Air-breathing hypersonic engines

Al Globus wrote:

>While the fuel is not particularly expensive, it needs large tanks to
>hold it,
>
Only somewhat. The Shuttle's especially huge tank is because it uses
liquid hydrogen. But liquid hydrogen has appalling low density. LOX and
Kero is much, much denser. Exhaust velocity isn't so high, so you need 2
stages. But then again- the Shuttle uses multiple stages anyway, so why
use liquid hydrogen? And kerosene is much cheaper to handle and to buy,
and about 17 times denser than LH. Oh yeah, BTW that's a problem with
scramjets- the tanks are really, really huge with pure LH, (the LOX
brings up the average density of the Shuttles propellent tank), and
scramjets use more liquid hydrogen than the Shuttle does anyway.

> pumping systems to move it,
>
You don't always require pumps in fact. Just having tanks pressurised
above the combustion chamber pressure works, but is heavy. There's also
been some recent advances in this area- www.flometrics.com have a new,
simple, cheap pump with the same power/weight ratio as turbopumps. Still
undergoing development, but looks very promising indeed.

> insulation on the external tank to fall off and put holes in wings.
>
That was a total fuck-up in the Shuttle design. I'm not at all happy
with the idea of wings on space vehicles. I think they are unnecessary;
and sticking them underneath a huge cryotank- don't do that. Still, I
think probably NASA will solve the insulation issues well enough, but
possibly not completely. But the Shuttle architecture is pretty poor
IMHO- I generally prefer VTVL designs (Yay DC-X!) I think they are
potentially more reliable.

> The extra weight puts additional structural loads during launch.
>
Doesn't seem too bad a problem. Structural failures are fairly rare in
practice.

> It's explosive nature requires all kinds of safety measures. Etc.
>
Yes. That's true. Liquid oxygen supports combustion of even the metal
parts of the vehicle. Still, it is usually pretty difficult to trigger
combustion- the metal has to reach far over a 1500C to burn. Having
oxygen onboard usually exacerbates minor problems with the vehicle further.

Even hydrogen can explode in the absence of any oxidiser. Liquid
hydrogen expands enormously upon heating and then any pressure vessels
will burst; and you need cryogenic fuel for scramjets.

I'm currently working on a two stage launcher. I think about $1000/kg
(price) is achieveable, with decent profit margins. That corresponds to
a space tourism price of about $200,000 per person. I also think it will
be more reliable than the Shuttle. But I hope to see.

>Al Globus
>CSC at NASA Ames Research Center
>http://www.nas.nasa.gov/~globus/home.html
>
--
-Ian

Motto: "You're Not Authorized to Know Our Motto."
So, like, how many lives DOES Shroedinger's cat have anyway?