Instrumentation for Mars Sample Return Basic Characterisation

<p dir="ltr">Pre-Basic and Basic Characterisation (BC) are a set of non-contact measurements to identify the basic physical and geological characteristics of returned samples from the joint ESA-NASA Mars Sample Return (MSR) campaign in order to inform its later, detailed analysis. They will be performed on all returned samples. Strict contamination control measures must be taken for planetary protection and to prevent contamination of the samples by Earth’s environment, so Pre-BC and BC will be carried out under high containment, which poses technical challenges. This work investigates X-ray Computed Tomography (CT) and synchrotron X-ray Diffraction (XRD) for the Pre-BC phase, and optical imaging for BC.</p><p dir="ltr">Analogues for returned Mars2020 samples and the sample tubes were prepared. A BC visible light imager was developed which meet a proposed set of BC minimum measurement requirements. The imager’s spatial resolution and other image quality characteristics were measured and test BC of sample analogues performed, which confirmed that an imager with equivalent zoom range, spatial resolution, and field of view can successfully carry out BC.</p><p dir="ltr">The required operating conditions for BC using micro-CT have been defined using a Nikon XTH225 microtomography scanner. Sample analogues were scanned inside and outside sample tube analogues, and BC requirements exceeded. Features such as grain size and porosity could be measured down to the scale of very fine sand (~60 μm).</p><p dir="ltr">Powder XRD on sample analogues inside and outside sample tubes was tested using Diamond Light Source’s I12 beamline in order to determine whether this technique could be incorporated into Pre-BC. It was found that identification and quantification of the mineralogy of sealed Mars sample tubes was feasible, and the effect of the tube walls on analysis was small. Recommendations for future experiments to address observed challenges with BC instrumentation are made, and next steps to develop final BC instruments described.</p>