The exact power level that qualifies as “high-power” in Hall thrusters is a shifting target. In the 1990s anything over a kilowatt would have been considered high power, yet with the advent of thrusters like the 50-kW NASA 457M and more recently nested thrusters like the X2, the bar has shifted and now it would be fair to say that “high-power” begins in the 5-10 kW range, if not higher. This increase in electrical power is largely driven by a decrease in the cost of onboard electrical power for spacecraft and the ever-present desire for increased thrust, which requires an increase in mass flow rate and thus electrical current as each propellant atom is ionized and ejected. In contrast the voltage range of Hall thrusters has remained surprisingly steady over the past few decades, residing generally in the 300 V range up until the early 2000s, when research at PEPL outlined improved magnetic circuit designs for efficient operation at higher voltages (see ref. 2). While Hall thrusters are still often run in the low hundreds of volts, operation at high efficiency up to 1000 V has been demonstrated at PEPL, approaching a domain traditionally reserved for gridded ion thrusters.

PEPL has designed, built, and extensively researched a family of 5-6 kW single channel thrusters, beginning with the 5-kW class P5 (co-developed with the AFRL, see ref. 1), followed by the 5-kW class NASA 173Mv1 and v2 (co-developed with NASA Glenn, see ref. 2), and more recently with a 6-kW laboratory model Hall thruster (co-developed with the AFRL and NASA JPL, see ref. 3). These thrusters have demonstrated improvements in magnetic field design and anode flow uniformity (see ref. 4) that push anode efficiencies up to nearly 70%. Leveraging these results and new design concepts like nesting and magnetic shielding, PEPL has recently designed and characterized higher-power thrusters: the two-channel X2 (10-kW class), the three-channel X3 (100-kW class), and the magnetically-shielded H9 (9 kW).

In addition to the above, PEPL is investigating alternative Hall thruster propellants. Krypton offers a cheaper, lower-thrust and higher-Isp alternative to xenon as a Hall thruster propellant. Historically, krypton performance has been limited by mass utilization efficiency, causing a large gap between krypton and xenon efficiencies. PEPL is continuing investigation into the causes of this difference, as well as how magnetic shielding may affect it.