Jet engine 1st stage

I am sure this topic has been covered here at some time but I missed
it.

Would it be feasible to use air breathing jet engines as the 1st stage
(or as strap-ons) of a launch system? Of course, that is exactly what
White Knight is but what about on a larger scale unmanned? This would
mean you do not have to lift the oxidizer for the 1st stage but max
altitude is limited. Re-use would be a problem if you drop em in the
ocean.

wrote in message
ups.com...
I am sure this topic has been covered here at some time but I missed
it.

Would it be feasible to use air breathing jet engines as the 1st stage
(or as strap-ons) of a launch system? Of course, that is exactly what
White Knight is but what about on a larger scale unmanned? This would
mean you do not have to lift the oxidizer for the 1st stage but max
altitude is limited. Re-use would be a problem if you drop em in the
ocean.

There was quite a detailed discussion of this many years ago. Back then, I
remember it being called "pogo". If you do a Google Groups search for "pogo
jet engine first stage", you'll find news articles about this concept.

The above led me to he

POGO (a.k.a. Jet Engine Launch Assist Concept (JELAC))
http://www.alt-accel.com/pogo/pogo.htm

Jeff
--
Remove icky phrase from email address to get a valid address.

On Mon, 19 Sep 2005 16:25:28 -0400, "Jeff Findley"
wrote:
wrote in message
oups.com...
I am sure this topic has been covered here at some time but I missed
it.

Would it be feasible to use air breathing jet engines as the 1st stage
(or as strap-ons) of a launch system? Of course, that is exactly what
White Knight is but what about on a larger scale unmanned? This would
mean you do not have to lift the oxidizer for the 1st stage but max
altitude is limited. Re-use would be a problem if you drop em in the
ocean.

There was quite a detailed discussion of this many years ago. Back then, I
remember it being called "pogo". If you do a Google Groups search for "pogo
jet engine first stage", you'll find news articles about this concept.

The above led me to he

POGO (a.k.a. Jet Engine Launch Assist Concept (JELAC))
http://www.alt-accel.com/pogo/pogo.htm

Short version:

It might help slightly, but the added drag quickly eats up the
advantage of not carrying oxidizer as speed increases in a vertical
launch. In addition, modern jet engines are not designed to be at
their best under these circumstances. You'd probably be better off
with a big crude 1950's style engine than a modern turbofan. In
addition, jet engines aren't disposable on the scale of minutes of
operation, and it would probably cost too much to make it practical.

Regards,
Jack Tingle

In article . com,
wrote:
Would it be feasible to use air breathing jet engines as the 1st stage
(or as strap-ons) of a launch system?

Yes, but with the exceptions of air launch from an existing aircraft, and
systems which use the jets for some other purpose as well, using rockets
is better.

Jet engines and their air intakes are complex and heavy, work only over
limited ranges of speed and altitude, and are quite fussy about the
smoothness of the incoming airflow (which means you can't just hang them
on anywhere). Rocket engines are light and compact, don't care about
speed or airflow, and work *better* as altitude increases.

This would mean you do not have to lift the oxidizer for the 1st stage...

Why is that an advantage? Liquid oxygen is compact, relatively easy to
store and handle, and so inexpensive that it's nearly free. It *is*
heavy... but with rockets, extra thrust is cheap.

Design group after design group has come up with an elegant jet/rocket
design, and as an afterthought compared it to an all-rocket approach...
and been startled to discover that the all-rocket system looked to be
simpler, more capable, and cheaper both to develop and to operate.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

"jtingle" wrote in message
...
Short version:

It might help slightly, but the added drag quickly eats up the
advantage of not carrying oxidizer as speed increases in a vertical
launch. In addition, modern jet engines are not designed to be at
their best under these circumstances. You'd probably be better off
with a big crude 1950's style engine than a modern turbofan. In
addition, jet engines aren't disposable on the scale of minutes of
operation, and it would probably cost too much to make it practical.

I wouldn't go all the way back to 50's style engines. Any modern turbojet
(used in any modern jet fighter) would suffice. For a demonstrator (e.g.
DC-X like vehicle), you could use turbojets from just about any retired jet
fighter.

The advantage here is that you can use proven turbojet technology to create
a reusable first stage that's far cheaper to operate than your typical
expendable rocket powered first stage and goes faster and/or higher than air
launch from a jet aircraft. True the performance may not be all that great
by rocket powered first stage standards, but it's far better than air launch
from a jet aircraft, and the cost may not be that much higher than using a
carrier aircraft since it's using much the same technology (turbojets).

Jeff
--
Remove icky phrase from email address to get a valid address.

(Henry Spencer) wrote:

...
Design group after design group has come up with an elegant jet/rocket
design, and as an afterthought compared it to an all-rocket approach...
and been startled to discover that the all-rocket system looked to be
simpler, more capable, and cheaper both to develop and to operate.

Which begs the question, why don't we use them for aircraft? I'm not
trying to argue that we should, it's just that every time I see this kind
of discussion, that comparison is left hanging.

What is it about space launches that makes rockets better, and what is it
that is different about atmospheric flight that makes jets better? Is it
reusability? Fuel economy (and why doesn't that matter for space
launches)? The altitude/pressure thing (surely that wouldn't be such an
issue for first stages)? Weight (why isn't that a problem for aircraft)?
Raw peak thrust? Maybe it's the fact that space launches are so brief we
need less fuel?

I can make some uneducated guesses, but I'd really appreciate having the
comparison clarified.

/kenw
Ken Wallewein
K&M Systems Integration
Phone (403)274-7848
Fax (403)275-4535

www.kmsi.net

"Henry Spencer" wrote in message
...
In article . com,
wrote:
Would it be feasible to use air breathing jet engines as the 1st stage
(or as strap-ons) of a launch system?

Yes, but with the exceptions of air launch from an existing aircraft, and
systems which use the jets for some other purpose as well, using rockets
is better.

Jet engines and their air intakes are complex and heavy, work only over
limited ranges of speed and altitude, and are quite fussy about the
smoothness of the incoming airflow (which means you can't just hang
them on anywhere). Rocket engines are light and compact, don't care
about speed or airflow, and work *better* as altitude increases.

This would mean you do not have to lift the oxidizer for the 1st stage...

Why is that an advantage? Liquid oxygen is compact, relatively easy to
store and handle, and so inexpensive that it's nearly free. It *is*
heavy... but with rockets, extra thrust is cheap.

Design group after design group has come up with an elegant jet/rocket
design, and as an afterthought compared it to an all-rocket approach...
and been startled to discover that the all-rocket system looked to be
simpler, more capable, and cheaper both to develop and to operate.

Hi, Henry - what then are your thoughts on MIPCC??

To a layman, it *seems* like it might work (as a first stage).. with a huge
cross-range advantage over all-rocket.

Thanks,
Cameron:-)

Henry Spencer wrote:
In article . com,
wrote:
Would it be feasible to use air breathing jet engines as the 1st stage
(or as strap-ons) of a launch system?

Yes, but with the exceptions of air launch from an existing aircraft, and
systems which use the jets for some other purpose as well, using rockets
is better.

Though modern carbon fibre technologies also make possible low cost,
custom aircraft, as proposed by T-Space:

http://www.transformspace.com/index....F15F270F2B83AA

"t/Space is working with Scaled Composites to create a custom Very
Large Aircraft(VLA), which will carry the CXV and the QuickReach 2
booster underneath its' body. This is an approach very similar to the
White Knight carrying SpaceShipOne. The CXV and its booster are too
heavy to be carried under the wing of an aircraft, like the Pegasus
from Orbital Sciences is carried under the wing of an L-1011 airliner.
It's also too large to be carried and launched from the cargo bay of an
aircraft like the QuickReach, which will roll out the cargo hold of a
C-17 or C5A. An alternative to the custom VLA is to modify and extend
the landing gear of a B-747 to provide sufficient ground clearance to
carry the CXV and booster."

Henry Spencer wrote:
Yes, but with the exceptions of air launch from an existing aircraft, and
systems which use the jets for some other purpose as well, using rockets
is better.

That "for some other purpose as well" raises a question that's been
kicking around in my head for a while.

If a launcher has jet engines for cruise back/landing, what benefit can
those engines deliver during launch? Would it be enough to help
minimize the weight penalty of the engine and landing fuel?

Mike Miller

Ken Wallewein wrote:

What is it about space launches that makes rockets better, and
what is it that is different about atmospheric flight that
makes jets better?

Short answer: space launches are acceleration missions while
atmospheric flights are predominantly cruise missions.

Jim Davis