Performance and Evolution of Stationary Plasma Thruster Electric Propulsion for Large Communications Satellites

Space Systems/Loral (SS/L) has extensive experience with electric propulsion dating back to the early 1990s when an agreement was made to develop the newly available Russian manufactured Stationary Plasma Thruster (SPT-100) for use on western communications satellites. The western qualification and integration of the SPT-100 subsystem onto SS/L spacecraft was completed in 2001 with the first flight in 2004. SS/L has now launched six spacecraft with SPT-100 electric propulsion subsystems, with ten more satellites under construction. The SPT-100 subsystem provides impulse for on-orbit inclination management (north-south stationkeeping), eccentricity control, and momentum wheel unloads, as well as orbit raising capability when desired. It enables a large reduction of on-orbit propellant mass and thereby significant increases in communications payload mass and capability. The SPT subsystem now has more than thirteen years of cumulative on orbit experience, with a single thruster accumulating over 6 years of near-daily operation in orbit. This paper summarizes SS/L’s experience from the western qualification of the SPT-100 subsystem through successful deployment and operation on orbit. The evolution of the subsystem building on this experience is described, including an already flight-proven universal thruster module and the qualification of the higherthrust SPT-140 subsystem. These advancements will further capitalize on the benefits of electric propulsion, including significant electric orbit raising as well as orbit control of very large spacecraft to support ever more complex and capable communications payloads.