Large-aperture telescope system based on a secondary optical beam expander with tracking precision of 100 nanoradians

Minimizing laser beam divergence is the most effective method for achieving long-distance optical transmission, which requires deploying acquisition, tracking, and pointing (ATP) systems with larger apertures to enhance tracking accuracy. To enable efficient optical signal transmission over 10,000 kilometers, we developed a spaceborne ATP system equipped with a 680 mm-aperture telescope. With the divergence angle compressed to 2.6 µrad, tracking accuracy exceeding 100 nrad must be achieved. This paper employs a dual-axis turntable with a biased unbalanced structure, combined with detector positioning error correction algorithms and high-precision composite-axis servo control technology to achieve high-accuracy tracking. Under conditions of gravity unloading and micro-vibration, the system ultimately attained a tracking accuracy of ~76 nrad. This provides a viable technical solution for implementing terminal engineering projects involving longer-distance beam transmission.