People have been digging in dirt for hundreds of thousands of years, gaining much experience thereby. Yet we are always searching for more efficient, more effective methods. And when we begin digging on the surfaces of bodies other than Earth, such as the Moon and Mars, we must resort to a higher degree of automation and remote operation than many construction and mining engineers are comfortable with. This is made more difficult by the inherently uncertain and variable nature of dirt, soil, and regolith. This paper reports on the beginning of a sensitivity study of some of the important factors that control the excavatability of natural granular materials. Initial results reveal a complex interplay of behaviors affected by grain shape and compaction. These factors must eventually be understood more directly in space operations.