<P> It was used for orbital space missions by NASA, the US Department of Defense, the European Space Agency, Japan, and Germany . The United States funded Shuttle development and operations except for the Spacelab modules used on D1 and D2--sponsored by Germany . SL - J was partially funded by Japan . </P> <P> At launch, it consisted of the "stack", including the dark orange external tank (ET) (for the first two launches the tank was painted white); two white, slender solid rocket boosters (SRBs); and the Orbiter Vehicle, which contained the crew and payload . Some payloads were launched into higher orbits with either of two different upper stages developed for the STS (single - stage Payload Assist Module or two - stage Inertial Upper Stage). The Space Shuttle was stacked in the Vehicle Assembly Building, and the stack mounted on a mobile launch platform held down by four frangible nuts on each SRB, which were detonated at launch . </P> <P> The Shuttle stack launched vertically like a conventional rocket . It lifted off under the power of its two SRBs and three main engines, which were fueled by liquid hydrogen and liquid oxygen from the ET . The Space Shuttle had a two - stage ascent . The SRBs provided additional thrust during liftoff and first - stage flight . About two minutes after liftoff, frangible nuts were fired, releasing the SRBs, which then parachuted into the ocean, to be retrieved by NASA recovery ships for refurbishment and reuse . The orbiter and ET continued to ascend on an increasingly horizontal flight path under power from its main engines . Upon reaching 17,500 mph (7.8 km / s), necessary for low Earth orbit, the main engines were shut down . The ET, attached by two frangible nuts was then jettisoned to burn up in the atmosphere . After jettisoning the external tank, the orbital maneuvering system (OMS) engines were used to adjust the orbit . The orbiter carried astronauts and payloads such as satellites or space station parts into low Earth orbit, the Earth's upper atmosphere or thermosphere . Usually, five to seven crew members rode in the orbiter . Two crew members, the commander and pilot, were sufficient for a minimal flight, as in the first four "test" flights, STS - 1 through STS - 4 . The typical payload capacity was about 50,045 pounds (22,700 kg) but could be increased depending on the choice of launch configuration . The orbiter carried its payload in a large cargo bay with doors that opened along the length of its top, a feature which made the Space Shuttle unique among spacecraft . This feature made possible the deployment of large satellites such as the Hubble Space Telescope and also the capture and return of large payloads back to Earth . </P> <P> When the orbiter's space mission was complete, it fired its OMS thrusters to drop out of orbit and re-enter the lower atmosphere . During descent, the orbiter passed through different layers of the atmosphere and decelerated from hypersonic speed primarily by aerobraking . In the lower atmosphere and landing phase, it was more like a glider but with reaction control system (RCS) thrusters and fly - by - wire - controlled hydraulically actuated flight surfaces controlling its descent . It landed on a long runway as a conventional aircraft . The aerodynamic shape was a compromise between the demands of radically different speeds and air pressures during re-entry, hypersonic flight, and subsonic atmospheric flight . As a result, the orbiter had a relatively high sink rate at low altitudes, and it transitioned during re-entry from using RCS thrusters at very high altitudes to flight surfaces in the lower atmosphere . </P>

Where do space shuttles fly in the atmosphere