Seismic While Drilling (SWD) methodology in support to Moon subsurface stratigraphy investigations

The knowledge of the Moon subsoil geophysical properties is of great importance, for scientific reasons for the development of the Lunar exploration activities and the envisaged exploitation of its planetary resources. The Moon surface is characterized by the presence of regolith, a powdered material made up of unconsolidated, porous and highly brecciated rock fragments of several different grain sizes and lithologies. Beneath the regolith, a transition zone showing higher acoustic velocities may be present down to the solid bedrock. The bedrock consists of basaltic layers characterized by high seismic velocity and low seismic attenuation. In these conditions, human civil engineering and rover activities, including drilling may be subject to risk due to the lack of knowledge of the complex subsoil properties. Seismic While Drilling is a method used on Earth to support from geophysical point of view the drilling for oil and gas and geothermal exploration. In this application, the characterization of the stratigraphy by vertical seismic profiles in the drilled section, providing seismic images of the to-be-drilled substructures, is obtained using the drill-bit radiated energy. We present the result of a project that studies the adaptation of the method for Lunar drilling purposes, taking into account the specific issues related to the Moon environment and remote communication aspects. The results of a laboratory test conducted in the framework of a European Space Agency project (completed in 2009) with a planetary drill prototype and a simulator of a complete remote system are presented and discussed together with the perspectives for the seismic-while-drilling application for planetary missions.