🚀 go-pugleaf

roelle@uars_mag.jhuapl.edu (Curtis Roelle)
>>Suffice it to say that Mercury, Gemini, and Apollo astronauts worked in a
>>5 psi pure O2 environment.  This simplified the environmental control system
>>and eliminated the need to purge N2 prior to EVA.  
> 
>Are you certain that Apollo astronauts breathed pure O2?  I thought that
>after the fatal Apollo 1 fire, which killed astronauts Grissom, White, and
>Chaffee on January 27, 1967, pure O2 was no longer used because it was a
>proven fire hazard.  Or did NASA simply reduce the cabin pressure as
>suggested by Carl Lydick?

    People can withstand a long term pure O2 environment, as long as the
O2 pressure is on the order of the partial pressure of O2 in standard
air. Since oxygen is about 20% of the atmosphere, about 3psi of oxygen
would suffice. Somewhat higher pressure (the 5psi referred to) would be
preferable simply for reasons of sound and temperature conduction. 15psi
of oxygen is manageble for a time but not a good idea for the long run,
due to problems with flammability, and I believe to problems related to
hyperventilating (I could be wrong on the last point). 

    The fatal Apollo fire happened with 15psi oxygen in the cabin during
a ground test. That was an intermediate step leading to 5psi oxygen for
orbital conditions, where the standard atmosphere was flushed. Following
this the flushdown procedure was changed, as well as the Apollo hatch.
The original hatch design sealed under positive pressure and opened
inward: the new design, although heavier, opened owtward and therefore
could be opened under a high internal pressure, such as that caused by a
fire. The cabin atmosphere expansion of the fire effectively sealed the
cabin until far too late for the crew. 

    Incidentally, a number of the spacesuit designs have specified
internal pressures on the order of 3psi in order to simplify design,
including the Space Activity Suit of the early 70's, which was basically
a multilayer leotard with a air tight neck seal. The air bag for the
head and chest was at 200 torr (760 torr in one atmosphere) with
pressure tapering to ~150 torr at the extremities, supplied by the
stretch of the suit. (Sorry, pet project of mine, had to throw it in...)

                                                    kwr

Internet: kr0u+@andrew.cmu.edu