[AR] Re: Hydrogen and oxygen used as pressurizing gasses
- From: David Weinshenker <daze39@xxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sun, 13 Dec 2015 17:39:30 -0800
On 12/13/2015 03:30 PM, Wyatt Rehder wrote:
Wouldn't using a pressure fed system with hydrogen on an upper stage be
optimizing for the worst characteristics of each system? You have the
least dense fuel possible making the largest tanks, in a system where
your tanks have to be rated for high pressures and very heavy, on the
stage where every pound counts.
This is actually more true for a first stage than an upper stage, which
(by suitable nozzle design for expansion into vacuum) can run at a high
expansion pressure ratio (and hence high Isp) even with a low chamber
pressure. Lower stages which must expand into atmosphere will benefit
much more from a high operating pressure, and are hence pushed deeper
into the tradeoff corner of high-pressure tanks vs. pump complexity
(though less sensitive to the mass ratio of the lower stage itself).
-dave w
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