Event-triggered fault-tolerant attitude tracking control for spacecraft with fixed-time controller and disturbance observer under input constraints.

• A fixed-time disturbance observer is proposed under the event-triggered technique to provide an attenuation effect on multi-source disturbances such as exogenous disturbances, system uncertainties, actuator faults, periodic vibrations and uncertain modeled disturbance of actuator, and input saturation. • Propose a fault-tolerant fixed-time controller to track the attitude of spacecraft under multi-source disturbances and limited communication framework. The proposed controller overcomes the unwinding phenomenon, and results show that attitude attitude-tracking path described by quaternion is the shortest maneuvering path. • Stability analysis of a closed-loop system ensures that both disturbance estimation error and the attitude tracking error of the system converge to a final boundary within a fixed time. Moreover, Zeno-free behavior is always guaranteed. This paper studies the attitude tracking problem for rigid spacecraft under restricted communication resources. This work proposes a novel composite control scheme for spacecraft subjected to system uncertainty, exogenous disturbance, periodic vibrations and uncertain modeled disturbance of actuator, actuator faults, and input saturation, which consists of a fixed-time controller (FiTC) based on an integral non-singular fast terminal sliding mode technique and a fixed-time disturbance observer (FiTDO). The FiTDO estimates the total disturbance (combination of the abovementioned effects) within a fixed time. Further, it improves the attenuation disturbance property of the composite controller by feedforward compensation. The proposed controller relaxes the prior upper-bound knowledge of the total disturbance and has anti-unwinding characteristics. Moreover, the designed event-triggered mechanism reduces control workload reduction and guarantees the Zeno-free behavior in the proposed composite scheme. The stability analysis of the closed-loop system under the proposed scheme using Lyapunov theory ensures the system states converge to a small invariant set within a fixed time. Simulation analysis and comparative studies demonstrate that the proposed scheme is effective in terms of convergence time, steady-state performance, and anti-interference ability, rate of controller update. [ABSTRACT FROM AUTHOR]