Linear Time-Varying Passivity-Based Attitude Control Employing Magnetic and Mechanical Actuation

Spacecraft attitude control using both magnetic and mechanical actuation is considered. Attitude control is composed of quaternion-based proportional control and passivity-based rate (angular velocity) control. A passivity-based scheme is adopted in order to guarantee robust closed-loop stability. Motivated by the nearly periodic nature of the Earth's magnetic field, a linear time-varying input strictly passive system is used within the rate control. Conditions that ensure a linear time-varying system is input strictly passive are given and are used in conjunction with the linear quadratic regulator formulation to design and synthesize the rate control. The attitude control formulation ensures that as time goes to infinity the spacecraft attitude and angular velocity go to zero. Simulation results are included that highlight the robust nature of the closed loop subject to both orbit and spacecraft model uncertainty.