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According to NASA, roughly "1,000 pounds of methane are produced on International Space Station and dumped overboard as waste gas every year"[1].

It seems like an awful waste to just get rid of it. The Morpheus Project page talks about possibly using the methane as fuel, it's curious that they don't do that already. What is all that methane gas a byproduct of, and why can't it be used for something more productive?

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    $\begingroup$ Belching astronauts? ;-) $\endgroup$
    – gerrit
    Jul 16, 2013 at 22:05
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    $\begingroup$ What productive use do you envision? Burning it would require Oxygen. $\endgroup$
    – hunter2
    Jul 31, 2013 at 10:12
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    $\begingroup$ I have significant doubts as to the veracity of this claim. Every source at nasa.gov for this is worded exactly the same, always from the Morpheus team, and there's never a citation to ISS documentation. I can't find a thing elsewhere nasa.gov that confirms this. NASA did fly a Sabatier process machine to the ISS in 2011, but that appears to have been an experimental rather than operational device. It's easy to transport oxygen (use water). This device would instead require a regular resupply of hydrogen. I don't see hydrogen on any recent manifests but I do see lots of water. $\endgroup$
    – David Hammen
    Sep 5, 2014 at 1:21
  • $\begingroup$ @DavidHammen The hydrogen comes from the OGS (Oxygen Generating System) that splits water into O2 and H2; the CO2 comes from the CDRA. The Sabatier was run (at least when I left in 2014) on a "service contract" approach where NASA paid Ham Standard only for the water they generated from it. It's all part of the fancy Regenerative ECLSS (which breaks down a lot). $\endgroup$
    – Organic Marble
    Oct 11, 2017 at 0:49

2 Answers 2

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The methane is produced as a by-product of the Sabatier Reaction, where Carbon Dioxide is removed from the air using a catalyst and hydrogen.

The other waste product is water, which can then be split into Hydrogen and Oxygen.

So basically, the amount of methane is directly related to the amount of Carbon Dioxide the astronauts breathe out.

As @KeithS commented:

For the second part of the question, "why can't it be used for something more useful," the answer there is that almost anything you'd do with the methane involves combustion, requiring O2 (more than you'd get back from the Sabatier reaction in the first place). Energy is relatively plentiful on the ISS; it's got two tennis-court-sized solar arrays providing virtually all of the ISS's power needs. What's scarce is oxygen, so they retain as much of it as they can

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  • $\begingroup$ If they burned the methane, I'm fairly sure that they would get some or all of the carbon dioxide back. $\endgroup$
    – Emilio M Bumachar
    Mar 7, 2018 at 18:58
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    $\begingroup$ @EmilioMBumachar If they burned the methane as fuel as mentioned in the question, I'm fairly certain they wouldn't be getting much carbon dioxide back. If they are getting it back, I don't think they'll be able to worry about it for very long, because something has gone very, very wrong and the ISS is likely undergoing an immediate unplanned decommissioning. $\endgroup$
    – 8bittree
    Mar 8, 2018 at 15:25
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The methane is produced as a by-product of the Sabatier reaction, where carbon dioxide is removed from the air using a catalyst and hydrogen.

CO2 + 4H2 → CH4 + 2H2O

The molar mass of Methane is 16.0425 (grams per mole) and the molar mass of carbon dioxide is 44.0095 (grams per mole).

That means that the 1000 pounds of methane came from about 2700 pounds of carbon dioxide.

The 2700 pounds of carbon dioxide per year is about 3 people.

The water produced by the Sabatier reaction can be split into hydrogen and oxygen providing about half of the 300 pounds per year of hydrogen that this reaction needs.

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