Design and Test of a Deployable Radiation Cover for the REgolith X-ray Imaging Spectrometer David B. Carte*, Niraj K. Inamdar**, Michael P. Jones*and Rebecca A. Masterson* Abstract The REgolith X-ray Imaging Spectrometer (REXIS) instrument contains a one-time deployable radiation  cover that is opened using a shape memory alloy actuator (a “Frangibolt”) from TiNi Aerospace and two  torsion springs. The door will be held closed by the bolt for several years in cold storage during travel to  the target asteroid, Bennu, and it is imperative to gain confidence that the door will open at predicted operational temperatures. This paper briefly covers the main design features of the radiation cover and measures taken to mitigate risks to cover deployment. As the chosen FD04 model Frangibolt actuator has minimal flight heritage, the main focus of this paper is the testing, results and conclusions with the FD04  while discussing key lessons learned with respect to the use of the FD04 actuator in this application. Introduction REXIS is a student collaboration experiment aboard the Origins, Spectral Interpretation, Resource  Identification, and Security Regolith Explorer (OSIRIS-REx) spacecraft. OSIRIS-REx is a NASA New  Frontiers mission planned for launch in 2016 that will travel to near-Earth asteroid 101955 Bennu and return at least 60 g (0.013 lbm) of asteroid regolith to Earth in 2023. REXIS uses coded-aperture imaging X-ray spectroscopy to image Bennu in the soft X-ray range of 0.5-7.5 keV and develop an elemental  abundance map of the asteroid [1]. REXIS is engineered primarily by students, with supervision and support from professional scientists and engineers at the MIT Space Systems Laboratory; MIT Department of Earth, Atmospheric, and Planetary Sciences; Harvard-Smithsonian Center for  Astrophysics; the MIT Kavli Institute; MIT Lincoln Laboratories; and Aurora Flight Sciences.  REXIS requires a one-time deployable cover door to protect its charge-coup led device (CCD) imagers  from radiation damage during the three-year cruise to Bennu. The door is positioned on top of the  instrument and is closed from launch in 2016 until asteroid observation in 2019, at which point the door  will be opened, providing the CCDs a view of the asteroid. Without this cover, space radiation will cause displacement damage in the detectors and degrade spectral resolution [2]. Use of a radiation cover will  limit damage so that the REXIS detectors can meet measurement objectives in its primary mission phase.  In this paper, we focus on the mechanical design of the radiation cover and the opening mechanism. The  4-mm (0.2-in) thick aluminum (Al) cover rotates about a custom spring hinge and is opened upon arrival  at Bennu through the use of an FD04 Frangibolt from TiNi Aerospace, which is part of a newly- introduced  Mini Frangibolt family. This family of Frangibolts incorporates cylinders made from Single Crystal Sh ape  Memory Alloy that offer 3 times the stroke performance of equivalent products from the Standard  Frangibolt family (FCx). Other advantages of this product are its low power requirement, small form factor, and low cost. However, the Mini Frangibolt product family has minimal flight heritage. Successful actuation of the FD04 Frangibolt is highly sensitive to the thermal and structural design of the bolted joint. Given the minimal flight heritage for FD04, prototype testing of the REXIS radiation cover has focused onestablishing confidence in the FD04 Frangibolt mechanism as a reliable actuator for this application and  creating a robust design for the radiation cover. This paper presents the overall radiation cover design,  provides an overview of the testing performed, and discusses the lessons learned. * Space Systems Laboratory, Massachusetts Institute of Technology, Cambridge, MA ** Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA /g51/g85/g82/g70/g72/g72/g71/g76/g81/g74/g86/g3/g82/g73/g3/g87/g75/g72/g3/g23/g21/g81/g71/g3/g36/g72/g85/g82/g86/g83/g68/g70/g72/g3/g48/g72/g70/g75/g68/g81/g76/g86/g80/g86/g3/g54/g92/g80/g83/g82/g86/g76/g88/g80/g15/g3/g49/g36/g54/g36/g3/g42/g82/g71/g71/g68/g85 /g71/g3/g54/g83/g68/g70/g72/g3/g41/g79/g76/g74/g75/g87/g3/g38/g72/g81/g87/g72/g85/g15/g3/g48/g68/g92/g3/g20/g23/g16/g20/g25/g15/g3/g21/g19/g20/g23   145