Perturbation observer-based constrained fault tolerant control of flexible spacecraft using continuous predictive approach

This study presents anew constrained attitude control scheme for flexible spacecraft in the presence of system perturbations, including parametric uncertainties, external disturbances and actuator faults. In the proposed scheme, a baseline controller with increased robustness is firstly designed using an integral feedback- based continuous prediction approach to control the healthy spacecraft. At the same time, an extended state observer estimates the system perturbation. If the estimated perturbation exceeds a statistically predetermined threshold for aerodynamic/gravitational disturbances and the spacecraft's parametric uncertainties, it may indicate a potential fault in the system. Upon detecting a fault, the controller transitions to a fault-tolerant mode, where the estimated perturbation is utilized to compensate for the faults and disturbances. Constrained stability is analyzed for both controllers using Lyapunov method. Also, hardware-in the-loop simulations have been conducted using a Raspberry Pi to highlight the real-world applicability of the proposed structure. The results show that different fault scenarios for the three reaction wheels can be accurately detected and compensated for using the perturbation observer information, all within a simple structure. The comparative results with active and passive fault-tolerant controllers demonstrate the higher efficiency of the proposed control system. Additionally, an extensive statistical analysis is performed using Monte Carlo simulations to show the robustness and reliability of the proposed system under uncertain conditions for spacecraft and disturbance parameters.