Re: VTVL?


"Sylvia Else" <sylvia@xxxxxxxxxxxxxxxxxxx> wrote in message
news:46ae6237$0$15276$afc38c87@xxxxxxxxxxxxxxxxxxxxxxx
All existing launch vehicles are pure rocket powered, unwinged, and launch
vertically. It seems more than likely that the launch profiles used are
optimum for those vehicles. Otherwise one would have to assume gross
incompetence on the part of the engineers.

However, move away from pure rockets and add wings, and there's no reason
to suppose that the optimum profile remains the same.

Some posters seem to be taking the view that the launch profile used for
existing launchers is the optimum for all launchers, and from that
concluding that neither wings, nor air breathing engines, are viable. The
circularity of such an argument is obvious.

If you're talking a new aircraft with a hypersonic separation, to optimize
performance, then I think this approach is extremely challenging from an
economic point of view. Taking the approach of hypersonic separation from
the air breathing stage necessarily means development of an entirely new
aircraft. That's expen$ive! I'd guess that such a launch vehicle may be
cheaper than an all rocket powered launch vehicle if the air breathing part
of the vehicle is fully reusable and flight rate is sufficiently high that
you're launching it (or one of its sister ships) on the order of more than
one per day. Only then do I think you'd have a chance of eventually paying
for the development of the hypersonic air breather.

The only exception to this seems to be the case when you can take an off the
shelf aircraft, preferably a common, used aircraft (e.g. a used 747), and
cheaply convert it to drop launch your upper stage(s). Unfortunately, this
limits the performance gain of this approach. However, it does gain you
quite a bit of flexibility when it comes to launch operations.

However, if you need performance, replacing the subsonic carrier aircraft
with an all rocket powered stage will surely help. Look at Pegasus XL
versus Taurus.

http://www.astronautix.com/lvs/pegsusxl.htm
$12,000,000 to put around 1,000 lbs into LEO (1994 dollars)

http://www.astronautix.com/lvs/taurus.htm
$20,000,000 to put about 3,000 lbs into LEO (1999 dollars)

Granted, this is one data point, but it's an interesting one.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)


.

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