Ultrasonic/sonic driller/corer (USDC) as a sampler for planetary exploration

Future NASA exploration missions to Mars, Europa, Titan, comets, and asteroids will perform sampling, in-situ analysis and possibly the return of material to Earth for further tests. One of the major limitations of sampling in low gravity environments is that conventional drills need high axial force. An ultrasonic/sonic driller/corer (USDC) mechanism was developed to address these and other limitations of existing drilling techniques. The USDC is based on an ultrasonic horn that is driven by a piezoelectric stack. The horn drives a free-mass, which resonates, between the horn and drill stem. Tests have shown that this device addresses some of the key challenges to the NASA objective of planetary in-situ sampling and analysis. The USDC is lightweight (450 g), requires low pre-load (<5N) and can be driven at low power (5 W). The device was operated from such robotic platforms as the Sojourner rover and the FIDO robotic arm and it has been shown to drill various rocks including granite, diorite, basalt and limestone. The drill can potentially operate at high and low temperatures and does not require sharpening. Although the drill is driven electrically at 20 kHz, a substantial subharmonic acoustic component is found that is crucial to drilling performance. Models that explain this low frequency coupling in the horn, free-mass, drill stem and rock are presented. Efforts are currently underway to integrate the models and experimentally corroborate the predictions.