Gas turbines for assisting rockets.

Would a gas turbine attached to a large rocket such as the space
shuttle provide enough additional thrust to make it worth having for
the initial take off. It could be dropped with the normal boosters
before leaving the atmosphere and maybe reused for later flights.
Thrust could be provided upto mach 5 and I presume the space shuttle
is still in the atmosphere at this point in its flight.
I also thought that some kind of catapult ie. mag lev or even steam
catapult could provide an additional push allowing a much larger
payload to be carried.

In article ,
Stephen wrote:
Would a gas turbine attached to a large rocket such as the space
shuttle provide enough additional thrust to make it worth having for
the initial take off. It could be dropped with the normal boosters
before leaving the atmosphere and maybe reused for later flights.

It is hard to make such schemes pay for themselves, rockets being cheap
and powerful. If you want to add thrust to the shuttle, you add more
rockets, or more rocket fuel (there has been some work on longer SRBs).

There have been occasional proposals to replace *small* solid strap-ons,
such as those used on earlier Deltas, with recoverable jet-engine pods.
The idea is not ridiculous, but to date it hasn't looked promising enough
for anyone to pursue it.

Thrust could be provided upto mach 5...

Not with any ordinary sort of turbine engine. They are at their best
below Mach 1 and are pretty useless beyond Mach 3. They are also quite
fussy about smooth airflow into their intakes, and they are heavy.

I also thought that some kind of catapult ie. mag lev or even steam
catapult could provide an additional push allowing a much larger
payload to be carried.

It's difficult to get much gain that way for a large vertically-launched
vehicle. Indeed, the easiest kind of catapult to build is a rocket sled...
which gets you back to just adding some more rocket power if you need
more performance.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

Launch vehicles with turbines and rockets have been considered in
concepts called RBCC (rocket-based combined cycle). I think that his
concept has been dropped from further funding.

Stephen wrote:
Would a gas turbine attached to a large rocket such as the space
shuttle provide enough additional thrust to make it worth having for
the initial take off. It could be dropped with the normal boosters
before leaving the atmosphere and maybe reused for later flights.
Thrust could be provided upto mach 5 and I presume the space shuttle
is still in the atmosphere at this point in its flight.
I also thought that some kind of catapult ie. mag lev or even steam
catapult could provide an additional push allowing a much larger
payload to be carried.

Launch vehicles with turbines and rockets have been considered in
concepts called RBCC (rocket-based combined cycle). I think that his
concept has been dropped from further funding.

Not quite correct... RBCC uses no turbomachinery (rotating parts). The
principle of an RBCC is that you have a ramjet/scramjet engine with rocket
nozzles imbedded in the flowpath. At low speeds, it would be used in rocket
mode (with air augmentation) until at speeds the ramjet would run. At that
point, it comes out of rocket mode, and runs as a combined ramjet/scramjet
engine until reaching the upper limit of scramjet performance. Then, the
rocket mode kicks in to reach orbit. There's been a lot of work on RBCC
vehicles here at Georgia Tech... we very nearly used such a system in a
design study competition. Our advising professor has used RBCC technology
in many of his studies and research.

Realistically, you won't see RBCC/TBCC engines used except on reuseable
single- or two-stage RLV's.

Bob,

You're right about no turbomachinery in RBCC. For some reason, I've got
turbomachinery on the brain :-)

Does or did your advising professor do consulting work for the Marshall
center?

"Bob Martin" wrote in message
...
Launch vehicles with turbines and rockets have been considered in
concepts called RBCC (rocket-based combined cycle). I think that his
concept has been dropped from further funding.

Not quite correct... RBCC uses no turbomachinery (rotating parts). The
principle of an RBCC is that you have a ramjet/scramjet engine with rocket
nozzles imbedded in the flowpath. At low speeds, it would be used in
rocket
mode (with air augmentation) until at speeds the ramjet would run. At
that
point, it comes out of rocket mode, and runs as a combined ramjet/scramjet
engine until reaching the upper limit of scramjet performance. Then, the
rocket mode kicks in to reach orbit. There's been a lot of work on RBCC
vehicles here at Georgia Tech... we very nearly used such a system in a
design study competition. Our advising professor has used RBCC technology
in many of his studies and research.

Realistically, you won't see RBCC/TBCC engines used except on reuseable
single- or two-stage RLV's.

"steve podleski" wrote
Bob,

You're right about no turbomachinery in RBCC. For some reason, I've got
turbomachinery on the brain :-)

Does or did your advising professor do consulting work for the Marshall
center?

I don't know... Dr. Olds runs Spaceworks ( http://www.sei.aero/ ) and
I'm pretty sure they do some consulting and such. Also, Bill Escher
at SAIC helped us out... he's done a lot of work on RLV development
(several RBCC designs, too, I think).

If you want, you can read our final report here (hosted by our team
leader):

http://www.prism.gatech.edu/~gte799i...StarRunner.pdf


And, we'll be presenting it at the JPC this coming July.

"Bob Martin" wrote in message
m...
"steve podleski" wrote
Bob,

You're right about no turbomachinery in RBCC. For some reason, I've got
turbomachinery on the brain :-)

Does or did your advising professor do consulting work for the Marshall
center?

I don't know... Dr. Olds runs Spaceworks ( http://www.sei.aero/ ) and
I'm pretty sure they do some consulting and such. Also, Bill Escher
at SAIC helped us out... he's done a lot of work on RLV development
(several RBCC designs, too, I think).

If you want, you can read our final report here (hosted by our team
leader):

http://www.prism.gatech.edu/~gte799i...StarRunner.pdf


And, we'll be presenting it at the JPC this coming July.

I glanced at the report enough to get an idea of the architecture.
IMO it is not a combined cycle approach. It has independant turbofans,
ram/scramjets, and rockets, plus ACES oxygen collection on board
an SSTO. I have a rather difficult time believing that a vehicle with 3
engine types, one of which (ram/scamjet) operates in two modes, can
outperform a simpler vehicle. Hardware mass and simplicity is more
of a cost driver than pure GLOW as a yardstick of economy.

Your vehicle would appear to take off at a million pounds, of which
just over 600,000 pounds is liquid hydrogen, 25,000 pounds payload,
with the balance being vehicle hardware of various types. The ~370,000
pounds of hardware in the budget would be overkill for a pure rocket
SSTO given equivalent development funding. There would be no need
for the pure rocket SSTO to develop scramjets, ACES to flight weight,
or to constrain the vehicle shape to one that can handle
sub/super/hypersonic
air breathing propulsion.

A dense fuel SSTO (RLV assumed) should be able to lift that
25,000 pound payload with 100,000 pounds of hardware at a GLOW
of 2,000,000 pounds. That would be just over a quarter of the dry mass
at the cost of doubling the GLOW. This in a much simpler vehicle.
1,875,000 pounds of Kero/LOX
per flight should be less expensive than the 600,000 pounds of liquid
hydrogen your vehicle lifts with. A TSTO with dense fuels could do
some better even today, not requiring even the SSTO risk.

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
you are currently involved in. A lot of interesting info and a good
study vehicle though. If no one did the work you are doing, critics
like me wouldn't have the information available to be critical with.

John Hare

Bob,

Thanks for the copy of the paper.

"Bob Martin" wrote in message
m...
"steve podleski" wrote
Bob,

You're right about no turbomachinery in RBCC. For some reason, I've got
turbomachinery on the brain :-)

Does or did your advising professor do consulting work for the Marshall
center?

I don't know... Dr. Olds runs Spaceworks ( http://www.sei.aero/ ) and
I'm pretty sure they do some consulting and such. Also, Bill Escher
at SAIC helped us out... he's done a lot of work on RLV development
(several RBCC designs, too, I think).

If you want, you can read our final report here (hosted by our team
leader):

http://www.prism.gatech.edu/~gte799i...StarRunner.pdf


And, we'll be presenting it at the JPC this coming July.

(Bob Martin) wrote in message om...

If you want, you can read our final report here (hosted by our team
leader):

http://www.prism.gatech.edu/~gte799i...StarRunner.pdf

I finally found the time to read this report. I'm glad I did. If
anyone hasn't read this report, you're missing an excellent piece of
work. I may not agree with everything they did, but reading this
report, I can *tell* what they did. This is how a design study report
should be written.

The design:

It's ambitious. It's for an SSTO RLV, which is as hard a vehicle to
build as can realistically be imagined. I don't think the business
case closes - but neither do they; they assume substantial government
support both in development and as an anchor tenant customer.

The vehicle uses four different propulsion systems: turbofan, ramjet,
scramjet, and rocket. It uses seven unproven technologies:
LH2-burning turbofan, ACES inflight LOX collection, scramjet
propulsion, linear aerospike, a takeoff sled, conformal LH2 tanks, and
SHARP TPS. One could quibble and point to the Me-163 takeoff sled,
but considering the loss rate of that aircraft, who would want to?

The complexity and unproven technology make me cringe from a
reliability perspective, but the authors anticipated that. They say
that normally a design team would include cost, operations, and safety
evaluations in each iteration of the design cycle, but in this case,
the performance requirements were so extreme that that they only
applied cost, operations, and safety criteria as a pass/fail filter
for the completed design.

The only real problem with StarRunner from an operations perspective
is the lack of intact abort throughout the flight envelope. (This
assumes you can live with handling hundreds of tons of NBP
hydrogen...) The gear is sized to accomodate the empty weight of the
vehicle only. They calculated that if they modified it to accomodate
the takeoff weight of the vehicle, it would add 10% to the GLOW. For
my money, it's worth it. Otherwise, if you have to abort shortly
after takeoff, you drop the thing into the Atlantic Ocean because you
don't have time or altitude to dump enough fuel to land.

Full size gear would also allow for incremental testing, which a
vehicle with four propulsion systems really deserves.

BTW, they assume this critter will operate out of KSC. I think
Edwards is the better home for it; Edwards has many miles of lakebed
to handle a refused takeoff, which is an important consideration for a
million pound vehicle taking off at 250 knots. Boy is that a lot of
kinetic enrgy.

Another abort consideration surprised me. They talk about dumping
fuel during an abort, but not about dumping LOX. With 550,000 lb of
LH2 aboard and 850,000 lb of LOX, you dump the LOX first. You can fly
around all day on the turbofans if you keep the hydrogen. You can
always dump it later if you need to.

Another couple technologies are relatively unknown to me. The authors
propose to use metal matrix composites for structure, and I don't know
very much about how mature that technology is. They also propose to
use electro-mechanical actuators in place of hydraulics, and I have
heard EMAs don't have the power hydraulics do. Does the F-16 use
EMAs? If so, a production fighter, they must be good enough for Uncle
Sam.

Finally, a question of the design team, and the only question this
report didn't answer. For the Mach 3 transition from turbofan to
ramjet, the isentropic ramp moves to cover the turbofans and uncover
the ramjets. I assume that's done in reverse order? I would move the
ramp halfway, light the ramjets, make sure they are up to par, then
shut down the turbofans, cover them with the ramp. Is this the
sequence you designed?

Again, good report y'all, recommended reading.

-R

One could quibble and point to the Me-163 takeoff sled,
but considering the loss rate of that aircraft, who would want to?

Didn't one of the AR-234 versions use a takeoff sled? I think the
earlier models used one, with a landing skid, but later ones got full
tricycle retractable.


The only real problem with StarRunner from an operations perspective
is the lack of intact abort throughout the flight envelope. (This
assumes you can live with handling hundreds of tons of NBP
hydrogen...) The gear is sized to accomodate the empty weight of the
vehicle only. They calculated that if they modified it to accomodate
the takeoff weight of the vehicle, it would add 10% to the GLOW. For
my money, it's worth it.

And really, that's not even all it would add. We didn't have time to
reiterate a trajectory and propellant load, so that's just the empty
weight supplied by the spreadsheet. Had we gone back, reflown the
trajectory and such, then it would have required more fuel, possibly
another rocket motor, and definately another turbofan or two---which
would require more fuel, another engine, etc. The vehicle just barely
closed as it was, so with takeoff gear the GLOW would have probably
been another 10 percent greater, at least.

Otherwise, if you have to abort shortly
after takeoff, you drop the thing into the Atlantic Ocean because you
don't have time or altitude to dump enough fuel to land.

Depends on the abort... if you lose three or four (out of 14) engines
right after takeoff, yeah, you have a problem. But assuming you can
get clear of land, the vehicle has enough power to stay airborne after
one or two engine losses.


BTW, they assume this critter will operate out of KSC. I think
Edwards is the better home for it; Edwards has many miles of lakebed
to handle a refused takeoff, which is an important consideration for a
million pound vehicle taking off at 250 knots. Boy is that a lot of
kinetic enrgy.

That's the point of the sled, though... a full takeoff roll takes
about 5500 feet, as I recall (been a while since I've read that
section). The shuttle landing runway is 15,000 feet long. And since
the sled doesn't have to fly, you can make it nice and big, and give
it large enough brakes to stop 1.2 million pounds in the room
remaining.

Another abort consideration surprised me. They talk about dumping
fuel during an abort, but not about dumping LOX. With 550,000 lb of
LH2 aboard and 850,000 lb of LOX, you dump the LOX first. You can fly
around all day on the turbofans if you keep the hydrogen. You can
always dump it later if you need to.

That was one of my sections; I guess we didn't proofread enough. I
meant both the hydrogen and the LOX, and used "propellant" or "fuel"
incorrectly.

Abort modes and such were not a part of the requirements for this;
since the competition was technically the "engine design" one, that's
where we concentrated our efforts (optimization of the ram/scram
system and the turbines). I wrote the whole "operations and aborts"
section more for fun and to say that we did do something rather than
as serious studies. And, we had neither the time nor the equipment to
properly simulate abort scenarios (we had four months from receiving
the RFP until we had to present for the class). As bad as it sounds,
we just kind of waved our hands and said "that sounds like it would
work."

Another couple technologies are relatively unknown to me. The authors
propose to use metal matrix composites for structure, and I don't know
very much about how mature that technology is. They also propose to
use electro-mechanical actuators in place of hydraulics, and I have
heard EMAs don't have the power hydraulics do. Does the F-16 use
EMAs? If so, a production fighter, they must be good enough for Uncle
Sam.

Not the standard F-16, but at least one has flown successfully with
EMA's--I believe as a demonstrator for part of the JSF program.

Finally, a question of the design team, and the only question this
report didn't answer. For the Mach 3 transition from turbofan to
ramjet, the isentropic ramp moves to cover the turbofans and uncover
the ramjets. I assume that's done in reverse order? I would move the
ramp halfway, light the ramjets, make sure they are up to par, then
shut down the turbofans, cover them with the ramp. Is this the
sequence you designed?

Again, this is a case of hand-waving. We wouldn't have been able to
do a proper analysis, but the setup you described sounds good.




Again, good report y'all, recommended reading.

Thank you.

I would love to be able to go back into the design and refine it
further, maybe do some alternate ideas... but unless we get the
opportunity to do so for a class, we simply don't have the time.