A borehole jack for deformability, strength, and stress measurements in a 2-inch borehole

A borehole jack devised for lunar exploration is described and results of its use in simulated lunar solids are presented. A hydraulic cylinder mounted between two stiff plates acts to spread the plates apart against the borehole walls when pressured. The spreading is measured by a displacement transducer and the load is measured hydraulically. The main improvement over previous instruments is the increased stroke, which allows large deformations of the borehole. Twenty-eight pistons are used to obtain a high hydraulic efficiency, and three return pistons are also provided. Pressure-deformation curves were obtained for each test on Lunar Soil Simulant No. 2, a light gray silty basalt powder.