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Light curve measurements with a superconducting nanowire single-photon detector.

The superconducting nanowire single-photon detector (SNSPD) is used to detect the sunlight reflected by the artificial satellite and space debris. In the process, light curves of the satellite and space debris are successfully measured. In 2017, a space-debris laser ranging system with a four-element SNSPD is developed by Yunnan Observatories in China. During the ranging experiments, the detector works in a freely detecting state. It can detect photons not only of the laser echo, but also of the sunlight reflected by the target. After separating the data triggered by background light from the whole detected data set, the light curves of satellites, including Topex and several types of debris, are acquired. The apparent rotation rate of the satellite Topex is determined by analyzing the light curves by Fourier transform and phase dispersion minimization. On the basis of a laser ranging system using SNSPDs, the simultaneous measurement of the laser ranging and light curves of some space targets without any additional equipment is realized for the first time, to the best of our knowledge.