Adaptive hybrid dynamic programming for fault-tolerant attitude control of underactuated spacecraft

To address the attitude control problem of underactuated spacecraft subject to actuator faults, while simultaneously considering both tracking accuracy and control energy consumption, this paper proposes an optimal fault-tolerant control scheme based on Adaptive Hybrid Dynamic Programming (AHDP). First, under fault-free conditions, the control design is formulated as an optimal control problem, and AHDP is employed to derive an approximate optimal control law that balances energy expenditure against tracking performance. To enable fault tolerance, an online compensation framework is developed using adaptive fault observers to separately estimate multiplicative and additive fault parameters. Subsequently, these estimates are incorporated into a compensation control law so that the faulty actuator output closely approximates nominal behavior. A Lyapunov-based stability analysis proves closed-loop robustness of the tracking error in the presence of actuator faults. Comparative simulations demonstrate that, compared with conventional fault-tolerant methods, the proposed AHDP-based controller achieves improved attitude tracking accuracy and higher fault estimation fidelity.