The primary objective of the OSIRIS-REx mission is to collect a sample from an asteroid and return it to Earth but the spacecraft will also carry out an extensive remote-sensing campaign at asteroid Bennu using a suite of scientific instruments. These include cameras and various spectrometers to learn about the composition and appearance of the asteroid’s surface while gravity science will reveal what lies beneath.
One of five remote-sensing instruments, the REXIS is the Regolith X-Ray Imaging Spectrometer and represents a student collaboration experiment that is the result of a joint venture between MIT and Harvard University. The instrument is tasked with the creation of a global X-Ray map of asteroid Bennu to enhance the mission’s remote-sensing capabilities.
For more information, please see http://spaceflight101.com/osiris-rex/osiris-rex-instruments/