Lunar Dust 2020 (LPI Contrib. No. 2141) 5030.pdf

MEASUREMENT OF THE ANGLE OF REPOSE OF APOLLO 14 LUNAR SAMPLE 14163. C. I. Calle1 and C. R. Buhler1, 1Electrostatics and Surface Physics Laboratory, NASA, Kennedy Space Center FL, 32899, car- [email protected], [email protected].

Introduction: Knowledge of the physical proper- through the nozzle (Figure 1). The sample was kept ties of the lunar regolith is of crucial importance for flowing over for several seconds after the cone reached the planned exploration activities. The design and a steady-state configuration. planning of equipment for in situ resource utilization, soil collection and storage, site preparation, and habitat layout require an understanding of the physical behav- ior of the regolith. We report on our measurement of the rest angle of repose of pristine Apollo 14 lunar samples under high vacuum. The rest angle of repose of poured granular materi- al is the inclination of the slope formed after avalanch- ing has ceased. This angle depends on some of the physical properties of the grains such as their departure from spherical shape, their angularity, and their size. It also depends on the packing history, the surface charge of the grains, and on the properties of the surface with which it interacts [1,2]. Measurement of the angle of repose, θr, allows for the determination of the work of cohesion, C, given by

C = mg(sin θr – µ cos θr) where µ is the coefficient of friction, m is the mass, and g is the acceleration due to gravity. Figure 1. Angle of repose experiment with Apollo 14 sample Experimental Approach: There is a variety of –6 methods to measure the rest angle of repose of granular 14163 at an atmospheric pressure of 10 kPa. materials. For this experiment, we used a method simi- lar to the one planned for the MECA Patch Plate of the The same procedure was used with JSC-1A lunar cancelled Mars Surveyor Lander 2001 [3]. A polished simulant samples with granular sizes under 50 µm. This sample was kept for several months in a vacuum brass sphere 3.45 cm in diameter was placed in a vacu- oven and was processed under the N2 atmosphere in um chamber previously backfilled with N2. A glove the camber. We are assuming that the delivery method box door placed over the open chamber allowed access used for both samples removed the packing history to its interior without allowing air to reach the cham- constrain and provided a similar electrostatic charging ber. Pristine Apollo 14 lunar dust (sample number mechanism. 14163) was placed in a shaker cup exactly above the Results: Figure 2 is a diagram of the measurement brass sphere. The shaker cup was designed to deliver dust through a nozzle 4 mm in diameter after activation of the rest angle of repose θr. The value of θr for the with an electric motor. The contained with the Apollo Apollo 14 sample 14163 was measured to be 58°, sample, on loan from the Astromaterials Curation La- while the value for the JSC-1A simulant sample was boratory at NASA Johnson Space Center, was opened 37°. Table 1 shows the rest angle of repose of several inside the N2-filled chamber. This sample was pro- granular materials and of spherical glass beads. We cessed upon return to Earth in an N2 atmosphere. This soil has been chosen as one of the reference soils for note that our result for the JSC-1A simulant sample is the lunar highlands suite [4]. This sample contains a similar to that of beach sand and that result for the large percentage of glass, much of it agglutinate glass Apollo sample is in the same range as that for quartz. [5], although some of it has the composition of mare These values are not unexpected, since the lunar grains have a much larger angularity and surface tension than basalt [6]. the JSC-1A simulant grains (Figures 3 and 4). After the chamber was evacuated to 10–6 kPa, the

shaker containing the Apollo granular sample was ac- tivated. The sample was deposited on the brass sphere Lunar Dust 2020 (LPI Contrib. No. 2141) 5030.pdf

θr

Figure 2. Schematic diagram of the rest angle of repose measurement. Figure 4. JSC-1 glass (GL) and olivine (OL) grains. SEM Table 1. Angle of repose of several materials. secondary electron image. Frame width = 1100 µm (NASA Material θr Reference Johnson Space Center). Glass beads 53-75 µm 32° [6] References: [1] Möller L.E., Tuller M., Baker L., Mojave dune sand <53 µm 31° [6] Marshall J., Castigliione P. and Kuhlman K. (2003) Quartz dust 54° [6] LPS XXXIV, Abstract #1526. [2] Carrigy M.A., (2006) JSC-1A simulant <50 µm 37° This work Sedimentology, 147-158. [3] Kuhlman K.R. et al, Apollo 14 sample 14163 58° This work (2002) IEEEAEC, paper #329. [4] Labotka T.C., Kem- pa M.J., White C., Oaoike J.J., and Laul J.C., (1972) Proc. 3rd Lunar Science Conference, 1181-1200. [5] Carr M.H. and Mayer C,E. (1972) Proc. 3rd Lunar Sci- ence Conference, 1015-1027. [6] Simon S.B., Papike J.J., and Laul L.C. (1981) LPS XII, 371-388. [6] Möller L.E., Kuhlman K., Marshall J., and Towner M.C. (2002) LPS XXXIII, Abstract #201 5.

Figure 3. SEM image of Apollo 14 grain showing angularity and large surface area. Frame with = 230 µm. (Electrostatics and Surface Physics Laboratory, NASA Kennedy Space Center)