It is of great interest to the scientific community to have the ability to analyze drilled boreholes in situ on the surfaces of the Moon and Mars. The goal of this work was to design and fabricate a Downhole Regolith Interrogation with Helium-assisted Drill and Laser Induced Breakdown Spectroscopy (LIBS) system (DIHeDRAL) targeted towards such applications. A DIHeDRAL instrument would provide synchronous exposure and analysis of volatiles using laser pulses, preserve borehole stratigraphy information, assess regolith mechanical properties through drilling telemetry, and analyze sensitive elemental composition.
The system uses an architecture whereby the laser, spectrometer, and driving electronics are all located above ground level. LIBS uses a high-energy laser pulse to generate a plasma on the surface of the sample under test. The pulse is carried to the downhole sensor head over a large-diameter optical fiber. Optics in the sensor head focus the pulse onto the borehole wall, where it ablates a small amount of material and excites it, creating a plasma. The atoms in the plasma emit photons at wavelengths characteristic for each element. This emitted light is collected by the sensor head optics and conveyed via fiber to a broadband spectrometer located on the surface. The resulting spectrum can be used to infer the elemental concentration of the sample.
Rather than bringing a sample to the surface for LIBS analysis, this technology brings LIBS equipment to the underground sample for in situ analysis. The LIBS sensor head has been repackaged to fit down a borehole, and positioned so that the sample is within the focal image. The drill rig can identify minerals and materials under the ground for the entire length of the hole drilled.