Atmospheric Flight to Orbit

On Mar 1, 5:12 pm, (Henry Spencer) wrote:
In article . com,

Quadibloc wrote:
So why not get rid of the first stage, fly a plane as high and fast as
we can, and then have the rocket start its journey from the moving
plane? That way, we build a much smaller rocket for the same payload,
and the big expensive first stage is replaced by an airplane trip.

The idea is not ridiculous, but whether you can get big cost reductions
that way is unproven, at best. A rocket first stage is not particularly
costly, especially if you can recover and reuse it; it is the upper stage
that's expensive to build and maintain. And big airplanes are expensive,
and *custom-built* big airplanes are very expensive.

My feeling is that it's potentially a sensible idea, if you can fit on an
existing aircraft. Building your own aircraft, it's much more difficult
to see a net gain.

Even with an existing aircraft, it's by no means clear that you save
money. The example of Pegasus and Taurus is not encouraging. Pegasus is
air-launched from under a slightly-modified ex-airliner TriStar. Taurus
is essentially a wingless Pegasus on top of a big existing solid rocket
motor, for ground launch. Taurus's price is about 50% more than Pegasus's,
but it has about 3x the payload. (Of course, cost and price are different
things, but cost is harder to assess...)

Perhaps the problem is that the first stage of a rocket makes the
rocket go really fast, and an airplane burning atmospheric oxygen
doesn't go nearly that fact, so you can't really eliminate a whole
stage that way, making the benefits not worth the bother.

An aircraft, especially an off-the-shelf airliner, indeed doesn't give you
as much boost as a good rocket first stage. However, it probably is
*enough* to eliminate a stage -- even people who don't think SSTO is
possible will reluctantly concede that a really good upper stage doesn't
need a *lot* of initial boost to reach orbit with a modest payload.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

".... big airplanes are expensive, and *custom-built* big airplanes
are very expensive."

For that matter, custom-built *small* airplanes are pricey. I believe
the cost overruns for the DARPA RASCAL's launcher plane were the main
reason for its eventual cancellation.

IIRC, in RASCAL they wanted to use a trick employed by Soviet
interceptor jets as far back as the late 50s: carry along LOX and
inject it into the (otherwise air-breathing) engines late in the
climb, when air starts to get thin. To make this approach work
optimally, you undoubtedly need to design a whole new aircraft with
the technique in mind. But that takes you down relatively unexplored
evolutionary paths, and that kind of thing almost always gets
expensive in aerospace engineering. Given the mission rationale of
Soviet interceptor jets -- taking down strategic bombers -- they could
rationalize this innovative use of existing flight hardware pushed to
its upward screaming limits, and accept the risk of possible loss of
craft and crew. Milions of lives would be at stake, after all. But
if you're pioneering new space access ideas, on a modest budget, it's
a different game, with different rules.

-michael turner

Craig Fink wrote:

:I would think that the advantages of airbreathing engines are tremendous. A
ayload increase in the 100% to 1000% range. There is a huge performance
:gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
:airbreathing engines. From 600 for the best chemical rockets to the
:1000-4000 for airbreathing engines. Doubling the ISP of the best rocket
:engine will more than double the payload.
:
:In my opinion, not much has been done or studied to bridge this gap. If your
:trades don't give a serious advantage then something is wrong with your
:trades. Like, maybe they had the wrong engine.

Perhaps you'd care to actually make your case with a hypothetical
vehicle?

Remember, the goal is to get stuff to orbit (or beyond).

--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw

"Craig Fink" wrote in message
ink.net...
I would think that the advantages of airbreathing engines are tremendous. A
payload increase in the 100% to 1000% range. There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines. Doubling the ISP of the best rocket
engine will more than double the payload.

In my opinion, not much has been done or studied to bridge this gap. If
your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.

The regulars here have excersized diplomacy in not pointing out that
I have a vested interest in finding a use for air breathing engines for
spaceflight. I did a short talk on an air breathing engine I invented
at Space Access 04. On paper it should have a very high T/W ratio
with fair fuel consumption. Better than any jet flying today. I did
the trades. On pure performance, pure rocket wins every time. I
have to find other reasons to justify use of my concept.

The ABE Isp is only good for narrow bands of speed and altitude. The
very high weight of most air breathing engines is dead mass for the
rockets to carry from their cut off velocity to the vehicle final velocity.
That dead mass eats up far more fuel than is saved in the early climb.
My concept engine, a variation on the air-turborocket, should get
25+ to 1 thrust to weight, with an Isp well over 1,000. The trades still
don't close for it on performance alone.

--
Craig Fink
Courtesy E-Mail Welcome @
--

john hare wrote:

My thinking is use enough airbreathing engine to safely fly the stage
back from serious down/cross range distances. Any advantage in
airbreathing engines will not be in performance. It will be in
operational
flexibility. If the trades do not give serious advantages in that aspect,
then the airbreathing engines should be dropped.

Cool, so your engine is an attempt to bridge the ISP gap between jets and
rockets. Sounds like it does.

A child must learn to crawl before it can walk, then walk before it can run.
Sounds like your engine is in the crawling stage of Atmospheric Flight to
Orbit. Does your engine take you from 0 to 5k-6k fps with an ISP of 1000+?

It also sounds like your study was attempting to run all the way to Orbit.
An SSTO? If you turned the engine off, you should have dropped it. What was
your performance gain when you turned the engine off? Could I have a copy
of your paper? Sounds like interesting reading.

--
Craig Fink
Courtesy E-Mail Welcome @
--

john hare wrote:


"Craig Fink" wrote in message
ink.net...
I would think that the advantages of airbreathing engines are tremendous.
A
payload increase in the 100% to 1000% range. There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines. Doubling the ISP of the best rocket
engine will more than double the payload.

In my opinion, not much has been done or studied to bridge this gap. If
your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.

The regulars here have excersized diplomacy in not pointing out that
I have a vested interest in finding a use for air breathing engines for
spaceflight. I did a short talk on an air breathing engine I invented
at Space Access 04. On paper it should have a very high T/W ratio
with fair fuel consumption. Better than any jet flying today. I did
the trades. On pure performance, pure rocket wins every time. I
have to find other reasons to justify use of my concept.

The ABE Isp is only good for narrow bands of speed and altitude. The
very high weight of most air breathing engines is dead mass for the
rockets to carry from their cut off velocity to the vehicle final
velocity. That dead mass eats up far more fuel than is saved in the early
climb. My concept engine, a variation on the air-turborocket, should get
25+ to 1 thrust to weight, with an Isp well over 1,000. The trades still
don't close for it on performance alone.

In article . net,
Craig Fink wrote:
I would think that the advantages of airbreathing engines are tremendous.

Yes, many people keep thinking that, and it accounts for the continuing
obsession with the subject. As John noted, when you look more carefully
at the issues, the rocket engines actually win on performance every time.

...There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines.

Only at low speeds. An orbital vehicle does much of its accelerating at
very high speeds, where the Isp advantage is much smaller and the
technical problems of airbreathing are daunting.

And even at low speeds, that price for that high-sounding Isp is very
heavy engines.

Doubling the ISP of the best rocket
engine will more than double the payload.

Uh, no, it's not that simple. Other things being equal, such a gain in
Isp would indeed have fairly impressive effects on payload... but other
things are *not* equal. Isp is not the only important number in *vehicle*
performance.

To take a simpler case, I believe the highest Isp ever actually measured
for a chemical rocket is still the 542s of the Li/F2/H2 engine tested in
the early 1960s. Yet if you sketch out a *vehicle* using that
combination, you find that for Earth-to-orbit, it never performs better
than LOX/LH2, despite an Isp advantage of nearly 100s. Its density is so
low that the vehicle hardware ends up quite heavy, and that completely
wipes out the Isp advantage.

(And similarly, LOX/LH2 has an Isp advantage of over 100s over the older
combinations like LOX/kerosene... yet achieving high *stage* performance
is actually easier with LOX/kerosene. The handling complications and low
density of LH2 more than cancel the Isp advantage.)

Air is the same way, only worse, much worse. Even at sea level it's three
orders of magnitude less dense than LOX, and the impact of that on engine
mass is tremendous. A jet engine with thrust/weight of 10 is impressive,
while a rocket engine with T/W of 100 is nothing very special. And those
are the numbers at sea level: as the air thins out, the jet's T/W
deteriorates rapidly, while the rocket's *increases*.

In my opinion, not much has been done or studied to bridge this gap. If your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.

It's been studied incessantly, and the answer keeps coming out the same:
for getting into space, rockets are better. The airbreathing-engine
enthusiasts keep insisting that this result *cannot possibly* be right --
that the Emperor just *couldn't* be standing there without any clothes on,
so therefore he somehow isn't. Need more studies, with yet more newer and
better assumptions -- they *know* what the answer is supposed to be, by
God, and they won't give up until they get it!

The most ingenious of the airbreathing folks in recent times, the HOTOL
designers, have recently shamefacedly admitted that when they compared
HOTOL to an all-rocket solution, to their horror they found that the
rockets looked better...
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

"Craig Fink" wrote in message
nk.net...
Cool, so your engine is an attempt to bridge the ISP gap between jets and
rockets. Sounds like it does.

A child must learn to crawl before it can walk, then walk before it can
run.
Sounds like your engine is in the crawling stage of Atmospheric Flight to
Orbit. Does your engine take you from 0 to 5k-6k fps with an ISP of 1000+?

It is an engine concept with a reasonable chance of working, not hardware.
It would be usefull to about that speed if very active measures were taken
to handle intakes and thermal problems. The variable intakes to handle that
mach variety mass more than the engine itself. The heat loads on the
vehicle
and engine through that range add considerable mass, complexity and design
problems.

It also sounds like your study was attempting to run all the way to Orbit.
An SSTO? If you turned the engine off, you should have dropped it. What
was
your performance gain when you turned the engine off? Could I have a copy
of your paper? Sounds like interesting reading.

I didn't do a formal paper. To get an idea of the concept, look up
air-turborockets.
Then check out centrifugal compressors and radial inflow turbines. My
concept
recognizes the similarity between a squirrel cage fan and those two
turbomachines
to give a regen cooled engine.

My point is that I have a vested interest in air breathing engines for this
purpose,
and they fail.
--
Craig Fink
Courtesy E-Mail Welcome @
--

john hare wrote:


"Craig Fink" wrote in message
ink.net...
I would think that the advantages of airbreathing engines are tremendous.
A
payload increase in the 100% to 1000% range. There is a huge performance
gap (ISP to SPF Specific Fuel Consumption) between rocket engines and
airbreathing engines. From 600 for the best chemical rockets to the
1000-4000 for airbreathing engines. Doubling the ISP of the best rocket
engine will more than double the payload.

In my opinion, not much has been done or studied to bridge this gap. If
your
trades don't give a serious advantage then something is wrong with your
trades. Like, maybe they had the wrong engine.

The regulars here have excersized diplomacy in not pointing out that
I have a vested interest in finding a use for air breathing engines for
spaceflight. I did a short talk on an air breathing engine I invented
at Space Access 04. On paper it should have a very high T/W ratio
with fair fuel consumption. Better than any jet flying today. I did
the trades. On pure performance, pure rocket wins every time. I
have to find other reasons to justify use of my concept.

The ABE Isp is only good for narrow bands of speed and altitude. The
very high weight of most air breathing engines is dead mass for the
rockets to carry from their cut off velocity to the vehicle final
velocity. That dead mass eats up far more fuel than is saved in the early
climb. My concept engine, a variation on the air-turborocket, should get
25+ to 1 thrust to weight, with an Isp well over 1,000. The trades still
don't close for it on performance alone.

On 2 Mar, 01:12, (Henry Spencer) wrote:
In article . com,

Quadibloc wrote:
So why not get rid of the first stage, fly a plane as high and fast as
we can, and then have the rocket start its journey from the moving
plane? That way, we build a much smaller rocket for the same payload,
and the big expensive first stage is replaced by an airplane trip.

The idea is not ridiculous, but whether you can get big cost reductions
that way is unproven, at best. A rocket first stage is not particularly
costly, especially if you can recover and reuse it; it is the upper stage
that's expensive to build and maintain. And big airplanes are expensive,
and *custom-built* big airplanes are very expensive.

T-Space have argued otherwise. I suspect they would argue that custom
built big planes were very expensive, when prototypes were needed and
then aluminium moldings. However, carbon fibre can be formed quite
cheaply in one-offs, and the simulations can be done on computer. All
this could be true as long as the plane doesn't need good performance
or good economy.

And with the T-Space approach, the launch speed is trivial. The
benefit comes from a higher launch altitude and more escape options if
something goes wrong.

(Henry Spencer) wrote:

The airbreathing-engine
enthusiasts keep insisting that this result *cannot possibly* be right --
that the Emperor just *couldn't* be standing there without any clothes on,
so therefore he somehow isn't. Need more studies, with yet more newer and
better assumptions -- they *know* what the answer is supposed to be, by
God, and they won't give up until they get it!

That's why I keep suggesting that they leave it to military and
commercial aviation -- which have much bigger markets, development
budgets, and constituencies than space.

When air forces and/or airlines demonstrate sustained flight with
worthwhile loads at Mach 5 or 10, then -- not before -- I'll be happy,
nay eager, to think about replacing those loads with a cheap and
cheerful rocket stage to orbit.

Monte Davis
http://montedavis.livejournal.com

In article .com,
Alex Terrell wrote:
The idea is not ridiculous, but whether you can get big cost reductions
that way is unproven, at best. A rocket first stage is not particularly
costly, especially if you can recover and reuse it; it is the upper stage
that's expensive to build and maintain. And big airplanes are expensive,
and *custom-built* big airplanes are very expensive.

T-Space have argued otherwise.

T/Space, so far, is using existing aircraft... and existing aircraft paid
for by other people, at that. Unless things have changed recently, the
farthest they've suggested going toward a custom aircraft is putting
longer landing gear on a 747. (And note that even a stock 747 is a $200M
aircraft, unless you can get a good deal on an old used one.)

I suspect they would argue that custom
built big planes were very expensive, when prototypes were needed and
then aluminium moldings. However, carbon fibre can be formed quite
cheaply in one-offs, and the simulations can be done on computer.

Yes, if all you want is an *experimental* aircraft, it might not be all
that costly any more. Something that can be certified -- so it can carry
cargo for paying customers -- is a very different kettle of fish. Getting
a new aircraft certified costs 10-100x the cost of the prototype. (And a
big all-new design by a new company is going to be at the high end.)

It's easy to grossly underestimate just how difficult and expensive it is
to build, test, and certify a new aircraft. Even Burt Rutan has been
tripped up by this.

By the way, simulations are not the same thing as flight tests. To
quote Brig. Gen. Duane W. Deal, USAF, one of the members of the Columbia
accident-investigation board:

"To ensure it employs technology over technique, an organization must,
if possible, certify all critical hardware through testing -- not just
analysis. However, if analysis must be used, it should be verified by
testing. For example, even today's computerized aircraft-design process
does not eliminate the necessity for flight-testing..."

--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

On Sun, 4 Mar 2007 18:35:25 GMT, in a place far, far away,
(Henry Spencer) made the phosphor on my monitor
glow in such a way as to indicate that:

In article .com,
Alex Terrell wrote:
The idea is not ridiculous, but whether you can get big cost reductions
that way is unproven, at best. A rocket first stage is not particularly
costly, especially if you can recover and reuse it; it is the upper stage
that's expensive to build and maintain. And big airplanes are expensive,
and *custom-built* big airplanes are very expensive.

T-Space have argued otherwise.

T/Space, so far, is using existing aircraft... and existing aircraft paid
for by other people, at that.

As long as they continue to get support from the Air Force. If the
blue suiters pull out, but DARPA wants to continue the program, it
would be interesting to see what they do. Go to Canada, perhaps? :-)


Unless things have changed recently, the
farthest they've suggested going toward a custom aircraft is putting
longer landing gear on a 747. (And note that even a stock 747 is a $200M
aircraft, unless you can get a good deal on an old used one.)

You actually can get a good deal on a used one, but they don't have
tail doors, do they? All of the 747Fs that I'm aware of are side
loaders.

I suspect they would argue that custom
built big planes were very expensive, when prototypes were needed and
then aluminium moldings. However, carbon fibre can be formed quite
cheaply in one-offs, and the simulations can be done on computer.

Yes, if all you want is an *experimental* aircraft, it might not be all
that costly any more. Something that can be certified -- so it can carry
cargo for paying customers -- is a very different kettle of fish. Getting
a new aircraft certified costs 10-100x the cost of the prototype. (And a
big all-new design by a new company is going to be at the high end.)

That's an interesting legal question. It seems to me that if that's
its only purpose, you simply declare it a flyback first stage, and get
a launch license for it with the rest of the vehicle. No
certification required. ;-)

In fact, I wonder if OSC got a special type certification for
Stargazer, when they modded the Tri-Star to carry Pegasus? If not,
they're flying "uncertified" as well. With paying customers.