Sep 17, 2018

On Sept. 14, the spacecraft’s REXIS instrument opened its Radiation Cover and REXIS now has a clear view of space for the first time. The Radiation Cover protected the detectors from radiation damage during the cruise to Bennu, but it also blocked the aperture of the instrument. With OSIRIS-REx nearing Bennu, the mission team opened the cover to enable REXIS to observe external calibration targets like the Crab Nebula, as well as ultimately the asteroid.

The Radiation Cover had been held shut by a Frangibolt since before launch. On Friday, the Frangibolt was actuated by heating it up, which expanded a shape-memory alloy cylinder, breaking the titanium bolt holding the cover shut. By inspecting heater and temperature telemetry and comparing the difference between spectra taken before and after the Frangibolt firing, the REXIS team was able to determine that the cover opened successfully and the instrument is now seeing the cosmic X-ray background. Going forward, REXIS will take measurements on several astrophysical X-ray sources in preparation for observations of Bennu starting next summer.