A new approach to magnetic angular momentum management for large scientific satellites

This paper presents a new approach to develop satellite angular momentum management based on new magnetic unloading control laws. The primary features of the approach are that environmental disturbance torque is estimated and canceled instantaneously to the level for the angular momentum not to accumulate, that unloading is performed over an orbital period by applying nonlinear magnetic unloading control, and that the unloading torque does not change rapidly so as not to disturb a satellite's attitude. The approach is applied to two types of large scientific satellites of ISAS (Institute of Space and Astronautical Science), an astronomical observatory with an inertially-fixed attitude, and an infrared imaging surveyor in a near polar orbit with an earth-pointing attitude. A three-dimensional unloading law is developed for the former satellite as a generic case. Independent two-dimensional in-plane and one-dimensional out-of-plane unloading laws are developed for the latter satellite as a specific case. Simulation studies are also performed for the two satellites. The simulation results indicate that the angular momentum residual is contained within a zone that is well below the zone achieved by a conventional algorithm, contributing to momentum wheels size and weight reduction. The simulation results also indicate that the energy consumption is reduced, making it possible to reduce the size and the weight of magnetic torquers and their power supply systems. The unloading torque has no abrupt change in magnitude, preventing the attitude accuracy deterioration. Validity for the unloading algorithms is discussed by checking the criterion for the unloading capability and by evaluating the energy consumption.