Attitude Control for Spacecraft with Swinging Large-scale Payload

The primary sensor of astronomy observation satellite (AOS) is mounted on a gimbal base which connects directly with the satellite platform and has two degrees of freedom. Attitude control for AOS with a swinging sensor will be highlighted in this paper. Due to the non-negligible mass and length of the sensor, the internal motion between the satellite and the sensor will change the attitude, the position of center of mass and moment of inertia of the SYSTEM (consists of the satellite and the sensor). According to moment of momentum theorem, a rigid two-body dynamic model is derived, which can be used to determine the inertial tensor of the SYSTEM. Modulating the satellite's present and desired quaternions results in quasi-Euler angles and normalizing these resultant parameters can ensure that the channel corresponding to each quasi-Euler angle is in the charge of each component of the control torque. Based on the normalized quasi-Euler angles, a switching attitude control law is proposed. With the control law, the corresponding phase trajectory will slide along the switching surface to the origin (corresponding to the desired states). Simulation results show that the satellite can be controlled perfectly by thrusters with the proposed control law, even in the case of structural asymmetry and serious coupling between the control channels.