Laser measurement technology is inherently high accurate and will play an important role in precise orbit determination, accurate catalog, surveillance to space debris. Shanghai Astronomical Observatory (SHAO) has been developing the technology of laser measurement to space debris for several years. Based on the first successful laser ranging measurement to space debris in country, by applying one new set of high power 532nm wavelength laser system with 200Hz repetition rate, and adopting low dark noise APD detector with high quantum efficiency and high transmissivity of narrow bandwidth spectral filter, SHAO have achieved hundreds of passes of laser data from space debris in 2014, and the measured objects with distance between 500km and 2200km, Radar Cross Section (RCS) of >10m2 to <0.5m2 at the precision of <1m RMS for small RCS targets ,and the success rate of measured passes of up to 80%. The results show that laser ranging technology in China can routinely measure space debris and provide enough measurement data with high accuracy to space debris applications and researches such as surveillance activities in the future.
SLR (Satellite Laser Ranging) is the common satellite observation technology with the highest single shot precision. The 532nm wavelength laser signal derived from 1064nm wavelength laser system is generally adopted to laser measurement to satellites. The 1064nm wavelength laser signal has better performances than 532nm ones in atmospheric attenuation, photon number, laser power, development and price, and so on, which is beneficial to enhance the detection ability of measuring system, and carry out the goal of weak signal detection. In this paper, the relevant techniques are presented in building up SLR system with 1064nm wavelength, and the corresponding solutions are put forward. With these techniques, the 1064nm wavelength high precise SLR measurement was successfully carried out by using si-detector for the first time in Shanghai Astronomical Observatory (SHAO) and the experimental foundations have been laid for the further development and applications in the field of far distance and weak signal space targets observation.
Laser ranging technology can directly measure the distance between space targets and ground stations with the highest
measurement precision and will play an irreplaceable role in orbit check and calibrating microwave measurement
system. The precise orbit determination and accurate catalogue of space targets can also be realized by laser ranging with
multi-stations. Among space targets, most of ones are inactive targets and space debris, which should be paid the great
attentions for the safety of active spacecrafts. Because of laser diffuse reflection from the surface of targets, laser ranging
to space debris has the characteristics of wide coverage and weak strength of laser echoes, even though the powerful
laser system is applied. In order to increase the receiving ability of laser echoes, the large aperture telescope should be
adopted. As well known, some disadvantages for one set of large aperture telescope, technical development difficulty
and system running and maintenance complexity, will limit its flexible applications. The multi-receiving telescopes
technology in laser ranging to space targets is put forward to realize the equivalent receiving ability produced by one
larger aperture telescope by way of using multi-receiving telescopes, with the advantages of flexibility and maintenance.
The theoretical analysis of the feasibility and key technologies of multi-receiving telescopes technology in laser ranging
to space targets are presented in this paper. The experimental measurement system based on the 60cm SLR system and
1.56m astronomical telescopes with a distance of about 50m is established to provide the platform for researching on the
multi-receiving telescopes technology. The laser ranging experiments to satellites equipped with retro-reflectors are
successfully performed by using the above experimental system and verify the technical feasibility to increase the ability
of echo detection. And the multi-receiving telescopes technology will become a novel effective way to improve the
detection ability of laser ranging to space debris.
The first Chinese mission of Laser Time Transfer (LTT) between ground and Chinese Navigation Satellites was successfully implemented by Shanghai Astronomical Observatory of Chinese Academy of Sciences. Because of LTT payloads onboard the High Earth Orbiting (HEO) satellites with orbit altitude of 21,500 to 36,000 km, the photon counting technology was adopted to increase the success rate of laser signal detection on satellites. The detection chip operates in a Geiger Mode with single photon sensitivity. It has a diameter of 40 um, it is produced by Czech Technical University. In order to reduce the background noise in space, the gated mode and two separated channels with different Field Of View (FOV) were used for the detector. The improvements for the next version of the LTT detector resulted in a lower background noise and better laser detection rate. It is also been demonstrated in the onboard experiments that the photon counting detector works well after sunlight directly entered into its optical window. Finally the LTT experiments result on Chinese Navigation Satellites are present in this paper. The clock and relative frequency difference were obtained with the single shot measuring resolution of about 300ps and 30 ps precision.