poor man's rocket

"Zoltan Szakaly" wrote in message I want to come clear
here, the reason I am so interested in this
because I have an engine that has a high Isp (over 4,000) and is light
weight and cheap so it can achieve a thrust to weight of 100. (I
realize that thrust is force and weight is mass, I am using the terms
loosely here, I am dividing pounds by pounds) I am working on the
development of a flying car but I am hoping to also use the engine as
a first stage engine to put payloads into orbit.

I think the air breather wins no matter what somebody just needs to
have enough balls to build one and fly it.

Zoltan

I've posted an idea for a peroxide powered turbo-prop vtol spaceplane on the
halfbakery website at:

http://www.halfbakery.com/idea/prope...rocket_20plane



I've included a link to an aerobatic plane that can fly vertically in
sustained flight (someone else has included a link to a biplane equivalent),
a link to Glen Olson's pogo page and a link to Armadillo Aerospace but i
couldn't find a link to a self standing, simple explanation of a 'walter
style' peroxide turbine. Does anyone know of a site which I could include a
link to?

Toby

(Zoltan Szakaly) :

Jet engine:
Isp= 5,000 Thrust to weight: 10

Rocket engine:
Isp= 350 Thrust to weight: 100

Rocket system ok but does not account for gravity losses or air drag.

There are clearly variations but these are somewhat representative
numbers. The jet engine's weight limits the mass ratio that can be
accomplished. Here I will try to compute performance for both.

If I start with a 100 ton take off mass, the rocket would have a 150
tons of thrust and a 1.5 ton engine. The payload, fuel tanks,
structure would limit the mass fraction to between 0.88 and 0.95 so
the velocity increment achieved would be between 7,280 and 10,300
m/sec

Jet Design mass ratio ok. Lets assume it lifts at .5 G away from Earth, the
mass ratio is not going to change much with the claimed ISP

The air breathing engine based vehicle would have a mass fraction of
between 0.73 and 0.8 and the velocity increment would be 64,222 to
78,942 m/sec

Clearly the air breathing engine wins. Of course I assumed no air drag
here.

Really, after 100 seconds if your jet works as claimed if you went straight
up you would be at 49 kilometers where no jet engine would work well. But
your speed would be only 500 meters per second, you still need those rockets,
but now you mass ratio is far worse.

I want to come clear here, the reason I am so interested in this
because I have an engine that has a high Isp (over 4,000) and is light
weight and cheap so it can achieve a thrust to weight of 100. (I
realize that thrust is force and weight is mass, I am using the terms
loosely here, I am dividing pounds by pounds) I am working on the
development of a flying car but I am hoping to also use the engine as
a first stage engine to put payloads into orbit.

Try for the flying car, it should always be flying relatively low, but I
think you need to fly it (your engine design) to see the real results.

I think the air breather wins no matter what somebody just needs to
have enough balls to build one and fly it.

I think you need to do a lot more math modelling, it just can't work once you
climb high enought, and you can't get the speed if you fly low enough.

Zoltan

Earl Colby Pottinger


--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
the time? http://webhome.idirect.com/~earlcp

Penguinista wrote

Still, a jet powered first stage dropping of ~mach 3 could
make sense.

There are two categories of things that we want to put into LEO - people and
dumb mass (satellites, fuel etc). People must ride on man-rated equipment,
but that doesn't matter for dumb mass.

Not making that distinction is one of the main problems with the STS design
imo. In-space rendezvous and docking are well established.


People:

Take a shuttle and divide by 3. That's nine tons payload. Use five tons in
improving reuseability and safety, and perhaps not discarding an ET (though
that could even save payload).

Spend two tons of that on the single STS engine. Can you imagine what the
Rocketdyne engineers could do for immediate reusability with an extra two
tons to play with? Or the Shuttle safety guys, with nine tons to play with?
I can hear them drooling from England!

That's still four tons payload. 20 people at 200 kg, or ten at 400kg. Plenty
of carry-on baggage.

Let's look at a typical shuttle flightpath. At SRB seperation the mission is
flying at 4,300 ft/s and is 41 miles up. It's used up 2/3 of it's takeoff
mass. Our 1/3 model would mass around 150 tons at that point.



Could we build a jet to do that? Not yet. 3,400 ft/s and 18 miles up is
about the limit (SR-71). But we could build a piloted jet with a
kerosene/lox rocket boost that would do it, reusing some civilian airliner
parts like landing gear. Around 400 tons mission take-off, about the same as
a 747.

In-air loxing could more than half that, but landing is harder on gear and
runways than take-off, so you wouldn't gain much, and the engines have to be
pretty powerful anyway!


Dumb mass (cargo):

Could we also use the jets for cargo? Yes. We'd get around 15 tons useable
payload if we used single stage discardable rockets and only worried about
pre-separation safety. That's enough for most comsats and the like, and we
could also reassemble stuff in orbit if something larger was needed.


Build five jets and thirty orbiters, and you have a cheapish, safe,
high-capacity man-rated LEO system, which could be in operation in three to
five years. No scramjets. No new technology apart from the
immediately-reusable engines etc. No SRB's. No ET's. Just two manned,
immediately-reusable after refuelling, craft.


Just my 2c, and there are probably better ways. A mach ~3 separation would
still help.


--
Peter Fairbrother

Earl Colby Pottinger wrote in message

Really, after 100 seconds if your jet works as claimed if you went
straight
up you would be at 49 kilometers where no jet engine would work well.
But
your speed would be only 500 meters per second, you still need those
rockets,
but now you mass ratio is far worse.


...


Earl Colby Pottinger

My plan is to start vertically and then pitch over to say 45 degrees
and sustain 4G acceleration for about 70 seconds. This gets me near
mach 8, or 2,700 m/s speed. Somewhere between mach 6 and 8 I close the
air inlets and use oxidizer injection. (Here we are no longer talking
about a turbine engine, the vehicle under discussion is my ramjet
based SSTO) After mach 8 I clearly use the ramjet in pure rocket mode.

The SR71 uses turbines but it switches to ramjet mode at some
speed/altitude.

My "poor man's rocket" would simply be a suborbital spaceplane that
uses turbine jet engines with air first and oxidizer injection later.

Zoltan

Henry Spencer wrote

In article ,
Peter Fairbrother wrote:
There are two categories of things that we want to put into LEO - people and
dumb mass (satellites, fuel etc). People must ride on man-rated equipment,
but that doesn't matter for dumb mass.
Not making that distinction is one of the main problems with the STS design
imo...

Contrariwise: thinking that there is an important distinction there is
a sign of the immaturity of the field. Much of that "dumb" mass is
extremely expensive. Nobody would ship a $100M satellite to the Cape on
an unmanned cargo aircraft. Just reducing the chances of losing the cargo
is reason enough to put a crew aboard; any vehicle that is safe enough to
carry such costly cargos is safe enough to carry people.

(Moreover, any reusable vehicle that is reliable enough to pay off its
purchase price is safe enough to carry people. The hard, cold truth is
that the orbiters, not the crews, were the biggest losses on 28 Jan 1986
and 1 Feb 2003.)

(That's a political reality now, which you would now do better to consider
as becoming outdated)

The real question is: why are sats so expensive? It's because the mission
cost is lower bounded by the launch cost.

I could sell a comsat for $1M that would have a 95+% chance of having the
same eventual performance as the $100M sat, and pocket more than 1/2 of that
to boot. But if my sat went wrong, they'd have to spend another $gazillion
cost and wait on the launch of a replacement. That's what they spend the
other $99M for.

The "guy who pays"(tm) can spend lunch cost or more again on the sat,
without significantly affecting his balance sheet. Yes it's a lot more
complex than that, and involves many risk calculations, like the
availability of funding etc, but as far as he is concerned (and without him
it won't happen at all) he can risk twice or more launch cost on the sat.




Suppose it cost $500 to launch a satellite, at a 95% launch success
probablility. Would anyone risk of a life on that? Would anyone spend $100M
on a sat, if they could get a sat with a few fractions of a percent less
reliability for $100,000, and they didn't have to spend a $gazillion to
launch a replacement?


What stopped the STS launches? The bad publicity. People died. The money
equation wasn't affected. A far as that went, they could relaunch today.


What it comes down to is, you can launch sats at 98% launch success, but you
can't launch people at that probability. No matter the financial costings.


I give my respect to all who died. I already had it to give. I apologise if
any of them seem to be regarded as other than real, living people in
anything I have said here. You aren't.

--
Peter Fairbrother

Zoltan Szakaly wrote:

If you do not use
turbine blades for intake air compression you save weight and
your engine performance will improve with airspeed (ramjet).

In general specific impulse for airbreathers will fall off with
increased airspeed. At low speeds Isp might increase because of
increased efficiency but eventually the airbreather will come against
fundamental thermodynamic limits and Isp will drop as airspeed
increases. For example, you mentioned that your engine has an Isp of
5000 seconds. Assuming that your engine is indeed an airbreather and
that it is hydrogen powered, the highest airspeed at which it can
possibly deliver 5000 s is 2500 m/s where it will be operating at
100% efficiency. At higher speeds Isp must go down.

Jim Davis

(Zoltan Szakaly) writes:

Under what conditions are those numbers measured? Jet-engine Isp falls
off rapidly as speed builds up, and T/W falls off rapidly as altitude
builds up. (One reason why late-50s jet fighters sometimes had optional
rocket packs was that quite a small rocket made a huge difference in
power and maneuverability at high altitude.) Those are probably
sea-level-static numbers, which are grossly unrealistic as averages over
an accelerating, climbing trajectory.

The jet engine Isp falls off with speed because the turbine blades
become an impediment and the thrust falls off with altitude because of
the lack of air pressure. If you do not use turbine blades for intake
air compression you save weight and your engine performance will
improve with airspeed (ramjet).

Sorry, wrong. You forgot a little thing called "inlet drag." Ramjet
performance _also_ falls off with airspeed, as does scramjet performance.
A reasonable approximation is that the effective I_sp of an air-breathing
engine is _INVERSELY_ proportional to airspeed --- see the following very
widely reproduced figu

http://lifesci3.arc.nasa.gov/SpaceSettlement/Nowicki/SPBI1AB.HTM

Combining this approximation with the fact that the lousy thrust-to-mass ratio
of an airbreathing engine implies that an airbreathing vehicle almost certainly
=CANNOT= accelerate at more than one gee, and will therefore need wings, results
in the "Air-Breather's Burden" formula quoted by Henry Spencer:

http://www.islandone.org/Propulsion/SCRAM-Spencer1.html.


At high speeds the speed will compensate for the reduced air density
to a point.

....Except that the inlet drag rises even faster with airspeed.
TANSTAAFL.

-- Gordon D. Pusch

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

"Zoltan Szakaly" wrote:
The jet engine Isp falls off with speed because the turbine blades
become an impediment and the thrust falls off with altitude because of
the lack of air pressure. If you do not use turbine blades for intake
air compression you save weight and your engine performance will
improve with airspeed (ramjet).

Thank you for demonstrating you know absolutely nothing about
ramjets. This will help to put your future posts in their
proper perspective (e.g one of farcical, fantastical, naive, or
extraordinarily ill-informed, though there may be other
categories I have not identified yet).

Peter Fairbrother wrote:

Penguinista wrote

Still, a jet powered first stage dropping of ~mach 3 could
make sense.

There are two categories of things that we want to put into LEO - people and
dumb mass (satellites, fuel etc). People must ride on man-rated equipment,
but that doesn't matter for dumb mass.

Um, not if it's *your* dumb mass.

Really. If it's your very expensive satellite, you may well want the
chances of successful placement into orbit to be pretty close to that
expected of a manned vehicle. As might your insurers, if you can get
any.

Even if it's *just* fuel or water, presumably it was launched to
serve some other piece of expensive hardware that's already up there, or
waiting to launch soon after, and there may be stationkeeping, life
support, or mission launch window issues involved for whatever needs it.

Remember, we make no such distinctions with aeronautical or maritime
transportation....

Joann Evans wrote:

Peter Fairbrother wrote:
Remember, we make no such distinctions with aeronautical or maritime
transportation....

We do in postage. I usually do not pay more for invitations, bill
payments, etc. because the US postal system is good enough. Once
in a while I do pay more to have a lower chance of problems (like
when I sent our family's 120-yr old Bible across the county back
to my Aunt).

I think there would be a market for very high reliability launch
and high reliability launch.

-paul-
--
Paul E. Black )