Within a space vessel such as the ISS for example, how do the astronauts regulate the level of CO₂ they are breathing and how is the air scrubbed exactly?
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The US side of ISS uses a cyclic machine called the Carbon Dioxide Removal Apparatus (CDRA) to absorb CO2 from the air and then vent it to space.
You can read about the cycles of the CDRA in this answer and its linked references.
Older spacecraft used lithium hydroxide (LiOH) canisters, which were a disposable item, and therefore more problematic for the ISS.
US spacesuits used to use LiOH as well, but in recent years have turned to a regenerable metal oxide (Metox) system. This answer has links to more info about Metox.
answered Nov 8, 2020 at 22:06
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$\begingroup$ I know ISS has used both amine and Sabatier processes to perform the CO2 removal. I don't know what process CDRA uses though. $\endgroup$– TristanCommented Nov 9, 2020 at 15:47
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$\begingroup$ @Tristan at least when I last worked there in 2014 the CDRA used zeolite beds. The Sabatier system used CO2 removed by the CDRA (along with H2 from another source) to create water. I believe the Sabatier has since been removed, but I don't have ready access to current info. space.stackexchange.com/q/44225/6944 ISTR the shuttle regenerative CO2 removal system used amine beds. $\endgroup$ Commented Nov 9, 2020 at 15:58