Pre- and In-flight Performance of Terrain Relative Navigation on PIXL's Micro Context Camera, M2020

The thermal environment on the surface of Mars presents a challenge to any mission and instrumentation conducting surface operations on Mars, and the Planetary Instrument for X-Ray Lithochemistry (PIXL) is no exception. The martian diurnal temperature swing can span almost 100 degrees Celsius, depending on season and location on the planet. Being required to operate under such large thermal span, while performing proximity science, acquiring measurements accurate to tens of microns, calls for novel solutions. PIXL's Micro Context Camera (MCC) provides multispectral context to the XRF data captured by PIXL and provides navigational solutions using structured light and floodlight in combination with advanced image processing. This includes highly accurate range measurements, in addition to accurate and robust Terrain Relative Navigation (TRN). For PIXL, being an X-ray Fluorescence microscope with a beam size of ~120 microns, it is essential to obtain a highly accurate correlation, or mapping, of the XRF measurements to the optical context recorded by the MCC. Such correlation needs to be at microscopic level with a typical scan area for PIXL of 4x12.5 mm, with XRF measurements at more than 3000 locations. The majority of PIXL scans are executed during nighttime operations, where all other maneuverability of Perseverance is halted. The robotic arm dedicated for proximity science, which PIXL is mounted on, is challenged in maintaining an accuracy in the order of tens of microns as the ambient temperature on the surface of Mars declines about 80°C during the nighttime on Mars. To compensate for the thermal drift of the instrument, relative to the surface, Terrain Relative Navigation (TRN) is utilized to track the relative position and use PIXL's own motion capabilities, in the form of a hexapod, to stay on track with the scan executed on the surface of Mars. This technology measures relative position to an accuracy of 20 microns, and achieves a robust solution over a catch range of up to 20 mm translation. Here we present an overview of the implementation for the Micro Context Camera, report on the pre-flight verification results followed by inflight performance validation throughout the first 921 Sols of operation on Mars. This novel solution significantly increases the possibility for autonomous operations, hereby enabling the overarching goal of NASA's Perseverance for geologic exploration, determining the habitability and search for biosignatures, followed by sample collection.