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

Jaesub Hong, Richard P. Binzel, Branden Allen, David Guevel, Jonathan Grindlay, Daniel Hoak, Rebecca Masterson, Mark Chodas, Madeline Lambert, Carolyn Thayer, Ed Bokhour, Pronoy Biswas, Jeffrey A. Mendenhall, Kevin Ryu, James Kelly, Keith Warner, Lucy F. Lim, Arlin Bartels, Dante S. Lauretta, William V. BoyntonHeather L. Enos, Karl Harshman, Sara S. Balram-Knutson, Anjani T. Polit, Timothy J. McCoy, Benton C. Clark

Research output: Contribution to journalReview articlepeer-review

1 Scopus citations


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.

Original languageEnglish (US)
Article number83
JournalSpace Science Reviews
Issue number8
StatePublished - Dec 2021


  • Asteroids
  • X-ray astrophysics
  • X-ray fluorescence

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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