Robust flexible spacecraft attitude tracking under measurement errors, actuator nonlinearities, and faults

Reliable spacecraft attitude maneuver is one of the core research areas of the space industry due to the need for sustainable space exploration and advancements in the space technology. The paper presents an observer-based adaptive backstepping (OB-ABST) fault-tolerant control scheme for a flexible spacecraft attitude tracking under the effect of state measurement errors, inertial uncertainties, external disturbances, multiple actuator faults, and input nonlinear saturation (INS) while suppressing vibrations due to flexible modes. Initially, we design an adaptive backstepping controller to mitigate the system's unwanted nonlinearities and observers to get estimates of the attitude dynamics in a recursive design framework. Later, the control structure incorporates a simple actuator saturation compensator to tackle input torque saturation in the system. The critical feature of the proposed OB-ABST control structure is to ensure precise attitude-tracking maneuvers and vibration suppression without intelligent materials such as shape memory alloys (SMA) and piezoelectric material (PZT). Lyapunov stability analysis proves practical finite-time convergence of the system state errors, observation errors, and actuator saturation compensators. Moreover, we provide specific conditions to tune design parameters. Finally, comparative simulation experiments validate the control performance of the proposed controller in the presence of multiple challenges.