Air breathing re-entry concept

I have been contemplating various reentry options for my imaginary air
breathing SSTO vehicle. If I can solve the problem of going to orbit
by using an air breathing engine in the beginning until mach 8 and
switch to hydrocarbon (propane-LOX)rocket propulsion to go to orbit it
would be nice to have a good reentry strategy.

I read the article again in the Nov 2000 popular mechanics that
describes the air force's saucer shaped orbital vehicle called
Lenticular Reentry Vehicle.

It seems to me that the saucer shape has many advantages, namely low
drag, good lift, large usable interior volume.

Now I am wondering if I can just reenter with a vehicle like this and
use a shallow reentry profile, to spread the heat over a longer time,
to reduce the heat load on the structure.

The other alternative I am contemplating is to use an air scoop to
collect air during reentry and use one or more air breathing engines
to more quickly decelerate before I get into the denser atmosphere.
Basically if I gather some air in the upper atmosphere I can use the
air breather to loose my orbital velocity and then just drop down to
earth without all the heating. The fuel used is not terribly much.

Zoltan

Using the air breathing scopp, I guess you mean some kind of scramjet... you
use this for retro-fire, decellerating past the speed required to scoop
sufficient air and... your light goes out? Seems like scramjets are great for
going up, maybe not so much for coming back down?

On 14 Sep 2003 14:47:24 -0700, (Zoltan Szakaly)
wrote:

Penguinista wrote in message m...
Zoltan Szakaly wrote:
I have been contemplating various reentry options for my imaginary air
breathing SSTO vehicle. If I can solve the problem of going to orbit
by using an air breathing engine in the beginning until mach 8 and
switch to hydrocarbon (propane-LOX)rocket propulsion to go to orbit it
would be nice to have a good reentry strategy.

I read the article again in the Nov 2000 popular mechanics that
describes the air force's saucer shaped orbital vehicle called
Lenticular Reentry Vehicle.

It seems to me that the saucer shape has many advantages, namely low
drag, good lift, large usable interior volume.

Now I am wondering if I can just reenter with a vehicle like this and
use a shallow reentry profile, to spread the heat over a longer time,
to reduce the heat load on the structure.

For a shallow reentry you want high lift, not so much high lift/drag.
As it happens, max lift for a hypersonic lifting body is in the
neighborhood of 60 degrees angle of attack, with a rather low lift/drag
around 1/2. (presuming newtonian flow, valid at very high speeds and
altitudes.)

The other alternative I am contemplating is to use an air scoop to
collect air during reentry and use one or more air breathing engines
to more quickly decelerate before I get into the denser atmosphere.
Basically if I gather some air in the upper atmosphere I can use the
air breather to loose my orbital velocity and then just drop down to
earth without all the heating. The fuel used is not terribly much.

Zoltan

Forget the engines. Simple drag works very well. Drag from your scoops
would probably slow you more than the engines they feed. For a saucer
just fly belly first. Once past reentry turn edge on to glide.

Basically I would like to decelerate from orbit significantly before I
dip into the dense atmosphere. This way I avoid reentry heating. The
vehicle already has air breathing engines, so I am just contemplating
using them on the way home.

The Isp for the air breather is over 4,000 so I could decelerate from
orbital velocity to 0 in about 200 seconds at 4g using about a 1.2
mass ratio. This might be lighter than the weight of the thermal
protection system.

Zoltan

Key word being imaginary... I wonder if anyone has contimplated a
Ramjet retro rocket, where inlet and compresor drag is as good as
thrust. There wuuld seem to be insurmountable heating problems, and
the addition of fuel would fuction first as transpiration cooling.

Alan

(Zoltan Szakaly) writes:

I just had another idea for reentry cooling which is related to but
different from what we discussed in this thread.

What if I have a metal nose cone filled with a liquid and as the
liquid is heated it boils out through a hole at the very tip.

This has been proposed N++ times. In fact, there are at least two other
threads in this newsgroup discussing this very topic right now.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

(Zoltan Szakaly) writes:

I admit that I am somewhat liberal in my pursuit of new ideas, but I
think that's how good brainstorming is done.

There is such a thing as being so "open minded" that your brains fall out...


1. You guys probably think that ramjets do not work at a stand-still,
under static conditions.

Using the standard engineering definition of the word "ramjet," they don't.
(You, however, appear to believe in the Humpty-Dumpty school of linguistics,
in which words mean whatever you want them to mean...)


I have three in my garage that work at 0 velocity, they suck in air and
they pump out heated air.

....And by your description of them on your webpages, they are =NOT=
"ramjets," but what are usually known as "ejector jets" powered by
an "expander cycle" They do not seem to be significantly different
in principle from the Gluhareff "pressure jet" engine, except that
your design appears to be rather more primitive than his...


They burn fuel with the air as oxidizer. They have no moving parts and
get an Isp of over 4,000.

At zero airspeed. Above their optimum airspeed, as it becomes harder and
harder for combustion to significantly heat the already hot ram-compressed air,
and inlet drag continues to rise rapidly with airspeed, their effective I_sp
will fall off drastically --- asymptotically roughly as 1/airspeed.

I think you will find that Mach 25 is significantly above their optimum
airspeed, and that their effective I_sp at that speed will not be worth squat.


2. It is true that coming back from space I am moving at a high speed
and at such high speed the air breathing engine (or ramjet) is not
effective for propulsion. But:

A. If I am trying to accomplish retro-propulsion the drag losses of
the airscoop are a benefit and not a loss.

Not after it melts down to slag in the Mach 25 slipstream, which has a
stagnation temperature of several tens of thousands of degrees...


B. The air breather will work as long as it gets air, it does not care
where it comes from.

i.) It won't be "air," it will be an ionized plasma, at a temperature of
tens of thousands of degrees.

ii.) Have you ever bothered to look up just _how_ thin the air is up around
250,000 feet ??? By any reasonable standard, it is a darned good vacuum !!!


C. Sucking in the hot air and blowing it out the front might be better
than just using drag to slow down. I of course cool the critical parts
with fuel. I do cool my ramjet's combustion chamber with fuel. If I
just cooled the leading edges and or nosecone with fuel I would still
have to throw the fuel overboard after it is heated. Might as well
burn it and get retro thrust. I mean I already have engines, fuel
tanks etc.

You will find that when you attempt to combine fuel (=ANY= kind of fuel!)
with "air" that is so hot it is a plasma at tens of thousands of degrees,
it will not "burn" --- it will simply decomposes into ions, electrons, and
miscellaneous free radicals. The result will not be "combustion" ---
instead, the decomposition and ionization of the fuel will _absorb_ energy,
rather than releasing it.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

(Zoltan Szakaly) wrote in message . com...
I just had another idea for reentry cooling which is related to but
different from what we discussed in this thread.

What if I have a metal nose cone filled with a liquid and as the
liquid is heated it boils out through a hole at the very tip.

This would work for a conventional cylindrical rocket that comes back
nose first. The liquid (say water) would flow around the nosecone and
insulate it. Since the reentry does not last long this might be
lighter than having heat shielding structures.

This is an excellent idea if your task is to cruise at high speed
through the atmosphere. The problem is that for a reentry vehicle you
want to lose your velocity. The blunt nose of a reentry capsule
creates a detached shockwave and keeps much of the heat away from the
vehicle but it also creates drag to decelerate the vehicle rapidly.
With the tapered nosecone and drag-reducing gas flow layer the vehicle
would hit the dense lower atmosphere with much of its orbital
velocity. I think the result will not be pretty.

Oren

(Zoltan Szakaly) wrote in message
...
I admit that I am somewhat liberal in my pursuit of new ideas, but I
think that's how good brainstorming is done.

1. You guys probably think that ramjets do not work at a stand-still,
under static conditions. I have three in my garage that work at 0
velocity, they suck in air and they pump out heated air. They burn
fuel with the air as oxidizer. They have no moving parts and get an
Isp of over 4,000. I am experimenting with these because I want to
build a practical flying car.

You have working hardware. I applaud that. But they are not ramjets.
If the *suck* in the air rather than have it *rammed* in by ram
pressure they are not ramjets. Call them induction jets.

Here's what I would do for space access with a jet engine that is
cheap, reliable, has no moving parts, high thrust-to-weight and can be
scaled up to large sizes: I would build a reusable launch assist
platform that lifts a conventional rocket to a high altitude launch.

Air launching is currently limited by the carrying capacity of
existing aircraft and their physical configuration. Developing new
heavy lift aircraft is extremely expensive and cannot be justified for
a vehicle that will not be built in significant numbers. If such a
platform could be built from "dumb" components with cheap, heavy
materials and large margins its development should be relatively
cheap. It doesn't have to be anywhere near as efficient as
conventional aircraft - nobody is trying to save cheap fuel when
launching to space. It just needs to have an Isp high enough so that
its weight is not totally dominated by fuel like rockets. This way it
can be scaled up without having its size balloon out of control. I
think your induction jets might be suitable for such a platform.

Oren

Zoltan Szakaly wrote:

I have three in my garage that work at 0
velocity, they suck in air and they pump out heated air. They
burn fuel with the air as oxidizer. They have no moving parts
and get an Isp of over 4,000.

How do they manage to suck in air with no moving parts?

Jim Davis

In article ,
Zoltan Szakaly wrote:
What if I have a metal nose cone filled with a liquid and as the
liquid is heated it boils out through a hole at the very tip.
This would work for a conventional cylindrical rocket that comes back
nose first...

Schemes somewhat along those lines have reportedly been used for ICBM
warheads, which want to keep their velocity as much as they can (to make
interception difficult).

As others have already noted, for a reentering spacecraft, a sharp nose is
a ghastly mistake. Reentering spacecraft want as much drag as possible,
to slow down at high altitudes in thin air, so the blunter the better.
(Even the shuttle orbiter basically reenters belly-first, not nose-first.)

Given a blunt shape, cooling it with an expendable liquid is an attractive
idea, although the technology is poorly developed. It's essentially an
ablative heatshield where you can refurbish the ablator by refilling a
tank, which is very nice. But nobody has a very clear idea of how best to
arrange the details.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

(Zoltan Szakaly) :

1. You guys probably think that ramjets do not work at a stand-still,
under static conditions. I have three in my garage that work at 0
velocity, they suck in air and they pump out heated air. They burn
fuel with the air as oxidizer. They have no moving parts and get an
Isp of over 4,000. I am experimenting with these because I want to
build a practical flying car.

How much do they mass? How much thrust do they produce?

Does any model produce more thrust than the weight of the
(motor+fuel+piping+pumps+control systems) ?

Remember rockets easyly produce thrust ratios of 50-1 and 100-1.

Earl Colby Pottinger

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