Pioneer 3 and 4 were early satellites designed to be lofted toward Earth's Moon. They were equipped with Geiger counters to measure radiation in space.
Pioneer 3 was launched from Cape Canaveral, Florida, on December 6, 1958. Because of a slight error in the satellite's velocity and angle after burnout of the Juno II rocket, it did not reach the Moon; instead it achieved a peak altitude of 102,320 kilometers (63,580 miles). The satellite did, however, discover a second radiation belt around Earth during its flight. Pioneer 3 reentered Earth's atmosphere over equatorial Africa a day after launch.
Pioneer 4 was launched March 3, 1959, and successfully passed within 60,000 kilometers (37,300 miles) of the Moon the following day. The satellite was tracked for 82 hours to a distance of 655,000 kilometers (407,000 miles) from Earth, a record at that time. Pioneer 4 is now orbiting the Sun, the first U.S. spacecraft placed in solar orbit.
Mass: 5.87 kilograms (12.95 pounds)
Configuration: Cone-shaped, 58 centimeters (23 inches) high and 25 centimeters (10 inches) in diameter
Science instruments: Two Geiger-Mueller counters; photoelectric sensor
Pioneer 3 Launch: December 6, 1958
Pioneer 4 Launch: March 3, 1959
