Various shuttle concepts had been explored since the late 1960s. The program formally commenced in 1972, becoming the sole focus of NASA's manned operations after the Apollo, Skylab, and Apollo-Soyuz programs in 1975. The Shuttle was originally conceived of and presented to the public in 1972 as a 'Space Truck' which would, among other things, be used to build a United States space station in low Earth orbit during the 1980s and then be replaced by a new vehicle by the early 1990s. The stalled plans for a U.S. space station evolved into the International Space Station and were formally initiated in 1983 by President Ronald Reagan, but the ISS suffered from long delays, design changes and cost over-runs and forced the service life of the Space Shuttle to be extended several times until 2011 when it was finally retired—serving twice as long than it was originally designed to do. In 2004, according to President George W. Bush's Vision for Space Exploration, use of the Space Shuttle was to be focused almost exclusively on completing assembly of the ISS, which was far behind schedule at that point.
The first experimental orbiter Enterprise was a high-altitude glider, launched from the back of a specially modified Boeing 747, only for initial atmospheric landing tests (ALT). Enterprise's first test flight was on February 18, 1977, only five years after the Shuttle program was formally initiated; leading to the launch of the first space-worthy shuttle Columbia on April 12, 1981 on STS-1. The Space Shuttle program finished with its last mission, STS-135 flown by Atlantis, in July 2011, retiring the final Shuttle in the fleet. The Space Shuttle program formally ended on August 31, 2011.