Kent Gee

Super Heavy's Sonic Boom! What's going on here? As shot by @spacecoastwest, the @SpaceX Starship Super Heavy booster is descending toward the ocean at supersonic speeds for a test landing. The early morning sunlight and the intermittent clouds make the shock waves directly visible. Why are there shock waves? Shock waves form around any supersonic object. Since information in a fluid travels at the speed of sound, the surrounding air doesn't "know" it's supposed to make way for the supersonic object until it's almost too late. The shock waves are a neat physics phenomenon that fixes this problem and helps the air get out of the way. How does this relate to the sonic boom? The shock waves don't just stay near the vehicle. They travel away and can reach distances many miles from the vehicle. When the shock waves pass over you, we call it a sonic boom. The shocks aren't static either, they will merge and coalesce as they propagate. What is special about rocket booster sonic booms? As a general rule, sonic boom shocks merge into a single front shock and a single rear shock. When measured, the final sonic boom looks like a capital "N" and is called an "N-wave". This is true for almost everything that makes a sonic boom. But not for rockets. So far, all reusable rocket boosters with published data (i.e., Falcon 9, Starship Super Heavy) produce sonic booms with three distinct shocks, which I call the "triple sonic boom". The reason for this was a mystery until early last year, when we (myself and @KentLGee) published a paper in the @ASA_JASAEL scientific journal. We determined that the three shocks come from: 1. The bow shock, produced by the engine section. This wasn't a surprise because the front part of any supersonic geometry will make the first shock. 2. A combination of a shock from the grid fins and a "rarefaction wave" produced by the airflow as it rounds the corner of the booster's engine section. This was the exciting "extra" shock. 3. The tail shock, produced near the top of the booster as the airflow recovers. This one was also not a surprise. How does this video help improve the science? The video by @spacecoastwest confirms part of the theory. You can clearly see the shock by the engine section, a series of shocks near the grid fins, and the final shock near the top of the booster. While our original paper used awesome photographic evidence from @LaunchPhoto, the lighting in this Starship launch made it possible to see things much more clearly. Why does this matter? In the emerging world of spaceflight, rockets are going to be producing more and more sonic booms. While the powerful sounds of spaceflight can be really fun, it's not too hard to imagine a future where they also become a problem. Instead of waiting for that future to arrive, it's important to start working on these problems now. One of the first steps is to make sure that we understand the physics behind these sonic booms, especially when they differ from traditional aircraft. Want to know more? Feel free to check out our (free!) papers on rocket sonic booms and a @nytimes article by @kchangnyt that talks about our rocket sonic boom research: Triple Boom Initial Explanation Paper - doi.org/10.1121/10.0035649 Falcon 9 Sonic Boom Measurements - doi.org/10.1121/2.0001916 Starship Sonic Boom Measurements - doi.org/10.1121/10.0034453 New York Times Article - nytimes.com/2025/05/26/scien… Hope you found that useful and interesting! Thank you to @spacecoastwest for taking this great video and thank you to @NASASpaceflight as well. Keep up the great work! (Video footage re-used and colorized with permission of @spacecoastwest. I, @AerospaceMark, have no affiliation with @NASASpaceflight.)