The Space Shuttle orbiter was the spaceplane component of the Space Shuttle, a partially reusable orbital spacecraft system that was part of the discontinued Space Shuttle program. Operated from 1981 to 2011 by NASA, the U.S. space agency, this vehicle could carry astronauts and payloads into low Earth orbit, perform in-space operations, then re-enter the atmosphere and land as a glider, returning its crew and any on-board payload to the Earth. Six orbiters were built for flight: Enterprise, Columbia, Challenger, Discovery, Atlantis, and Endeavour. All were built in Palmdale, California, by the Pittsburgh, Pennsylvania-based Rockwell International company's North American Aircraft Operations branch. The first orbiter, Enterprise, made its maiden flight in 1977. An unpowered glider, it was carried by a modified Boeing 747 airliner called the Shuttle Carrier Aircraft and released for a series of atmospheric test flights and landings. Enterprise was partially disassembled and retired after completion of critical testing. The remaining orbiters were fully operational spacecraft, and were launched vertically as part of the Space Shuttle stack. Columbia was the first space-worthy orbiter; it made its inaugural flight in 1981. Challenger, Discovery, and Atlantis followed in 1983, 1984, and 1985, respectively. In 1986, Challenger was destroyed in a disaster shortly after its 10th launch, killing all seven crew members. Endeavour was built as Challenger's successor, and was first launched in 1992. In 2003, Columbia was destroyed during re-entry, leaving just three remaining orbiters. Discovery completed its final flight on March 9, 2011, and Endeavour completed its final flight on June 1, 2011. Atlantis completed the final Shuttle flight, STS-135, on July 21, 2011. In addition to their crews and payloads, the reusable orbiter carried most of the Space Shuttle's liquid-propellant rocket system, but both the liquid hydrogen fuel and the liquid oxygen oxidizer for its three main rocket engines were fed from an external cryogenic propellant tank. Two reusable solid rocket boosters (SRBs) provided additional thrust for approximately the first two minutes of launch. The orbiters themselves also carried hypergolic propellant for the onboard Reaction Control System (RCS) thrusters and Orbital Maneuvering System (OMS) engines.
Description About the size of a McDonnell Douglas DC-9, the Space Shuttle orbiter resembled an airplane in its design, with a standard-looking fuselage and two double delta wings, both swept wings at an angle of 81 degrees at their inner leading edges and 45 degrees at their outer leading edges. The vertical stabilizer of the orbiter had a leading edge that was swept back at a 45-degree angle. There were four elevons mounted at the trailing edges of the delta wings, and the combination rudder and speed brake was attached at the trailing edge of the vertical stabilizer. These, along with a movable body flap located underneath the main engines, controlled the orbiter during later stages of reentry. The prime contractor for the orbiter was Rockwell International, which built the pressurized cabin, thermal protection, forward attitude control system, and forward and aft fuselage in its Downey, California factory, the payload bay doors in its Tulsa, Oklahoma factory, and the body flap in its Columbus, Ohio factory. Subcontractors included Convair in San Diego for the midsection, Fairchild Aircraft in Farmingdale, New York for the vertical stabilizer, Grumman in Bethpage, New York for the wings, Marquardt Corporation in Van Nuys, California for the attitude control propulsion, Aerojet in Rancho Cordova, California for the orbital insertion and deorbit propulsion, McDonnell Douglas for the surrounding pods, and Rocketdyne in Canoga Park, Los Angeles for the launch and ascent propulsion. 12,000 Rockwell workers were assigned to orbiter construction at the program's peak in the Downey plant. Final assembly was carried out at United States Air Force Plant 42 near Palmdale, California.
Attitude control system
The Reaction Control System (RCS) was composed of 44 small liquid-fueled rocket thrusters and their very sophisticated fly-by-wire flight control system, which utilized computationally intensive digital Kalman filtering. This control system carried out the usual attitude control along the pitch, roll, and yaw axes during all of the flight phases of launching, orbiting, and re-entry. This system also executed any needed orbital maneuvers, including all changes in the orbit's altitude, orbital plane, and eccentricity. These were all operations that required more thrust and impulse than mere attitude control. The forward rockets of the Reaction Control System, located near the nose of the Space Shuttle orbiter, included 14 primary and two vernier RCS rockets. The aft RCS engines were located in the two Orbital Maneuvering System (OMS) pods at the rear of the orbiter, and these included 12 primary (PRCS) and two vernier (VRCS) engines in each pod. The PRCS system provided the pointing control of the Orbiter, and the VRCS was used for fine maneuvering during the rendezvous, docking, and undocking maneuvers with the International Space Station, or formerly with the Russian Mir space station. The RCS also controlled the attitude of the orbiter during most of its re-entry into the Earth's atmosphere – until the air became dense enough that the rudder, elevons and body flap became effective. The orbiter's OMS and RCS fuel is monomethyl hydrazine (CH3NHNH2), and the oxidizer is dinitrogen tetroxide (N2O4). This particular propellant combination is extremely reactive and spontaneously ignites on contact (hypergolic) with each other. This chemical reaction (4CH3NHNH2 + 5N2O4 → 9N2 + 4CO2 + 12H2O) occurs within the engine's combustion chamber. The reaction products are then expanded and accelerated in the engine bell to provide thrust. Due to their hypergolic characteristics these two chemicals are easily started and restarted without an ignition source, which makes them ideal for spacecraft maneuvering systems. During the early design process of the orbiter, the forward RCS thrusters were to be hidden underneath retractable doors, which would open once the orbiter reached space. These were omitted in favor of flush-mounted thrusters for fear that the RCS doors would remain stuck open and endanger the crew and orbiter during re-entry.
Pressurized cabin
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