Paul Fields (
Mon, 27 Sep 1999 16:48:51 EDT

Gomen Nasai <Hangs Head in shame>


>From: Mark Simmons <>
>Subject: Re: [gundam] Fuel?
>Date: Mon, 27 Sep 1999 13:43:00 -0700
>Matt Hanyok asks,
> >well, that explains it. But, I thought the MS's used a kind of fusion
> >engine? I don't kow my science, but aren't those nuclear powered or
> >something, so why would they need fuel?
>Chris Beilby observes,
> >Exactly. The proper term isn't actually fuel, but rather 'reaction
> >While the Mobile Suits as seen use some sort of combustible oxidizing
> >reaction mass, it is entirely conceviable that they could even use
>And Paul Fields responds,
> >Actually Chris while you're right they could
> >use water, Mark would slap your hand on this
> >one... they use Helium 3 from Jupiter, hence
> >the dependence on the Jupiter Energy fleet
> >for fuel in Gundam...
> Actually, Chris is quite right. Helium 3 is used for _reactor_ fuel,
>and a little of it goes a long way. But using this stuff for bulk
>propellant would be a terrible waste of this precious substance, when
>just about any common gas or liquid would do.
> But what substance works best? Since we're only interested in this
>stuff for its raw physical properties, it doesn't matter whether it's
>combustible or not. In fact, where thermonuclear rockets of this kind are
>concerned, there's only one factor that determines its "fuel efficiency":
>The atomic weight of the propellant, the lower the better.* And any
>susbstance that works as propellant can do double duty as coolant, since
>both functions involve carrying heat away from the reactor.
> While liquid oxygen would be a stinky propellant, water is more
>attractive - the efficiency of the hydrogen somewhat balances out the
>inefficiency of the oxygen, giving you an overall efficiency of one-third
>that of hydrogen. Plus, water is easy to handle, store, and pump. It's
>also implied that regular helium might be used in space mobile suits
>(witness the Gundam's "helium control core" boxes, which have also been
>identified as cooling equipment), and this would have fully half the
>efficiency of pure hydrogen. Perhaps there's a lot of regular helium left
>over from helium-3 processing...
>-- Mark
>* This is because the temperature of the propellant equates to the
>average kinetic energy of each atom. Kinetic energy is proportional to
>atomic mass x velocity^2, so the velocity increases when the atomic mass
>is smaller. Hydrogen, with an atomic weight of 1, is the most efficient
>propellant; pure oxygen, with an atomic weight of 16, has only a quarter
>of hydrogen's exhaust velocity at any given temperature. As a result, a
>kilogram of hydrogen gives you four times the thrust of a kilogram of
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