Advancing Ultra-High Precision in Satellite-Ground Time-Frequency Comparison: Ground-Based Experiment and Simulation Verification for the China Space Station

Establishing an ultra-high-precision link for time-frequency comparisons between satellites and ground stations is critically important. This endeavor is fundamental to the advancement of pioneering space science exploration and the development of a robust space-based time-frequency system featuring ultra-high-precision space atomic clocks. In response to the requirements for assessing the long-term stability of high-precision space atomic clocks, we have designed and implemented a satellite-ground microwave time-frequency comparison system and method based on a three-frequency mode. Ground-based experimental results demonstrate that the equipment layer can achieve a satellite-ground time comparison accuracy better than 0.4 ps (RMS), with the equipment delay stability (ADEV) for all three frequencies being better than 8 x 10-18 at 86,400. By leveraging the ground-based experimental results, we constructed a satellite-ground time-frequency comparison simulation and verification platform. This platform realizes ultra-high-precision satellite-ground time-frequency comparison based on the China Space Station (CSS). After correcting various transmission delay errors, the satellite-ground time comparison achieved an accuracy better than 0.8 ps and an ADEV better than 2 x 10-17 at 86,400. This validation of our novel satellite-ground time-frequency comparison system and method, capable of achieving an 10-17 magnitude stability, is not only a significant contribution to the field of space time-frequency systems but also paves the way for future advancements and applications in space science exploration.