Development of a Robust Mating System for Use in the Autonomous Assembly of Planetary Drill Strings

Volume-constrained robotic missions seeking to obtain samples from beneath a planetary subsurface may wish to use a rigid drill string consisting of multiple, individual drill bit sections connected together, as opposed to a single, lengthy drill bit. To ensure that drill strings can be assembled and disassembled reliably, it is essential that a robust connection system be used. The authors propose a geometry that seeks to address the requirements of such a mating interface. The proposed solution is based on the bayonet interface, using L- and T-shaped so-called female grooves and male studs connected and disconnected together through a series of clockwise and counterclockwise rotations and single-point clamping events. This routine allows the transfer of both percussion through the drill string and torque in both directions of rotation, while permitting the accurate disconnection of individual drills bits at the required location. Sustained laboratory and field drilling operations suggest that bayonet-style connections offer a reliable solution to the problem of autonomous assembly and disassembly of drill strings in a planetary exploration setting. This paper discusses the development of such a connection system, based on the bayonet connection, which has been implemented in the overall architecture of the Ultrasonic Planetary Core Drill (UPCD). The design trade-off study, which sought to evaluate the use of the bayonet system in comparison with the more conventional screw thread interface, will be discussed, alongside experimental results from percussion transmission testing and drill string assembly testing.