Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.u21b..02l&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #U21B-02
Other
1799 General Or Miscellaneous, 2720 Energetic Particles: Trapped, 2774 Radiation Belts
Scientific paper
The United States undertook the launching of an artificial Earth satellite as part of its contribution to the International Geophysical Year. The Vanguard program was established to meet that commitment, and it developed a launch vehicle, ground station network, and suite of scientific payloads, including the cosmic ray experiment proposed by James A. Van Allen. Although Vanguard eventually exceeded all of its pre-stated goals, the preemptive launches of Sputniks I and II by the Soviets in October and November 1957 spurred the U.S. into a frenzy of activity, resulting in the launches of Explorers I and III in January and March of 1958. The data from those two satellites quickly revealed the lower boundary of an unexpected region of high intensity radiation trapped in the Earth's magnetic field. The original announcement in May 1958 stated that the radiation was probably composed of either protons or electrons, and that, if electrons, it was probably bremsstrahlung formed in the satellite shell. Immediately following that announcement, approval was received for what became Explorer IV, whose announced purpose was to follow up on the new discovery. Another reason for the satellite, unmentioned at the time, was its inclusion as a component of the highly classified Argos program, a covert military program to test whether the detonation of nuclear devices at high altitude would inject measurable numbers of charged particles into durable trajectories in the Earth's magnetic field. Our team at Iowa produced the satellites under the oversight of, and with assistance by, the Army Ballistic Missile Agency in Huntsville, and with the contributions of key hardware from several other government laboratories. The project was completed in the unbelievably short period of seventy-seven days from approval to launch. Launched into a higher-inclination orbit than the earlier Explorers, Explorer IV confirmed the discovery and greatly expanded our understanding of the natural phenomenon. It also provided the first hint that there were two distinct radiation belts, although that conclusion was not reached until later. Although that new information was quickly announced, the results of the high altitude nuclear detonations were kept secret until well into 1959. They clearly revealed the charged particle shells created by the Argos nuclear detonations. The next major step in mapping and understanding the high-intensity radiation involved the launch of deep space probes Pioneers III and IV in December 1958 and March 1959. Although both launches fell short in their primary objective, to reach the moon, they traveled far enough from the Earth to fully meet the needs of the scientific experiment. They very clearly showed the two-radiation belt structure, and mapped its extent. They also showed the probable effect of a magnetic storm on 25 February, thus indicating the direct influence of solar activity on the outer belt. By the end of 1959, the existence of the Van Allen Radiation Belts and their general structure were solidly established, early information about the composition of the radiation was appearing in print, and energetic work was under way to understand the physics of the processes involved.
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