Why does the Falcon-9 booster make a triple sonic boom during flyback? An initial analysis.

Area of Science:

• Aerospace Engineering
• Acoustics
• Fluid Dynamics

Background:

• SpaceX Falcon-9 rocket boosters generate distinct sonic booms during atmospheric descent.
• The typical sonic boom signature is a two-shock N-wave.

Purpose of the Study:

• To investigate the origin of the three-shock sonic boom produced by the Falcon-9 rocket.
• To explain the deviation from the standard N-wave sonic boom pattern.

Main Methods:

• Application of sonic boom theory.
• Nonlinear acoustic propagation modeling.
• Computational fluid dynamics (CFD) simulations.
• Analysis of photographic evidence.

Main Results:

• Identified an additional, central shock in the far-field sonic boom.
• The third shock arises from the interaction of compression and rarefaction waves.
• Grid fins generate a forward-propagating compression wave.
• Booster lower sections and landing legs produce a rearward-propagating rarefaction wave.

Conclusions:

• The merging of these specific waves creates the unique three-shock sonic boom.
• This finding clarifies a complex aerodynamic acoustics phenomenon.
• Provides a basis for understanding and potentially mitigating complex sonic boom signatures.