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Updated: May 28, 2025

Optimization, Test and Diagnostics of Miniaturized Hall Thrusters
Published on: February 16, 2019
Why does the Falcon-9 booster make a triple sonic boom during flyback? An initial analysis
1Department of Physics and Astronomy, Brigham Young University, Provo, Utah 84602, USAmark.anderson@byu.net, kentgee@byu.edu.
Abstract:
When the SpaceX Falcon-9 rocket booster descends through the atmosphere after a launch, it produces a sonic boom with three shocks in the far field, rather than the usual two-shock N-wave. In this Letter, the additional shock's origin is explained using sonic boom theory, nonlinear propagation modeling, computational fluid dynamics, and photographic evidence. The extra central shock results from a forward-migrating compression wave caused by the grid fins merging with a rearward-migrating rarefaction wave caused by the lower portions of the booster, including the folded landing legs.
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