• Chinese Journal of Lasers
  • Vol. 50, Issue 18, 1804004 (2023)
Renfang Geng1、2, Zhibo Wu1、3、*, Yong Huang1, Haisheng Lin4, Rongzong Yu5, Kai Tang1, Haifeng Zhang1、3, and Zhongping Zhang1、3
Author Affiliations
  • 1Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China
  • 2University of Chinese Academy of Sciences, Beijing 100049, China
  • 3Key Laboratory of Space Object and Debris Observation, Chinese Academy of Sciences, Nanjing 210008, Jiangsu, China
  • 4School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200444, China
  • 5School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China
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    DOI: 10.3788/CJL220964 Cite this Article Set citation alerts
    Renfang Geng, Zhibo Wu, Yong Huang, Haisheng Lin, Rongzong Yu, Kai Tang, Haifeng Zhang, Zhongping Zhang. Experimental Study of Forward Laser Time Transfer Based on Satellite Retroreflector[J]. Chinese Journal of Lasers, 2023, 50(18): 1804004 Copy Citation Text show less

    Abstract

    Objective

    Satellite Laser Ranging (SLR) has contributed a new prospect to clock comparison and monitoring with higher precision and accuracy. Several laser time transfer projects, such as Time Transfer by Laser Link (T2L2), and Laser Time Transfer in China’s Space Station (CLT), have been conducted over the past 20 years. However, the traditional laser time transfer is limited because of incident light intensity and ambient temperature on onboard hardware. Alternatively, Forward Laser Time Transfer (FLTT) based on curved mirrors is a new type of laser time transfer technology with great application potential, which has the advantages of zero-time delay in the forward process, high reliability, long service life, and high measurement accuracy. However, due to the lack of suitable satellite experimental platforms, experimental data and performance evaluation results of the FLTT have not been obtained. The current research is only limited to theoretical analysis. In this study, we investigated the FLTT with two adjacent SLR systems as the test station and the retroreflectors on the cooperative target satellite as the forward payload. Our research should provide some technical reserves for the curved mirror based FLTT and evaluate the feasibility and performance of FLTT technology.

    Methods

    First, we briefly introduced the basic principles and difficulties of FLTT, including one-way and two-way FLTT modes. Furthermore, the clock difference extraction algorithm of a one-way FLTT was improved to make it suitable for laser time transfer scenarios with high precision and accuracy. Then, two sets of FLTT test systems were built through the adaptive transformation of the SLR systems of the Shanghai Astronomical Observatory (SHAO). Among them, we added the precise control circuit of the laser emission epoch, the calibration device of the FLTT system time delay, and the clock difference extraction module. Depending on the two FLTT systems, we carried out one-way and two-way FLTT experiments, homologous clock FLTT experiments for BDS45 and BDS22 satellites, and non-homologous clock FLTT experiments for BDS21 and Galileo206 satellites. In addition, we obtained the real clock difference of the two FLTT systems with a DG645 delay signal generator, which is the clock difference obtained by the electrical signals, and then the reliability of the clock difference of one-way and two-way FLTT experiments was demonstrated. Finally, we analyzed the FLTT results and studied the main factors that affect the performance of this technology.

    Results and Discussions

    Based on BDS45, BDS22, and other satellites, the FLTT experiments in one-way and two-way modes were carried out, and both obtained a precision better than 100 ps (Fig. 8, Fig. 9, Fig. 10, Fig. 11). There are two critical issues to realize FLTT using curved mirrors. One is the limited hitting probability at the right time and another issue is the weak strength of reflected signals. Therefore, the one-way FLTT mode will have better applicability in the future. The results of the one-way FLTT were similar to those of the two-way FLTT (Fig. 10 vs Fig. 11, Fig. 11 vs Fig. 12), which verified the reliability of the improved clock difference extraction algorithm in this study. Compared the FLTT experiment results and the clock difference obtained by the DG645 electrical signals, the absolute accuracy was better than 2 ns, demonstrating the reliability of the FLTT experiments (Fig. 12). However, there was plenty of room for improvement. In the FLTT with the homologous clock, the clock difference jump phenomenon was caused by the synchronization of the event timer and clock. In the FLTT with non-homologous clocks, the clock difference fluctuated greatly due to the poor stability of the End-run clock.

    Conclusions

    The curved mirror-based FLTT has been considered a more accurate and stable time transfer technique than existing methods, which is a popular scheme for the next generation of laser time transfer. However, there is a lack of suitable test platforms for validation purposes, and the current research interests in FLTT remain in theoretical simulation. In this study, we selected satellite reflectors instead of curved mirrors as a forwarding payload for the FLTT experiments, demonstrating the feasibility and performance of this technique. We improved the clock difference extraction algorithm of the one-way FLTT and proposed a high-precision interpolation model. It was shown from the results that the precision was better than 100 ps with an absolute accuracy of 2 ns, and the one-way FLTT was feasible. Of course, the FLTT will probably face other challenges in practical application, such as weak laser echo signal recognition, and the probability of success is affected by the attitude and rotation period of satellites. This study provides significant support for FLTT development, such as in laser emission timing control, data processing, and more.

    Renfang Geng, Zhibo Wu, Yong Huang, Haisheng Lin, Rongzong Yu, Kai Tang, Haifeng Zhang, Zhongping Zhang. Experimental Study of Forward Laser Time Transfer Based on Satellite Retroreflector[J]. Chinese Journal of Lasers, 2023, 50(18): 1804004
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