Magnetoplasmadynamic thruster

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An MPD thruster during test firing

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 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. 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.[1]

According to

exhaust velocity 15–60 kilometers per second, thrust 2.5–25 newtons and efficiency 40–60 percent. However, additional research has shown that exhaust velocities can exceed 100 kilometers per second.[2][3]

One potential application of magnetoplasmadynamic thrusters is the main propulsion engine for heavy cargo and piloted space vehicles (example engine for human mission to Mars).[2][3]

Advantages

In theory, MPD thrusters could produce extremely high specific impulses (Isp) with an exhaust velocity of up to and beyond 110000 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) (45 lbF ), by far the highest for any form of electric propulsion, and nearly as high as many interplanetary chemical rockets.[citation needed] 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.[4]

Development

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 generators 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

TOPAZ.[7]

Plans to develop a megawatt-scale nuclear reactor for the use aboard a crewed spaceship were announced in 2009 by Russian nuclear

Roskosmos,[9] and confirmed by Russian President Dmitry Medvedev in his November 2009 address to the Federal Assembly.[10]

Another plan, proposed by

bandgap of 1.43 eV to each other produces an estimated conversion efficiency of 59% and a predicted power density of up to 540 kW/m2. This would be sufficient to power a MPD upper stage, perhaps to lift satellites from LEO to GEO.[11]

Another problem with MPD technology has been the degradation of cathodes due to evaporation driven by high current densities (in excess of 100 A/cm2). 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.[12]

Research

Research on MPD thrusters has been carried out in the US, the former

RKK Energiya, National Aerospace University, Kharkiv Aviation Institute, Institute of Space Systems of the University of Stuttgart, 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 Isp = 4665 s and 2.75 N of thrust.[13]

See also

References

  1. ^ "PROPELLANTS". history.nasa.gov. Retrieved 2022-11-05.
  2. ^ a b "Choueiri, Edgar Y. (2009). New dawn of electric rocket. Next-Generation Thruster". Archived from the original on 2016-10-18. Retrieved 2016-10-18.
  3. ^
    doi:10.1038/scientificamerican0209-58
  4. ^ Kurchatov Institute with Roskosmos renewed the work over developing nuclear energy sources for interplanetary flights, June 2009, (in Russian
  5. ^ Global Communications Satellite Using Nuclear Power Archived 2008-07-09 at the Wayback Machine
  6. ^ "The USSR/Russia – RORSAT, Topaz, And RTG".
  7. ^ "TOPAZ".
  8. ^ Kurchatov Institute with Roskosmos renewed the work over developing nuclear energy sources for interplanetary flights, June 2009, (in Russian)
  9. RIAN
    , October 2009, (in Russian)
  10. ^ "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 Address to the Federal Assembly[permanent dead link].
  11. ^ Edwards, Bradley C. Westling, Eric A. The Space Elevator: A revolutionary Earth-to-space transportation system. 2002, 2003 BC Edwards, Houston, TX.
  12. S2CID 1405279
    .
  13. ^ Boxberger, Adam; Behnke, Alexander; Herdrich, Georg (2019). "Current Advances in Optimization of Operative Regimes of Steady State Applied Field MPD Thrusters" (PDF). International Electric Propulsion Conference (IEPC). IEPC-2019-585. Archived (PDF) from the original on 2022-10-09.

External links

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