Hybrid Open/Closed-Loop Attitude Control Method for Imaging Satellites

In this work, we focus on the attitude control problem of an imaging satellite required to acquire and accurately track a target area on the Earth's surface. The proposed hybrid methodology combines an open-loop implementation of a near-optimal trajectory for the initial acquisition phase and a quaternion feedback proportional-derivative controller for the subsequent tracking phase. The fast prototyping of the near-optimal attitude trajectory is achieved by integrating a direct method, the inverse dynamics in the virtual domain, and a nonlinear programming solver, the sequential gradient-restoration algorithm. The optimization criteria taken under analysis are the target acquisition time and the maneuver energy associated to the actuation torques. To assess the effectiveness of the proposed approach, we compare its performance against two standard closed-loop attitude controllers, namely, a classical quaternion feedback proportional-derivative controller and a linear quadratic regulator. Simulation results, in a hi-fi environment, show that the proposed controller achieves better tracking accuracy and optimality than the other controllers. (C) 2021 American Society of Civil Engineers.