On Tue, 1 Apr 2003, David Weinshenker wrote:
> I note that, after extolling the handling convenience of alcohol,
> y'all are now going to kerosene? What variety are you using? Can
> you get RP-1, or is there a "jet" grade of comparable quality
> available these days?
If you cool with the oxidizer instead of the fuel, and avoid using a
fuel-rich gas generator for pump drive, RP-1 has no particular advantages
to make up for its high price and limited availability. If all you're
going to do is inject it into the chamber, ordinary jet fuel does just
fine as a rocket fuel.
There are scary superstitions about oxidizer cooling, but in fact it works
just fine, and the ex-Rotary-Rocket folks on the XCOR team have previous
experience with it. It does add some design constraints, e.g. with LOX
you almost certainly need pumps (because LOX's liquid range is fairly
narrow unless you're above its critical pressure, which is sizable).
As for pump drive, one approach is to run the gas generator's burner at a
balanced mixture ratio, and use water injection to cool the gas down
enough to be compatible with the pump materials. (Arianes 1-4 did this.)
There are commercial hydrocarbon mixes that might be as good as RP-1 at
resisting polymerization and coking, e.g. USP Mineral Oil, but I don't
know that anybody's really explored them.
As to why they did it, the obvious reason is that somebody who was putting
up money for development work had a preference for it. In business,
unless you're really doing well and have more work than you can handle,
when somebody wants to pay you to do something you're not keen on, the
answer is not "forget it" but "it'll cost you extra".
Henry Spencer
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