VELOCITY-MEASUREMENTS OF IMPACT EJECTA FROM REGOLITH TARGETS

We performed new experiments with impacts on regolith-like layers of g lass spheres to investigate the spatial and velocity distributions of ejecta with velocities higher than several hundred m sec(-1). Spherica l nylon projectiles of 7.0 mm diameter were accelerated to about 4 km sec(-1) using a two-stage light-gas gun, The ejecta were detected by t hin Al foil targets of different thickness, and the resulting holes on the foil were counted to derive the velocity distribution using an em pirical threshold penetration formula, The spatial distribution of the ejecta was also derived from the analysis of the position of the pene tration holes, The high velocity ejecta were concentrated toward the d ownrange azimuth of the impacting projectile because of the oblique im pacts of the projectiles into the targets, In order to estimate the to tal volume of ejecta with velocity higher than a given velocity, the m easured spatial distributions were extrapolated to regions where no Al targets were exposed, The results were compared to a sealing formula based on low velocity data of the ejecta from sand targets, Though our results on the volume of ejecta with higher velocity lie below the ex trapolation of the lower velocity data, the differences were within ab out one order of magnitude. (C) 1997 Academic Press.