Len Lekx wrote in message . ..
On Fri, 28 Nov 2003 00:50:59 GMT, "johnhare"
wrote:

I do advocate some forms of air breathing propulsion for some
acceleration missions. I do not believe in hauling it all to orbit, or
increasing architectural complexity of the vehicles to the degree

I tried posting this on sci.space.tech, but it doesn't seem to have
gotten there... :-(

I've had no luck either over the past two months or so.

I was reading a textbook the other day ("Space Propulsion Analysis
and Design" - Humble, Henry & Larson, McGraw-Hill, 1995) Under the
topic of 'Advanced Propulsion Techniques', they described a rocket
motor that uses ram-air to augment the on-board oxidizer supply -
using some air to aid in burning a fuel-rich mixture.

Which got me to thinking - could it be turned around...? Add a
supplementary oxidizer to current turbojet engine designs? This way,
the engine could still operate at higher altitudes. Also, using an
oxidizer that could absorb sufficient heat from the incoming airstream
(cryogens, maybe...?) would reduce the air temperature, thus allowing
the engine to operate at higher Mach numbers. Where air becomes too
thin, the air inlets could be closed, and the engine would operate in
a purely rocket mode.

Not being an engineer, I have *no* idea what the kind of pitfalls
would be to such a system... but might it be worth exploring?

The main problem tends to be the inlet. As one goes
higher and faster, gathering the air gets to be more
and more of a problem. Lift (and drag) increase with
the square of the velocity; the amount of air increases
only with the first power. This results in a greater
and greater mismatch between the lifting surfaces and
the airbreathing system. I have never found airbreathing
better than rocket for anything but a relatively low
delta vee first stage. I have only recently realized
that rocket is also superior even for subsonic climb,
when trying to reach altitudes that are rather extreme
for subsonic speed.

One can add liquid air and/or LOX to the system; however.
a pure rocket usually works better--except for requiring
its own base area.

At higher speed and altitude, one can add water (or other
fluids)--a la DARPA's RASCAL. This effectively makes the
engine think that it is at lower speed and altitude.
But this does not obviate the need for collecting the air
in the first place--which means bigger and bigger inlets.
Our post-RASCAL F-14 concept uses only a rocket system
to enable better performance with surplus F-14As and very
little modification other than addition of the rocket
system. Much simpler and much cheaper than our RASCAL
concept. Alas, its hard to raise money for simpler and
cheaper concepts.

Best regards,
Len (Cormier)
PanAero, Inc.
(change x to len)
http://www.tour2space.com