Carbon Dioxide RCS

[Misguided Kerbal]

Is Carbon Dioxide RCS feasible? For example, all the CO2 exhaled by the crew could go to a tank and be used for RCS. What do you guys think?

[mikegarrison]

CO2 as a cold gas is probably feasible, although nitrogen is really nice because it's inert and it's easily obtained from the ambient Earth atmosphere.

But extracting CO2 in-situ from crew breath is likely not feasible.

[cubinator]

It certainly can be done (and is used in some cases). It might be a good option on Mars because there's lots of it floating around. As for crew breath, I don't think there's enough of that to fill a meaningful pressure tank - it would be recycled into breathing oxygen and drinking water.

[mikegarrison]

13 minutes ago, cubinator said:

It might be a good option on Mars because there's lots of it floating around.

Only relative to other gasses. In absolute terms....

[Nightside]

Why bother with harvesting CO2 when humans produce more volatile stuff already?

[sevenperforce]

1 hour ago, Misguided_Kerbal said:

Is Carbon Dioxide RCS feasible? For example, all the CO2 exhaled by the crew could go to a tank and be used for RCS. What do you guys think?

You probably know this but humans only exhale trace CO2. We mostly exhale nitrogen and oxygen.

[wafflemoder]

For RCS, like most forms of propulsion, the molar mass of the exhaust gases has a very important role in determining specific impulse. Generally speaking, gasses with lower molar masses will give greater specific impulses when used as a reaction mass.

CO2 has a molar mass of 44 g/mol, compared to O2 (32g/mol), N2 (28g/mol), H2O, (18g/mol), and H2 (4g/mol).

Considering that O2 and/or N2 would be far more abundant than CO2 in crewed vehicles, using CO2 instead of straight air would not only be more difficult, but would also be less effective and have a much more limited supply.

If power is abundant, than it may be feasible to electrolyze the CO2 into CO and O2, and use them as a bipropellant mixture. This is actually one of the proposed ISRU pathways for a mars mission, because CO2 is so abundant on Mars (24 terratons in the atmosphere, twice that in the polar ice caps, and many times more in carbonate minerals in the regolith)

[DDE]

12 hours ago, Misguided_Kerbal said:

Is Carbon Dioxide RCS feasible?

Oh yee of little faith

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