The Stellar Death Clock: Empirical Validation of REBOUND Using 3I/ATLAS and Application to Earth-Moon Migration

The Stellar Death Clock is a multi-paper framework addressing Earth's long-term habitability through civilizational-scale astroengineering, specifically via controlled orbital migration of the Earth-Moon system. This fourth and final installment presents an empirical validation of the REBOUND N-body integrator under extreme dynamical conditions, using the hyperbolic retrograde trajectory of the interstellar object 3I/ATLAS (C/2025 N1). By coupling the IAS15 integrator with a heliocentric reference frame and incorporating the three-dimensional non-gravitational force tensor (Marsden et al., 1973), we achieve sub-meter convergence (0.000049 km) against NASA/JPL Horizons ephemerides over a 365-day integration period. We then apply this validated framework to a controlled scattering maneuver involving asteroid 137 Meliboea, optimized via a Nelder-Mead simplex algorithm. The simulation demonstrates a non-disruptive Earth flyby at 16.97 Earth radii, achieving a precise heliocentric displacement of 21.40 km while empirically confirming the adiabatic coupling of the Earth-Moon system (Δr_Moon ≈ 20.87 km). Nearby bodies (Mars, Venus) show sub-meter orbital variances, confirming simulation stability. These results establish REBOUND as a robust tool for modeling civilizational-scale orbital migration, filling a critical gap in computational validation of long-term astroengineering architectures. Thus, the Stellar Death Clock framework concludes with a fully validated, high-fidelity digital twin capable of guiding future efforts to mitigate stellar evolution threats.