Analysis Of Influence Of Wind Load On Tracking Error Of Large-aperture Optical Telescope

Telescope is the most important instrument in astronomical observation. In theprocess of development of space observation, the diameter of telescope is bigger andbigger. For better observation condition, telescope installation elevation is increasing.These two factors can truly improve the performance of telescope, at the same time,it also brings a lot of tracking and observation error for telescope. One of theimportant error source is environmental wind load on the telescope. Wind load willcause vibration of telescope, which will cause beam wavefront tilt received by thetelescope tracking observation system. This paper focus on the analysis of wind loadeffect on tracking error of large-aperture optical telescope.Firstly, a theoretical analysis of two important source of telescope trackingerror: wind load disturbance and atmospheric turbulence is made. According to thetheory of engineering optics and telescope assembly, analysis of aberration which iscaused by relative displacement of the primary and secondary mirror belong totelescope is made, and the conclusion is that eccentricity and tilt of secondary mirrorcaused by wind load is important source of wavefront tilt. Combining with thevibration theory and the characteristic of atmospheric turbulence---spatial correlationand time correlation, an analysis of the secondary mirror vibration model underdynamic wind load and atmospheric turbulence model is made. The result shows thatboth model can be fitted by2-order AR model.Secondly, based on modern power spectrum estimation algorithm, a new kindof search iterative algorithm based on AR model is proposed. The power spectrum ofatmospheric turbulence is better estimated by continuously searching and iteratingobservation data to eliminate vibration power. Thus the vibration power spectrum isseparated from the power spectrum of wavefront tilt signal by difference method.Finally, in the1.8m telescope platform, with real time detection ofenvironmental wind load through aerovane, several stars have been selected to beobserved, according to three typical kind of observation model. An analysis of theinfluence of wind load on the telescope tracking error is made by applying the searchiterative algorithm based on AR model to analysize the received tracking wavefronttilt signal. The result shows that the tracking error of telescope is directly related todirect and speed of wind load, and the wind load effect point of telescope is trusssystem instead of telescope tube.In this paper, the analysis of specific process of wind load effect on thetelescope is made, and the experiment result can help us to to understand andanalysize the wind load effect on tracking error of optical telescope moreaccurately,which can provide reference for the design of better truss system structureof wind resistance of telescope.