An investigation of stationary plasma thruster performance with krypton propellant
The objective of this research was to characterize the performance of a 1.35 kW stationary plasma thruster (SPT) with krypton as the propellant. Research carried out by Bugrova et al. [l] demonstrated that SPT performance on krypton is comparable to that on xenon if the krypton propellant flow rate is properly selected. Our investigation was an attempt to demonstrate this process by matching the thruster efficiency and plume divergence characteristics on krypton with those traditionally observed with xenon by selecting the proper krypton mass flow rate. The advantages of krypton in comparison to xenon include lower cost and predicted higher SPT specific impulse for a given discharge voltage. The latter is attractive for future interplanetary space missions where input voltages may be limited to a few hundred volu (e.g.. direct drive schemes). In the experiment reported below, once the proper operating regime for krypton was found, an array of probe-based diagnostics including a retarding potential analyzer. emissive probes, and a Faraday probe, was used the characterize the plumes for both conditions. The results suggest that by operating the SPT at a krypton flow rate which is 18% higher than the xenon flow rate at the nominal condition. the thruster plume divergence pattern for both propellants are the same. While the thrust was higher by 9%. the Isp with the krypton propellant was 7% lower than the Isp calculated for xenon resulting in an efficiency loss of 5%.
