The flying around monitoring task of space tumbling target is one of the key links of its on-orbit service. Considering the practical constraints of system inertia uncertainty, external disturbance, actuator saturation, and fault in engineering practice, a robust composite controller based on radial basis function (RBF) neural network is proposed. First, in a new line of sight rotation (RLOS) coordinate system, the relative attitude kinematics and dynamics equations between the tracker and tumbling target based on the error quaternion are established; second, the RBF neural network is used to estimate the additive and multiplicative faults of the system, and the fast nonsingular terminal sliding mode surface (FNTSMS) is combined with the active disturbance rejection control (ADRC) technology to design a finite-time faulttolerant control (FTC) strategy with high accuracy, strong robustness, and anti-saturation based on the RBF neural network. It is proven that the designed robust fault-tolerant controller can ensure that the system state error converges to a small region containing the origin in a limited time under the Lyapunov framework. Finally, the effectiveness and superiority of the control strategy were verified by numerical simulation.

Aiming at the practical problems of external unknown disturbance and internal modeling uncertainty, when space tumbling target flies around in close range, a sliding mode controller (SMC) based on active disturbance rejection control (ADRC) technology is proposed to realize real-time estimation and compensation of ''total disturbance.'' Firstly, according to the motion characteristics of space tumbling target, the relative motion equation in rotating line of sight (RLOS) coordinate system is established; Secondly, the compound controller is designed, and the convergence of the nonlinear state expansion observer and the stability of the closed-loop system are analyzed based on the root locus method and Lyapunov function method respectively; Finally, the simulation results show that the SMC based on ADRC technology can effectively suppress the disturbance and overcome the chattering problem of traditional sliding mode controller. It has a good control quality, and strong robustness is an easy method for engineering practice.