Calibration and Performance of the REgolith X-Ray Imaging Spectrometer (REXIS) Aboard NASA’s OSIRIS-REx Mission to Bennu

• Published in: Space science reviews Vol. 217; no. 8
• Main Authors: Hong, Jaesub, Binzel, Richard P., Allen, Branden, Guevel, David, Grindlay, Jonathan, Hoak, Daniel, Masterson, Rebecca, Chodas, Mark, Lambert, Madeline, Thayer, Carolyn, Bokhour, Ed, Biswas, Pronoy, Mendenhall, Jeffrey A., Ryu, Kevin, Kelly, James, Warner, Keith, Lim, Lucy F., Bartels, Arlin, Lauretta, Dante S., Boynton, William V., Enos, Heather L., Harshman, Karl, Balram-Knutson, Sara S., Polit, Anjani T., McCoy, Timothy J., Clark, Benton C.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.12.2021; Springer Nature B.V
• Subjects: Aerospace Technology and Astronautics; Apollo asteroids; Asteroid missions; Asteroids; Astrophysics and Astroparticles; Calibration; Fluorescence; Imaging spectrometers; Physics; Physics and Astronomy; Planetology; Regolith; Solar x-rays; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Special Communication; Spectroscopy; X ray binaries; X ray imagery; X ray sources; X ray spectrometers; X ray stars; X-ray fluorescence; X-ray fluxes; X-ray spectroscopy; X-rays; X-ray astrophysics; Asteroids; X-ray fluorescence
• ISSN: 0038-6308; 1572-9672
• DOI: 10.1007/s11214-021-00853-4

The REgolith X-ray Imaging Spectrometer (REXIS) instrument on board NASA’s OSIRIS-REx mission to the asteroid Bennu is a Class-D student collaboration experiment designed to detect fluoresced X-rays from the asteroid’s surface to measure elemental abundances. In July and November 2019 REXIS collected ∼615 hours of integrated exposure time of Bennu’s sun-illuminated surface from terminator orbits. As reported in Hoak et al. (Results from the REgolith X-ray Imaging Spectrometer (REXIS) at Bennu, 2021 ) the REXIS data do not contain a clear signal of X-ray fluorescence from the asteroid, in part due to the low incident solar X-ray flux during periods of observation. To support the evaluation of the upper limits on the detectable X-ray signal that may provide insights for the properties of Bennu’s regolith, we present an overview of the REXIS instrument, its operation, and details of its in-flight calibration on astrophysical X-ray sources. This calibration includes the serendipitous detection of the transient X-ray binary MAXI J0637-430 during Bennu observations, demonstrating the operational success of REXIS at the asteroid. We convey some lessons learned for future X-ray spectroscopy imaging investigations of asteroid surfaces.