Development status of the HT5k high voltage model

Since 2013, SITAEL has been developing its 5kW-class Hall thruster unit, the HT5k-TU, comprising the HT5k thruster and the HC20 hollow cathode. Through several supporting projects, the thruster unit has undergone three design iterations and is now in the Engineering Model definition phase. As the design of the thruster unit evolved towards higher levels of maturity, multiple test campaigns were performed including several characterization tests, magnetic field topology optimization for life extension, tests with alternative propellants, assessment of operation in direct-drive mode, facility background pressure effects tests at two different pressure levels, thermal cycling and endurance test. As a result, the HT5k-TU thruster family cumulated more than 700 hrs of firing, demonstrating stable and efficient thruster operation in the power range of 3 to 7 kW. One important modification in the design of the HT5k thruster was the implementation of magnetic shielding of the discharge channel walls, eliminating in this way one main failure mode of the thruster. This improvement results in increasing the thruster lifetime by at least two orders of magnitude, making the thruster design further apt for station-keeping and deep-space robotic exploration missions of long lifetime. These scenarios typically necessitate operating the thruster at relatively-high specific impulses. However, operation of the thruster unit in the high-voltage range (500-800 V) require updating several design solutions, particularly from the perspective of voltage isolation and heat management. In this respect, to better understand the implications and requirements of high-voltage Hall thruster operation, the HT5k-TU models, both unshielded and shielded, were tested in this voltage range. The aim was to investigate the performance and stability of the thruster, in addition to better understanding the impacts from the design compatibility point of view. This paper presents an overview of the development activities performed on the various models of the HT5k-TU, focusing on the characterization results in the high-voltage regime. Furthermore, we also discuss the solutions devised for addressing the technological requirements of high-voltage Hall thruster's operation.