Re: Announce: Grace project site operational

["Robert I. Eachus" <rieachus@attbi.com>]

Wes Groleau wrote:

 
> I didn't believe it when I read how he took
> "one -10" (a drop in temperature of ten degrees)
> and turned it into "the other -10" (ten degrees
> below freezing).


The worst case resulted in the Apollo fire that killed three astronauts. 
  Two tests were combined.  One that required operation in 3 psi oxygen, 
and another that required pressurization of the command module to 3 psi 
(above the surrounding pressure) for leak testing.  The medical doctor 
who signed off on the combined test did so because all of the medical 
documentation read 3 psi oxygen, which is about the partial pressure of 
oxygen in the atmosphere.  Forget for a moment that pressurizing the 
capsule with 18 psi oxygen made it a bomb, ask your doctor what would 
happen to your lungs on 18 psi oxygen, 0% CO2, 0% H2O, 0% N2, for that 
matter 0% anything else.

In scuba diving, the partial pressure of O2 can get that high in 
"technical" diving (below 150 feet), but the usual for technical diving 
is to use a helium/oxygen mix, and keep the oxygen partial pressure to 
reasonable levels.  "Oxygen tents" in hospitals seldom go above 7 or 8 
psi oxygen partial pressure, in other words a 50/50 mix of oxygen and 
air. Mountain climbers use pure oxygen above around 20,000 feet, but 
again the absolute O2 pressure is below 3 or 4 psi.

One of the changes made subsequent to the Apollo fire was to a 50/50 
He/O2 mix.  This allowed the command capsule to be filled with the mix 
at atmospheric pressure before launch, then reduce to 5 psi (2.5 psi O2 
pp) on orbit.

Incidently I always thought that the most frightening part of the early 
spacecraft flights was taking off in a container with a hole in it to 
let the air out and hoping that the hole would close properly.  Once the 
rockets stopped firing you could do something about it, but you would 
probably be out of oxygen by then.  This is one of the things the Space 
Shuttle fixed--no venting required during the boost phase.  Along with a 
max-Q where you could do something other than holding on until the 
shaking stopped.

Yes, the astronauts are strapped in, but I mean it literally.  In 
Mercury, Gemini, and Apollo, if you didn't hold on to keep your hands 
from uncontrollably banging around at max-Q, you could damage your 
hands--and the spacecraft.  Add the pogo effect, see Apollo 6, and you 
were just glad to survive the ride. (The pogo effect resulted from 
resonances between the Saturn I structure and the pipes bringing fuel to 
the engines.  This resulted in the momentary g-forces banging back and 
forth between 0 and 10 gs or so.  On Apollo 6 it was so bad that parts 
of the lunar module adapter, which contained the LM and connected the 
command/service module to the Saturn booster fell off. The cure was to 
fill parts of the Saturn with helium before launch to change the 
resonant frequencies.)