Event-triggered nonsingular fast terminal sliding mode control for attitude synchronization of multiple spacecraft

This paper presents a robust control strategy for achieving synchronized and accurate attitude tracking of multiple spacecraft in the presence of uncertainties, communication constraints, and input saturation. A new controller is proposed that combines a nonsingular fast terminal sliding mode control (NSFTSMC) with a dynamic event-triggered (ET) mechanism. The NSFTSMC ensures robustness against exogenous disturbances, while the ET strategy mitigates the effects of limited communication bandwidth by reducing the control update frequency. The ET method implements an aperiodic control update approach, that is, the actuator output gets updated only when a predefined triggering condition is satisfied. Until then, the actuator output maintains its previous output. Lyapunov stability analysis confirms that the proposed composite controller guarantees practical finite-time convergence of all error states to a small neighborhood around the origin. Moreover, the non-existence of Zeno behavior under the proposed ET scheme is also demonstrated theoretically. Finally, the effectiveness of the proposed control method is demonstrated through comparative simulations with recent ET-based schemes. Simulation results across various performance metrics highlight the superiority of the proposed approach.