[AR] Re: pressurization
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 23 Apr 2016 14:33:44 -0400 (EDT)
On Sat, 23 Apr 2016, John Dom wrote:
I read the Atlas ICBM balloon tanks were kept rigid with bottled nitrogen
while stationed empty in their launch pits (maybe filtered air from a
compressor was only used for the later Atlas museum exhibits).
That all seems plausible. Bottled nitrogen gives you more certainty about
what's in the tanks -- a bit of oil residue from a compressor is no
problem for a museum exhibit but is a real issue in a tank you're going to
want to fill with LOX.
But was nitrogen also used for tanks pressurization during flight?
No, not on Atlas. Booster-phase pressurization was with helium (although
nitrogen was indirectly involved -- the helium bottles had LN2 jackets to
chill the helium for denser storage, with the LN2 dumped just before
launch). After booster-engine jettison, pressurization was blowdown!
The pressurization system was on the booster-engine ring, and departed
with the booster engines. By that time, the tanks were largely empty, so
the helium already in them was enough to finish the job, with some help
from hydrostatic head induced by acceleration.
I suppose that after the closing the LOX tank valve the GO2 amount
boiling off would be insufficient for pressure control to the pump
inlets, or?
Not really enough, especially since going to flight pressure means the LOX
(which has been boiling at countdown pressure) is slightly subcooled and
isn't boiling much for the moment.
Henry
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