As I understand it Apollo 13 had plenty of oxygen for the crew members but the CO[sub]2[/sub] scrubbers in the Lunar module didn’t have enough endurance to last the entire trip, hence requiring them to make the adapter for the scrubbers from the command module.
Hypothetically speaking, if that wasn’t an option, would it have been possible to evacuate the Lunar module to get rid of the CO[sub]2[/sub] when it gets too high and refill it with O[sub]2[/sub] from the tanks? I read somewhere that the atmosphere in Apollo was pure O[sub]2[/sub] at low pressure to begin with so that part at least shouldn’t pose a problem.
In theory that should work. The lunar module was designed to be decompressed, since it didn’t have an airlock and needed to decompress in order for the astronauts to exit onto the lunar surface. In practice, it would have taken a lot of oxygen to then depressurize the module. I don’t know how often they’d have to do this, or if they’d have enough oxygen to re-pressurize it enough times.
Good point. How quickly would carbon dioxide build up in the Lunar module? I found a reference that says an adult exhales about 1 kg of CO[sub]2[/sub] per day. I couldn’t find info on the capacity of the scrubbers in the LM but this site says that they were short by at least 48 hours.
The cockpit volume for the Lunar module is 6.7 m[sup]3[/sub], according to wiki. If I’m reading this right the atmosphere pressure in the LM cabin during orbit would have been around 3.5 psi of oxygen.
Given the reduced atmospheric pressure, how would CO[sub]2[/sub] toxicity work, exactly? Is it based on partial pressure or just percentage of gas? How often would they have to replace the air?
Hazardous gas levels for occupational situations are almost always given in % or ppm, as here, but this assumes standard atmospheric pressure. Gas exchange in the lungs is driven by absolute partial pressures of the particular gases involved; afterall, this is why the astronauts were able to survive in a reduced-pressure environment, as long as the absolute partial pressure of the O2 was high enough.
Not clear to me whether the percentages on that site are by volume or mass. If by volume, then take the percentage there and multiply by 14.7 psi to determine the absolute partial pressure needed in the spacecraft to achieve the same toxic effect.