Pioneer 3
Image of the Pioneer 3.
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| Mission type | Lunar flyby |
|---|---|
| Operator | NASA / ABMA |
| Harvard designation | 1958 Theta 1 |
| SATCAT no. | 111 |
| Mission duration | 1 day and 14 hours |
| Apogee | 102,360 kilometers (63,600 mi) |
| Spacecraft properties | |
| Manufacturer | Jet Propulsion Laboratory |
| Dry mass | 5.87 kilograms (12.9 lb) |
| Start of mission | |
| Launch date | December 6, 1958, 05:44:52 UTC |
| Rocket | Juno II |
| Launch site | Cape Canaveral LC-5 |
| End of mission | |
| Decay date | December 7, 1958, 19:51 UTC |
Pioneer 3 was a spin stabilized spacecraft launched at 05:45:12 UTC on 6 December 1958 by the U.S. Army Ballistic Missile Agency in conjunction with the National Aeronautics and Space Administration, using a Juno II rocket. This spacecraft was intended as a lunar probe, but failed to go past the Moon and into a heliocentric orbit as planned, but did reach an altitude of 102,360 km before falling back to the Earth. 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.
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 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 degrees Celsius. 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 was 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.
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