Performance and flatness of a multiple-cathode, rectangular ion thruster discharge chamber

Results from the extended life test of the Deep Space One flight spare ion engine show that enlargement of the discharge cathode assembly orifice due to erosion of the orifice by ion bombardment limits the throughput of the ion thruster, and therefore limits its operational lifetime to approximately three years. Future deep-space missions will require significantly longer operational lifetime, perhaps as long as 7-14 years. In an effort to increase lifetime, an ion thruster discharge chamber designed for operation with multiple discharge cathode assemblies was investigated. The multiple-cathode discharge chamber approach attempts to increase lifetime by operating three discharge cathode assemblies sequentially. Simulated ion thruster operation of the multiple-cathode discharge chamber with the active discharge cathode assembly located on centerline and off centerline for a variety of magnetic field configurations was accomplished. Results indicate that the configuration with permanent magnets and 0 A electromagnet current provided the best performance and flatness with optimum values of 194 ± 6 W/A at 0.89 ± 0.03 propellant efficiency and 0.55 ± 0.02, respectively. Finally, operation of the dormant cathodes with propellant flow is suggested to reduce preoperation erosion of those units.