Disturbance Observer-Based Constrained Attitude Control for Flexible Spacecraft

This article investigates the difficult issue of fixed-time constrained attitude control for a flexible spacecraft under the influence of the system uncertainties, environmental disturbance, and abrupt actuator faults. The contributions of the proposed control framework are twofold. First, an observer is presented to precisely reconstruct the uncertain dynamics within a fixed time regardless of the initial estimation error while the settling time is given as a specific parameter. Second, using a combination of prescribed performance control (PPC) and barrier Lyapunov function approaches, a simple structure constrained attitude control for flexible spacecraft is proposed while desired performance specifications for both quaternion and rotation velocity are indirectly achieved by constraining the sliding manifold. A distinctive feature of the suggested control framework is that the settling time of the closed-loop system is finite and explicitly expressed as two tunable gains even when abrupt actuators faults happen. Numerical simulations substantiate the ability of the offered control to effectively accomplish favorable attitude maneuver under the negative effect of the inertia matrix uncertainty, external disturbances, flexible structures vibration, and actuators faults.