Long Life Cathode Heaters for Hollow Cathodes

Present and future NASA missions, including the Asteroid Redirect Mission and efficient cargo delivery to mars, require a substantial increase in lifetime for ion engines and Hall thrusters. This has led to the development of long-life lanthanum hexaboride (LaB6) hollow cathode emitters, which operate at temperatures >1600⁰C. Current state-of-the-art co-axial swaged cathode heaters use magnesium oxide (MgO) insulators, which experience a significant drop in insulation resistance at temperatures of 1300⁰C, causing heater failure. Hollow cathode failure caused by the failure of an external cathode heater is the single most critical event that controls the thruster lifetime. While alumina (Al2O3) has recently been used as a replacement insulator material, it has questionable reliability due to grain growth and void formation at temperatures >1600⁰C. In Phase I, we will formulate a new ceramic insulator using sound scientific principles, and develop a long-life cathode heater that can operate reliably at high power levels (>200 W) at high temperatures greater than 1600⁰C for use in long duration space propulsion missions. We will design, fabricate and test prototype swaged coaxial heaters to demonstrate the superior performance of the new insulators.

Swaged coaxial heaters for hollow cathodes are used in ion propulsion systems including in flight Hall thrusters and in the Hall Effect Rocket with Magnetic Shielding (HERMeS) for the Asteroid Redirect Mission. Hollow cathodes have widespread use on spacecraft, on communication satellites, the electrodynamic tether, and space station structure and other space environments that include those of low-earth orbits, sun-synchronous high inclination orbits, and geosynchronous orbits.

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