Objective  Satellite laser ranging (SLR) is a highly accurate space geodesy technology that uses short pulse lasers, optical receivers, onboard reflectors, and event timers to measure the distance between a satellite and the ground, with a measurement accuracy of up to sub-centimeter level. It is widely used in various scientific studies, including the precise geocentric position and motion of ground stations, satellite orbits, Earth's gravity field components and their temporal variations, and Earth's directional parameters. The SLR system calibrates its delay by measuring a ground target at a known distance, which enables calibration accuracy to reach millimeter level. This calibration method is currently used in most SLR stations. With the development of SLR technology, new applications have emerged, such as one-way laser ranging, laser time transfer, interplanetary laser ranging, and multi-station collaborative laser ranging. These applications require accurate one-way delay calibration of the SLR system, which is difficult to obtain by measuring ground targets, limiting the development of these applications. To meet the requirements of laser time transfer at the Chinese Space Station (CSS) and carry out high-precision system transmission and reception delay calibration research, this article focuses on calibrating the one-way delay of the SLR system.

  Methods  This paper presents a high-precision method for measuring the transmission and reception delay of SLR. Firstly, the composition delay of the SLR system was comprehensively analyzed, which includes the optical delay generated during laser propagation, the photoelectric conversion delay during photon detection, and the electrical delay of transmitting electrical signals (Fig.1). Secondly, various time delays were measured, such as electrical, optical, and optoelectronic conversion at the Shanghai Astronomical Observatory (SHAO). For this purpose, an event timer A033 with a measurement accuracy of 3 ps, a dead time of 50 ns, a signal generator ETTG-100 with an accuracy of 4 ps, a laser with a 532 nm wavelength, 2 kHz repetition rate, and energy fluctuation of less than 3%, as well as adapters and signal converters are used. And a high measurement accuracy of these delays was achieved, reaching the picosecond level. Finally, the time delay of each segment is combined to calibrate the transmission delay (Fig.4), reception time delay (Fig.5), and ground target distance of the SLR system.

  Results and Discussions   The SLR system of SHAO was used as an experimental platform to measure time delays. The cable delay was measured at (107 100 ± 2) ps, the delay of the optical path from the 45° mirror of the transmitting cylinder to the fixed target was measured at (8 563 ± 2) ps, and the delay of the linear detector was measured at (13 444 ± 8) ps. The accuracy of these measurements was at the picosecond level, which meets the required standards. Using these measurement results, the transmission and reception delay were calibrated with calibration results of −4 698 ps and 192 269 ps, respectively. The calibration accuracy was better than 11 ps and 13 ps (Tab.5). This calibration method was then applied to verify the ground target distance deviation, and the difference between the calibration results and the feedback value from the International Laser Ranging Organization was only 11 ps.

  Conclusions  In this paper, a novel method for accurately measuring the transmission and reception delay of the satellite laser ranging system is presented. This method is crucial in meeting the requirements of the laser time comparison task at CSS. The method comprehensively considers the delay of the signal transmission cable, optical path, lens, and linear detector, resulting in picosecond calibration of their delay. The calibration of the transmission and reception delay of the SLR system at SHAO was achieved with calibration errors of less than 11 ps and 13 ps, respectively. This method can reduce the systematic deviation of observation stations when applied to the calibration of fixed ground target distance deviation. Moreover, it provides technical support for laser time comparison engineering and a reference for improving the quality of the SLR data.