Editing Ion thruster (section)

== 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.<ref>Sutton & Biblarz, ''Rocket Propulsion Elements'', 7th edition.</ref>

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).<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>

Some older ion thruster designs used [[mercury (element)|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<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 [[Minamata Convention on Mercury]].<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=[[IEEE Spectrum]] |date=19 April 2022 |language=en}}</ref>

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.<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 [[argon]] 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 [[bismuth]] and [[iodine]], 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>

[[Iodine]] was used as a propellant for the first time in space, in the [[NPT30|NPT30-I2]] [[gridded ion thruster]] by [[ThrustMe]], 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 ''[[Nature (journal)|Nature]]''.<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"/>

[[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.