Hollow Cathode Life Issues

Abstract

L-3 Communications ETI (formerly Boeing Electron Dynamics Division and, prior to that, a division of Hughes Space and Communications) is a company with significant background in both cathodes (used in Space Traveling Wave Tubes) and Electric Propulsion. L-3 ETI has been responsible for developing a Cathode Life Model [1] that is recognized throughout the industry and has also been a key enabler in the development and manufacture of gridded ion thrusters. Testing of the 25 cm Xenon Ion Propulsion System (XIPS) has demonstrated 2 potential ignition issues associated with the hollow cathode assembly: delayed ignition due to barium depletion and heater failure. In its role in satellite station-keeping, the XIPS engine is ignited daily over a 15 year mission so that a detailed understanding of the ignition process is important in evaluating its life. The heater used to ignite the XIPS cathode assembly represents a single point failure so that dealing with potential failure mechanisms is critical in ensuring mission life. Operation of the XIPS thrusters involves 2 hollow cathodes: the neutralizer and the discharge cathode. The discharge cathode provides the source of ionization electrons used in the primary discharge while the neutralizer provides the source of electrons that balances the ion beam extracted from the main discharge and prevents charging of the spacecraft.