The Origins Spectral Interpretation Resource Identification 
    Security-Regolith Explorer (OSIRIS-REx) spacecraft is a derivative 
    of the Mars Reconnaissance Orbiter (MRO) and Mars Atmosphere and
    Volatile EvolutioN (MAVEN) spacecraft, leveraging the key heritage
    design components of these two missions.  Healthy resource margins
    across the vehicle, fully redundant spacecraft sub-systems with 
    extensive cross strapping, and high heritage hardware enable
    flexibility throughout the spacecraft development and during
    flight operations [SKEENETAL2015]
    
    Telecommunications Subsystem
    ----------------------------
      The telecom subsystem utilizes X-band communications, using
      a MAVEN build-to-print high gain antenna and MRO heritage 
      traveling wave tube amplifier for science high data rate downlink. 
      A medium gain antenna is utilized during the TAG mission phase.  
      Also two low gain antennas are available for TAG but also used for
      nominal (and safe-mode) engineering data downlink and uplink 
      commanding [SKEENETAL2015].
 
    Guidance, Navigation and Control (GNC)
    -------------------------------------------
      The GNC subsystem includes four reaction wheel assemblies 
      (RWAs) for performing spacecraft slewing and low jitter 
      pointing during science operations.  These reaction wheels 
      also store system momentum between desaturation events.  
      The GNC subsystem is responsible for commanding all of the
      thrusters on the spacecraft including executing trajectory
      correction maneuvers and RWA desats.  The GNC subsystem utilizes
      an inertial measurement unit (IMU) and flight-proven star 
      trackers to deter-mine and propagate on-board attitude knowledge.
      Sun sensors additionally support spacecraft autonomous safing 
      operations. Two GNC sensors provide measurements used for relative
      navigation: a GNC LIDAR is used for ranging to the surface to 
      support TAG operations, and a TAG camera system (TAGCAMS) 
      supports ground based navigation throughout proximity operations
      and autonomous on-board optical based navigation during the TAG
      phase [SKEENETAL2015].
 
    Propulsion Subsystem
    --------------------
      The high heritage propulsion subsystem is a single fault tolerant
      monopropellant system.  The propulsion subsystem includes main 
      engines, trajectory correction maneuver thrusters, attitude 
      control system thrusters, and low thrust reaction engine 
      assemblies [SKEENETAL2015].   

    Power Subsystem
    ---------------
      The power subsystem includes two rigid solar arrays, gimbaled about
      the spacecraft Y and Z axes.  In addition, two batteries are utilized
      for off-sun maneuvering, including the critical TAG mission phase [SKEENETAL2015].
 
    TAGSAM 
    ---------------------
      The TAGSAM is the key flight system component, used for making 
      contact and acquiring sample from the surface of Bennu during the
      TAG mission phase. TAGSAM is designed to collect greater than 150 g
      to provide margin to the 60 g mission requirement.  The TAGSAM 
      functions by fluidizing regolith with high pressure gaseous 
      nitrogen flow to transport it to a sample container located in 
      the TAGSAM ?head?.  The TAGSAM is made up of a single planar, 
      articulating arm with redundant motor windings at the shoulder, 
      elbow, and wrist and provides large structural, torque, and alignment
      margins, ultimately ensuring successful sample acquisition and
      stowage of the TAGSAM head into the SRC [SKEENETAL2015].
 
    Sample Return Capsule (SRC)
    ------------
      To safely return the collected sample to Earth, OSIRIS-Rex capitalizes
      on the success of NASA?s Stardust mission.  The proven Stardust SRC
      technology and capsule, mission operations, and mission de-sign are 
      all reused on OSIRIS-Rex for Bennu sample return [SKEENETAL2015].
 
    Science Sensors
    ---------------
      The OSIRIS-REx Spacecraft is host to the following scientific 
      instruments that are used to characterize the surface of 
      asteroid Bennu for sample-site selection and for longer term
      scientific analysis:
 
      (1) OSIRIS-REX Camera Suite (OCAMS)
      (2) OSIRIS-REx Laser Altimeter (OLA)
      (3) OSIRIS-REx Thermal Emission Spectrometer (OTES)
      (4) OSIRIS-REx Visible and Near Infrared Spectrometer (OVIRS)
      (5) Regolith X-Ray Imaging Spectrometer (REXIS)
    
      Radio Science investigations are carried out using
      the on-board and ground elements of the Telecommunications
      Subsystem. More information on instrumentation for
      each of the science investigations can be found elsewhere.
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