Adaptive robust fault-tolerant control scheme for spacecraft proximity operations under external disturbances and input saturation

This study presents an adaptive robust fault-tolerant control (FTC) method for spacecraft proximity operations, in the presence of external disturbances, actuator faults, and input saturation. Firstly, a coupled 6-degrees-of-freedom dynamics model is constructed to show the relative motion of the pursuer spacecraft to the target spacecraft. To deal with actuator faults and external disturbances, a basic robust FTC method is designed. Subsequently, an adaptive robust FTC approach is developed to address the negative effect from the input saturation. In particular, by incorporating a novel dead-zone model to represent the saturation nonlinearity, an adaptive technology is applied to compensate for the nondifferentiable integral term in the saturation model. According to Lyapunov stability theory, all the signals in the whole system are proved to be ultimately bounded, and the relative motion tracking errors can converge to arbitrarily small neighborhood around the origin by choosing the suitable parameters. Last but not least, comparative simulations are carried out to validate the superiority of the proposed control strategy.