theseeker189 wrote:And there is a modern day fuel system called ion fusion that uses xenon as its fuel,..
The ion drive is not based on fusion, but electromagnetism. Here is what I found (apologies for any mistakes, would appreciate any corrections, thanks):
An ion-drive garners its thrust like a conventional rocket (action/reaction), but instead of using a chemical combustion-reaction to provide the propulsion thrust, it uses an electromagnetic process to eject a series of ions in the exhaust direction to provide thrust.
Since each ion has little mass, the generated thrust (from the action/reaction law) is quite small, so the ship's initial speed is small. In space, however, each ion-ejection adds thrust in a cumulative manner becasue there is no air friction to rob a ship of its momentum and therefore it continually increases its velocity; given enough time and fuel (and the laws of inertia), it can obtain high velocities.
This is relatively new technology and NASA is testing it with the
Dawn probe mentioned by seeker189. It appears to be working quite well. This is a most promising technology, in particular for long-range probes, because of the long periods of time required.
Although it is not a fusion reaction, the
Dawn's ion-drive does use xenon as the medium to ionize. In a nutshell:
- electricity (from solar panels) is used to ionize xenon
- the ions are then accelerated via magnets
- the accelerated ions are then ejected into the exhaust direction
- action/reaction law provides thrust per each ejected ion

Here is a comparison for similar deep space propulsion engines (thrust figure done by NASA, with my conversions):
An ion drive:
- burns its fuel slowly over time
- provides a small initial velocity
- powered by electricity
- Thrust = 0.09 N = 0.02 pounds
(great for long-range voyages, but not for launching)
A conventional chemical-rocket:
- burns its fuel quickly
- provides a large initial velocity
- powered by chemical combustion reaction
- Thrust = 500 N = 112 pounds
(great for launching, but not for long-range voyages).
http://dawn.jpl.nasa.gov/mission/ion_prop.asp
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theseeker189 wrote:I can't remember so correct me if I'm wrong, xenon is rare on earth but is abundant on the moon?
I do not think so Seeker. Xenon is a rare element and is usually in gaseous form. Here on Earth, it is typically found in and extracted from the atmosphere. In the Solar System, only Jupiter's atmosphere has a much larger concentration.
http://adsabs.harvard.edu/abs/2000JGR...10515061M
It seems without an atmosphere, xenon is just not going to be present in any significant fashion.