Spacecraft attitude dynamics and control in the presence of large magnetic residuals

This paper deals with the analysis and the control of the attitude dynamics of low earth orbit (LEO) satellites with large magnetic residual dipoles. The state dependent nature of the interaction of the spacecraft with the Earth's magnetic field is addressed and a model of the attitude dynamics augmented with the magnetic field is derived. The stability of the open-loop system is studied by linearization and tools from periodic systems theory. The effects of perturbations of the orbit parameters on the system stability are addressed. The analysis is the basis for the design of an attitude control strategy that allows to minimize the required control torque while satisfying an absolute pointing error constraint whenever direct compensation of magnetic disturbance torque is not achievable. Finally, the proposed approach is applied to the definition of a preliminary attitude control strategy for the AMS-02 mission and its performance is compared with the one attainable using a classical three-axis state feedback controller.