[tectonic]

"Unlike rocket-powered craft sent to Mars, Jupiter and other planets, Dawn is driven by a weak-but-steady ion engine. Powered by solar panels, Dawn’s engines zap a gas, xenon, with an electrical charge. As the charged gas shoots out a nozzle, it imparts a gentle push — equivalent to the weight of a sheet of paper sitting on your hand, said Mark Rayman, chief engineer for Dawn at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

But what Dawn lacks in power, it makes up in stamina. Its engines have been thrusting for some 1,000 days, steadily adding speed.

Sipping just milligrams of xenon a day, the super-efficient engines leave Dawn with enough fuel to push itself toward a second asteroid. If all goes well, next summer the 65-foot-wide craft will depart Vesta and head toward the largest asteroid in the solar system, Ceres, with arrival scheduled for 2015. Ceres intrigues scientists because it apparently holds a huge reservoir of water, Russell said."