This paper investigates an adaptive model-free constrained prescribed performance control approach for flexible spacecraft with an unknown captured object subject to unknown inertial properties, elastic vibration, actuator saturation, and external disturbance. First, the attitude kinematics and dynamics of the postcapture flexible spacecraft are transformed into a Euler–Lagrange form, based on which a model-free constrained attitude prescribed performance controller comprising a nominal control term and an adaptive compensation control term is developed. Then, by employing norm equalities of the Euler–Lagrange systems, a model-free adaptive scheme is designed to improve the robustness with respect to uncertainty, actuator saturation, and external disturbance just only using the state information. Compared with the existing works, the primary advantage is that the resultant controller and adaptive scheme are computationally very simple without any requirement of unknown inertial information. But the transient and steady-state performance is a priori guaranteed without resorting to repeated regulations of the controller parameters. Finally, the application to attitude stabilization and tracking of postcapture flexible spacecraft along with active vibration suppression is employed to validate the effectiveness of the proposed approach.
