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this post was submitted on 10 May 2024
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100% oxygen in the suits would cause them to spontaneously combust.
But ok. Whatever.
Pretty much all modern EVA suits (like the ones used by US, China, Russia) run a pure oxygen at about .20 ATM so that the internal pressure is lower but the amount of oxygen the astronaut is breathing is the same density of oxygen as at 1 ATM. This allows much better maneuverability in the space suit, because any air mixture at 1 ATM makes it nearly immediately to move in a space suit (they become too stiff).
Point is, we have been doing spacewalks like this since spacewalks started and no one has spontaneously combusted on one.
Ok fair enough. My dilettante knowledge of chemistry let me down.
A little bit of knowledge is a dangerous thing, unlike pure oxygen at only a little bit of pressure.
That’s what they said in the interview. And didn’t Apollo also had a pure oxygen environment? As long as there isn’t a spark it wouldn’t combust, right?
Even the command module was pure oxygen at 5 psi. There was the Apollo 1 fire, but otherwise I don't remember that there were any major issues.
The pressure in the Apollo 1 capsule was 16.7 PSI or 1.14 atmospheres of pure oxygen. That's almost 5.5 times the partial pressure of oxygen at sea level. At 5 PSI, the Polaris crew will only be at 1.6 times the partial pressure of oxygen at sea level.
You're right, the Apollo 1 was significantly higher pressure. Didn't know that. 😲 Makes somewhat more sense they could keep a pure oxygen atmosphere even after the accident.
Also, calculating partial pressures in psi is really annoying.
kPa and Bar are obviously superior units!
With 100% oxygen you will be fine down to 4 psi or so. Mixed gas would need substantially higher pressure and that would likely make those suits too stiff to move.
100% oxygen doesn’t cause humans to spontaneously combust. It does make them more flammable, but that’s already controlled for in spaceflight.