Open-loop and closed-loop attitude dynamics and controls of miniature spacecraft using pseudowheels

This paper presents open-loop and closed-loop attitude control strategies of miniature spacecraft using pseudowheels, which are composed of multiple bimorphs and are mounted on the three principal axes of the spacecraft. Due to the conservation of angular momentum, the vibrations of the bimorph excited by applied voltages can rotate the spacecraft. By applying a sequence of rotations along the three axes, the attitude of the spacecraft can be changed. The modeling of the spacecraft–pseudowheel system includes the inverse piezoelectric effect and the gravity gradient torques. Since one cannot guarantee that a solution will be found for every rotation sequence, this paper proposes an approach to solve this problem. In addition, the voltages applied to the bimorphs are reduced to meet the specifications of the voltage amplifiers. Furthermore, a closed-loop attitude control strategy is presented to reduce the applied voltages and to compensate the attitude error caused by the gravity gradient torques.