Fault-tolerant attitude control for flexible spacecraft subject to input and state constraint

This paper considers the problem of fault-tolerant attitude control for a flexible spacecraft subject to input and state constraint. Particularly, a new sliding mode-based attitude control with fixed-time convergent for the flexible spacecraft is developed in which the convergence rate of the system state is improved both far from and at close range of the origin. In contrast to the existing complicated prescribed performance controls (PPC), the proposed PPC possesses a much simpler structure due to the use of a novel constraint concept without employing error transformation. It also introduces a modified prescribed performance function (MPPF) to explicitly determine the settling time. It is rigorously proved that the attitude variable is kept within the predefined constraint boundaries even when the actuator saturation is taken into account. Moreover, the proposed controller is inherently continuous and the chattering is effectively reduced. An adaptive mechanism is developed in which no prior knowledge of the lumped uncertainties is required. Finally, numerical simulations are presented to demonstrate that the proposed controller is able to successfully accomplish attitude control with high attitude pointing accuracy and stability. More specifically, it provides faster convergence (improvement percentage of convergence time (IP_CT) is about 18%) and more accurate control (improvement percentages of MRPs (IP_MRPs) and angular velocity (IP_AV) are about 60% and 80%, respectively) under healthy actuators. Values of IP_CT, IP_CT, and IP_AV are 50%, 99.9% and 99.9% under faulty actuators, respectively.