Apollo - Soyuz Test Project
Discussion
Russian spacecraft used a normal air mixture of oxygen and nitrogen.
The Apollo spacecraft used a pure oxygen atmosphere only.
That is why there had to be a fairly large docking adapter between the two vehicles. As well as providing a common interface between the two very different docking systems used by Soyuz and Apollo, it served as an acclimatisation chamber where the crews could pre-breath as they moved from one spacecraft to the other.
The main issue was transferring from Soyuz to Apollo. Because the Soyuz atmosphere contained nitrogen, a straight transfer into the lower pressure pure oxygen atmosphere of the Apollo spacecraft could have resulted in a case of the bends.
Moving from Apollo to Soyuz was not such a problem.
The Apollo spacecraft used a pure oxygen atmosphere only.
That is why there had to be a fairly large docking adapter between the two vehicles. As well as providing a common interface between the two very different docking systems used by Soyuz and Apollo, it served as an acclimatisation chamber where the crews could pre-breath as they moved from one spacecraft to the other.
The main issue was transferring from Soyuz to Apollo. Because the Soyuz atmosphere contained nitrogen, a straight transfer into the lower pressure pure oxygen atmosphere of the Apollo spacecraft could have resulted in a case of the bends.
Moving from Apollo to Soyuz was not such a problem.
Although the Space Shuttle and the ISS also used/use a normal air mixture (like Soyuz still does), the change from air to pure oxygen is still an issue - namely when someone needs to perform an EVA.
Spacesuits still use pure oxygen systems. Before an astronaut performs a spacewalk, they need to purge any nitrogen from their blood. This involves pre-breathing oxygen for a while before donning the spacesuit. The ratio between nitrogen and oxygen in the ISS is also amended before a spacewalk to allow the transition to happen more speedily.
Spacesuits still use pure oxygen systems. Before an astronaut performs a spacewalk, they need to purge any nitrogen from their blood. This involves pre-breathing oxygen for a while before donning the spacesuit. The ratio between nitrogen and oxygen in the ISS is also amended before a spacewalk to allow the transition to happen more speedily.
Edited by Eric Mc on Thursday 16th July 13:44
With a pure oxygen atmosphere the pressure has to be kept much lower - otherwise you will cause brain damage to the occupant and/or create an extreme fire risk.
The Apollo 1 fire of 1967 happened not because the atmosphere in the cabin was pure oxygen. It was because the atmosphere in the cabin was pure oxygen at 14 psi. In space, the normal pressure in the Apollo spacecraft (and in Mercury, Gemini and even Skylab) was only 5 psi.
The suits still operate at these low pressures for much the same reasons - as well as the fact that a suit pumped up to 14 psi would become far too rigid and ballooned up to be usable.
The Apollo 1 fire of 1967 happened not because the atmosphere in the cabin was pure oxygen. It was because the atmosphere in the cabin was pure oxygen at 14 psi. In space, the normal pressure in the Apollo spacecraft (and in Mercury, Gemini and even Skylab) was only 5 psi.
The suits still operate at these low pressures for much the same reasons - as well as the fact that a suit pumped up to 14 psi would become far too rigid and ballooned up to be usable.
Obviously, Deke was selected as part of the Mercury selection process but he was an astronaut throughout the Mercury, Gemini and Apollo missions. He just happened to be a grounded astronaut. He was head of crew selection for all that period so was intimately involved in all three projects and took part in crew training throughout.
He never gave up the expectation that one day he would get a flight.
He never gave up the expectation that one day he would get a flight.
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