(Henry Spencer) wrote in
:

In article ,
Pat Flannery wrote:
Did anyone take a crack at hydrazine monopropellant RCS for
a manned spacecraft?

Not that I'm aware of... although I don't remember what
X-38 was going to use.

For big vehicles, people tend to be attracted to biprop
systems for lower fuel mass. And most of the little
vehicles were designed back before good hydrazine catalysts
were developed.

(Monoprop hydrazine didn't get popular until the mid-60s,
when the first hydrazine catalysts which *didn't* need
preheating were found. Preheating was marginally
acceptable for major burns -- for example, Mariner 4's
midcourse-correction system threw in a squirt of N2O4,
running briefly as a biprop to get its catalyst hot -- but
was utterly impractical for RCS systems, which need to fire
frequently and on short notice.)

I noticed LockMart's CEV proposal used nitrous oxide as a
monoprop; I'm curious about the Isp and the possible catalyst.
Seem like the performance would be somewhat low, despite
the advantages of low toxicity, easier handling and simpler
system overall. I don't recall nitrous being used this way
before; is it something new?

--Damon