[AR] Re: SpaceX F9 Launch/Update -- Live Link
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sun, 27 Dec 2015 22:39:44 -0500 (EST)
On Sun, 27 Dec 2015, David Weinshenker wrote:
Because the US has no suitable large liquid engines...
In other words, we've (post-SSME) let our design pipeline for large
booster engines run dry...
Pretty much so, yes. The systematic thing to do would have been to start
development of a flyback (or similar) liquid-fuel shuttle booster -- the
natural customer for such an engine -- as shuttle development tapered off.
But developing the shuttle under severe cost caps was such a challenge
that many other things got put on hold, or at least suffered, and there
was a lot of pressure to fund things other than more rockets for a while.
Or put another way, once you have an incoming launch vehicle
requirement, it may be too late - especially in the context
of the compressed budget and schedule expectations which seem
to be the "modern" fashion - to initiate an applicable engine
development project.
Yes, it's long been gospel in both aviation and rocketry that "engines
take longer than airframes".
(Note that the F-1 work began well before anything resembling the
Saturn/Apollo launch configuration, as such, had been explicitly
specified - but it was foreseen that lunar missions might be proposed,
and it could be anticipated that these would require large launch
vehicles and new high-thrust engines.)
More precisely, it was foreseen that more ambitious space missions --
lunar or otherwise -- would probably appear, and launch vehicles would
grow to match. F-1 work started before the Moon became the Big Goalpost
In The Sky (and long before it became the Only Goalpost In The Sky -- in
the early-mid 60s, it was explicit policy that the Moon was just the first
step).
This did have some negative aspects. It meant fixing the specs early,
without knowing exactly what the vehicle might want; one thing the vehicle
designers did complain about is that the engine fairings and fins of the
Saturn V could probably have been eliminated if the F-1 had been able to
tolerate higher aerodynamic loads and had wider gimbaling range (the fins
being mainly there to help handle engine-out failures). Worse, it tempts
the engine designers to "throw problems over the wall" to the vehicle
designers -- for example, by demanding relatively high inlet pressures to
make the pumps easier and lighter, even though the impact on tanks and
pressurization is probably worse.
Henry
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