Yaw-Steered Payload Pointing and Orbital Control for a HIEO Spacecraft

This article outlines a novel thruster use for orbital control and momentum management on a current Space Systems/Loral 1300 series spacecraft. The strategy employed for steering a large unfurlable transmit antenna (9 meters in diameter) mounted on a satellite operating in a highly inclined elliptical orbit (HIEO) towards the continental U.S. (CONUS) is outlined. The onboard EIRP-Steering strategy ensures that the Equivalent Isotropic Radiated Power (EIRP) from the satellite to the intended CONUS is maximized during the service delivery period. The EIRP-steering algorithm is driven by the on-board control system and is fully autonomous, even in the event of orbital perturbations. Electrical power considerations require that the satellite be yaw steered about the electrical boresight of the transmit antenna. Given the 9-meter reflector and tight pointing requirements, the use of bipropellant thrusters for orbital control is minimized. Instead, the method chosen for orbital control are the north, south, and west-mounted stationary plasma thrusters (SPTs). Whenever possible, momentum management is also performed by the SPTs due to their significantly higher specific impulse (Isp). For attitude control, the satellite uses a star tracker, with a high fidelity onboard orbit propagator that models all significant disturbances, including SPT and bi-propellant thruster actuations. Orbital perturbations and effects on momentum management from SPT plume impingement on the spacecraft surfaces are accounted for. Summary plots showing various aspects of the missions profile and relavant momentum management results are also included.