Morphology of meteoroid and debris impact craters formed in soft metal targets on the LDEF satellite

We have measured the depths, average diameters and circularity indices of over 600 micrometeoroid and space debris impact craters formed in surfaces exposed to space aboard the Long Duration Exposure Facility satellite. The target surfaces had a variety of orientations and physical properties. The average depth-diameter ratio of craters formed in aluminum targets by nearly normal impacts is between 0.56 and 0.60, higher than the canonical and widely accepted value of 0.50 which corresponds to a hemispherical shape. The depth-diameter ratio does not change significantly with target Brinell hardness values between 40 and 90, or with average impact velocity above 5 km s −1. The depth-diameter ratio is found to vary as roughly the one-tenth power of target density. Less than 10% of the craters examined had major-to-minor axis ratios higher than 1.5, consistent with the production of shallow, elongated craters exclusively by grazing impacts. The variation in depth-diameter ratio for circular craters most likely results from variation in projectile shapes.