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| Explorer 4 "Goldcraft" launch cover postmarked at Patrick Air Force Base (PAFB) on July 26, 1958. |
Explorer 4 was launched on July 26, 1958. The Department of Defense's Advanced Research Projects Agency (ARPA) had originally intended to launch two satellites to study the Van Allen radiation belts and the impact of nuclear explosions on these belts, as well as the Earth's magnetosphere more broadly. However, Explorer 4 was the only satellite successfully launched, as the other satellite, Explorer 5, experienced a launch failure.
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| Explorer 4 "Sarzin" launch cover postmarked at Port Canaveral on July 26, 1958. |
Explorer 4 was a cylindrical satellite equipped to conduct the first detailed measurements of charged particles (protons and electrons) trapped in the Earth's radiation belts. This experiment aimed to build upon the initial measurements of the trapped radiation belts identified by Explorer 1 and Explorer 3, as well as to record data on artificially injected electrons resulting from three high-altitude Argus nuclear detonations.
The mission was kept secret from the public for six months. The satellite's telemetry was analyzed in relation to three Operation Argus nuclear weapons tests conducted at high altitudes. Explorer 4 was operational and in orbit during the three Project Argus launches, which took place between August 27 and September 6, 1958. One of the mission's objectives was to observe the effects of these high-altitude atomic bomb detonations on the surrounding space environment.
(Reference from
Explorer 4)
