- Pulsed plasma thruster
Pulsed plasma thrusters are a method of
spacecraft propulsionwhich use an arc of electric current adjacent to a solid propellant, to produce a quick and repeatable burst of impulse. PPTs are excellent for attitude control, and for main propulsion on particularly small spacecraftwith a surplus of electricity (those in the hundred-kilogram or less category). However they are also one of the least efficient electric propulsion systems, with a thrust efficiency of less than 10%.
PPTs have much higher
exhaust velocitythan chemical propulsion engines. According to the Tsiolkovsky equationthis results in proportionally higher final velocity of propelled craft. The principle of operation is acceleration of ionsin a strong electric fieldto the velocities of the order of hundreds km/s - which is much higher than the thermal velocityof chemical engines. Chemical propulsion engines with their limited by rate of chemical reaction exhaust velocity (which is in the range of 2-3 km/s) become exponentially ineffective (see Tsiolkovskyequation) to achieve high interplanetary speeds (which in Solar system is in 20-70 km/s range).
Pulsed plasma thrusters were the first electric thrusters to be deployed in space, used for attitude control on the Soviet probes
Zond 2, from parking at Earth orbit to Mars on November 30, 1964, and Zond 3in 1965. The active gas used in the Soviet plasma propulsion engines was argonand helium. Soviet engineers subsequently returned to the use of high-pressure nitrogen jets.
Pulsed plasma thrusters were flown in November, 2000 as a flight experiment on the NASA Goddard Space Flight Center EO-1 spacecraft. The thrusters successfully demonstrated the ability to perform roll control on the spacecraft and also demonstrated that the electromagnetic interference from the pulsed plasma did not affect other spacecraft systems. These experiments used Teflon as the propellant.
Hall effect thruster
* [http://alfven.princeton.edu/papers/tem_jpc2002abstext.htm Design of a High-energy, Two-stage Pulsed Plasma Thrust]
* [http://eo1.gsfc.nasa.gov/miscPages/TechForumPres/25-PPT.pdf EO1 Pulsed Plasma Thruster]
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