Active and passive microvibration control in telescope structures

Precise large astronomical telescopes require proper control and minimization of static and dynamic structural distortions caused by different loads e.g. from gravity, wind, temperature and equipment noise. This equally holds for the main structure as well as for the component level. Examples for the first are the alignment of secondary and primary mirror, and for the latter the shape error minimization of the reflecting surfaces. In this paper, essential concepts for passive and active distortion control are presented and discussed. Some of these concepts are demonstrated for the case of a big representative truss structure and the influence of modal reduction is pointed out. The tools developed to simulate and optimize active damping systems on truss structures are flexible and extendable and could be applied to big telescope structures like for example the OWL structure.