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 ti•ench, 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 lateraJ 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 anaJyses 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.Studies of the soil (regolith) at the Apollo 14 site have been made (1) to obtain data on the compositional, textural, and mechanical properties of lunar' soils and the variations of these properties with depth and location at and among Apollo landing sites; (2) to use these data to Detailed study of the Surveyor 3 camera revealed a distinct shadow pattern on the paint, and this pattern was shown [Ja#e, 1971] to arise from a lunar soil sand blasting. It was demonstrated, moreover, that the sand-blasting particles came from the Apollo 12 landing site rather than from a sequence of points along its landing track. The particles must have had a velocity greater than about 70 meters per second with a shallow angle trajectory to have reached the Surveyor spacecraft and must have arrived at a fairly high concentration to have achieved the sharpness of shadow effect observed. The abrasion appears to be uniform, and there is no indication of individual impacts. Therefore, the surface or surface coating has been struck by so many particles that their impact areas overlap. It will be assumed that the majority of particles reaching Surveyor were of micrometer size or larger and that the average diameter of each impact might be of the order of 10 •m. If it is further assumed that the area of impacts just saturates the surface (conservative), it appears that each square centimeter of the abraded area was subjected to impact by about 106 particles. One of us (Scott) has examined the Surveyor 3 surface sampler (also exposed to blowing dust) in detail at about 100 magnification, at which he should certainly have ...

A crater and its ejecta: An interpretation of Deep Impact

“…The strength of lunar regolith near the surface is of order 1 kPa (Mitchell et al, 1972) and 3 kPa at 1 m depth (Gromov, 1998). The tensile strength of snow is larger than 500 Pa (Sommerfeld, 1974).…”

P/2010 a2 Linear

“…This low strength corresponds to a loose powdery surface, comparable to lunar soil (Y ∼ 1 kPa, Mitchell et al 1972) and snow (Y ∼ 0.5 kPa, Sommerfeld 1974). A caveat is the fact that the concept of material strength in impacts is not well defined, so the Y given is a formal value with an uncertain physical interpretation.…”

Compressive deformation of porous lunar regolith

“…The regolith taken from multiple sites of the Apollo 12 and 14 missions, as well as other missions, had a median grain size of 0.05 mm to 0.735 mm and went as low as 40 mm [2,15,16]. This means the powders could be sieved to the sized used in this experiment without any extra processing.…”