The advent of artificial earth satellites in 1957-58 opened a new dimension in the field of geophysical exploration. Discovery of the earth's radiation belts, consisting of energetic electrons and ions (chiefly protons) trapped by the geomagnetic field, followed almost immediately 1,2]' This largely unexpected development spurred a continuing interest in magnetospheric exploration, which so far has led to the launching of several hundred carefully instrumented spacecraft. Since their discovery, the radiation belts have been a subject of intensive theoretical analysis also. Over the years, a...