After 8 years, Dawn probe brings Ceres into closest focus | Science Wire | EarthSky
The ion engines use xenon gas, a chemical cousin of helium and neon. With electrical power from Dawn’s large solar panels, the xenon is given an electrical charge in a process called ionization. The engines use high voltage to accelerate the ions. They’re then shot out of the engines at up to 90,000 mph. When the ions leave the spacecraft at this fantastically high speed, it’s pushed in the opposite direction. Dawn’s ion propulsion system is exceptionally efficient – 10 times as efficient as conventional spacecraft propulsion. It’s comparable to your car getting 250 miles per gallon.