Mission Overview
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[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
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PIONEER VENUS ORBITER VENUS ORBITAL OPERATIONS
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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

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