Re: [FT] Railgun/Fuel Chat Results

On Fri, 27 Nov 1998, Sean Bayan Schoonmaker wrote:
> Just thought I'd put in a quick summary of last night's chat for those
who
> missed it.
> Fuel
> We pretty much agreed that purified liquid H2 for a fusion reactor was
the
> best bet.

hmm - the inner politburo has met and pronounced the Truth (tm) ...

executive summary: fusion fuel is not an issue. reaction mass is
probably 
an issue.

hydrogen is the best fuel for fusion. it is best stored as lithium
hydride
- you can blast it with neutrons from the core to convert the lithium to
fusion fuel.

however, the amount of hydrogen you need to run a fusion reactor is tiny
-
fusion-powered ships would probably never be refuelled over their whole
lifetime. think how infrequently nuclear warships today need to refuel,
and then multiply. hydrogen has a vastly higher energy density.

the question is, how are you going to turn this energy into thrust? if
you have grav drives or photon drives, then it is complicated but just
requires some machinery. if you are going to use a reaction drive (ie a
nuclear rocket), you will need reaction mass. you may well need a lot of
reaction mass, depending on how fast you can accelerate it. if you go
for
boiling water with the fusion energy and venting it into space, you will
need an immense amount, and will need to replenish frequently - icy
comets, asteroids, planetary ring bodies, etc, are possible sources. if
you are using a super-high-velocity ion drive, then your reaction mass
needs will be more modest.

Tom