The US launched Explorer 4 to study Earth's radiation belts
On this day · 26 July 1958
Months after America's first satellite hinted at radiation rings around Earth, Explorer 4 went up to map them in detail.
On July 26, 1958, the United States launched Explorer 4 from Cape Canaveral to make the first detailed measurements of the charged particles trapped in Earth’s radiation belts. The cylindrical satellite was instrumented by the group of physicist James Van Allen, whose name the belts now carry.
Earlier in 1958, Explorer 1’s Geiger counter had detected intense radiation, suggesting that bands of trapped particles ringed the planet. Explorer 4 carried detectors designed to chart those regions more precisely, and its data helped reveal a second, outer belt encircling the inner one.
Explorer 4 also doubled as a sensor for secret high-altitude nuclear tests.
The satellite observed the Project Argus atomic detonations of late August and early September 1958, gauging how nuclear blasts disturbed the belts. Part of its instrumentation failed on September 3, 1958, but by then it had firmly established the structure of the radiation environment surrounding Earth.
Sources & references
2 referencesWell-established. Corroborated by 2 independent sources.
