starship-design: Re: Your help on starship engines

[Kelly St <KellySt@aol.com>]

In a message dated 1/20/98 10:42:35 PM, you wrote:

>I ran across your stardrive article in the Lunar Institute of Technology web
page.
>I found it insightful for my personal research. I was wondering if you could
help
>me out with a problem that has been bothering me for sometime.
>
>Could you have nuclear fission rocket in which the uranium or plutonium was
in
>a gasseous state? I read about it in a book called "Thrust Into Space" by
Maxwell
>W. Hunter the 2nd. Its a gasseous fission engine. The pressure inside the
reactor
>is between 500 and 1500 atmospheres. The gasseous uranium or plutonium would
be
>compact enough to provide a chain reaction. The advantage, so says the book,
over
>a fission reactor using this instead of a solid reactor would be that the
gasseous
>reactor could have higher temperatures. Up to 200,000 degrees F. The higher
the
>temperature the higher the energy that can be put into the reaction mass. The
book
>also suggests that by using the only the heat transfered by radiation alone
at
>those temperatures one could energize the reaction mass without losing any
fissionable
>material. The reaction mass would have to be opaque. The blacker throughout
the
>entire EM spectrum the better. The reaction mass is on one side of a
transpatent
>wall and the core is on the other. The only way I could figure out how this
method
>would allow higher temperatures than a  solid core would be because sense the
fissionable
>material was in a gas state it could be set to never actually touch the sides
of
>the chamber its in by using a magnetic field. I see this type of engine being
a
>centrifuge that rotates rapidly forcing the gas outward. A magnetic field
keeps
>it from touching the chamber wall. Through the center is a transparent tube
that
>the reaction mass runs through.
>
>The problem with all of this is that the book was written in 1966 and I can't
find
>any reference of this type of engine anywhere else. In a book or the
internet.
>I was wondering what your thoughts on this are. Any help would be
appreciated.
>
>CygnusXY@aol.com


I've also heard of the engine.  Its called a gas core nuclear rocket, or
something.  You've listed the design pretty well.  (Also there is a design
where the fission products are directly exausted out the back for thrust.)
Because the materials are allowed to get so hot that they boil, they are at
far higher temps.  All else being equal, higher temps led to higher thrust
efficency.  But this idea is considered so hard to do, no ones been really
interested in trying it for decades.  i.e., if you need that high a thrust,
you might as well put the effort into a laser pulsed fusion drive or
something.  The fusion systems would be far cleaner and safer, probably easier
to develop, far less contraversial with the public, and provide more thrust
efficency.

Hope this helps.

Kelly