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Re: starship-design: Staged Fusion Power
On Sun, 16 Aug 1998, Steve VanDevender wrote:
> Zach Johnson writes:
> > N. Lindberg wrote:
> > > I was reading some of the numbers for the various engines that
> > > could be used to power a starship, and I noticed that every fusion
> > > reaction shown only used its fuel once. If a closed powerplant (not
> > > rocket) could be run hot enough, there's no reason I can see not to run
> > > the fuel up to heavier elements instead of just throwing it away after it
> > > turns to helium. Note: I didn't do any math for this one, it might be
> > > impractical. Although I realize that a scheme like this would require
> > > reactors far superior to a today's can't-quite-ignite tokamaks, it might
> > > be doable in fifty years. The power from this type of reactor could be
> > > used to power a laser or ion drive, the latter prehaps adding the
> > > reactor exhaust to the Xenon reaction mass.
> > > The upshot is, exhaust recycling could reduce the amount of fuel
> > > required by which is one of the major hurdles of starflight.
> > > Best Regards,
> > > Nels Lindberg
> > Could you combine fusion and fision to produce a continous reaction?
> Well, conservation of energy says that there has to be some limit
> to that. You should also remember that both fission and fusion
> conserve nucleons (although beta decay and inverse beta decay may
> change a neutron into a proton and electron and neutrino, or vice
> versa). So that puts an even more stringent limit on the amount
> of energy you could get; no matter what happens, the energy tied
> up in the nucleon's masses is never released, only the binding
> energy holding them together.
> One problem with a multi-element fusion reactor is that it takes
> progressively higher temperatures and pressures to induce fusion
> in heavier nuclei. So the cost of fusing the heavier elements
> may not be well offset by the additional energy provided.
Actually combining fusion and fission is a total waste...
For all elements ligther than Iron (Fe) Fusion produces power and fision
costs power... Vice Versa for elements Heavier than Iron.
As for using some kinda multi-stage Fusion device I personnaly think that
it will both be MUCH simpler (from an engineering POV) and more efficient
to just use the fusion products (probably Helium) as reaction mass.
Just my 2c