3 ms·

They say oxygen with 98% purity. What's the other 2%?

ComputerGuru 3y ago
I’m guessing CO2 that didn’t undergo conversion? Or the non-CO2 gases (comprising ~5% of the Martian atmosphere) that made it into the system and thus weren’t affected? Or the CO byproduct that wasn’t expelled separately? Edit: thinking about the numbers some, I think non-CO2 (Martian!) atmospheric gases is a good guess for the bulk because they’re 5% of the atmosphere and the conversion input is two CO2 for one O2 out, so at the 2:1 ratio with 0.95 of the input converted you end up with 98.96% converted to either O2 or CO, and the rest is whatever else you had mixed in there, if I did the math right. Depending on how the O2 and CO are separated, the non-CO2 gases not affected by the conversion/reaction could plausibly end up all with the O2, all with the CO, or some mix of the two (probably by weight?). Add in a few ppm of CO2 that slipped through the process unconverted and Bob’s your uncle. Maybe.
- marcosdumay 3y ago
  Hum... If you don't expel the CO separately, you will very soon get all of your CO2 back and have no CO.
  - ComputerGuru 3y ago
    Obviously the bulk of it is expelled separately - I’m just saying it could be an imperfect process.
marcosdumay 3y ago
Probably CO2, as it's the main gas in the atmosphere there. The wikipedia page on the mission has more information, including that they managed to get up to 99.6% purity. That later number makes the resulting atmosphere not toxic anymore (assuming the impurity is CO2). But it still doesn't specify the impurity.
- ComputerGuru 3y ago
  I came to a different conclusion (see sibling comment to yours) in part because I don’t believe the 98% O2 solution was toxic (and it would be if the other 2% were CO2, no?). I don’t have hard evidence for that belief, but I just expect that if it were toxic it would have been mentioned and NASA wouldn’t have been celebrating. (My guess was non-CO2 atmospheric gases.)
  - marcosdumay 3y ago
    AFAIK, a 2% CO2 concentration is just toxic enough to cause long term health issues, and people can deal with it for months without a lot of problems. (And that's at sea level pressure, at a 0.3 atm O2-only atmosphere, I have no idea.) NASA may quite well consider it livable. I have no idea what kinds of missions they have in mind. (But there are some low confidence studies claiming it makes people stupid.) Anyway, the wikipedia page's language implies the CO2 is purified before going into the Moxie. And from what I can tell, you can't reach even 94% purity without that step, so I assume it's there.

I’m guessing CO2 that didn’t undergo conversion? Or the non-CO2 gases (comprising ~5% of the Martian atmosphere) that made it into the system and thus weren’t affected? Or the CO byproduct that wasn’t expelled separately? Edit: thinking about the numbers some, I think non-CO2 (Martian!) atmospheric gases is a good guess for the bulk because they’re 5% of the atmosphere and the conversion input is two CO2 for one O2 out, so at the 2:1 ratio with 0.95 of the input converted you end up with 98.96% converted to either O2 or CO, and the rest is whatever else you had mixed in there, if I did the math right. Depending on how the O2 and CO are separated, the non-CO2 gases not affected by the conversion/reaction could plausibly end up all with the O2, all with the CO, or some mix of the two (probably by weight?). Add in a few ppm of CO2 that slipped through the process unconverted and Bob’s your uncle. Maybe.

marcosdumay 3y ago
Hum... If you don't expel the CO separately, you will very soon get all of your CO2 back and have no CO.
- ComputerGuru 3y ago
  Obviously the bulk of it is expelled separately - I’m just saying it could be an imperfect process.

marcosdumay 3y ago

Probably CO2, as it's the main gas in the atmosphere there. The wikipedia page on the mission has more information, including that they managed to get up to 99.6% purity. That later number makes the resulting atmosphere not toxic anymore (assuming the impurity is CO2). But it still doesn't specify the impurity.

ComputerGuru 3y ago
I came to a different conclusion (see sibling comment to yours) in part because I don’t believe the 98% O2 solution was toxic (and it would be if the other 2% were CO2, no?). I don’t have hard evidence for that belief, but I just expect that if it were toxic it would have been mentioned and NASA wouldn’t have been celebrating. (My guess was non-CO2 atmospheric gases.)
- marcosdumay 3y ago
  AFAIK, a 2% CO2 concentration is just toxic enough to cause long term health issues, and people can deal with it for months without a lot of problems. (And that's at sea level pressure, at a 0.3 atm O2-only atmosphere, I have no idea.) NASA may quite well consider it livable. I have no idea what kinds of missions they have in mind. (But there are some low confidence studies claiming it makes people stupid.) Anyway, the wikipedia page's language implies the CO2 is purified before going into the Moxie. And from what I can tell, you can't reach even 94% purity without that step, so I assume it's there.