I just re-read the book The Martian, and a question came to mind:
Why did the Ares missions use a 1 atm nitrogen-oxygen atmosphere instead of a lower pressure pure oxygen one?
AFAIK, pure oxygen is harmful to humans only when the partial pressure is higher than that on Earth. In fact, many real world space missions (including Apollo) used low pressure pure oxygen.
It would have several benefits:
- less gas to carry around
- less strong pressure vessels required
- less complex Atmospheric Regulator (it would only need to cool the air to the freezing point of CO2, which is much higher than the melting point of oxygen)
- the EVA suits would be more flexible (high pressures "inflate" the EVA suit, which makes the hand and arm joints more stiff and thus harder to work in)
- faster airlock operation (less air to remove)
I understand why this was chosen by the author, as several plot elements hinge on having a mixed N2-O2 atmosphere. Is there any explanation or justification for why NASA made this decision in the story?