Engineer preparing the Hall Effect Rocket with Magnetic Shielding (HERMeS) for testing in a vacuum chamber that simulates the environment in space. This is a high-power solar electric propulsion system being developed by NASA for deep space exploration. HERMes is a type of ion thruster, an engine that uses an ionised propellent to generate thrust. It uses an electric field to accelerate the exhaust speeds of the propellent, increasing the specific impulse (a measure of the efficiency of the engine). Solar electric propulsion systems offer savings in spacecraft mass and size over conventional chemical propulsion systems. Photographed at the NASA Glenn Research Center, Cleveland, Ohio, USA.