Abstract

Rocket launches generate extremely high acoustic levels, particularly in the low-frequency range, posing risks to both launch vehicle integrity and surrounding infrastructure. This thesis investigates the use of near-field acoustic intensity measurements to localize sound sources on moving launch vehicles, with a focus on characterizing source behavior during the early phases of liftoff. Using data from the Antares 230 NG-19 mission, acoustic pressure was recorded at multiple stations surrounding the pad, and the Phase and Amplitude Gradient Estimator (PAGE) method was employed to compute intensity vectors as a function of frequency and time. Signal processing parameters were systematically evaluated, including comparisons of Hann and Tukey windowing functions and varying block sizes, revealing that small adjustments can affect temporal and spectral resolution but have minimal impact on overall level estimates. A directivity analysis using spatio-spectral techniques found that the near-field peak radiation angles differed from far-field norms, shifting from the expected 70° to approximately 60°, indicating the influence of geometric and plume interactions at close range. The Oertel convective Mach number was calculated and used to determine the peak directivity angle based on vehicle parameters. This model resulted in a $70^o$ peak angle. Assuming this is true, an estimate of the extended source region in diameters downstream of the plume is also given by assuming a $70^o$ angle. Sound source localization results show that the dominant low-frequency energy (centered around 40 Hz) originated near the pad center at ignition, migrated through the flame trench, and returned to align with the vehicle's upward trajectory--all within the first ten seconds of launch. These findings underscore the dynamic nature of rocket noise sources and highlight the limitations of static models for acoustic prediction. The results also affirm the PAGE method's value for low-frequency localization and support its application in future launch campaigns.

Degree

College and Department

Computational, Mathematical, and Physical Sciences; Physics and Astronomy

Rights

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