The Pioneer mission to Venus consisted of two components, launched separately. Pioneer Venus 1 or Pioneer Venus Orbiter was launched in 1978 and studied the planet for more than a decade after orbital insertion in 1978. Pioneer Venus 2 or Pioneer Venus Multiprobe sent four small probes into the Venusian atmosphere. This was managed by NASA Ames Research Center as part of the Pioneer series of spacecraft that included Pioneer 10 and Pioneer 11.
Pioneer Venus Orbiter
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):
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 conjunction with the recently-arrived Magellan probe. 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.
Pioneer Venus Multiprobe
The Pioneer Venus Multiprobe consisted of a bus which carried one large and three small atmospheric probes. None of these atmospheric probes had photographic imaging capabilities and were not designed for soil analysis. They weren't even designed for a soft landing; the large probe had a parachute that was designed to cut loose at a certain altitude, and the small probes had no parachute at all. Survival to the surface was considered a bonus. All the entry probes survived the density of the Venusian atmosphere at least until impact, but only one probe survived for a significant period after impact.
The Pioneer Venus bus portion of the spacecraft was targeted to enter the Venusian atmosphere at a shallow entry angle and transmit data until destruction by the heat of atmospheric friction. The objective was to study the structure and composition of the atmosphere down to the surface, the nature and composition of the clouds, the radiation field and energy exchange in the lower atmosphere, and local information on the atmospheric circulation pattern.
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.
With no heat shield or parachute, the bus made upper atmospheric measurements with two instruments, an Ion Mass Spectrometer (BIMS) and a Neutral Mass Spectrometer (BNMS), up to an altitude of about 165 km before disintegrating on December 9, 1978.
The Pioneer Venus Large probe was equipped with 7 science experiments, contained within a sealed spherical pressure vessel. The science experiments were:
This pressure vessel was encased in a nose cone and aft protective cover. After deceleration from initial atmospheric entry at about 11.5 km/s near the equator on the Venus night side, a parachute was deployed at 47 km altitude. The large probe was about 1.5 m in diameter and the pressure vessel itself was 73.2 cm in diameter.
The three small probes were identical to each other, 0.8 m in diameter. These probes also consisted of spherical pressure vessels surrounded by an aeroshell, but unlike the large probe, they had no parachutes and the aeroshells did not separate from the probe.
Each small probe carried a nephelometer and temperature, pressure, and acceleration sensors, as well as a net flux radiometer experiment to map the distribution of sources and sinks of radiative energy in the atmosphere. The radio signals from all four probes were also used to characterize the winds, turbulence, and propagation in the atmosphere.
The small probes were each targeted at different parts of the planet and were named accordingly.
Halley's Comet in 1986
Pioneer Venus Orbiter orbiting Venus had a front row seat when Halley's Comet was more or less hidden behind the Sun during February 1986. Its UV-spectrometer observed the water loss when Halley's Comet was at perihelion February 9th.
Published - July 2009
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