Nonlinear Sliding Mode Based Attitude Control Of Spacecraft Subject To Control And Angular Velocity Limits

Spacecraft attitude control, which plays a key role in spacecraft operations, is the process that actuators provide control torques according to the control law and re-orient the spacecraft to a desired orientation. However, in a realistic environment, the attitude control has to suffer from various limits, such as control and angular velocity limits, due to the physical constraints of actuators, gyros, and the specific requirement of spacecraft operations. These issues may cause considerable difficulties in the design of the attitude control system to meet the high precision pointing requirement. Considering these problems, the main contents of this paper are as follows:Before the controller formulation, the background of the limits listed above are introduced firstly, and the purpose of this research is clarified. Then, the attitude model of rigid spacecraft subject to various limits is built, which is the basis for the synthesis and analysis of the controllers.In the first stage of the control law formulation, the control limits are investigated firstly. At this stage, an asymptotically stabilizing controller and a finite time controller that consider actuator saturation, are proposed, and also adaptive controllers that take actuator saturation and actuator uncertainties into account simultaneously. The stability of the system subject to actuator saturation is maintained and the actuator uncertainties are well offset with these controllers.In the second stage of the control law formulation, the angular velocity limit is further studied. At this stage, adaptive controller s that consider actuator saturation or actuator nonlinearities and the angular velocity limit simultaneously, are proposed. The stability of the system subject to actuator saturation is maintained, the actuator dead zone is well offset and the angular velocity limit is satisfied with these controllers.In addition, the anti-unwinding phenomenon which is caused by the quaternion-based attitude representation, is studied and solved by the definition of a novel attitude error function and vector. And it’s notable that, all the designed controllers in this paper are strongly robust the bounded external disturbance and system uncertainties.Numerical comparative simulation results are conducted to verify the effectiveness of the proposed controllers.