GPS (Global Positioning System) Magnetic Momentum Dumping Feasibility Study

The NAVSTAR/GPS NDS-2 satellite has been designed with two electromagnets aboard to interact with the earth's magnetic field and cancel disturbance torques during normal on-orbit operations. Because the magnets can generate more torque than is necessary to merely cancel disturbances, they can be used to dump excess momentum from the reaction wheels without disturbing the precise ephemeris of the vehicle. The report analyzes the earth's magnetic field, ground station location, strength, number and orientation of spacecraft electromagnets and determines that magnetic dumping is possible and is practical for use in this particular satellite system. The report concludes that momentum dumping is best with three orthogonal magnets but is possible with only two. The study assumes a circular twelve-hour orbit at 63 degree inclination. It introduces a control effectiveness parameter that indicates acceptability of a control setting in terms of both magnet strength vs momentum storage capability and relative effect on the axis of interest. 150 computer plots are included.