Research On Coordinated Attitude Control Within A Formation Of Spacecraft Under Communication Constraint

As one of the most important technologies applied to spacecraft formation flying, coordinated attitude control within a formation of spacecraft has been an absorbing area for researchers. Due to the influence of model uncertainty, external perturbations and partial loss of actuator effectiveness, it is of great practical significance to develope a coordinated attitude controller with strong robustness. Information interaction is constrainted by formation structure and some other factor, so communication constraint must be considered when we design coordinated attitude controllers. Thus, in the background of spacecraft attitude coordination control, considering communication delay and the situation that only a subset of the group members has access to the common reference attitude, respectively,sliding mode controllers are investigated in this paper.Firstly, relative attidute kinematics and dynamics equations and the topology of the information flow between spacecraft are given under the assumption that all members have access to the common reference attitude. By designning an integral sliding mode surface and a PI controller, the influence of model uncertainty, external perturbations and partial loss of actuator effectiveness can be compensated. Therefore, a nominal system is obtained.Then, based on the nominal system and Lyapunov stability theory, two controllers with time-varying parameters are investgated without time delay and with time delay, respectively. They can use the state of the system to adjust their parameters. The controller without time delay can not only keep the system asymptotically stable but also reduce the relative attitude error between the member spacecrafts. Then controller with time delay use angular velocity and unit quaternion to design an auxiliary variable. Based on Lyapunov stability theory and the auxiliary variable, it can be proved that the system is asymptotically stable. Numerical simulations are presented to demonstrate that the proposed controllers are characterized by strong robustness, and to investigate the effect of controller parameters.Under the situation that only a subset of the group members has access to the common reference attitude, a sliding mode observer is given. The observer can be stable in finite time, so the observer and the controller can be designed separately. Then, a sliding variable is given and it can be proved that the system state is asymptotically stable when the sliding variable is on the sliding manifold, and the property of a part of sliding variable is studied with norm theory. Based on unit-vector control, a controller is proposed. However, the controller has chattering problem and it can only drive the sliding variable into a neighborhood of the sliding manifold, so an adaptive Super-Twisting controller is addressed. According to the property of second-order system, it can be proved that the system with adaptive Super-Twisting controller is asymptotically stable. Finally,numerical simulations are presented to show the performance of the proposed distributed controllers.