Hybrid magnetic attitude controller for low earth orbit satellites using the time-varying Linear Quadratic Regulator

The following is a study of an attitude control system (ACS) for a low earth orbit nanosatellite. Control actuation is applied using three reaction wheels and three mutually orthogonal current-driven magnetorquers which produce torques by interacting with the earth's magnetic field. Control torques are distributed amongst the actuators allowing them to work together in concert. This type of control is referred to as hybrid magnetic attitude control. To account for the nearly periodic behavior of the earth's magnetic field, control torques are assigned using periodic and optimal control theory. The primary focus is to apply the time-varying Linear Quadratic Regulator controller to test the stability and energy consumption of the ACS when reaction wheels are removed from the control law, or are simulated to be missing. Other situations studied include the effects of control saturation, introducing uncertainty in the orbital inclination, and observing performance as the number of magnetic coils is increased.