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|Thermal Cycle Lifetest of Swaged Cathode Heaters|
|Keywords: Swaged heater, Thermal cycle lifetest, Ion propulsion|
|The Dawn mission is designed to rendezvous with Vesta and Ceres, two large main belt asteroids, using ion propulsion. Each of the three ion thrusters on the Dawn spacecraft has two hollow cathodes that serve as electron sources for the discharge that produces the ions and the neutralizer which neutralizes the ion beam. These hollow cathodes require resistance heaters to preheat them to approximately 1200°C prior to discharge ignition. During long periods without thruster operation the heater temperature may drop to as low as –100°C. This presentation describes a cyclic lifetest of the heaters over the temperature extremes. The coaxial heaters have a center refractory metal conductor and an outer sheath with a ceramic insulator between them. The two conductors are welded together at one end. At the other end, the center conductor and outer sheath are connected to a power supply capable of up to 8.5 A heater current. For this test, commercial power supplies are being used to warm the heaters to the maximum temperature and a liquid nitrogen-cooled shroud is used to chill them to the minimum temperature. A total of 1200 cycles will be accumulated.|
|Jay Polk, Principal Engineer
Jet Propulsion Laboratory