Curiously--give it was developed by the liquid rocket engineers that new
space loves to hate--the Liquid Rocket Engine Cost Model (LRECM), when used
in a parameterized study, showed that Staged Combustion engines had
development costs about 12% higher and first unit costs about 6% higher
than a GG engine (lox / hydrocarbon). This study was for rather larger
engines than being discussed here (125k lbsf thrust) but the result seems
interesting, even surprising.
The overall increase in performance (Isp & T/W combined) is typically much
higher than those numbers, so it would appear that SC engines may offer
lower cost / performance (a good thing) than GG engines; particularly if
they are actually lower cost than MSFC experience would estimate.
Bill
On Tuesday, August 9, 2016, Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:
On Tue, 9 Aug 2016, Lars Osborne wrote:
And Ursa Major Technologies is working on a 5klbf LOX/Kero staged
combustion engine...
Wow. Stage combustion sounds very challenging to scale down.
Well, bear in mind that staged combustion has an evil reputation in the
West mostly because it's been used only a couple of times, by national
megaprojects trying to meet very ambitious specs with inadequate funding.
The Russians don't think it's that scary, partly because every substantial
rocket engine they've built for 50+ years has used staged combustion. (Most
of them with oxygen-rich preburners, too -- something the West tended to
reject as prohibitively hard.) Booster engines, upper-stage engines,
maneuvering engines, the works.
There's no question that it *is* harder to develop, and certain aspects
may get... interesting... in smaller sizes, but its reputation is somewhat
exaggerated.
Henry
