Space Shuttle

At one time, both the United States and the Soviet Union envisioned complex space programs that included space stations orbiting the Earth and reusable shuttle spacecraft to transport people, equipment, raw materials, and finished products to and from these space stations. Because of the high cost of space flight, however, each nation eventually ended up concentrating on only one aspect of this program. The Soviets built and for many years operated space stations (Salyut, 1971–1991, and Mir, 1986–2001), while Americans have focused their attention on the space shuttle. The brief Soviet excursion into shuttle design (Buran) and the U.S. experiment with Skylab (1973–1979) were the only exceptions to this pattern.

The U.S. shuttle system—which includes the shuttle vehicle itself, launch boosters, and other components—is officially termed the Space Transportation System (STS). Lacking a space station to which to travel until 1998, when construction of the International Space Station began, the shuttles have for most of their history operated with two major goals: (1) the conduct of scientific experiments in a microgravity environment and (2) the release, capture, repair, and re-release of scientific, commercial, and military satellites. Interplanetary probes such as the Galileo mission to Jupiter have been transported to space by the shuttle before launching themselves on interplanetary trajectories with their own rocket systems. Since 1988, the STS has also been essential to the construction and maintenance in orbit of the International Space Station.

The STS depends partly on contributions from nations other than the U.S. For example, its Spacelab modules—habitable units, carried in the shuttle's cargo bay, in which astronauts carry out most of their experiments—are designed and built by the European Space Agency, and the extendible arm used to capture and release satellites—the "remote manipulator system" or Canadarm—is constructed in Canada. Nevertheless, the great majority of STS costs continue to be borne by the United States.