FIELD FRAGMENTATION OF MACROSCOPIC TARGETS SIMULATING ASTEROIDAL CATASTROPHIC COLLISIONS

We report the results from a series of experiments in which spherical macroscopic targets of artificial rock were disrupted using contact charges, and concentrate on the detailed analysis of four tests. The experiments were performed in the open, so we have been able to identify the shape and measure the sizes of fragments from the primary fragmentation event and to record the uninterrupted ballistic trajectories of the fragments. The targets were spheres of about 21 cm in diameter, two of them with stronger cores. From the recorded distribution of fragments on the ground, and using fast framing photography and our own image processing computer system, it has been possible to obtain the mass, shape, velocity, and angular velocity for several hundred fragments and from these to deduce the corresponding statistical distributions, as well as information concerning the geometry of the ejection velocity field and the correlations between different fragment properties. Most results compare satisfactorily with the predictions of the numerical model by Paolicchi et al. (Icarus 77, 187-212 (1989); Celest. Mech. 57, 49-56 (1993)). The presence of a core inside the target is found to influence the dynamics of the fragmentation process and the resulting velocity field, albeit not the fragment size distribution. The experimental fragments share some observed statistical properties of the asteroid families, in particular the higher dispersions of ejection velocity and rotation rate for smaller bodies. (C) 1994 Academic Press, Inc.