Pioneer Venus Probe Bus

Description

The spacecraft was the Bus portion of the Pioneer Venus Multiprobe mission. On this mission four instrumented atmospheric entry Probes were carried by this Bus to the vicinity of Venus and released for descent through the atmosphere to the planetary surface. The trip to Venus took 123 days. The Large Probe separated from the Bus on 16 November and the Small Probes on 20 November. Two Small Probes entered on the nightside, and one Small Probe and the Large Probe entered on the dayside of the planet. The spacecraft was spin-stabilized. The Large Probe took 1-1/2 h to descend through the atmosphere, while the three smaller probes reached the surface of the planet 75 min after entry. The Bus portion of the spacecraft was targeted to enter the Venusian atmosphere at a shallow entry angle and transmit data to Earth until the Bus was destroyed by the heat of atmospheric friction during its descent. Investigators emphasized the study of 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. A sister mission, Pioneer Venus Orbiter, placed an orbiting spacecraft around Venus 5 days before the Probes entered the atmosphere. Simultaneous measurements by the probes and orbiter permitted relating specific local measurements to the general state of the planet and its environment as observed from orbit. The Probes stopped transmitting temperature data about 15 km above the surface of Venus, but two Probes survived on the surface and transmitted other data for a matter of seconds to minutes. The Bus ceased transmitting data at an altitude of about 165 km. The total cost of building and operating the probes was $83 million.