Pioneer 3 was a spin-stabilized spacecraft launched at 05:45:12 GMT on 6 December 1958 by the U.S.

Army Ballistic Missile Agency The Army Ballistic Missile Agency (ABMA) was formed to develop the United States Army, U.S. Army's first large ballistic missile. The agency was established at Redstone Arsenal on 1 February 1956, and commanded by Major General John Bruce Meda ...

in conjunction with the

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

, using a Juno II rocket. This spacecraft was intended as a lunar probe, but failed to go past the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

and into a

heliocentric orbit A heliocentric orbit (also called circumsolar orbit) is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun i ...

as planned. It did however reach an altitude of 102,360 km before falling back to

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. The revised spacecraft objectives were to measure radiation in the outer Van Allen radiation belt using two Geiger-Müller tubes and to test the trigger mechanism for a lunar photographic experiment.

Spacecraft design

Pioneer 3 was a cone-shaped probe 58 cm high and 25 cm diameter at its base. The cone was composed of a thin

fiberglass Fiberglass (American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cloth ...

shell coated with a gold wash to make it electrically conducting and painted with black and white stripes to maintain the temperature between 10 and 50 °C. At the tip of the cone was a small probe which combined with the cone itself to act as an antenna. At the base of the cone, a ring of mercury batteries provided power. A photoelectric sensor protruded from the center of the ring. The sensor was designed with two photocells which would be triggered by the light of the Moon when the probe was within about 30,000 km of the Moon. Under original plans, the probe would have carried a camera capable of taking a single photograph of the Moon, but after the discovery of the Van Allen Belts by Explorer 1, the camera was replaced with a Geiger counter for radiation measuring. At the center of the cone were a voltage supply tube and two Geiger-Müller tubes. A transmitter with a mass of 0.5 kg delivered a phase-modulated signal of 0.1 W at a frequency of 960.05 MHz. The modulated carrier power was 0.08 W and the total effective radiated power 0.18 W. A despin mechanism consisted of two 7 gram weights which could be spooled out to the end of two 150 cm wires when triggered by a hydraulic timer 10 hours after launch. The weights would slow the spacecraft spin from 400 rpm to 6 rpm and then weights and wires would be released. While the Thor-Able Pioneer probes were designed to go into orbit around the Moon, the Juno Pioneer probes would crash land instead, although, given the crude launch vehicle guidance system and direct ascent trajectory, the odds of hitting the Moon were slim. However, a lunar flyby rather than impact would still be considered a successful mission.

Mission

The flight plan called for the Pioneer 3 probe to pass close to the Moon after 33.75 hours and then go into solar orbit. The Juno II lifted off from LC-5 at 05:45:12 GMT on 6 December 1958. The launch went entirely according to plan until the first stage cutoff, when the engine cut off 3.7 seconds early due to a failure of the propellant depletion sensors, leaving a velocity shortfall of several hundred feet per second. The injection angle was also about 71° instead of the planned 68°, and the de-spin mechanism also failed to operate. The spacecraft reached an altitude of 102,360 km (109,740 km from the center of the Earth) before falling back to Earth. It re-entered Earth's atmosphere and burned up over

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

on 7 December at approximately 19:51 GMT (2:51 p.m. EST) at an estimated location of 16.4° N, 18.6° E. The probe returned

telemetry Telemetry is the in situ data collection, collection of measurements or other data at remote points and their automatic data transmission, transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Gr ...

for about 25 hours of its 38-hour-6-minute journey. The other 13 hours were blackout periods due to the location of the two tracking stations. The returned information showed that the internal temperature remained at about 43 °C over most of the period. While Pioneer 3 did not meet its primary mission objective of a lunar flyby, the data obtained was of particular value to

James Van Allen James Alfred Van Allen (September 7, 1914August 9, 2006) was an American space scientist at the University of Iowa. He was instrumental in establishing the field of magnetospheric research in space. The Van Allen radiation belts were named aft ...

. The Pioneer 3 probe data in addition to the data from the previous

Explorer 1 Explorer 1 was the first satellite launched by the United States in 1958 and was part of the U.S. participation in the International Geophysical Year (IGY). The mission followed the first two satellites the previous year; the Soviet Union's ...

and Explorer 3 satellites led to the discovery of a distinct second radiation belt around the

. The trapped radiation starts at an altitude of several hundred miles from Earth (where the outer belt was first observed by

Sputnik 2 Sputnik 2 (, russian: Спутник-2, ''Satellite 2''), or Prosteyshiy Sputnik 2 (PS-2, russian: Простейший Спутник 2, italic=yes, ''Simplest Satellite 2'') was the second spacecraft launched into Earth orbit, on 3 November 195 ...

and

Sputnik 3 Sputnik 3 (russian: Спутник-3, Satellite 3) was a Soviet satellite launched on 15 May 1958 from Baikonur Cosmodrome by a modified R-7/SS-6 ICBM. The scientific satellite carried a large array of instruments for geophysical research of t ...

) and extends for several thousand miles into space. These Van Allen radiation belts surrounding the Earth are named for Dr.

, in honor of his discovery.

References

External links

''United States Space Program Progress 1958''
discusses Pioneer 0 - 3 at YouTube
NSSDC Master Catalog: Spacecraft Pioneer 3

''Pioneer III'' scientific instrument
{{Orbital launches in 1958 Spacecraft launched in 1958 Missions to the Moon Pioneer 03 Spacecraft which reentered in 1958 Lunar flybys