Inaugurating the era of space exploration for the US,
a thirty pound satellite, was launched
into Earth orbit on February 1, 1958 by the
Army Ballistic Missle Agency.
carried instruments to measure temperatures,
micrometeorite impacts, and an experiment designed by
Van Allen to measure
the density of electrons and ions in space.
The measurements made by Van Allen's experiment led to an unexpected and
discovery -- an earth-encircling belt of high energy electrons
and ions trapped in the
now known as the
Allen Radiation Belt.
Explorer I ceased transmitting on February 28 of that year but
remained in orbit until March of 1970.
James Van Allen died on August 9th
at the age of 91.