The Pioneer Venus spacecraft program

The Pioneer Venus program consist of two spacecraft: an orbiter and a multiprobe. Both arrived at Venus in early December 1978. The orbiter collected data on the upper atmosphere and fields and particles and sensed the clouds and surface remotely from a 75° inclined orbit. The multiprobe consisted of a bus, three small probes, and a large probe. All five objects entered the Venus atmosphere and transmitted data on its characteristics directly to Earth while descending to the surface. The development of these spacecraft required the solution of many difficult and unique technique problems.