This work investigates the potential use of direct ultrasonic vibration as an aid to penetration of granular material. Compared with non-ultrasonic penetration, required forces have been observed to reduce by an order of magnitude. Similarly, total consumed power can be reduced by up to 27%, depending on the substrate and ultrasonic amplitude used. Tests were also carried out in high-gravity conditions, displaying a trend that suggests these benefits could be leveraged in lower gravity regimes.

Future exploration missions to rocky bodies within the Solar System may wish to utilize drill systems on landed vehicles which simply cannot deliver the weight on bit, or accommodate the mass and volume levels which are required for the use of existing drill technology. This issue is being tackled by the development of the Ultrasonic Planetary Core Drill (UPCD) project. This paper shall detail the development effort of this drill to date, describing how lessons learned from early technology have informed the current design. Details of the Concept of Operations, the routine by which the drill samples and caches rocks for later analysis will also be presented, with an emphasis on the effect that the refinement of this process has had on the overall design.

Abstract-Traditional rotary drilling for planetary rock sampling, in-situ analysis and sample return, is challenging because the axial force and holding torque requirements are not necessarily compatible with lightweight spacecraft architectures in low-gravity environments. This article seeks to optimize an ultrasonic-percussive drill tool to achieve rock penetration with lower reacted force requirements, with a strategic view towards building an Ultrasonic Planetary Core Drill (UPCD) device. The UPCD is a descendant of the Ultrasonic/Sonic Driller/Corer (USDC) technique. In these concepts, a transducer and horn (typically resonant at around 20kHz) is used to excite a toroidal free-mass which oscillates chaotically between the horn tip and drill base at lower frequencies (generally between 10Hz to 1kHz). This creates a series of stress pulses which are transferred through the drill-bit to the rock surface and, while the stress at the drill-bit tip/rock interface exceeds the compressive strength of the rock, cause fractures that result in fragmentation of the rock. This facilitates augering and downward progress. In order to ensure that the drill-bit tip delivers the greatest effective impulse (the time-integral of the drill-bit tip/rock pressure curve exceeding the strength of the rock), parameters such as the spring rates and the mass of the free-mass, drill-bit and transducer have been varied and compared in both computer simulation and in practical experiment. The most interesting findings, and those of particular relevance to deep drilling, indicate that increasing the mass of the drill-bit has a limited (or even positive) influence on the rate of effective impulse delivered.

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This paper describes the effects of ultrasonically-assisted penetration of granular materials, in high gravity situations. The experimental rig, instrumented to obtain penetration force, rate and power both with and without ultrasonic assistance, was used to drive a penetrator into a granular material inside the ESA Large Diameter Centrifuge at accelerations of up to 10 g during early September 2015. Ultrasonic penetration proved to be most beneficial at lower levels of accelerations, reducing the required overhead weight by 80%, and the total power consumption by 27%.