Meteoroid impacts as sources of seismicity on the Moon

In conjunction with the Apollo lunar passive seismic experiment, a study was undertaken to determine the efficiency of meteoroid impacts on the lunar surface as potential sources of seismic energy. This study is based on experiments performed at Ames Research Center to determine the coupling between an impacting projectile and seismic waves. High‐velocity guns at Ames were used to fire projectiles into targets in a vacuum chamber. Projectile velocities ranged from less than 1 to more than 7 km/sec; projectile masses ranged from about 0.25 to 5 grams. Targets were of two types having considerably different elastic properties. Experimental results indicate that the seismic source function of an impact can be expressed as a function of the kinetic energy of the projectile. Extrapolating our results up to the kinetic energies of meteoroids, it is possible to predict the number of impacts that will be detected by the Apollo passive seismic experiment during its nominal lifetime of one year if assumptions are made about the physical properties of the moon. For the most optimistic set of assumptions, the instrument will detect about 370 meteoroid impacts; for the most pessimistic, about 3 impacts. Most of these impacts will be within 10 to 20 km from the seismometers. The experimental data of this study can be used to estimate the effectiveness of impacting spent spacecraft stages as artificial seismic sources. The results suggest that surface waves generated by the impact of the Saturn S‐IVB stage of the Apollo booster would be detected at distances of from 41 to 681 km from the seismometer, depending on the properties assumed for the lunar surface material.