Explorer 1 was the first American satellite to reach orbit on January 31, 1958. It is famous for salvaging American space pride, which was damaged after the first two Soviet Sputniks orbited Earth. This small satellite also achieved a significant scientific result, as its instruments enabled American space scientist James Van Allen to present the case that Earth was circled by radiation belts. What is less well known is that the Explorer program in its various forms continues to the present day, making it the longest running program of scientific space exploration in history. At this stage, 92 Explorer-class satellites have been launched, and more are promised for the coming years. They are the principal instrument for American space discovery in near Earth orbit. The importance of the humble Explorer program may have been overlooked by more high profile large, scientific missions (e.g.

, Hubble) and by extraordinary American successes in planetary probes in the Solar System. Few, if any, have chronicled the Explorer series of missions, its scientific results over sixty years, and the value of such small spacecraft as instruments of scientific discovery. Harvey summarizes the personalities key to the ongoing Explorer operations and the achievements of the series as a whole; the difficulties and problems that arose; and how the program evolved over time. The books looks at the principal scientific outcomes, their impact on our knowledge of near-Earth space and the value of small spacecraft as instrument of space exploration.