Pioneer

The Pioneer series is a long running series of space probes which started with Pioneers 1-3 in 1958 which never got far from the Earth but provided new data about the Earth, the Van Allen Belts, magnetic fields, etc. Pioneer 4 made it to within 60,000 km of the Moon in 1959 but had been upstaged by the Soviet Luna I which had passed within 7,500 km two months earlier. After intervening deep space probes which gave much information about the Sun, Pioneer 10 was launched outward toward Jupiter. After passing through the asteroid belt unharmed, Pioneer 10 passed Jupiter on December 3, 1973 and continued to send back data after it passed the orbit of Pluto in April 1983.

Pioneer 11 was launched in April of 1973 and reached Saturn on Sep 1, 1979. It came within 21,000 km of Saturn and only 2,000 to 10000 km below the visible rings. Pioneer Venus was launched on May 20, 1978 and was inserted into orbit around Venus on Dec 4, 1978 (198 day trip). Pioneer Venus launched a "multiprobe" consisting of five separate instrument packages on Aug 8, 1978 and it reached Venus on Dec 9, 1978 (123 day trip). At this point it made an hour-long descent to the Venus surface, returning information about the variation of density, temperture and chemical composition of the atmosphere with height. The orbiter stayed at an altitude of 150 km and mapped most of the planet's surface.

Pioneer 3 and 4

Pioneer 4 was the first U.S. spacecraft to escape the Earth. It was launched on March 3, 1959 and passed the Moon at a distance of 60,000 km (37,300 mi). It was tracked to 655,000 km before its batteries were depleted at about 84 hours. Pioneer 3 was the same kind of craft. It was launched on Dec 6, 1958 and reached an altitude of 101,367 km but failed to escape the Earth's gravity. It reentered the atmosphere after 38 hrs. The Geiger-Mueller counters aboard Pioneers 3 and 4 discovered and mapped the second Van Allen radiation belt around the Earth.