New type of Space propulsion

The xenon ion propulsion system, or XIPS (pronounced "zips"), is the culmination of nearly four decades of research into the use of electric propulsion as an alternative to conventional chemical propulsion. Available on the Boeing 601HP, or high power, and Boeing 702 satellite models, the increased efficiency possible with XIPS allows for a reduction in propellant mass of up to 90% for a satellite designed for 12 to 15 years operation. Less propellant results in reduced cost for launch, an increase in payload, or an increase in satellite lifetime, or any combination of the above.
http://www.boeing.com/defense-space/space/bss/factsheets/xips/xips.html

An ion thruster (or ion drive), one of several types of spacecraft propulsion, uses beams of ions — electrically charged atoms or molecules— for propulsion. The precise method for accelerating the ions may vary, but all designs take advantage of the charge-to-mass ratio of ions to accelerate them to very high velocities using a high electric field. Ion thrusters are therefore able to achieve high specific impulse, reducing the amount of reaction mass required, but increasing the amount of power required compared to chemical rockets. Ion thrusters can deliver one order of magnitude greater propellant efficiency than traditional liquid fuel rocket engines, but are constrained to very low accelerations by the power/weight ratios of available power systems.
The first ion thrusters, known as Kaufman-type ion thrusters, were developed by Harold R. Kaufman, working for NASA in the 1960s, and were based on the Duoplasmatron.
http://en.wikipedia.org/wiki/Ion_drive