Abstract

An ultrahigh precise clock (space optical clock) will be installed onboard a low-orbit spacecraft (a usual expression for a low-orbit satellite operating on an orbit at an altitude of less than 1000 km) in the future, which will be expected to obtain better time-frequency performance in a microgravity environment, and provide the possible realization of ultrahigh precise long-range time synchronization. The advancement of the microwave two-way time synchronization method can offer an effective solution for developing time-frequency transfer technology. In this study, we focus on a method of precise satellite-ground two-way time synchronization and present their key aspects. For reducing the relativistic effects on two-way precise time synchronization, we propose a high-precision correction method. We show the results of tests using simulated data with fully realistic effects such as atmospheric delays, orbit errors, and earth gravity, and demonstrate the satisfactory performance of the methods. The accuracy of the relativistic error correction method is investigated in terms of the spacecraft attitude error, phase center calibration error (the residual error after calibrating phase center offset), and precise orbit determination (POD) error. The results show that the phase center calibration error and POD error contribute greatly to the residual of relativistic correction, at approximately 0.1~0.3 ps, and time synchronization accuracy better than 0.6 ps can be achieved with our proposed methods. In conclusion, the relativistic error correction method is effective, and the satellite-ground two-way precise time synchronization method yields more accurate results. The results of Beidou two-way time synchronization system can only achieve sub-ns accuracy, while the final accuracy obtained by the methods in this paper can improved to ps-level.

Highlights

  • The invention of atomic clocks provides an effective time solution for precision positioning, navigation, and timing (PNT) [1]

  • We mainly focus on using simulation data to verify the accuracy of the relativistic effect correction method and the realization of the satellite-ground two-way time synchronization method

  • We studied a precise method of time synchronization between a spacecraft and a ground station, to achieve ps-level time synchronization accuracy

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Summary

Introduction

The invention of atomic clocks provides an effective time solution for precision positioning, navigation, and timing (PNT) [1]. China plans to deploy high-precision atomic clocks (including space optical clocks with a stability better than 1E-17@1day) on the Chinese Space Station (CSS) to develop an ultrahigh precise time reference in space to further improve two-way time synchronization accuracy [8]. This research focuses on a high-precision time synchronization method, which depends on the two-way links between ground stations and low-orbit satellites equipped with high-precision atomic clocks. Considering the complicated space environment of spacecrafts in low-orbit, we introduce a variety of errors to generate the simulation data On this basis, we describe the relativistic effects and deduce the correction methods. We analyze the impact of different orbital errors (including attitude error, phase center calibration error, and precise orbit determination error) on the relativistic effects, and derive the final results of satellite-ground two-way time synchronization.

Two-Way Time Synchronization Method with GSLs
Relativistic Effects and Corrections
Relativistic Effect on Frequency
Relativistic Path Range Effect
Simulation and Discussion
Data Generation
Validating the Methods with Simulated Data
Conclusions
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