As the most important feedback source of the FAST telescope control system, the measurement system directly determines the overall performance and observing efficiency of FAST. High-precision total station measurement equipment is used in real-time measurement of the FAST reflector and the feed cabin. Because the measurement accuracy of total station is easily influenced by the atmospheric environment, in this paper, we established the distribution model of temperature, humidity and pressure through the meteorological information collected by the weather stations evenly distributed in the reflector. We analyzed the changes of atmospheric environment caused by FAST topography and calculated the real-time atmospheric correction at each location within the coverage of the weather station based on the formula. Finally, according to the variation of the atmospheric correction value in the measurement path, the optimal atmospheric correction parameter of the path is obtained, so as to improve the measurement accuracy of the FAST reflector.
The Five-hundred-meter Aperture Spherical radio Telescope (FAST) project locates in the mountainous region of Guizhou Province, China. Due to the huge scale of the project and the precise observation performance requirements of the telescope, the reflector unit is required to have characteristics of small quality and high precision. Due to the high humidity on the site, it is necessary to ensure that the reflective surface unit has good anti-corrosion properties. This article studies how to solve the problem of the structural performance of the reflective surface unit and its implementation method. Based on the research in this paper, the error of the surface accuracy of the reflecting surface unit is less than 2.5 mm, and the central deflection of the block constituting the unit is less than 1 mm. In addition, this type of unit has good anti-corrosion properties. This paper also proposes the method of accuracy assurance in the construction process. In the end, the research results were successfully applied to the FAST project.
The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is currently under construction at a Karst
depression in the Guizhou province of China. The active reflector of the telescope is composed of 4395 triangular panels
laid on a cable-net structure. The aperture of the spherical surface is 500 meters, with open angle of about 110~120
degrees. Acting as the nodes of the reflector, the joint of these panels are adjusted by 2235 down-tie cables drawn by
actuators. The RMS error of the parabola reflector is expected to be 5mm.
To form the parabola shape of the reflector, for each of the actuators, a minimal working stroke of 950mm is required,
with maximal speed of 1.6mm/s at the load of 50kN. Considering the elastic deformation of the down-tie cable and other
factors, a positioning error within 0.25mm is required for the actuators.
In this paper, the base formula for the motion of a general actuator at a typical observation time is studied analytically.
The results are used to estimate the control error of the actuators and the pointing error of the whole reflector. Based on
the designed error budgets, a statistical method is employed to estimate the overall surface error of the parabola reflector.
The overall surface error is a comprehensive result of the panel design error, panel fabrication error, thermal deformation
error, panel wind load induced error, cable-net error, installation error, measurement and control error etc. The results
may be used as a reference in the measurement and control of the active reflector when in operation.