This object is a flight spare of the Pioneer IV spacecraft, which was launched March 3, 1959, on a Juno II launch vehicle. The principal objectives of Pioneer IV were to measure radiation in space, test a photo-electric sensor in the vicinity of the Moon, sample the Moon's radiation, and test long-range tracking. On March 4, 1959, it came within 37,300 miles of the Moon, which was somewhat short of the original goal of 20,000 miles. It was tracked for 82 hours to a distance of 407,000 miles. Currently, Pioneer IV is in solar orbit.
The Jet Propulsion Laboratory donated this object to the Museum in 1961.
The Pioneer series was initiated to explore the space environment in the vicinity of the moon. Pioneers 1, 2, and 5 were assigned to the Space Technology Laboratories, Inc. and used the Thor-Able launch vehicle; Pioneers 3 and 4 were assigned to the Army Ballistic Missile Agency and the Jet Propulsion Laboratory (JPL). Pioneers 3 and 4 were launched by Juno II vehicles. Pioneer 3 was launched on 6 December 1958 and reached a maximum altitude of 102,300 kilometers (63,580 miles), never achieving escape velocity from the earth. Pioneer 4 was launched on 3 March 1959 and did achieve escape velocity, passing some 62,000 kilometers (37,300 miles) by the moon and then into orbit around the sun, the first American space probe to do so. The spacecraft shell was a conical structure made of gold-washed fiberglass painted with white stripes, which was a configuration used to establish passive thermal control. The cone was 23 centimeters (9 inches) in diameter at the base and 51 centimeters (20 inches) tall. It weighed 6.08 kilograms (13.4 pounds).
Instruments on board Pioneer 4 included two Geiger counters and a photoelectric sensor meant as a prototype trigger for a future television system. Pioneer 4 also had a mechanical despinning mechanism which consisted of weights attached to long wires wrapped around the base of the cone. After the spacecraft was placed into its Earth-Moon trajectory, the weights were released to unwind. Like the extended arms of an ice skater, these weights increased the moment of inertia of the spacecraft, slowing its rate of spin.
Pioneer 4 did not pass close enough to the moon's surface (32,000 kilometers or (20,000 miles) to trigger the photocell or to obtain any useful radiation measurements from the moon. Excellent radiation data was obtained from both the inner and outer van Allen radiation belts, however. Anton type 213 Geiger counters were prepared by James Van Allen's team from the State University of Iowa for both Pioneer 3 and 4 and were integrated into a telemetry/antenna/battery pack and payload structure built by JPL. The Pioneer 4 counters had additional shielding and were designed to maximize dynamic range. Ground stations at Cape Canaveral, Mayaguez and Goldstone were augmented by the recently completed 250-foot fully steerable Jodrell Bank radio telescope, which was capable of picking up extremely faint signals from the craft out to a geocentric distance of 658,30 km (103 earth radii), over three times the lunar distance. The data from Pioneer "confirmed the inner zone/outer zone structure of the geomagnetic trapping region" and revealed that the outer zone intensity varied greatly. (Van Allen, p. 90)
The artifact in the collection is a fully instrumented flight spare which, like the actual spacecraft, was built at JPL, with instruments provided by the State University of Iowa. It was donated by JPL in August 1961.
James A. Van Allen, Origins of Magnetospheric Physics. Washington: Smithsonian, 1983.
Henry L. Richter, ed., Spacecraft Measurement Survey - Instruments and Spacecraft, October 1957 - March 1965. NASA SP-3028 (1966).