Using dense, low melting point projectiles to simulate hypervelocity impacts on typical spacecraft shields

Abstract

In this paper the authors investigate the use of a dense, low melting point projectile, i.e., cadmium, launched at light-gas gun velocities, to simulate higher velocity, lower density projectiles such as aluminum. This technique was first suggested by Morrison [l], for craters in semi-infinite targets. Hypervelocity tests performed at the University of Dayton Research Institute, using cadmium projectiles to impact aluminum Whipple and multiple, NextelTM ceramic-bumper shields are described, and the results are compared with similar Whipple shields tested at the NASA Ames Research Center, using aluminum projectiles at maximum light-gas gun speeds. The cadmium and aluminum projectiles had the same masses, and the initial impact momenta were maintained as close as possible, i.e., 92 to 96%. Computer simulations of two of the cadmium projectile-aluminum Whipple shield tests are presented, together with the physical states in the debris-bubble and the impact momentum on the rear-wall. These results are compared with sequential X-radiographs of the impact debris and the damage sustained by the rear walls. Photographic evidence of the damage is included in the report. The calculations of the aluminum projectile mass and velocity that match the cadmium results and give the equivalent impulsive loading on the rear-wall are discussed, and scaling analysis is used to determine the appropriate size and speed of the projectile. The enhanced all-aluminum verification test capability resulting from the technique described in this paper is shown to be at least 8.3 km/s, a 30% increase over the normal light-gas gun velocity for the mass in question.