Finite-time cooperative attitude control for leader-follower spacecraft with fixed-time observer

This article investigates the problem of distributed attitude tracking control for the leader-follower spacecraft in the presence of the external disturbances, model uncertainties, and actuator faults. First, a novel fixed-time observer is developed to estimate the angular velocity of the leader. In contrast to the existing finite-time observer design methods, the settling time is independent of the initial conditions, and the upper bound of the angular acceleration of the leader is not required for each follower. To estimate and compensate the total uncertainties with finite-time convergence, a fraction-based adaptive scheme is designed. Based on the fixed-time observer and the adaptive scheme, a continuous finite-time distributed control law is developed such that the stability of the observer-controller closed-loop system is guaranteed. Numerical simulations are illustrated to demonstrate the performance of the control scheme.