The first artificial satellites launched into Earth orbit were part of an international scientific program called the International Geophysical Year. They returned data on Earth and its space environment. Before long, the United States and the Soviet Union began sending spacecraft to study the Moon and, later, other planets.

Sending Spacecraft to the Planets

The U.S. Ranger spacecraft (1961-1965) were designed to crash into the Moon, transmitting television images right up to the moment of impact. The Surveyor spacecraft (1966-1968) soft-landed on the Moon, verifying that the lunar surface would support an Apollo lander, taking pictures of the surface surroundings, and performing the first crude geochemical analyses of lunar rocks. A series of Lunar Orbiter spacecraft photographed the Moon, developed the film onboard, scanned the developed images, and transmitted the scans to Earth. The Orbiter photographs constituted the primary database for...