The Mercury and Gemini spacecraft, and in space the Apollo spacecraft, didn't pressurize their cockpits to 1 atm with Earth-like atmospheric composition; instead, they used pure oxygen at much lower pressure levels. This allowed for lighter spacecraft. Now, since the astronauts were breathing pure oxygen in lower total pressure but actually more oxygen than on Earth, I wonder whether that was noticeable for the astronauts – and if so, what effects did this markedly un-Earthlike atmosphere have on them? Reportedly, more oxygen would make people more happy. Did the astronauts feel happier in the oxygen-rich air, for instance?
Cabin pressures of American spacecraft using pure O2 cabin atmosphere:
- Mercury: 5.5 psi / 0.38 bar
- Gemini: 5.3 psi / 0.37 bar
- Apollo: 5 psi / 0.34 bar