Simulation-based height of burst map for asteroid airburst damage prediction

摘要

Entry and breakup models predict that airburst in the Earth's atmosphere is likely for non-metallic asteroids with diameters up to approximately 200 meters. (Collins, 2005; Collins, 2017; Wheeler, 2017). Objects of this size can deposit over 250 megatons of energy into the atmosphere. Fast-running ground damage prediction codes for such events rely heavily upon methods developed from nuclear weapons research to estimate the damage potential for an airburst at altitude (Collins, 2005; Mathias, 2017; Rumpf, 2017; Rumpf, 2016; Hills, 1993). In particular, these tools rely upon the powerful yield scaling laws developed for point-source blasts that are used in conjunction with a Height of Burst (HOB) map to predict ground damage for an airburst of a specific energy at a given altitude. While this approach works extremely well for yields as large as tens of megatons, it becomes less accurate as asteroid size and effective yields increase to the hundreds of megatons potentially released in larger airburst events. Accordingly, this study revisits the assumptions underlying this approach and shows how atmospheric buoyancy becomes important as yield increases beyond a few megatons. We then use large-scale three-dimensional simulations to construct numerically generated Height of Burst maps that are appropriate at the higher energy levels associated with the entry of asteroids with diameters of hundreds of meters. These numerically generated HOB maps can then be incorporated into engineering methods for damage prediction, significantly improving their accuracy for asteroids with diameters greater than 80-100 m.