Editing Magnetoplasmadynamic thruster (section)

== 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>