CYCLOGRAMS OF THE ST-25 HALL THRUSTER STARTING
The results of the start sequence diagram selection and experimental tests of the ST-25 Hall thruster intended for using on small spacecraft are presented. In order to reduce the mass and dimensions of the power processing unit of the propulsion system, it is proposed to exclude the hollow cathode keeper power supply from the structure of the power processing unit. The exclusion of the keeper power supply from the power processing unit made it necessary to select the thruster start sequence diagram. Four start sequence diagrams of the ST-25 Hall thruster start-up are considered: a) using a separate high voltage power supply for the hollow cathode keeper; b) using a separate low voltage power supply for the hollow cathode keeper; c) using a discharge power supply connected to the keeper through a high-resistance resistor to the hollow cathode keeper; d) connecting the keeper of the hollow cathode to the discharge power supply through an electronic switch with the possibility of adjusting the duration of the keeper connection to the discharge power supply. The graphs of changes in the thruster’s currents and voltages for various power supply circuits of the hollow cathode keeper are presented. The results of the choice of the start sequence diagram for the Hall engine ST-25 and the experimental studies carried out have shown that the use of an electronic switch with a steep pulse front makes it possible to obtain a reliable thruster start-up when a separate power supply for the keeper is excluded from the power processing unit of the propulsion system. As a result of the work carried out, it became possible to place the power processing unit for a propulsion system based on the ST-25 thruster in a volume of 2U. The possibility of using ST-25 thruster on spacecraft, the onboard electrical power of which is limited up to 200 W were confirmed.
As a result of the analysis of the four considered startup sequences of the ST-25 Hall thruster with a filament hollow cathode, it was shown that it is possible to exclude the keeper power supply from the PPU of the propulsion system.
When starting the ST-25 engine, it is proposed to use the discharge voltage supplied to the keeper through a high-speed electronic switch to supply the hollow cathode keeper.
The sequence diagram for starting the ST-25 thruster was worked out without using a separate power supply for the hollow cathode keeper, which ensures a reliable engine starting process.
The accepted technical solutions made it possible to significantly reduce the weight and dimensions of the PPU of the electric propulsion system with the ST-25 thruster and place the PPU in the volume of 2U (200x100x100 mm).