An MPD thruster during test firing

The Magnetoplasmadynamic (MPD) thruster (MPDT) is a form of electric propulsion (a subdivision of spacecraft propulsion) which uses the Lorentz force (a force resulting from the interaction between a magnetic field and an electric current) to generate thrust. It is sometimes referred to as Lorentz Force Accelerator (LFA) or (mostly in Japan) MPD arcjet. Generally, a gaseous fuel is ionized and fed into an acceleration chamber, where the magnetic and electrical 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. As with other electric propulsion variations, both specific impulse and thrust increase with power input. 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, hydrazine, and lithium have been used, with lithium generally being the best performer. MPD thrust-small, blurry From http://powerweb. ... MPD thrust-small, blurry From http://powerweb. ... This article or section does not cite its references or sources. ... A remote camera captures a close-up view of a Space Shuttle Main Engine during a test firing at the John C. Stennis Space Center in Hancock County, Mississippi Propulsion means to add speed or acceleration to an object, by an engine or other similar device. ... In physics, the Lorentz force is the force exerted on a charged particle in an electromagnetic field. ... ... In physics, the Lorentz force is the force exerted on a charged particle in an electromagnetic field. ... Specific impulse (usually abbreviated Isp) is a way to describe the efficiency of rocket and jet engines. ... Thrust is a reaction force described quantitatively by Newtons Second and Third Laws. ... General Name, Symbol, Number xenon, Xe, 54 Chemical series noble gases Group, Period, Block 18, 5, p Appearance colorless Standard atomic weight 131. ... General Name, Symbol, Number neon, Ne, 10 Chemical series noble gases Group, Period, Block 18, 2, p Appearance colorless Standard atomic weight 20. ... General Name, Symbol, Number argon, Ar, 18 Chemical series noble gases Group, Period, Block 18, 3, p Appearance colorless Standard atomic weight 39. ... Hydrazine is the chemical compound with formula N2H4. ... General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/grey Standard atomic weight 6. ...

Advantages

In theory, MPD thrusters could produce extremely high specific impulses (I_sp) of up to and beyond 11,000 s (110 km/s exhaust velocity), triple the value of current xenon-based ion thrusters, and about 20 times better than liquid rockets. MPD technology also has the potential for thrust levels of up to 200 newtons (N) (45 lbf), by far the highest for any form of electric propulsion, and nearly as high as many interplanetary chemical rockets. 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. Specific impulse (usually abbreviated Isp) is a way to describe the efficiency of rocket and jet engines. ... General In general physics delta-v is simply the change in velocity. ...

Problems with MPDT

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; namely, extreme power requirements on the order of megawatts (MW) are required for optimum performance. Current interplanetary spacecraft power systems (such as radioisotope thermoelectric generators (RTGs)) and solar arrays are incapable of producing these power levels. Even NASA's Project Prometheus reactor is expected to generate power only in the hundreds of kilowatts range. While this would be a major leap in spacecraft power systems, it is still insufficient by an order of magnitude. Self-field MPD thruster-CGI illustration From http://www. ... Self-field MPD thruster-CGI illustration From http://www. ... // A radioisotope thermoelectric generator (RTG) is a simple electrical generator which obtains its power from radioactive decay. ... This article does not cite its references or sources. ... Nuclear reactors may be used to power ion engines such as this one used on Deep Space 1 Project Prometheus was established in 2003 by NASA to develop nuclear-powered systems for long-duration space missions. ...

Other problems with MPD technology include the degradation of cathodes which generate the magnetic field. As a result, MPD thrusters have not yet been used as propulsion on any spacecraft.

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, University of Stuttgart, ISAS, Centrospazio, Alta S.p.A.,Osaka University, University of Southern California, Princeton University's Electric Propulsion and Plasma Dynamics Lab (EEPDyL) (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. S.P. Korolev Rocket and Space Corporation Energia (also known as RKK Energiya) is a Russian manufacturer of spacecraft and space station components. ... The Universität Stuttgart is the University of Stuttgart. ... The Japan Aerospace eXploration Agency (JAXA) is Japans aerospace agency. ... Osaka University (大阪大学 ÅŒsaka Daigaku; abbreviated to 阪大 Handai) is a public coeducational research university in Suita, Osaka, Japan. ... Doheny Library. ... Princeton University is a private coeducational research university located in Princeton, New Jersey, in the United States of America. ... The National Aeronautics and Space Administration (NASA) is an agency of the United States federal government, responsible for the nations public space program. ... For the singer/songwriter, see Jon Peter Lewis. ... Aerial View of Glenn Research Center at Lewis Field The Glenn Research Center is a NASA center, located in Cleveland, Ohio between Cleveland Hopkins International Airport and the Rocky River Reservation (part of the Cleveland Metroparks). ...

A Japanese MPD test, the EPEX (Electric Propulsion EXperiment) was deployed on shuttle mission STS-72. To date, is is the only operational MPD thruster to have flown in space. STS-72 is a Space Shuttle program mission. ...

See also

• Hall effect thruster
• Magnetic sail
• Pulsed plasma thruster
• Ion thruster
• Spacecraft propulsion

2 kW Laboratory Hall Thruster in operation at the Princeton Plasma Physics Laboratory A Hall effect thruster is a type of ion thruster in which the propellant is accelerated by an electric field in a plasma discharge with a radial magnetic field. ... A magnetic sail or magsail is a proposed method of spacecraft propulsion. ... Pulsed plasma thrusters use an arc of electric current adjacent to a solid propellant (almost always teflon), to produce a quick and repeatable burst of impulse. ... This article does not cite any references or sources. ... A remote camera captures a close-up view of a Space Shuttle Main Engine during a test firing at the John C. Stennis Space Center in Hancock County, Mississippi Propulsion means to add speed or acceleration to an object, by an engine or other similar device. ...

External links

• Search engine for a large archive of technical papers on MPD thruster research