No nukes first.

Message text written by INTERNET:spacesettlers@yahoogroups.com
>But I happen to think that mass drivers are good. None of the other
high-efficiency/low thrust electric drives being promoted can use something
as simple and unprocessed as dirt for reaction mass. None of them can use
liquefied O2 as reaction mass, and when we start processing space
materials,
we'll have more of that than any other single element.

Regards,

Mike Combs<

I have a small company which is working on an RF plasma thruster. It has
no grids or electrodes and so could handle oxygen quite easily. My
graduate school advisor (after I finished) received a contract from NASA to
make an RF oxygen beam source to study shuttle glow. VASIMR could also use
oxygen with an increased magnetic field to bring the ion cyclotron
frequency into a reasonable range for RF amplifiers. This would also
reduce the exhaust velocity for VASIMR, increasing its thrust.

I have run the RF plasma thruster in the lab and have been funded under a
Phase I SBIR, but would need to get a Phase II to do thrust stand
measurements and mature the technology. A patent examiner has approved a
patent on the technology (after a long and difficult struggle which was no
fun at all), but I have not yet received the final piece of paper.

Another alternative is to use RF as a discharge source, instead of the
hollow cathodes used on most Hall and gridded ion thrusters. The Germans,
British, and Japanese have all done significant work on this for ion
thrusters. The German RITA is on the Artemis satellite which was just
placed in a wrong orbit by Ariane 5. RITA and a Hall thruster also on
board may be used to put Artemis in its correct orbit. The other
satellite launched by the Ariane 5 is probably a total writeoff, since it
has only chemical thrusters and would have to use all its fuel to reach the
proper orbit.

No one that I am aware of has used an RF discharge for the Hall thruster,
but it should be possible.

Regards,

Lynn Olson