Modal Parameter Identification and Correlation of Launch Vehicle Interstage Using "Output-Only" Experimental Data

The Output-Only analysis typically allows to identify the modal parameters of a given structure on the base of the data achieved by the operative conditions or environment of such a device. In the design development of a Launch Vehicle (LV) the vibration tests for launch qualification are performed with the main objective to verify that the acceleration levels of the structure, attached systems, and payloads, do not exceed a prescribed design level. Thus, these kind of tests are performed by sensoring the output responses (i.e., the acceleration levels) only. In the present paper, the modal parameter identification and correlation of a LV inter-stage based on Output-Only (OO) experimental data will be presented. The practical advantage arisen by using this technique will be pointed out. It has essentially consisted of utilizing the same data collected during qualification tests. Therefore, this has reduced the overall cost required for setting up a further experimental test that should be explicitly dedicated to the modal parameter identification. Moreover, the obtained modal estimates, based on the OO approach, have been also used for correlating the numerical Finite-Element model of the LV inter-stage that have been previously used for design purposes.