Pioneer Venus Missions
Pioneer Venus Orbiter
Launch Date: May 20, 1978
Mission Project Home Page - http://heasarc.nasa.gov/docs/heasarc/missions/pvo.html
The Pioneer mission consisted of two components, launched separately: an Orbiter and a Multiprobe. The Orbiter was launched on 20 May 1978; on 4 December 1978, it was injected into a highly elliptical orbit around Venus. The orbit permitted global mapping of the clouds, atmosphere and ionosphere; measurement of upper atmosphere, ionosphere, and solar wind-ionosphere interaction; and mapping of the planet's surface by radar. For the first 19 months of the mission, the periapis was maintained at about 150 km by periodic maneuvers. As propellant began to run low, the maneuvers were discontinued, and Solar gravitational effects caused the periapsis to rise to about 2,300 km. By 1986, the gravitational effects caused the periapsis to start falling again, and the orbiter instruments could again make direct measurement within the main ionosphere. During the Orbiter's mission, opportunities arose to make systematic observations of several comets.
The Pioneer Venus bus also carried two experiments, a neutral mass spectromenter and an ion mass spectrometer to study the composition of the atmosphere. With no heat shield or parachute, the bus survived and made measurements only to about 110 km altitude before burning up. The bus was a 2.5 m diameter cylinder weighing 290 kg, and afforded us our only direct view of the upper Venus atmosphere, as the probes did not begin making direct measurements until they had decelerated lower in the atmosphere.
On 8 October 1992, its fuel supply exhausted, the Orbiter ended its mission as a meteor flaming through the dense atmosphere of Venus.
Launch Date: 20 May 1978
Launch Vehicle: Atlas-Centaur
On-orbit mass: 517 kg
Power System: Solar Array of 312 W