The Smart-1 Electric Propulsion Subsystem

Abstract

Onboard the ESA SMART-1 spacecraft, (Small Mission for Advanced Research and Technology), the primary Electric Propulsion Subsystem (EPS) must operate at optimum performance under limited power available and with a variable power feature. As EPS Contractor for ESA-ESTEC, SNECMA present in detail the major's features of the complete electric propulsion system, as well as the development efforts of each main component. The development tests of the PPS-1350-G hall effect plasma thruster, including an extensive number of start-up tests in the whole useful operational domain have been performed. This paper describes the results of the PPS-1350 low-power characterization tests, and presents the new approach for having a limited inrush power when the thruster is switched on. The test campaign has been successful and the results obtained during the campaign have been fully taken into account in an optimization process for providing the foreseen performances of the SMART-1 mission. Those performances are the thrust, the total xenon flow, the specific impulse and the additional magnet trim current. Acceptance tests of each components of the EPS have been performed and finally an to end test has been successfully performed at satellite level. These new features of primary electric propulsion subsystem and especially the low-power start-up and variable power features can be also a significant added value for any commercial application using electric propulsion for station-keeping and/or orbit transfer. Introduction Although High Specific Impulse Thrusters have already propelled numerous satellites in the frame of station-keeping missions, their use for orbit transfer and deep space missions has only recently begun, bringing out a need for new thrust strategies. The Snecma PPS1350-G Hall-effect thruster is primarily intended for North South station keeping of Geo-stationary satellites. For that kind of application, the spacecraft available power is much higher than the PPU maximum power demand, so there is no risk to overload the spacecraft power bus. In the case of SMART-1 , on the contrary, the PPU power could exceed the total spacecraft power. In addition, the thruster shall be able to work with less than half its nominal power. To fulfil these requirements, it was necessary to modify the thruster/PPU interfaces and to validate these modifications by tests. SMART-1 Electric Propulsion Subsystem (EPS) The SMART-1 power is generated by two solar panels enabling thruster operation at a discharge power of maximum 1190 W at beginning of life . In some cases, (e.g. failure of one solar wing in addition to solar cells) the available power can be reduced to 700 W or less. This is therefore an essential requirement for thruster and PPU to work within a range of pre-set power levels. This capability is also required for deep-space missions involving variable sun distances. The whole EPS is designed for the three following main functions : u Xenon system u Electrical power system and thruster u Digital interface and communication system 39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit 20-23 July 2003, Huntsville, Alabama AIAA 2003-4545 Copyright © 2003 by Snecma Moteurs and ESA. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. 2 PPU/TSU Bus Input, Input Switch