Air breathing Engines

In article ,
Allen Meece wrote:
Surely this can not be purely justified on the bases of
reduced fuel (oxidiser) payload? ...

Well, If oxidiser is 1/4 to 1/3 of the weight you're trying to get off the
ground, it makes sense to burn the oxygen in the air.

No it doesn't, not when you consider the extra technical problems and the
extra engine mass.

What we care about is *cost*, not *mass*. LOX is cheap. Tanks to contain
it are cheap and compact. There is no inherent virtue in reducing how
much LOX gets carried.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

Well, If oxidiser is 1/4 to 1/3 of the weight you're trying to get off
the
ground, it makes sense to burn the oxygen in the air.
No it doesn't, not when you consider the extra technical problems and the
extra engine mass.
Well, the theory out of the AFRL is that PDE combined cycle air-breathing
rockets will have *less* mass than rockets with turbopumps and *big* LOX tanks.
[air breathing rockets will still need tanks above the atmosphere but no *big*
pumps because the injection occurs at low chamber pressure]
Also, less fuel mass means less horsepower required which means less engine
weight. It's very hard to see why Henry says it's fine to go big and heavy if
it's cheap. Weight's never cheap in the space game.
^
//^\\
~~~ near space elevator ~~~~
~~~members.aol.com/beanstalkr/~~~

Stephen:
Hi, Just like to say cheers for all the messages :-), they will
certainly keep me thinking. I have one final question, I know that the
Brits have flown a scramjet engine (missile scale model), but, I also
know that the Australians and the Americans (X-43) have had several
attempts. I was just woundering if anybody could tell me who did it
first!
--------
For air-augmentation the earliest I have found is the PR-90 (Russia)
60's. An ICBM version (Gnom) was designed but did not see production.

http://www.astronautix.com/lvs/gnom.htm

Reading the above the air-augmented stage was to range between Mach 1.75
to Mach 5.5 lasting less than 70 seconds at an impulse of 550 seconds.
It could only work for that short period of time the craft was still in
useful air.
--

Anvil wrote:
For air-augmentation the earliest I have found is the PR-90 (Russia)
60's. An ICBM version (Gnom) was designed but did not see production.

http://www.astronautix.com/lvs/gnom.htm

Reading the above the air-augmented stage was to range between Mach 1.75
to Mach 5.5 lasting less than 70 seconds at an impulse of 550 seconds.

As they noted in the text, that's about twice that of a solid rocket
over that regime; 550 seconds is extremely respectable; and the first 70
seconds is the thick/heavy end of a rocket. Imagine what an airbreathing
Kerosene or even a hydrogen version would be like. You'd be looking at
perhaps 600-800 seconds and 900-1100 seconds. With luck you would have
spare fuel to send it back home with.

It could only work for that short period of time the craft was still in
useful air.

Clearly, however the ISP over that time is extremely high for a solid,
and reduces the GLOW of the vehicle quite a bit- the vehicle delivers a
fairly respectable payload fraction on what must be nearly an orbital
trajectory.

"Anvil" wrote in message
om...
Stephen:
Hi, Just like to say cheers for all the messages :-), they will
certainly keep me thinking. I have one final question, I know that the
Brits have flown a scramjet engine (missile scale model), but, I also
know that the Australians and the Americans (X-43) have had several
attempts. I was just woundering if anybody could tell me who did it
first!
--------
For air-augmentation the earliest I have found is the PR-90 (Russia)
60's. An ICBM version (Gnom) was designed but did not see production.

http://www.astronautix.com/lvs/gnom.htm

Reading the above the air-augmented stage was to range between Mach 1.75
to Mach 5.5 lasting less than 70 seconds at an impulse of 550 seconds.
It could only work for that short period of time the craft was still in
useful air.
--

Interesting reference. They had a GLOW half that of comparable
rockets with similar payload. It took me several minutes to figure out why
their numbers were different than what I have read and figured out.
They were comparing low performance solids against air augmented
solids.

Better rocket performance is available for space launchers that don't
have to be on alert for several years. This tends to drop the value of air
augmentation to parity or less compared to all liquid rockets.

In article ,
Ian Woollard wrote:
It could only work for that short period of time the craft was still in
useful air.

Clearly, however the ISP over that time is extremely high for a solid,
and reduces the GLOW of the vehicle quite a bit...

And we care about that... why, exactly?

A great many misconceptions, superstitions, and outright myths about
launcher design can be traced to the habit -- inappropriately inherited
from the missile business -- of thinking of gross liftoff weight as an
important figure of merit.

Especially when the reduction in weight is coming out of the propellants,
the cheapest and most easily-designed part of the whole vehicle.

"Gross weight is not a primary consideration in the design of space
vehicles... paper studies based on weight optimization have ... vastly
overrated the importance of weight, particularly for the booster stage,
which is of course the heaviest stage..." -- Del Tischler, 1962

--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

(Henry Spencer) wrote:
In article ,
Ian Woollard wrote:
It could only work for that short period of time the craft was still in
useful air.

Clearly, however the ISP over that time is extremely high for a solid,
and reduces the GLOW of the vehicle quite a bit...

And we care about that... why, exactly?

Depends on the objective. If one's intent is a SSTO _and_ SSTE (Single
Stage to Earth) RLV then I'd expect a designer would not want to deal with
the problems of de-orbiting a behemoth.

I'd like to know how you plan to return your behemoths from orbit, get them
back to your launch site, and do repeated launches with them without
breaking the bank on the extra ground infrastructure costs associated with
handling behemoths. There are advantages to keeping SSTO/SSTE launch
vehicles as compact as possible - within reason.

A great many misconceptions, superstitions, and outright myths about
launcher design can be traced to the habit -- inappropriately inherited
from the missile business -- of thinking of gross liftoff weight as an
important figure of merit.

Especially when the reduction in weight is coming out of the propellants,
the cheapest and most easily-designed part of the whole vehicle.

"Gross weight is not a primary consideration in the design of space
vehicles... paper studies based on weight optimization have ... vastly
overrated the importance of weight, particularly for the booster stage,
which is of course the heaviest stage..." -- Del Tischler, 1962

--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |


keep on preachin brother!

especially when ultralight, high performance aerospace widgets are measured in
thousands of dollars per ounce and fuel and normal metal parts are measured in
dollars per pound!

Blll "big dumb booster fan" Fish

Henry Spencer wrote:
In article ,
Ian Woollard wrote:

It could only work for that short period of time the craft was still in
useful air.

Clearly, however the ISP over that time is extremely high for a solid,
and reduces the GLOW of the vehicle quite a bit...

And we care about that... why, exactly?

Only because the GLOW suggested that the airbreathing was working. The
GLOW is reasonably unimportant, but ISP clearly isn't. Airbreathing for
a first stage (*not* an upper, orbital stage) is a much more respectable
concept, atleast two launchers use that- Pegasus, and SpaceShip One; and
several others, such as Black Horse (fuel would be lifted using a
transport plane) have proposed to use it. It was seriously considered
for the Space Shuttle and the N-1 IRC.

James Logajan wrote:

(Henry Spencer) wrote:
In article ,
Ian Woollard wrote:
It could only work for that short period of time the craft was still in
useful air.

Clearly, however the ISP over that time is extremely high for a solid,
and reduces the GLOW of the vehicle quite a bit...

And we care about that... why, exactly?

Depends on the objective. If one's intent is a SSTO _and_ SSTE (Single
Stage to Earth) RLV then I'd expect a designer would not want to deal with
the problems of de-orbiting a behemoth.

I'd like to know how you plan to return your behemoths from orbit, get them
back to your launch site, and do repeated launches with them without
breaking the bank on the extra ground infrastructure costs associated with
handling behemoths. There are advantages to keeping SSTO/SSTE launch
vehicles as compact as possible - within reason.

Assuming they're VTVL (and above a certain size range, they pretty
much have to be), a roughly bell-shaped 'behemoth' may still have pretty
low re-entry surface heat load. And unless there's an emergency, one
simply lands *at* the launch site (maybe, maybe not in an adjacent
fresh-water body), unless there's scheduling reasons to land at a
different launch site, and re-launch with other payloads from there.

And moving big (but after landing, not terribly heavy, as a chemical
SSTO must necessairily be) objects on land isn't new technology. Check
any strip mine...



--

You know what to remove, to reply....