DEVELOPMENT OF OPERATIONAL MODAL ANALYSIS TECHNIQUES FOR LAUNCH DATA

Correlation-based Operational Modal Analysis (OMA) has been used to act as a pathfinder for the development of techniques to process launch data. This activity, which emphasizes the estimation of modal damping, operates in an extremely challenging environment due to the rapidly changing modal properties, loading conditions, and vehicle configuration as well as the limited response data that is available. A historical review of these efforts is provided. Recent work with launch environment data has identified two issues for immediate attention: beat-like phenomena in the correlation functions of short time records and potential interactions between the vehicle control systems and extracted damping in the lowest bending modes of the vehicles. A working hypothesis and mitigation for the first problem (beat-like phenomena) has been developed but a convergence metric was needed. This paper provides a first generation metric to allow the development to continue. The second problem of potential control system interactions is still being scoped and has become the near-term driver for the development of higher-fidelity tools (as the beating mitigation).