Another design provides for a bit comprising multiple tubular segments with an inner alignment string, similar to a foldable tent pole comprising multiple tubular segments with an inner elastic cable connecting the two ends. At the beginning of deployment, all segments except the first (lowermost) one remain folded, and the ultrasonic/sonic actuator is clamped to the top of the lowermost segment and used to drive this segment into the ground. When the first segment has penetrated to a specified depth, the second segment is connected to the upper end of the first segment to form a longer rigid tubular bit and the actuator is moved to the upper end of the second segment. The process as described thus far is repeated, adding segments until the desired depth of penetration has been attained.

Yet other designs provide for bits in the form of bistable circular- or rectangular-cross-section tubes that can be stowed compactly like rolls of flat tape and become rigidified upon extension to full length, in a manner partly similar to that of a common steel tape measure. Albeit not marketed for use in tool bits, a bistable reeled composite product that transforms itself from a flat coil to a rigid tube of circular cross section when unrolled, is commercially available under the trade name RolaTube™ and serves as a model for the further development of tool bits of this subtype.

This work was done by Yoseph Bar-Cohen, Mircea Badescu, Theodore Iskenderian, Stewart Sherrit, Xiaoqi Bao, and Randel Lindemann of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at under the Mechanics/Machinery category. NPO-45289