An iodine electric thruster firing in a vacuum chamber. (Image: ThrustMe)

Extant satellites orbiting the Earth typically use electric ion drives for propulsion. There’s a few different types of ion drives, but the most common type relies on ionized xenon gas that is driven out of the craft by natural forces. Thanks to Newton’s third law

Source: Hot Hardware – ThrustMe’s Sexy New Iodine-Fueled Electric Propulsion System Could Transform Space Travel