Instrument Host Overview  ========================    For most Mars Odyssey experiments, data were collected by    instruments on the spacecraft.  Those data were then relayed    via the telemetry system to stations of the NASA Deep Space    Network (DSN) on the ground.  Radio Science observations (such    as radio tracking) required that DSN hardware also participate    in data acquisition.  The following sections provide an    overview first of the spacecraft and then of the DSN ground    system as both supported Mars Odyssey science activities.  Instrument Host Overview - Spacecraft  =====================================    The Mars Odyssey spacecraft was built by Lockheed Martin    Astronautics (LMA).  The spacecraft structure was divided into    two modules: the equipment module and the propulsion module.    The shape was not uniform, but can be approximated by    envisioning a box 2.2 x 1.7 x 2.6 meters.  The framework was    composed of aluminum and titanium.  Most spacecraft systems    were redundant in order to provide backup should a device fail.    For more information, see [JPLD-16303].    Command and Data Handling    -------------------------      This subsystem handled all computing functions for Mars      Odyssey.  It ran the flight software and controlled the      spacecraft through interface electronics.  The system was      based around a RAD6000 computer with 128 megabytes of      random access memory (RAM) and 3 megabytes non-volatile      memory, which allowed data to be maintained by the system      in the event of a power failure.  The interface      electronics were computer cards that communicated with      external peripherals.  The cards fit into the computer's      main board.  There were two identical sets of the      computer and interface electronics for back up in case      one failed.  One card was not redundant.  It was a one      gigabyte mass memory card that was used to store imaging      data.    Telecommunications    ------------------      The telecommunication subsystem was composed of two parts.      The first was a radio system that operated in the X-band      microwave frequency range.  It was used for communications      between Earth and the spacecraft.  The other system operated      in the ultra high frequency (UHF) range for communications      between future Mars landers and Odyssey.      Communication between the spacecraft and Earth occurred      through the use of three antennas.  The high-gain antenna was      a dish with 1.3 meter diameter (4.25 feet).  It was used      during the late Cruise and Science and relay phases of the      mission when data rates were high.  It simultaneously      received commands from Earth and transmitted science data to      Earth.  The medium-gain antenna was a 7.1 cm (2.8 inch) wide      rectangular horn antenna that protruded through the high-gain      dish.  The low-gain antenna was 4.4 cm (1.75 inches) and      provided wide- angle communications in emergencies or when      the high-gain antenna was not pointed directly at Earth.    Electrical Power    ----------------      A 7 square meter (75 square feet) solar panel containing an      array of gallium arsenide cells generated power for the      spacecraft.  The power distribution and drive unit sent power      to the electrical loads of the spacecraft through a system of      switches.    Guidance, Navigation and Control    --------------------------------      This subsystem used three redundant pairs of sensors to      determine the spacecraft's attitude.  A star camera was used      to look at star fields and a sun sensor detected the position      of the Sun in order to back up the star camera.  The inertial      measurement unit collected spacecraft orientation data      between star camera updates.  The reaction wheels along with      the thrusters operated to control the attitude.  There were      four reaction wheels - three primary and one for backup.      Odyssey was a three-axis stabilized spacecraft.    Propulsion    ----------      The propulsion system comprised a main engine, which aided in      placing Odyssey in orbit around Mars, and sets of small      thrusters, which performed attitude control and trajectory      correction maneuvers.  The main engine produced a thrust of      about 695 Newtons (156 pounds of force).  Each of the four      attitude controlling thrusters produced a thrust of 0.9      Newtons (0.2 pounds of force) and the four spacecraft turning      thrusters produced a force of 22 Newtons (5 pounds of force).      The propulsion system also included one gaseous helium tank      used to pressurize the fuel and oxidizer tanks, miscellaneous      tubing, pyro valves, and filters.    Structures    ----------      The spacecraft was composed of two modules - propulsion and      equipment.  The propulsion module contained tanks, thrusters,      and associated plumbing.  The equipment module consisted of      the equipment deck, which supported the Mars Radiation      Environment Experiment (MARIE), and engineering components.      The other component of the equipment module was the science      deck which housed the Thermal Emission Imaging System      (THEMIS), Gamma Ray Spectrometer (GRS), High-Energy Neutron      Detector (HEND), Neutron Spectrometer (NS), and star cameras      on top and engineering components and the GRS central      electronics box on the underside.    Thermal Control    ---------------      A combination of heaters, radiators, louvers, blankets, and      thermal coatings maintained each spacecraft component's      temperature within its allowable limits.    Mechanisms    ----------      Odyssey functioned via several mechanisms, many of which were      associated with the high-gain antenna.  The antenna was      locked down during launch, cruise, and aerobraking through      three 'retention and release devices,' or latches.  The      antenna was released and deployed with a motor-driven hinge      once the science orbit around Mars was attained. A two-axis      gimbal assembly controlled the position of the antenna. The      solar array used four latches which folded together and      locked down the panels during launch.  After deployment, a      two-axis gimbal assembly controlled the solar array.  The      last mechanism was a latch for the deployment of the 6-meter      GRS boom.    Flight Software    ---------------      Odyssey received commands from Earth via radio and then      translated them into spacecraft actions. The flight software      had the capability to run many sequences concurrently in      addition to executing received commands immediately.      The data collection software was quite flexible.  The science      and engineering data were collected and then put in a variety      of holding bins called Application Identifiers (APIDs).  Ground      commands could easily modify the data routing and sampling      frequency.      A number of autonomous spacecraft performance functions were      part of the flight software.  The spacecraft ran routines      to control attitude and orientation without commands sent      from Earth.  The software also executed fault protection      routines to determine if any internal problem occurred.  If      a problem was found, a number of automatic preset actions      would occur to resolve the problem and put the spacecraft      into a standby mode until ground controllers provided      further direction.    Coordinate System    -----------------      The spacecraft frame is defined with the X axis parallel to      the stowed HGA boresight, the Y axis normal to the stowed      solar arrays, and the Z axis in the direction of the main      engine thrust (see figure below).  The origin of the frame      is centered on the launch vehicle separation plane.                                 _______________ HGA                                 \             /              Science        ..   `._________.'               Orbit         || ._______________.             Velocity        || |       ^+Xsc   | Science Deck                ^.           || |       |       |                  `.         || |       |       |                    `.       || +Ysc    |       |                             ||@| <-----o +Zsc (out of page)                             || |               |                             || |               |                             || | Science Deck  |                      Solar  || ._______________.                      Array  ..                                   /                                  /                                 /                                V Nadir  Instrument Host Overview - DSN  ==============================    The Deep Space Network is a telecommunications facility managed    by the Jet Propulsion Laboratory of the California Institute of    Technology for the U.S. National Aeronautics and Space    Administration (NASA).    The primary function of the DSN is to provide two-way    communications between the Earth and spacecraft exploring the    solar system.  To carry out this function it is equipped with    high-power transmitters, low-noise amplifiers and receivers,    and appropriate monitoring and control systems.    The DSN consists of three complexes situated at approximately    equally spaced longitudinal intervals around the globe at    Goldstone (near Barstow, California), Robledo (near Madrid,    Spain), and Tidbinbilla (near Canberra, Australia).  Two of    the complexes are located in the Northern Hemisphere while the    third is in the Southern Hemisphere.    Each complex includes several antennas, defined by their    diameters, construction, or operational characteristics:    70-m diameter, standard 34-m diameter, high-efficiency 34-m    diameter (HEF), and 34-m beam waveguide (BWG).