On Sat, 12 Jun 2004, Brandon Fosdick wrote:
> A lot of this discussion seems to be driven by the unpredictability of
> the engines. Is this a characteristic of the chosen propellants? Would a
> different propellant combination be inherantly more (or less) predictable?
It's a characteristic of the combination of the propellant, the catalysts,
and the ignition approach. John's engines are actually fairly complicated
systems, and some parts of their behavior are temperature-sensitive, and
he hasn't done the sort of thorough study of the ignition process that
would be needed to make it fully controlled and predictable. (Doing that
could take years of work and considerable expense, and as he's said more
than once, he's more interested in flying vehicles.)
My feeling is that he's probably stuck with some variability so long as
he's using solid catalysts and relatively dilute peroxide (which he can't
safely jack up to higher concentrations, given his mixed-monopropellant
approach, even aside from the supply problems). The classical way you
cure ignition variability is to beat it to death with a sledgehammer --
make the ignition process so energetic, so strongly favored, that it just
overwhelms other variables. I don't immediately see any way of doing that
with John's system; it looks like he'd either have to go full biprop with
more concentrated peroxide, or switch to a much more aggressive catalyst
(which would probably have to be expendable, and probably liquid).
Henry Spencer
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