###### Abstract  
Debris laser ranging (DLR) is receiving considerable attention as an accurate and effective method of determining and predicting the orbits of space debris. This paper reports some technologies of DLR, such as the high pulse repetition frequency (PRF) laser pulse, large-aperture telescope, telescope array, multi-static stations receiving signals. DLR with a picosecond laser at the Shanghai Astronomical Observatory is also presented. A few hundred laps of space debris laser-ranging measurements have been made. A double-pulse picosecond laser with an average power of 4.2 W, a PRF of 1 kHz, and a wavelength of 532 nm has been implemented successfully in DLR, it's the first time that DLR technology has reached a ranging precision at the sub-decimeter level. In addition, the characteristics of the picosecond-pulse-width laser transmission with the advantages of transmission in laser ranging were analyzed. With a mode of the pulse-burst picosecond laser having high average power, the DLR system has tracked small debris with a radar cross-section (RCS) of 0.91 m\({}^{2}\) at a ranging distance up to 1726.8 km, corresponding to an RCS of 0.1 m\({}^{2}\) at a distance of 1000 km. These works are expected to provide new technologies to further improve the performance of DLR. space debris laser ranging; single-photon detection; picosecond laser; pulse-bursts +
Footnote †: journal: _sciences_  
of space debris [3]. The probability of a catastrophic collision has been calculated as 3.7% for each vehicle in orbit, and the probability of a non-catastrophic collision is as high as 20% [3]. Various satellite internet constellation programs, such as the One Web, SpaceX Starlink, Telesat, and Hongyan constellations, will launch thousands of satellites into orbit to provide global broadband internet services, which will greatly affect the Earth's orbital resources. Space debris has become an important factor threatening space safety. The European Space Agency issues early warnings of collisions between space debris and spacecraft more than 50 times per year on average, and the number of collision avoidance maneuvers required annually has reached 22 [5]. Ensuring spacecraft safety after launch requires the orbits of space debris to be determined accurately. Compared with microwave technology for tracking space debris, laser technology is characterized by a short wavelength, small divergence angle, good directivity and monochromaticity, and strong anti-interference. A laser can be used for a real-time measurement technology with a ranging precision reaching a sub-decimeter level, which is two orders of magnitude better than the ranging precision of a microwave radar or optical telescope. The use of a laser improves the accuracy of the determination of the space debris orbit and plays an important role in enhancing spacecraft collision warning capabilities [4; 5; 6]. Many countries, including the United States, Australia, Austria, Russia, Poland, and China, have developed high-precision laser ranging technology for debris laser ranging (DLR) [7; 8; 9; 10; 11; 12; 13]. The International Laser Ranging Service [14] established a space debris laser tracking and measurement working group in 2014 to promote the research and application of high-precision space debris measurement technology and allow the high-precision monitoring and early warning of space debris in space activities, which will enhance the early warning capabilities of space targets for space situational awareness. In DLR, the surface of the measured target diffusely reflects the incident laser beam and the return laser signal is so weak that it makes measurements difficult [11]. Improving the laser emission capability, signal receiving, and detection capabilities of the ground station is, therefore, important to DLR technologies. In recent years, DLR has advanced in terms of the pulse repetition frequency (PRF) and pulse width of the laser, single photon detection, and signal receiving.