How the season affects if you hear a sonic boom during rocket ascent

Mark Anderson – anderson.mark.az@gmail.com

X: @AerospaceMark
Brigham Young University
Provo, UT 84602
United States

Additional Authors
Kent L. Gee
X: @KentLGee
Brigham Young University

Lucas K. Hall
California State University Bakersfield

Institutional Social Media
Brigham Young University
X: @BYU
Instagram: @brighamyounguniversity

Department of Physics and Astronomy
X: @BYU_PhysAstro

Popular version of 2aNSb9 – Modeling seasonal variation in rocket ascent sonic booms
Presented at the 189th ASA Meeting
Read the abstract at https://eppro02.ativ.me//web/index.php?page=IntHtml&project=ASAASJ25&id=3989257

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

Residents in Southern California have reported hearing sudden, explosion-like sounds that have been startling individuals and causing vibrations in buildings. It turns out, these sounds are actually the sonic booms from rockets launched 70 or more miles away. And whether you’ll hear one is often determined by the season.

These sonic booms are produced during the rocket’s ascent toward orbit (see Fig. 1). As the vehicle pitches over during flight, it produces a sonic boom that can hit the ground below. This has happened with every orbital rocket, including the Saturn V and Space Shuttle, all the way to the modern Falcon 9. The difference is that while, historically, these sonic booms have only been audible over the ocean, rockets today are being launched closer to the coast, making these sonic booms audible on land.

A SpaceX Falcon 9 rocket launches to orbit. Photo credit: SpaceX. CC BY-NC 2.0 (https://www.flickr.com/photos/spacex/51027443336/). Annotation by the authors.

As part of a project funded by Vandenberg Space Force Base, researchers at Brigham Young University and California State University Bakersfield have teamed up to measure these rocket ascent sonic booms. Almost immediately, a question arose: why is it that we can measure sonic booms on land for a few months, followed by a period of almost nothing, even if the rocket’s trajectory stays the same? To answer this question, we used NASA’s state-of-the-art sonic boom modeling software, PCBoom. After verifying that we could reproduce our measured results using day-of weather data inputs, we simulated a commonly flown coastal trajectory using five and a half years’ worth of weather balloon data. This trajectory is among the closest currently-flown trajectories to the coast.

The results came back clearly. The seasonal weather causes predictable patterns in where sonic booms are most likely to be heard on land. More specifically, it typically comes down to which direction the upper-level winds (above 10 miles) are blowing, either from the east (summer) or the west (spring/fall). Because these winds change rather predictably throughout the year, we conclude that, for this launch trajectory, sonic booms on land are most likely to be heard in the spring and fall, with somewhat fewer in the winter and very few in the summer. To visualize these trends, Fig. 2 shows representative examples of where the sonic boom will land for each of the four seasons.

Representative sonic boom footprints from each of the four seasons, generated using PCBoom with day-of weather inputs. Actual footprints for a given day are subject to daily weather differences and thus will not exactly match these plots.

With this new understanding of how the seasonal weather affects the sonic boom footprint, we will continue to work with Vandenberg Space Force Base on further rocket ascent sonic boom research. We hope that one day this research will contribute to a world where future rockets can launch regularly while minimizing disruptions to communities and environments.