Independent analysis of the space station node modal test data

With complex structures, comparison of independently derived sets of experimental modal parameters is an excellent way to increase confidence in the results. Modal identification results are presented using the eigensystem realization algorithm on frequency response functions from the modal test of the space station resource node. The resource node is the first U.S.-built structure for the International Space Station. The modal test was conducted by the NASA Marshall Space Flight Center in January 1997 for The Boeing Company, who designed and built the node. The calculated parameters are compared with independent results obtained by the test team using commercial software. There was excellent correlation of mode shapes between the two sets of results for the first 21 vibration modes of the structure up to 35 Hz. From 35 to 50 Hz, about 60% of 25 additional modes had excellent correlation. Natural frequencies and damping factors of most modes agreed within 0.1 Hz and 0.2%, respectively.