[AR] Re: pressurization (was Re: Portland State Aerospace Society)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Fri, 22 Apr 2016 23:19:57 -0400 (EDT)
On Fri, 22 Apr 2016, Paul Mueller wrote:
Thank you. So the Delta I/II/III used nitrogen? I guess not all Western
rockets (or all "dino-space") use/used helium for LOX pressurization.
Nope, not all. As per previous discussion, it *is* the easiest way, but
it's not the only way. Goddard used nitrogen too. If memory serves, so
did the X-1.
Now I'm curious about Falcon 9 and Ariane V.
The Falcons all use helium. Ariane 5 uses helium for LOX and GH2 for LH2.
I can see where nitrogen could be a problem with the densified, chilled
LOX in the latest Falcon 9s.
Doesn't make it impossible, but would make it harder. Even in rockets
which don't explicitly subcool their LOX below boiling point, usually the
flight pressure of the LOX tank is higher than the pressure used during
most of the countdown. That means the LOX is slightly subcooled once the
pressure is boosted to flight pressure just before launch, because at
higher pressure the boiling point is higher. (The late change in pressure
is done for the same reason SpaceX is subcooling its LOX: colder LOX is
denser. So if the LOX is going to reach boiling point while waiting on
the pad, you want it to do that at low pressure where the boiling point is
lower.)
Henry
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