There have long been dreams of a permanently inhabited base or station in space. In 1957 it first became possible to put human-made objects into orbit around Earth. But while both the United States and the Soviet Union raced to send a man to the Moon in the 1960s, the goal of a space station in orbit was secondary. It was after the United States won that "space race" in 1969 that both spacefaring countries sought new directions for their human spaceflight programs.

Previous Space Stations

Shortly before the National Aeronautics and Space Administration (NASA) launched the first Moon mission, the agency began focused design work on America's first orbiting laboratory—Skylab—a converted Saturn Moon rocket stage. Only 36 meters (117 feet) long, it did not rotate to create the artificial gravity that physiologists of two decades earlier believed would be required for humans to live in...