How do space stations keep the air breathable?
In: Engineering
They use an ILPE (Integrated low level electrolizer) to split hydrogen and oxygen apart from water (2 hydrogen 1 Oxygen in H2O). To clean co2, which is a byproduct of breathing, they use a scrubber. It basically uses MEA (a chemical) that absorbs CO2 from the air. Finally they have backup oxygen candles, which when burnt create oxygen chemically, as a backup and lithium hopcalite as a backup to the scrubbers, which is a byproduct of running the scrubbers.
They have filters to take out excessive co2 from the air. Oxygen is replenished by bringing it from Earth, or is made from water (which is also brought in from Earth).
The ISS, for example, has a number of systems to do this:
– It has a system which removes carbon dioxide and other contaminants from the air.
– They electrolyze water, splitting it apart, to generate oxygen (and hydrogen).
– Oxygen can also be manually supplied to the station via tanks.
This process is called “Air revitalisation” and it consists primarily of two processes: removing Carbon Dioxide (CO2) and adding back in Oxygen O2.
On the ISS, O2 is added back in by using Electrolysis which uses Electricity to turn water into Hydrogen and O2, the water is supply has to be regularly refilled during resupply Missions.
Removing CO2 can be done in a lot of different ways, the simplest which was used on Apollo and the Space Shuttle, was Lithium Hydroxide (LiOH), which is a chemical that absorbs CO2 from the air, but this is a single use system. Once the LiOH is fully saturated, you need to replace the canister.
The method the ISS primarily uses is molecular sieves. This system works similar to LiOH, except it’s not single use, and if you expose the molecular sieve to a vacuum, the CO2 is pulled out, and you can reuse the sieve again. These systems always have two beds, one that is absorbing CO2 and one that is desorbing it, once the first is full, they switch, that way you constantly have CO2 removal.
Now a problems with venting the CO2 to the vacuum of space is that you lose the O2 that is part of it, so to recover that there’s been some new technologies that are being tested. On the ISS they have started using a Sabatier reactor. This is a device that runs a chemical process turning CO2 and Hydrogen gas (H2) into water (H2O) and Methane (CH4), you can then use the water in the ISS’ Electrolysis set up to recover the oxygen.
And a very new technology that is currently being tested on the new Mars Rover is called Solid Oxide Electrolysis, this system works like water electrolysis, using electric power to split CO2 into CO and O2, allowing you to recover some of the oxygen in CO2
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