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{{short description|Spacecraft engine that generates thrust by generating a jet of ions}}
] ion thruster for the ] spacecraft during a hot fire test at the Jet Propulsion Laboratory]]
{{About|a kind of reaction engine|the air propulsion concept|ionocraft}}
{{Use American English|date=November 2020}}
{{use dmy dates |date=December 2020}}


] ion thruster developed by ] for the ] spacecraft during a hot fire test at the ] (1999)]]
An '''ion thruster''' is a form of ] used for ]. It creates ] by accelerating ]s with ]. The term refers strictly to gridded ]s, but may more loosely be applied to all electric propulsion systems that accelerate ], since plasma consists of ions.
]
]


An '''ion thruster''', '''ion drive''', or '''ion engine''' is a form of ] used for ]. An ion thruster creates a cloud of ] from a neutral gas by ionizing it to extract some ]s from its ]s. The ]s are then accelerated using ] to create ]. Ion thrusters are categorized as either ] or ].
Ion thrusters are categorized by how they accelerate the ions, using either ] or ] force. Electrostatic thrusters use the ] and accelerate the ions in the direction of the ]. Electromagnetic thrusters use the ]. In either case, when an ion passes through an electrostatic grid engine, the ] of the ] converts to the ion's ].


] thruster ions are accelerated by the ] along the ] 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.
Ion thrusters have an input ] need of 1–7&nbsp;kW, ] 20–50&nbsp;km/s, thrust 25–250 ]s and ] 65–80%.<ref name="autogenerated1"></ref><ref name="Choueiri" />


By contrast, ] thruster ions are accelerated by the ] to accelerate all species (free electrons as well as positive and negative ions) in the same direction whatever their ], and are specifically referred to as ]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>
The ] spacecraft, powered by an ion thruster, changed velocity by 4.3&nbsp;km/s while consuming less than 74 kilograms of ]. The ] spacecraft broke the record, with a velocity of {{formatnum:10}}&nbsp;km/s.<ref name="autogenerated1" /><ref name="Choueiri" />


Ion thrusters in operation typically consume 1–7&nbsp;kW of ], have ] around 20–50&nbsp;km/s (] 2000–5000{{nbsp}}s), and possess thrusts of 25–250&nbsp;mN and a ] 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>
Applications include control of the orientation and position of orbiting ]s (some satellites have dozens of low-power ion thrusters) and use as a main propulsion engine for low-mass robotic space vehicles (such as Deep Space&nbsp;1 and Dawn).<ref name="autogenerated1" /><ref name="Choueiri" />


The '']'' spacecraft, powered by an ion thruster, changed velocity by {{cvt|4.3|km/s}} while consuming less than {{cvt|74|kg}} of ]. The ] spacecraft broke the record, with a ] 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>
The ion thruster is not the most promising type of ] (although the most successful in practice).<ref name="Choueiri">{{cite journal |last1= Choueiri |first1= Edgar Y |year= 2009 |title= New dawn of electric rocket |url= http://www.nature.com/scientificamerican/journal/v300/n2/full/scientificamerican0209-58.html |journal= ] |volume= 300 |issue= |pages= 58–65 |doi= 10.1038/scientificamerican0209-58 |subscription= yes}}</ref> An ion drive would require two days to accelerate a car to highway speed. The technical characteristics, especially ], are considerably inferior to the prototypes described in literature,<ref name="autogenerated1" /><ref name="Choueiri" /> technical capabilities are limited by the ] created by ions. This limits the thrust density (] per cross-sectional ] of the engine).<ref name="Choueiri" /> Ion thrusters create small thrust levels (the thrust of Deep Space 1 is approximately equal to the weight of one sheet of paper<ref name="Choueiri" />) compared to conventional ]s, but achieve high ], or propellant mass efficiency, by accelerating the exhaust to high speed. The ] imparted to the exhaust increases with the square of exhaust velocity while thrust increase is linear. Conversely, chemical rockets provide high thrust, but are limited in total ] by the small amount of ] that can be stored chemically in the propellants.<ref>, ESA Science & Technology</ref> Given the practical weight of suitable power sources, the acceleration from an ion thruster is frequently less than one thousandth of ]. However, since they operate as electric (or electrostatic) motors, they convert a greater fraction of input power into kinetic exhaust power. Chemical rockets operate as ]s, and ] limits the exhaust velocity.


Applications include control of the orientation and position of orbiting ]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 ] and ]s (e.g. ]).<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 |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 practical only in the vacuum of space and cannot take vehicles through the atmosphere because ion engines do not work in the presence of ions outside the engine. Spacecraft rely on conventional chemical rockets to initially reach ].


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 ']' 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 ] from any celestial body with significant surface ]. For these reasons, spacecraft must rely on other methods such as conventional chemical rockets or ] to reach their initial ].
==Origins==
]
Wernher von Braun." is first person to mention the idea publicly was ] in 1911.<ref name=choueiri /> However, the first document to consider electric propulsion is ]'s handwritten notebook in an entry dated September 6, 1906.<ref>Mark Wright, April 6, 1999, science.nasa.gov, </ref> The first experiments with ion thrusters were carried out by Goddard at ] from 1916–1917.<ref name="SIA1">{{cite web |author= |title=Robert H. Goddard: American Rocket Pioneer |work=Smithsonian Scrapbook |publisher=] |url=http://siarchives.si.edu/history/exhibits/documents/goddardmarch1920.htm |accessdate=March 28, 2012}}</ref> The technique was recommended for near-vacuum conditions at high altitude, but thrust was demonstrated with ionized air streams at atmospheric pressure. The idea appeared again in ]'s "Wege zur Raumschiffahrt” (Ways to Spaceflight), published in 1923, where he explained his thoughts on the mass savings of electric propulsion, predicted its use in ] and ] control, and advocated electrostatic acceleration of charged gases.<ref name=choueiri>{{cite web |url=http://alfven.princeton.edu/publications/choueiri-jpp-2004|title=A Critical History of Electric Propulsion: The First 50 Years (1906–1956)|accessdate=2016-10-18 |first= E. Y. |last= Choueiri}}</ref>


== Origins ==
A working ion thruster was built by in 1959 at the NASA ] facilities. It was similar to a gridded electrostatic ion thruster and used ] for propellant. Suborbital tests were conducted during the 1960s and in 1964, the engine was sent into a suborbital flight aboard the ] (SERT 1).<ref name='Ion 1964'>{{cite web|url=http://www.nasa.gov/centers/glenn/about/history/ds1.html|title=Contributions to Deep Space 1|work=NASA}}</ref><ref name = "Cybulski">Ronald J. Cybulski, Daniel M. Shellhammer, Robert R. LoveII, Edward J. Domino, and Joseph T. Kotnik, , NASA Technical Note D2718 (1965).</ref> It successfully operated for the planned 31 minutes before falling to Earth.<ref name="Glenn">{{cite web |url=http://www.nasa.gov/centers/glenn/about/fs08grc.html|title=Innovative Engines - Glenn Ion Propulsion Research Tames the Challenges of 21st Century Space Travel|accessdate=2007-11-19}}</ref> This test was followed by an orbital test, SERT-2, in 1970.<ref>NASA Glenn, " (Accessed July 1, 2010)</ref><ref> page at Astronautix (Accessed July 1, 2010)</ref>
]


The first person who wrote a paper introducing the idea publicly was ] in 1911.<ref name="choueiri2">{{cite web |title=Ion Propulsion – Over 50 Years in the Making |url=http://science.nasa.gov/newhome/headlines/prop06apr99_2.htm |url-status=dead |archive-url=https://web.archive.org/web/20100327120759/http://science.nasa.gov/newhome/headlines/prop06apr99_2.htm |archive-date=2010-03-27 |work=Science@NASA}}</ref> The technique was recommended for near-vacuum conditions at high altitude, but thrust was demonstrated with ionized air streams at atmospheric pressure. The idea appeared again in ]'s ''Wege zur Raumschiffahrt'' (1929; ''Ways to Spaceflight''),<ref>{{Cite journal |last=Wolf |first=K. |date=1931-12-01 |title=Wege zur Raumschiffahrt |journal=Monatshefte für Mathematik und Physik |language=de |volume=38 |issue=1 |pages=A58 |doi=10.1007/BF01700815 |s2cid=115467575 |issn=1436-5081|doi-access=free }}</ref> where he explained his thoughts on the mass savings of electric propulsion, predicted its use in ] and ], and advocated electrostatic acceleration of charged gasses.<ref name="choueiri3">{{cite web |url=https://massless.info/images/choueiri-jpp-2004.pdf |archive-url=https://web.archive.org/web/20221010091826/https://massless.info/images/choueiri-jpp-2004.pdf |archive-date=2022-10-10 |url-status=live |title=A Critical History of Electric Propulsion: The First 50 Years (1906–1956) |access-date=2016-10-18 |first= E. Y. |last=Choueiri}}</ref>
An alternate form of electric propulsion, the ] was studied independently in the U.S. and the ] in the 1950s and 1960s. Hall effect thrusters had operated on Soviet satellites since 1972. Until the 1990s they were mainly used for satellite stabilization in North-South and in East-West directions. Some 100–200 engines completed missions on Soviet and ]n satellites until the late 1990s.<ref name="NK">{{cite web| url=http://novosti-kosmonavtiki.ru/content/numbers/198/35.shtml|title=Native Electric Propulsion Engines Today|publisher=Novosti Kosmonavtiki| date= 1999| issue=7|archiveurl=https://web.archive.org/web/20110606033558/http://www.novosti-kosmonavtiki.ru/content/numbers/198/35.shtml| archivedate=6 June 2011|language=ru}}</ref> Soviet thruster design was introduced to the West in 1992 after a team of electric propulsion specialists, under the support of the ], visited Soviet laboratories.


A working ion thruster was built by ] in 1959 at the ] ] facilities. It was similar to a gridded electrostatic ion thruster and used ] for propellant. Suborbital tests were conducted during the 1960s and in 1964, and the engine was sent into a suborbital flight aboard the ] (SERT-1).<ref name='Ion 1964'>{{cite web |url=http://www.nasa.gov/centers/glenn/about/history/ds1.html |title=Contributions to Deep Space 1 |date=14 April 2015 |publisher=NASA}} {{PD-notice}}</ref><ref name="Cybulski">{{cite web |first1=Ronald J. |last1=Cybulski |first2=Daniel M. |last2=Shellhammer |first3=Robert R. |last3=Lovell |first4=Edward J. |last4=Domino |first5=Joseph T. |last5=Kotnik |url=https://ntrs.nasa.gov/api/citations/19650009681/downloads/19650009681.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://ntrs.nasa.gov/api/citations/19650009681/downloads/19650009681.pdf |archive-date=2022-10-09 |url-status=live |title=Results from SERT I Ion Rocket Flight Test |id=NASA-TN-D-2718 |publisher=] |date=1965}}{{PD-notice}}</ref> It successfully operated for the planned 31 minutes before falling to Earth.<ref name="Glenn">{{cite web |title=Innovative Engines – Glenn Ion Propulsion Research Tames the Challenges of 21st Century Space Travel |url=http://www.nasa.gov/centers/glenn/about/fs08grc.html |url-status=dead |archive-url=https://web.archive.org/web/20070915023928/http://www.nasa.gov/centers/glenn/about/fs08grc.html |archive-date=2007-09-15 |access-date=2007-11-19}} {{PD-notice}}</ref> This test was followed by an orbital test, SERT-2, in 1970.<ref name="sert2">{{cite web |publisher=] |url=http://www.grc.nasa.gov/WWW/ion/past/70s/sert2.htm |title=Space Electric Rocket Test II (SERT II) |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 |access-date=1 July 2010}}{{PD-notice}}</ref><ref>{{Cite web |date=October 25, 2010 |title=Encyclopedia Astronautica Index: 1 |url=http://www.astronautix.com/4/404page.html |access-date=2024-05-17 |website=www.astronautix.com}}</ref>
==General description==

Ion thrusters use beams of ]s (electrically charged atoms or molecules) to create ] in accordance with ]. The method of accelerating the ions varies, but all designs take advantage of the ]/] ratio of the ions. This ratio means that relatively small potential differences can create high exhaust velocities. This reduces the amount of ] or propellant required, but increases the amount of specific ] required compared to ]s. Ion thrusters are therefore able to achieve high ]s. The drawback of the low thrust is low acceleration because the mass of the electric power unit directly correlates with the amount of power. This low thrust makes ion thrusters unsuited for launching spacecraft into orbit, but effective for in-space propulsion.
On the 12 October 1964 ] carried out tests with ion thrusters that had been attached to the exterior of the spacecraft.<ref name="SiddiqiION">{{cite book |last=Siddiqi |first=Asif A. |url=https://history.nasa.gov/SP-4408pt1.pdf |title=Challenge To Apollo: The Soviet Union and The Space Race, 1945–1974 |date=2000 |publisher=NASA |page=423 |language=en-us}}</ref>

An alternate form of electric propulsion, the ], was studied independently in the ] and the ] in the 1950s and 1960s. Hall-effect thrusters operated on Soviet satellites from 1972 until the late 1990s, mainly used for satellite stabilization in north–south and in east–west directions. Some 100–200 engines completed missions on Soviet and ]n satellites.<ref name="NK">{{cite web |url=http://novosti-kosmonavtiki.ru/content/numbers/198/35.shtml |title=Native Electric Propulsion Engines Today |publisher=Novosti Kosmonavtiki |date=1999
|issue=7 |archive-url=https://web.archive.org/web/20110606033558/http://www.novosti-kosmonavtiki.ru/content/numbers/198/35.shtml |archive-date=6 June 2011 |language=ru}}</ref> Soviet thruster design was introduced to the West in 1992 after a team of electric propulsion specialists, under the support of the ], visited Soviet laboratories.

== General working principle ==
Ion thrusters use beams of ]s (electrically charged atoms or molecules) to create ] in accordance with ]. The method of accelerating the ions varies, but all designs take advantage of the ]/] ratio of the ions. This ratio means that relatively small potential differences can create high exhaust velocities. This reduces the amount of ] or propellant required, but increases the amount of specific ] required compared to ]s. Ion thrusters are therefore able to achieve high ]s. The drawback of the low thrust is low acceleration because the mass of the electric power unit directly correlates with the amount of power. This low thrust makes ion thrusters unsuited for launching spacecraft into orbit, but effective for in-space propulsion over longer periods of time.


Ion thrusters are categorized as either ] or ]. The main difference is the method for accelerating the ions. Ion thrusters are categorized as either ] or ]. The main difference is the method for accelerating the ions.
*Electrostatic ion thrusters use the ] and accelerate the ions in the direction of the electric field. * Electrostatic ion thrusters use the ] and accelerate the ions in the direction of the electric field.
*Electromagnetic ion thrusters use the ] to move the ions. * Electromagnetic ion thrusters use the ] to accelerate the ions in the direction perpendicular to the electric field.


Power supplies for ion thrusters are usually electric ] but at sufficiently large distances from the sun, nuclear power is used. In each case, the power supply mass is proportional to the peak power that can be supplied, and both provide, for this application, no limit to the energy. Electric power for ion thrusters is usually provided by ]s. However, for sufficiently large distances from the sun, ] may be used. In each case, the power supply mass is proportional to the peak power that can be supplied, and both provide, for this application, almost no limit to the energy.<ref>{{cite web |title=Ion Propulsion: Farther, Faster, Cheaper |url=https://www.nasa.gov/centers/glenn/technology/Ion_Propulsion1.html |website=NASA |access-date=4 February 2022 |archive-date=11 November 2020 |archive-url=https://web.archive.org/web/20201111185012/https://www.nasa.gov/centers/glenn/technology/Ion_Propulsion1.html |url-status=dead }}</ref>


Electric thrusters tend to produce low thrust, which results in low acceleration. Using 1&nbsp;g is 9.81&nbsp;m/s<sup>2</sup>; F = m a ⇒ a = F/m. An ] thruster producing a thrust (force) of 92&nbsp;mN<ref name=ns20070928/> will accelerate a satellite with a mass of 1&nbsp;000&nbsp;kg by 0.092&nbsp;N / 1&nbsp;000&nbsp;kg = {{gaps|0.000|092}}&nbsp;m/s<sup>2</sup> (or 9.38{{e|−6}}&nbsp;g). Electric thrusters tend to produce low thrust, which results in low acceleration. Defining <math>1g = 9.81\; \mathrm{m/s^2}</math>, the ], and noting that <math>F = ma \implies a = F/m</math>, this can be analyzed. An ] thruster producing a thrust force of 92&nbsp;mN<ref name=ns20070928/> will accelerate a satellite with a mass of 1{{nbsp}}] by 0.092{{nbsp}}N / 1000&nbsp;kg = 9.2{{e|−5}}{{nbsp}}m/s{{sup|2}} (or 9.38{{e|−6}}{{nbsp}}''g''). However, this acceleration can be sustained for months or years at a time, in contrast to the very short burns of chemical rockets.


F = 2*η*P/(g * I<sub>sp</sub>) <math display="block">F = 2 \frac{\eta P}{g I_\text{sp}}</math>
<br />Where Where:
: F is the thrust (force) in N, * ''F'' is the thrust force in N,
: η is the efficincy, a dimensionless value between 0 and 1 (70% efficiency is 0.7), * ''η'' is the ]
: P is the electrical power energy going into the thruster in W, * ''P'' is the electrical power used by the thruster in W, and
* ''I''<sub>sp</sub> is the ] in seconds.
: g is a constant, the acceleration due to gravity 9.81&nbsp;m/s<sup>2,</sup>
: I<sub>sp</sub> is the ] in s.


The ion thruster is not the most promising type of ], but it is the most successful in practice to date.<ref name="Choueiri">{{cite journal|last1=Choueiri |first1=Edgar Y.|year=2009|title=New dawn of electric rocket|journal=Scientific American|volume=300|issue=2|pages=58–65|doi=10.1038/scientificamerican0209-58|pmid=19186707|bibcode=2009SciAm.300b..58C}}</ref> An ion drive would require two days to accelerate a car to highway speed in vacuum. The technical characteristics, especially ], are considerably inferior to the prototypes described in literature,<ref name="autogenerated1"/><ref name="Choueiri"/> technical capabilities are limited by the ] created by ions. This limits the thrust density (] per cross-sectional ] of the engine).<ref name="Choueiri"/> Ion thrusters create small thrust levels (the thrust of ''Deep Space 1'' is approximately equal to the weight of one sheet of paper<ref name="Choueiri"/>) compared to conventional ]s, but achieve high ], or propellant mass efficiency, by accelerating the exhaust to high speed. The ] imparted to the exhaust increases with the square of exhaust velocity while thrust increase is linear. Conversely, chemical rockets provide high thrust, but are limited in total ] by the small amount of ] that can be stored chemically in the propellants.<ref>{{Cite web |title=ESA Science & Technology – Electric Spacecraft Propulsion |url=https://sci.esa.int/web/smart-1/-/34201-electric-spacecraft-propulsion?fbodylongid=1535 |access-date=2024-05-17 |website=sci.esa.int}}</ref> Given the practical weight of suitable power sources, the acceleration from an ion thruster is frequently less than one-thousandth of ]. However, since they operate as electric (or electrostatic) motors, they convert a greater fraction of input power into kinetic exhaust power. Chemical rockets operate as ]s, and ] limits the exhaust velocity.
==Electrostatic ion thrusters==


===Gridded electrostatic ion thrusters=== == Electrostatic thrusters ==
=== Gridded electrostatic ion thrusters ===
{{main|Gridded ion thruster}} {{main|Gridded ion thruster}}
]


] 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 ] 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>
]
''']''' commonly utilize ] gas. This gas has no charge and is ] by bombarding it with energetic electrons. These electrons can be provided from a hot ] ] and when accelerated in the electrical field of the cathode, fall to the anode. Alternatively, the electrons can be accelerated by the oscillating electric field induced by an alternating magnetic field of a coil, which results in a self-sustaining discharge without a cathode (radio frequency ion thruster).


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 ] ] 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 an extraction system consisting of 2 or 3 multi-aperture grids. After entering the grid system by the plasma sheath, the ions are accelerated by the potential difference between the first and second grid (named screen and accelerator grid) to the final ion energy of (typically) 1–2 keV, generating the thrust.


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 positive charged xenon ions only. To avoid charging up the spacecraft, another ] is placed near the engine to emit an electron current into the ion beam with net neutral electrostatic charge.<ref name="Glenn" /> This prevents the beam of ions from being attracted (and returning) to the spacecraft, cancelling the thrust.{{citation needed|date=August 2012}}

Ion thrusters emit a beam of positively charged ions. To keep the spacecraft from accumulating a charge, another ] 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): Gridded electrostatic ion thruster research (past/present):
*] (NSTAR) - 2,3&nbsp;kW, used on two successful missions * ] (NSTAR), 2.3&nbsp;kW, used on two successful missions
*NASA’s Evolutionary Xenon Thruster (]) - 6,9&nbsp;kW, flight qualification hardware built * NASA's Evolutionary Xenon Thruster (]), 6.9&nbsp;kW, flight qualification hardware built; used on ]
*Nuclear Electric Xenon Ion System (NEXIS) * Nuclear Electric Xenon Ion System (NEXIS)
*High Power Electric Propulsion (]) - 25&nbsp;kW, test example built and run briefly on the ground * High Power Electric Propulsion (]), 25&nbsp;kW, test example built and run briefly on the ground
*EADS Radio-Frequency Ion Thruster (RIT) * EADS Radio-frequency Ion Thruster (RIT)
*] (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 |accessdate = 2007-06-29 |quote = }}</ref><ref>{{cite web |url=http://prl.anu.edu.au/SP3/research/SAFEandDS4G/webstory |title=ANU and ESA make space propulsion breakthrough |accessdate=2007-06-30 |author=ANU Space Plasma, Power & Propulsion Group (SP3) |authorlink= |date=2006-12-06 |work=DS4G Web Story |publisher=The Australian National University |pages= |archiveurl = https://web.archive.org/web/20070627103001/http://prl.anu.edu.au/SP3/research/SAFEandDS4G/webstory <!-- Bot retrieved archive --> |archivedate = 2007-06-27 |quote= }}</ref> * ] (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>


===Hall effect thrusters=== === Hall-effect thrusters ===
{{main|Hall effect thruster}} {{Main|Hall-effect thruster}}
]


]s accelerate ions by means of an electric potential between a cylindrical anode and a negatively charged plasma that forms the cathode. The bulk of the propellant (typically xenon) is introduced near the anode, where it ionizes and flows toward the cathode; ions accelerate towards and through it, picking up electrons as they leave to neutralize the beam and leave the thruster at high velocity.
]
''']s''' accelerate ions by means of an electric potential between a cylindrical anode and a negatively charged plasma that forms the cathode. The bulk of the propellant (typically xenon) is introduced near the anode, where it ionizes and flows toward the cathode; ions accelerate towards and through it, picking up electrons as they leave to neutralize the beam and leave the thruster at high velocity.


The anode is at one end of a cylindrical tube. In the center is a spike that is wound to produce a radial magnetic field between it and the surrounding tube. The ions are largely unaffected by the magnetic field, since they are too massive. However, the electrons produced near the end of the spike to create the cathode are trapped by the magnetic field and held in place by their attraction to the anode. Some of the electrons spiral down towards the anode, circulating around the spike in a Hall current. When they reach the anode they impact the uncharged propellant and cause it to be ionized, before finally reaching the anode and closing the circuit.<ref name="Oleson">{{cite web |url=http://gltrs.grc.nasa.gov/reports/2001/TM-2001-210676.pdf|title=Advanced Hall Electric Propulsion for Future In-Space Transportation|accessdate=2007-11-21|last1= Oleson |first1= S. R. |last2= Sankovic| first2= J. M.}}</ref> The anode is at one end of a cylindrical tube. In the center is a spike that is wound to produce a radial magnetic field between it and the surrounding tube. The ions are largely unaffected by the magnetic field, since they are too massive. However, the electrons produced near the end of the spike to create the cathode are trapped by the magnetic field and held in place by their attraction to the anode. Some of the electrons spiral down towards the anode, circulating around the spike in a ]. When they reach the anode they impact the uncharged propellant and cause it to be ionized, before finally reaching the anode and completing the circuit.<ref name="Oleson">{{cite web|url=http://gltrs.grc.nasa.gov/reports/2001/TM-2001-210676.pdf|title=Advanced Hall Electric Propulsion for Future In-Space Transportation|access-date=2007-11-21|last1=Oleson|first1=S. R.|last2=Sankovic|first2=J. M.|url-status=dead|archive-url=https://web.archive.org/web/20040122155512/http://gltrs.grc.nasa.gov/reports/2001/TM-2001-210676.pdf|archive-date=2004-01-22}} {{PD-notice}}</ref>


===Field-emission electric propulsion=== === Field-emission electric propulsion ===
{{main|Field-emission electric propulsion}} {{main|Field-emission electric propulsion}}
''']''' (FEEP) thrusters use either ] or ] as the propellant. The design comprises a small propellant reservoir that stores the liquid metal, a narrow tube or a system of parallel plates that the liquid flows through and an accelerator (a ring or an elongated aperture in a metallic plate) about a millimeter past the tube end. Caesium and indium are used due to their high atomic weights, low ionization potentials and low melting points. Once the liquid metal reaches the end of the tube, an electric field applied between the emitter and the accelerator causes the liquid surface to deform into a series of protruding cusps ("]s"). At a sufficiently high applied voltage, positive ions are extracted from the tips of the cones.<ref>{{cite web |url=http://www.alta-space.com/index.php?page=feep|title=FEEP - Field-Emission Electric Propulsion|accessdate=2012-04-27}}</ref><ref name="JPP98">{{cite web |url=http://www.alta-space.com/uploads/file/publications/feep/Marcuccio-JPP14_5_1998.pdf|title=Experimental Performance of Field Emission Microthrusters|author=Marcuccio, S.|display-authors=etal|accessdate=2012-04-27}}</ref><ref name="Nasa">{{cite web |url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/11649/1/02-0194.pdf|title=In-FEEP Thruster Ion Beam Neutralization with Thermionic and Field Emission Cathodes|quote=liquid state and wicked up the needle shank to the tip where high electric fields deform the liquid and extract ions and accelerate them up to 130 km/s through 10 kV.|accessdate=2007-11-21|first1= Colleen |last1= Marrese-Reading |first2= Jay |last2= Polk |first3= Juergen |last3=Mueller |first4= Al |last4= Owens}}</ref> The electric field created by the emitter and the accelerator then accelerates the ions. An external source of electrons neutralizes the positively charged ion stream to prevent charging of the spacecraft.


] (FEEP) thrusters may use ] or ] propellants. The design comprises a small propellant reservoir that stores the liquid metal, a narrow tube or a system of parallel plates that the liquid flows through and an accelerator (a ring or an elongated aperture in a metallic plate) about a millimeter past the tube end. Caesium and indium are used due to their high atomic weights, low ionization potentials and low melting points. Once the liquid metal reaches the end of the tube, an electric field applied between the emitter and the accelerator causes the liquid surface to deform into a series of protruding cusps, or '']s''. At a sufficiently high applied voltage, positive ions are extracted from the tips of the cones.<ref>{{cite web |title=FEEP – Field-Emission Electric Propulsion |url=http://www.alta-space.com/index.php?page=feep |url-status=dead |archive-url=https://web.archive.org/web/20120118051025/http://www.alta-space.com/index.php?page=feep |archive-date=2012-01-18 |access-date=2012-04-27}}</ref><ref name="JPP98">{{cite web|url=http://www.alta-space.com/uploads/file/publications/feep/Marcuccio-JPP14_5_1998.pdf|title=Experimental Performance of Field Emission Microthrusters|author=Marcuccio, S.|display-authors=etal|access-date=2012-04-27|url-status=dead|archive-url=https://web.archive.org/web/20130520151812/http://www.alta-space.com/uploads/file/publications/feep/Marcuccio-JPP14_5_1998.pdf|archive-date=2013-05-20}}</ref><ref name="Nasa">{{cite web|url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/11649/1/02-0194.pdf|title=In-FEEP Thruster Ion Beam Neutralization with Thermionic and Field Emission Cathodes|quote=liquid state and wicked up the needle shank to the tip where high electric fields deform the liquid and extract ions and accelerate them up to 130 km/s through 10 kV|access-date=2007-11-21|first1=Colleen|last1=Marrese-Reading|first2=Jay|last2=Polk|first3=Juergen|last3=Mueller|first4=Al|last4=Owens|url-status=dead |archive-url=https://web.archive.org/web/20061013162109/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/11649/1/02-0194.pdf|archive-date=2006-10-13}} {{PD-notice}}</ref> The electric field created by the emitter and the accelerator then accelerates the ions. An external source of electrons neutralizes the positively charged ion stream to prevent charging of the spacecraft.
==Electromagnetic thrusters==

== Electromagnetic thrusters ==
{{main|Plasma propulsion engine}}
{{Self-contradictory|section=about=electromagnetic thrusters|article=Electrically powered spacecraft propulsion|date=April 2018}}


===Pulsed inductive thrusters=== === Pulsed inductive thrusters ===
{{main|Pulsed inductive thruster}} {{main|Pulsed inductive thruster}}
]s (PIT) use pulses instead of continuous thrust and have the ability to run on power levels on the order of megawatts (MW). PITs consist of a large ] encircling a cone shaped tube that emits the propellant gas. ] is the gas commonly used. For each pulse, a large charge builds up in a group of capacitors behind the coil and is then released. This creates a current that moves circularly in the direction of jθ. The current then creates a magnetic field in the outward radial direction (Br), which then creates a current in the gas that has just been released in the opposite direction of the original current. This opposite current ionizes the ammonia. The positively charged ions are accelerated away from the engine due to the electric field jθ crossing the magnetic field Br, due to the Lorentz Force.<ref>{{cite web |url=http://gltrs.grc.nasa.gov/reports/2003/CR-2003-212714.pdf|title=Pulsed Inductive Thruster (PIT): Modeling and Validation Using the MACH2 Code|accessdate=2007-11-21|first=Pavlos G. |last= Mikellides}}</ref>


]s (PITs) use pulses instead of continuous thrust and have the ability to run on power levels on the order of megawatts (MW). PITs consist of a large ] encircling a cone shaped tube that emits the propellant gas. ] is the gas most commonly used. For each pulse, a large charge builds up in a group of capacitors behind the coil and is then released. This creates a current that moves circularly in the direction of jθ. The current then creates a magnetic field in the outward radial direction (Br), which then creates a current in the gas that has just been released in the opposite direction of the original current. This opposite current ionizes the ammonia. The positively charged ions are accelerated away from the engine due to the electric field jθ crossing the magnetic field Br, due to the Lorentz force.<ref>{{cite web|url=http://gltrs.grc.nasa.gov/reports/2003/CR-2003-212714.pdf|title=Pulsed Inductive Thruster (PIT): Modeling and Validation Using the MACH2 Code |access-date=2007-11-21|first=Pavlos G.|last=Mikellides|url-status=dead|archive-url=https://web.archive.org/web/20061010033732/http://gltrs.grc.nasa.gov/reports/2003/CR-2003-212714.pdf|archive-date=2006-10-10}} {{PD-notice}}</ref>
===Magnetoplasmadynamic / Lithium Lorentz force accelerator===

=== Magnetoplasmadynamic thruster ===
{{main|Magnetoplasmadynamic thruster}} {{main|Magnetoplasmadynamic thruster}}
] (MPD) thrusters and lithium Lorentz force accelerator (LiLFA) thrusters use roughly the same idea. The LiLFA thruster builds off of the MPD thruster. ], ], ] and ] can be used as propellant. In a certain configuration, the ambient gas in ] (LEO) can be used as a propellant. The gas enters the main chamber where it is ionized into ] by the electric field between the ] and the ]. This plasma then conducts electricity between the anode and the cathode, closing the circuit. This new current creates a magnetic field around the cathode, which crosses with the electric field, thereby accelerating the plasma due to the Lorentz force.


] (MPD) thrusters and ] (LiLFA) thrusters use roughly the same idea. The LiLFA thruster builds on the MPD thruster. ], ], ] and ] can be used as propellant. In a certain configuration, the ambient gas in ] (LEO) can be used as a propellant. The gas enters the main chamber where it is ionized into ] by the electric field between the ] and the ]. This plasma then conducts electricity between the anode and the cathode, closing the circuit. This new current creates a magnetic field around the cathode, which crosses with the electric field, thereby accelerating the plasma due to the Lorentz force.
The LiLFA thruster uses the same general idea as the MPD thruster, with two main differences. First, the LiLFA uses lithium vapor, which can be stored as a solid. The other difference is that the single cathode is replaced by multiple, smaller cathode rods packed into a hollow cathode tube. MPD cathodes are easily corroded due to constant contact with the plasma. In the LiLFA thruster the lithium vapor is injected into the hollow cathode and is not ionized to its plasma form/corrode the cathode rods until it exits the tube. The plasma is then accelerated using the same Lorentz Force.<ref name="Sankaran">{{cite web |url=http://alfven.princeton.edu/publications/sankaran-icnta-2003|title=A Survey of Propulsion Options for Cargo and Piloted Missions to Mars|accessdate=2016-10-18|first1=K. |last1=Sankaran |first2= L. |last2= Cassady |first3= A.D. |last3= Kodys |first4= E.Y. |last4= Choueiri}}</ref><ref>{{cite web|url=http://gltrs.grc.nasa.gov/reports/2001/CR-2001-211114.pdf |title=High Power MPD Thruster Development at the NASA Glenn Research Center |accessdate=2007-11-21 |first1=Michael R. |last1=LaPointe |first2=Pavlos G. |last2=Mikellides |deadurl=yes |archiveurl=https://web.archive.org/web/20061011063710/http://gltrs.grc.nasa.gov/reports/2001/CR-2001-211114.pdf |archivedate=October 11, 2006 }}</ref><ref>{{cite web|url=http://dspace.mit.edu/bitstream/handle/1721.1/31061/33887503.pdf?sequence=1 |title=Utilization of Ambient Gas as a Propellant for Low Earth Orbit Electric Propulsion |date=May 22, 1999 |first=Buford Ray |last=Conley |deadurl=yes |archiveurl=https://web.archive.org/web/20110629174257/http://dspace.mit.edu/bitstream/handle/1721.1/31061/33887503.pdf?sequence=1 |archivedate=June 29, 2011 }}</ref>


The LiLFA thruster uses the same general idea as the MPD thruster, though with two main differences. First, the LiLFA uses lithium vapor, which can be stored as a solid. The other difference is that the single cathode is replaced by multiple, smaller cathode rods packed into a ] tube. MPD cathodes are easily corroded due to constant contact with the plasma. In the LiLFA thruster, the lithium vapor is injected into the hollow cathode and is not ionized to its plasma form/corrode the cathode rods until it exits the tube. The plasma is then accelerated using the same ].<ref name="Sankaran">{{cite journal|url=https://massless.info/images/sankaran-icnta-2003.pdf |archive-url=https://web.archive.org/web/20221010091830/https://massless.info/images/sankaran-icnta-2003.pdf |archive-date=2022-10-10 |url-status=live|title=A Survey of Propulsion Options for Cargo and Piloted Missions to Mars|access-date=2016-10-18|first1=K. |last1=Sankaran|first2=L.|last2=Cassady|first3=A.D.|last3=Kodys|first4=E.Y.|last4=Choueiri|journal=Annals of the New York Academy of Sciences|year=2004|volume=1017|issue=1|pages=450–467|doi=10.1196/annals.1311.027 |pmid=15220162|bibcode=2004NYASA1017..450S|s2cid=1405279}}</ref><ref>{{cite web|url=http://gltrs.grc.nasa.gov/reports/2001/CR-2001-211114.pdf|title=High Power MPD Thruster Development at the NASA Glenn Research Center|access-date=2007-11-21|first1=Michael R.|last1=LaPointe|first2=Pavlos G.|last2=Mikellides|url-status=dead|archive-url=https://web.archive.org/web/20061011063710/http://gltrs.grc.nasa.gov/reports/2001/CR-2001-211114.pdf |archive-date=October 11, 2006}} {{PD-notice}}</ref><ref>{{cite web|url=http://dspace.mit.edu/bitstream/handle/1721.1/31061/33887503.pdf?sequence=1|title=Utilization of Ambient Gas as a Propellant for Low Earth Orbit Electric Propulsion|date=May 22, 1999|first=Buford Ray|last=Conley|url-status=dead|archive-url=https://web.archive.org/web/20110629174257/http://dspace.mit.edu/bitstream/handle/1721.1/31061/33887503.pdf?sequence=1|archive-date=June 29, 2011}}</ref>
In 2013 Russian company the ] successfully conducted a bench test of their MPD engine for long-distance space travel.<ref>{{cite web|url=http://sdelanounas.ru/blogs/44948|title="В Воронеже создали двигатель для Марса" в блоге "Перспективные разработки, НИОКРы, изобретения" - Сделано у нас|work=Сделано у нас}}</ref>


In 2013, Russian company the ] successfully conducted a bench test of their MPD engine for long-distance space travel.<ref>{{cite web |date=17 December 2013 |title="В Воронеже создали двигатель для Марса" в блоге "Перспективные разработки, НИОКРы, изобретения" - Сделано у нас |url=http://sdelanounas.ru/blogs/44948 |publisher=Сделано у нас |language=ru}}</ref>
===Electrodeless plasma thrusters===

=== Electrodeless plasma thrusters ===
{{main|Electrodeless plasma thruster}} {{main|Electrodeless plasma thruster}}
]s have two unique features: the removal of the anode and cathode electrodes and the ability to throttle the engine. The removal of the electrodes eliminates erosion, which limits lifetime on other ion engines. Neutral gas is first ionized by ] and then transferred to another chamber where it is accelerated by an oscillating electric and magnetic field, also known as the ]. This separation of the ionization and acceleration stages allows throttling of propellant flow, which then changes the thrust magnitude and specific impulse values.<ref>{{cite web |url=http://www.elwingcorp.com/files/IEPC05-article.pdf| title= Development of a High Power Electrodeless Thruster|accessdate=2007-11-21|first= Gregory D. |last= Emsellem}}</ref>


]s have two unique features: the removal of the anode and cathode electrodes and the ability to throttle the engine. The removal of the electrodes eliminates erosion, which limits lifetime on other ion engines. Neutral gas is first ionized by ] and then transferred to another chamber where it is accelerated by an oscillating electric and magnetic field, also known as the ]. This separation of the ionization and acceleration stages allows throttling of propellant flow, which then changes the thrust magnitude and specific impulse values.<ref>{{cite web|url=http://www.elwingcorp.com/files/IEPC05-article.pdf|title=Development of a High Power Electrodeless Thruster|access-date=2007-11-21|first=Gregory D.|last=Emsellem |archive-url=https://web.archive.org/web/20080515145645/http://www.elwingcorp.com/files/IEPC05-article.pdf|archive-date=2008-05-15|url-status=dead}}</ref>
===Helicon double layer thrusters===

=== Helicon double layer thrusters ===
{{main|Helicon double-layer thruster}} {{main|Helicon double-layer thruster}}
A helicon double layer thruster is a type of plasma thruster that ejects high velocity ] gas to provide ]. In this design, gas is injected into a tubular chamber (the ''source tube'') with one open end. ] AC power (at ] in the prototype design) is coupled into a specially shaped ] wrapped around the chamber. The ] emitted by the antenna causes the gas to break down and form a plasma. The antenna then excites a ] in the plasma, which further heats it. The device has a roughly constant ] in the source tube (supplied by ] in the prototype), but the magnetic field diverges and rapidly decreases in magnitude away from the source region and might be thought of as a kind of magnetic ]. In operation, a sharp boundary separates the high density plasma inside the source region and the low density plasma in the exhaust, which is associated with a sharp change in electrical potential. Plasma properties change rapidly across this boundary, which is known as a ''current-free electric ]''. The electrical potential is much higher inside the source region than in the exhaust and this serves both to confine most of the electrons and to accelerate the ions away from the source region. Enough electrons escape the source region to ensure that the plasma in the exhaust is neutral overall.


A helicon double layer thruster is a type of plasma thruster that ejects high velocity ] gas to provide ]. In this design, gas is injected into a tubular chamber (the ''source tube'') with one open end. ] AC power (at ] in the prototype design) is coupled into a specially shaped ] wrapped around the chamber. The ] emitted by the antenna causes the gas to break down and form a plasma. The antenna then excites a ] in the plasma, which further heats it. The device has a roughly constant ] in the source tube (supplied by ]s in the prototype), but the magnetic field diverges and rapidly decreases in magnitude away from the source region and might be thought of as a kind of magnetic ]. In operation, a sharp boundary separates the high density plasma inside the source region and the low density plasma in the exhaust, which is associated with a sharp change in electrical potential. Plasma properties change rapidly across this boundary, which is known as a ''current-free electric ]''. The electrical potential is much higher inside the source region than in the exhaust and this serves both to confine most of the electrons and to accelerate the ions away from the source region. Enough electrons escape the source region to ensure that the plasma in the exhaust is neutral overall.
=== VASIMR ===

=== Variable Specific Impulse Magnetoplasma Rocket (VASIMR) ===
{{main|Variable Specific Impulse Magnetoplasma Rocket}} {{main|Variable Specific Impulse Magnetoplasma Rocket}}


The proposed ] (VASIMR) functions by using ] to ionize a ] into a plasma, and then using a ] to accelerate the plasma out of the back of the ] to generate thrust. The VASIMR is currently being developed by ], headquartered in ], ], with help from ]-based ], producing the 200&nbsp;kW RF generators for ionizing propellant. Some of the components and "plasma shoots" experiments are tested in a laboratory settled in ]. This project is led by former NASA astronaut ] (CRC-USA). A 200&nbsp;kW VASIMR test engine was in discussion to be fitted in the exterior of the ], as part of the plan to test the VASIMR in space; however, plans for this test onboard ISS were canceled in 2015 by ], with a free flying VASIMR test being discussed by Ad Astra instead.<ref name="VASiMRscrapped"/> An envisioned 200&nbsp;MW engine could reduce the duration of flight from Earth to Jupiter or Saturn from six years to fourteen months, and Mars from 7 months to 39 days.<ref>{{cite web|last=Zyga|first=Lisa|date=2009|title=Plasma Rocket Could Travel to Mars in 39 Days|url=http://phys.org/news174031552.html|work=]}}</ref>
VASIMR, or Variable Specific Impulse Magnetoplasma Rocket, works by using ] to ionize a ] into a plasma and then a ] to accelerate the plasma out of the back of the ] to generate thrust.
The VASIMR is currently being developed by the private company ], headquartered in Houston, TX with of help from a NS Canada based company ], producing the 200&nbsp;kW RF generators for ionizing propellant. Some of the components and "Plasma Shoots" experiments are tested in a laboratory settled in ].
This project is led by former NASA astronaut Dr. ] (CRC-USA).
Recently the Costa Rican Aerospace Alliance announced its cooperation with this project by developing an exterior support device for the VASIMR to be fitted in the exterior of the ], as part of the plan to test the VASIMR in space, this test phase is now expected to be conducted in 2016. The supposed 200 megawatt engine could reduce the duration of flight from Earth to Jupiter or Saturn from six years to fourteen months, and Mars from 6 months to 39 days.<ref>Zyga, Lisa (2009). Plasma Rocket Could Travel to Mars in 39 Days, http://phys.org/news174031552.html Physorg</ref>


===Microwave electrothermal thrusters=== === Microwave electrothermal thrusters ===
{{multiple image {{multiple image
| align = right | align = right
| footer = Microwave Electrothermal Thruster. | header = ]
| caption_align = center | caption_align = center
|header_align=center | header_align = center
| image1 = MET Sketch 1.jpg | total_width = 500

| width1 = 1221
| image1 = MET Sketch 1.jpg
| alt1 = Thruster components
| width1 = 1221
| caption1 = <small style="font-size:90%;">''Thruster components''</small>
| height1 = 629
| image2 = MET Sketch 2.jpg
| width2 = 1233 | alt1 = Thruster components
| caption1 = <small style="font-size:90%;">Thruster components</small>
| alt2 = Discharge Chamber

| caption2 = <small style="font-size:90%;">''Discharge chamber''</small>
| image2 = MET Sketch 2.jpg
| total_width = 400
| height1 = 629 | width2 = 1233
| height2 = 1297 | height2 = 1297
| alt2 = Discharge Chamber
| caption2 = <small style="font-size:90%;">Discharge chamber</small>
}} }}


Under a research grant from the ] during the 1980s and 1990s, Martin C. Hawley and Jes Asmussen led a team engineers in developing a Microwave Electrothermal Thruster (MET).<ref>{{cite news | title = Less Fuel, More Thrust: New Engines are Being Designed for Deep Space| newspaper = The Arugus-Press| location = Owosso, Michigan| pages = 10 | volume= 128 | number= 48 | date = 26 February 1982 }}</ref> Under a research grant from the ] during the 1980s and 1990s, Martin C. Hawley and Jes Asmussen led a team of engineers in developing a microwave electrothermal thruster (MET).<ref>{{cite news|title=Less Fuel, More Thrust: New Engines are Being Designed for Deep Space|newspaper=The Arugus-Press|location=Owosso, Michigan|page=10|volume=128|number=48
|date=26 February 1982}}</ref>


In the discharge chamber, ] (MW) energy flows into the center containing a high level of ]s (I), causing neutral species in the gaseous ] to ionize. Excited species flow out (FES) through the low ion region (II) to a neutral region (III) where the ions complete their ], replaced with the flow of neutral species (FNS) towards the center. Meanwhile, energy is lost to the chamber walls through heat ] and ] (HCC), along with ] (Rad). The remaining energy absorbed into the gaseous propellant is converted into ]. In the discharge chamber, ] (MW) energy flows into the center containing a high level of ]s (I), causing neutral species in the gaseous ] to ionize. Excited species flow out (FES) through the low ion region (II) to a neutral region (III) where the ions complete their ], replaced with the flow of neutral species (FNS) towards the center. Meanwhile, energy is lost to the chamber walls through heat ] and ] (HCC), along with ] (Rad). The remaining energy absorbed into the gaseous propellant is converted into ].


== Radioisotope thruster ==
==Comparisons==
A theoretical propulsion system has been proposed, based on ]s ({{chem|He|2+}} or {{chem|4|2|He|2+}} indicating a helium ion with a +2 charge) emitted from a ] uni-directionally through a hole in its chamber. A neutralising electron gun would produce a tiny amount of thrust with high specific impulse in the order of millions of seconds due to the high relativistic speed of alpha particles.<ref>{{cite journal|title=Revisiting alpha decay-based near-light-speed particle propulsion|journal=Applied Radiation and Isotopes|volume=114|pages=14–18|doi=10.1016/j.apradiso.2016.04.005|year=2016 |last1=Zhang|first1=Wenwu|last2=Liu|first2=Zhen|last3=Yang|first3=Yang|last4=Du|first4=Shiyu|pmid=27161512|doi-access=free|bibcode=2016AppRI.114...14Z }}</ref>
{{refimprove section|date=April 2009}}


A variant of this uses a graphite-based grid with a static ] high voltage to increase thrust as ] has high transparency to ]s if it is also irradiated with short wave ] at the correct wavelength from a solid-state emitter. It also permits lower energy and longer half-life sources which would be advantageous for a space application. ] backfill has also been suggested as a way to increase electron mean free path.
{| class="wikitable"

|+Test data of some ion thrusters
== Comparisons ==
{| class="wikitable sortable"
|+ Test data of some ion thrusters
|-
! Thruster
! Propellant
! data-sort-type=number | Input <br/>power (kW)
! ] (s)
! Thrust <br/>(mN)
! Thruster <br/>mass (kg)
! Notes
|- |-
| ]
!Engine
| ]
!Propellant
| 2.3
!Required power<br>(kW)
| {{val|1700}}–{{val|3300}}<ref>{{cite web|url=http://eccentric.mae.cornell.edu/Boydgroup/jbala/IonPropulsion.html|title=Ion Propulsion|archive-url=https://web.archive.org/web/19990222082331/http://eccentric.mae.cornell.edu/Boydgroup/jbala/IonPropulsion.html|archive-date=1999-02-22}}</ref>
!]<br>(s)
| 92 max.<ref name=ns20070928/>
!Thrust<br>(mN)
| 8.33 <ref>{{cite journal |vauthors= Polk J, Kakuda R, Anderson J, Brophy J, Rawlin V, Patterson M, Sovey J, Hamley J |date= 2001-01-08|title= Performance of the NSTAR ion propulsion system on the Deep Space One mission.|journal= 39th Aerospace Sciences Meeting and Exhibit|pages= 965|doi= 10.2514/6.2001-965|url= https://trs.jpl.nasa.gov/bitstream/handle/2014/12165/01-0061.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://trs.jpl.nasa.gov/bitstream/handle/2014/12165/01-0061.pdf |archive-date=2022-10-09 |url-status=live|access-date=2021-09-16}}</ref>
!Thruster mass<br>(kg)
|Used on the '']'' and '']'' space probes.
|- |-
| ] Hall effect || Xenon || 1.5 || {{val|1660}} || 90 || 5.3
|]
|Xenon
|2.3
|3,300 to 1,700<ref>{{cite web|url=http://eccentric.mae.cornell.edu/Boydgroup/jbala/IonPropulsion.html|title=Ion Propulsion|publisher=}}</ref>
|92 max.<ref name=ns20070928/>
| |
|- |-
|]<ref name=ns20070928>{{cite news|last=Shiga|first=David|title=Next-generation ion engine sets new thrust record |url=http://www.newscientist.com/article/dn12709-nextgeneration-ion-engine-sets-new-thrust-record.html |accessdate=2011-02-02 |newspaper=NewScientist |date=2007-09-28}}</ref> | ]<ref name=ns20070928>{{cite news|last=Shiga|first=David|title=Next-generation ion engine sets new thrust record|url=https://www.newscientist.com/article/dn12709-nextgeneration-ion-engine-sets-new-thrust-record.html|access-date=2011-02-02|newspaper=NewScientist|date=2007-09-28}}</ref>
|Xenon | Xenon
|6.9<ref name='gizmag2013'>{{cite web| url=http://www.gizmag.com/next-ion-thruster-duration-record/28067/ |title= NASA's NEXT ion thruster runs five and a half years nonstop to set new record |first= David |last= Szondy |accessdate=June 26, 2013}}</ref> | 6.9<ref name='gizmag2013'>{{cite web|url=http://www.gizmag.com/next-ion-thruster-duration-record/28067/|title=NASA's NEXT ion thruster runs five and a half years nonstop to set new record|first=David |last=Szondy|access-date=June 26, 2013}}</ref>
|4,190<ref name='gizmag2013' /><ref name=IAC-08-C442>{{cite web |url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080047732_2008047267.pdf |title= The NASA Evolutionary Xenon Thruster (NEXT): the next step for US deep space propulsion |first1= George R. |last1= Schmidt| first2= Michael J. |last2= Patterson |first3= Scott W. |last3= Benson}}</ref><ref name='2010 Qualification'>{{citation |first = Daniel A. |last = Herman |contribution = NASA’s Evolutionary Xenon Thruster (NEXT) Project Qualifi cation Propellant Throughput Milestone: Performance, Erosion, and Thruster Service Life Prediction After 450 kg |title = 57th Joint Army-Navy-NASA-Air Force (JANNAF) Propulsion Meeting |publisher = NASA - Glenn Research Center |place = Colorado Springs, Colorado, USA |date = May 3–7, 2010| id = |contribution-url = http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110000521.pdf |accessdate = 2014-03-08}}</ref> | {{val|4190}}<ref name='gizmag2013'/><ref name=IAC-08-C442>{{cite web|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080047732_2008047267.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080047732_2008047267.pdf |archive-date=2022-10-09 |url-status=live|title=The NASA Evolutionary Xenon Thruster (NEXT): the next step for US deep space propulsion|first1=George R.|last1=Schmidt|first2=Michael J.|last2=Patterson|first3=Scott W.|last3=Benson}}</ref><ref name='2010 Qualification'>{{citation|first=Daniel A. |last=Herman|contribution=NASA's Evolutionary Xenon Thruster (NEXT) Project Qualifi cation Propellant Throughput Milestone: Performance, Erosion, and Thruster Service Life Prediction After 450 kg|title=57th Joint Army-Navy-NASA-Air Force (JANNAF) Propulsion Meeting|publisher=NASA - Glenn Research Center|place=Colorado Springs, Colorado, United States|date=3–7 May 2010|contribution-url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110000521.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110000521.pdf |archive-date=2022-10-09 |url-status=live|access-date=2014-03-08}} {{PD-notice}}</ref>
|<!-- 327 ? -->236 max<ref name=ns20070928/><ref name='2010 Qualification'/> |<!-- 327 ? -->236 max.<ref name=ns20070928/><ref name='2010 Qualification'/>
|<13.5 <ref>{{cite journal |vauthors= Shastry R, Soulas G, Aulisio M, Schmidt G|date=2017-09-25 |title= Status of NASA's NEXT-C Ion Propulsion System Development Project|url= https://core.ac.uk/download/pdf/154737946.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://core.ac.uk/download/pdf/154737946.pdf |archive-date=2022-10-09 |url-status=live|journal= 68th International Astronautical Congress |access-date=2021-09-16}}</ref>
| Used in ]
|-
| ]<ref name='popularmechanics2017'>{{cite web|url=https://www.popularmechanics.com/space/moon-mars/news/a28754/new-ion-thruster-breaks-records-power-thrust/|title='Mars Engine' Shatters Records for Ion Propulsion|first=Jay |last=Bennett|date=24 October 2017 |access-date=May 30, 2021}}</ref> Hall effect
| Xenon or ]<ref name='espressoinsight2020'>{{cite web|url=https://espressoinsight.com/2020/11/25/x3-ion-thruster/|title='Deep Space Travel: X3 Ion Thruster 2021 update|date=Nov 25, 2020|access-date=May 30, 2021}}</ref>
| 102<ref name='popularmechanics2017'/>
| 1800–2650<ref name='umich2017'>{{cite web|url=https://pepl.engin.umich.edu/project/x3-nested-channel-hall-thruster/|title=X3 – Nested Channel Hall Thruster|access-date=May 30, 2021}}</ref>
| {{val|5400}}<ref name='popularmechanics2017'/>
| {{val|230}}<ref name='umich2017'/><ref name='popularmechanics2017'/>
| |
|- |-
|NEXIS<ref>, 2006-02-10 (Polk, Jay E., Goebel, Don, Brophy, John R., Beatty, John, Monheiser, J., Giles, D.), Scientific Commons</ref> | NEXIS<ref> {{Webarchive |url=https://web.archive.org/web/20110522122351/http://en.scientificcommons.org/20787584|date=2011-05-22}} 2006-02-10 (Polk, Jay E., Goebel, Don, Brophy, John R., Beatty, John, Monheiser, J., Giles, D.) Scientific Commons</ref>
|Xenon | Xenon
|20.5 | 20.5
|
| |
| |
| |
|- |-
|RIT 22<ref>, EADS Astrium {{webarchive |url=https://web.archive.org/web/20090613015624/http://cs.astrium.eads.net/sp/SpacecraftPropulsion/Rita/RIT-22.html |date=June 13, 2009 }}</ref> | RIT 22<ref> EADS Astrium {{webarchive |url=https://web.archive.org/web/20090613015624/http://cs.astrium.eads.net/sp/SpacecraftPropulsion/Rita/RIT-22.html|date=June 13, 2009}}</ref>
|Xenon | Xenon
|5 | 5
|
| |
| |
| |
|- |-
|BHT8000 <ref></ref> | ]<ref>{{cite web|url=http://www.busek.com/index_htm_files/70000703%20BHT-8000%20Data%20Sheet%20Rev-.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.busek.com/index_htm_files/70000703%20BHT-8000%20Data%20Sheet%20Rev-.pdf |archive-date=2022-10-09 |url-status=live|title=BHT-8000 Busek Hall Effect Thruster}}</ref>
|Xenon | Xenon
|8 | 8
|2210 | {{val|2210}}
|449 | 449
|25 | 25
|
|- |-
|Hall effect | Hall effect
|Xenon | Xenon
|75{{citation needed|date=August 2012}} | 75{{citation needed|date=August 2012}}
| |
| |
| |
|
|-
| FEEP
| ]
| data-sort-value=0.0006 | 6×10<sup>−5</sup>–0.06
| {{val|6000}}–{{val|10000}}<ref name="JPP98"/>
| 0.001–1<ref name="JPP98"/>
|
|
|-
| ]
| ]
| data-sort-value=0.055 | 0.034–0.066 <ref name=NPT30>{{cite journal| title = ''In-orbit demonstration of an iodine electric propulsion system''| year = 2021| doi = 10.1038/s41586-021-04015-y| last1 = Rafalskyi| first1 = Dmytro| last2 = Martínez| first2 = Javier Martínez| last3 = Habl| first3 = Lui| last4 = Zorzoli Rossi| first4 = Elena| last5 = Proynov| first5 = Plamen| last6 = Boré| first6 = Antoine| last7 = Baret| first7 = Thomas| last8 = Poyet| first8 = Antoine| last9 = Lafleur| first9 = Trevor| last10 = Dudin| first10 = Stanislav| last11 = Aanesland| first11 = Ane| journal = Nature| volume = 599| issue = 7885| pages = 411–415| pmid = 34789903| pmc = 8599014| bibcode = 2021Natur.599..411R}}</ref>
| {{val|1000}}–{{val|2500}}<ref name=NPT30/>
| 0.5–1.5<ref name=NPT30/>
| 1.2 <!-- mass kg -->
|
|-
|] Hall effect<ref name=":0">{{Cite web |date=February 26, 2023 |title=SpaceX on X: "Among other enhancements, V2 minis are equipped with new argon Hall thrusters for on orbit maneuvering Developed by SpaceX engineers, they have 2.4x the thrust and 1.5x the specific impulse of our first gen thrusters. This will also be the first time ever that argon Hall thrusters are operated in space Argon Hall thruster tech specs: - 170 mN thrust - 2500 s specific impulse - 50% total efficiency - 4.2 kW power - 2.1 kg mass - Center mounted cathode" |url=https://x.com/SpaceX/status/1629948869239873538?s=20 |url-status=live |archive-url=https://web.archive.org/web/20230301003229/https://twitter.com/SpaceX/status/1629948869239873538 |archive-date=March 1, 2023 |website=]}}</ref>
|]<ref name=":0" />
|
|~1667
|~70.83
|
|
|-
|] Hall effect<ref name=":0" />
|]<ref name=":0" />
|4.2<ref name=":0" />
|2500<ref name=":0" />
|170<ref name=":0" />
|2.1<ref name=":0" />
|Used in ] satellites.
|-
| ]<ref name=AEPS>{{Cite journal|last=|first=|date= |title=Status of Advanced Electric Propulsion Systems for Exploration Missions |url=https://www.researchgate.net/publication/328997773|journal=Aerojet Rocketdyne |volume=|pages=|via=ResearchGate}}</ref>
| Xenon
| 13.3
| 2900
| 600
| 25
| To be used in ] ]
|- |-
| ] T6
|FEEP
| Xenon
|Liquid Caesium
| 4,6
|6×10<sup>−5</sup>–0.06
| 4300
|6,000–10,000<ref name="JPP98" />
| 145
|0.001–1<ref name="JPP98" />
| |
| Used in European-Japanese ].<ref> {{Webarchive |url=https://web.archive.org/web/20160812075030/http://erps.spacegrant.org/uploads/images/2015Presentations/IEPC-2015-132_ISTS-2015-b-132.pdf|date=12 August 2016}} R. A. Lewis, J. Pérez Luna, N. Coombs. 30th International Symposium on Space Technology and Science 34th International Electric Propulsion Conference and 6th Nano-satellite Symposium, Hyogo-Kobe, Japan, 4–10 July 2015</ref><ref> {{Webarchive|url=https://web.archive.org/web/20171215162142/http://erps.spacegrant.org/uploads/images/2015Presentations/IEPC-2015-131_ISTS-2015-b-131.pdf |date=15 December 2017 }} Mark Hutchins, Huw Simpson. 30th International Symposium on Space Technology and Science 34th International Electric Propulsion Conference and 6th Nano-satellite Symposium, Hyogo-Kobe, Japan, 4–10 July 2015</ref>
|} |}


{| class="wikitable" {| class="wikitable sortable"
|+Experimental thrusters (no mission to date) |+ Experimental thrusters (no mission to date)
|- |-
! Thruster
!Engine
!Propellant ! Propellant
! data-sort-type=number | Input <br/>power (kW)
!Required power<br>(kW)
!]<br>(s) ! ] (s)
!Thrust<br>(mN) ! Thrust <br/>(mN)
!Thruster mass<br>(kg) ! Thruster <br/>mass (kg)
! Notes
|- |-
|Hall effect | Hall effect
|Bismuth | ]
|1,9<ref name=Bi-Szabo>Szabo, J., Robin, M., Paintal, Pote, B., S., Hruby, V., "High Density Hall Thruster Propellant Investigations," 48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, AIAA Paper 2012-3853, July 2012.</ref> | 1.9<ref name=Bi-Szabo>Szabo, J., Robin, M., Paintal, Pote, B., S., Hruby, V., "High Density Hall Thruster Propellant Investigations", 48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, AIAA Paper 2012-3853, July 2012.</ref>
|1&nbsp;520 (anode)<ref name=Bi-Szabo/> | {{val|1520}} (anode)<ref name=Bi-Szabo/>
|143 (discharge) <ref name=Bi-Szabo/> | 143 (discharge)<ref name=Bi-Szabo/>
|
| |
|- |-
|Hall effect | Hall effect
|Bismuth | Bismuth
|25{{citation needed|date=August 2012}} | 25{{citation needed|date=August 2012}}
|
| |
| |
| |
|- |-
|Hall effect | Hall effect
|Bismuth | Bismuth
|140{{citation needed|date=August 2012}} | 140{{citation needed|date=August 2012}}
|
| |
| |
| |
|- |-
|Hall effect | Hall effect
|Iodine | ]
| 0.2<ref name=I2-Szabo>{{cite journal |last1=Szabo|first1=J. |last2=Pote|first2=B. |last3=Paintal|first3=S. |last4=Robin|first4=M. |last5=Hillier|first5=A. |last6=Branam|first6=R. |last7=Huffman|first7=R. |title=Performance Evaluation of an Iodine Vapor Hall Thruster
|0,2 <ref name=I2-Szabo>{{cite web
|journal=Journal of Propulsion and Power|volume=28|issue=4|pages=848–857|doi=10.2514/1.B34291|year=2012}}</ref>
|last=Szabo, J., Pote, B., Paintal, S., Robin, M., Hillier, A., Branam, R., Huffman, R.
| {{val|1510}} (anode)<ref name=I2-Szabo/>
|title= Performance Evaluation of an Iodine Vapor Hall Thruster
| 12.1 (discharge)<ref name=I2-Szabo/>
|url=http://arc.aiaa.org/doi/abs/10.2514/1.B34291
|
|publisher=Journal of Propulsion and Power, 28, 4, 2012.
}}</ref>
|1&nbsp;510 (anode)<ref name=I2-Szabo/>
|12,1 (discharge) <ref name=I2-Szabo/>
| |
|- |-
|Hall effect | Hall effect
|Iodine | Iodine
| 7<ref name="I2_hp-Szabo">{{cite journal |last1=Szabo |first1=J. |last2=Robin |first2=M. |last3=Paintal |first3=S. |last4=Pote |first4=B. |last5=Hruby |first5=V. |last6=Freeman |first6=C. |year=2015 |title=Iodine Plasma Propulsion Test Results at 1–10 kW |journal=IEEE Transactions on Plasma Science |volume=43 |issue=1 |pages=141–148 |bibcode=2015ITPS...43..141S |doi=10.1109/TPS.2014.2367417 |s2cid=42482511}}</ref>
|7 <ref name=I2_hp-Szabo>{{cite web
| {{val|1950}}<ref name=I2_hp-Szabo/>
|last=Szabo, J., Robin, M., Paintal, S., Pote, B., Hruby, V., Freeman, C.,
| 413<ref name=I2_hp-Szabo/>
|title= Iodine Plasma Propulsion Test Results at 1-10 kW
|
|url=http://arc.aiaa.org/doi/abs/10.1109/TPS.2014.2367417
|publisher=IEEE Transactions on Plasma Science, Special Issue – Plasma Propulsion, Vol. 43, No. 1, 2015.
}}</ref>
|1&nbsp;950 <ref name=I2_hp-Szabo/>
|413 <ref name=I2_hp-Szabo/>
| |
|- |-
|] | ]
|Xenon | Xenon
|20–50<ref name=hipepinfo/> | 20–50<ref name=hipepinfo/>
| {{val|6000}}–{{val|9000}}<ref name=hipepinfo>{{cite web|title=High Power Electric Propulsion Program (HiPEP)|url=http://www.grc.nasa.gov/WWW/ion/present/hipep.htm|archive-url=https://web.archive.org/web/20090305101503/http://www.grc.nasa.gov/WWW/ion/present/hipep.htm|archive-date=2009-03-05|publisher=]|url-status=dead|date=2008-12-22}} {{PD-notice}}</ref>
|6&nbsp;000–9&nbsp;000<ref name=hipepinfo>{{cite web|title=HIGH POWER ELECTRIC PROPULSION PROGRAM (HiPEP)
| 460–670<ref name=hipepinfo/>
|url=http://www.grc.nasa.gov/WWW/ion/present/hipep.htm |publisher=NASA |date=2008-12-22}}</ref>
|
|460–670<ref name=hipepinfo />
| |
|- |-
|] | ]
|Hydrogen | ]
| {{val|1500}}<ref name="MPDT">{{cite web|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880020476.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880020476.pdf |archive-date=2022-10-09 |url-status=live|title=Performance and Lifetime Assessment of MPD Arc Thruster Technology|access-date=2019-05-09|author=James S. Sovey and Maris A. Mantenieks|date=January 1988 |page=11}} {{PD-notice}}</ref>
|1&nbsp;500
| {{val|4900}}<ref name="MPDT"/>
|4&nbsp;900{{citation needed|date=August 2012}}
|26&nbsp;300{{citation needed|date=August 2012}} | {{val|26300}}{{citation needed|date=August 2012}}
|
| |
|- |-
|] | ]
|Hydrogen | Hydrogen
| {{val|3750}}<ref name="MPDT"/>
|3&nbsp;750
| {{val|3500}}<ref name="MPDT"/>
|3&nbsp;500{{citation needed|date=August 2012}}
|88&nbsp;500{{citation needed|date=August 2012}} | {{val|88500}}{{citation needed|date=August 2012}}
|
| |
|- |-
|] | ]
|Hydrogen | Hydrogen
|7&nbsp;500{{citation needed|date=August 2012}} | {{val|7500}}{{citation needed|date=August 2012}}
|6&nbsp;000{{citation needed|date=August 2012}} | {{val|6000}}{{citation needed|date=August 2012}}
|60&nbsp;000{{citation needed|date=August 2012}} | {{val|60000}}{{citation needed|date=August 2012}}
|
| |
|- |-
|LiLFA | LiLFA
|Lithium Vapor | Lithium vapor
|500 | 500
|4&nbsp;077{{citation needed|date=August 2012}} | {{val|4077}}{{citation needed|date=August 2012}}
|12&nbsp;000{{citation needed|date=August 2012}} | {{val|12000}}{{citation needed|date=August 2012}}
|
| |
|- |-
|FEEP | FEEP
|Liquid Caesium | Liquid caesium
|6×10<sup>−5</sup>–0.06 | data-sort-value=0.0006 | 6×10<sup>−5</sup>–0.06
|6&nbsp;000–10&nbsp;000<ref name="JPP98" /> | {{val|6000}}–{{val|10000}}<ref name="JPP98"/>
|0,001–1<ref name="JPP98" /> | 0.001–1<ref name="JPP98"/>
|
| |
|- |-
|] | ]
|Argon | ]
|200 | 200
|3&nbsp;000–12&nbsp;000<!-- the fiso20110119 source shows 5000 to be about the optimum Isp, but has no data on the min/max Isp. --> | {{val|3000}}–{{val|12000}}<!-- the fiso20110119 source shows 5000 to be about the optimum Isp, but has no data on the min/max Isp. -->
| ] {{val|5000}}<ref name=fiso20110119> {{Webarchive|url=https://web.archive.org/web/20110311141639/http://spirit.as.utexas.edu/%7Efiso/telecon/Glover_1-19-11/Glover_1-19-11.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://spirit.as.utexas.edu/%7Efiso/telecon/Glover_1-19-11/Glover_1-19-11.pdf |archive-date=2022-10-09 |url-status=live|date=2011-03-11}}, Tim Glover, Future in Space Operations (FISO) Colloquium, 2011-01-19, accessed 2011-01-31.</ref>
|~5&nbsp;000<ref name=fiso20110119>
| 620<ref>{{cite web|url=http://www.adastrarocket.com/IEPC13-149_JPSquire_submit.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.adastrarocket.com/IEPC13-149_JPSquire_submit.pdf |archive-date=2022-10-09 |url-status=live|title=VASIMR® Spaceflight Engine System Mass Study and Scaling with Power IEPC-2013-149}}</ref>
, Tim Glover, Future in Space Operations (FISO) Colloquium, 2011-01-19, accessed 2011-01-31.</ref>
|
|620<ref></ref>
|- |-
|CAT<ref name="CAT_thruster_Space">{{cite news |last1=Mike Wall |title=New Space Engine Could Turn Tiny CubeSats into Interplanetary Explorers |url=http://www.space.com/21867-cubesat-deep-space-propulsion-kickstarter.html |accessdate=June 25, 2015 |work=Space.com |publisher=Purch |date=July 8, 2013 }}</ref> | CAT<ref name="CAT_thruster_Space">{{cite news|last1=Mike Wall|title=New Space Engine Could Turn Tiny CubeSats into Interplanetary Explorers|url=http://www.space.com/21867-cubesat-deep-space-propulsion-kickstarter.html|access-date=June 25, 2015|website=]|publisher=]|date=July 8, 2013}}</ref>
|Xenon, Iodine, water<ref name="CAT_thruster_PEPL">{{cite web |title=PEPL Thrusters: CubeSat Ambipolar Thruster |url=http://pepl.engin.umich.edu/thrusters/CAT.html |website=pepl.engin.umich.edu |publisher=University of Michigan |accessdate=June 25, 2015 }}</ref> | Xenon, iodine, water<ref name="CAT_thruster_PEPL">{{cite web|title=PEPL Thrusters: CubeSat Ambipolar Thruster|url=http://pepl.engin.umich.edu/thrusters/CAT.html|website=pepl.engin.umich.edu|publisher=University of Michigan|access-date=June 25, 2015|archive-date=12 May 2015|archive-url=https://web.archive.org/web/20150512105036/http://pepl.engin.umich.edu/thrusters/CAT.html|url-status=dead}}</ref>
|0,01 | 0.01
|690<ref name="MARS-CAT">{{cite web |title=MARS-CAT Mission Implementation |url=http://www.marscat.space/science/implementation |website=www.marscat.space |publisher=University of Houston College of Natural Sciences and Mathematics |accessdate=June 25, 2015 }}</ref> | 690<ref name="MARS-CAT">{{cite web|title=MARS-CAT Mission Implementation|url=http://www.marscat.space/science/implementation|archive-url=https://web.archive.org/web/20150626112412/http://www.marscat.space/science/implementation|url-status=dead|archive-date=26 June 2015|website=marscat.space|publisher=University of Houston College of Natural Sciences and Mathematics|access-date=June 25, 2015}}</ref><ref name="P4_RF_Thruster">{{cite web|title=Phase Four: Game-Changing Spacecraft propulsion|url=http://www.phasefour.io|website=phasefour.io|access-date=June 5, 2017}}</ref>
| 1.1–2 (73&nbsp;mN/kW)<ref name="CAT_thruster_PEPL"/>
|1,1-2
|<1 (73&nbsp;mN/kW)<ref name="CAT_thruster_PEPL"/> | <1<ref name="CAT_thruster_PEPL"/>
|
|- |-
|] | ]
|Xenon | Xenon
|250 | 250
| {{val|19300}}
|19&nbsp;300
|2&nbsp;500 max. | {{val|2500}} max.
|5 | 5
|
|- |-
|] | ]
|Krypton | ]
| 0.5<ref name=ifpilm>{{cite web |url=http://www.ifpilm.pl/ifpilm.pl/en/achievements/87-krypton-hall-effect-thruster-for-space-propulsion |title=Krypton Hall effect thruster for space propulsion |archive-url=https://archive.today/20140129162249/http://www.ifpilm.pl/ifpilm.pl/en/achievements/87-krypton-hall-effect-thruster-for-space-propulsion |archive-date=2014-01-29 |work=IFPiLM.pl |access-date=2014-01-29}}</ref>
|0,5<ref name=ifpilm>
, IFPiLM, accessed 2014-01-29.</ref>
| |
| |
|4<ref name=ifpilm /> | 4<ref name=ifpilm/>
|
|-
| ID-500
| Xenon<ref>{{Cite web|date=29 January 2020|title=Transport and Energy Module: Russia's new NEP Tug|url=https://beyondnerva.com/2020/01/29/transport-and-energy-module/|website=Beyond NERVA|access-date=16 November 2020|archive-date=27 November 2020|archive-url=https://web.archive.org/web/20201127160913/http://beyondnerva.com/2020/01/29/transport-and-energy-module/|url-status=dead}}</ref>
| 32–35
| 7140
| 375–750<ref>{{Cite web|last=Teslenko|first=Vladimir|date=31 August 2015|title=Space nuclear propulsion systems are now possible only in Russia (In Russian)|url=https://www.kommersant.ru/doc/2810188|website=Kommersant}}</ref>
|34.8
| To be used in ]
|} |}


==Lifetime== == Lifetime ==
Ion thrusters' low thrust requires continuous thrust for a long time to achieve the necessary change in velocity (]) for a particular mission. Ion thrusters are designed to provide continuous operation for intervals of weeks to years. Ion thrusters' low thrust requires continuous operation for a long time to achieve the necessary change in velocity (]) for a particular mission. Ion thrusters are designed to provide continuous operation for intervals of weeks to years.


The lifetime of electrostatic ion thrusters is limited by several processes.
The lifetime of electrostatic ion thrusters is limited by several processes. In electrostatic gridded designs, charge-exchange ions produced by the beam ions with the neutral gas flow can be accelerated towards the negatively biased accelerator grid and cause grid erosion. End-of-life is reached when either the grid structure fails or the holes in the grid become large enough that ion extraction is substantially affected; e.g., by the occurrence of electron backstreaming. Grid erosion cannot be avoided and is the major lifetime-limiting factor. Thorough grid design and material selection enable lifetimes of 20&nbsp;000 hours or more.


=== Gridded thruster life===
A test of the ] (NSTAR) electrostatic ion thruster resulted in 30&nbsp;472 hours (roughly 3,5 years) of continuous thrust at maximum power. Post-test examination indicated the engine was not approaching failure.<ref>{{cite web |url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/39521/1/05-2793.pdf|title=Destructive Physical Analysis of Hollow Cathodes from the Deep Space 1 Flight Spare Ion Engine 30,000 Hr Life Test|accessdate=2007-11-21}}</ref>
In electrostatic gridded designs, charge-exchange ions produced by the beam ions with the neutral gas flow can be accelerated towards the negatively biased accelerator grid and cause grid erosion. End-of-life is reached when either the grid structure fails or the holes in the grid become large enough that ion extraction is substantially affected – e.g., by the occurrence of electron backstreaming. Grid erosion cannot be avoided and is the major lifetime-limiting factor. Thorough grid design and material selection enable lifetimes of 20,000 hours or more.


A test of the ] (NSTAR) electrostatic ion thruster resulted in 30,472 hours (roughly 3.5 years) of continuous thrust at maximum power. Post-test examination indicated the engine was not approaching failure.<ref>{{cite web|url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/39521/1/05-2793.pdf|title=Destructive Physical Analysis of Hollow Cathodes from the Deep Space 1 Flight Spare Ion Engine 30,000 Hour Life Test|access-date=2007-11-21|url-status=dead|archive-url=https://web.archive.org/web/20090227050954/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/39521/1/05-2793.pdf|archive-date=2009-02-27}} {{PD-notice}}</ref><ref name=autogenerated1/><ref name="Choueiri"/> NSTAR operated for years on ''Dawn''.
The NASA Evolutionary Xenon Thruster (NEXT) Project operated continuously for more than 48 000 hours.<ref>{{cite web |url=http://spacefellowship.com/news/art34276/nasa-thruster-achieves-world-record-5-years-of-operation.html|title=NASA Thruster Achieves World-Record 5+ Years of Operation|accessdate=2012-06-27}}</ref> The test was conducted in a high vacuum test chamber. Over the course of the 5 1/2 + year test, the engine consumed approximately 870 kilograms of xenon propellant. The total impulse generated would require over 10,000 kilograms of conventional rocket propellant for a similar application.


The ] (NEXT) project operated continuously for more than 48,000 hours.<ref>{{cite web |title=NASA Thruster Achieves World – Record 5+ Years of Operation |url=http://spacefellowship.com/news/art34276/nasa-thruster-achieves-world-record-5-years-of-operation.html |access-date=2012-06-27}}</ref> The test was conducted in a high-vacuum test chamber. Over the course of the test, which lasted more than five and a half years, the engine consumed approximately 870 kilograms of xenon propellant. The total impulse generated would require over 10,000 kilograms of conventional rocket propellant for a similar application.
Hall thrusters suffer from strong erosion of the ceramic discharge chamber by impact of energetic ions: a test reported in 2010<ref name="leipzig">{{cite web |url=http://www.uni-leipzig.de/~iom/muehlleithen/2010/Bundesmann_2010.pdf |title=A closer look at a stationary plasma thruster}}</ref> showed erosion of around 1&nbsp;mm per hundred hours of operation, though this is inconsistent with observed on-orbit lifetimes of a few thousand hours.


===Hall-effect thruster life===
NASA's ]'s ion drives have provided continuous operation of more than 3 years.<ref name=autogenerated1 /><ref name="Choueiri"/>
Hall-effect thrusters suffer from strong erosion of the ceramic discharge chamber by impact of energetic ions: a test reported in 2010 <ref name="leipzig">{{cite web|url=http://www.uni-leipzig.de/~iom/muehlleithen/2010/Bundesmann_2010.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.uni-leipzig.de/~iom/muehlleithen/2010/Bundesmann_2010.pdf |archive-date=2022-10-09 |url-status=live|title=A closer look at a stationary plasma thruster}}</ref> showed erosion of around 1&nbsp;mm per hundred hours of operation, though this is inconsistent with observed on-orbit lifetimes of a few thousand hours.


The ] (AEPS) is expected to accumulate about 5,000 hours and the design aims to achieve a flight model that offers a half-life of at least 23,000 hours<ref name='AEPS 2017'/> and a full life of about 50,000 hours.<ref name="Rocketdyne 2016"> Aerojet Rocketdyne Press release, 28 April 2016 Accessed: 27 July 2018.</ref>
==Propellants==
] energy represents a large percentage of the energy needed to run ion drives. The ideal propellant is thus easy to ionize and has a high mass/ionization energy ratio. In addition, the propellant should not erode the thruster to any great degree to permit long life; and should not contaminate the vehicle.<ref>Rocket Propulsion Elements&nbsp;— Sutton & Biblarz 7th edition</ref>


== Propellants ==
Many current designs use ] gas, as it is easy to ionize, has a reasonably high atomic number, is inert and causes low erosion. However, xenon is globally in short supply and expensive.
] represents a large percentage of the energy needed to run ion drives. The ideal propellant is thus easy to ionize and has a high mass/ionization energy ratio. In addition, the propellant should not erode the thruster to any great degree, so as to permit long life, and should not contaminate the vehicle.<ref>Sutton & Biblarz, ''Rocket Propulsion Elements'', 7th edition.</ref>


Many current designs use ] gas, as it is easy to ionize, has a reasonably high atomic number, is inert and causes low erosion. However, xenon is globally in short supply and expensive (approximately $3,000 per kg in 2021).<ref name=Iodine-1>{{cite web| url = https://cosmosmagazine.com/space/exploration/iodine-powered-spacecraft-tested-in-orbit/| title = ''Iodine-powered spacecraft tested in orbit for the first time'' Nov 2021| date = 18 November 2021}}</ref>
Older designs used ], but this is toxic and expensive, tended to contaminate the vehicle with the metal and was difficult to feed accurately.


Some older ion thruster designs used ] propellant. However, mercury is toxic, tended to contaminate spacecraft, and was difficult to feed accurately. A modern commercial prototype may be using mercury successfully<ref>{{cite news|last1=Elgin|first1=Ben|title=This Silicon Valley Space Startup Could Lace the Atmosphere With Mercury|url=https://www.bloomberg.com/news/articles/2018-11-19/this-space-startup-could-lace-the-atmosphere-with-toxic-mercury|access-date=19 November 2018|publisher=Bloomberg News|date=19 November 2018}}</ref> however, mercury was formally banned as a propellant in 2022 by the ].<ref>{{cite news |last1=Koziol |first1=Michael |title=U.N. Kills Any Plans to Use Mercury as a Rocket Propellant |url=https://spectrum.ieee.org/mercury-ion-thruster-banned |access-date=2 May 2022 |work=] |date=19 April 2022 |language=en}}</ref>
Other propellants, such as ] and ], show promise, particularly for gridless designs, such as Hall effect thrusters.<ref name=Bi-Szabo/><ref name=I2-Szabo/><ref name=I2_hp-Szabo/>

From 2018–2023, ] was used to fuel the Hall-effect thrusters aboard ] internet satellites, in part due to its lower cost than conventional ] propellant.<ref name=TC-starlink>{{cite web |url=https://techcrunch.com/2019/05/24/spacex-reveals-more-starlink-info-after-launch-of-first-60-satellites/|title=SpaceX reveals more Starlink info after launch of first 60 satellites|date=24 May 2019 |access-date=25 May 2019}}</ref> Starlink V2-mini satellites have since switched to ] Hall-effect thrusters, providing higher specific impulse.<ref>{{Cite tweet |title=Among other enhancements, V2 minis are equipped with new argon Hall thrusters for on orbit maneuvering|number=1629898794874687489|user=SpaceX |access-date=2023-02-26 |website=Twitter |language=en}}</ref>

Other propellants, such as ] and ], show promise both for gridless designs such as Hall-effect thrusters,<ref name=Bi-Szabo/><ref name=I2-Szabo/><ref name=I2_hp-Szabo/> and gridded ion thrusters.<ref>{{Cite journal |last1=Grondein|first1=P. |last2=Lafleur|first2=T. |last3=Chabert|first3=P. |last4=Aanesland|first4=A. |date=March 2016|title=Global model of an iodine gridded plasma thruster |url=http://aip.scitation.org/doi/10.1063/1.4944882|journal=Physics of Plasmas |language=en |volume=23|issue=3|pages=033514 |doi=10.1063/1.4944882|bibcode=2016PhPl...23c3514G |issn=1070-664X}}</ref>

] was used as a propellant for the first time in space, in the ] ] by ], on board the Beihangkongshi-1 mission launched in November 2020,<ref>{{Cite news|title=Spacety launches satellite to test ThrustMe iodine electric propulsion and constellation technologies|work=SpaceNews|url=https://spacenews.com/thrustme-2020-demonstration/}}</ref><ref>{{Cite news |title=Iodine thruster could slow space junk accumulation |url=http://www.esa.int/Applications/Telecommunications_Integrated_Applications/Iodine_thruster_could_slow_space_junk_accumulation |work=European Space Agency}}</ref><ref>{{Cite web|title=Beihangkongshi 1 (TY 20)|url=https://space.skyrocket.de/doc_sdat/beihangkongshi-1.htm|website=Gunter's Space Page}}</ref> with an extensive report published a year later in the journal '']''.<ref name=Nature1 >{{cite journal |last1=Rafalskyi |first1=Dmytro |last2=Martínez Martínez |first2=Javier |last3=Habl |first3=Lui |last4=Zorzoli Rossi |first4=Elena |last5=Proynov |first5=Plamen |last6=Boré |first6=Antoine |last7=Baret |first7=Thomas |last8=Poyet |first8=Antoine |last9=Lafleur |first9=Trevor |last10=Dudin |first10=Stanislav |last11=Aanesland |first11=Ane |date=17 November 2021 |title=In-orbit demonstration of an iodine electric propulsion system |journal=Nature |volume=599 |pages=411–415 | issue=7885|doi=10.1038/s41586-021-04015-y|pmid=34789903 |pmc=8599014 |bibcode=2021Natur.599..411R |s2cid=244347528 |issn=0028-0836 |quote=''Both atomic and molecular iodine ions are accelerated by high-voltage grids to generate thrust, and a highly collimated beam can be produced with substantial iodine dissociation.''}}</ref> The CubeSat Ambipolar Thruster (CAT) used on the Mars Array of Ionospheric Research Satellites Using the CubeSat Ambipolar Thruster (MARS-CAT) mission also proposes to use solid iodine as the propellant to minimize storage volume.<ref name="MARS-CAT"/><ref name="P4_RF_Thruster"/>


] design (and other plasma-based engines) are theoretically able to use practically any material for propellant. However, in current tests the most practical propellant is ], which is relatively abundant and inexpensive. ] design (and other plasma-based engines) are theoretically able to use practically any material for propellant. However, in current tests the most practical propellant is ], which is relatively abundant and inexpensive.


== Energy efficiency ==
The CubeSat Ambipolar Thruster (CAT) used on the Mars Array of Ionospheric Research Satellites Using the CubeSat Ambipolar Thruster (MARS-CAT) mission proposes to use solid ] as the propellant to minimize storage volume.<ref name="MARS-CAT"/>
]


==Energy efficiency==
]
Ion thruster efficiency is the kinetic energy of the exhaust jet emitted per second divided by the electrical power into the device. Ion thruster efficiency is the kinetic energy of the exhaust jet emitted per second divided by the electrical power into the device.


Overall system energy efficiency is determined by the ], which depends on vehicle speed and exhaust speed. Some thrusters can vary exhaust speed in operation, but all can be designed with different exhaust speeds. At the lower end of I<sub>sps</sub> the overall efficiency drops, because ionization takes up a larger percentage energy and at the high end propulsive efficiency is reduced. Overall system ] is determined by the ], which depends on vehicle speed and exhaust speed. Some thrusters can vary exhaust speed in operation, but all can be designed with different exhaust speeds. At the lower end of specific impulse, ''I''<sub>sp</sub>, the overall efficiency drops because ionization takes up a larger percentage energy and at the high end propulsive efficiency is reduced.


Optimal efficiencies and exhaust velocities for any given mission can be calculated to give minimum overall cost. Optimal efficiencies and exhaust velocities for any given mission can be calculated to give minimum overall cost.


==Missions== == Missions ==
Ion thrusters have many in-space propulsion applications. The best applications make use of the long mission interval when significant ] is not needed. Examples of this include orbit transfers, ] adjustments, ] compensation for ]s, fine adjustments for scientific missions and cargo transport between ]s, e.g., for chemical fuels. Ion thrusters can also be used for interplanetary and deep-space missions where acceleration rates are not crucial. Continuous thrust over a long interval can reach high velocities while consuming far less fuel than traditional chemical rockets. Ion thrusters have many in-space propulsion applications. The best applications make use of the long mission interval when significant ] is not needed. Examples of this include orbit transfers, ] adjustments, ] compensation for ]s, fine adjustments for scientific missions and cargo transport between ]s, e.g., for chemical fuels. Ion thrusters can also be used for interplanetary and deep-space missions where acceleration rates are not crucial. Ion thrusters are seen as the best solution for these missions, as they require high change in velocity but do not require rapid acceleration. Continuous thrust over long durations can reach high velocities while consuming far less propellant than traditional chemical rockets.

Among electric thrusters, ion thrusters have received the most serious commercial and academic consideration. Ion thrusters are seen as the best solution for these missions, as they require high change in velocity but do not require rapid acceleration.


===Demonstration vehicles=== === Demonstration vehicles ===
==== SERT ====
Ion propulsion systems were first demonstrated in space by the ] (now Glenn Research Center) missions ] and SERT-2A.<ref name="Sovey" /> A ] suborbital flight was launched on 20 July 1964, and successfully proved that the technology operated as predicted in space. These were ]s using ] and ] as the reaction mass. SERT-2A, launched on 4 February 1970,<ref name="sert2"/><ref> {{webarchive|url=https://web.archive.org/web/20101025005136/http://www.astronautix.com/craft/sert.htm|date=2010-10-25}} at Astronautix (Accessed July 1, 2010).</ref> verified the operation of two mercury ion engines for thousands of running hours.<ref name="sert2"/>


====SERT==== === Operational missions ===
Ion thrusters are routinely used for station-keeping on commercial and military communication satellites in geosynchronous orbit. The Soviet Union pioneered this field, using ] (SPTs) on satellites starting in the early 1970s.
Ion propulsion systems were first demonstrated in space by the ] (now Glenn Research Center) missions "] I and II.<ref name="Sovey">{{cite journal| first1= J. S. |last1= Sovey |first2= V. K. |last2= Rawlin |first3= M. J. |last3= Patterson |title= Ion Propulsion Development Projects in U. S.: Space Electric Rocket Test 1 to Deep Space 1 |journal= Journal of Propulsion and Power| volume= 17 |number= 3 |date=May–June 2001 |pages= 517–526 |doi=10.2514/2.5806}}</ref> ]<nowiki/> was launched July 20, 1964, and successfully proved that the technology operated as predicted in space. These were ]s using mercury and cesium as the reaction mass. SERT-II, launched on February 3, 1970,<ref>, NASA Glenn Research Center. Accessed July 1, 2010.</ref><ref> at Astronautix (Accessed July 1, 2010)</ref> verified the operation of two mercury ion engines for thousands of running hours.<ref> at NASA.gov</ref>


Two geostationary satellites (ESA's ] in 2001–2003<ref>{{cite web|url=http://www.esa.int/esaTE/SEM1LT0P4HD_index_0.html|title=Artemis team receives award for space rescue |access-date=2006-11-16|publisher=ESA}}</ref> and the United States military's ] in 2010–2012<ref>{{cite web|url=http://www.airforce-magazine.com/MagazineArchive/Pages/2012/January%202012/0112space.aspx|title=Rescue in Space}}</ref>) used the ion thruster to change orbit after the chemical-propellant engine failed. ]<ref>{{cite web |url=http://spaceflightnow.com/news/n1203/19boeing702sp/|title=Electric propulsion could launch new commercial trend|publisher=Spaceflight Now}}</ref> began using ion thrusters for station-keeping in 1997 and planned in 2013–2014 to offer a variant on their 702 platform, with no chemical engine and ion thrusters for orbit raising; this permits a significantly lower launch mass for a given satellite capability. ] used a chemical engine to raise perigee to {{cvt|16330|km}} and proceeded to ] using electric propulsion.<ref name=aehf2-sfn>{{cite web |url=https://spaceflightnow.com/atlas/av031/lae/|title=Spaceflight Now &#124; Atlas Launch Report &#124; AEHF 2 communications satellite keeps on climbing|website=spaceflightnow.com}}</ref>
===Operational missions===
Ion thrusters are routinely used for station-keeping on commercial and military communication satellites in geosynchronous orbit. The Soviet Union pioneered this field, using ] thrusters on satellites starting in the early 1970s.


==== In Earth orbit ====
Two geostationary satellites (ESA's ] in 2001–03<ref>{{cite web |url=http://www.esa.int/esaTE/SEM1LT0P4HD_index_0.html |title=Artemis team receives award for space rescue |accessdate=2006-11-16 |author=ESA |authorlink=European Space Agency}}</ref> and the US military's ] in 2010–12<ref>{{cite web |url=http://www.airforce-magazine.com/MagazineArchive/Pages/2012/January%202012/0112space.aspx |title=Rescue in Space}}</ref>) used the ion thruster to change orbit after the chemical-propellant engine failed. Boeing<ref>{{cite web |url=http://spaceflightnow.com/news/n1203/19boeing702sp/ |title=Electric propulsion could launch new commercial trend |author=Spaceflight Now}}</ref> began using ion thrusters for station-keeping in 1997 and planned in 2013–14 to offer a variant on their 702 platform, with no chemical engine and ion thrusters for orbit raising; this permits a significantly lower launch mass for a given satellite capability. ] used a chemical engine to raise perigee to 10,150 miles and proceeded to ] using electric propulsion.<ref name=aehf2-sfn>{{cite web |url=http://www.spaceflightnow.com/atlas/av031/lae/ |title=AEHF 2 communications satellite keeps on climbing}}</ref>
===== Tiangong space station =====
China's ] is fitted with ion thrusters. Its ] is propelled by both chemical thrusters and four Hall-effect thrusters,<ref>{{cite web|url=https://spectrum.ieee.org/everything-you-need-to-know-about-chinas-space-station-tianhe-launch|title=Three Decades in the Making, China's Space Station Launches This Week |website=IEEE |date=28 April 2021 |first=Andrew |last=Jones}}</ref> which are used to adjust and maintain the station's orbit. The development of the Hall-effect thrusters is considered a sensitive topic in China, with scientists "working to improve the technology without attracting attention". Hall-effect thrusters are created with crewed mission safety in mind with effort to prevent erosion and damage caused by the accelerated ion particles. A magnetic field and specially designed ceramic shield was created to repel damaging particles and maintain integrity of the thrusters. According to the ], the ion drive used on Tiangong has burned continuously for 8,240 hours without a glitch, indicating their suitability for the Chinese space station's designated 15-year lifespan.<ref>{{cite web|url=https://www.scmp.com/news/china/science/article/3135770/how-chinas-space-station-could-help-power-astronauts-mars |title=How China's space station could help power astronauts to Mars |date=2 June 2021 |first=Stephen |last=Chen}}</ref> This is the world's first Hall thruster on a human-rated mission.<ref name="human_ion" />


====In Earth orbit==== ===== Starlink =====
]'s ] ] uses ]s powered by ] or ] to raise orbit, perform maneuvers, and de-orbit at the end of their use.<ref>{{cite web |url=https://techcrunch.com/2019/05/24/spacex-reveals-more-starlink-info-after-launch-of-first-60-satellites/|title=SpaceX reveals more Starlink info after launch of first 60 satellites|date=24 May 2019 |access-date=30 July 2020}}</ref>


===== GOCE ===== ===== GOCE =====
]'s ] (GOCE) was launched on 16 March 2009. It used ion propulsion throughout its twenty-month mission to combat the air-drag it experienced in its low orbit (altitude of 255 kilometres) before intentionally deorbiting on 11 November 2013.


==== In deep space ====
]'s ] was launched on March 16, 2009. It used ion propulsion throughout its twenty-month mission to combat the air-drag it experienced in its low orbit before intentionally deorbiting on November 11, 2013.
===== Deep Space 1 =====
] developed the ] ion engine for use in interplanetary science missions beginning in the late 1990s. It was space-tested in the space probe '']'', launched in 1998. This was the first use of electric propulsion as the interplanetary propulsion system on a science mission.<ref name="Sovey"/> Based on the NASA design criteria, ] developed the ] (XIPS) for performing ] on ]s.<ref>{{cite journal |author1=Rawlin |first=V. K. |author2=Patterson |first2=M. J/ |author3=Gruber |first3=R. P. |date=1990 |title=Xenon Ion Propulsion for Orbit Transfer |url=https://ntrs.nasa.gov/api/citations/19910002485/downloads/19910002485.pdf |url-status=live |journal=NASA Technical Memorandum 103193 |issue=AIAA-90-2527 |page=5 |archive-url=https://ghostarchive.org/archive/20221009/https://ntrs.nasa.gov/api/citations/19910002485/downloads/19910002485.pdf |archive-date=2022-10-09 |access-date=25 January 2022}}</ref> ] manufactured the NSTAR thruster used on the spacecraft.


====In deep space==== ===== Hayabusa and Hayabusa2 =====
The ] ] space probe was launched in 2003 and rendezvoused with the asteroid ]. It was powered by four xenon ion engines, which used microwave ] to ionize the propellant and an erosion-resistant carbon/carbon-composite material for its acceleration grid.<ref>{{cite web|url=http://www.ep.isas.ac.jp/muses-c/|title=小惑星探査機はやぶさ搭載イオンエンジン (Ion Engines used on Asteroid Probe Hayabusa)|access-date=2006-10-13|publisher=ISAS |language=ja|url-status=dead|archive-url=https://web.archive.org/web/20060819093452/http://www.ep.isas.ac.jp/muses-c/|archive-date=2006-08-19}}</ref> Although the ion engines on ''Hayabusa'' experienced technical difficulties, in-flight reconfiguration allowed one of the four engines to be repaired and allowed the mission to successfully return to Earth.<ref>{{cite news|first=Hiroko |last=Tabuchi |author-link=Hiroko Tabuchi |url=https://www.nytimes.com/2010/07/02/business/global/02space.html |title=Faulty Space Probe Seen as Test of Japan's Expertise |newspaper=The New York Times |date=1 July 2010}}</ref>


], launched in 2014, was based on Hayabusa. It also used ion thrusters.<ref>Nishiyama, Kazutaka; Hosoda, Satoshi; Tsukizaki, Ryudo; Kuninaka, Hitoshi. , ], January 2017.</ref>
=====Deep Space 1=====
] developed the ] ion engine for use in interplanetary science missions beginning in the late-1990s. It was space-tested in the highly successful space probe ], launched in 1998. This was the first use of electric propulsion as the interplanetary propulsion system on a science mission.<ref name="Sovey" /> Based on the NASA design criteria, ], developed the Xenon Ion Propulsion System (XIPS) for performing ] on ]s.{{Citation needed|date=February 2011}}. ] manufactured the NSTAR thruster used on the spacecraft.


=====Hayabusa===== ===== Smart 1 =====
The ]'s satellite '']'' launched in 2003 using a ] ]-G Hall thruster to get from ] to lunar orbit. This satellite completed its mission on 3 September 2006, in a controlled collision on the ]'s surface, after a trajectory deviation so scientists could see the 3-meter crater the impact created on the visible side of the Moon.
The Japanese space agency's ] launched in 2003 and successfully rendezvoused with the asteroid ] and remained in close proximity for months to collect samples and information. It was powered by four xenon ion engines. Its xenon ions were generated by microwave ] and an erosion-resistant carbon/carbon-composite material for its acceleration grid.<ref>{{cite web |url=http://www.ep.isas.ac.jp/muses-c/ |title=小惑星探査機はやぶさ搭載イオンエンジン (Ion Engines used on Asteroid Probe Hayabusa) |accessdate=2006-10-13 |author=ISAS |authorlink=Institute of Space and Astronautical Science |language=Japanese}}</ref> Although the ion engines on Hayabusa had technical difficulties, in-flight reconfiguration allowed one of the four engines to be repaired and allowed the mission to successfully return to Earth.<ref>{{cite news| first= Hiroko |last= Tabuchi |url= http://www.nytimes.com/2010/07/02/business/global/02space.html |title= Faulty Space Probe Seen as Test of Japan’s Expertise |newspaper= The New York Times| date= 1 July 2010}}</ref>

=====Smart 1=====
The ]'s satellite ] launched in 2003 using a Snecma ]-G Hall thruster to get from ] to lunar orbit. This satellite completed its mission on September 3, 2006, in a controlled collision on the ]'s surface, after a trajectory deviation so scientists could see the 3 meter crater the impact created on the visible side of the moon.


===== Dawn ===== ===== Dawn =====
] launched on September 27, 2007, to explore the asteroid ] and the dwarf planet ]. It used three ] heritage xenon ion thrusters (firing one at a time). An extended mission to explore other asteroids is possible. Dawn's ion drive is capable of accelerating from 0 to {{convert|60|mi/h|km/h|abbr=on}} in 4 days of continuous firing.<ref>, September 13, 2007, NASA Jet Propulsion Laboratory</ref> ] launched on 27 September 2007, to explore the asteroid ] and the dwarf planet ]. It used three '']'' heritage xenon ion thrusters (firing one at a time). ''Dawn''{{'s}} ion drive is capable of accelerating from 0 to {{cvt|97|km/h}} in 4 days of continuous firing.<ref> {{Webarchive|url=https://web.archive.org/web/20110605015515/http://www.jpl.nasa.gov/news/features.cfm?feature=1468 |date=5 June 2011 }}, 13 September 2007, NASA Jet Propulsion Laboratory {{PD-notice}}</ref> The mission ended on 1 November 2018, when the spacecraft ran out of ] chemical propellant for its attitude thrusters.<ref name="DawnEOM">{{cite web|url=https://www.nasa.gov/press-release/nasa-s-dawn-mission-to-asteroid-belt-comes-to-end|title=NASA's Dawn Mission to Asteroid Belt Comes to End|date=1 November 2018 |publisher=NASA}} {{PD-notice}}</ref>


===Planned missions=== ==== LISA Pathfinder ====
] is an ] spacecraft launched in 2015 to orbit the Sun-Earth L1 point. It does not use ion thrusters as its primary propulsion system, but uses both ]s and ] for precise ] – the low thrusts of these propulsion devices make it possible to move the spacecraft incremental distances accurately. It is a test for the ] mission. The mission ended on 30 December 2017.
Several missions are planned to use ion thrusters:


====BepiColombo==== ==== BepiColombo ====
]'s ] mission was launched to ] on 20 October 2018.<ref name="BepiLaunch">{{cite web |url=https://www.esa.int/Our_Activities/Operations/BepiColombo_s_beginning_ends|title=BepiColombo's beginning ends|date=22 October 2018|access-date=1 November 2018|publisher=ESA}}</ref> It uses ion thrusters in combination with ] to get to Mercury, where a chemical rocket will complete orbit insertion.


==== Double Asteroid Redirection Test ====
] plans to launch the ] mission to ] in 2017. It uses ion thrusters in combination with swing-bys to get to Mercury, where a chemical rocket will complete orbit insertion.
NASA's ] (DART) was launched in 2021 and operated its ] xenon ion thruster for about 1,000 hours to reach the target asteroid on 28 September 2022.


==== LISA Pathfinder ==== ==== Psyche ====
NASA's ] was launched in 2023 and is operating its ] xenon ion thruster in order to reach asteroid ] in August 2029.

] is an ] spacecraft launched in 2015. It does not use ion thrusters as its primary propulsion system, but uses both ]s and ] for precise ] — the low thrusts of these propulsion devices make it possible to move the spacecraft incremental distances accurately. It is a test for the possible LISA mission.


=== Proposed missions ===
==== International Space Station ==== ==== International Space Station ====
{{as of|2011|March}}, a future launch of an Ad Astra VF-200 {{nowrap|200 kW}} ] electromagnetic thruster was under consideration for testing on the ] (ISS).<ref name="aaESummary20100124">{{cite web|url=http://www.adastrarocket.com/EXECUTIVE%20SUMMARY240110.pdf|title=Executive summary|date=January 24, 2010|publisher=Ad Astra Rocket Company|access-date=2010-02-27|url-status=dead|archive-url=https://web.archive.org/web/20100331171616/http://www.adastrarocket.com/EXECUTIVE%20SUMMARY240110.pdf|archive-date=March 31, 2010}}</ref><ref name="dn20080807">{{cite web |url=http://dsc.discovery.com/news/2008/08/07/plasma-rocket.html|title=Plasma Rocket May Be Tested at Space Station|date=7 August 2008|first=Irene|last=Klotz|publisher=Discovery News|access-date=2010-02-27}}</ref> However, in 2015, NASA ended plans for flying the VF-200 to the ISS. A NASA spokesperson stated that the ISS "was not an ideal demonstration platform for the desired performance level of the engines". Ad Astra stated that tests of a VASIMR thruster on the ISS would remain an option after a future in-space demonstration.<ref name="VASiMRscrapped">Irene Klotz (17 March 2015). ''SEN News.''</ref>


{{as of|2011|March}}, a future launch of an Ad Astra VF-200 {{nowrap|200 kW}} ] electromagnetic thruster was under consideration for testing on the ].<ref name="aaESummary20100124">{{cite web |url=http://www.adastrarocket.com/EXECUTIVE%20SUMMARY240110.pdf |title=Executive summary |date=January 24, 2010 |publisher=Ad Astra Rocket Company |accessdate=2010-02-27 }}</ref><ref name="dn20080807">{{cite web |url=http://dsc.discovery.com/news/2008/08/07/plasma-rocket.html |title=Plasma Rocket May Be Tested at Space Station |date=7 August 2008 |first= Irene |last= Klotz |publisher=Discovery News |accessdate=2010-02-27 }}</ref> The VF-200 is a flight version of the ].<ref name="Yahoo News">{{cite web |url=https://news.yahoo.com/nasa-test-vf-200-vasimr-plasma-rocket-iss-20110310-155100-110.html |title=NASA to Test VF-200 VASIMR Plasma Rocket at the ISS |date=March 10, 2011 |first= Mark |last= Whittington |publisher=Yahoo |accessdate=2012-01-27 }}</ref><ref name="Yahoo">{{cite web |url=http://www.dailytech.com/Commercially+Developed+Plasma+Engine+Soon+To+Be+Tested+In+Space/article12612.htm |title=Commercially Developed Plasma Engine Soon to be Tested in Space |date=August 11, 2008 |first= Jason |last= Mick |publisher=DailyTech |accessdate=2010-02-27 }}</ref> Since the available power from the ISS is less than 200&nbsp;kW, the ISS VASIMR would include a trickle-charged battery system allowing for 15 min pulses of thrust. Testing the engine on ISS is valuable, because it orbits at a relatively ] and experiences fairly high levels of ], requiring ] Altitude reboosting by chemical rockets fulfills this requirement. If the tests of VASIMR reboosting goes according to plan, the increase in specific impulse could mean that the fuel cost will be one-twentieth of the current $210 million annual cost.<ref name="aaESummary20100124" /> VASMIR could reduce the a mount spent of fuel for maintaining ISS altitude, using as little as 300 kg of Argon gas instead of 7.5 tonnes of chemical fuel.<ref></ref> It can use less fuel because exhaust velocity is higher, so the same acceleration is achieved with a smaller amount of propellant compared to a greater amount of fuel at a lower velocity.<reF></reF> The VF-200 would have been a flight version of the ].<ref name="Yahoo News">{{cite web|url=https://news.yahoo.com/nasa-test-vf-200-vasimr-plasma-rocket-iss-20110310-155100-110.html|title=NASA to Test VF-200 VASIMR Plasma Rocket at the ISS|date=March 10, 2011|first=Mark|last=Whittington|publisher=Yahoo|access-date=2012-01-27}}</ref><ref name="Yahoo">{{cite news |url=http://www.dailytech.com/Commercially+Developed+Plasma+Engine+Soon+To+Be+Tested+In+Space/article12612.htm|title=Commercially Developed Plasma Engine Soon to be Tested in Space|date=August 11, 2008 |first=Jason|last=Mick|publisher=DailyTech|access-date=2010-02-27|archive-url=https://web.archive.org/web/20150222124839/http://www.dailytech.com/Commercially+Developed+Plasma+Engine+Soon+To+Be+Tested+In+Space/article12612.htm|archive-date=February 22, 2015|url-status=dead}}</ref> Since the available power from the ISS is less than 200&nbsp;kW, the ISS VASIMR would have included a trickle-charged battery system allowing for 15 minutes pulses of thrust. The ISS orbits at a relatively ] and experiences fairly high levels of ], requiring ] a high-efficiency engine (high specific impulse) for station-keeping would be valuable; theoretically VASIMR reboosting could cut fuel cost from the current US$210 million annually to one-twentieth.<ref name="aaESummary20100124"/> VASIMR could in theory use as little as 300&nbsp;kg of argon gas for ISS station-keeping instead of 7500&nbsp;kg of chemical fuel the high exhaust velocity (high ]) would achieve the same acceleration with a smaller amount of propellant, compared to chemical propulsion with its lower exhaust velocity needing more fuel.<ref name="newscientist.com">{{cite web|last=Shiga|first=David|url=https://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine/|title=Rocket company tests world's most powerful ion engine|publisher=New Scientist|date=2009-10-05|access-date=2019-11-16}}</ref> ] is generated by the ISS as a by-product and is vented into space.

] is generated by the ISS as a by-product and is vented into space.


NASA previously worked on a 50 kw ion hall thruster for ISS, but work was stoppped on it in 2005.<ref></reF> NASA previously worked on a 50&nbsp;kW Hall-effect thruster for the ISS, but work was stopped in 2005.<ref name="newscientist.com"/>


==== Lunar Gateway ====
ISS uses about 7.5 tonnes of propellant for station keeping each year, whereas a good ion engine might be able to use as litte as 0.3 tonnes.<ref></ref> Because it so expensive to launch mass into space, this could save millions every year.<reF></ref> Also, advanced ion engines pave the way for trips to more distant destinations.<reF>https://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine/ </reF> One candidate for use of an Ion engine is trips to Mars.<reF>https://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine/ </reF>
The ] is a module on the ] that provides power generation and propulsion capabilities. It is targeting launch on a commercial vehicle in January 2024.<ref>{{cite web |url=https://www.oversight.gov/sites/default/files/oig-reports/IG-21-004.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.oversight.gov/sites/default/files/oig-reports/IG-21-004.pdf |archive-date=2022-10-09 |url-status=live |title=Report No. IG-21-004: NASA's Management of the Gateway Program for Artemis Missions |pages=5–7 |work=] |publisher=] |date=10 November 2020 |access-date=28 December 2020}}</ref> It would probably use the 50&nbsp;kW ] (AEPS) under development at NASA ] and ].<ref name="AEPS 2017">Daniel A. Herman, Todd A. Tofil, Walter Santiago, Hani Kamhawi, James E. Polk, John S. Snyder, Richard R. Hofer, Frank Q. Picha, Jerry Jackson and May Allen. , NASA/TM—2018-219761 35th International Electric Propulsion Conference, Atlanta, Georgia, 8–12 October 2017, Accessed: 27 July 2018.</ref>


==== MARS-CAT ====
==== NASA high-power SEP system demonstration mission ====
The MARS-CAT (Mars Array of ionospheric Research Satellites using the CubeSat Ambipolar Thruster) mission is a two 6U ] concept mission to study Mars' ionosphere. The mission would investigate its plasma and magnetic structure, including transient plasma structures, magnetic field structure, magnetic activity and correlation with solar wind drivers.<ref name="MARS-CAT"/> The CAT thruster is now called the ] thruster and manufactured by Phase Four.<ref name="P4_RF_Thruster"/>


==== Interstellar missions ====
In February 2012 NASA awarded a contract to ] for a test mission (probably using the ] engine) capable of extension to 300&nbsp;kW electrical power.<ref name="NNC11ZMA017K-award">{{cite web |url=http://www.energymatters.com.au/index.php?main_page=news_article&article_id=3041 |title=NASA Awards Solar Electric Propulsion Flight System Contract}}</ref>
] proposed using an ion thruster powered by a space-based laser, in conjunction with a lightsail, to propel an interstellar probe.<ref>{{cite journal |last=Landis |first=Geoffrey A. |date=1991 |title=Laser-Powered Interstellar Probe |journal=] |volume=36 |issue=5 |pages=1687–1688}}</ref><ref>{{cite web|url=http://www.geoffreylandis.com/laser_ion.htp |first=Geoffrey A. |last=Landis |title=Laser-powered Interstellar Probe |date=1994 |archive-url=https://web.archive.org/web/20120722013713/http://www.geoffreylandis.com/laser_ion.htp |archive-date=2012-07-22 |work=GeoffreyLandis.com}}</ref>

==== Mars Array of Ionospheric Research Satellites Using the CubeSat Ambipolar Thruster ====

The MARS-CAT mission is a two 6U ] mission to study Mars' ionosphere. The mission will investigate its plasma and magnetic structure, including transient plasma structures, magnetic field structure, magnetic activity and correlation with solar wind drivers. The Mars transit proposed is piggyback with Mars2020 using a CubeSat Ambipolar Thruster (CAT) burn for Mars orbit insertion and station keeping.<ref name="MARS-CAT" />

====Interstellar probe====
] proposed to use a space laser source and ion thruster to propel an interstellar probe.<ref>{{cite web|url=https://scholar.google.com/scholar?cluster=13405813666529688188&hl=en&as_sdt=2005&sciodt=0,5|title=- Google Scholar|publisher=}}</ref><ref> on the . papers available on the web</ref>


== Popular culture == == Popular culture ==
The idea of an ion engine first appeared in Donald W Horner's ''By Aeroplane to the Sun: Being the Adventures of a Daring Aviator and his Friends'' (1910).<ref>{{cite web|url=http://sf-encyclopedia.com/entry/ion_drive|title=Themes : Ion Drive : SFE : Science Fiction Encyclopedia|publisher=}}</ref> * The idea of an ion engine first appeared in Donald W. Horner's ''By Aeroplane to the Sun: Being the Adventures of a Daring Aviator and his Friends'' (1910).<ref>{{cite web|url=http://sf-encyclopedia.com/entry/ion_drive|title=Themes: Ion Drive |website=Science Fiction Encyclopedia}}</ref>
* Ion propulsion is the main thrust source of the spaceship ''Kosmokrator'' in the East German/Polish science fiction film {{lang|de|]}} (1960).<ref>{{cite book |last1=Kruschel|first1=Karsten|title=Leim für die Venus – Der Science-Fiction-Film in der DDR |lang=de |trans-title=Glue for Venus – The science fiction film in the GDR |date=2007 |publisher=Heyne |isbn=978-3-453-52261-9|pages=803–888}}</ref> Minute 28:10.
* In the 1968 '']'' episode "]", ] is repeatedly impressed by a civilization's use of ion power.<ref>{{cite web |url=http://www.chakoteya.net/StarTrek/61.htm|title=The Star Trek Transcripts – Spock's Brain|website=chakoteya.net}}</ref><ref>{{cite web|url=https://www.tor.com/2016/06/07/star-trek-the-original-series-rewatch-spocks-brain/|title=Star Trek The Original Series Rewatch: 'Spock's Brain'|first=Keith R. A.|last=DeCandido|date=June 7, 2016|website=tor.com}}</ref>
* The popular ] spacecraft from the ] are propelled by twin ion engines, hence the name.
* Ion propulsion is used by the ''Hermes'' spacecraft in the ] novel '']'' to transfer crew between Earth and Mars.<ref>{{Cite web |date=19 August 2015 |editor-last=Fox |editor-first=Steve |title=Nine Real NASA Technologies in 'The Martian' |url=https://www.nasa.gov/feature/nine-real-nasa-technologies-in-the-martian |access-date=30 June 2023 |website=NASA |archive-date=20 June 2018 |archive-url=https://web.archive.org/web/20180620125937/https://www.nasa.gov/feature/nine-real-nasa-technologies-in-the-martian/ |url-status=dead }}</ref>


== See also ==
] films and literature refer to ]. Also nearly all other star wars crafts are propepelled by ion motors according to sources such as wookieepedia,<ref>{{cite web|url=http://starwars.wikia.com/Ion_drive|title=Ion drive, Wookiepedia}}</ref> but the technology is highly different from real ion motors.
{{colbegin|colwidth=27em}}

* ]
==See also==
* ]
{{portal|energy}}
* ]
{{colbegin|2}}
* ]
*]
* ]
*]
*] * ]
* ]
*]
*] * ]
* ]
*]
* ]
*]
*] * ]
*] * ]
*] * ]
*]
{{colend}} {{colend}}


==References== == References ==
{{reflist}}


===Footnotes=== === Bibliography ===
{{reflist|30em}}

===Bibliography===
{{refbegin}} {{refbegin}}
*{{cite journal |last=Lerner |first=Eric J. |authorlink=Eric Lerner |date=October 2000 |title=Plasma Propulsion in Space |journal=The Industrial Physicist |volume=6 |issue=5 |pages=16–19 |id= |url= http://www.aip.org/tip/INPHFA/vol-6/iss-5/p16.pdf |accessdate= 2007-06-29 |quote= |format=PDF }} * {{cite journal|last=Lerner|first=Eric J.|author-link=Eric Lerner|date=October 2000|title=Plasma Propulsion in Space|journal=The Industrial Physicist|volume=6|issue=5|pages=16–19 |url=http://www.aip.org/tip/INPHFA/vol-6/iss-5/p16.pdf|access-date=2007-06-29|url-status=dead|archive-url=https://web.archive.org/web/20070316160623/http://www.aip.org/tip/INPHFA/vol-6/iss-5/p16.pdf |archive-date=2007-03-16}}
*, RMCybernetics. * RMCybernetics
{{refend}} {{refend}}


==External links== == External links ==
{{Commons category|Ion propulsion}} {{Commons category|Ion propulsion}}
* *
* *
*]: * ]:
* * {{Webarchive|url=https://web.archive.org/web/20161018201525/http://alfven.princeton.edu/publications/choueiri-sciam-2009 |date=18 October 2016 }}
* *
* {{Webarchive|url=https://web.archive.org/web/20140107041836/http://www.rocket.com/files/aerojet/documents/Capabilities/PDFs/Electric%20Propulsion%20Data%20Sheets.pdf |date=7 January 2014 }}
*


===Articles=== === Articles ===
*, ''The Daily Galaxy'' April 13, 2009. * ''The Daily Galaxy'' 13 April 2009.
*, ''The Daily Galaxy'', July 7, 2009. * ''The Daily Galaxy'', 7 July 2009.
*An early experimental Ion engine is on display at the Aerospace Discovery at the Florida Air Museum. * An early experimental ion engine is on display at the Aerospace Discovery at the ].


{{Spacecraft propulsion}} {{Spacecraft propulsion}}
{{Emerging technologies}} {{emerging technologies|topics=yes|space=yes}}
{{portal bar|Energy|Astronomy|Spaceflight}}


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Latest revision as of 11:06, 3 January 2025

Spacecraft engine that generates thrust by generating a jet of ions This article is about a kind of reaction engine. For the air propulsion concept, see ionocraft.

The 2.3 kW NSTAR ion thruster developed by NASA for the Deep Space 1 spacecraft during a hot fire test at the Jet Propulsion Laboratory (1999)
NEXIS ion engine test (2005)
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 electric propulsion used for spacecraft propulsion. An ion thruster creates a cloud of positive ions from a neutral gas by ionizing it to extract some electrons from its atoms. The ions are then accelerated using electricity to create thrust. Ion thrusters are categorized as either electrostatic or electromagnetic.

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, 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 engines, where the electric field is not in the direction of the acceleration.

Ion thrusters in operation typically consume 1–7 kW of power, have exhaust velocities around 20–50 km/s (Isp 2000–5000 s), and possess thrusts of 25–250 mN and a propulsive efficiency 65–80% though experimental versions have achieved 100 kW (130 hp), 5 N (1.1 lbf).

The Deep Space 1 spacecraft, powered by an ion thruster, changed velocity by 4.3 km/s (2.7 mi/s) while consuming less than 74 kg (163 lb) of xenon. The Dawn spacecraft broke the record, with a velocity change of 11.5 km/s (7.1 mi/s), though it was only half as efficient, requiring 425 kg (937 lb) of xenon.

Applications include control of the orientation and position of orbiting satellites (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), and serving as propulsion thrusters for crewed spacecraft and space stations (e.g. Tiangong).

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' 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 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 launch technologies to reach their initial orbit.

Origins

SERT-1 spacecraft

The first person who wrote a paper introducing the idea publicly was Konstantin Tsiolkovsky in 1911. The technique was recommended for near-vacuum conditions at high altitude, but thrust was demonstrated with ionized air streams at atmospheric pressure. The idea appeared again in Hermann Oberth's Wege zur Raumschiffahrt (1929; Ways to Spaceflight), where he explained his thoughts on the mass savings of electric propulsion, predicted its use in spacecraft propulsion and attitude control, and advocated electrostatic acceleration of charged gasses.

A working ion thruster was built by Harold R. Kaufman in 1959 at the NASA Glenn Research Center facilities. It was similar to a gridded electrostatic ion thruster and used mercury for propellant. Suborbital tests were conducted during the 1960s and in 1964, and the engine was sent into a suborbital flight aboard the Space Electric Rocket Test-1 (SERT-1). It successfully operated for the planned 31 minutes before falling to Earth. This test was followed by an orbital test, SERT-2, in 1970.

On the 12 October 1964 Voskhod 1 carried out tests with ion thrusters that had been attached to the exterior of the spacecraft.

An alternate form of electric propulsion, the Hall-effect thruster, was studied independently in the United States and the Soviet Union in the 1950s and 1960s. Hall-effect thrusters operated on Soviet satellites from 1972 until the late 1990s, mainly used for satellite stabilization in north–south and in east–west directions. Some 100–200 engines completed missions on Soviet and Russian satellites. Soviet thruster design was introduced to the West in 1992 after a team of electric propulsion specialists, under the support of the Ballistic Missile Defense Organization, visited Soviet laboratories.

General working principle

Ion thrusters use beams of ions (electrically charged atoms or molecules) to create thrust in accordance with momentum conservation. The method of accelerating the ions varies, but all designs take advantage of the charge/mass ratio of the ions. This ratio means that relatively small potential differences can create high exhaust velocities. This reduces the amount of reaction mass or propellant required, but increases the amount of specific power required compared to chemical rockets. Ion thrusters are therefore able to achieve high specific impulses. The drawback of the low thrust is low acceleration because the mass of the electric power unit directly correlates with the amount of power. This low thrust makes ion thrusters unsuited for launching spacecraft into orbit, but effective for in-space propulsion over longer periods of time.

Ion thrusters are categorized as either electrostatic or electromagnetic. The main difference is the method for accelerating the ions.

  • Electrostatic ion thrusters use the Coulomb force and accelerate the ions in the direction of the electric field.
  • Electromagnetic ion thrusters use the Lorentz force to accelerate the ions in the direction perpendicular to the electric field.

Electric power for ion thrusters is usually provided by solar panels. However, for sufficiently large distances from the sun, nuclear power may be used. In each case, the power supply mass is proportional to the peak power that can be supplied, and both provide, for this application, almost no limit to the energy.

Electric thrusters tend to produce low thrust, which results in low acceleration. Defining 1 g = 9.81 m / s 2 {\displaystyle 1g=9.81\;\mathrm {m/s^{2}} } , the standard gravitational acceleration of Earth, and noting that F = m a a = F / m {\displaystyle F=ma\implies a=F/m} , this can be analyzed. An NSTAR thruster producing a thrust force of 92 mN will accelerate a satellite with a mass of 1 ton by 0.092 N / 1000 kg = 9.2×10 m/s (or 9.38×10 g). However, this acceleration can be sustained for months or years at a time, in contrast to the very short burns of chemical rockets.

F = 2 η P g I sp {\displaystyle F=2{\frac {\eta P}{gI_{\text{sp}}}}} Where:

  • F is the thrust force in N,
  • η is the efficiency
  • P is the electrical power used by the thruster in W, and
  • Isp is the specific impulse in seconds.

The ion thruster is not the most promising type of electrically powered spacecraft propulsion, but it is the most successful in practice to date. An ion drive would require two days to accelerate a car to highway speed in vacuum. The technical characteristics, especially thrust, are considerably inferior to the prototypes described in literature, technical capabilities are limited by the space charge created by ions. This limits the thrust density (force per cross-sectional area of the engine). Ion thrusters create small thrust levels (the thrust of Deep Space 1 is approximately equal to the weight of one sheet of paper) compared to conventional chemical rockets, but achieve high specific impulse, or propellant mass efficiency, by accelerating the exhaust to high speed. The power imparted to the exhaust increases with the square of exhaust velocity while thrust increase is linear. Conversely, chemical rockets provide high thrust, but are limited in total impulse by the small amount of energy that can be stored chemically in the propellants. Given the practical weight of suitable power sources, the acceleration from an ion thruster is frequently less than one-thousandth of standard gravity. However, since they operate as electric (or electrostatic) motors, they convert a greater fraction of input power into kinetic exhaust power. Chemical rockets operate as heat engines, and Carnot's theorem limits the exhaust velocity.

Electrostatic thrusters

Gridded electrostatic ion thrusters

Main article: Gridded ion thruster
A diagram of how a gridded electrostatic ion engine (multipole magnetic cusp type) works

Gridded electrostatic ion thrusters development started in the 1960s and, since then, they have been used for commercial satellite propulsion and scientific missions. Their main feature is that the propellant ionization process is physically separated from the ion acceleration process.

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 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 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.

Gridded electrostatic ion thruster research (past/present):

  • NASA Solar Technology Application Readiness (NSTAR), 2.3 kW, used on two successful missions
  • NASA's Evolutionary Xenon Thruster (NEXT), 6.9 kW, flight qualification hardware built; used on DART mission
  • Nuclear Electric Xenon Ion System (NEXIS)
  • High Power Electric Propulsion (HiPEP), 25 kW, test example built and run briefly on the ground
  • EADS Radio-frequency Ion Thruster (RIT)
  • Dual-Stage 4-Grid (DS4G)

Hall-effect thrusters

Main article: Hall-effect thruster
Schematic of a Hall-effect thruster

Hall-effect thrusters accelerate ions by means of an electric potential between a cylindrical anode and a negatively charged plasma that forms the cathode. The bulk of the propellant (typically xenon) is introduced near the anode, where it ionizes and flows toward the cathode; ions accelerate towards and through it, picking up electrons as they leave to neutralize the beam and leave the thruster at high velocity.

The anode is at one end of a cylindrical tube. In the center is a spike that is wound to produce a radial magnetic field between it and the surrounding tube. The ions are largely unaffected by the magnetic field, since they are too massive. However, the electrons produced near the end of the spike to create the cathode are trapped by the magnetic field and held in place by their attraction to the anode. Some of the electrons spiral down towards the anode, circulating around the spike in a Hall current. When they reach the anode they impact the uncharged propellant and cause it to be ionized, before finally reaching the anode and completing the circuit.

Field-emission electric propulsion

Main article: Field-emission electric propulsion

Field-emission electric propulsion (FEEP) thrusters may use caesium or indium propellants. The design comprises a small propellant reservoir that stores the liquid metal, a narrow tube or a system of parallel plates that the liquid flows through and an accelerator (a ring or an elongated aperture in a metallic plate) about a millimeter past the tube end. Caesium and indium are used due to their high atomic weights, low ionization potentials and low melting points. Once the liquid metal reaches the end of the tube, an electric field applied between the emitter and the accelerator causes the liquid surface to deform into a series of protruding cusps, or Taylor cones. At a sufficiently high applied voltage, positive ions are extracted from the tips of the cones. The electric field created by the emitter and the accelerator then accelerates the ions. An external source of electrons neutralizes the positively charged ion stream to prevent charging of the spacecraft.

Electromagnetic thrusters

Main article: Plasma propulsion engine
Exclamation mark with arrows pointing at each otherThis article or section appears to contradict the article Electrically powered spacecraft propulsion. Please see the talk page for more information. (April 2018)

Pulsed inductive thrusters

Main article: Pulsed inductive thruster

Pulsed inductive thrusters (PITs) use pulses instead of continuous thrust and have the ability to run on power levels on the order of megawatts (MW). PITs consist of a large coil encircling a cone shaped tube that emits the propellant gas. Ammonia is the gas most commonly used. For each pulse, a large charge builds up in a group of capacitors behind the coil and is then released. This creates a current that moves circularly in the direction of jθ. The current then creates a magnetic field in the outward radial direction (Br), which then creates a current in the gas that has just been released in the opposite direction of the original current. This opposite current ionizes the ammonia. The positively charged ions are accelerated away from the engine due to the electric field jθ crossing the magnetic field Br, due to the Lorentz force.

Magnetoplasmadynamic thruster

Main article: Magnetoplasmadynamic thruster

Magnetoplasmadynamic (MPD) thrusters and lithium Lorentz force accelerator (LiLFA) thrusters use roughly the same idea. The LiLFA thruster builds on the MPD thruster. Hydrogen, argon, ammonia and nitrogen can be used as propellant. In a certain configuration, the ambient gas in low Earth orbit (LEO) can be used as a propellant. The gas enters the main chamber where it is ionized into plasma by the electric field between the anode and the cathode. This plasma then conducts electricity between the anode and the cathode, closing the circuit. This new current creates a magnetic field around the cathode, which crosses with the electric field, thereby accelerating the plasma due to the Lorentz force.

The LiLFA thruster uses the same general idea as the MPD thruster, though with two main differences. First, the LiLFA uses lithium vapor, which can be stored as a solid. The other difference is that the single cathode is replaced by multiple, smaller cathode rods packed into a hollow cathode tube. MPD cathodes are easily corroded due to constant contact with the plasma. In the LiLFA thruster, the lithium vapor is injected into the hollow cathode and is not ionized to its plasma form/corrode the cathode rods until it exits the tube. The plasma is then accelerated using the same Lorentz force.

In 2013, Russian company the Chemical Automatics Design Bureau successfully conducted a bench test of their MPD engine for long-distance space travel.

Electrodeless plasma thrusters

Main article: Electrodeless plasma thruster

Electrodeless plasma thrusters have two unique features: the removal of the anode and cathode electrodes and the ability to throttle the engine. The removal of the electrodes eliminates erosion, which limits lifetime on other ion engines. Neutral gas is first ionized by electromagnetic waves and then transferred to another chamber where it is accelerated by an oscillating electric and magnetic field, also known as the ponderomotive force. This separation of the ionization and acceleration stages allows throttling of propellant flow, which then changes the thrust magnitude and specific impulse values.

Helicon double layer thrusters

Main article: Helicon double-layer thruster

A helicon double layer thruster is a type of plasma thruster that ejects high velocity ionized gas to provide thrust. In this design, gas is injected into a tubular chamber (the source tube) with one open end. Radio frequency AC power (at 13.56 MHz in the prototype design) is coupled into a specially shaped antenna wrapped around the chamber. The electromagnetic wave emitted by the antenna causes the gas to break down and form a plasma. The antenna then excites a helicon wave in the plasma, which further heats it. The device has a roughly constant magnetic field in the source tube (supplied by solenoids in the prototype), but the magnetic field diverges and rapidly decreases in magnitude away from the source region and might be thought of as a kind of magnetic nozzle. In operation, a sharp boundary separates the high density plasma inside the source region and the low density plasma in the exhaust, which is associated with a sharp change in electrical potential. Plasma properties change rapidly across this boundary, which is known as a current-free electric double layer. The electrical potential is much higher inside the source region than in the exhaust and this serves both to confine most of the electrons and to accelerate the ions away from the source region. Enough electrons escape the source region to ensure that the plasma in the exhaust is neutral overall.

Variable Specific Impulse Magnetoplasma Rocket (VASIMR)

Main article: Variable Specific Impulse Magnetoplasma Rocket

The proposed Variable Specific Impulse Magnetoplasma Rocket (VASIMR) functions by using radio waves to ionize a propellant into a plasma, and then using a magnetic field to accelerate the plasma out of the back of the rocket engine to generate thrust. The VASIMR is currently being developed by Ad Astra Rocket Company, headquartered in Houston, Texas, with help from Canada-based Nautel, producing the 200 kW RF generators for ionizing propellant. Some of the components and "plasma shoots" experiments are tested in a laboratory settled in Liberia, Costa Rica. This project is led by former NASA astronaut Franklin Chang-Díaz (CRC-USA). A 200 kW VASIMR test engine was in discussion to be fitted in the exterior of the International Space Station, as part of the plan to test the VASIMR in space; however, plans for this test onboard ISS were canceled in 2015 by NASA, with a free flying VASIMR test being discussed by Ad Astra instead. An envisioned 200 MW engine could reduce the duration of flight from Earth to Jupiter or Saturn from six years to fourteen months, and Mars from 7 months to 39 days.

Microwave electrothermal thrusters

Microwave electrothermal thrusterThruster componentsThruster componentsDischarge ChamberDischarge chamber

Under a research grant from the NASA Lewis Research Center during the 1980s and 1990s, Martin C. Hawley and Jes Asmussen led a team of engineers in developing a microwave electrothermal thruster (MET).

In the discharge chamber, microwave (MW) energy flows into the center containing a high level of ions (I), causing neutral species in the gaseous propellant to ionize. Excited species flow out (FES) through the low ion region (II) to a neutral region (III) where the ions complete their recombination, replaced with the flow of neutral species (FNS) towards the center. Meanwhile, energy is lost to the chamber walls through heat conduction and convection (HCC), along with radiation (Rad). The remaining energy absorbed into the gaseous propellant is converted into thrust.

Radioisotope thruster

A theoretical propulsion system has been proposed, based on alpha particles (He
or
2He
indicating a helium ion with a +2 charge) emitted from a radioisotope uni-directionally through a hole in its chamber. A neutralising electron gun would produce a tiny amount of thrust with high specific impulse in the order of millions of seconds due to the high relativistic speed of alpha particles.

A variant of this uses a graphite-based grid with a static DC high voltage to increase thrust as graphite has high transparency to alpha particles if it is also irradiated with short wave UV light at the correct wavelength from a solid-state emitter. It also permits lower energy and longer half-life sources which would be advantageous for a space application. Helium backfill has also been suggested as a way to increase electron mean free path.

Comparisons

Test data of some ion thrusters
Thruster Propellant Input
power (kW)
Specific
impulse
(s)
Thrust
(mN)
Thruster
mass (kg)
Notes
NSTAR Xenon 2.3 1700–3300 92 max. 8.33 Used on the Deep Space 1 and Dawn space probes.
PPS-1350 Hall effect Xenon 1.5 1660 90 5.3
NEXT Xenon 6.9 4190 236 max. <13.5 Used in DART mission.
X3 Hall effect Xenon or krypton 102 1800–2650 5400 230
NEXIS Xenon 20.5
RIT 22 Xenon 5
BHT-8000 Xenon 8 2210 449 25
Hall effect Xenon 75
FEEP Liquid caesium 6×10–0.06 6000–10000 0.001–1
NPT30-I2 Iodine 0.034–0.066 1000–2500 0.5–1.5 1.2
Starlink Gen1 Hall effect Krypton ~1667 ~70.83
Starlink Gen2 Hall effect Argon 4.2 2500 170 2.1 Used in Starlink V2 mini satellites.
AEPS Xenon 13.3 2900 600 25 To be used in Lunar Gateway PPE module.
Qinetiq T6 Xenon 4,6 4300 145 Used in European-Japanese BepiColombo.
Experimental thrusters (no mission to date)
Thruster Propellant Input
power (kW)
Specific
impulse
(s)
Thrust
(mN)
Thruster
mass (kg)
Notes
Hall effect Bismuth 1.9 1520 (anode) 143 (discharge)
Hall effect Bismuth 25
Hall effect Bismuth 140
Hall effect Iodine 0.2 1510 (anode) 12.1 (discharge)
Hall effect Iodine 7 1950 413
HiPEP Xenon 20–50 6000–9000 460–670
MPDT Hydrogen 1500 4900 26300
MPDT Hydrogen 3750 3500 88500
MPDT Hydrogen 7500 6000 60000
LiLFA Lithium vapor 500 4077 12000
FEEP Liquid caesium 6×10–0.06 6000–10000 0.001–1
VASIMR Argon 200 3000–12000 Approximately 5000 620
CAT Xenon, iodine, water 0.01 690 1.1–2 (73 mN/kW) <1
DS4G Xenon 250 19300 2500 max. 5
KLIMT Krypton 0.5 4
ID-500 Xenon 32–35 7140 375–750 34.8 To be used in TEM

Lifetime

Ion thrusters' low thrust requires continuous operation for a long time to achieve the necessary change in velocity (delta-v) for a particular mission. Ion thrusters are designed to provide continuous operation for intervals of weeks to years.

The lifetime of electrostatic ion thrusters is limited by several processes.

Gridded thruster life

In electrostatic gridded designs, charge-exchange ions produced by the beam ions with the neutral gas flow can be accelerated towards the negatively biased accelerator grid and cause grid erosion. End-of-life is reached when either the grid structure fails or the holes in the grid become large enough that ion extraction is substantially affected – e.g., by the occurrence of electron backstreaming. Grid erosion cannot be avoided and is the major lifetime-limiting factor. Thorough grid design and material selection enable lifetimes of 20,000 hours or more.

A test of the NASA Solar Technology Application Readiness (NSTAR) electrostatic ion thruster resulted in 30,472 hours (roughly 3.5 years) of continuous thrust at maximum power. Post-test examination indicated the engine was not approaching failure. NSTAR operated for years on Dawn.

The NASA Evolutionary Xenon Thruster (NEXT) project operated continuously for more than 48,000 hours. The test was conducted in a high-vacuum test chamber. Over the course of the test, which lasted more than five and a half years, the engine consumed approximately 870 kilograms of xenon propellant. The total impulse generated would require over 10,000 kilograms of conventional rocket propellant for a similar application.

Hall-effect thruster life

Hall-effect thrusters suffer from strong erosion of the ceramic discharge chamber by impact of energetic ions: a test reported in 2010 showed erosion of around 1 mm per hundred hours of operation, though this is inconsistent with observed on-orbit lifetimes of a few thousand hours.

The Advanced Electric Propulsion System (AEPS) is expected to accumulate about 5,000 hours and the design aims to achieve a flight model that offers a half-life of at least 23,000 hours and a full life of about 50,000 hours.

Propellants

Ionization energy represents a large percentage of the energy needed to run ion drives. The ideal propellant is thus easy to ionize and has a high mass/ionization energy ratio. In addition, the propellant should not erode the thruster to any great degree, so as to permit long life, and should not contaminate the vehicle.

Many current designs use xenon gas, as it is easy to ionize, has a reasonably high atomic number, is inert and causes low erosion. However, xenon is globally in short supply and expensive (approximately $3,000 per kg in 2021).

Some older ion thruster designs used mercury propellant. However, mercury is toxic, tended to contaminate spacecraft, and was difficult to feed accurately. A modern commercial prototype may be using mercury successfully however, mercury was formally banned as a propellant in 2022 by the Minamata Convention on Mercury.

From 2018–2023, krypton was used to fuel the Hall-effect thrusters aboard Starlink internet satellites, in part due to its lower cost than conventional xenon propellant. Starlink V2-mini satellites have since switched to argon Hall-effect thrusters, providing higher specific impulse.

Other propellants, such as bismuth and iodine, show promise both for gridless designs such as Hall-effect thrusters, and gridded ion thrusters.

Iodine was used as a propellant for the first time in space, in the NPT30-I2 gridded ion thruster by ThrustMe, on board the Beihangkongshi-1 mission launched in November 2020, with an extensive report published a year later in the journal Nature. The CubeSat Ambipolar Thruster (CAT) used on the Mars Array of Ionospheric Research Satellites Using the CubeSat Ambipolar Thruster (MARS-CAT) mission also proposes to use solid iodine as the propellant to minimize storage volume.

VASIMR design (and other plasma-based engines) are theoretically able to use practically any material for propellant. However, in current tests the most practical propellant is argon, which is relatively abundant and inexpensive.

Energy efficiency

Plot of   instantaneous propulsive efficiency and   overall efficiency for a vehicle accelerating from rest as percentages of the engine efficiency. Note that peak vehicle efficiency occurs at about 1.6 times exhaust velocity.

Ion thruster efficiency is the kinetic energy of the exhaust jet emitted per second divided by the electrical power into the device.

Overall system energy efficiency is determined by the propulsive efficiency, which depends on vehicle speed and exhaust speed. Some thrusters can vary exhaust speed in operation, but all can be designed with different exhaust speeds. At the lower end of specific impulse, Isp, the overall efficiency drops because ionization takes up a larger percentage energy and at the high end propulsive efficiency is reduced.

Optimal efficiencies and exhaust velocities for any given mission can be calculated to give minimum overall cost.

Missions

Ion thrusters have many in-space propulsion applications. The best applications make use of the long mission interval when significant thrust is not needed. Examples of this include orbit transfers, attitude adjustments, drag compensation for low Earth orbits, fine adjustments for scientific missions and cargo transport between propellant depots, e.g., for chemical fuels. Ion thrusters can also be used for interplanetary and deep-space missions where acceleration rates are not crucial. Ion thrusters are seen as the best solution for these missions, as they require high change in velocity but do not require rapid acceleration. Continuous thrust over long durations can reach high velocities while consuming far less propellant than traditional chemical rockets.

Demonstration vehicles

SERT

Ion propulsion systems were first demonstrated in space by the NASA Lewis (now Glenn Research Center) missions Space Electric Rocket Test (SERT)-1 and SERT-2A. A SERT-1 suborbital flight was launched on 20 July 1964, and successfully proved that the technology operated as predicted in space. These were electrostatic ion thrusters using mercury and caesium as the reaction mass. SERT-2A, launched on 4 February 1970, verified the operation of two mercury ion engines for thousands of running hours.

Operational missions

Ion thrusters are routinely used for station-keeping on commercial and military communication satellites in geosynchronous orbit. The Soviet Union pioneered this field, using stationary plasma thrusters (SPTs) on satellites starting in the early 1970s.

Two geostationary satellites (ESA's Artemis in 2001–2003 and the United States military's AEHF-1 in 2010–2012) used the ion thruster to change orbit after the chemical-propellant engine failed. Boeing began using ion thrusters for station-keeping in 1997 and planned in 2013–2014 to offer a variant on their 702 platform, with no chemical engine and ion thrusters for orbit raising; this permits a significantly lower launch mass for a given satellite capability. AEHF-2 used a chemical engine to raise perigee to 16,330 km (10,150 mi) and proceeded to geosynchronous orbit using electric propulsion.

In Earth orbit

Tiangong space station

China's Tiangong space station is fitted with ion thrusters. Its Tianhe core module is propelled by both chemical thrusters and four Hall-effect thrusters, which are used to adjust and maintain the station's orbit. The development of the Hall-effect thrusters is considered a sensitive topic in China, with scientists "working to improve the technology without attracting attention". Hall-effect thrusters are created with crewed mission safety in mind with effort to prevent erosion and damage caused by the accelerated ion particles. A magnetic field and specially designed ceramic shield was created to repel damaging particles and maintain integrity of the thrusters. According to the Chinese Academy of Sciences, the ion drive used on Tiangong has burned continuously for 8,240 hours without a glitch, indicating their suitability for the Chinese space station's designated 15-year lifespan. This is the world's first Hall thruster on a human-rated mission.

Starlink

SpaceX's Starlink satellite constellation uses Hall-effect thrusters powered by krypton or argon to raise orbit, perform maneuvers, and de-orbit at the end of their use.

GOCE

ESA's Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) was launched on 16 March 2009. It used ion propulsion throughout its twenty-month mission to combat the air-drag it experienced in its low orbit (altitude of 255 kilometres) before intentionally deorbiting on 11 November 2013.

In deep space

Deep Space 1

NASA developed the NSTAR ion engine for use in interplanetary science missions beginning in the late 1990s. It was space-tested in the space probe Deep Space 1, launched in 1998. This was the first use of electric propulsion as the interplanetary propulsion system on a science mission. Based on the NASA design criteria, Hughes Research Labs developed the Xenon Ion Propulsion System (XIPS) for performing station keeping on geosynchronous satellites. Hughes (EDD) manufactured the NSTAR thruster used on the spacecraft.

Hayabusa and Hayabusa2

The Japanese Aerospace Exploration Agency's Hayabusa space probe was launched in 2003 and rendezvoused with the asteroid 25143 Itokawa. It was powered by four xenon ion engines, which used microwave electron cyclotron resonance to ionize the propellant and an erosion-resistant carbon/carbon-composite material for its acceleration grid. Although the ion engines on Hayabusa experienced technical difficulties, in-flight reconfiguration allowed one of the four engines to be repaired and allowed the mission to successfully return to Earth.

Hayabusa2, launched in 2014, was based on Hayabusa. It also used ion thrusters.

Smart 1

The European Space Agency's satellite SMART-1 launched in 2003 using a Snecma PPS-1350-G Hall thruster to get from GTO to lunar orbit. This satellite completed its mission on 3 September 2006, in a controlled collision on the Moon's surface, after a trajectory deviation so scientists could see the 3-meter crater the impact created on the visible side of the Moon.

Dawn

Dawn launched on 27 September 2007, to explore the asteroid Vesta and the dwarf planet Ceres. It used three Deep Space 1 heritage xenon ion thrusters (firing one at a time). Dawn's ion drive is capable of accelerating from 0 to 97 km/h (60 mph) in 4 days of continuous firing. The mission ended on 1 November 2018, when the spacecraft ran out of hydrazine chemical propellant for its attitude thrusters.

LISA Pathfinder

LISA Pathfinder is an ESA spacecraft launched in 2015 to orbit the Sun-Earth L1 point. It does not use ion thrusters as its primary propulsion system, but uses both colloid thrusters and FEEP for precise attitude control – the low thrusts of these propulsion devices make it possible to move the spacecraft incremental distances accurately. It is a test for the LISA mission. The mission ended on 30 December 2017.

BepiColombo

ESA's BepiColombo mission was launched to Mercury on 20 October 2018. It uses ion thrusters in combination with swing-bys to get to Mercury, where a chemical rocket will complete orbit insertion.

Double Asteroid Redirection Test

NASA's Double Asteroid Redirection Test (DART) was launched in 2021 and operated its NEXT-C xenon ion thruster for about 1,000 hours to reach the target asteroid on 28 September 2022.

Psyche

NASA's Psyche spacecraft was launched in 2023 and is operating its SPT-140 xenon ion thruster in order to reach asteroid 16 Psyche in August 2029.

Proposed missions

International Space Station

As of March 2011, a future launch of an Ad Astra VF-200 200 kW VASIMR electromagnetic thruster was under consideration for testing on the International Space Station (ISS). However, in 2015, NASA ended plans for flying the VF-200 to the ISS. A NASA spokesperson stated that the ISS "was not an ideal demonstration platform for the desired performance level of the engines". Ad Astra stated that tests of a VASIMR thruster on the ISS would remain an option after a future in-space demonstration.

The VF-200 would have been a flight version of the VX-200. Since the available power from the ISS is less than 200 kW, the ISS VASIMR would have included a trickle-charged battery system allowing for 15 minutes pulses of thrust. The ISS orbits at a relatively low altitude and experiences fairly high levels of atmospheric drag, requiring periodic altitude boosts – a high-efficiency engine (high specific impulse) for station-keeping would be valuable; theoretically VASIMR reboosting could cut fuel cost from the current US$210 million annually to one-twentieth. VASIMR could in theory use as little as 300 kg of argon gas for ISS station-keeping instead of 7500 kg of chemical fuel – the high exhaust velocity (high specific impulse) would achieve the same acceleration with a smaller amount of propellant, compared to chemical propulsion with its lower exhaust velocity needing more fuel. Hydrogen is generated by the ISS as a by-product and is vented into space.

NASA previously worked on a 50 kW Hall-effect thruster for the ISS, but work was stopped in 2005.

Lunar Gateway

The Power and Propulsion Element (PPE) is a module on the Lunar Gateway that provides power generation and propulsion capabilities. It is targeting launch on a commercial vehicle in January 2024. It would probably use the 50 kW Advanced Electric Propulsion System (AEPS) under development at NASA Glenn Research Center and Aerojet Rocketdyne.

MARS-CAT

The MARS-CAT (Mars Array of ionospheric Research Satellites using the CubeSat Ambipolar Thruster) mission is a two 6U CubeSat concept mission to study Mars' ionosphere. The mission would investigate its plasma and magnetic structure, including transient plasma structures, magnetic field structure, magnetic activity and correlation with solar wind drivers. The CAT thruster is now called the RF thruster and manufactured by Phase Four.

Interstellar missions

Geoffrey A. Landis proposed using an ion thruster powered by a space-based laser, in conjunction with a lightsail, to propel an interstellar probe.

Popular culture

  • The idea of an ion engine first appeared in Donald W. Horner's By Aeroplane to the Sun: Being the Adventures of a Daring Aviator and his Friends (1910).
  • Ion propulsion is the main thrust source of the spaceship Kosmokrator in the East German/Polish science fiction film Der Schweigende Stern (1960). Minute 28:10.
  • In the 1968 Star Trek episode "Spock's Brain", Scotty is repeatedly impressed by a civilization's use of ion power.
  • The popular Imperial TIE Fighter spacecraft from the Star Wars franchise are propelled by twin ion engines, hence the name.
  • Ion propulsion is used by the Hermes spacecraft in the Andy Weir novel The Martian to transfer crew between Earth and Mars.

See also

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