Soil mechanical properties at the Apollo 14 site

Abstract

The Apollo 14 lunar landing provided a greater amount of information on the mechanical properties of the lunar soil than previous missions because of the greater area around the landing site that was explored and because a simple penetrometer device, a special soil mechanics trench, and the modularized equipment transporter (Met) provided data of a type not previously available. The characteristics of the soil at shallow depths varied more than anticipated in both lateral and vertical directions. While blowing dust caused less visibility impairment during landing than on previous missions, analysis shows that eroded particles were distributed over a large area around the final touchdown point. Measurements on core-tube samples and the results of transporter track analyses indicate that the average density of the soil in the Fra Mauro region is in the range of 1.45 to 1.60 g/cm^3. The soil strength appears to be higher in the vicinity of the site of the Apollo 14 lunar surface experiments package, and trench data suggest that strength increases with depth. Lower-bound estimates of soil cohesion give values of 0.03 to 0.10 kN/m^2, which are lower than values of 0.35 to 0.70 kN/m^2 estimated for soils encountered in previous missions. The in situ modulus of elasticity, deduced from the measured seismic-wave velocity, is compatible with that to be expected for a terrestrial silty fine sand in the lunar gravitational field.