SSTO propulsion overview

In article ,
Ian Woollard wrote:
...You've turned a rocket first stage into
a jet first stage. In the process, you've made it harder to build and
more difficult to develop. For what? To save *LOX*? WHY???

A reusable flyback booster?

Almost certainly, the flyback propulsion system is going to end up being
separate from the boost propulsion system. For flyback, you want maximum
economy and modest thrust at medium-subsonic cruise speed; for boost,
reasonable economy and high thrust over a wide speed range.

Flyback propulsion almost certainly wants to be jets (although Kistler
proposed to do rocket lob-back), but that doesn't mean boost propulsion
has to be jets. The mother of all flyback boosters was the "Flyback F-1"
proposed for the shuttle: a Saturn V first stage with a big delta wing
and a row of ten jet engines under it. The jets didn't get involved until
after reentry.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

(Ian Woollard) wrote in message . com...
(Henry Spencer) wrote in message ...
Basically my calculations show that you can save the entire first
stage if you build an air breathing booster.

That's plausible. But so what? You've turned a rocket first stage into
a jet first stage. In the process, you've made it harder to build and
more difficult to develop. For what? To save *LOX*? WHY???

A reusable flyback booster?


http://www.grc.nasa.gov/WWW/RT1998/5...laszewski.html

Atomic rocket fuels - aka mon-atomic rocket fuels - contain vast
amounts of energy and yeild very low molecular weights, thus, produce
(theoretically) very high performances of 600 to 1,600 sec Isp. High
enough for SSTO performance with quite modest rocket designs.

Basically, H2 is converted into a stable form of 2 H atoms and mixed
with normal liquid hydrogen and kept at liquid helium temps to keep it
all from exploding. You end up with a monopropellant that's very
powerful, and a very simple rocket - either VTVL, HTHL, or some combo
- take your pick - all with structural fractions we've already
achieved.

http://sbir.grc.nasa.gov/launch/foctopsb.htm

Here's another roadmap to high performance.

"Henry Spencer" wrote in message
...
In article ,
johnhare wrote:
...the oxygen content of air is *four orders of magnitude*
less, per unit volume, than that of LOX. So you inevitably need big
heavy
machinery to handle air.

What is the maximum possible T/W you see from a turbine based
air breathing engine. How inevitable is the question. Do you see
a fundamental T/W limit at 100, 40, 15, or some other number?

I'm not a turbine-engine guy, so it's a little hard for me to call. My
understanding is that the fighter-engine guys are now in the 10-11 range,
and it's taken them thirty years to get there from the 7-8 range. The air
temperature at the turbine inlet is now well above the melting point of
the turbine blades (!). (The blades are single crystals of very stubborn
alloys, with cooling vents blowing [relatively] cool air out onto their
surfaces to keep the hot stuff at a distance.) That technology isn't too
far from its limits. 15, maybe?

Radical design changes might perhaps take it farther. But that's harder
to predict. I'd be surprised to see 25. (I do get surprised sometimes.)

I am actively working on surprising you. Not building a full up unit in
my garage. Just demonstration hardware of a different approach that
should reach that goal after real engineers do some analysis and a little
CFD work.

Systems which don't use turbomachinery can do better on mass, but they
have a hard time doing as well on air handling, and they generally don't
work at low speeds. (Mind you, the turbomachinery tends not to work very
well beyond about Mach 3.)

Mach 3 is past time to get out of the air anyway. IMO, that is where thermal
issues on the rest of the airframe begin to clearly out weigh any
theoretical
gain from an airbreather. Unless the airbreather can provide much more
acceleration than commonly assumed. Which implies a better T/W including
intakes than I believe likely in the near term.

Hybrid systems, rocket/airbreather combinations, can do still better.
The question there is whether there's enough Isp gain to be worth it.

That is the question. There is obviously a curve in there. Less clear is
exactly where the curve is.

At what T/W do air breathing engines become performance
competative with the lower stage rocket thrust they replace?
Competative does not necessarily mean desirable in this case,
just not a penalty.

Given the other constraints they impose -- for example, they tend to need
reasonably clean airflow, which is not easy to come by on the surface of a
lower stage -- I think I'd call for at least 40, and that's not going to
be easy, especially as speed builds up. (Good LOX/kerosene rocket engines
with sea-level nozzles are up around 125.)

Sounds like a reasonable requirement if the airbreather has other uses.
At one point I figured that an airbreather would have to exceed the
T/W of a rocket if only used in the launch phase.

During a previous discussion I accepted that 120/M seemed to
be a reasonable break even for an air breather that supplies all
the acceleration from the ground. I suggested a few weeks ago
that for a VTVL SSTO, 28 to 43 might be a reasonable requirement
for units designed for the landing mass only, not operating supersonic at
all during launch phase. Would you agree with these requirements
for break even performance?

I wouldn't strongly *disagree*, but that reflects limited feel for the
problem rather than deep conviction that those are good numbers. :-)
--
I have been sort of digging for a well researched paper that would give
a range of honest curves. It seems quite strange that the vast quantity
of material on the subject would not have a clear requirements breakdown
somewhere handy. A generic set of go-no go curves would be nice.
All I have been able to find so far is single project justifications,
usually
GLOW based.

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

(william mook) wrote in message . com...
Atomic rocket fuels - aka mon-atomic rocket fuels - contain vast
amounts of energy and yeild very low molecular weights, thus, produce
(theoretically) very high performances of 600 to 1,600 sec Isp. High
enough for SSTO performance with quite modest rocket designs.

Basically, H2 is converted into a stable form of 2 H atoms

Which doesn't exist.


and mixed
with normal liquid hydrogen and kept at

...well below...

liquid helium temps to keep it
all from exploding.

If you're lucky.


You end up with a monopropellant that's very
powerful, and a very simple rocket - either VTVL, HTHL, or some combo
- take your pick - all with structural fractions we've already
achieved.

It's ease of use quite handily explains why every
one is using it today to get to orbit.

Richard Schumacher wrote in message ...
Ian Woollard wrote:

(Henry Spencer) wrote in message ...
Basically my calculations show that you can save the entire first
stage if you build an air breathing booster.

That's plausible. But so what? You've turned a rocket first stage into
a jet first stage. In the process, you've made it harder to build and
more difficult to develop. For what? To save *LOX*? WHY???

A reusable flyback booster?

You can have that without using jets on the ascent, only during the return
flight. That is a solved problem. Heck, they can even use the same fuel as
the ascent rocket engines, for sane choices of fuel :_

So, you're saying that a very tiny jet engine used during the return
flight makes more sense than a very large jet engine used during
ascent.

I guess I agree with this idea, since it moves us in the right
direction - namely, zero jet engines!

Let's look at things in terms of delta-vee.

To get to orbit you've got to be capable of carrying a vehicle through
a delta vee of about 9 km/sec. Orbital velocity near Earth's surface
is about 7 km/sec - and you've got about 2 km/sec of gravity and air
drag losses if you do things efficiently - to get you 9 km/sec. If
you want some legs on your vehicle you, to reach more than minimum
altitudes, you might want to add a few tenths of a km/sec more. Of
course, to reach higher orbits requires additional delta vee. But
those a generally reserved for kick stages operated on orbit, so lets
not try to do everything at once.

Okay, so you've got 9+ a fraction km/sec delta vee to achieve.

On return atmospheric drag does most of the work for you, taking speed
away. So, all you've got to do to return is slow the vehicle down
enough to lower its perigee to about 50 km to 70 km or so.

If you only added say 2 tenths of a km/sec to your minimum orbital
speed, you only need the same amount to be able to deorbit.

So, now your total delta vee is about 9.4 km/sec, say.

The atmosphere will slow you down to subsonic speeds since your
surface area is large and your mass is low. You're basically piloting
a big propellant tank system - no matter if its one stage or two. So,
you start out at near orbital velocity and end up subsonic.

The speed of sound is around 0.3 km/sec (depending on local temps) and
with proper vehicle shaping you could easily get your terminal speed
down to about 0.2 km/sec. With wings, even less (as the Space Shuttle
so ably demonstrates)

Now, does it make sense to carry wings that mass more than three times
your payload to orbit and back to cancel this final 2 tenths of a
km/sec?

No. Smaller wings, or lifting body shapes, or parachutes, sure. A
small quantity of rocket propellant burnt at the last possible second
to slow a ballistic descent to zero at the surface, sure.

Another question given the range of speeds we're talking about;

Does it make sense --using today's propellant combinations and
materials-- to spend inordinate effort to build SSTO, rather than
TSTO?

No.

What does make sense;

(a) Build vehicles around existing proven technologies that quickly
give us the cost and performance we need to carry space travel to the
next stage and do so for far less than the President's proposed $12
billion study of the subject.

(b) Continue research in truly ground breaking technologies, which
include;

(i) High performance chemical fuels - such as monatomic fuels
(ii) High peformance chemical rockets - such as ARPA's propulsive
skin concept
(iii) Improved materials and propellants for improved structural
fractions
(iv) High performance nuclear thermal rockets
(v) High performance nuclear electric rockets
(vi) High performance nuclear pulse rockets
(vii) High performance laser detonation rockets
(viii) High performance laser light sails
(ix) Tethers
(x) Large space structures

A near term vehicle that would meet the President's goal of sending
people to mars might consist of seven flight elements all similar,
built around a fully resuable Space Shuttle External Tank.

This improved External Tank would have the minimum thermal protection
needed and have small deployable wings like that of a cruise missle.
It would be equipped with five to seven SSME derived engines, but
these improved engines would have a far lower recurring cost than
today's SSME. These tanks would be equipped with cross-feeding. And
they would incorporate the latest materials improvements that could
easily and cheaply be used to maintain a very reasonable structural
fraction (the same one a plain vanilla ET has today) despite the added
hardware just described.

Now, these seven improved ETs would operate together at launch. From
above they would have the following configuration;

(1)(2)
(3)(4)(5)
(6)(7)

Now, propellant would flow from 1 to 3 and from 6 to 3 and then from 3
to 4, and propellant would flow from 2 to 5 and from 7 to 5 and from 5
to 4 in such a way as to drain 1,2,6,7 during launch. This would be
the first stage.

These four elements would be drained and dropped, and they would slow,
and deploy their winglets, and be snagged with a towline downrange,
where jets modified from airline jets, would tow them back to the
launch center for release and landing.

Meanwhile, elements 3 and 5 are feeding themselves along with 4.
Until 3 and 5 are drained. 3 and 5 are jettisoned, they re-enter the
atmosphere, slow, and descend on winglets they deploy, to a point
where additional tow jets are waiting to snag them and tow them back
to the launch center, using techniques developed way back in the 1950s
for recovering film from orbit.

Element 4 continues on to nearly orbital speed and orbital altitude.
4 doesn't quite attain orbit as its perigee will bring it to ground 44
minutes after reaching apogee. However, while at apogee 4 releases
its payload, and begins its descent while the payload's internal
engine circularizes its orbit. 4 continues around the Earth,
descending to the point where the landing center was 88 minutes
earlier. But at this point too, after slowing and deploying winglets,
there waits a tow jet to take 4 back to the launch center for release
and landing at the airstrip there.

The payload lofted to orbit this way is 550 tons. More than four
times the capacity of the Saturn moonship. The cost to build it, less
than $12 billion - about what President Bush proposed spending on
studying our return to mars. The time to get it flight ready, less
than three years.

Adapting what we've learned durig Apollo and building the space
station to quickly build manned flight elements capable of returning
to the moon and going on to mars - would yeild similar savings.

Using today's computing and material processing technologies we could
send a small crew on a Mars flyby using a 2 year orbit connecting
Earth and Mars. This brings the crew back to Earth in 2 years -
without any further propulsive inputs. But, it gives a two week
window where they approach mars closely - and can deploy hardware that
falls to Mars' surface via airbraking - hardware that is controlled
realtime via telerobotics, without the delay of distance. Telerobots
that could later be controlled by Earth based researchers - and by
later crews that return to orbit the Red Planet.

Mission 2, could orbit Mars and 'land' on Phobos and Diemos, again
deploying remotely controlled robots from orbit.

Mission 3, could land directly on Mars, using Zubrin's excellent
approach - and having tested most of the elements in the previous two
missions.

This would get us to mars quickly, cheaply, and sustainably.

All without SSTO I'm afraid.

Even so, I do believe SSTO deserves research and development funding.
I just don't think we should tie our success in space to this
technology. Its fine for small payloads where the massive quantities
of propellant per useful payload aren't too troubling. And it has a
great spinoff in that quick response weapons and spy hardware with
global reach are possible with SSTO technology.

"Henry Spencer" wrote in message
...
In article ,
James Graves wrote:
...any type of air-breathing for orbital launch is a waste of time
and money. Turbojets, scramjets, whatever. It just makes getting into
orbit harder, not easier.
The only exception to this is an aircraft carrier 1st stage...

I'm inclined to say that the jury is still out on LACE and its relatives
(such as Alan Bond's concepts) and on things like the original Roton,
which airbreathe a little bit at the start of a largely rocket-powered
ascent. The idea is plausible; what remains unproven is that it's any
better than a pure rocket. I wouldn't build one myself, but wouldn't
exclude the possibility of success that way.

While this is drifting off-topic for this newsgroup, can someone explain
to me why so many in the aero/astro field still think hypersonics for
orbital launch are a good idea?

To some extent this is a lingering echo of the idea that spaceships are,
or *should be*, just especially high-performance aircraft. There has
never been any very strong justification for this belief, but it remains
an article of faith for many from the "aero" side of aerospace.

And to some extent, it's pure public-relations hype, the result of the
hypersonics people -- who have been largely rejected by the aero side of
the house -- trying to find funding from the space side (which has long
been the rich side of the family).

And are hypersonics a good idea for anything at all?

For high-speed cruise within the atmosphere -- assuming you have some
urgent reason to want to do that -- they look promising. But they have
nothing much to do with spaceflight.
--


Wouldn't a hypersonic carrier be an ideal lauch platform for a manned
shuttle-type vehicle - a type of TSTO or 3STO if the shuttle had some small
drop tanks?

"Joseph S. Powell, III" writes:

Wouldn't a hypersonic carrier be an ideal lauch platform for a manned
shuttle-type vehicle - a type of TSTO or 3STO if the shuttle had some
small drop tanks?

No, because even a _supersonic_ separation of two vehicles at any significant
atmospheric density is not merely difficult, but outright =DANGEROUS= !!!
Attempting a separation at hypersonic velocities, with every leading-edge
surface experiencing absurdly high dynamic pressures while glowing red to
white hot, is an exercise only for insane lunatics. Look it up near the top
of the list of "Stupid Things You Will Not Live Through If You Attempt."


-- Gordon D. Pusch

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

In article ,
Joseph S. Powell, III wrote:
And are hypersonics a good idea for anything at all?
For high-speed cruise within the atmosphere -- assuming you have some
urgent reason to want to do that -- they look promising. But they have
nothing much to do with spaceflight.

Wouldn't a hypersonic carrier be an ideal lauch platform for a manned
shuttle-type vehicle...

Maybe. As Gordon has already noted, there's a big problem with separating
cleanly from such a carrier in a hypersonic environment, and for that
matter with surviving that environment long enough to reach separation
time. (Launchers normally reach such velocities only in very thin air,
but a hypersonic aircraft needs to stay in air that's thick enough for its
engines and wings.)

That aside, such an aircraft would certainly be interesting for such
uses... *if* it already existed. It's very unlikely to be cost-effective
to build such a thing solely as part of a launch system. A rocket stage,
even a reusable one, is easier and cheaper.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

Gordon D. Pusch wrote:
No, because even a _supersonic_ separation of two vehicles at any
significant atmospheric density is not merely difficult, but
outright =DANGEROUS= !!! Attempting a separation at hypersonic
velocities, with every leading-edge surface experiencing absurdly
high dynamic pressures while glowing red to white hot, is an
exercise only for insane lunatics. Look it up near the top of the
list of "Stupid Things You Will Not Live Through If You Attempt."

What was the atmosphereic density going to be for separation of HyperX
(wasn't that the name of the hypersonic test vehicle that was to be
boosted by a Pegasus dropped from a B52?)

rick jones
--
oxymoron n, commuter in a gas-guzzling luxury SUV with an American flag
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to raj in cup.hp.com but NOT BOTH...

In article ,
(Henry Spencer) wrote:

That aside, such an aircraft would certainly be interesting for such
uses... *if* it already existed. It's very unlikely to be cost-effective
to build such a thing solely as part of a launch system. A rocket stage,
even a reusable one, is easier and cheaper.

Burt Rutan did design (and build) an aircraft specifically for his
X-Prize entry. It's not hypersonic (AFAIK), but its existence does
suggest that designing a custom launch aircraft is a viable approach.

--
Joe Claffey | "Make no small plans."
| -- Daniel Burnham