From: henry@spsystems.net
In article ,
Damon Hill wrote:
>>>Dumb question - is this the first large rocket to use only LH2/LOX at
>>>liftoff?
>> Indeed it is. Nobody else has thought that was a good idea.
>
>...Given the well-established practice of denser propellants in the
>first stage (or boosters), there must have been a compelling reason
>that outweighed known disadvantages...
It could just have been a bad case of hydrogen religion on the part of
someone influential. There's still a lot of that around.
However, a more pragmatic issue may have been engine development status.
My impression is that the RS-68 is derived fairly directly from the
NASA-funded STME effort some years ago. That being the case, coming up
with a LOX/LH2 engine of about the right size would have been a low-cost
low-risk short-schedule development project, because much of the work was
already done. But the existing US-made LOX/kerosene engine designs are
all the wrong size -- the F-1 is too big, everything else is too small --
and development of a new one would have to start very nearly from scratch.
(Mind you, "too big" is a relative term, and there is a lot to be said for
building launchers a bit oversize -- it costs very little extra, if things
like engines already exist, and provides valuable insurance against
payload growth. McDD could have built a very nice launcher, with a lot of
growth potential, using a single F-1 in a new first stage and basing the
second stage on Douglas's old S-IV design with clustered RL10s. Whether
it could have won the EELV competition is another question, however...)
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"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert | henry@spsystems.net
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