Argus and Explorers IV and V

T

here was no time for relaxation following the Explorer III launch. Even before the public announcement of the discovery of the high-intensity radiation on 1 May 1958, immense pressure was building in the United States for follow-on missions to address the questions posed by the data from the first two successful Explorers.

The Army group at Huntsville was already working on a next logical step—the substitution of the Jupiter missile for the Redstone as the first stage. The larger booster would be topped by the same cluster of solid fuel upper stages as employed in the Jupiter C-Juno I configuration. They dubbed the enhanced vehicle Juno II, and work quickly began at Huntsville on designing a satellite for that launcher. That satellite was referred to as the IGY Heavy Payload initially, and, after NASA was formed in October 1958, it was given the prelaunch designation Payload 16 (PL-16). When its second launch attempt was successful in October 1959, it became Explorer 7.

However, work on that satellite was interrupted by another new project, Argos and Explorers IV and V