Estimates of FRFs from output-only data of a space mission payload component

The Large Area Telescope, LAT, is the core of the Gamma-ray Large Area Space Telescope, GLAST, space mission whose launch is scheduled for 2006. The aim of this mission is the exploration and the study of the high-energy phenomena of the universe by tracking the electron or positron produced from an initial gamma-ray with an high accuracy with respect to the previous available instruments. The LAT consists basically of a four-by-four array of tower modules. Each tower is formed by 19 composite tray structures. Since the dynamic behavior of the tray structures is of great importance for a good working instrument (and then for the whole space mission), and since the high number of composite trays that have to be built, an efficient experimental procedure for the dynamic system identification has to be introduced in order to monitor the "health" of the composite plates. Among the different experimental techniques developed for the dynamic characterization of structures, in this paper those based on the analysis of Output-Only data, also known as Operative Modal Analysis, have been considered since their promising overall efficiency coming from the absence of any measure of the input loading. Moreover, the actual capability of the output-only experimental analysis to estimate the frequency response functions of the composite trays of the LAT instrument is investigated through the analysis of the effects of different mass distribution on the estimate of the modal masses. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.