Time-Optimal Magnetic Attitude Maneuvers

Time-optimal magnetic attitude maneuvers near-Earth spin-stabilized spacecraft are treated using Pontryagin's Principle. A nonlinear bang-bang switching function is derived the electromagnets' polarity. The approach is quite general, allowing user-prescribed orbit dynamics models and geomagnetic field models. For the case of a single electromagnet aligned with the nominal spin axis of a symmetric satellite, and retaining general orbit and geomagnetic models, the determination of time-optimal magnetic maneuvers reduces to a bounded one-dimensional search of an initial costate variable. The formulation is used to construct extremal field maps of typical optimal maneuvers and is further used to determine for example time-optimal maneuvers the NOVA navigational satellite scheduled launch in the spring of 1981.