Characterization of a 100-kW Class Nested-Channel Hall Thruster

Abstract

The next generation of electric propulsion consists of systems in excess of 300 kW of power. These systems enable a wide variety of missions, including crewed missions to near-Earth asteroids and Mars. Hall thrusters are a particularly attractive technology for these missions, but development and demonstration of 100-kW class devices has been limited to date. Here, a 100-kW class three-channel nested Hall thruster called the X3 was operated up to 102 kW total discharge power. The three channels of the X3 can be operated in any combination, providing seven unique configurations and a total throttling envelope of 2-200 kW. Previous testing of the X3 was limited to 30 kW and showed that it was not providing state-of-the-art performance.

Two low-power test campaigns were completed at the University of Michigan which identified potential mechanisms for this under-performance. Improvements to the thruster were made before a high-power performance characterization at NASA Glenn Research Center. There, the X3 was operated on xenon propellant from 5-102 kW total power. The thruster demonstrated stable operation in all seven channel combinations at discharge voltages from 300 V to 500 V and three different current densities. All seven channel combinations demonstrated similar performance at a given discharge voltage and current density. The largest thrust recorded was 5.4 N, and total efficiency and specific impulse ranged from 0.54 to 0.67 and 1800 seconds to 2650 seconds, respectively. For all channel combinations, total efficiency values greater than 0.63 were demonstrated.

In addition to the performance measurements, a suite of plasma diagnostics and a high-speed camera were used to study the operation of the thruster in greater detail. The probe results are compared against those in the literature and show that the X3, even in multi-channel operation, is producing similar charge, mass, current, and voltage utilization efficiencies as the NASA-300M 20-kW Hall thruster, a state of the art high-power thruster designed with similar design principles as the X3. High-speed camera analysis identified that the X3 operated in a similar mode of discharge current oscillations at nearly all conditions tested. This oscillatory behavior was characterized by the entire discharge channel oscillating as a whole (a so-called breathing mode oscillation) in a random, non-sinusoidal manner. Analysis indicated that when channels were operating together their oscillations did not correlate with one another either in sync or with a phase delay. Oscillatory behavior was also confirmed with high-speed discharge current analysis. Additionally, a preliminary calculation of cross-channel ingestion and its effect on thruster efficiency was made.

This work represents the highest total power (102 kW), thrust (5.4 N), and discharge current (247 A) demonstrated by a Hall thruster to date, improvements of 6%, 64%, and 119% respectively over previous values. These results are discussed in the context of continued high-power Hall thruster development and future mission applications.