Was the internal atmosphere of Mercury capsule and CSMs of Apollo missions filled with pure oxygen at low pressure, and was the ambiance controlled to match closely to that on earth (e.g. humidity, temp. etc), during their flights? If yes, why did the astronauts wear their suits while inside the capsule/CSMs?
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1$\begingroup$ Related: space.stackexchange.com/q/42092/6944 $\endgroup$– Organic MarbleCommented Feb 27, 2021 at 13:39
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1$\begingroup$ Related: space.stackexchange.com/q/25690/6944 $\endgroup$– Organic MarbleCommented Feb 27, 2021 at 13:40
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2$\begingroup$ Answering the second question only, redundancy is crucial for safety. If anything happened to puncture the hull, whatever atmosphere there was would quickly escape into space, leaving the astronauts in vacuum. They wore suits so that those would also have to be punctured before their air supply was destroyed. $\endgroup$– Ryan CCommented Feb 27, 2021 at 14:55
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1$\begingroup$ By Apollo, suits were only worn during dangerous procedures (liftoff, docking, EDL, etc) $\endgroup$– ikraseCommented Mar 1, 2021 at 1:43
1 Answer
The Apollo astronauts only wore their suits for a short time after launch. After they left the Earth orbit, they doffed the space suits.
When the two astronauts prepared for Moon landing, they donned space suits again.
Space suits were worn inside the CM and the LM only during critical intervals of the flight. If the capsule gets a hole, the astronauts continue breathing in their suits.
Of course the cabin and the suit atmosphere used both pure oxygen at the same low pressure. Temperature and humidity were controlled, both the cabin and the suit atmosphere.
After returning from the Moon surface, the astronauts repressurized the LM and removed their helmets to be able to eat and drink. The helmet could be removed and replaced much faster than the full suit.
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1$\begingroup$ To don a suit of clothes means, to put it on--to wear it. Is that what you meant when you said, "they donned the space suits?" $\endgroup$ Commented Feb 28, 2021 at 21:17
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$\begingroup$ @SolomonSlow Thanks for finding the wrong 'donned'. $\endgroup$– UweCommented Feb 28, 2021 at 21:27