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From: (Henry Spencer)
Subject: Re: X-30 Space Plane
Date: Wed, 14 Jun 2000 18:25:54 GMT

In article <>,
doug holverson  <> wrote:
>Does anybody really know the story on why the X-30 Space Plane program came
>and went? It looked so cool at the time.

Well, why it came was that it looked like a neat idea.  Whether it was
really a good idea is debatable; it's not clear that airbreathing engines
are the preferred way to get to orbit, given that you can buy an awful lot
of liquid oxygen for what it takes to develop a hypersonic airbreathing
engine.  The idea of building a reusable single-stage-to-orbit research
vehicle made a lot of sense, but the choice of technologies didn't.

(NASA's own internal studies showed this:  rocket vehicles with the same
performance were half the size, had half the dry mass, had less than half
the propellant cost, experienced maximum dynamic pressure 2-4 times lower,
and saw *orders of magnitude* lower heating loads.  They were much more
likely to be capable of aircraft-like operations than the X-30 was.
Release of those studies was delayed quite considerably by management's
dislike for the results.)

As for why it went...  It was deliberately doing things the hard way,
requiring use of poorly-developed technologies.  It was not well managed.
Finally, the non-negotiable demand that the very first X-30 be (a) manned
and (b) orbital sealed its fate, by making a difficult research aircraft
using major new technologies (a) big and (b) very sensitive to technical
difficulties and performance shortfalls.  The result was a very costly
program with a high risk of failure or massive cost overrun, a combination
which did not appeal to Congress when it came time to start writing really
big checks for full-scale development.

Had the program been conceived as a series of research aircraft, the first
more or less an airbreathing X-15 and later ones working up from there, it
might have gotten somewhere.  Had it been willing to use non-airbreathing
engines, it might have been viable as an experimental SSTO or near-SSTO.
But the combination of unproven technology and ambitious requirements was
too much for it.
Microsoft shouldn't be broken up.       |  Henry Spencer
It should be shut down.  -- Phil Agre   |      (aka

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