Development of the next generation of spaceflight vehicles has prompted a renewed focus on sound source characterization and near-field propagation modeling. Without advancements in these areas, large uncertainties in vibro-acoustic loading estimates on space vehicles and payloads may result in structural designs that are either insufficient or excessive.

In the near field, even accurate acoustic pressure measurements are insufficient. A set of pressure measurements can reveal the local sound pressure levels at the sensor locations. However, because of the frequencies and source size inherent to a rocket plume, it would require an extremely large array of distributed microphones to adequately map out the critical near-field region and establish how tile sound energy is traveling outside that region. An improved system for determining this near-field energy flow provides source characterization capabilities beyond traditional pressure measurements.

This project has resulted in the development of a new energy-based measurement and analysis system for rocket noise. The robust hardware and novel signal processing algorithms provide NASA with the a unique capability to characterize the near-plume noise environment of full-scale rocket motors. This characterization is necessary to develop physics-based, near-motor noise propagation models that will aid in improving vibro-acoustic loading estimates on space vehicles and payloads.

The hardware and software development consists of four principal innovations:

  • An improved energy-based acoustic probe design that extends the operational frequency bandwidth, minimizes scattering, and provides easy access to microphone components for calibration, while being robust enough for harsh near-field rocket environments and inexpensive enough to remain accessible.
  • Improved energy-based signal processing and analysis methods using a newly developed phase and amplitude gradient estimation (PAGE) that provides consistently superior results in comparison to previous methods.
  • A rugged and reliable field-deployable data acquisition system that will reduce field test setup time and complexity.
  • Results from energy-based and other data analyses that detail the near-field intensity flow, assessment of near-field relationships between energy quantities, and other measures of interest, including rms and peak levels, acceleration, etc.

This work was done by Kent Gee of Brigham Young University and Michael James of Blue Ridge Research and Consulting LLC for Marshall Space Flight Center. For more information, contact Ronald C. Darty, Licensing Executive in the MSFC Technology Transfer Office, at This email address is being protected from spambots. You need JavaScript enabled to view it.. Refer to MFS-33179-1.