CALIBRATION OF THE SNOOPY ANGLE OF REPOSE INSTRUMENT

Martian dust and windblown particulates will present significant difficulties in the future exploration of Mars. These difficulties include the environmental challenges to materials, machines and people. Knowledge of the angle of repose (qr) of Martian dust would be useful in the design of exploration and support systems.  Previous work has shown the ability of small cylindrical or spherical instruments to determine angle of repose with lunar and Martian simulants.  Initial work has been carried out on calibrating the Student Nanoexperiments for Outreach and Observational Planetary InquirY (SNOOPY) Angle of Repose experiment to determine qr of a range of simulants and reference materials on spherical surfaces of different materials.   Custom ball bearings were obtained from Salem Specialty Ball Company, Canton, CT, USA.  The balls included 7075 aluminum (5 mm, 10 mm, and 15 mm), alumina oxide ceramic (10 mm) and Teflon® (10 mm) each processed to a tolerance of 25 mm.  The reference materials and simulants were obtained from various sources: JSC-1 Mars Simulant, 53-75 mm glass beads, 80/120 glass beads, 0.1 mm amorphous silica, kaolin, quartz flour, 90-125 mm olivine, 53-75 mm olivine,  125 mm Bishop tuff 1066, Mojave dune sand (MDS), unsieved MDS, > 177 mm MDS, 104-177 mm MDS, 53-104 mm MDS and < 53 mm MDS. The experimental platform was a 15 cm x 15 cm aluminum plate with a 5 x 5 array of 2 mm holes drilled on 2 cm centers. The plate was grounded. The 25 ball bearings were randomly placed on the array.  Dust was applied to the spheres by shaking or pouring by hand from above. The angle of repose has been experimentally shown to depend on the shape and roughness of the particles, typically measuring 22º for smooth spherical particles and 33 ± 2º for aeolian sand.  Additionally, there is significant variation of qr with the method of measurement. Smaller particulates can have a qr that is greatly affected by electrostatic interactions. These experiments were carried out at normal Earth surface conditions.  New experiments are examining qr of Martian dust simulants and reference materials inside a chamber simulating more Mars-like conditions including a temperature of ~260 K, relative humidity <1%, and atmospheric composition of 97% CO2 and 3% N2.  These experiments will examine parameters including shape and roughness of the dust particles.