Effect of the rail unevenness on the pointing accuracy of large radio telescope

Considering the stringent requirement of the pointing accuracy up to 2.5″ of the World largest full steerable telescope, this paper presents a coarse-fine mixed model to describe the azimuth rail unevenness. First, the coarse-fine mixed model is proposed. In the model, the trigonometric function is utilized to describe the error with long wavelength whilst the fractal function is used for the short wavelength errors, separately. Then the mathematic model of the pointing accuracy is developed mathematically. Finally, the coarse-fine model and point accuracy model are applied to Green Bank Telescope with valuable result. This paved the way for predicting point error of Qi Tai Telescope.