Enhanced pointing of telescopes by smart structure concepts based on modal observers

Telescopes are pointed to their targets on the sky by the movement of their optical system (reflectors, mirrors) in two or three axes. The achievable pointing accuracy is depending on the quality of the elasto-mechanical system, which is supporting the optics, and the drive system, which is actuating the axes movements, and limited in existing telescopes by the number of sensors and actuators in the axes. With the classical arrangements only the rigid body regime of the structural system can be controlled. Effects in the quasi-static regime and in the flexible body regime of structural deformations are out of influence of the position sensors and drives of the axes and must be handled by other means. With now available smart structure concepts it is possible to overcome these restrictions and to enhance the pointing accuracy of the telescopes by rather inexpensive additional means. In the paper a smart system approach is described, which is based on a modal observer concept. The observer uses the eigenmodes of the structural system to predict the deformation behavior based on the measurements of modal sensors. Results of the achievable improvements are demonstrated by two telescope projects, in which the modal observer enhancement will be realized.