System identification of the Green Bank Telescope structure and servo system

The Green Bank Telescope is a fully steerable 100 m aperture radio telescope in Green Bank, West Virginia used for cutting edge astronomical research. It is a large flexible structure which requires very high precision motion with accuracy of few arc seconds against errors induced by wind disturbances. The current servo system does not have high enough bandwidth and good vibration suppression properties to reject wind induced disturbances making high frequency astronomical observations difficult. As a first step towards designing high precision robust controllers for the telescope servo system, model identification of the structure and its servo system was carried out. This paper explains the identification experiment and its results. We identify the linear model of closed velocity loop and open position loop for the azimuth and elevation axes of the telescope.