* Astronomy

Explorer 4 (satellite 1958 epsilon) was a US satellite launched on July 26, 1958. It was instrumented by Dr. James van Allen's group. The Department of Defence's Advanced Research Projects Agency had initially planned two satellites for the purposes of studying the Van Allen radiation belts and the effects of nuclear explosions upon these belts (and the Earth's magnetosphere in general), however Explorer 4 was the only such satellite launched.

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