Reservoir Hollow Cathode for Electric Space Propulsion

We report on a mechanically robust reservoir-type hollow cathode suitable for use in electric space propulsion for long duration space flights. It represents the first instance in which the reservoir technology has been successfully adapted to the hollow geometry used in ion engines and Hall thrusters. A novel construction technology was employed that uses flexible elements to reduce stress concentrations in the reservoir wall due to transient thermal effects. The new design was subjected to 12000 thermal cycles without degradation in performance. Seventeen new cathodes were constructed and tested in both vacuum and xenon discharge modes. Four cathodes were vacuum and xenon discharge pulse tested for periods up to 10000 h, with no degradation in performance. One cathode was tested in DC discharge mode for 1000 h at Colorado State University with no change in performance. Life test details will be presented. Both discharge and vacuum emission performance on the new cathodes were measured and compared with their impregnated cathode counterparts. A variety of compositions, both in the matrix and emissive material, were studied in the reservoir geometry. These provide the basis for a more exhaustive study of specific formulations in future work. In particular, cathodes with mixed metal matrices, consisting of tungsten-iridium and tungsten-osmium were tested and compared with pure tungsten. They were tested in both vacuum and discharge modes and provided superior performance over tungsten matrices. A tungsten-osmium matrix achieved a discharge current of 50 A at a temperature 100 °C lower than cathodes with tungsten matrices.