On Wed, 2003-10-15 at 22:21, John Carmack wrote:
> Consider this:
>
> Aluminum hydride ( AlH3 ) combustion with 98% peroxide has a theoretical
> Isp of over 400, and a density-Isp of over 600. Great SSTO propellant.
>
> AlH3 has a density of 1.48 g/cc, and 98% peroxide has a density of 1.44
> g/cc. AlH3 is not hygroscopic, and is stable to 150 C. If you mixed
> powdered AlH3 into 98% peroxide, it would not dissolve, and the densities
> are close enough that the powder would stay suspended for quite some time.
>
> Without miscability, there shouldn't be a significant additional detonation
> risk, and the powder and liquid could be mixed right as the propellant is
> being loaded, minutes before a launch. You still need to cool the engines,
> but otherwise the tankage, plumbing, injection, and control system is just
> like a monoprop.
>
> Given a good carbon fiber tank / nose, our X-Prize vehicle layout would go
> to orbit with that.
I think my brain just melted... how would you cool the engine? To get
that kind of Isp even with Al2O3 in the exhaust, it must burn
ferociously hot. And I have a very hard time believing that the
combination isn't poorly behaved in some noisy way. It's so energetic
and there's no obvious reason for it to be stable, ergo I consider it
safer to assume that it's not stable. Ignition! has caused me to be very
leery of that sort of experimentation.
-p
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