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1 The Pioneer Venus Orbiter

• Launch Date: 20 May 1978
• Launch Vehicle: Atlas- Centaur
• On-orbit mass: 517 kg
• Power System: Solar Array of 312 W

The Pioneer Venus Orbiter was inserted into an elliptical orbit around Venus on December 4, 1978. 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. It was manufactured by Hughes Aircraft Company.

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 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 windA solar wind is a stream of particles (mostly high-energy protons ~ 500 keV) which are ejected from the upper atmosphere of a star. In the solar system, the composition of this plasma is identical to the Sun's corona, 73% hydrogen and 25% helium with the plasmaFor the fluid portion of blood, see blood plasma; also, other uses. There is debate as to whether plasma is an individual state of matter or simply a type of gas. In physics and chemistry, plasma (also called an ionised gas is an energetic gas-phase state analyzer to measure properties of the solar wind
• a magnetometer to characterize the magnetic fieldIn physics, a magnetic field is an entity produced by moving electric charges ( electric currents) that exerts a force on other moving charges. The quantum-mechanical spin of a particle produces magnetic fields and is acted on by them as though it were a at Venus
• an electric field detector to study the solar wind and its interactions
• an electronThe electron (also called negatron commonly represented as e&minus is a subatomic particle. In an atom the electrons surround the nucleus of protons and neutrons in an electron configuration. Electrons have the smallest electrical charge and when they mov temperature probe to study the thermal properties of the ionosphereThe ionosphere is the part of the atmosphere that is ionized by solar radiation, and too tenuous to be cooled by contact with other air. It forms the inner edge of the magnetosphere and has practical importance because it reflects radio waves to distant p
• an ion mass spectrometer to characterize the ionospheric ion population
• a charged particle retarding potential analyzer to study ionospheric particles
• two radioFor other uses see: radio (disambiguation Radio is a technology that allows the transmission of signals by modulation of electromagnetic waves with frequencies below those of light. Radio waves Radio waves are a form of electromagnetic radiation, and are science experiments to determine the gravityThis article covers the physics of gravitation. See also gravity (disambiguation). Gravitation is the tendency of masses to move toward each other. The first mathematical formulation of the theory of gravitation was made by Sir Isaac Newton and proved ast 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

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 until the fuel ran out and atmospheric entry destroyed the spacecraft the following August.