View source for Magnetoplasmadynamic thruster

{{short description|Form of electrically powered spacecraft propulsion}}
[[Image:MPD plume.jpg|thumb|right|An MPD thruster during test firing]]
[[File:Plasma propulsion engine.webp|thumb|3D sketch of an [[electromagnetic propulsion]] [[Plasma propulsion engine|fusion plasma]] thruster]]

A '''magnetoplasmadynamic''' ('''MPD''') '''thruster''' ('''MPDT''') is a form of [[electrically powered spacecraft propulsion]] which uses the [[Lorentz force]] (the force on a charged particle by an electromagnetic field) to generate thrust. It is sometimes referred to as a Lorentz Force Accelerator (LFA) or (mostly in Japan) MPD [[arcjet]].

Generally, a gaseous material is [[ionized]] and fed into an acceleration chamber, where the magnetic and electric fields are created using a power source. The particles are then propelled by the Lorentz force resulting from the interaction between the current flowing through the plasma and the magnetic field (which is either externally applied or induced by the current) out through the exhaust chamber. Unlike chemical propulsion, there is no combustion of fuel.{{Citation needed|date=February 2025}} As with other electric propulsion variations, both [[specific impulse]] and [[thrust]] increase with power input, while thrust per watt drops.

There are two main types of MPD thrusters, applied-field and self-field. Applied-field thrusters have magnetic rings surrounding the exhaust chamber to produce the magnetic field, while self-field thrusters have a cathode extending through the middle of the chamber. Applied fields are necessary at lower power levels, where self-field configurations are too weak. Various propellants such as [[xenon]], [[neon]], [[argon]], [[hydrogen]], [[hydrazine]], and [[lithium]] have been used, with lithium generally being the best performer.<ref>{{Cite web |title=PROPELLANTS |url=https://history.nasa.gov/conghand/propelnt.htm |access-date=2022-11-05 |website=history.nasa.gov}}</ref>

According to [[Edgar Choueiri]] magnetoplasmadynamic thrusters have input [[Power (physics)|power]] 100–500 kilowatts, [[exhaust velocity]] 15–60 kilometers per second, [[thrust]] 2.5–25 [[newton (unit)|newtons]] and [[efficiency]] 40–60 percent. However, additional research has shown that exhaust velocities can exceed 100 kilometers per second.<ref name="alfven.princeton.edu">{{cite web| url = http://alfven.princeton.edu/publications/choueiri-sciam-2009| title = Choueiri, Edgar Y. (2009). New dawn of electric rocket. Next-Generation Thruster| access-date = 2016-10-18| archive-date = 2016-10-18| archive-url = https://web.archive.org/web/20161018201525/http://alfven.princeton.edu/publications/choueiri-sciam-2009| url-status = dead}}</ref><ref name="Choueiri">Choueiri, Edgar Y. (2009) [http://www.nature.com/scientificamerican/journal/v300/n2/full/scientificamerican0209-58.html New dawn of electric rocket] ''[[Scientific American]]'' 300, 58–65 {{doi|10.1038/scientificamerican0209-58}}</ref>

One potential application of magnetoplasmadynamic thrusters is the main propulsion engine for heavy cargo and piloted space vehicles (example engine <math>a^2</math> for [[human missions to Mars]]).<ref name="alfven.princeton.edu"/><ref name="Choueiri"/>

== Advantages ==
In theory, MPD thrusters could produce extremely high specific impulses (I<sub>sp</sub>) with an exhaust velocity of up to and beyond {{val|110000|u=m/s}}, triple the value of current xenon-based ion thrusters, and about 25 times better than liquid rockets. MPD technology also has the potential for thrust levels of up to 200 newtons (N) ({{val|45|u=lbf}}), by far the highest for any form of electric propulsion, and nearly as high as many interplanetary chemical rockets.{{citation needed|reason=Cited article does not mention 200N figure|date=March 2015}} This would allow use of electric propulsion on missions which require quick [[delta-v]] maneuvers (such as capturing into orbit around another planet), but with many times greater fuel efficiency.<ref>Kurchatov Institute with Roskosmos renewed the work over developing nuclear energy sources for interplanetary flights, June 2009, (in Russian</ref>

== Development ==
[[Image:Self-field MPD thruster-CGI illustration.jpeg|thumb|CGI rendering of Princeton University's lithium-fed self-field MPD thruster (from Popular Mechanics magazine)]]MPD thruster technology has been explored academically, but commercial interest has been low due to several remaining problems. One small problem is that power requirements on the order of hundreds of kilowatts are required for optimum performance. Current interplanetary spacecraft power systems (such as [[radioisotope thermoelectric generator]]s and solar arrays) are incapable of producing that much power. NASA's [[Project Prometheus]] reactor was expected to generate power in the hundreds of kilowatts range but was discontinued in 2005.

A project to produce a space-going nuclear reactor designed to generate 600 kilowatts of electrical power began in 1963 and ran for most of the 1960s in the [[USSR]]. It was to power a communication satellite which was in the end not approved.<ref>[http://www.astronautix.com/craft/glopower.htm Global Communications Satellite Using Nuclear Power] {{webarchive|url=https://web.archive.org/web/20080709001934/http://astronautix.com/craft/glopower.htm |date=2008-07-09 }}</ref> Nuclear reactors supplying kilowatts of electrical power (of the order of ten times more than current RTG power supplies) have been orbited by the USSR: [[RORSAT]];<ref>{{cite web| url = http://www.space4peace.org/ianus/npsm2.htm#2_2_1| title = The USSR/Russia – RORSAT, Topaz, And RTG| access-date = 2008-05-28| archive-date = 2012-03-05| archive-url = https://web.archive.org/web/20120305144654/http://www.space4peace.org/ianus/npsm2.htm#2_2_1| url-status = dead}}</ref> and [[Topaz Nuclear Reactor|TOPAZ]].<ref>{{cite web| url = http://www.space4peace.org/ianus/npsm2.htm#2_2_2| title = TOPAZ| access-date = 2008-05-28| archive-date = 2012-03-05| archive-url = https://web.archive.org/web/20120305144654/http://www.space4peace.org/ianus/npsm2.htm#2_2_2| url-status = dead}}</ref>

Plans to develop a megawatt-scale nuclear reactor for the use aboard a crewed spaceship were announced in 2009 by Russian nuclear [[Kurchatov Institute]],<ref>[http://www.atomic-energy.ru/node/4440 Kurchatov Institute with Roskosmos renewed the work over developing nuclear energy sources for interplanetary flights], June 2009, (in Russian)</ref> national space agency [[Roskosmos]],<ref>[http://www.rian.ru/science/20091028/191007002.html Roskosmos prepared a project of a crewed spaceship with a nuclear engine], [[RIAN]], October 2009, (in Russian)</ref> and confirmed by Russian President [[Dmitry Medvedev]] in his November 2009 address to the [[Federal Assembly (Russia)|Federal Assembly]].<ref>"Developments in the nuclear field will be actively applied ... also for creating propellant devices capable of ensuring space flights even to other planets", from the November 2009 [http://eng.kremlin.ru/speeches/2009/11/12/1321_type70029type82912_222702.shtml Address to the Federal Assembly]{{dead link|date=November 2017 |bot=InternetArchiveBot |fix-attempted=yes }}.</ref>

Another plan, proposed by [[Bradley C. Edwards]], is to beam power from the ground. This plan utilizes 5 200&nbsp;kW [[free electron laser]]s at 0.84 micrometres with [[adaptive optics]] on the ground to beam power to the MPD-powered spacecraft, where it is converted to electricity by [[GaAs]] [[photovoltaic panels]]. The tuning of the laser wavelength of 0.840 micrometres ({{val|1.48|u=eV}} per photon) and the photovoltaic panel [[bandgap]] of {{val|1.43|u=eV}} to each other produces an estimated conversion efficiency of 59% and a predicted power density of up to {{val|540|u=kW/m<sup>2</sup>}}. This would be sufficient to power a MPD upper stage, perhaps to lift satellites from LEO to GEO.<ref>Edwards, Bradley C. Westling, Eric A. ''The Space Elevator: A revolutionary Earth-to-space transportation system.'' 2002, 2003 BC Edwards, Houston, TX.</ref>

Another problem with MPD technology has been the degradation of cathodes due to evaporation driven by high current densities (in excess of {{val|100|u=A/cm<sup>2</sup>}}). The use of lithium and barium propellant mixtures and multi-channel hollow cathodes has been shown in the laboratory to be a promising solution for the cathode erosion problem.<ref>{{cite journal |last1=Sankaran |first1=K. |last2=Cassady |first2=L. |last3=Kodys |first3=A.D. |last4=Choueiri |first4=E.Y. |title=A Survey of Propulsion Options for Cargo and Piloted Missions to Mars |journal=Annals of the New York Academy of Sciences |date=2015 |volume=1017 |issue=1 |pages=450–467|doi=10.1196/annals.1311.027 |pmid=15220162 |s2cid=1405279 }}</ref>

== Research ==
Research on MPD thrusters has been carried out in the US, the former [[Soviet Union]], Japan, Germany, and Italy. Experimental prototypes were first flown on Soviet spacecraft and, most recently, in 1996, on the Japanese [[Space Flyer Unit]], which demonstrated the successful operation of a quasi-steady pulsed MPD thruster in space. Research at [[Moscow Aviation Institute]], [[RKK Energiya]], [[:ru:Национальный аэрокосмический университет имени Н. Е. Жуковского|National Aerospace University, Kharkiv Aviation Institute]], Institute of Space Systems of the [[University of Stuttgart]], [[Institute of Space and Astronautical Science|ISAS]], [[Centrospazio]], [[Alta S.p.A.]], [[Osaka University]], [[University of Southern California]], [[Princeton University]]'s [[Electric Propulsion and Plasma Dynamics Lab]] (EPPDyL) (where MPD thruster research has continued uninterrupted since 1967), and  [[NASA]] centers ([[Jet Propulsion Laboratory]] and [[Glenn Research Center]]), has resolved many problems related to the performance, stability and lifetime of MPD thrusters.

An MPD thruster was tested on board the Japanese Space Flyer Unit as part of EPEX (Electric Propulsion Experiment) that was launched March 18, 1995 and retrieved by  space shuttle mission [[STS-72]] January 20, 1996. To date, it is the only operational MPD thruster to have flown in space as a propulsion system. Experimental prototypes were first flown on Soviet spacecraft.

The applied-field MPD thruster in development at the Institute of Space Systems of the [[University of Stuttgart]] reached a thruster efficiency of 61.99% in 2019, corresponding to a specific impulse of I<sub>sp</sub> = 4665 s and 2.75 N of thrust.<ref>{{cite journal|last1=Boxberger|first1=Adam|last2=Behnke|first2=Alexander|last3=Herdrich|first3=Georg|title=Current Advances in Optimization of Operative Regimes of Steady State Applied Field MPD Thrusters|journal=International Electric Propulsion Conference (IEPC)|volume=IEPC-2019-585|date=2019|url=http://electricrocket.org/2019/585.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://electricrocket.org/2019/585.pdf |archive-date=2022-10-09 |url-status=live}}</ref>

== See also ==
* [[Hall effect thruster]]
* [[Ion thruster]]
* [[Magnetohydrodynamics]]
* [[Magnetic sail]]
* [[Pulsed plasma thruster]]
* [[Solar panels on spacecraft]]
* [[Spacecraft propulsion]]
* [[VASIMR]]
* [[Yttrium barium copper oxide]] (YBCO) - [[High-temperature superconductivity|High-temperature superconductor]]

== References ==
<references/>

==External links ==
* [http://alfven.princeton.edu/publications/choueiri-sciam-2009 Choueiri, Edgar Y. (2009). New dawn of electric rocket. Next-Generation Thruster] {{Webarchive|url=https://web.archive.org/web/20161018201525/http://alfven.princeton.edu/publications/choueiri-sciam-2009 |date=2016-10-18 }}
* [http://alfven.princeton.edu/publications Search engine for a large archive of technical papers on MPD thruster research]
* [https://web.archive.org/web/20130518011639/http://www.alta-space.com/index.php?page=magnetoplasmadynamic-prop MPD - MagnetoPlasmaDynamic Propulsion]

{{spacecraft propulsion}}

[[Category:Spacecraft propulsion]]
[[Category:Magnetic propulsion devices]]