Magnetic torquer attitude control via asymptotic periodic linear quadraticregulation

A method of using magnetic torque rods to do three-axis spacecraft attitude control has been developed. The goal of this system is to achieve a nadir- pointing accuracy on the order of 0.1-1.0 deg without the need for thruster s or wheels. The open-loop system is underactuated because magnetic torque rods cannot torque about the local magnetic field direction. This direction moves in space as the spacecraft moves along an inclined orbit, and the re sulting system is roughly periodic. Periodic controllers are designed using an asymptotic linear quadratic regulator technique. The control laws inclu de integral action and saturation logic. This concept has been studied,ia a nalysis and simulation. The resulting closed-loop systems exhibit robustnes s with respect to parametric modeling uncertainty. They converge from initi al attitude errors of 30 deg per axis, and they achieve steady-state painti ng errors on the order of 0.5-1.0 deg in the presence of drag torques and u nmodeled residual dipole moments.