INSTRUMENT HOST OVERVIEW
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      The main body of the spacecraft is a flat cylinder 2.5 meters
      in diameter and 1.2 meters high.  In the upper end of this
      cylinder there is a circular equipment shelf with an area of
      4.37 square meters on which all the scientific instruments and
      electronic subsystems are mounted.  The shelf is mounted on the
      forward end of a thrust tube that connects the spacecraft to
      the launch vehicle.  Below the shelf, 15 thermal louvers
      control heat radiation from an equipment compartment located
      between the shelf and the top of the spacecraft.  A cylindrical
      solar array attached to the shelf by 24 brackets forms the
      circumference of the flat cylinder of the spacecraft.  On top
      of the spacecraft, a 1.09 meter diameter, despun, high-gain,
      parabolic dish antenna is mounted on a mast so that its line of
      sight clears equipment mounted outside the spacecraft.  The
      despun design allows the antenna to be mechanically directed to
      Earth from the spinning spacecraft.  The antenna operates at S-
      and X-bands.  The spacecraft also carries a solid propellant
      rocket motor.  Including the antenna mast, the Orbiter is
      almost 4.5 meters high, and it weighed 553 kg when launched.
      The launch weight included 45 kg of scientific instruments and
      179 kg of rocket propellant.