High Specific Impulse Thermal Arc Jet Thrustor Technology. Part II. Performance of Hall Arc Jets with Lithium Propellant.

摘要

The objective of this program is to develop efficient electric arcjet thrustors for high specific impulse and long life. Power levels between 10 and 50 kW, specific impulse between 1500 and 6500 seconds are sought with power input-to-thrust ratios less than 190 kW/lb for durations up to 100 hours. The approach combines analytical and experimental research to investigate and develop thrustors using lithium and other alkali metals as propellants. The present approach has relied predominantly on Hall current interactions with an applied magnetic field. Thrustors of this type have been designated ALPHA (Alkali Plasma Hall Accelerator). During the second phase of the program the following advances have been made. The effects of the testing environment upon the measured performance have been investigated. Two major modifications to the design of the engine have been made: (1) the cylindrical cathode has been replaced by a buffered cathode with separate propellant injection, thereby increasing the thrust per unit current, decreasing the cathode power loss per unit current, increasing the insulator lifetime, and helping to separate the ionization and acceleration processes; (2) the region of strong magnetic field has been extended downstream by placin g a second coil on the engine, reducing magnet power requirement by a factor of almost five. Thrust balance has been improved. A new feed system has been designed to provide continuous operation for periods over 100 hours at levels around 10 mg/sec. A theory has been developed for the operation of ALPHA. Calculations based on this theory indicate that significant improvements can be made over present performance. (Author)