Integrated modeling has become a standard tool for evaluating performance of optical telescopes for design optimization and controller development. The integrated model combines structural dynamics, optics and control systems into a single simulation which outputs optical metrics of the telescope under the action of disturbances. The latter include external loads on the telescope, such as wind, seismic or temperature loads, as well as control inputs, which are provided by the actuators of the telescope system. Structural dynamics is a central part of the integrated model and its accurate representation is essential for high fidelity simulation. Traditionally, a structural dynamics model is derived from finite element analysis of the telescope and it is prohibitively large in size for practical simulation. In this paper, we investigate the use of model order reduction (MOR) techniques to resolve this problem for a Very Large Optical Telescope (VLOT). We propose a practical two-step procedure for obtaining a reduced model of the telescope. The finite element model is first reduced by truncating modes above a certain eigenfrequency. Subsequently, this truncated model is further reduced by a suitable MOR method to retain the more relevant lower frequency modes. In this paper, we compare several MOR methods both in frequency and time domain. The reduced models’ dynamic characteristics are compared with the truncated model of the telescope system. Finally, delivered image quality predictions are compared for the reduced systems of VLOT subject to wind loading.

Date Published: 16 September 2004
PDF: 12 pages
Proc. SPIE 5497, Modeling and Systems Engineering for Astronomy, (16 September 2004); doi: 10.1117/12.552499

Published in SPIE Proceedings Vol. 5497:
Modeling and Systems Engineering for Astronomy
Simon C. Craig; Martin J. Cullum, Editor(s)