Re-entry and Burn Up of Starlink-2382 Satellite: Estimating Trajectory and Ablation Coefficient from Acoustic and Coupled Seismic Waves

Summary On August 27th, 2024, at approximately 19:30 UTC, the Starlink-2382 satellite entered the Earth’s atmosphere following an uncontrolled re-entry manoeuvre over Central Europe. This event resulted in a relatively low-angle re-entry of the satellite into the atmosphere, which might have provided sufficient time to 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 process A-S recordings of Austrian, French, German, Italian, Slovenian, 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 120.5°±0.4° from North and an initial elevation angle of 1.5° ±0.7°, together with an entry velocity of approximately 8.9 ±0.7 km s−1. Our findings indicate that this acoustic-seismic approach, including travel time effects due to wind, achieves a better fit to our large dataset compared to the trajectory solutions from optical methods in this specific context. Furthermore, we calculate an effective ablation coefficient of 0.11 ±0.02 s2 km−2 for the main satellite fragment. Within the limits of this estimate, this is consistent with a scenario in which the main fragment, with a mass of c. 100 kg could have experienced near-complete ablation during atmospheric descent. Finite-difference modelling illustrates the complex acoustic wavefield resulting from the satellite’s deceleration and shows the expected widening of the Mach Cone. This 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 4.31 $\times $ 10−10 m s−1 Pa−1 to 5.86 $\times $ 10−7 m s−1 Pa−1 across our station sites, which is primarily explained by differences in stiffness of surface rocks.