Research On Thermal Deformation Error Compensation Of Large Radio Telescope Under Non-uniform Sunshine

Large radio telescope is the key equipment to detect and receive radio waves emitted by celestial bodies in the universe.With the improvement of astronomical observation targets and receiving accuracy,the aperture of telescope reflector is increasing,and the requirements for receiving performance are getting higher and higher.Among them,the non-uniform temperature field in the sunshine environment causes thermal deformation of large antenna,and the reduction of antenna receiving performance has seriously restricted the demand of astronomical observation.Based on the cooperation project of the National Astronomical Observatory of the Chinese Academy of Sciences,this paper takes the 120 m radio telescope in Jingdong,Yunnan Province as the specific research object,and studies the thermal deformation error compensation of the large main-focus feed single-aperture radio telescope in non-uniform sunshine environment.Firstly,the sunlight temperature field of the telescope mount and reflector is analyzed,and the daily variation law and annual variation law are explored.The temperature field simulation analysis of the feed adjustment mechanism under the sunlight convergence phenomenon is carried out.It is found that: 1)The temperature difference between day and night has little effect on the temperature field of the telescope frame,and the maximum temperature gradient is 2.5°C.The temperature gradient of summer solstice at noon is smaller than other seasons.2)The temperature difference between day and night has a significant effect on the temperature field of the telescope reflector.The change of azimuth angle has a great influence on the temperature gradient,while the change of pitch angle has little effect on the temperature gradient.Among them,the influence of azimuth angle on the temperature field at noon on summer solstice is the smallest than that in other seasons.3)the temperature of the feed adjustment mechanism is high and the temperature difference is large under the extreme conditions of sunshine convergence.Secondly,based on the non-uniform temperature field of the telescope,the daily variation and annual variation of the thermal deformation of the mount and the reflector are explored,and the pointing error caused by the thermal deformation of the mount and the receiving accuracy error caused by the thermal deformation of the reflector and feed system are analyzed.It is found that: 1)in the horizontal coordinate system,the pointing error corresponding to the thermal deformation of the frame is small at night and large at daytime,and the pointing in the vertical plane deflects to the left first and then to the right,and the pointing error in the vertical plane is the largest at the summer solstice,during the day,the pointing in the horizontal plane first deflects to the right and then to the left,and the pointing error in the horizontal plane at the vernal equinox is the largest.2)the thermal deformation of the reflector is uniform at night and has poor symmetry and uniformity in the daytime,and the distribution characteristics are strongly correlated with the azimuth;the uniformity of thermal deformation at the Winter Solstice is poor,while the uniformity at the Summer Solstice is better.The uniformity at the Spring Equinox and Autumnal Equinox has the same trend and the difference is small.Again,the error compensation analysis is carried out for the thermal deformation of the main reflector,the strut and the feed adjustment mechanism under the sunlight convergence phenomenon.The research shows that: 1)The error of the main reflector and the strut on the z-axis is larger than that on the x-axis and y-axis,and it increases first and then decreases in the 7:00-18:00.2)the thermal deformation of feed adjustment mechanism is mainly characterized by large deflection angle around y axis.3)Combined with the thermal deformation error of the summer solstice feed adjustment mechanism,the z-axis error is the largest at 12:00,reaching 9.87 mm,and the y-axis deflection error is the largest,reaching 2.26°.Finally,through the field test and theoretical analysis of the temperature field distribution of 50 m single-aperture main-focus feed telescope in Beijing Miyun station under the sunlight environment,the analogical thermal experiment is carried out to verify the correctness of thermal analysis of Jingdong 120 m single-aperture main-focus feed telescope under construction.Limited by the construction conditions of the 50 m telescope,only the solar temperature field experiment was carried out on its pedestal.The results show that the simulation results of ’A’ beam have the same trend with the experimental results,and the maximum error is 7.5%,which verifies the correctness of the thermal analysis method of 120 m telescope.In this paper,the methods and results used in the study of thermal deformation error of Jingdong 120 m radio telescope under non-uniform sunshine are studied,including the loading of non-uniform sunshine thermal load,the thermal deformation of reflector and signal receiving error,and the error analysis caused by thermal deformation of feed adjustment mechanism.It provides a new idea and practical reference for the suppression of non-uniform thermal deformation error of large radio telescope.