[AR] Re: thinking big once more
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Wed, 28 Sep 2016 16:36:41 -0400 (EDT)
On Wed, 28 Sep 2016, Eric Robbins wrote:
Interesting design choice, it would seem that for a certain number of
engines N that the chance of at least 1 engine failing approaches 100%.
The key question is not really the probability of an engine failure -- the
question is the probability of an *unsurvivable* engine failure. Rockets
with more than 3-4 engines often can survive a single engine out, provided
it doesn't fail violently and destructively enough to knock out others.
Four of the Saturns survived (and completed their missions) with engines
out. For that matter, one Falcon 9 had a moderately violent first-stage
engine failure in flight, and made it to orbit.
I wonder what N is? I can't imagine it being 3 digits, I would not be
surprised if it were around 40-50.
It depends greatly on the reliability of the individual engines. With a
good engine like the RL10, it could easily be in three digits. (Back in
the 80s, when Hughes was studying its Jarvis launcher concept, they had a
problem with availability of suitable engines. They looked seriously at a
first stage with about 200 [!] RL10s.)
Henry
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