Gridded ion thruster

The second test, SERT-II, launched on February 3, 1970,[3][4] verified the operation of two mercury ion engines for thousands of running hours.

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.

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).

The final ion energy is determined by the potential of the plasma, which generally is slightly greater than the screen grids' voltage.

This can fail due to insufficient negative potential in the grid, which is a common ending for ion thrusters' operational life.

Lower-energy electrons are emitted from a separate cathode, called the neutralizer, into the ion beam to ensure that equal amounts of positive and negative charge are ejected.

In January 2006, the European Space Agency, together with the Australian National University, announced successful testing of an improved electrostatic ion engine, the Dual-Stage 4-Grid (DS4G), that showed exhaust speeds of 210 km/s, reportedly four times higher than previously achieved, allowing for a specific impulse which is four times higher.

The second pair, operating at low voltage, provides the electrical field that accelerates the particles outwards, creating thrust.

This reduces the propellant needed to correct the orientation of the spacecraft due to small uncertainties in the thrust vector direction.