Sander Pool wrote:
> Just so we're all talking about the same thing, the early Soviet missiles
> had what, 24 engines? I would consider this a multi-engine missile. Anything
> less than 6 falls into the category of 'few' engines. Saturn 5, Titan, Space
> Shuttle, Ariane all fall into this category.
>
> I maintain that for an SSTO it's better to have five than to have 20 engines
> for the reason I mentioned: inspection and maintenance effort. We are
> talking about a ship that can be turned around quickly, right?
Yes we are, but we're also talking about designing the engines for
easy inspection and replacement if needed. A large engine that
requires two or three people to handle is less efficient than a small
engine that one person cah remove and replace.
As for number, Max Hunter and I had several discussions on this during
our trips back and forth to ERPS meetings. His original opinion was
that 8 was the right number - small enough that the plumbing wasn't a
nightmare, large enough that you could throttle or shut down without
falling below minimum thrust. I was advocating a truncated aerospike
arrangement with 18 edge engines and 1 center one to provide back
pressure for the spike. I used 18 based of estimated engine size and
diameter and the Rule of 6 for circumferences. Max pointed out at one
point that the trouble with 18 engines was you get 6 clusters of 3
engines or 3 clusters of 6 engines - neither of which lent themselves
to efficient vectoring. He suggested 24 outer and 1 inner engine -
allowing for 4 six engine clusters or 8 three engine clusters. Within
each cluster of 3 you could kill one engine and run on two, then kill
two and relight the center - giving additional deep throttle capabilities.
It seemed to make a lot of sense to me.
> I guess the question is, where is the sweet spot? I'd say it is as few
> engines as possible while still being able to throttle back sufficiently by
> shutting down engines. How does/did Atlas accomplish this with only 2
> engines ?
Atlas has "sustainer" engines that were jettisoned after use.
Michael
----------------------------------------------------------------------
Michael Wallis KF6SPF (408) 396-9037 [EMAIL PROTECTED]
President, Wallis International http://www.wallis.com
Coleman Orr:
"You either drift through life, or drive through it."
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