http://www.cnn.com/2006/TECH/space/09/03/europe.moon.ap/index.html

below copied from above link

The spacecraft is at the end of a three-year mission that scanned the lunar surface from orbit and tested a new, efficient, ion-propulsion system that officials hope to use on future interplanetary missions.

Launched into Earth's orbit by an Ariane-5 booster rocket from Kourou, French Guiana, in September 2003, SMART-1 used its ion engine to slowly raise its orbit over 14 months until the moon's gravity grabbed it.

The engine, which uses electricity from the craft's solar panels to produce a stream of charged particles called ions, generates only small amounts of thrust but only needed 80 kilograms of xenon fuel.

Edit:SMART-1, a cube measuring roughly a meter on each side, took the long way to the moon -- more than 100 million kilometers instead of the direct route of 350,000 to 400,000 kilometers.

http://www.theodoregray.com/PeriodicTable/Elements/054/index.s7.html


http://i.a.cnn.net/cnn/2006/TECH/space/09/03/europe.moon.ap/story.europe.space.ap.jpg