Editing Pioneer 3 (section)

== Mission ==

[[Image:Pioneer IV flight spare 01.jpg |thumb|right|Pioneer 4 flight spare, identical to Pioneer 3.]]
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&nbsp;km (109,740&nbsp;km from the center of the Earth) before falling back to Earth. It re-entered Earth's atmosphere and burned up over [[Africa]] on 7 December at approximately 19:51 GMT (2:51&nbsp;p.m. EST) at an estimated location of 16.4° N, 18.6° E. The probe returned [[telemetry]] 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&nbsp;°C over most of the period.<ref name=Hess/>

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]]. The Pioneer 3 probe data in addition to the data from the previous [[Explorer 1]] and [[Explorer 3]] satellites led to the discovery of a distinct second radiation belt around the [[Earth]]. The trapped radiation starts at an altitude of several hundred miles from Earth (where the outer belt was first observed by [[Sputnik 2]] and [[Sputnik 3]]) and extends for several thousand miles into space. These [[Van Allen radiation belt]]s surrounding the Earth are named for Dr. [[James Van Allen]], in honor of his discovery.<ref name=nssdc2/>