The term “rotary percussive autogopher” denotes a proposed addition to a family of apparatuses, based on ultrasonic/sonic drill corers (USDCs), that have been described in numerous previous NASA Tech Briefs articles. These apparatuses have been designed, variously, for boring into, and/or acquiring samples of, rock or other hard, brittle materials of geological interest. In the case of the rotary percussive auto-gopher, the emphasis would be on developing an NTB 05Mech/Mach 0809:Layout 1 7/20/09 9:54 AM Page 38 apparatus capable of penetrating to, and acquiring samples at, depths that could otherwise be reached only by use of much longer, heavier, conventional drilling-and-sampling apparatuses.
To recapitulate from the prior articles about USDCs: A USDC can be characterized as a lightweight, low-power jackhammer in which a piezoelectrically driven actuator generates ultrasonic vibrations and is coupled to a tool bit through a free mass. The bouncing of the free mass between the actuator horn and the drill bit converts the actuator ultrasonic vibrations into sonic hammering of the drill bit. The combination of ultrasonic and sonic vibrations gives rise to a hammering action (and a resulting chiseling action at the tip of the tool bit) that is more effective for drilling than is the microhammering action of ultrasonic vibrations alone. The hammering and chiseling actions are so effective that the size of the axial force needed to make the tool bit advance into soil, rock, or another material of interest is much smaller than in ordinary rotary drilling, ordinary hammering, or ordinary steady pushing.
The predecessor of the rotary percussive auto-gopher is an apparatus, now denoted an ultrasonic/sonic gopher and previously denoted an ultrasonic gopher, described in “Ultrasonic/Sonic Mechanism for Drilling and Coring” (NPO-30291), NASA Tech Briefs Vol. 27, No. 9 (September 2003), page 65. The ultrasonic/sonic gopher is intended for use mainly in acquiring cores. The name of the apparatus reflects the fact that, like a gopher, it periodically stops advancing at the end of the hole to bring excavated material (in this case, a core sample) to the surface, then re-enters the hole to resume the advance of the end of the hole. By use of a cable suspended from a reel on the surface, the gopher is lifted from the hole to remove a core sample, then lowered into the hole to resume the advance and acquire the next core sample.
The rotary percussive auto-gopher would include an ultrasonic/sonic gopher, to which would be added an anchoring and a rotary mechanism and a fluted drill bit (see figure). If, as intended, the ultrasonic/sonic gopher were rotated, then as in the case of an ordinary twist drill bit, the flutes would remove cuttings from the end of the hole, thereby making it possible to drill much faster than would be possible by ultrasonic/sonic hammering and chiseling action alone. The anchoring mechanism would brace itself against the wall of the drilled hole to enable the rotary mechanism to apply a small torque and a small axial preload to rotate the ultrasonic/ sonic gopher drill bit and push the drill bit against the end of the hole. The anchoring and rotary mechanisms would be parts of an assembly that would follow the ultrasonic/sonic gopher down the hole.
This work was done by Yoseph Bar-Cohen, Mircea Badescu, and Stewart Sherrit of Caltech for NASA’s Jet Propulsion Laboratory. NPO-45949