Pioneer 12

Launch data: Designation 10911 / 78051A Launch date 20 May 1978 - 13:13 UT Launch site CC, LC-36A Launch vehicle Altas-SLV3D Centaur-D1AR (#5030/AC-50) Mission Interplanetary Venus orbiter Heliocentric orbit Perihelion / Aphelion  0.70? x 1.30? A.U. Eccentricity  0.30? Inclination  2.3? deg Period  365 days? Venus orbit on 1978 Dec 04.67 Perihelion / Aphelion  378 x 64645 km Eccentricity  0.833 Inclination  105 deg Period  1391.4 min Venus orbit on 1978 Dec 6.83 Perihelion / Aphelion  233 x 65983 km Eccentricity  0.839 Inclination  105 deg Period  1423.9 min

Specifications: Prime contractor  Hughes Operator  NASA Platform  HS-507 Mass at launch  580 kg (full) Dry Mass  370 kg (empty) Dimension  1.2 long - 2.4 dia Basic shape  Cylinder Propulsion  Star-24 Stabilization

Decay:

Mission details:

• Pioneer Venus 1 entered Venus orbit on 1978 Dec 4.67.
  The Orbiter was a flat cylinder 2.5 m in diameter and 1.2 m high. All instruments and spacecraft subsystems were mounted on the forward end of the cylinder, except the magnetometer, which was at the end of a 4.7 m boom. A solar array extended around the circumference of the cylinder. A 1.09 m despun dish antenna provided S and X band communication with Earth.
• The Pioneer Venus Orbiter carried 17 experiments (with a total mass of 45 kg):
  • a cloud photopolarimeter to measure the vertical distribution of the clouds
  • a surface radar mapper to determine topography and surface characteristics
  • an infrared radiometer to measure IR emissions from the Venus atmosphere
  • an airglow ultraviolet spectrometer to measure scattered and emitted UV light
  • a neutral mass spectrometer to determine the composition of the upper atmosphere
  • a solar wind plasma analyzer to measure properties of the solar wind
  • a magnetometer to characterize the magnetic field at Venus
  • an electric field detector to study the solar wind and its interactions
  • an electron temperature probe to study the thermal properties of the ionosphere
  • an ion mass spectrometer to characterize the ionospheric ion population
  • a charged particle retarding potential analyzer to study ionospheric particles
  • two radio science experiments to determine the gravity field of Venus
  • a radio occultation experiment to characterize the atmosphere
  • an atmospheric drag experiment to study the upper atmosphere
  • a radio science atmospheric and solar wind turbulence experiment
  • a gamma ray burst detector to record gamma ray burst events
• Periapsis height was reduced by manoeuvres to 149 km by 1979 Jan 1.
• From Venus orbit insertion to July 1980, periapsis was held between 142 and 253 km (at 17 degrees north latitude) to facilitate radar and ionospheric measurements. The spacecraft was in a 24 hour orbit with an apoapsis of 66,900 km. Thereafter, the periapsis was allowed to rise (to 2290 km at maximum) and then fall, to conserve fuel. In 1991 the Radar Mapper was reactivated to investigate previously inaccessible southern portions of the planet. In May 1992 Pioneer Venus began the final phase of its mission, in which the periapsis was held between 150 and 250 km.
• Main thruster propellant exhausted 1992 Oct 3; transmissions ceased Oct 8, decayed in Venusian's atmosphere at an altitude of 128 km after fuel exhausted.