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starship-design: RE: Perihelion Maneuver

Lee writes:

>You really ought to check out Penn State's page on ICAN and the antimatter
>catalyzed fission/fusion rocket. It is basically a modified Orion concept
>that is much more refined than the original. Besides the fact that the
>hardware is already being tested, it offers a lot more in near term
>improvement potential.
>The current reaction is D/T but with a few years of operation and improved
>confinement technology which seems likely, we should be able to move on to
>He3 with a second or third generation design. If you assume another ten
>years of research on the current generation (it would actually be in
>service by the end of this period), twenty years for research and
>development of second generation (same fuel, just more efficient
>confinement and improved systems), twenty years for third generation (use
>improved confinement and systems to fuse He3) then that puts us at fifty
>I haven't even used any hardware here that isn't already in existence or
>made any assumptions that are really weird. In the short run, we could use
>this in a brute force approach and simply add engines and increase the fuel
>supply to raise the cruise velocity. It has sufficient ISP for the
>"supertanker" category.

Yeah, I do like this idea.  But "scaling" it up is going to be harder than 
it sounds, because most of the "fuel" isn't the DT or DHe3; it's the SiC 
plasma that gets shot out the back.  With a 1000-1 SiC/DT ratio here you're 
never going to be able to make a ship that could go to another star with 
less than a 100,000 - 1 fuel/payload ratio; ridiculously high.

Are there any ideas out there as to how to transfer raw fusion energy to 
propellent more efficiently??  One possibility would be to use the fusion 
products themselves as propellant, but for this scheme that merely increases 
the amount of antimatter you need by three orders of magnitude; no easy feat 
when it's already more than we can make.  I think someone calculated that 
the ideal propellant speed is about 0.1c.  Has anyone looked into how to 
make this type of engine, assuming fusion is possible?