Earth's Magnetic Field Models for Dumping Momentum Magnetically on GPS Satellites

This paper discusses the relative performance of various Earth magnetic field models in a system for using onboard electromagnets to dump unwanted reaction wheel momentum on Global Positioning System satellites. The system uses the interaction between the Earth's magnetic field and the satellite's electromagnetically induced field to control the reaction wheel angular momentum vector using magnet switch-time and power settings produced by a ground-based computer program. The control performance and computational efficiencies of four magnetic field models are compared: the Mead-Fairfield (used in the original program), a quadrupole, a tilted dipole, and a spin dipole model. Results indicate that savings in computer time can be obtained using the simpler magnetic field models with very little loss of performance. Data have been verified by testing on actual satellites in orbit.