Re: fuel chat

[Thomas Anderson <thomas.anderson@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>]

On Wed, 2 Dec 1998, Nyrath the nearly wise wrote:
> Thomas Anderson wrote:
> > > Metastable Atoms (e.g. Helium)                3,150
> > eh? (a) how is helium metastable? (b) how does a helium-fuelled rocket
> > work?
> 	Atoms can be "excited" by thrusting their electrons into
> 	higher orbitals.  Such electrons quickly fall back into
> 	their base state, re-emitting the energy.
> 	Metastable atoms have their electrons excited in such
> 	a way that they stay in the higher orbitals.
> 	For a while, at least.

sounds sort of feasible, even if i can't see any metastable energy levels
in helium. however, i did recently discover (ie in a quantum mechanics
lecture this morning) another alternative. we all know that helium does
not form chemical bonds: the He2 molecule is not stable. however, it turns
out that He2+ (two heliums, with one electron missing) is stable; a
mixture of He2+ and F- (fluorine is good at holding onto a -ve charge)
might be metastable, and could be 'burned' to helium and fluorine gas.
just a thought.

> > these are the options we have run over, i think. i have read of GCNRs. i
> > thought they were of similar efficiency to scnr (nerva type), but
> > apparently they are much, much better. better, in fact, than orion. 
> 	Yes, but Nerva rockets at least have the decency to
> 	keep their fuel elements of glowing radioactive death
> 	sealed in the reactor.  GCNR are much like slow
> 	reacting Orions, spraying vaporized plutonium
> 	like a radioactive crop duster.

they are designed to minimise fuel leakage, however; various schemes have
been developed whereby the coolant and fuel streams do not mix. i don't
understand it myself, but it is probably similar to the problems faced by
fusion engineers in getting the flow of plasma in a tokamak right.

> 	This wouldn't matter much in space, but 
> 	it would be unwise to use one to lift off into
> 	orbit.  At least not from a spaceport based
> 	on a continent you like.

there is a semi-alternate history story called 'moon six' by stephen
baxter, in which the british have a nuclear moon rocket. they launch it
from australia ...

> > > BORON FUSION                  Isp = 1e6
> > hmm, now this is getting a bit blue-sky. ultraviolet-sky? i've never heard
> > of boron fusion before; sounds like a bit of a daft idea to me.
> 	No, actually boron fusion would be marvelous, if we could
> 	only figure out how to ignite the reaction.
> 	Here's the relevant section from rec.arts.sf.science:
> 
> nyrath@clark.net (Winchell Chung)
> BORON FUSION
> 11             4 
>   B5 + p -> 3(  He  ) + 16Mev
>    5              2 

eh? how does going from boron to helium make energy? the binding energy
per nucleon goes up! i suppose that free proton must be the key. still, it
produces less energy per unit mass than proton-proton fusion.

> > excellent stuff! added to my collection of reference works cribbed from
> > Nyrath ... shall i webbify this (and star-list?) or are you on the case?
> 	Go ahead and webbify it, it will be a while before I get 
> 	around to it.

it will soon be done. see

users.ox.ac.uk/~univ0938/nyrath/

for an index to the Words of Nyrath archive!

Tom