Study on Dynamics of Penetrator into Ice

To realize a penetrator mission for icy objects in the solar system, a fundamental study on the penetration dynamics into ice has been made. In the experiments, projectiles of the mass about 2.5 g were tested for the target made from water ice by the ballistic range at the impact velocity 100-350 m/s, and the behavior of the projectile and target was observed by the high-speed video camera. Unlike the case of the soil target, the outward normal jet-like stream of fragmented ice pieces continued for a long time after the impact, and often pushed back the penetrator from the target. The mathematical model to describe the force acting on the body surface has been developed, based on the panel method and the shock wave theory. It includes two parameters representing the effective acoustic speed of ice and the damping of pitching motion. Fairly good agreement with the experiments was obtained with respect to the stop conditions of the penetrator by setting the parameters appropriately. The computational result assuming a flight model of the mass 15 kg and the impact speed 300 m/s shows that the maximum deceleration G is in the same order as that for the lunar penetrator.