fresh_42 said:Has anyone references whether they really run the station on 1 atm?
I meant it as an interesting question, rather than a criticism. I guess they also lose a bit of pressure while outside missions or during docking maneuvers. As pressure might cause material fatigue it would be interesting to know what medical needs require - or what pressure the MIR had. E.g. on the ASTP mission 1975 there was a difference (Wikipedia):Cutter Ketch said:Ah, yes. Forgot about that. A quick Google search indicates they do actually pressurize to 1 atmosphere, but, that didn’t have to be the case. Actually, why do they? Important for long duration?
As the atmosphere aboard the Apollo pure oxygen was used with a pressure of 34% of the Earth's atmosphere. On board the Soyuz, on the other hand, normal air (nitrogen-oxygen mixture) was breathed under normal pressure.
The cabin is pressurized to 14.7 psia, plus or minus 0.2 psia, and maintained at an average 80-percent nitrogen and 20-percent oxygen mixture by the air revitalization system. Oxygen partial pressure is maintained between 2.95 and 3.45 psi, with sufficient nitrogen pressure of 11.5 psia added to achieve the cabin total pressure of 14.7 psia, plus or minus 0.2 psia.
Steelwolf said:The All Oxy Atmosphere, aside from EVA in suits, was discontinued after the Apollo 1 fire on the ground, with Chaffee, White and Grissom. Since then it has been mixed gas due to the extreme fire hazard of the electronics and avionics packages.
This doesn't quite match up withSteelwolf said:The All Oxy Atmosphere, aside from EVA in suits, was discontinued after the Apollo 1 fire on the ground, with Chaffee, White and Grissom. Since then it has been mixed gas due to the extreme fire hazard of the electronics and avionics packages.
anorlunda said:It is true that radiation from the solar wind would be harmful to life as we know it. But non-carbon based life forms have been discussed many times on past PF threads. Lacking details, its hard to say how sensitive they might be to radiation.
It is also true that we have life on Earth at the mid-ocean vents so deep in water as to be unaffected by radiation at the surface.
So it comes down to the perpetually elusive problem, Provide an all-inclusive definition of life.
Nugatory said:A bit of a digression, but the Apollo 1 fire has already been mentioned, and it is relevant to the tradeoffs between pressure and composition of atmosphere...
Apollo 1 was designed to operate in space with about 5 psi internal pressure, about what you'd find at the top of the highest mountain peaks. This lowered the required structural strength and hence the weight of the spacecraft , but required an oxygen atmosphere just as mountaineers require oxygen at altitude. (The oxygen atmosphere also simplified preparations for space walks, as the space suits operated on pure oxygen).
However, on the ground the capsule is subject to 14.7 psi external air pressure and cannot be operated with negative internal pressure, so the Apollo 1 test was done at an internal pressure of a bit over 16 psi. 16 psi oxygen is an extraordinarily high fire risk - any random spark can turn anything that will oxidize in air when heated into pyrotechnics, and that's what happened to Apollo 1.
There were several other oxygen atmosphere accidents at about that time and together they led to a consensus that the engineering advantages of pure oxygen atmospheres justified the fire risk only when low pressure and weight was absolutely paramount. And even then much effort goes into eliminating flammable materials around oxygen under pressure.
LURCH said:For that matter, how was the leak in the OP dealt with?
Very likely not too much. However other structures such as the Bigelow inflatable space habitat structures, it's everything.anorlunda said:I wonder. How significant the internal pressure could be to the ISS structural rigidity calculations?