Full-scale rocket motor acoustic tests and comparisons with empirical source models

Abstract

Development of the next-generation space flight vehicles has prompted a renewed focus on rocket sound source characterization and near-field propagation modeling. Improved measurements of the noise near the rocket plume are critical for direct determination of the noise environment. They are also crucial in providing inputs to empirical models and in validating computational aeroacoustics models. NASA's SP-8072 acoustic load prediction model (1971) is a widely used method for predicting liftoff acoustics. The method implements two Distributed Source Methods (DSM-1 and DSM-2), which predict the loading as the sum of the radiated field from each source distributed along the plume. In this paper, measurements of a static horizontal firing of an Alliant Techsystem (ATK) Orion 50S XLG are analyzed with respect to the historical data that drive the SP-8072 prediction models. Comparisons include total sound power and sound power spectrum, and the distribution of the sound power and sound power spectrum along the length of the plume. Scalar pressure measurements yield reasonable agreement between the Orion-50S XLG data and both methods for undeflected plumes in the original SP-8072. However, development of these comparisons has prompted significant questions regarding the underlying physics of the two methods.