Also the percentage difference between the 2KLbF of both LR-101's against
the 360KLbF of the main and sustainer engines was small so a small loss in
ISP didn't have much impact on mission performance. Another reason ISP was
below par was O/F was only 1.8. They definitely were only concerned about
reliability not performance. If the verniers had been designed in modern
times they may have used a better performing system design. Anyone one want
to plug in the #'s between an ISP diff of 200 vs 250 with over 1/2% of
total mass flow?
K
On Wed, Jan 27, 2021 at 11:06 AM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Wed, 27 Jan 2021, Wyatt Rehder wrote:
Something to consider on the LR-101 was its intended application. Which
was as a vernier control thruster for the Altas. So they had other
driving design constraints than just performance. I'd hazard a guess
that they were happy to take a hit on performance if it made the
packaging smaller...
Bear in mind that the Atlas verniers were mounted externally -- not flush
with the surface like a lot of RCS thrusters -- and ran continuously from
main-engine start to final cutoff. (They were controlled with gimbaling,
not on-off pulsing.) Which is to say, I don't think they had any major
packaging constraints, and they did care somewhat about performance.
The Buran RCS thrusters are also noteworthy small LOX/kerosene engines,
although I'm not sure how much technical information on them is available.
Henry