Experiments and Computations of Momentum Enhancement of Rubble Pile Simulants at 2 and 5.35 km/s

The Double Asteroid Redirection Test (DART) demonstrated the ability to impart momentum to an asteroid through a hypervelocity impact. This impact was for the asteroid Dimorphos with a size of 150 m and an unknown density. In our group we have performed impacts, some before the DART impact and some after, into rubble pile simulant targets made of crushed basalt. Target size was on the order of 60 x 60 x 30 cm, exceeding 200 kg. Such large targets are required because in our previous experimentation the absolute size of the impactor affects both the amount of ejecta material and the momentum enhancement. Compressive strength and density were measured for the crushed basalt targets. Experiments were performed utilizing two launchers: a 38-mm two-stage light gas gun and a 50-mm powder gun. Aluminum spheres of three sizes were launched: diameters 2, 3 and 4.45 cm. The momentum delivered to the target was measured by pendulum swing. The crushed basalt targets had momentum enhancement β (the momentum transferred divided by the projectile momentum) ranging from 2.12 to 2.83 for the 5.35 km/s shots and 1.52 to 2.51 for the 2 km/s shots. To compare, in previous work where rock was held with cement, β was 3.4 for an impact of a 3-cm-diameter Al sphere at 5.44 km/s; and the current estimated for β for the DART impact is 3.6 for a 6.14 km/s impact by the much larger but (on average) lower density spacecraft. In addition to the experiments, computations with CTH and EPIC were performed and will be compared with the experiments.