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For space travel: would you need to recreate earths air composition? Or could you just get by with the top 2 or 3 main components, i.e. either 78% nitrogen and 22% oxygen, or 78% nitrogen, 21% oxygen and 1% carbon dioxide?

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  • $\begingroup$ Yes. Top 2 for humans, Top 3 If you want to grow plants. $\endgroup$ – Joe Kissling May 18 '17 at 5:11
  • $\begingroup$ Although not bad per se, this q does not require creativity and is just asking for information that is easily found already posted elsewhere. It’s not quite the level of www.lmgtfy.com, but close enough to draw admonishment. $\endgroup$ – JDługosz May 18 '17 at 6:37
  • $\begingroup$ I'm pretty sure something similar was asked already. Can't v find it now... $\endgroup$ – Mołot May 18 '17 at 6:57
  • $\begingroup$ The Apollo expeditions to the Moon used 0.2 atm pure oxygen. Nitrogen is not needed by humans, and they reasoned that carrying around a useless gas was not worth it; this increased the risk of fire, of course. $\endgroup$ – AlexP May 18 '17 at 8:43
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    $\begingroup$ You do know that space travel exists in reality and you could check out what they use? This is a problem about which you will find a lot of information online. $\endgroup$ – Raditz_35 May 18 '17 at 12:00
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In principle it is sufficient to ensure the partial pressure of Oxygen we have at sea level on Earth. Therefore roughly 0.2 atm of O2 would be enough.

Further dilution in inert gases like Nitrogen is preferred to prevent risks related to a pure oxygen atmosphere, but again what matters is the Oxygen partial pressure. So one could also live with a 0.7 atm pressure, given by 0.5 atm N2 and 0.2 atm O2.

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    $\begingroup$ thanks for accepting the answer, however if you had waited at least 24 hours you could have received more answers. The pool of users here is spread allround the world, and most of them is not logged 24/7. $\endgroup$ – L.Dutch May 18 '17 at 5:25
  • $\begingroup$ ill keep that in mind the next time i come round here, its just from other resources i was looking through i was coming across roughly the same answer as you gave me, and with 5 or 6 different places saying roughly the same point i figured that was goid enough, is just for a game of dnd/ space marines, not like im writing an essay on space travel, but none of the sources specifically said if any of the smaller amounts played a part with some small function somewhere( sorry if issues typing on phone and enter is right next to backspace) $\endgroup$ – kev May 18 '17 at 5:31
  • $\begingroup$ 0,2atm oxygen isn't a hard requirement. At some point earth's atmosphere contained 35% oxygen and life did just fine, though gas exchanged organs were usually smaller in these creatures than is now considered to be the norm. (Source en.wikipedia.org/wiki/Geological_history_of_oxygen ) $\endgroup$ – Hyfnae May 18 '17 at 11:44
  • $\begingroup$ For space travel, you will not need sea level of oxygen. The level you have in a normal jet airliner will definitely suffice. $\endgroup$ – user2707001 May 21 '17 at 11:44
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There's a wide range of potential atmospheres that could be used.

  • The ISS uses a mix of oxygen and nitrogen at around 1 atmosphere (14 psi), recreating the air at sea level reasonably well.

  • The Apollo program flights used pure oxygen to save weight, at much lower pressure than a standard atmosphere (5 psi).

Anything between those extremes would work just fine. You could also mix in other inert gases, like argon or krypton, if you had the need, though you'd have to be careful.

Which option you choose depends on a lot of factors. If you have powerful engines and aren't too worried about weight, re-creating Earth's atmosphere would be ideal, since the nitrogen dilution reduces flammability. If you're trying to save weight, pure oxygen will do, but you need to be worried about fire.

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You basically need oxygen to breathe. Everything else is not strictly necessary. The limits you are willing to take depend on how much of a mountaineer and how much of a diver you are.

These two articles explain the upper and lower limits for oxygen partial pressure for humans: https://en.wikipedia.org/wiki/High-altitude_adaptation_in_humans https://en.wikipedia.org/wiki/Maximum_operating_depth

Where the Tibetan highlanders live, the oxygen level is only about 60% of that at sea level. Most people will tolerate this level as a minimum, so you will have ~100mbar/10kpa of pure oxygen as a "minimum atmosphere". Breathing pure oxygen works well, as every tech diver will tell you. Still, everything that's not wet or otherwise inflammable will burn VERY easily, so that's why this is not a great atmosphere for space travel. Put something in to dilute it - like Nitrogen or Argon e.g.

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