Dynamic analysis of a segmented telescope testbed

This paper describes the control analysis and simulation of a test rig currently being designed within the Gran Telescopio Canarias (GTC) project. This project is now in the preliminary stage of development and consists in designing a very large optical and infrared telescope with a segmented primary mirror in the range of 10+ meters in diameter. A primary mirror active control system (ACS) will dynamically adjust the segments´ positions, for approximating them to an hyperboloid global surface. Under operation, the segmented primary is perturbed by gravity, temperature, and wind effects within a somewhat large frequency spectrum. The telescope structure natural modes limit the bandwidth of the control system. A structure design goal is obtaining a robust, lightweight mirror tube with its lowest resonant mode as high as possible. But the interaction between the segment alignment control system, wind disturbances, and telescope structural dynamics impacts the telescope optical performance. This results in a loss of the optical resolution, in the range of sub-arcseconds. We show the proposed control system structure and the simulations performed on a model of a reduced telescope test platform.