In situ flash X-ray observation of projectile penetration processes and crater cavity growth in porous gypsum target analogous to low-density asteroids

► We studied crater formation processes with projectile penetration on porous targets. ► We did laboratory impact experiments for gypsum targets by using flash X-rays. ► Crater shapes were divided into penetration hole and hemispherical cavity. ► Cd were 0.9 for a penetration hole and 2.3-3.9 for a hemispherical cavity. ► Scaled transient crater volume was almost proportional to a scaled time πt.