Numerical Simulations of the Apollo S-IVB Artificial Impacts on the Moon

The third stage of the Saturn IV rocket used in the five Apollo missions made craters on the Moon similar to 30 m in diameter. Their initial impact conditions were known, so they can be considered controlled impacts. Here, we used the iSALE-2D shock physics code to numerically simulate the formation of these craters, and to calculate the vertical component of seismic moment (similar to 4 x 10(10) Nm) and seismic efficiency (similar to 10(-6)) associated with these impacts. The irregular booster shape likely caused the irregular crater morphology observed. To investigate this, we modeled six projectile geometries, with footprint area between 3 and 105 m(2), keeping the mass and velocity of the impactor constant. We showed that the crater depth and diameter decreased as the footprint area increased. The central mound observed in lunar impact sites could be a result of layering of the target and/or low density of the projectile. Understanding seismic signatures from impact events is important for planetary seismology. Calculating seismic parameters and validating them against controlled experiments in a planetary setting will help us understand the seismic data received, not only from the Moon, but also from the InSight Mission on Mars and future seismic missions. Plain Language Summary Observations of meteoroid strikes on the Moon, including artificial impacts made by the Saturn boosters from the Apollo missions, present valuable information for connecting impact conditions with seismic properties of the lunar and planetary crusts. These artificial impacts on the Moon were made by irregularly shaped spacecraft with low density. We numerically simulated these artificial impacts, using several different projectile geometries in order to represent the spacecraft's low density and shape. We found that the projectile representation affected the crater size. We calculated the amount of energy transferred into seismic waves and seismic moment created in these impacts to be consistent with previous studies. These parameters did not change with different projectile representations, but were affected by the material properties of the impact site. The aim is to use the results from the controlled lunar impacts to help understand the seismic signatures of impacts on Mars.