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The Space Transportation System, better known as the Space Shuttle, meant a revolution to space flight in many ways. It was the first reusable space craft, and allowed not only to take satellites into space but also to take them back to Earth. Furthermore, many of today's Shuttle flights are non-military operations
The Shuttle project was started in 1972. A spacecraft that could be used over and over again proved to be a difficult task for the constructors. Insulating Tiles that are able to stand the heat of the reentry and better engines which can survive many missions had to be invented.
Space Shuttles are very different from the previous types of space crafts. They look a little bit like airplanes and have got three main engines. These engines burn the liquid hydrogen and oxygen that are stored in the large External Tank. Most of the thrust for the lift-off, however, is derived from the two Solid Rocket Boosters which are attached to the tank. Two minutes after lift-off they have burnt out and they are dropped into the ocean for recovery. Eight minutes after he start the Shuttle has reached the orbit and the Shuttles own engines are deactivated as well.
The Space Shuttle has a 18 meter long cargo bay where additional modules can be placed. Respective to their mission the Space Shuttles can be equipped with mission specific tools or modules. One of them is the Spacelab Module. It was built by the European Space Agency and provides the astronauts with a fully equipped laboratory. It allows scientists to conduct experiments ranging in subject matter from astronomy to biomedical examinations. Another important tool is the Remote Manipulator System, a 15 meter crane. It is used to move heavy payloads such as satellites in and out of the Shuttle. The Manned Maneuvering Unit backpack changed the art of space walking. With it the astronauts could move outside their spacecraft without a connecting tether and therefore work faster in their spacesuits.
In 1995 a new capability was added to the repertoire of the Shuttle. In order to prepare for the service on the International Space station, Shuttle crews began a series of dockings with the Russian space station Mir. U.S. astronauts sometimes spent months in space so that they get used to living and working in space.
Today the Space Shuttles make up a fleet of four spacecrafts. The first one, Atlantis, entered service in 1981. It was followed by the Challenger (1983), the Discovery (1984) and the Columbia (1985), and the Endeavour (1991).
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