Re: Atmospheric Flight to Orbit

Hi Len,

Well were not in agreement here.

To say that we've studied many concepts and none of them worked, therefore
no concept will work, is fallacious.

As far as I know, in a Newtonian world, the physics of propulsion will
always favor pushing on some other reaction mass (something else). If I
have a cart full of rocks, I'm going to get a lot further pulling or
pushing it than I am if I start throwing the rocks out. If I have a boat
full of rocks, I going to get a lot further paddling than throwing rocks
out. If the cart has wing and I'm in the air, I'm still going to get
further pushing on the air than throwing rocks out. If I'm in Space in a
vacuum with a cart full of rocks, well I guess I'm going to have to throw
rocks then.

I'm going to take a break for a while this particular part of the tread,
till all the rock throwing settles down a bit. Last time I brought up this
vary basic concept, there was a bunch of rock throwing too.

Don't forget all that "great" Nitrogen in the air, as long as it's leaving
the vehicle faster than it arrived it's helping.

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

Len wrote:

On Mar 8, 9:21 am, Craig Fink <WeBeG...@xxxxxxxxx> wrote:
Your arguments are fallacious.

If you are looking for fallacious arguments,
run the numbers. If you want to take
oxygen from the air, you have to take in
five times as much air--which generally
increases the delta-vee requirements by
about 50 percent. This is a real killer when
you are dealing with a logarithmic equation.
Run the simulation, and you will start to
discover the real facts. And then there
are other devils in the detail: 1) the
disastrous impact on structures; 2) the
much higher costs and masses of
airbreathing engines and, even more
importantly, inlets; and 3) many etc.s.

To me, Chemical Rocket Engines are to Orbital Flight as Balloons were to
Human Atmospheric Flight. Yes, you can fly in a balloon, but you don't
see very many people doing it these days. All through history there have
been the nay sayers, who have eventually been proven wrong. If man were
meant to fly, he'd have wings, as he watches the bird fly over his head.

You focus on the negative, throw your hands up in the air and quit. And
worst, you try to convince everyone else to quit with you. Pointing to
all the studies of things than don't work, is not proof than everything
can't work. Many of the studies done by large government institutions
that are more interested in using them for military purposes, or at the
very best some sort of dual use (military purposes again). And you can't
even talk about them because they don't publish their results, like the
HOTOL project.

Lets go ahead a take a look at the
HOTOL.http://en.wikipedia.org/wiki/HOTOL ...unique air-breathing engine,
the RB545...http://en.wikipedia.org/wiki/RB545 The exact details of this
engine are covered by the UK's Official Secrets Act... Kind of futile to
talk about what they did wrong and how it can be improved, isn't it.
Pointing to studies you can't read, as proof you can't do it.

Then you bring up the Emperor, who in the story *is* naked. To that I
respond:

Ahh, the pyramid builders. Yes, each generation is blessed, or cursed,
with those who will take from others with grand schemes to build the
pyramids of there time. The age old problem of getting the attention of
those ignorant few in power. Internal life can be yours, just fund my
project with the fruits of society and it is yours.

How do you get funding for your pyramid? The brass ring. Go for the brass
ring. Round and round we go, up and down, reaching each time the ring
comes around. Fund mine, I'll get it this time, I'll give you the brass
ring.

SSTO being the brass ring. Without staging, we would still be standing on
the ground with Chemical Rockets. Staging vastly simplifies the problem
and brings a better understanding of it. What is the performance gain
during the Crawl Stage of Atmospheric Flight to Orbit?

Not necessarily so. I have spent 50 years
looking at all types of concepts, including
a number of airbreathing concepts. A
chemically powered SSTO space transport
appears possible if it is large enough.
However, large SSTOs do not make as much
economic sense as smaller TSTOs while we
are still fighting the traffic-level problem. Once
high traffic levels are established, many types
and sizes of space transports may make sense
--just as many types of sizes of aircraft now
make sense.

With a large dose of optimism, a smaller SSTO
seems possible. However, the airbreather
is even more sensitive to assumptions; any
possibility of actually working tends to
evaporate on a realistic day.

You talk about big and bulky hardware, pointing to a low density/high isp
rocket, because it can beat another low density/high isp rocket. Yes, LH2
is a wonderful rocket fuel, isn't it. It's also a great fuel to burn with
air. Only uses one Oxygen atom to burn two Hydrogen, unlike Carbon.

Even in Orbit, Chemical Rockets will be replaced, with big and bulky
hardware. Enjoy the Golden Age of Chemical Rockets, because it's days are
numbered before it is replaced with something better.

And then you put the cart before the horse wanting to talk about all the
high speed acceleration in the final Run Stage to Orbit. Which by the
way, for Rockets the least amount of energy is consumed. Even here, the
physics of the problem are not nearly so bleak as the picture you paint.

Before we start running, don't you think we should learn to walk, and
before that crawl? What is the performance difference between a rocket
and Atmospheric Flight to Orbit vehicle in the Crawl Stage?

The physics and time are on my side of this argument...

If you want to cite physics, you had better
run the numbers in realistic simulations.

Henry's arguments are not fallacious.

Len

--
Craig Fink
Courtesy E-Mail Welcome @ WeBeG...@xxxxxxxxx
--

Henry Spencer wrote:
In article <zRWFh.7664$_73.5...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Craig Fink <WeBeG...@xxxxxxxxx> 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...

--
Craig Fink
Courtesy E-Mail Welcome @ WeBeGood@xxxxxxxxx
.

Relevant Pages

  • Re: Atmospheric Flight to Orbit
    ... pushing it than I am if I start throwing the rocks out. ... rocket approach is counter-intuitive. ... airbreathing engines and, even more ... engine are covered by the UK's Official Secrets Act... ...
    (sci.space.policy)
  • Re: Atmospheric Flight to Orbit
    ... Chemical Rocket Engines are to Orbital Flight as Balloons were to ... The exact details of this engine are covered by the UK's Official Secrets ... because it can beat another low density/high isp rocket. ... Even in Orbit, Chemical Rockets will be replaced, with big and bulky ...
    (sci.space.policy)
  • Re: Atmospheric Flight to Orbit
    ... Chemical Rocket Engines are to Orbital Flight as Balloons were to ... The exact details of this engine are covered by the UK's Official Secrets ... You talk about big and bulky hardware, pointing to a low density/high isp ... Even in Orbit, Chemical Rockets will be replaced, with big and bulky ...
    (sci.space.policy)
  • Re: Atmospheric Flight to Orbit
    ... the rocket engines actually win on performance every time. ... where the Isp advantage is much smaller and the ... engine will more than double the payload. ... despite an Isp advantage of nearly 100s. ...
    (sci.space.policy)
  • Re: Atmospheric Flight to Orbit
    ... the rocket engines actually win on performance every time. ... where the Isp advantage is much smaller and the ... engine will more than double the payload. ... despite an Isp advantage of nearly 100s. ...
    (sci.space.policy)