The gridded ion thruster is a common design for ion thrusters, a highly efficient low-thrust spacecraft propulsion method running on electrical power by using high-voltage grid electrodes to accelerate ions with electrostatic forces. History The ion engine was first demonstrated by German-born NASA scientist Ernst Stuhlinger, and developed in practical form by Harold R. Kaufman at NASA Lewis (now Glenn) Research Center from 1957 to the early 1960s. The use of ion propulsion systems were first demonstrated in space by the NASA Lewis "Space Electric Rocket Test" (SERT) I and II. These thrusters used mercury as the reaction mass. The first was SERT-1, launched July 20, 1964, which successfully proved that the technology operated as predicted in space. The second test, SERT-II, launched on February 3, 1970, verified the operation of two mercury ion engines for thousands of running hours. Despite the demonstration in the 1960s and 70s, though, they were rarely used before the late 1990s.'' NASA Glenn continued to develop electrostatic gridded ion thrusters through the 1980s, developing the NASA Solar Technology Application Readiness (NSTAR) engine, that was used successfully on the Deep Space 1 probe, the first mission to fly an interplanetary trajectory using electric propulsion as the primary propulsion. It is currently flying the Dawn asteroid mission. Hughes Aircraft Company (now L-3 ETI) has developed the XIPS (Xenon Ion Propulsion System) for performing station keeping on its geosynchronous satellites (more than 100 engines flying). NASA is currently working on a 20-50 kW electrostatic ion thruster called HiPEP which will have higher efficiency, specific impulse, and a longer lifetime than NSTAR. In 2006, Aerojet completed testing of a prototype NEXT ion thruster. Beginning in the 1970s, radio-frequency ion thrusters were developed at Giessen University and ArianeGroup. RIT-10 engines are flying on the EURECA and ARTEMIS. Qinetiq (UK) has developed the T5 and T6 engines (Kaufman type), used on the GOCE mission (T5) and the BepiColombo mission (T6). From Japan, the µ10, using microwaves, flew on the Hayabusa mission. In 2021, DART launched carrying a NEXT-C xenon ion thruster. In 2021, ThrustMe reported satellite orbit changes using their NPT30-I2 iodine ion thruster. Method of operation Propellant atoms are injected into the discharge chamber and are ionized, forming a plasma. There are several ways of producing the electrostatic ions for the discharge chamber: electron bombardment (Kauffman type) by a potential difference between a hollow cathode and anode (NSTAR, NEXT,