Crystal Clear SSI for Operational Modal Analysis of Aerospace Vehicles∗

In this paper we revisit the problem of the modal analysis of space launchers. We consider the Ariane 5 launcher with its usual equipment during a commercial flight under the natural unknown excitation. The case of space launchers is a typical example of a complex structure with sub-structures strongly and quickly varying in time. This issue becomes especially important in e.g. estimation of damping of aerospace vehicles. The eigenfrequencies are also sliding during the flight but the modeshapes are more stable. Recently, a new implementation of the subspace identification method has been proposed, leading to cleaner and more stable stabilization diagrams. We monitor the behavior of estimated modal parameters by applying this “crystal clear” implementation of the data driven and the covariance driven Stochastic Subspace Identification algorithms. We show the importance of “crystal clear” to monitor successfully frequencies and damping estimates over time in such a non stationary case.