Henry Spencer wrote:
On Sat, 17 Apr 2004, Ian Woollard wrote:
And there's a further point, that the article mentions that this
technology might be needed for orbital taxis, (but then never mentions
why you would want the high chamber pressure that helps cause these
problems in such an engine anyway- you very probably don't...
There is *some* benefit to be had from high chamber pressure even in
vacuum.
Well, thrust scales with chamber pressure; but I would expect that
thrust isn't massively important for orbital taxis in a lot of cases.
Yes, you could get the same expansion ratio at lower chamber
pressure just by making the nozzle longer...
Yes... if you need the same thrust due to the orbital mechanics.
but you would take a small
performance penalty from things like nozzle drag and minimum-gauge issues.
You could avoid these by having multiple chambers. On the plus side,
your propellent feed is at a lower pressure; so the pumps and feeds
weigh less.
And higher pressure suppresses dissociation, so the flame is a bit hotter
and that helps a little bit too.
But these effects are quite small.
Mind you, most designers would conclude that it's far more trouble than
it's worth. But NASA rocketry has a long history of obsession with
performance regardless of practical issues.
Yes, although the Shuttle's OMS runs at 125 psi or so, so it doesn't
/always /work out like that.
Henry Spencer
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