|Launch Date||December 6, 1958 | 05:44:52 UT|
|Launch Site||Cape Canaveral, Florida, USA | Launch Complex 5|
Fly past the moon, study interplanetary space and test a sensor for future imaging systems.
A malfunction in a booster rocket trapped the spacecraft in an unstable Earth orbit. In its 38 hours 6 minutes of spaceflight, Pioneer 3 detected and mapped the outer Van Allen radiation belt around Earth. (The inner Van Allen belt was discovered earlier in 1958 by Explorer 1).
This mission was the first of two U.S.Army launches to the Moon.
Pioneer 3 was a spin-stabilized probe (up to 700 rpm) whose primary goal was to fly by the Moon. Two special 0.21-ounce weights were to spin out on 5 foot (1.5- meter) wires and reduce spin to 12 rpm once the mission was under way.
The spacecraft carried an optical sensor to test a future imaging system. If the sensor received, from a source such as the Moon, a collimated beam of light that was wide enough to pass through a lens and fall simultaneously on two photocells, then the sensor would send a signal to switch on an imaging system (not carried on this spacecraft).
In the event, the main booster engine shut down 4 seconds earlier than planned due to propellant depletion. Once put on its trajectory, Pioneer 3 was about 640 mph (1,030 kph) short of escape velocity. It eventually reached an altitude of 63,580 miles (102,322 kilometers) and then fell back to Earth and burned up over Africa 38 hours 6 minutes after launch.
The spacecraft contributed to the major scientific discovery of dual bands of radiation around Earth.
Launch Vehicle: Juno II (no. AM-11)
Spacecraft Mass: 13 pounds (5.87 kg)
- photoelectric sensor trigger
- two Geiger-Mueller counters
Siddiqi, Asif A. Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, NASA, 2002.