Use of a large microphone array to identify noise sources during a rocket engine test firing and a rocket launch

Abstract

A 70 microphone, 10 ft×10 ft, microphone phased array was built for use in the harsh environment of rocket launches. The array was setup at NASA Wallops launch pad 0A during a static test firing of Orbital Sciences’ Antares engines, and again during the first launch of Antares vehicle. It was placed 400 ft away from the pad, and was hoisted on a scissor lift 40 ft above ground. The data sets provided unprecedented insights into rocket noise sources. The duct exit was found to be the primary source during the static test firing; the large amount of water injected beneath the nozzle exit quenched all other sources. The noise maps during launch were found to be time-dependent. As the engines came to full power and became louder, the primary source switched from the duct inlet to the duct exit. Further elevation of the vehicle caused spilling of the hot plume, resulting in a distributed noise map covering most of the pad. As the entire plume emerged from the duct, and the on-deck water system came to full power, the plume itself became the loudest noise source. These noise maps will help to improve the sound suppression system for future launches.