Gemini Preprint #79

Modal and Operating Characterization of an Optical Telescope

Peter Avitabile, Johann Teutsch, Keith Weech, David R. Smith
Modal Analysis and Controls Laboratory, University of Massachusestts Lowell, Lowell MA 01 85

Geoff Gwaltney
Keweenaw Research Center, Michigan Technological University

Michael Sheehan
Gemini Observatory


As part of the overall assessment of the dynamic characteristics of the Gemini Optical Telescope, an experimental modal test was performed on this structure along with collection of operating data. For the modal testing, multiple reference impact testing was performed to characterize the structure. Time data was acquired and processed to compute multiple referenced frequency response functions. Modal parameters were extracted as part of the overall aassessment of this optical telescope.

For the operating assessment, many operating tests were conducted to determine the effects of wind loading on the structure. A variety of different structural configurations were evaluated during a series of tests at the Gemini Optical Telescope. Several days and nights were used to measure the telescope's behavior under a variety of different wind loading conditions. Operating data was collected and reduced for all of the tests conducted to identify wind loading conditions that hinder normal operations of the telescope.

This paper presents some of the significant considerations regarding the data obtained and the determination of the modal and operating mode shapes. Some thoughts on the acquisition of the data and its reduction are presented along with the extraction of modal parameters and operating shapes.

To appear in the Proceedings of the 19th International Modal Analysis Conference.

Download the PDF file.

Ruth A. Kneale / / November 2, 2001