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Measurements of solid rocket motor head end pressure and structural acceleration recorded during flights of a heavy lift launch vehicle are used to investigate if an interaction between the motor internal flow and structural motion exists. These data reveal that a locking of frequency and phase occurs over a 34-s period towards the end of the motor burn. A feedback relationship involving the motor pressure oscillations and structural accelerations, therefore, exists for this launch vehicle. The observed interaction significantly increases the pressure oscillation amplitudes relative to those measured in ground tests at the same burn time. This finding highlights a limitation of motor stability analysis methodology, in which structural motion is traditionally neglected. It appears that the potential for coupling between the motor pressure oscillations and structural response should be accounted for in predictions of solid rocket motor stability. The observed interaction also has implications for the prediction of loads induced by solid rocket motor pressure oscillations. Under some conditions the use of forcing functions based solely on ground test pressure measurements may underpredict flight loads. Nomenclature a = acceleration signal, ĝ a = Hilbert transform of a, g f 0 = generalized force normalized with respect to unit lb m , in:=s 2 q = modal structural displacement, in. t = time after ignition (burn time), s x = structural displacement; also, oscillatory pressure normalized with respect to gas weight density, in. o , e = nominal and effective damping (as a ratio to the critical value), dimensionless = phase, rad = phase difference between structural velocity and fluid force, rad ! o , ! e = nominal and effective circular natural frequency, rad=s

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Public reporting burden tor this collection of information is estimated to average 1 hour per response, includinq the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden 'to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington. VA 22202-4302, and A methodology developed to derive forcing functions from the turbulent component of measured wind profiles for a new Monte Carlo gust loads analysis approach is described. Several large sets of forcing functions were developed by extracting the short-duration, random component of measured Jimsphere wind profiles. A database consisting of Jimsphere wind soundings measured over the past three decades at the Eastern and Western Ranges of the United States was used to derive the forcing functions. Validity of these forcing functions for heavy-lift and medium-lift launch vehicles was established by examining the error contributions from various sources within the wind measurement system and the application of a noise-reducing filter. A unique aspect of the method is the extraction of the relatively rapidly changing turbulent component associated with the non-persistent wind features which are expected over a given observation time period. SUBJECT TERMS AbstractA methodology is developed to derive gust forcing functions from the turbulent components of measured wind profiles. Several large sets of forcing functions were developed by extracting the short-duration, random component of measured Jimsphere wind profiles. A database consisting of Jimsphere wind soundings measured over the past three decades at the Eastern and Western Ranges of the United States was used to derive the forcing functions. Validity of these forcing functions for heavy-lift and medium-lift launch vehicles was established by examining the error contributions from various sources within the wind measurement system and the application of a noise reducing filter. A unique aspect of the method is the extraction of the relatively rapidly changing turbulent component associated with the non-persistent wind features which are expected over a given observation time period. The gust forcing functions can be used in a Monte Carlo analysis to determine launch vehicle loads for the Eastern and Western Ranges.