Editing Ion thruster (section)

=== Gridded electrostatic ion thrusters ===
{{main|Gridded ion thruster}}
[[File:Ion engine.svg|thumb|upright=1.8|A diagram of how a gridded electrostatic ion engine (multipole magnetic cusp type) works]]

[[Gridded ion thruster|Gridded electrostatic ion thrusters]] development started in the 1960s<ref>{{cite journal |last1= Mazouffre|date= 2016|title= Electric propulsion for satellites and spacecraft: Established technologies and novel approaches|url= https://www.scopus.com/record/display.uri?eid=2-s2.0-84973355693&origin=inward&txGid=d2acc43c5b6bd3518f0fda0be9a7a74e|journal= Plasma Sources Science and Technology|volume= 25|issue= 3|page= 033002|doi= 10.1088/0963-0252/25/3/033002|bibcode= 2016PSST...25c3002M|s2cid= 41287361|access-date=July 29, 2021}}</ref> and, since then, they have been used for commercial satellite propulsion<ref>{{cite web|author1=|title=601 Satellite Historical Snapshot|url=https://www.boeing.com/history/products/601-satellite.page|website=Boing|date=|access-date=2021-07-26}}</ref><ref>{{Cite web|url=http://www.aerospace.org/crosslinkmag/fall-2014/electric-propulsion-at-aerospace/|title=Electric Propulsion at Aerospace {{!}} The Aerospace Corporation|website=www.aerospace.org|access-date=2016-04-10|archive-date=20 April 2016|archive-url=https://web.archive.org/web/20160420102803/http://www.aerospace.org/crosslinkmag/fall-2014/electric-propulsion-at-aerospace/|url-status=dead}}</ref><ref>{{Cite web|url=http://www.daviddarling.info/encyclopedia/X/XIPS.html|title=XIPS (xenon-ion propulsion system)|website=www.daviddarling.info|access-date=2016-04-10}}</ref> and scientific missions.<ref name="Sovey">J. S. Sovey,  V. K. Rawlin, and M. J. Patterson, "Ion Propulsion Development Projects in U. S.: Space Electric Rocket Test 1 to Deep Space 1", ''Journal of Propulsion and Power, Vol. 17'', No. 3, May–June 2001, pp. 517–526.</ref><ref>{{Cite web |url=http://www.grc.nasa.gov/WWW/ion/past/70s/sert2.htm |title=Space Electric Rocket Test |access-date=2010-07-01 |archive-url=https://web.archive.org/web/20110927004353/http://www.grc.nasa.gov/WWW/ion/past/70s/sert2.htm |archive-date=2011-09-27 |url-status=dead }}</ref> Their main feature is that the propellant [[ionization]] process is physically separated from the ion acceleration process.<ref>{{cite journal|last1=SANGREGORIO|first1=Miguel|last2=XIE|first2=Kan|date=2017|title=Ion engine grids: Function, main parameters, issues, configurations, geometries, materials and fabrication methods|journal=Chinese Journal of Aeronautics|volume=31|issue=8|pages=1635–1649 |doi=10.1016/j.cja.2018.06.005|doi-access=free}}</ref>

The ionization process takes place in the discharge chamber, where by bombarding the propellant with energetic electrons, as the energy transferred ejects valence electrons from the propellant gas's atoms. These electrons can be provided by a hot [[cathode]] [[electrical filament|filament]] and accelerated through the potential difference towards an anode. Alternatively, the electrons can be accelerated by an oscillating induced electric field created by an alternating electromagnet, which results in a self-sustaining discharge without a cathode (radio frequency ion thruster).

The positively charged ions are extracted by a system consisting of 2 or 3 multi-aperture grids. After entering the grid system near the plasma sheath, the ions are accelerated by the potential difference between the first grid and second grid (called the screen grid and the accelerator grid, respectively) to the final ion energy of (typically) 1–2&nbsp;keV, which generates thrust.

Ion thrusters emit a beam of positively charged ions. To keep the spacecraft from accumulating a charge, another [[cathode]] is placed near the engine to emit electrons into the ion beam, leaving the propellant electrically neutral. This prevents the beam of ions from being attracted (and returning) to the spacecraft, which would cancel the thrust.<ref name="Glenn"/>

Gridded electrostatic ion thruster research (past/present):
* [[NASA Solar Technology Application Readiness]] (NSTAR), 2.3&nbsp;kW, used on two successful missions
* NASA's Evolutionary Xenon Thruster ([[NEXT (ion thruster)|NEXT]]), 6.9&nbsp;kW, flight qualification hardware built; used on [[DART mission]]
* Nuclear Electric Xenon Ion System (NEXIS)
* High Power Electric Propulsion ([[HiPEP]]), 25&nbsp;kW, test example built and run briefly on the ground
* EADS Radio-frequency Ion Thruster (RIT)
* [[Dual-Stage 4-Grid]] (DS4G)<ref>{{cite press release|title=ESA and ANU make space propulsion breakthrough|publisher=ESA|date=2006-01-11|url=http://www.esa.int/esaCP/SEMOSTG23IE_index_0.html|access-date=2007-06-29}}</ref><ref>{{cite web |author=Australian National University Space Plasma, Power & Propulsion Group |date=2006-12-06 |title=ANU and ESA make space propulsion breakthrough |url=http://prl.anu.edu.au/SP3/research/SAFEandDS4G/webstory |archive-url=https://web.archive.org/web/20070627103001/http://prl.anu.edu.au/SP3/research/SAFEandDS4G/webstory |archive-date=2007-06-27 |access-date=2007-06-30 |publisher=The Australian National University}}</ref>