An Instrumented Laboratory Drill to Investigate Mechanical Properties of Rocks with Rover Drilling Systems

Rosalind Franklin’s drill
The Rosalind Franklin rover, scheduled for launch in 2028, will drill into the Martian ground in its quest to unravel the planet’s history and search for biomarkers. Equipped with a drilling system capable of reaching depths of up to two meters, it will record hyperspectral measurements along the borehole and collect samples for analysis with experiments within the body of the rover [1].

Drill telemetry analysis for subsurface investigation
To improve and extend the characterization of the subsurface, the instruments’ measurements can be complemented with information about the mechanical behaviour of drilled materials. While the rover’s science payload does not include any dedicated instrument for directly measuring rock mechanical properties, we can use the drill itself for this purpose: useful information can be retrieved from housekeeping telemetry data generated while drilling [2,3]. During its operation, the drill system records parameters useful for geotechnical characterization of the rocks, including temperature, force, torque, and speed readings.
To prepare for the scientific analyses and interpretations of these data, we are developing dedicated data analysis techniques and tools [3].

Developing an instrumented laboratory drill
The development of dedicated data analysis tools and techniques and their validation requires a reference dataset that encompasses a wide range of different drilling conditions and rock samples. So far, we’ve been using drill telemetry data recorded during drilling tests conducted with the rover GTM (Ground Test Model), an almost identical replica of the flight model rover. Further development of analysis techniques would greatly benefit form a larger and more varied reference dataset.
To build an additional, extensive reference dataset, we are developing an instrumented laboratory drill. This will allow us to easily test drilling operations in the lab and collect data on a variety of rock samples. This laboratory drill is equipped with sensors that will record a range of important quantities that are also reported in Rosalind Franklin’s drill telemetry and employed in our analyses.
This laboratory drill will help us improve our understanding of rock drilling and support the development of data analysis techniques. Data collected with it will complement telemetry data stemming from GTM drilling tests. It will contribute to expand the range of drilling scenarios in our reference dataset. We intend to use this data to improve and validate our analysis techniques and machine learning models. We will then work to adapt some of the best performing techniques to the specifics of Rosalind Franklin’s drill and employ them for the investigation of the Martian subsurface.

Design concept
The design of this first iteration of the laboratory drill does not aim to reproduce exactly the mechanics of the rover’s drill nor to exactly simulate drilling telemetry generated by the rover’s drilling system. Rather, our goal is to develop a simple and versatile laboratory instrument that can be easily adapted to various drilling scenarios.
The laboratory drill is powered by an electric motor coupled to a planetary gearhead. The motor also includes a rotary encoder for the precise measurement of its rotation speed by its control electronics. Drilling torque and vertical force are measured by two dedicated strain-gauge load cells. A linear encoder measures the vertical position of the drill with respect to its stationary frame as it slides on a linear rail. This will provide a measure of the drill tip depth and of the rate of penetration (ROP), an important drilling performance parameter.

Looking forward
The procurement of components needed to build the first iteration of the laboratory setup is currently underway. Once it is assembled and tested, it will be used on a variety of rock samples returned from geologic fieldwork, building a library of observation on rocks and soils with analogies in their composition or evolution to the rock we observe from remote sensing at the landing site. The resulting data will support the development of our data analysis techniques. Further evolutions of the instrument’s design will build on the experience gained with the first design and expand its capabilities and representativeness, with the goal of eventually resulting in a portable instrument that can also be used in the field.

References
[1]    Vago J.L. et al, Astrobiology, vol 17, n.6-7 (2017), https://doi.org/10.1089/ast.2016.1533
[2]    Altieri F. et al., Advances in Space Research (2023), https://doi.org/10.1016/j.asr.2023.01.044
[3]    Rossi L. et al., Proceedings of IAC2024, https://doi.org/10.52202/078357-0048