Pre-flight Geometric and Optical Calibration of the Planetary Instrument for X-ray Lithochemistry (PIXL)

The Planetary Instrument for X-ray Lithochemistry (PIXL) is a micro-focus X-ray fluorescence spectrometer that is mounted on the robotic arm of NASA’s Perseverance rover. PIXL scans target surfaces with high spacial resolution yielding detailed analyses of rock or soil elemental chemistry. The elemental maps are produced by a narrow 120 μm X-ray beam. These scans are correlated to images captured by PIXL’s Micro Context Camera (MCC) which tie the X-ray measurements to the visual texture and structure of the sample, revealing the distribution and variations of chemical elements within the rock. The PIXL subsystem that determines this correspondence is the Optical Fiducial System (OFS), which is comprised of the MCC, two Structured Light Illuminators (SLI) and a Floodlight Illuminator (FLI). This paper discusses the pre-flight calibration of the OFS, including optical calibration of the MCC, radiometric calibration of the floodlight system and geometric calibration of the structured light illumination beam together with an overall geometric calibration of the OFS and the X-ray beam. Finally, results from the performance verification are presented.