Superconducting nanowire single-photon detectors (SNSPDs) at a wavelength of 532 nm were designed and fabricated aiming to satellite laser ranging (SLR) applications. The NbN SNSPDs were fabricated on one-dimensional photonic crystals with a sensitive-area diameter of 42 μm. The devices were coupled with multimode fiber (ϕ = 50 μm) and exhibited a maximum system detection efficiency of 75% at an extremely low dark count rate of <0.1 Hz. An SLR experiment using an SNSPD at a wavelength of 532 nm was successfully demonstrated. The results showed a depth ranging with a precision of ~8.0 mm for the target satellite LARES, which is ~3,000 km away from the ground ranging station at the Sheshan Observatory.

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 m² at a ranging distance up to 1726.8 km, corresponding to an RCS of 0.1 m² at a distance of 1000 km. These works are expected to provide new technologies to further improve the performance of DLR.

A critical requirement to achieve high efficiency of debris laser tracking is to have sufficiently accurate orbit predictions (OP) in both the pointing direction (better than 20 arc seconds) and distance from the tracking station to the debris objects, with the former more important than the latter because of the narrow laser beam. When the two line element (TLE) is used to provide the orbit predictions, the resultant pointing errors are usually on the order of tens to hundreds of arc seconds. In practice, therefore, angular observations of debris objects are first collected using an optical tracking sensor, and then used to guide the laser beam pointing to the objects. The manual guidance may cause interrupts to the laser tracking, and consequently loss of valuable laser tracking data. This paper presents a real-time orbit determination (OD) and prediction method to realize smooth and efficient debris laser tracking. The method uses TLE-computed positions and angles over a short-arc of less than 2 min as observations in an OD process where simplified force models are considered. After the OD convergence, the OP is performed from the last observation epoch to the end of the tracking pass. Simulation and real tracking data processing results show that the pointing prediction errors are usually less than 10″, and the distance errors less than 100 m, therefore, the prediction accuracy is sufficient for the blind laser tracking.

Orientation information of space debris is required to improve the orbital prediction accuracy for mitigation or elimination of a significant threat to not only human space activities but also operational satellites. Obtaining orientation information is currently achievable by applying photometry, adaptive optics (AO) and satellite laser ranging (SLR) technologies. In this study, a new method is proposed based on an echo laser pulse waveform (ELPW) for the orientation determination of space debris; its feasibility was also investigated by numerical simulations. Unlike the photometry and AO technologies available just under the sun-illumination condition and the SLR technology applicable only for cooperative targets, the ELPW is achievable by using a high power laser regardless of the above measurement constraints. A mathematical model is derived to generate the ELPW, and the beam broadening and spreading due to the atmospheric turbulence is taken into account. The Gaussian decomposition based on a genetic algorithm was employed to the ELPWs in order to analyze the orientation features. It is demonstrated from the numerical simulations that the ELPWs have distinctive shapes characterizing the orientation of space debris and therefore our approach was capable of providing orientation information.

Classical satellite laser ranging (SLR) technology based on 532 nm wavelength usually adopts low energy laser to measure cooperative objects. However, for a very weak target, such as debris and lunar reflector arrays, laser ranging system should have much stronger detection capability than the laser ranging system for traditional application. A common way to improve system detection capability is to use high energy laser. With an additional frequency doubling crystal, it is more difficult to make a high energy laser based on 532 nm than that based on 1.06 μm, which restricts the improvement of system detection capability, and also gives rise to the short lifetime, poor system stability problems. Compared with 532 nm laser, the 1.06 μm laser has many advantages of high laser energy and power, high atmospheric transmissivity, and low background noise, thereby making it an ideal substitution for the traditional 532 nm SLR system. In this paper, we comparatively analyze the above-mentiond advantages of the 1.06 μm laser and other system’s key parameters such as detector efficiency and target reflection efficiency, calculate the echo photons one can obtain, and establish a 1.06 μm laser ranging system based on the existing 532 nm SLR at Shanghai Astronomical Observatory. Owing to the using of an InGaAs single photon detector, the system turns very compact, low cost, easy-to-be-installed and has almost no additional operation complexity than the 532 nm system. With this system, the high precision 1.06 μm laser ranging for cooperative objects based on InGaAs detector is carried out for the first time in China, and a ranging for space debris 1500 km away can also be realized. The ranging experiment shows with the same laser, SLR using 1.06 μm output reaches a detection efficiency of 7 times the detection efficiency the SLR using 532 nm output reaches, and the background noise only 1/5. This approves the advantages and feasibility of 1.06 μm system, and also shows its great potential application prospects in the high precision weak target laser detection in the day and night time. This paper provides a very easy operation, high compact and low cost method for the future high precision weak target laser ranging.