Keyhole-AwareTarget Site Selection forKinetic Impact Missions to Near-Earth Asteroids

We introduce a new method for selecting kinetic impactor target sites on near-Earth asteroids. Most asteroids that possess a significant impact risk with Earth admit multiple impacting trajectories. Uncontrolled deflection of such asteroids might dismiss the immediate impact risk but can also push the asteroid into a `keyhole', which would lead to a future impact. Our method maps potential outcomes of a kinetic impactor mission to the surface of the asteroid, allowing us to identify the optimal target site and rotation phase that minimizes the risk of pushing the asteroid off the Earth and into a keyhole. In this work, we illustrate this process using the keyholes for asteroid (101955) Bennu. We map the Bennu keyholes onto shape models of various asteroids to demonstrate the influence of shapes on the deflection outcomes. By computing the per-facet impact probability for different shapes, we can assess the dependence of the optimal target site on the asteroid's shape and spin state. Our results indicate that an optimal kinetic impact mission must take the spin state and shape of the target asteroid into account to minimize post-deflection impact risk. We also assess the effect of varying the targeting uncertainty of the kinetic impactor spacecraft in anticipation of future improvements. This work provides a framework for selecting optimal timing and target locations for kinetic impact missions at near-Earth asteroids, which can be used by mission designers to inform future asteroid impact hazard mitigation efforts.