Instrument Host Overview
  ========================

    The Venus Climate Orbiter (VCO, also known as PLANET-C and AKATSUKI)
    spacecraft is box-shaped with approximate dimensions of
    1.04 x 1.45 x 1.40 meters. Two solar array paddles each with an area
    of 1.4 square meters provide power for the spacecraft. The spacecraft
    launch mass was 517.6 kg including 196.3 kg fuel. Mono-propellant
    reaction control system (RCS) thrusters and a bi-propellant orbital
    maneuvering engine (OME) are equipped for both the attitude and orbit
    maneuvers. RCS thrusters are composed of 12 thrusters in total. Each
    thruster has 23 N thrust for larger 8 thrusters and 3 N thrust for
    smaller 4 thrusters. OME has 500 N in thrust power.


  System Description
  ==================

    The spacecraft coordinate system has the high gain antennas (XHGA-T and
    XHGA-R) pointing in the +Z direction. The medium gain antennas (XMGA-A
    and XMGA-B) are mounted on the +Y-plane, and the low gain antennas are
    mounted on the +X-plane (XLGA-A) and on the -X-plane (XLGA-B). All
    antennas use the X-band frequency range. Two solar array paddles (SAP1
    and SAP2) are connected perpendicularly to the +Y-plane and the
    -Y-plane, respectively. The science instruments, UVI, IR1, IR2, and LIR
    are hard mounted to the spacecraft on the -Y-plane, and LAC is hard
    mounted to the spacecraft on the +Y-plane.


  Communications Subsystem
  ========================

    The communications subsystem includes the high gain antenna for
    transmission with the diameter of 0.9 m (XHGA-T), the high gain antenna
    for receiving with the diameter of 0.3 m (XHGA-R), two medium gain
    antennas (XMGA-A and XMGA-B), and two low gain antennas (XLGA-A and
    XLGA-B). The XHGA-T and the XHGA-R are radial line slot antennas covered
    with white, flat radomes, the XMGA-A and the XMGA-B are single axis
    gimbal horn antennas, and the XLGA-A and the XLGA-B are wide-angle lens
    antennas. The uplink frequency is 7.1 GHz and the downlink frequency is
    8.4 GHz. The signal has right hand circular polarization. The X-band
    transponders (XTRP-A and XTRP-B) receive and demodulate command signals
    and receive and filter range signals. The maximum transmitter power is
    20 W and the bit rates can be set at 8, 16, 32, 64, 128, 256, 512, 1024,
    2048, 4096, 8192, 16384, or 32768 bps with a maximum of about 84 MB per
    day, if 6 hours are used for the data transmission per day.


  Command and Data Handling System
  ================================

    The Data Handling System (DHS) is the updated version of the Hayabusa's
    Data Handling Subsystem (DHS). The DHS comprises the Data Handling Unit
    (DHU), the Peripheral Interface Module (PIM), the Telemetry Command
    Interface Unit (TCIU), and the sensor digital electronics unit (DE)
    including the Data Recorder (DR). The functions provided by the DHU are
    command management, telemetry management, and autonomous operations. The
    DR is placed inside the DE, so for storing image data except for LAC,
    it's able to store data directly to DR without using PIM bus interface.
    The PIM provides the interface between the DHU and intelligent
    subsystems, and the TCIU provides the interface between the DHU and
    non-intelligent subsystems.

    The command function operates on inputs from the two command receivers
    at one of three rates: 15.625 bps, 125 bps, or 1000 bps. The format of
    the uplinked commands is Consultative Committee for Space Data Systems
    (CCSDS) compliant. DHU supports decoding of TC Command Packet for
    non-intelligent subsystem that doesn't have an interface with PIM but
    have an interface with TCIU, and also supports sending commands to
    non-intelligent subsystem based on the decoded TC Command Packet. These
    commands include discrete commands that are used to turn on or off a
    function provided by a spacecraft subsystem and serial magnitude
    commands that are used to set values to one or more parameters of a
    subsystem. A series of commands that perform a specific function can be
    stored as a command macro that can be executed with a command sent from
    the ground or by one of the methods described below.

    The DHU can also store a sequence of time-tagged commands or command
    macros, which is called a timeline, for later execution at specified
    spacecraft times.  When the DHU detects an anomaly, it can autonomously
    execute a command or command macro. Intelligent subsystems can also
    request the DHU to issue a command or command macro to another
    subsystem. During normal operations, most of commands are executed from
    a timeline that have been pre-stored from the ground. In this way, most
    operations are carried out when the spacecraft is out of ground contact.

    The telemetry function collects engineering status and science data
    using dedicated serial interfaces from non-intelligent subsystems
    (or components), or using the data bus from intelligent subsystems
    (or components). These data are always packetized either by the DHU
    or by intelligent subsystems (or components), and placed into CCSDS-
    compliant transfer frames. The transfer frames are directed to the DR,
    the downlink, or both. Data recorded on the DR are read back, packed
    into transfer frames and placed into the downlink on command. Recorder
    playback data can be interleaved with real time data on the downlink.

    The downlink data rate is selectable among 13 rates ranging from 32768
    bps to 8 bps to match the communication link capability throughout the
    mission.