Your arguments are fallacious.
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
Lets go ahead a take a look at the HOTOL.
...unique air-breathing engine, the 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
Then you bring up the Emperor, who in the story *is* naked. To that I
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?
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...
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Post by Henry Spencer
Post by Craig Fink
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.
Post by Craig Fink
...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
Post by Craig Fink
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*
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*.
Post by Craig Fink
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.
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...