Not long after the Soviet Union launched the first satellite in 1957, satellites began to play an increasingly important role in our lives. The first satellites were small because of the lack of powerful launch vehicles, and almost all had scientific missions. However, as larger rockets became available and engineers used new technologies to build more efficient payloads, the first prototypes of many of the satellites that were still in use in 2001 were launched and changed our world.

Observing Earth

One of the earliest classes of satellites was designed to observe Earth from orbit. Among the first were military reconnaissance satellites, such as the American Corona and the Soviet Zenit, which took photographs with film that had to be returned to Earth to be developed. Over the years more sophisticated electronic imaging technology made it possible for spy satellites to obtain very high-resolution images and...