Abstract

On August 27th, 2024, at approximately 19:30 UTC, the Starlink-2382 satellite entered the Earth's atmosphere following a controlled re-entry manoeuvre over Central Europe. This event resulted in a relatively low-angle re-entry of the satellite into the atmosphere, which was intended to provide sufficient time to fully burn up the satellite before reaching the Earth's surface. This study employs acoustic-seismic (A-S) data from 226 recording stations to analyse the trajectory of Starlink-2382's re-entry, utilizing 3-D atmosphere models including wind data and acoustic ray tracing methods. To identify signals emitted by the falling satellite, we analyse A-S recordings of Austrian, French, German, and Swiss regional seismic networks. We compute the satellite trajectory with a novel ray-based direct-search optimization method and find an azimuth angle of 114°±0.7° from north and an initial elevation angle of 0.1° ±0.2°, together with an entry velocity of approximately 10.1 ±0.6 km/s. Our findings indicate that this acoustic-seismic approach, including travel time effects due to wind, allows to achieve higher accuracy than optical-trajectory solutions in this specific context. Furthermore, we calculate an ablation coefficient of 0.12 ±0.03 s2 km-2, which implies that the 260 kg heavy satellite possibly fully burned up in the Earth's atmosphere during its descent.

Finite-difference modelling confirms that the Mach Cone, generated by the satellite, opens dynamically as the satellite decelerates, leading to a complex acoustic wavefield. This effect highlights the importance of accounting for trajectory curvature and time-varying Mach angles when modelling acoustic wave propagation from low-angle re-entering objects. For recording sites with both, acoustic (infrasound) and seismic sensors, the acoustic-to-seismic ground coupling coefficients are determined. These vary up to three orders of magnitude, from 4.31e-10 m s-1 Pa-1 to 5.86e-7 m s-1 Pa-1 across our station sites, what is primarily explained with differences in stiffness of surface rocks.