In this article, the electric propulsion system SPS-25, designed by Space Electric Thruster Systems (SETS) is presented. The system has 150 – 250W input power, and consists of Hall thruster ST-25; Xenon storage and feed system (XFS) and Power processing unit (PPU). At the referenced input power (150 – 250W) ST-25 provides a thrust 5 – 11mN, specific impulse up to1200 s and efficiency in the range 26 – 32%. The feature of the ST-25 structure is that in order to reduce of electric power for the formation of a radial magnet field in the acceleration channel, a permanent magnet in the central magnet pole was used. Xenon storage and feed system consists of the tank from polymeric composition materials for storage of working substance, providing storage of Xenon at pressure 150 bar; high-pressure unit, that provides the decline of pressure in an accumulator tank to the level 1.0-1.2 bar and the low-pressure unit, that provides the feed of working substance from the accumulator tank to the anode unit and hollow cathodes with the set level of mass flow rates. For the structure of the storage and feed system of working substance, the SETS Company has designed the valves of high (up to 200 bar) and low pressure (up to 5 bar). For providing of the set mass flow rate of working substance to the anode and hollow cathode by a company SETS corresponding flow restrictor were developed. The Power processing unit consists of a few independent sources of power supply: the discharge power supply for the anode unit; the source of current for electromagnets of the thruster; source of current of hollow cathode heater; source of voltage for the feed system. The Power processing unit contains also the control unit of the propulsion system that gets on-off commands for the propulsion system, provides work of the propulsion system and forms the telemetry signals about subsystems status of the propulsion system and signals transmission to control system.
Keywords: Electric propulsion system, Hall thruster, magnet system with permanent magnet, Xenon storage and feed subsystem, power-processing unit
One of the modern trends in the development of space technology is the reduction in the mass of spacecraft and, accordingly, the decrease in electric power on board. This implies the task of creating electric propulsion systems with relatively small (200 – 300 W) electric power. To create the electric propulsion thruster with the input power 150-200 watts, SETS suggested using a permanent magnet as part of Hall’s magnetic system. As a result, the ST-25 Hall thruster was developed, which became part of the SPS-25 electric propulsion system.
Electric thruster system SPS-25 consists of following subsystems:
- Hall thruster ST-25 with input power 100 – 200 W;
- Xenon storage and feed subsystem (XFS), ensures the mass flow rate feeding and control to anode and cathodes of the thruster;
- Power processing unit (PPU), ensures the transform of onboard power supply energy to voltages and currents, which are needs for the electric propulsion subsystems operating.
2. ST-25 Hall Thruster
Specific of the ST-25 structure (Fig. 1) is that in order to reduce the cost of electric energy for the formation of a radial magnetic field in the accelerating channel of the thruster in the area of the central magnetic circuit, a permanent magnet is used [1, 3].
The permanent magnet is fabricated from material SmCo (YXG32M), Curie point of it is 650 – 700°С, that is why such permanent magnet can be used at operating temperature about 350°С. As the external electromagnets, four of the traditional electromagnets were used. Direct referenced current is passed through electromagnets from separate direct current power supply.