Online Reference: http://www-pdsimage.wr.usgs.gov/PDS/public/mapmaker/mapmkr.htm

 
 
    The Viking spacecraft consisted of two orbiters, each with
    a heat-sterilized lander within a capsule. Together with
    fuel they each weighed 3530 kg just after launch. After
    landing, their masses were about 900 kg for the orbiters
    and 600 kg for each lander.
 
    The orbiters, derived from earlier Mariner designs, were
    powered by solar panels and were stabilized in three axes
    by use of solar and star sensors in conjunction with
    attitude control jets. Three remote sensing science
    investigations resided on the two-axis scan platform: a
    pair of high resolution slow scan televison framing cameras
    (the Visual Imaging Subsystem, or VIS); a near-infrared
    spectrometer for atmospheric water detection (the Mars
    Atmosphere Water Detector, MAWD); and a visual and thermal
    infrared radiometer system (Infrared Thermal Mapper, IRTM).
 
    The landers each carried two facsimile cameras providing
    stereo views of the surface; a boom-mounted set of
    meteorology instruments; an X-ray fluorescence experiment
    for inorganic chemical analysis of soil; a gas
    chromatograph mass spectrometer to measure the soil and
    atmosphere; three biology experiments: the pyrolytic
    release, labeled release, and gas exchange systems; a
    seismometer; a magnetic properties experiment. Soil
    physical properties experiments were carried out using
    several of the abovementioned systems. Upper atmosphere
    measurements were performed using detectors on the landers
    during entry through the atmosphere. Finally, radio science
    was done using transmitters and receivers on both the
    orbiters and landers. An extensible arm and scoop system on
    each lander was programmable to acquire samples of soil and
    rock for analysis on board the landers and to affect the
    local environment for visual inspection.
 
  Platform Descriptions
  =====================
    Platform SCAN PLATFORM
    ----------------------
      The three Viking orbiter science instruments are mounted on
      a scan platform that provides temperature control for them
      and pointing in two axes: cone and clock. The platform can
      be rotated in cone and/or clock at rates of 0.25 or 1.0
      degree/sec. Subroutines stored in the memory of the
      on-board computer can be called upon to move the platform
      in specified patterns. The nominal range of motion possible
      for the scan platform is from 45 to 175 degrees cone and 80
      to 310 clock; however, there are mechanical constraints
      that reduce this range. See reference.