PROPELLANT UTILIZATION IN HALL THRUSTERS

Fuel-optimal trajectories for electrically propelled spacecraft requir e a varying thrust trajectory, To achieve this requirement, the electr ic thruster has to be operated with a variable thrust-to-power ratio a t the maximum available input power, To implement this operating mode with a Hall thruster it is necessary to modify both the mass now rate and the discharge voltage during the flight time, A crucial problem as sociated with Hall thruster operation in a variable-thrust mode is the degradation of thruster performance under mass flow rate variations, Experiments with a laboratory Hall thruster have indicated that this d egradation is mainly caused by a reduction of the propellant utilizati on at lower values of the mass now rate, By modifying the channel geom etry, namely, the channel length and channel profile, improvements in the behavior of the propellant utilization at small mass now rates and , consequently, an improved thruster performance have been achieved. R esults of experimental tests of a Hall thruster at various operating p oints and geometry are presented.