An approach to magnetic torque attitude control of satellites via ´H∞´ control for LTV systems

A new approach to the three-axis attitude control of satellites using magnetic torque rods is detailed in this paper. The system is under-actuated, as the magnetic torque rods cannot apply torque in a direction parallel to the Earth´s magnetic field. However for orbits inclined to the Earth´s magnetic equator, the direction of the field vector changes and this fact can be used to design controllers for the system. An extension of the H_∞ control technique to LTV systems is used to design periodic controllers for the periodic system. The resulting controllers are simulated on the full non-linear system. The stability and accuracy of the closed-loop system, to less than a degree of pointing error, is demonstrated in the presence of disturbances including gravity-gradient torques, drag torques, and solar radiation pressure torques.