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.)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |