On Thu, 9 Jan 2003, Ian Woollard wrote:
> So, in theory, for this application, energy/mass density is important...
Actually it always is. Neglecting issues of conversion efficiency --
which cannot safely be neglected! -- Isp is roughly sqrt(energy/mass).
> so a lox/aluminum powder monoprop mixture has great energy per unit mass
> (16KJ/g) and could be good (better than LH/LOX at 13KJ/g).
Unfortunately, one still has to worry about converting that energy into a
useful form. If you want to do it like a rocket, expanding a gas through
a nozzle, there is an awkward problem with LOX/Al in that its combustion
product is a refractory solid, not a gas. If you mix it with plenty of
air, maybe...
> [Well, beryllium + ozone is better- 26KJ/g, but... ;-) Lithium and
> oxygen manages 20KJ/g, that's not quite so bad ]
Try lithium and fluorine. :-) That has the major bonus that LiF has a
fairly low boiling point, so it is a gas for rocket purposes.
> I did some BOE that suggested it could be just a few hundred kg of fuel
> for 7 tonnes to 30km, but the equipment to heat the air and put it
> through a nozzle is complex and possibly too heavy.
Quite so. Lousy thrust/weight is where airbreathers really lose; liquid
oxidizer may be heavy but the hardware to handle it is light.
This has all gotten rather far afield from ERPS projects...
Henry Spencer
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