Performance Characteristics of a Cluster of 5 kW Laboratory Hall Thrusters

The University of Michigan and United States Air Force Research Laboratory have jointly created a cluster composed of two P5 Hall effect thrusters. The P5 is a 5 kW class laboratory model Hall thruster developed to investigate a thruster similar to that specified by Integrated High Payoff Rocket Propulsion Technology (IHPRT) goals. In this study, the performance characteristics of each of the P5 Hall thrusters are measured in the Large Vacuum Test Facility (LVTF) at the University of Michigan at three facility pumping speeds. The thrusters are evaluated over the range of 300 600 V at 5.25 mg/s and 10.46 mg/s. The two thrusters are then operated simultaneously and the thrust of the cluster is measured over the same thruster operating conditions. Analysis of the monolithic thrust measurements shows that as the facility backpressure increases, the thruster discharge current and thrust increase because more background xenon gas is ingested into the thruster discharge chamber. The percent difference between the measured cluster thrust and the sum of the thrust measured for each monolithic thruster for the 10.46 mg/s anode flow rate varies from 11% to 16% as the operating pressure varies from 5.3x10 Torr to 2.8x10 Torr. This is greater than the percent difference in thrust for the 5.25 mg/s flow rate, which varies from 0% to 6% as the operating pressure varies from 3.5x10 Torr to 1.5x10 Torr. This difference is caused by the ingestion of background gas and thus, the difference in thrust decreases as the cluster operating pressure decreases. In addition, the anode efficiency and specific impulse of the cluster is greater than that of a single monolithic thruster. Comparison of the performance characteristics of the cluster and the monolithic thruster for conditions of nearly equal operating pressure shows that for the 5.25 mg/s anode flow rate the cluster thrust is simply the addition of the two monolithic thrusters. In addition, the anode efficiency and specific impulse are approximately equal to that of the monolithic thruster. These trends do not hold at the 10.46 mg/s anode flow rate for conditions of equal operating pressure because each cluster element elevates the operating pressure in the immediate vicinity of the adjacent thruster.