Editing Ion thruster (section)

== General working principle ==
Ion thrusters use beams of [[ion]]s (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 [[electric charge|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 (physics)|power]] required compared to [[chemical rocket]]s. Ion thrusters are therefore able to achieve high [[specific impulse]]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 [[electrostatics|electrostatic]] or [[electromagnetism|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 panel]]s. However, for sufficiently large distances from the sun, [[Nuclear power in space|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.<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. Defining <math>1g = 9.81\; \mathrm{m/s^2}</math>, the [[gravity of Earth|standard gravitational acceleration of Earth]], and noting that <math>F = ma \implies a = F/m</math>, this can be analyzed. An [[NASA Solar Technology Application Readiness|NSTAR]] thruster producing a thrust force of 92&nbsp;mN<ref name=ns20070928/> will accelerate a satellite with a mass of 1{{nbsp}}[[metric ton|ton]] 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.

<math display="block">F = 2 \frac{\eta P}{g I_\text{sp}}</math>
Where:
* ''F'' is the thrust force in N,
* ''η'' is the [[efficiency]]
* ''P'' is the electrical power used by the thruster in W, and
* ''I''<sub>sp</sub> 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.<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 [[thrust]], are considerably inferior to the prototypes described in literature,<ref name="autogenerated1"/><ref name="Choueiri"/> technical capabilities are limited by the [[space charge]] created by ions. This limits the thrust density ([[force]] per cross-sectional [[area]] 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 [[chemical rocket]]s, but achieve high [[specific impulse]], or propellant mass efficiency, by accelerating the exhaust to high speed. The [[power (physics)|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 (physics)|impulse]] by the small amount of [[energy]] 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 [[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 engine]]s, and [[Carnot's theorem (thermodynamics)|Carnot's theorem]] limits the exhaust velocity.