"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 think that group must be about dead. I see a handfull of postings
every week or so. I think the spam overload is a factor.

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.

Ejector ramjet is the common term. Advanced is frequently used
to describe things that are merely different.

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.

I believe the Rascal program is based on this technique. Precooling
is described by the Japanese for their ATREX engine. A major
problem that is frequenly not mentioned is that the intake for supersonic
engines can mass more than the engine itself.

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?

I did some numbers a while back. To beat a pure rocket, you have
to get nearly insane performance from an air breathing engine at higher
altitudes and airspeeds. Your mass penalties are from an engine as
much as ten times the mass of an equivilent thrust rocket, an intake
probably at least as heavy as the engine, Less efficient vehicle structure
to accomodate the aero surfaces and bulky airbreathers, and dead
mass to drag around during your main acceleration.

The engine I am proposing should get a thrust/weight of 25 with
a net Isp of 1,000. Only for subsonic use and carried inside the
flight surfaces instead of pods or the fusilage.