Requirements and considerations of the surface error control for the active reflector of FAST

摘要

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is currently under construction at a Karstdepression in the Guizhou province of China. The active reflector of the telescope is composed of 4395 triangular panelslaid on a cable-net structure. The aperture of the spherical surface is 500 meters, with open angle of about 110~120degrees. Acting as the nodes of the reflector, the joint of these panels are adjusted by 2235 down-tie cables drawn byactuators. 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 otherfactors, 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 onthe 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 deformationerror, panel wind load induced error, cable-net error, installation error, measurement and control error etc. The resultsmay be used as a reference in the measurement and control of the active reflector when in operation.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.