Penetrometers measure the material properties of soft substances by penetrating them. Most work by measuring resistance as they are slowly pushed into the material, but the BOLAS penetrometer works on impact.

The outer shell of the sphere includes an accelerometer that records the impact acceleration curve. The protected inner shell contains the battery and control electronics. Between the inner and outer shells is a dodecahedral void filled with memory foam. It’s a dodecahedron because of its symmetry and because it gives large flat surfaces on which to place foam pieces. The filling is memory foam because it can’t plastically deform, ensuring repeatable tests on the prototype. Shown above is an Earth-use low-impact prototype.

Selected impact acceleration curves. The data at this stage is preliminary but one can still discern that snow is softer than sawdust, and snow is collapsible while sawdust is compressible.

We roughly followed the analysis in McCarty and Carden 1968, who proposed dropping spherical penetrometers from Apollo landing craft to evaluate the quality of landing sites.