Re: National Aerospace Plane (X-30) announced 20 years ago

*From:* "Ian Woollard" <ian.woollard@xxxxxxxxx>
*Date:* Wed, 15 Mar 2006 19:42:39 -0000

mike Williamson wrote:
Wings do not allow for less energy to be used to orbit a craft-
while
they provide lift they do not provide any energy. In fact, since
they
also generate drag, a winged vehicle would almost certainly require
more fuel to reach orbit, since the tubular design will have less
drag to overcome.

Careful here. Wings do indeed save energy; this is because wings have
a
lift/drag ratio, the drag is approximately equal to the engine thrust,
and so thrust can be reduced- reducing the propellant needed to carry
the vehicle whilst within the atmosphere.

The root cause of the energy saving is that the vehicle uses wing to
throw air downwards relatively slowly; the slow speed represents lower
energy needed to carry the vehicle; the high exhaust speed of rocket
engines uses more energy (since energy goes as a square law on the
exhaust velocity), although it saves propellant mass.

Even with Apollo, studies showed that a lifting approach did indeed
increase payload (although the payload increase was very marginal.)

The big downside of wings is after you leave the atmosphere- wings
push
up dry mass, and then it is very easy to lose everything that was
gained during ascent and then some; a good mass ratio is essential
particularly toward the end of the burn.

Mike

So the obvious approach is a two-stage one - fly the wings and
atmospheric engines away once they no longer serve a good purpose.

Spaceship One on steroids...
.

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