Instrument Host Overview
      ========================
 
      Phobos was a next generation spacecraft after those of the Venera-
      type, last used in the Vega mission (1984-86).  The total weight
      of the spacecraft was 6,200 kg, of which 3,600 kg was the weight
      of the propulsion system, which was to be separated from the
      spacecraft after the most power-consuming maneuvers of the
      spacecraft were performed in setting up the reference orbit. In
      accordance with the scientific aims of the mission, the
      instrumentation may be classified as planetary, plasma and solar.
      The planetary data of the mission was to result from the
      exploration of Phobos, the martian surface and atmosphere.
      Instruments involved to this end (spectrometers, cameras,
      radiometers, and a neutron detector) were mounted within the
      spacecraft so that their sensitive elements were oriented in an
      anti-sunward direction (with the exception of the optical
      radiation spectrometer (ISO)).  The spacecraft was to change its
      orientation to point the instruments towards Phobos or Mars while
      in martian orbit.  One of the Phobos landers was capable of
      remaining at the surface for a long time and contained instruments
      for celestial mechanics experiments, analysis of regolith and for
      television imaging of landing places.  The other lander, called a
      'hopper', could jump over the surface to study the composition of
      the Phobos soil in several places.  The plasma part of the
      programme concentrated on the exploration of the magnetic field
      and plasma environment of Mars, measurements of the parameters of
      the interplanetary medium, the Sun and cosmic rays.
 
      Platform
      ========
 
      The Phobos spacecraft instruments were mounted directly to the
      spacecraft structure; there was no scan platform.