A miniaturized XRF instrument for in situ planetary exploration: The Active X-Ray Spectrometer (AXRS)

The Active X-Ray Spectrometer (AXRS) was developed at Johns Hopkins Applied Physics Lab (APL) to be utilized in landed planetary exploration spacecraft seeking to better understand bulk rock geochemistry of lithophile materials. The AXRS sensor head has a mass of 360 g, fits within an envelope of 11 x 6 x 5 cm(3), and consumes <5 W during operation. AXRS has an average relative uncertainty of 9% for deriving the abundances of major and minor elements, and measurement precision <= 10% for all elements. Measurements were made with powdered samples, analogous to high-processed regoliths as expected on the surfaces of airless planetary objects. These specifications are equal to or better than those published for other x-ray instruments used in landed planetary exploration missions. We explored several mission applications for AXRS via analysis of planetary materials under mission conditions. These include the ability to: 1) resolve sub-type of carbonaceous chondrite meteorite via measured abundances of various lithophile element ratios based on volatility, 2) identify low-Fe lunar anorthosite, from high-Fe lunar anorthosite, from lunar mare using bulk Ca, Al, Fe, Mg, and 3) resolve various Venus- and Mars-like volcanic rocks utilizing bulk Si, K, and Na.