17 Lightweight Low Force Rotary  Percussive Coring Tool fo r Planetary Applications 

Ross Hironaka * and Scott Stanley ** 

   Abstract 

A prototype low-force rotary-percussive rock coring tool for use in acquiring samples for geological  surveys in future planetary missions was developed. The coring tool could eventually enable a lightweight  robotic system to operate from a rela tively small (less than 200 kg) mobile or fixed platform to acquire and  cache Mars or other planetary rock samples for eventual return to Earth for analysis. To gain insight  needed to design an integrated coring tool, the coring  ability of commercially available coring bits was  evaluated for effectiveness of varying key parameters : weight-on-bit, rotation speed, percussive rate and  force. Trade studies were performed for different met hods of breaking a core at its base and for retaining  the core in a sleeve to facilitate sample transfer. This led to a custom coring tool design which  incorporated coring, core breakage, core retention,  and core extraction functions. The coring tool was  tested on several types of rock and demonstrated the overall feasibility of this approach for robotic rock  sample acquisition.   Introduction   Current science for Mars and lunar exploration demands  that small diameter rock cores be acquired for  geologic evaluation. Tools to acquire these cores must  be lightweight, draw minimal power, and induce  low loads on their robotic platforms. Unfortunately,  no tools have yet been produced that meet these  requirements and produce a viable core. Tools developed to date are often complex, require large power and mass budgets, demand down forces beyond the capabilities of anticipated landers and rovers, and either take an inordinate amount of time to generate a core or introduce excessive energy into the core  sample, pulverizing it.     A rotary-percussive mechanism for rock drilling offers promise in addressing these requirements. Delivering hammer blows to a drill bit allows rock to be chiseled away as oppose d to being worn down by  friction alone. This can significantly reduce the amount of down-force, or weight- on-bit (WOB), required as  well as offer savings in power consumption.  In addition to raw coring ability, there are other chall enges in coring tool design that must be addressed  for successful sample acquisition.  A means of breaking off generated cores from the parent rock must be  included. The design must also provide a practical and reliable means for extracting and handling the generated cores. These are not trivial problems. Common rocks of interest, particularly sedimentary types, are easily fractured during the core generatio n process. This can cause mechanisms to bind or  jam, foiling sample retrieval efforts. In addition, for maximum geological significance, science demands maintaining the order in which fractu red rock core pieces are acquired. Finally, the ability to replace worn  drill bits is an important co nsideration for the coring tool design because some ro cks of interest, such as  basalt and sandstone, are particularly abrasive. A me chanism that allows for bit change-out must be  designed to work in concert with the rotary-percussive and core handling mechanisms.  This paper details the development of a rotary-p ercussive coring tool design that addresses core  generation, break-off, containment, and retrieval.                                                    * MDA ISI Space Division, Pasadena, CA   ** Techno Planet Inc., Northridge, CA 

Proceedings of the 40th Aerospace Mechanisms Symposium, NASA Kennedy Space Center, May 12-14, 2010  NASA/CP-2010-216272