and the materials used. This may have implications for the grid system operational lifetime. Specific impulse Electrostatic ion thrusters have also achieved a specific impulse of 30–100 kN·s/kg, better than most other ion thruster types. Electrostatic ion thrusters have accelerated ions to speeds reaching 100 km/s. Benefits of four grids 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. Conventional electrostatic ion thrusters possess only two grids, one high voltage and one low voltage, which perform both the ion extraction and acceleration functions. However, when the charge differential between these grids reaches around 5 kV, some of the particles extracted from the chamber collide with the low voltage grid, eroding it and compromising the engine's longevity. This limitation is successfully bypassed when two pairs of grids are used. The first pair operates at high voltage, possessing a voltage differential of around 3 kV between them; this grid pair is responsible for extracting the charged propellant particles from the gas chamber. The second pair, operating at low voltage, provides the electrical field that accelerates the particles outwards, creating thrust. Other advantages to the new engine include a more compact design, allowing it to be scaled up to higher thrusts, and a narrower, less divergent exhaust plume of 3 degrees, which is reportedly five times narrower than previously achieved. This reduces the propellant needed to correct the orientation of the spacecraft due to small uncertainties in the thrust vector direction. See also List of plasma (physics) articles Electrically powered spacecraft propulsion Ion thruster Dual-Stage 4-Grid Further reading In-orbit demonstration of an iodine electric propulsion system Nature 2021 Covers design detail that affect performance References External links Aerojet (Redmond, Washington USA) - Gridded Ion Thruster Vendor NSTAR ion engine Technologies to Improve Ion Propulsion System (PDF) Electric Thruster Systems (PDF) HiPEP ESA And ANU Make Space Propulsion Breakthrough Electrostatic motors Plasma physics Ion engines