water, not extracting it. $\endgroup$
    – Christopher James Huff
    Sep 7 at 17:15

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Filtering low concentration things out of any solvent is always very difficult: you need to find something that binds to the target, but only the target.

Meanwhile there are huge amounts of methane pouring into the atmosphere while you're trying to use a thimble to drain a bucket. A far more reasonable approach would be to invest in anti-leak work. Even across thousands of miles of pipeline this is cheaper than trying to remove a low concentration substance from the air.

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  • $\begingroup$ Even if the methane pipelines had no leaks and SpaceX used that methane, it would be still be releasing CO2 into the atmosphere. If one used methane already in the atmosphere, then it wouldn’t increase the greenhouse gases already present $\endgroup$
    – The Rocket fan
    Sep 7 at 15:43
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Energy. Air liquefaction requires a lot of energy. As noted in the comment by @CallMeTom to collect enough methane you have to liquefy huge amounts of air just to get some methane. However air liquefaction is a business with a lot of activity because it can separate all the gases it contains and all of them have a commercial value. Therefore if you consider air liquefaction for the purpose of extracting and selling all the other gases you could get methane as a byproduct. It would be expensive, for the moment the industry, to get the gases they need, prefers processes that are cheaper, but more polluting. Anyway, technically what you say is doable, but there are still economic and political hurdles.

If you want to do this in a carbon neutral manner you need to put a plant where there is a lot of renewable energy. There are not many places availble. For example you could put a plant in Patagonia powered by wind turbines. Or another remote area where the available renewables were never exploited for one reason or the other.

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    $\begingroup$ Although this question asked about quantity of gas production, it might be worthwhile to investigate how much waste heat would be produced per kg of methane extracted from the atmosphere. I have no data, but suspect it is probably equivalent to years or decades' worth of trapped heat if that gas was left in the atmosphere. $\endgroup$
    – Infinite_Maelstrom
    Sep 6 at 21:14
  • $\begingroup$ With its 1-2 parts-per-million concentration, the most energy efficient way to extract the methane from the atmosphere might actually be to catalytically oxidize it, extract the CO2 and water by adsorption or chemical reactions, and use them to re-form the methane. $\endgroup$
    – Christopher James Huff
    Sep 7 at 1:59
  • $\begingroup$ @Christopher James Huff It seems that my post was not very clear. I will rewrite it. $\endgroup$
    – FluidCode
    Sep 7 at 16:17

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