On Mon, 1 Jul 2002 14:26:12 -0500 (CDT), "Douglas E. Drummond"
<[EMAIL PROTECTED]> wrote:
> I came to the same conclusion modelling an X-Prize vehicle.
> My conclusion was that you don't even *think* of going supersonic
> below FL300 (30K feet), at which the density is about 1/4 of sea
> level. From there on up, it's a race between 'rho' and 'vee-squared.'
Did you try for any particular relationship? Keep drag loss and
gravity loss equal below a certain altitude, for instance?
> A secondary conclusion based on this model is that a turbojet engine
> makes an excelent first stage. In fact one of the most cost-effective
> first stages is a mass-produced jet transport aircraft. Pegasus has
> been doing good work in this area, and Pioneer uses this principle
> both for the spaceplane, and the tanker. Of course the jet engines
> on the spaceplane make early flight test and ferry operations a
> no-brainer.
They also make it require manned flight and certified airworthy jet
aircraft, not cheap options. As an example, if ERPS had started
working on them in 1993, we might well have engines akin to XCOR's 400
pounders by now (they wouldn't be anything like as reliable as
XCOR's). But there's no way we could ever afford a Long-EZ to put
them in.
Henry Spencer has argued, persuasively IMHO, that changing flight
modes - balloon to rocket, airplane to rocket - buys you altitude, but
at the cost of complexity, and that it's cheaper to just make the
rocket more capable and launch it from the ground. Mitch is not
persuaded, but he's a pilot - he wants stick time. :-)
-R
--
"Sutton is the beginning of wisdom -
but only the beginning."
-- Jeff Greason
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