USING DENSE, LOW-MELTING POINT PROJECTILES TO SIMULATE HYPERVELOCITY IMPACTS ON TYPICAL SPACECRAFT SHIELDS

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 alumin um. This technique was first suggested by Morrison [1], for craters in semi-infinite targets. Hypervelocity tests performed at the Universit y of Dayton Research Institute, using cadmium projectiles to impact al uminum Whipple and multiple, Nextel(TM) ceramic-bumper shields are des cribed, and the results are compared with similar Whipple shields test ed at the NASA Ames Research Center, using aluminum projectiles at max imum light-gas gun speeds. The cadmium and aluminum projectiles had th e same masses, and the initial impact momenta were maintained as close as possible, i.e., 92 to 96%. Computer simulations of two of the cadm ium projectile-aluminum Whipple shield tests are presented, together w ith the physical states in the debris-bubble and the impact momentum o n the rear-wall. These results are compared with sequential X-radiogra phs of the impact debris and the damage sustained by the rear walls. P hotographic evidence of the damage is included in the report. The calc ulations of the aluminum projectile mass and velocity that match the c admium results and give the equivalent impulsive loading on the rear-w all are discussed, and scaling analysis is used to determine the appro priate size and speed of the projectile. The enhanced all-aluminum ver ification test capability resulting from the technique described in th is paper is shown to be at least 8.3 km/s, a 30% increase over the nor mal light-gas gun velocity for the mass in question.