XTRA: eXtraTerrestrial Regolith Analyzer

The eXtraTerrestrial Regolith Analyzer (XTRA)  is a second-generation X-ray Diffraction / X-ray Fluorescence (XRD/XRF) instrument capable of quantitative analysis of as-received lunar regolith when deployed from a small lander or rover [Blake et al., 2019].

Notional design of the XTRA instrument., 240 X 150 X 130 mm (excluding cyclone funnel).

The mineralogical composition of lunar soil can be used to elucidate its petrogenesis and that of its parental lithologies (e.g., igneous rocks, impact breccias), as well as subsequent diagenetic or metamorphic events. In addition to its value to landed lunar science and as ground truth for orbital missions, in-situ mineralogical analysis can be used to evaluate potential In Situ Resource Utilization (ISRU) processes such as the production of water or oxygen, metallic Fe or Al, or of ceramic building materials. Mineralogical analysis can be used to discover ore deposits useful for Rare Earth Element extraction.

Mineralogical analysis using XRD/XRF

XRD is the only in-situ technique able to definitively identify, quantify and determine the elemental composition of minerals present in lunar regolith. XRD can also determine the quantity of X-ray amorphous material present in a regolith sample, and when combined with XRF, the elemental composition of the amorphous component(s). Taken together, these techniques provide a comprehensive analysis of lunar regolith mineralogy that can only be improved upon by sample return. Taylor et al. [2019] report the mineralogy of 118 returned Apollo regolith samples in the <150 µm grainsize range analyzed by Terra, a commercialized version of the CheMin instrument.  XRD patterns and mineral abundances are available on the Open Data Repository https://odr.io/lunar-regolith-xrd.

Instrument Concept

XTRA is a CheMin inspired XRD/XRF instrument with enhanced XRF capabilities (11<Z<30) due the incorporation of a Silicon Drift Diode (SDD) detector in reflection geometry, as well as its operation in vacuum at the lunar surface. As-received regolith samples are delivered to the XTRA instrument and placed in a vibrated, reflection geometry cell. Collimated X-rays from a Co anode X-ray tube intersect the sample surface at an acute angle. Diffracted CoKα photons between 15–60° 2θ are detected by an energy-discriminating, single photon counting CCD. These photons are identified by their energy and summed into a 2D array that constitutes the diffraction pattern of the sample. A histogram of the energies of all photons detected by the SDD detector constitutes an X-ray fluorescence spectrum of the sample. 

a) schematic diagram of XTRA diffraction and fluorescence geometry. CoKα X-rays (magenta) are identified by their energy. An image of these constitutes the 2-D diffraction pattern. b), The 2-D pattern is summed radially about the central beam to yield a 1- D diffractogram. c), fluorescence X-rays from the sample are detected by an SDD detector and summed into a histogram of photon energy vs. number of counts.

Sample acquisition and delivery to XTRA

XTRA will be integrated with a sample collection/delivery system developed by Honeybee Robotics. The sample delivery system is based on HBR’s PlanetVac system in which sample acquisition is achieved through a pneumatic system attached to the footpad of the lander. The system has been tested at lunar gravity in vacuum on the Zero-G airplane [Zacny et al, 2010].

References

  • Blake et al. (2019) XTRA: AN EXTRATERRESTRIAL REGOLITH ANALYZER FOR LUNAR SOIL. 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132)
  • Taylor et al. (2019) XTRA: AN EXTRATERRESTRIAL REGOLITH ANALYZER FOR RESOURCE EXPLORATION.  Developing a New Space Economy 2019 (LPI Contrib. No. 2152)
  • Zacny et al. (2010), AIAA Space 2010 Conference and Exposition.