In article ,
Brian Thorn wrote:

On Fri, 20 Apr 2012 00:56:49 +0200, Jochem Huhmann
wrote:

Still, for SLS (which is meant to fly crazily rarely anyway) it would
mean three different engines. Compared to using the SRBs for the
boosters (which at least have the tooling and propellants and everything
ready) I can't see the economic case for them for ten years or so and
even then...

SLS is already three different engines. The SRBs are still complex
machines built on production lines and shipped cross-country. They are
far from cheap, especially the new FSB. SRBs are and always will be
inherantly less safe than liquid engines. And since SLS's SRBs aren't
even recoverable, NASA won't have the advantage of inspecting them
post-flight for problems like they did in the Shuttle program. So an
F-1 based booster, especially if the production costs can be leveraged
with EELV's successor which should be coming along around the same
time, does make some sense. F-1 production costs could well be shared
with J-2X and SSME infrastructure to a degree as well, actually making
this system cheaper than SRB in the long run. (And propellant is ready
for F-1, too... it uses RP-1 just like Atlas 5 and Falcon 9.)

To put it into other words: SLS is a disaster, no matter what engines
you use.

Maybe, but I don't think it is quite as doomed as you suggest.

Brian

After 25 years dealing with large solids, I can see little benefit to
re-use of solid rocket motors. Even though the insulation protects the
case, I would not like to stake my life on a re-used motor casing.

About he only items I can see re-using would be the nozzle control
system; the nozzle and throat are designed for self-sacrifice during the
burn and should not be re-used.

Liquid motors are a different story. Turbopumps should be either
overhauled or replaced; motors are designed to use fuel to keep the
nozzles and throats cool. The viability of the stages themselves depends
on their recovery system.