lecture13_14

lecture13_14 - 16.522, Space Propulsion Prof. Manuel...

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16.522, Space Propulsion Lecture 13- 14 Prof. Manuel Martinez-Sanchez Page 1 of 25 16.522, Space Propulsion Prof. Manuel Martinez-Sanchez Lecture 13- 14: Electrostatic Thrusters Outline Page No. 1 Introduction…………………………………………………………………………………… 2 2 Principles of Operation…………………………………………………………………. . 2 3 Ion Extraction and Acceleration……………………………………………………. 3 4 Ion Production………………………………………………………………………………. 9 4.1 Physical Processes in Electron Bombardment Ionization Chambers………………………………. 9 4.2 Nature of the Losses………………………………………………………. . 10 4.3 Electron Diffusion and Confinement………………………………. . 11 4.4 Particle Production Rates…………………………………………………. 13 4.5 Lumped Parameter Performance Model…………………………… 15 5 Propellant Selection ………………………………….…………………………………. . 15 References………………………. 16
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16.522, Space Propulsion Lecture 13- 14 Prof. Manuel Martinez-Sanchez Page 2 of 25 Lecture 13- 14 Electrostatic Thrusters 1 Introduction Electrostatic thrusters (“ion engines”) are the best developed type of electric propulsion device, dating in conception to the ‘50’s, (1) and having been demonstrated in space in 1964 on a suborbital flight of the SERT I spacecraft (2) . The early history and concepts are well documented (1),(3) , and evolved through progressive refinements of various types of ion beam sources used in Physics laboratories, the improvements being essentially dictated by the needs for high efficiency, low mass and long life for these sources to be used in space. Of the various configurations discussed for example in Ref. 3 (ca. 1973), only the electron bombardment noble gas type, plus (in Europe) the radio-frequency ionized thruster (4) and (in Japan) the Electron Cyclotron Resonance thruster, have survived. Other interesting concepts, such as Cesium Contact thrusters and duo-plasmatron sources have been largely abandoned, and one new special device, the Field Emission Electrostatic (5) thruster has been added to the roster. The electron bombardment thruster itself has evolved in the same time interval from relatively deep cylindrical shapes with uniform magnetic fields produced by external coils and with simple thermoionic cathodes, to shallow geometrics using sharply nonuniform magnetic field configurations, produced by permanent magnets, and with hollow cathode plasma bridges used as cathode and neutralizer. Where a typical ion production cost was quoted in Ref. (3) as 400- 600 eV for Hg at 80% mass utilization fraction, recent work with ring-cusp thrusters has yielded for example a cost of 116 eV in Xenon at the same utilization (6) . Such reductions make it now possible to design for efficient operation (above 80%) with
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lecture13_14 - 16.522, Space Propulsion Prof. Manuel...

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