Instrument Overview
      ===================
      The ChemCam instrument suite includes both the LIBS (Laser Induced
      Breakdown Spectrometer) and the RMI (Remote Micro-Imager) components.
      The instrument suite consists of two major sections, the Mast Unit,
      housing the laser, RMI, telescope, and associated electronics, and the
      Body Unit, consisting of an optical demultiplexer, three spectrometers,
      the thermo-electric cooler, CCD electronics, spectrometer electronics,
      the data processing unit (DPU), and the low-voltage power supply.  The
      ChemCam mast unit is contained in the remote warm electronics box (RWEB)
      at the top of the rover's mast. The body unit is located in the rover
      body, attached to the rover accommodation mounting plate (RAMP).
      Besides the mast and body units, there are two other sections of the
      instrument.  A fiber optic cable transmits the plasma light between
      the two ChemCam units.  Finally, included on the rover deck is a
      calibration target assembly.
 
      The following text describes both the RMI and LIBS components, as
      they work together.
 
      Scientific Objectives
      =====================
      The ChemCam LIBS instrument's objective is to obtain major element
      compositions for rocks and soils within seven meters of the instrument
      to an accuracy of +/-10%. The instrument must be capable of removing
      dust and weathering rinds, and must be able to profile to a depth of 1
      mm into rocks.
 
      The ChemCam RMI instrument provides context imaging with
      sub-millimeter resolution comparable to a close-up camera, but at
      meter distances.
 
      Calibration
      ===========
      The reader is referred to the ChemCam calibration paper
      [WIENSETAL2013].
 
      Operational Considerations
      ==========================
      During the observation of the Sun by other instruments, the telescope
      is focused at 2 meters to avoid damages on the RMI detector or other
      optics.  Two exclusion zones have also been defined: 1.20 m - 1.36 m,
      1.942 m - 2.217 m to avoid laser reflections on some optical parts.
      These two exclusion zones  do not apply to activities implying RMI
      only.
 
      Detectors
      =========
      For detectors the ChemCam LIBS spectrometers employ E2V 42-10 back
      illuminated 2048 x 515 pixel CCDs that are operated in low-noise
      advanced inverted mode. Each pixel is 13.5 microns square, for an image
      area of 27.6 x 6.9 mm. The grade-zero units used in ChemCam were
      essentially off-the-shelf in terms of specifications with the exception
      of the anti-etalon coating mentioned above for the VNIR CCD. The full
      wells were measured at 255k, 190k, and 216k electrons for the UV, blue,
      and VNIR spectrometers, respectively.
 
      The ChemCam imager is a heritage unit from the CIVA experiment onboard
      the ESA Rosetta mission. The imager is composed of a camera head (3D
      cubes based on the TH 7888A CCD image sensor manufactured by Atmel)
      with specific optical systems.  It is a frame transfer CCD with a
      useful zone of 1024x1024 square pixels (14x14 microns square). Four
      extra lines and sixteen extra columns are provided for dark
      referencing. The 3D cube is equipped with FPGA based controller,
      which manages the CCD clocking and the analog to digital converter
      (10-bit ADC).
 
      Electronics
      ===========
      CCD Electronics
 
      There are three identical CCD cards, one for each of the optical
      spectrometers. The spectrometers were required to be thermally isolated
      from the rest of the body unit, so a separate CCD card for each
      spectrometer accommodated the thermal isolation.  The CCD card provides
      the first stage analog signal amplification, provides some of the
      required CCD voltages, and interfaces electrically to the CCDs. The CCD
      cards connect to the spectrometer electronics using a flex circuit,
      which also helps minimize the thermal path.
 
      The CCDs underwent normal factory testing provided for commercial
      units plus one hundred thermal cycles between -55 C and +70 C, as well
      as a 72 hour burn-in at 125 deg C. These were done at the factory prior
      to delivery. The units underwent characterization at JPL for dark
      current, gain, full well, optimal operating voltages, and any gross
      anomalies. Because of differences in clock speeds between the initial
      characterization and flight operation the units had to be tested again
      with the flight electronics in a socket prior to soldering them to the
      boards.
 
      Spectrometer Electronics
 
      The spectrometer electronics board operates the CCDs used by the three
      LIBS spectrometers. The functions include providing proper reference
      voltages to drive the CCDs, operating the CCDs, receiving the data
      from the CCDs, converting the signals to digital data, and passing the
      data to the DPU.
 
      Reference voltages are provided separately to each CCD, allowing
      preflight adjustment to optimize the voltages for each CCD as required
      to optimize performance. Adjustments are provided for the vertical and
      horizontal clock speeds. These are made via
      commands sent to the spectrometer field-programmable gate array (FPGA)
      where the CCD clocking control is performed. Nominal operation for 1D
      LIBS spectra uses a 56 kHz vertical transfer rate and a 550 kHz
      horizontal transfer rate as these appear optimal in terms of overall
      noise performance. The total transfer time for this setting is a
      maximum of ~13 ms if all rows are summed.
 
      When power is applied to the CCBU, all three CCDSs are turned on but
      are not clocked.  This saves power while warming up the CCDs to
      equilibrium temperature if required by performance measurements. Even
      though nominal operation uses all three CCDs, power to each unit is
      controlled separately in case of a failure of one in flight with one
      serendipitous exception:  UV and VNIR combination cannot be operated
      without the VIS spectrometer. The exact timing of each A-D conversion
      can be adjusted with a parameter sent to the spectrometer board FPGA,
      allowing optimization of performance.  The clocking parameters
      (horizontal, vertical and A/D sample point) are the same for all three
      CCDs.
 
      RMI Electronics
 
      The required supply voltages are +5, and +15 V, and receiving a +5 V
      command from the MU FPGA switches on the camera.
 
      Data Processing Unit (DPU)
 
      The DPU carries out the functions of taking commands from the rover,
      performing these commands, storing the data, and sending the data to
      the rover. In addition, the DPU sends commands to the mast unit and
      receives signals and data back in return.
 
      The DPU communicates with the mast unit through two communication
      links.  Commands and telemetry data between the body unit and mast
      unit are performed using a programmable universal asynchronous
      receiver transmitter (UART) link.  The UART link can run at 4 different
      speeds: 9.6 kbaud,  19.2 kbaud, 38.4 kbaud and 115.2 kbaud.   Images
      taken by the mast unit camera are sent from the mast unit to the body
      unit using a low voltage differential signal (LVDS) high speed serial
      link (HSS) that runs at 8.25 Mbps.
 
      The DPU communicates with the rover through a 2-way LVDS high speed
      serial link.  Command data from the rover to the body unit run at
      4.125 Mbps.  Telemetry data from the body unit to the Rover runs at
      8.25 Mbps.  The DPU contains a UTMC 80C196 microcontroller, which is
      supported by two Actel FPGAs.  One FPGA, called the Micro FPGA,
      contains the microcontroller logic control, the MU UART interface
      logic, state of health (SOH) interfacing and ground based test port.
      The second DPU FPGA, called the Memory FPGA, handles the interfaces to
      the  6 Megabyte DPU data memory bank,  the spectrometer interface, the
      mast unit HSS link and the rover HSS links.  Program memory is
      redundantly stored in two banks of EEPROM. One bank of EEPROM is
      hardware locked, in that the write line is tied off to the inactive
      state to guard against any memory corruption during flight. The other
      bank of EEPROM is capable of being reprogrammed in flight if the need
      arises, but is also protected from corruption by the EEPROM's
      built-in software data protection algorithm.  In addition the DPU also
      has a bank of scratchpad SRAM and a bank of data EEPROM.
 
      Some changes have already been made to the reprogrammable side. The
      handling of interrupts was modified to avoid conflicts which result in
      approximately 1% of commands rejected on the locked side. The locked
      side also operates with an RMI data transmission rate to the rover
      compute element (RCE) of only 2 MHz, while the reprogrammable side can
      transfer data at up to 8 MHz. The locked side also is missing headers
      on the RMI images, which was fixed in the reprogrammable side's
      program.
 
      Low-Voltage Power Supply
 
      The low-voltage power supply receives the nominal 28 V input from the
      rover, passes it on to the Mast Unit, and provides the Body Unit with
      +5 V digital, +/-5 V analog, +24 V digital, and +/-12 V analog. Each of
      these has a maximum of 5 W except the +12 V and +24 V, which are 2.5 W
      maximum. The DPU uses only the +/-5 V lines, while the spectrometer
      board uses all five supplies. Design goals were noise levels < 5 mV
      rms and spikes of < 20 mV amplitude. The LVPS board also provides
      connections for the PRT temperature sensors, two of which are on the
      spectrometers and two of which are on the CCD board covers.  The LVPS
      board uses commercially available Interpoint power converters with
      inline filters to achieve its voltage levels. The units were heat sunk
      to aluminum bars which extended to the edge of the board. The board is
      housed in a separate compartment accessed from the rover attachment
      side of the electronics box, where heat is most easily transmitted to
      the rover.
 
      Thermal modeling of the LVPS indicated that at the hot qualification
      temperature limit of 70 deg C, with the board averaging 77 deg C the
      +5 V converter, if operating at 120% with a 36 V bus input, could
      exceed 125 deg C. Additionally, in this scenario, two other converters
      could exceed 110 deg C. While the instrument was successfully tested
      at these levels, it is not expected to operate near these levels on
      Mars.
 
      Filters
      =======
      There are no filters on ChemCam.
 
      Optics
      ======
      The ChemCam telescope focalizes the system on a distance rock to (1)
      create a LIBS plasma and collect light from the plasma into an optic
      fiber (LIBS); or (2) to image the context around the laser pit (RMI).
      The telescope is designed to perform LIBS in the range of 1-7 m, and RMI
      in the range of 2-20 m, using a moving secondary miror. The primary
      mirror of the telescope is 110 mm in diameter. The RMI field of view is
      20 mrad. The optical system includes also a continuous laser and a
      photodiode to perform autofocus.
 
 
      Operational Modes
      =================
      ChemCam is designed and planned to be used daily on Mars. Operations
      planning divides the rover activities into reconnaissance sols
      (sol = Mars day), drive sols, approach sols, contact sols during which
      arm-mounted instruments APXS and MAHLI (hand lens imager) are used,
      and in-situ analysis sols during which CheMin and SAM analyses are
      carried out. ChemCam can be used to perform reconnaissance on both of
      the first two types of sols. During approach sols ChemCam data will
      help select the precise sample for in-situ analysis, and during contact
      and in-situ analysis sols ChemCam can perform additional surveys of
      surrounding materials. A typical analysis will consist of a number of
      laser pulses sufficient to remove surface dust, followed by a number
      of laser pulses (e.g., 30) that will be averaged together for better
      statistics. At times depth profiles will be performed to understand
      the compositions of dust and weathering layers as well as the rock
      composition. Because the LIBS analysis spot size is by necessity =
      0.5 mm in diameter, determining a whole-rock composition requires
      multiple analysis spots on the same rock for medium- and coarse-grained
      lithologies.
 
      Each analysis spot is expected to take about six minutes and two
      Watt-hrs, but in most cases it will be necessary to warm the laser
      from the -40 deg C survival temperature of the mast to its operation
      temperature of -10 deg C, taking about 20 minutes before the first
      analysis of the day. There is also some time required at the end of
      analyses to slowly cool the unit and to defocus to a sun-safe
      configuration and stow the mast. Of the actual analysis, the laser
      shots will normally operate at 3 Hz, taking only ~20 s, while up to
      3 minutes is required for focusing and some tens of seconds are
      required for transferring the data. RMI context images will be taken
      before and after each LIBS analysis, transmitting only the pixels
      corresponding to the LIBS spot on the second image.
 
 
 
      Subsystems
      ==========
      The major subsystems are:
 
      RMI subsystem - provides context images in visible light of target
        area sampled by LIBS system or can be used to provide narrow FOV
        images of other targets of interest.
 
      LIBS subsystem - provides LIBS spectra over the wavelength range
        from UV to VNIR of selected targets. Can also be used for passive
        spectroscopy of selected targets.
 
 
      Functional subsystems:
 
        ChemCam Mast Unit
        - Optical Box consisting of optical telescope, focus mechanism and
                focus laser
        - LIBS laser
        - Electronics box with laser capacitors, LVPS, HVPS, I/F electronics,
                FPGA and associated electronics
 
        ChemCam Optical Fiber
        - Fiber optic cable that transmits LIBS light from Mast Unit to
            Body Unit
 
        ChemCam Body Unit
        -  Demultiplexer that accepts LIBS photons from the fiber optic
           cable and separates light into UV, VIS and VNIR bands
        -  Spectrometers - UV, VIS and VNIR spectrometers that record
           the intensity of LIBS light in these wavebands.
        -  Electronics box with LVPS, CPU and I/F electronics board and
           spectrometer control board
        -  Thermoelectric cooler - used to cool Spectrometer CCDs
        -  Decontamination heaters - used to prevent contamination of
           the Body Unit optics
 
       In addition there are a variety of survival and laser heaters,
       temperature monitors and other minor subsystems in both the Mast and
       Body Units.
 
       ChemCam Calibration Targets - assembly mounted on Rover deck with
       rock and optical calibration targets
 
 
      Measured Parameters
      ===================
      The reader is referred to the ChemCam Instrument papers MAURICEETAL2012
      and WIENSETAL2012A published in Space Science Reviews; complete
      citations are in the reference catalog file CCAM_REF.CAT in the Catalog
      directory of the archive. Copies of these papers are provided in the
      Extras directory.