Optical and acoustic ground effects simulations from terminal defense asteroid disruption via the PI method
Our simulations suggest that PI ("Pulverize It"), a NASA Phase II NIAC study, is an effective multi-modal approach for planetary defense that can operate in extremely short interdiction modes (with intercepts as short as hours prior to atmospheric entry) as well as long interdiction time scales with months to years of warning. The basic process is complete disruption of the threat via fragmentation. In scenarios with sufficiently long warning time, the fragment cloud spreads enough to miss Earth, resulting in no ground effects. In "worst-case" scenarios, when the warning time is short, the fragments (typically <10 m in diameter) will enter Earth's atmosphere, where their energy is dissipated in a series of ground-level optical pulses and de-correlated shock waves, mitigating any significant damage. We investigate the optical and acoustic ground effects through a set of simulation codes that model the interaction of asteroid fragments with Earth's atmosphere following terminal threat interception. Even in short-warning time cases where fragments enter the atmosphere, our simulations suggest that threats mitigated by the PI method produce vastly less damage on the ground when compared to the same unfragmented case, yielding optical energy deposition below 200 kJ/m$^2$ and shock wave over-pressures under 3 kPa. Our simulations support the proposition that threats like 2023 PDC, the hypothetical 800 m diameter asteroid from the 2023 Planetary Defense Conference impact exercise, can be effectively mitigated through fragmentation. We find that a terminal defense mitigation scenario that disrupts 2023 PDC into 1 million fragments with an intercept of 60 days before ground impact results in minimal ground effects.