On Wed, 31 Jul 2002, Michael Wallis wrote:
> ...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.
Either should work fine for vectoring, if you're willing to impose a
straightforward transformation between the guidance-command coordinate
axes and the engine commands. (Such transformations are far from unknown;
the LM autopilot did one, although for different reasons.)
> 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...
No need to relight the center -- with eight clusters, thrust will remain
balanced if you simply kill the (say) clockwise engine in each cluster.
Again, you'll need a bit of a coordinate transformation for steering
thereafter, but that's routine rocket science. :-)
Note, by the way, that with plentiful engines, you can essentially get rid
of an engine failure at the next throttling point. With a bit of smarts
in the steering, you can pick which engines you cut off more or less
arbitrarily, so long as the result remains symmetrical and reasonably well
distributed. So if you have (say) eight engines and one dies, you cope
with that as necessary at the time (throttle up others, possibly cut the
corresponding engine on the other side)... but you also revise the
throttling pattern on the fly so *that* engine is one of the ones slated
to be off after the next throttling point. After that throttling point,
you're back to normal engine operation again.
Henry Spencer
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