From: henry@spsystems.net
In article <433F6EE2.E1192B83@nospam.com>,
Andrew Nowicki wrote:
>...This means that large rocket engines
>cannot be reusable and they are suitable for nuclear missiles only.
This would surprise the people who built the F-1, whose specs demanded
that it be reliably capable of 20 starts and a total run time exceeding
half an hour, even though its operational use required one start and a run
time of 2.5 minutes. Demonstrating the rated life required six test
engines to achieve more than double it without incident, which they did.
Your "fatal diseases" of large chambers and turbopumps are indeed
problems, but they can be avoided, and repeatedly have been.
>Small rocket engines have another important advantage: they
>have superior thrust-to-weight ratio due to the Cube-Square
>Law which states that as scale is reduced, properties which
>are a function of volume (mass) will decrease faster than
>those which are a function of area (thrust and strength).
It is not that simple, alas. You don't make a small engine by just
scaling down a big one. In particular, achieving adequate chamber
residence time for efficient combustion, other things being equal, tends
to require scaling only two of the three dimensions, which makes a hash of
your proposed application of the square-cube law.
>Small, simple engines can be made by robots, so they can
>be very cheap.
So can large, simple engines. Ask the Russians, who invested much more
heavily in production automation (and in design for easy production) than
the US ever did.
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