Methods and results of acoustical measurements made of a Delta IV Heavy launch

Abstract

On April 26, 2021 the Brigham Young University (BYU) acoustics research group made a number of acoustic noise measurements during the launch of a Delta IV Heavy rocket from Vandenberg Space Force Base in California. The sensors ranged in distance from 330 m to 19 km from the launch site. Some sensors were arranged in a rough arc of 1-2 km radius and others were placed along both an east-west line and a north-south line. This enabled the measurement of the distribution of the noise in the different directions and at different distances. Two of the sensors were 5-meter radius, 4-microphone intensity probes. Using these probes it was possible to track the trajectory of the rocket ascent; the acoustically traced trajectory agrees well with the trajectory data obtained from Vandenberg. The measurements showed that the peak directivity of the launch vehicle noise was at 70.4±2.1 degrees relative to the plume direction. The total acoustic power level was found to be 197 dB re 1 pW. This represents an acoustic radiation efficiency of about 0.3%, somewhat lower than is normally assumed.