James Graves wrote:

Henry Spencer wrote:

Catching up on some unread journals, I note that the March/April 2003
issue of JBIS has a very interesting paper: "A comparison of propulsion
concepts for SSTO reusable launchers", by Richard Varvill and Alan Bond.
While the authors have a mild case of hydrogen religion -- non-hydrogen
rockets are never mentioned -- and they obviously have their own axe to
grind, they generally give a good overview of the alternatives, including
why scramjets are such a lousy idea for space launch.

This is all my opinion, of course...

After reading this newsgroup for a while, I have come to the conclusion
that 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. There are
some advantages to high altitude launch (less altitude compensation
needed for your rocket nozzle, for example), and it can give you a lot
of flexibility with launch site location. But that's the only
exception in my view.

I just can't understand why so much time and research dollars are being
spent on hypersonic research. If you want to get into orbit, you want
to get _out_ of the atmosphere as soon as possible. It is completely
counter-intuitive to try and gain lots of velocity while still inside
the atmosphere, where you are subject to drag (inefficiency) and heating
(exotic materials and/or cooling systems needed).

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?

"If the only tool you have is a hammer, every problem looks like a
nail."

And to the less technically inclined, there's the carrot of not
carrying your oxidizer along. The price, of course, is taking it in at
increasing Mach numbers, and the drag imposed thereby, likely a heavier
engine for the same thrust, major thermal issues, etc. Everything you
said, and then some.

And LOX is cheap.

And are hypersonics a good idea for anything at all?

If all you *want* is high-altitude, hypersonic cruise (as opposed to
accelerationg to orbital velocity), sure. Recon, *perhaps* commercial
flights depending on the economics, etc. And perhaps expendable
hypersonic weapons.

But airbreathing to orbit, while it might yet be acheived, will be
only a niche application. Most access to LEO will be with rockets,
until/unless 'beanstalks' can be done, and even those will not
completely replace independent spacecraft.

James Graves


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