The Chinese Academy of Sciences Yunnan Observatory made a major breakthrough in the lunar laser ranging technology research on January 22nd. The research team successfully used the 1.2m telescope laser ranging system to successfully detect the laser pulse signal returned by the moon reflector Apollo No. 15 for the first time in the country.
Lunar laser distance measurement is to calculate the earth-to-moon distance by accurately measuring the round-trip time of the laser pulse from the ground observation station to the lunar surface reflector. This is an integrated technology that covers many subject areas such as laser, photoelectric detection, automatic control, space orbit, etc. It is the most accurate technical measure for the measurement of the distance between the earth and the moon. Its observational data is for astronomy and geodynamics The study of science, moon physics, and the verification of gravitational theory are of great value.
The Chinese Academy of Sciences Yunnan Astronomical Observatory applied astronomical research group has long been engaged in lunar laser ranging technology research. According to Li Yuqiang, deputy head of the research group and associate researcher, the distance measurement is to improve the pointing accuracy and tracking accuracy, improve the detection efficiency and optical transmission efficiency, and implement a number of key technologies.
Li Yuqiang said that from the perspective of traditional technology, the main difficulty of lunar laser ranging lies in laser emission and laser receiving conversion in the common optical system. It is necessary to ensure that the system can normally emit laser light and receive echo signals; the telescope tracks the pointing accuracy when the telescope points With an accuracy of 3 seconds, the distance between the center of the laser beam and the lunar reflector can be up to 6 km when pointing to the moon, and the largest reflector of the lunar surface - the effective reflection area of ​​the Apollo 15 is only 3402 cm2. Will directly affect the success of laser measurement. In addition, the quality of the laser beam and the efficiency of the optical system affect the actual emission energy and quality of the laser.
In order to solve the above problems, the research team independently researched and developed the Luminous Laser Luminometer System for communica- tions and conversions. The research team proposed that a local orientation correction model could be established to further improve the pointing accuracy of the telescope. Using a certain number of stars around the lunar orbit, they used local corrections to correct the model before each laser measurement, in order to ensure that the telescope achieves high pointing accuracy in angular seconds in the orbital region of the observation target. In 2017, after upgrading the optical system of the 1.2-meter telescope at the Yunnan Observatory, the Chinese Academy of Sciences increased the efficiency of the optical system and laid a good foundation for the lunar laser ranging. In addition, the research team has done a lot of work on weak signal detection and data processing.
The average distance between land and moon is 38,4403.9 kilometers. In the distance measurement experiment, the researchers took the common light path working method to perform distance measurement by the 1.2m telescope laser ranging system. The laser wavelength was 532 nm, the pulse width was 10 ns, the frequency was 10 Hz, and the single pulse energy was tested. It is 3.3 joules. On the evening of January 22 from 21:25 to 22:31, the measured data segment showed that the distance from the Apollo 15 reflector to the station was 385,823.433 km to 387,119.600 km, and the ranging accuracy was better than 1 meter. .
At present, the only countries in the world that successfully achieve lunar laser ranging are the United States, France, and Italy. The Yunnan Astronomical Observatory successfully implemented the lunar laser ranging to fill the gap in the field of lunar laser ranging in China. It will provide distance measurement technical support for the implementation of China’s Tianqin plan.
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