World Space Week Day 4 – The Space Shuttle

The Space Shuttle, part of the Space Transportation System (STS), is an American spacecraft operated by the National Aeronautics and Space Administration (NASA) for orbital human spaceflight missions, operational flights began in 1982. The system is scheduled to be retired from service in 2011 after 134 launches. Major missions have included launching numerous satellites and interplanetary probes, conducting space science experiments, and servicing and construction of space stations.

At launch, the Space Shuttle consists of the shuttle stack which includes a dark orange-colored external tank, two white, slender Solid Rocket Boosters and the Orbiter Vehicle which contains the crew and payload. The Space Shuttle is "stacked" in the Vehicle Assembly Building and the stack mounted on a mobile launch platform held down by four explosive bolts on each SRB which are detonated at launch.

The shuttle stack launches vertically, like a conventional rocket, from a mobile launch platform. It lifts off under the power of its two SRBs and the three main engines which are fueled by liquid hydrogen and liquid oxygen from the external tank. The Space Shuttle has a two stage ascent. The SRBs provide additional thrust during liftoff and first stage flight. About two minutes after liftoff explosive bolts are fired releasing the SRBs which parachute into the ocean to be retrieved for reuse. The shuttle orbiter and external tank continue to ascend on an increasingly horizontal flight path under power from the three main engines. Upon reaching 17,500 mph, necessary for low Earth orbit, the main engines are shut down. The external tank is then jettisoned downward to burn up in the atmosphere.

The orbiter carries a crew of 5 to 7 astronauts and payload. Two crew members, the Commander and Pilot, are sufficient for a minimal flight. A typical payload capacity is about 22,700 kilograms (50,000 lb), but can be raised depending on the choice of launch configuration. The orbiter carries the payload in a large cargo bay with doors that open along the length of its top, a feature which makes the Space Shuttle unique among present spacecraft. This feature made possible the deployment of large satellites such as the Hubble Space Telescope, and also to capture and return large payloads back to Earth.

When the orbiter's space mission is complete it fires its OMS thrusters to drop out of orbit and re-enter the lower atmosphere. In the lower atmosphere and landing phase, it acts as a glider. It then makes a landing on a long runway. The aerodynamic shape is a compromise between the demands of radically different speeds and air pressures during re-entry, subsonic atmospheric flight, and hypersonic flight.

With more than 2.5 million parts, the Space Shuttle has been called the most complex machine yet created by humanity.