CLJones.Multics@MIT-MULTICS@sri-unix (11/23/82)
A couple of notes on spacecraft atmospheres:
>From the beginning, the Soviet manned spacecraft have used "Earth-like" air--a
mixture of nitrogen and oxygen in roughly the same proportions and delivered
at roughly the same pressure as sea level here. For various reasons, all
American spacecraft used pure oxygen at 5 psi. Among these reasons are the
fact that the nitrogen has to be lifted into space, and our early boosters
just didn't have that kind of excess capacity, and the fact that the plumbing
is more complicated with a two gas system (unless you just deliver compressed
air and vent it overboard, which means you have to carry even more nitrogen).
For EVA, a low pressure is necessary to allow any flexibility in your suit. If
you lower the pressure, you must increase the oxygen content to stay near the
same partial pressure (since EVAs are strenuous, it is actually a good idea to
increase the partial pressure of oxygen). Even the Soviets have their
cosmonauts breathe pure oxygen when outside of the ship.
Skylab was the first US craft to have a mixed gas environment, although I
believe it was 80% oxygen and 20% nitrogen at a reduced pressure (I don't
recall what it was). It was also the first US spacecraft with an air-lock, so
that astronauts could decompress and purge the nitrogen from their blood
before EVAs. The shuttle is the first US spacecraft with an "Earth-like"
atmosphere.
Yes, one of the problems that had to be overcome when Apollo and Soyuz docked
was the atmosphere difference. This was accomplished by having the Soviets
fly with a reduced cabin pressure, and having the US carry a docking module
which was used as a compression/decompression chamber to allow crew members to
pass from one craft to the other.