Optimization of spatial acquisition systems for low-light-level robustness in space optical communications.

The channel establishment in space optical communications relies on the Acquisition, Tracking, and Pointing (ATP) systems to initially acquire and then stably track the beacon beam. However, insufficient optical power may lead to unstable acquisition or even acquisition failure. In this Letter, we describe the mechanisms causing the instability, and then propose an approach to constrain the acquisition velocity. The approach is based on velocity prediction obtained from the light spot centroids and angle measurement data. Theoretical and experimental results show that the acceptable minimum optical power for acquisition decreases by 5.5 dB after optimization, which effectively enhances the acquisition system's robustness under low-light-level conditions. This approach improves the adaptability of satellite-ground optical communications and also has practical value for deep-space optical communications.