Smooth time-optimal attitude control of spacecraft

In this paper, a trajectory optimization method for generating smooth and approximate time-optimal attitude maneuver trajectories of flexible spacecraft is proposed. Smooth attitude maneuver is highly desirable for flexible spacecraft, since vibration of flexible appendices can be suppressed. In order to obtain smooth and approximate time-optimal attitude trajectory, a novel objective function composed of two terms is developed in the problem of trajectory optimization: the first term is proportional to the total maneuver time and the other one is proportional to the integral of the squared control torque derivatives. This latter term ensures that the generated trajectory is smooth. The degree of the smoothness of the trajectory can be adjusted by the weights of these two terms. The constraints on angular velocity and angular acceleration are considered in the proposed method. A closed-loop tracking control law is then employed to track the optimized reference attitude trajectory. Numerical simulations and frequency domain analysis show that the proposed method can generate smoother trajectory than traditional time-optimal methods, which leads to less vibration during attitude maneuver of a flexible spacecraft.