Ejection angles during hypervelocity impacts on flat and spherical targets investigated with shock physics modeling

In NASA's 2022 Double Asteroid Redirection Test (DART) mission, the DART spacecraft collided with the asteroid Dimorphos, the satellite of the binary asteroid (65,803) Didymos. The recoil from the impact ejecta changed the orbital period of Dimorphos. For analysis of this mission, a more accurate method is needed to estimate the momentum carried away by the impact ejecta, so the momentum transfer from the impactor to the target (e.g., Dimorphos) can be properly characterized. Since ejection velocity and angle depend on the target curvature, the effects of the curvature on the impact outcomes should be addressed. This study investigated the ejection velocity and angle generated by hypervelocity impacts under microgravity conditions using a hydrocode simulation with two-dimensional cylindrical coordinates. The materials within an excavation flow on small bodies are sensitive to a process called sustained acceleration, which comes from the compressibility of the flow because of microgravity. We evaluated the effects of sustained acceleration and proposed an ejection threshold to estimate the ejection velocity and angle accurately under microgravity conditions. The effects of target curvature and material strength on the ejection behavior have also been investigated with our ejection threshold. Our method will be helpful for analyzing the excavation of small bodies.