On meteoroids and penetration

Abstract

Estimates of the meteoroid penetration of vehicles in space are improved from the author's 1957 values. The meteoritic data are improved by the measurement of luminous efficiency in the artificial meteor experiment of Trailblazer 1 analyzed by McCrosky and Soberman, and by independent determinations from three asteroidal meteors by Cook, Jaechia, and McCrosky. A review of the photographic meteor data leads to an adopted meteoroid density of 0.44 g cm−3 and a mass of 1.0 gram for a zero-magnitude visual meteor of velocity 30 km sec−1. Hawkins and Upton's influx rate of visual meteors is utilized after correction for the zero-magnitude mass. A mean velocity of 22 km sec−1 is adopted. The formula by Herrmann and Jones from their summary of hypervelocity impact experiments provides the penetration of a low-density body against a semi-infinite target. The ratio of perforation thicloiess for a thin target to the penetration in a semi-infinite target is adopted as 1.5. The calculated perforation rate on a 0.1-cm-thick plate of aluminum in the earth's neighborhood is reduced by a factor of more than 3000 from the 1957 estimate. The change logarithmically is divided about equally between the changes in meteoroid data and in the impact formula. The present calculations are still subject to considerable uncertainty and can be greatly improved by further research in both the areas of radar-meteors and hypervelocity experiments at velocities exceeding 20 km sec−1. Possibly an unobserved, large flux rate in the mass range 103 to 107 gram may exist.