Abstract: The pointing control strategy for the whole tracking process of a non-cooperative object via a two-axis turntable-based spacecraft is investigated, ranging from initial target acquisition to the subsequent visual tracking process. At target capture phase, considering camera installation errors and non-coincident centers of multiple-channel fields of view, the kinematic relationship of the image space is exploited and the pointing error of the camera is mapped to the attitude offset of the turntable. This enables high-precision target attitude calculation when the camera's line of sight is not perpendicular to the turntable's end axis, conquering the difficulty in deriving the analytical solution by the traditional method. At visual tracking phase, for the transient performance in the initial tracking stage, a self-adjusted image-plane trajectory planning scenario is developed based on the velocity constraint and the position deviation in the image space. To ensure the smoothness during the switching of multiple channels, a unified coordinate system in the focal plane is introduced by leveraging the consistency of the physical positions at the switching point. A visual feedback control protocol is then constructed based on a novel image-position observer, eliminating the dependency on image-space velocity measurements. To further optimize the control logic, the weighted forgetting factor is utilized in the visual controller design for a seamless connection of the two control stages，meeting the transient velocity constraint and enhancing the robustness of the control system. As for validation and application, the effectiveness of our methodology is verified through physical experiments and on-orbit applications. The high performance for the whole tracking process of the moving target is achieved by the cooperation of the aforementioned schemes. Therefore, the scheme solves the full-process pointing control problem of satellite-borne turntables under the constraints of camera imaging, and bears strong engineering practicability.

Key words: two-axis turntable, non-cooperative object, target acquisition/visual tracking, full process, physical experiments, on-orbit applications