L1 adaptive attitude control of satellites in elliptic orbits using solar radiation pressure

The development of an L-1 adaptive control system for the control of satellites in elliptic orbits using solar radiation pressure is the subject of this article. The nonaffine-in-control spacecraft model includes the gravity gradient torque, the control torque produced by two solar flaps, and external time-varying disturbance torque. The objective is to control the pitch angle of the spacecraft using the solar flaps. The design is based on the L-1 adaptive control theory for the control of nonlinear nonautonomous uncertain systems. The control system includes an adaptation law based on the state prediction error. Unlike traditional adaptive systems, the control input is obtained by filtering an estimated control signal through a low-pass filter. In the closed-loop system, the designed adaptive law accomplishes large angle maneuver. A special feature of the control system using filtered signal is that it is possible to select large adaptation gains for fast adaptation and to obtain quantifiable performance bounds. Simulation results are presented which show that in the closed-loop system, precise pitch angle control is accomplished, despite parameter uncertainties and external disturbance input in the model.