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Old May 12th 17, 11:43 AM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default RD-180 relplacement

In article ,
says...

JF Mezei wrote:

(aka: once beyond the first 6, would additional ones become competitive
on a per pound of payload basis ? (engine only).


One would expect subsequent RS-25 engines to cost less as the 'kinks'
are worked out of the production and test processes. However, these
engines will always be more expensive than engines like BE-4 or Raptor
(or even AR1), so they're never going to compete on a price per pound
basis.


I would expect this to be the case. Liquid hydrogen being a p.i.t.a. to
handle due to its very low density and very low temperatures. I'm sure
it's a lot easier to build turbopumps for kerosene or even liquid
methane than for liquid hydrogen. The shuttle program's experience with
liquid hydrogen is that it likes to leak out of plumbing and is tricky
to get sensors to work in it (ET LH2 sensors at the bottom of the tank
caused headaches) causing launch delays.

For commercial operations focused on low cost, LH2 is a bad choice for a
lower stage. It's not a terrible choice for a high energy upper stage,
which is why ULA is sticking with it for the ACES upper stage that they
are developing.

Jeff
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