Mission Overview
    ================
 
      [From COLIN1980B]
 
      Pioneer Venus consists of two basic spacecraft: Orbiter and
      Multiprobe [1].  The latter was separated into five separate
      vehicles near Venus.  These were the probe transporter (called
      the Bus), a large atmospheric entry probe (dubbed Sounder) and
      three identical smaller probes (called North, Day, and Night in
      accordance with their entry locations).  At Venus all six
      spacecraft communicated directly back to the Earth-based Deep
      Space Network (DSN) and, in the case of the Multiprobe mission,
      to two special receiving sites near Guam and Santiago (Chile).
 
      The Orbiter was launched on May 20, 1978, encountered Venus on
      December 4, 1978, was inserted into orbit on that same day
      after a Type II interplanetary cruise trajectory lasting 198
      days and covering more than 500 x 10^6 km.  Twelve scientific
      experiments were included in the instrumentation payload and a
      few radioscience investigations were planned using the S-band
      telemetry signal carrier and a special X-band beacon included
      as part of the spacecraft hardware.  Scientific observations
      were made both in-cruise and in-orbit.  The nominal in-orbit
      mission was designed to extend for one Venus year (243 days).
 
      During the nominal mission all but two experiments operated 100
      percent successfully.  One, the Radar Mapper, produced unusable
      data for a 32-day period from December 18, 1978 to January 19,
      1979.  The data lost [were to] be acquired during the extended
      Orbiter mission.  The other, the Infrared Radiometer, failed to
      operate after February 14, 1979, but had collected an enormous
      quantity of valuable information prior to that date.
 
      The Multiprobe was launched on August 8, 1978, encountered
      Venus on December 9, 1978 (just five days following the Orbiter
      insertion) after a Type I interplanetary cruise trajectory
      lasting 123 days and covering 330 x 10^6 km.  The Sounder was
      released from the Bus on November 15, 1978, and the three small
      probes were released simultaneously on November 19, 1978.  All
      probes entered (200-km altitude) the Venus upper atmosphere
      within a time span of about 11 min and descended to the surface
      in a period from 53 to 56 min, all the time performing
      scientific observations.  The Bus made a delayed (~90 min)
      entry relative to the probes into Venus' upper atmosphere and
      burned up at about 110-km altitude since it was not protected,
      as were the probes, with entry heat shields.  Scientific
      observations were made during the one-minute interval from 700
      to 110 km.  Although not designed for `survival' after impact,
      the Day probe managed to transmit for over 67 min on the
      surface (it in fact continued to transmit after the Bus
      transmission ceased).  Seven scientific experiments were
      included in the Sounder instrumentation payload, three
      identical experiments in each small probe, and two in the Bus.
      Again, radioscience experiments were performed using,
      separately or together, the S-band telemetry signal carriers
      emanating from the spacecraft and received at the Earth-based
      tracking stations.  In general, all instruments performed
      nominally, although certain instruments behaved anomalously on
      all four probes near the surface.
 
      References:
 
     [1] L. Colin and C.F. Hall, Space Sci. Rev., vol. 20,
         no. 3, p. 283, May 1977.
 
    Mission Phases
    ==============
 
      PIONEER VENUS ORBITER VENUS ORBITAL OPERATIONS
      ----------------------------------------------
        This mission phase 'orbiter operations' describes the entire
        mission of the Orbiter spacecraft.
 
        Spacecraft Id                  : PVO
        Target Name                    : VENUS
        Mission Phase Start Time       : 1978-12-05
        Mission Phase Stop Time        : 1992-10-02
        Spacecraft Operations Type     : ORBITER OPERATIONS
 
 
      PIONEER VENUS ORBITER VENUS ENCOUNTER
      -------------------------------------
        This mission phase 'encounter' describes all operations of
        the 5 separate probe components of the Multiprobe component
        of the Pioneer Venus mission.
 
        Spacecraft Id                  : PVMP
        Target Name                    : VENUS
        Mission Phase Start Time       : 1978-12-07
        Mission Phase Stop Time        : 1992-12-07
        Spacecraft Operations Type     : ATMOSPHERIC PROBE