Influence of Mechanical Properties Relevant to Standoff Deflection of Hazardous Asteroids

Abstract

The National Academy has recently produced reports on the potential hazard and mitigation strategies for near Earth objects (NEO) [1,2]. The NRC reported to Congress that nuclear explosives are the only current technology to protect the Earth from impact of large asteroids. This is mainly due to difficulties in predicting the impact with high confidence leading to a short time to impact. Thus, the velocity deflection required when they are determined to be potentially hazardous asteroids (PHA) can only be achieved with nuclear explosives. A standoff explosion, without direct contact with the Near Earth Object (NEO) is a robust option for a non-destructive push, which offers several advantages. We have investigated the efficiency of energy deposition and its dependence on porosity and strength properties of NEO. An Eulerian hydrocode (GEODYN) with an interface reconstruction algorithm, wide-range equation of states and a flexible constitutive model library was used for numerical studies. The largest difficulties in predicting deflection velocity and fragmentation of asteroids are related to uncertainty in composition and mechanical properties of NEO. To reduce this uncertainty, we performed simulations of normal impact cratering of an NEO surface and related results with observables such as the crater shapes, the critical crater diameter (necessary to remove previous craters) and the maximum crater size (necessary for asteroid break-up). The velocity distribution of the material ejected from the impact crater is also germane to the asteroid deflection problem where the ablated material provides the thrust resulting in a deflection velocity. We performed parametric studies on how porosity and strength of the asteroid would affect these results.