Geotechnical Properties of Fillite—Simulant for Planetary Rover Mobility Studies

Abstract

Earthbound testing of the mobility of lunar, Martian, and other extraterrestrial rovers benefits from the use of suitable soil simulants. To this end, a granular material called Fillite was selected as a simulant for modeling high-sinkage, high-slip situations that could be encountered by rovers, such as the one encountered by the Spirit rover on Mars. Fillite consists of alumino-silicate hollow microspheres harvested from the pulverized fuel ash of coal-fired power plants. It is available in large quantities at a reasonable cost and it is chemically inert. The focus of this paper is to summarize geotechnical characterization of Fillite, specifically the mechanical properties such as shear strength parameters, elastic modulus, Poisson’s ratio, and small-strain shear modulus. These measured properties are expected to enable analysis of rover mobility tests conducted in Fillite. The properties of Fillite are compared with the known and estimated properties of Martian and lunar regoliths as well as of other commonly used simulants. Fillite is quite dilatant. The peak and critical angles of internal friction of Fillite are smaller than those of most other simulants. Smaller shear strength, coupled with much smaller bulk unit weight as compared to other simulants, would result in smaller bearing and shearing resistances. This is expected to allow for better simulation of the intended high-sinkage, high-slip environment for rover mobility studies.