Goals: Pioneer 3 was intended to be a lunar flyby mission. The spacecraft carried an optical sensor to test future imaging systems. It also carried instruments to study radiation in interplanetary space.
Accomplishments: A malfunction in a booster rocket left the spacecraft without enough velocity to break out of Earth orbit. It fell back to Earth and burned up over Africa. However, 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).