Modal Identification of PPF/ENVISAT-1 Flight Model -Workpackage 1-

Abstract

Dynamic acceptance tests with the PPF/ENVISAT-1 Flight Model are planned to be performed in August 2000. As it is required to check and validate the structural dynamics model, it is desired to identify the modal parameters. First, the theory and the basic principles of modal identification by multi-axial base excitation are described. A frequency domain method, which is best suited for a general and reliable modal identification, is described in detail and the required steps for performing a modal identification are summarized. Recommendations are given for the performance of the base excitation tests. Also the proposed measurement point plan is reviewed. Apart from the lack of additional measurement points on the spacecraft core structure, which would allow a better global mode assessment, the measurement point plan seems to be adequate for modal identification. In order to have an alternative in case of difficulties with the HYDRA performance, a complementary modal identification method is proposed and described. The additional modal survey test shall be performed in a simplified manner with one single electrodynamic exciter.