Research On Solar Thermal Error And Compensation Of Large Aperture Radio Telescope

Reflector antennas have high gain and low sidelobe characteristics,widely used in aerospace,deep space exploration,extraterrestrial communication and other fields.To see further and more clearly,the National Development and Reform Commission and the Chinese Academy of Sciences plan to build a 110-meter aperture fully mobile radio telescope(Qi Tai Radio Telescope,or ’QTT’)in Qitai,Xinjiang province.With the increase of antenna aperture and frequency,the influence of structural deformation caused by solar heat on its performance becomes more and more serious.This paper takes the radio telescope as the research object,studies and summarizes the sunshine temperature field,deformation field and error change law of antenna structure under the action of solar radiation,and intends to study from the following three aspects :(1)Research on sunshine temperature field of large aperture radio telescope.Taking the antenna truss,main reflector and other components as the research object,the antenna thermodynamic finite element model considering solar radiation,far-space cooling radiation and shadow shielding of reflector is established.Typical working conditions are selected to analyze the sunshine temperature field of QTT,and the influence of wind speed,pitch angle and other factors on the antenna temperature field is discussed.The distribution characteristics of the temperature field of the antenna truss and the main reflector are obtained,and the temperature difference of the upper chord node of the back frame is analyzed.(2)Study on sunshine deformation field of large aperture radio telescope.The constraint method of the pitch axis of the QTT reflector is discussed,and the thermal deformation of the structure and the profile error of the reflector under two extremely constrained methods are analyzed.It is found that the symmetrical floating constraint of the pitch axis is closer to the actual situation.Based on this constraint method,the deformation field of the antenna truss under typical working conditions is obtained.Then,the solar incidence angle is proposed to describe the relative position between the antenna and the sun,and the relationship between the thermal deformation of the main reflecting surface and the solar incidence angle is studied.(3)Research on the solar thermal error and secondary reflector compensation of the 110 m radio telescope.Under the action of solar radiation,the upper chord structure of the back frame is deformed,which destroys the standard parabolic shape of the reflector,thus affecting the antenna performance.Based on the deformation data of the upper chord node of the QTT back frame,the accuracy of the main surface and the pointing accuracy after the thermal deformation of the QTT is evaluated by using the best-fit parabolic method.According to the relationship between the main and sub-surfaces of the antenna,the position of the best sub-reflector after the antenna deformation is obtained.Adjusting the position of the sub-surface to reduce the error caused by the thermal deformation of the antenna.Finally,the change of the optical path difference of the main surface before and after the secondary surface compensation is discussed.