Optimization of the Horn, Free-Mass, and Support Architecture of a Solid Ultrasonic Rock Coring System

Extracting cohesive samples from below planetary surfaces will require low mass, low reaction and low power drilling systems. Ultrasonic tools are considered to be a leading technology as they meet the above criteria, but mos t architectures so far proposed to deploy them require either that (i) the entire cutting gea r is sent downhole and repeatedly retrieved to empty the spoil, or (ii) the transducer remains on the surface and delivers its impulses through a long lance. Retrieving the cutting gear i n its entirety risks collapse of the shaft and presents control problems when reacquiring the opening, and long lances must be either assembled on-site or be limited to the dimensions o f the delivery aeroshell. This paper seeks to adapt traditional ultrasonic gear such that a ne w architecture may be employed to avoid these problems. Thus, the basic architecture of an ultrasonic coring device is derived from the step and dog-bone horn described in the literat ure and optimized by a process of finiteelement analysis. Examples of both horns are manufactured, tested using an experimental modal analysis technique to ensure their proper ope ration, and further tested using a force transducer to measure the impulse they deliver to a target through an optimized dynamic stack. The target is replaced with sandstone to ens ure that the measured impulses are sufficient to penetrate rock. Finally, the layout o f the optimized ultrasonic assembly is adapted such that it may be deployed by a coilable tube drillstring and thus avoid the operational difficulties described above. Mass and performance estimates are provided.