Editing Ion thruster (section)

{{short description|Spacecraft engine that generates thrust by generating a jet of ions}}
{{About|a kind of reaction engine|the air propulsion concept|ionocraft}}
{{Use American English|date=November 2020}}
{{use dmy dates |date=December 2020}}

[[File:Ion Engine Test Firing - GPN-2000-000482.jpg|thumb|upright=1.2|right|The 2.3{{nbsp}}kW [[NASA Solar Technology Application Readiness|NSTAR]] ion thruster developed by [[NASA]] for the [[Deep Space 1]] spacecraft during a hot fire test at the [[Jet Propulsion Laboratory]] (1999)]]
[[File:NEXIS thruster working.jpg|thumb|upright=1.2|right|NEXIS ion engine test (2005)]]
[[File:Xenon ion engine prototype.png|thumb|upright=1.2|A prototype of a xenon ion engine being tested at NASA's Jet Propulsion Laboratory (2005)]]

An '''ion thruster''', '''ion drive''', or '''ion engine''' is a form of [[electrically powered spacecraft propulsion|electric propulsion]] used for [[spacecraft propulsion]]. An ion thruster creates a cloud of [[cation|positive ions]] from a neutral gas by ionizing it to extract some [[electron]]s from its [[atom]]s. The [[ion]]s are then accelerated using [[electricity]] to create [[thrust]]. Ion thrusters are categorized as either [[electrostatics|electrostatic]] or [[electromagnetism|electromagnetic]].

[[electrostatics|Electrostatic]] thruster ions are accelerated by the [[Coulomb force]] along the [[electric field]] direction. Temporarily stored electrons are reinjected by a ''neutralizer'' in the cloud of ions after it has passed through the electrostatic grid, so the gas becomes neutral again and can freely disperse in space without any further electrical interaction with the thruster. 

By contrast, [[Electromagnetism|electromagnetic]] thruster ions are accelerated by the [[Lorentz force]] to accelerate all species (free electrons as well as positive and negative ions) in the same direction whatever their [[electric charge]], and are specifically referred to as [[plasma propulsion engine]]s, where the electric field is not in the direction of the acceleration.<ref name="Jahn 1968">{{cite book|last1=Jahn|first1=Robert G.|title=Physics of Electric Propulsion|date=1968|edition=1st|publisher=McGraw Hill Book Company|isbn=978-0070322448}} Reprint: {{cite book|last1=Jahn|first1=Robert G.|title=Physics of Electric Propulsion|date=2006|publisher=Dover Publications|isbn=978-0486450407}}</ref><ref name="Jahn-Choueiri 2002">{{cite book|last1=Jahn|first1=Robert G.|last2=Choueiri|first2=Edgar Y.|title=Encyclopedia of Physical Science and Technology|date=2003|edition=3rd|volume=5|publisher=Academic Press|chapter=Electric Propulsion|chapter-url=https://massless.info/images/ep-encyclopedia-2001.pdf |archive-url=https://web.archive.org/web/20221010091826/https://massless.info/images/ep-encyclopedia-2001.pdf |archive-date=2022-10-10 |url-status=live|pages=125–141|isbn=978-0122274107}}</ref>

Ion thrusters in operation typically consume 1–7&nbsp;kW of [[Electric power|power]], have [[exhaust velocity|exhaust velocities]] around 20–50&nbsp;km/s ([[Specific impulse|''I''<sub>sp</sub>]] 2000–5000{{nbsp}}s), and possess thrusts of 25–250&nbsp;mN and a [[propulsive efficiency]] 65–80%<ref name="autogenerated1">{{cite web|url=https://massless.info/images/choueiri-sciam-2009.pdf |archive-url=https://web.archive.org/web/20221010091833/https://massless.info/images/choueiri-sciam-2009.pdf |archive-date=2022-10-10 |url-status=live|title=Choueiri, Edgar Y., (2009) New dawn of electric rocket The Ion Drive}}</ref><ref name="Choueiri" /> though experimental versions have achieved {{cvt|100|kW}}, {{cvt|5|N}}.<ref>{{cite web|url=https://futurism.com/nasas-new-ion-thruster-breaks-records-could-take-humans-to-mars|title=NASA's new ion thruster breaks records, could take humans to Mars|website=futurism.com}}</ref>

The ''[[Deep Space 1]]'' spacecraft, powered by an ion thruster, changed velocity by {{cvt|4.3|km/s}} while consuming less than {{cvt|74|kg}} of [[xenon]]. The [[Dawn (spacecraft)|''Dawn'']] spacecraft broke the record, with a [[Delta-v|velocity change]] of {{cvt|11.5|km/s}}, though it was only half as efficient, requiring {{cvt|425|kg}} of xenon.<ref name='Dawn 2019'>{{cite web |url=http://www.jimhaldenwang.com/mars.htm|title=The Human Exploration of Mars|first=Jim|last=Haldenwang|work=Jim's Science Page|access-date=3 May 2019}}</ref>

Applications include control of the orientation and position of orbiting [[satellite]]s (some satellites have dozens of low-power ion thrusters), use as a main propulsion engine for low-mass robotic space vehicles (such as ''Deep Space 1'' and ''Dawn''),<ref name="autogenerated1"/><ref name="Choueiri"/> and serving as propulsion thrusters for [[crewed spacecraft]] and [[space station]]s (e.g. [[Tiangong space station|Tiangong]]).<ref name="human_ion">{{cite web |first=保淑 (Baoshu) |last=张 (Zhang) |title=配置4台霍尔电推进发动机 "天宫"掀起太空动力变革 [Hall-effect thruster for Tiangong set off space drive revolution ] |url=http://www.chinanews.com/gn/2021/06-21/9503717.shtml |website=中国新闻网 |accessdate=2021-07-18 |archive-url=https://web.archive.org/web/20210706020905/http://www.chinanews.com/gn/2021/06-21/9503717.shtml |archive-date=2021-07-06 |date=2021-06-21 |language=Chinese}}</ref>

Ion thrust engines are generally practical only in the vacuum of space as the engine's minuscule thrust cannot overcome any significant air resistance without radical design changes, as may be found in the '[[Atmosphere-breathing electric propulsion|Atmosphere Breathing Electric Propulsion]]' concept. The Massachusetts Institute of Technology (MIT) has created designs that are able to fly for short distances and at low speeds at ground level, using ultra-light materials and low drag aerofoils. An ion engine cannot usually generate sufficient thrust to achieve initial [[Takeoff|liftoff]] from any celestial body with significant surface [[gravity]]. For these reasons, spacecraft must rely on other methods such as conventional chemical rockets or [[Non-rocket spacelaunch|non-rocket launch technologies]] to reach their initial [[orbit]].