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Even before the Apollo moon landing in 1969, in October 1968 NASA began early studies of space shuttle designs.The early studies were denoted "Phase A", and in June 1970, "Phase B", which were more detailed and specific.

In 1969 President Richard M. Nixon formed the Space Task Group, chaired by vice president Spiro T. Agnew. Theyevaluated the shuttle studies to date, and recommended a national space strategy including building a spaceshuttle.

During early shuttle development there was great debate about the optimal shuttle design that best balancedcapability, development cost and operating cost. Ultimately the current design was chosen, using a reusablewinged orbiter, solid rocket boosters, and expendable external tank.

The Shuttle program was formally launched on January 5, 1972, when President Nixon announced that NASA wouldproceed with the development of a reusable Space Shuttle system. The final design was less costly to build andless technically ambitious than earlier fully reusable designs.

The first Space Shuttle, STS-1, waits on the pad before launch, March 1981.

The prime contractor for the program was North American Aviation (later Rockwell International), the samecompany responsible for the Apollo Command/Service Module. The contractor for the Space Shuttle Solid RocketBoosters was Morton Thiokol (now part of Alliant Techsystems), for the external tank, Martin Marietta (nowLockheed Martin), and for the Space shuttle main engines, Rocketdyne.

The first complete Orbiter was originally named Constitution, but a massive write-in campaign from fans of theStar Trek television series convinced the White House to change the name to Enterprise. Amid great fanfare, theEnterprise was rolled out on September 17, 1976, and later conducted a successful series of glide-approach andlanding tests that were the first real validation of the design.

The first fully functional Shuttle Orbiter was the Columbia, built in Palmdale, California. It was delivered to

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Kennedy Space Centre on March 25, 1979, and was first launched on April 12, 1981the 20th anniversary of YuriGagarin's space flightwith a crew of two. Challenger was delivered to KSC in July 1982, Discovery in November1983, and Atlantis in April 1985. Challenger was destroyed when it disintegrated during ascent on January 28,1986, with the loss of all seven astronauts on board. Endeavour was built to replace her (using spare partsoriginally intended for the other Orbiters) and delivered in May 1991; it was launched a year later. Seventeenyears after Challenger, Columbia was lost, with all seven crew members, during re-entry on February 1, 2003, andhas not been replaced.

Description

The Shuttle sits atop the Mobile Launcher Platform (MLP). It consists of Orbiter (on top), External Tank (at centre),and Solid Rocket Boosters (to the right and left of External Tank). Two Tail Service Masts (TSMs) to the either sideof the Orbiter's tail provide umbilical connections for propellant loading and electrical power. The Shuttle is apartially reusuable launch system composed of three main assemblies: the reusable Orbiter Vehicle (OV), the

expendable External Tank (ET), and the two reusable Solid Rocket Boosters (SRBs). The tank and boosters arejettisoned during ascent, so only the orbiter goes into orbit. The vehicle is launched vertically like a conventionalrocket, and the orbiter glides to a horizontal landing, after which it is refurbished for reuse.

The Orbiter resembles an airplane with double-delta wings, swept 81 at the inner leading edge and 45 at theouter leading edge. Its vertical stabilizer's leading edge is swept back at a 45 angle. The four elevons, mounted atthe trailing edge of the wings, and the rudder/speed brake, attached at the trailing edge of the stabilizer, withthe body flap, control the Orbiter during descent and landing.

The Orbiter's crew cabin consists of three levels: the flight deck, the mid-deck, and the utility area. The highestflight deck seats the commander and pilot, two mission specialists in the back. The mid-deck has three more seatsfor the rest of the crew members. Galley, toilet, sleep locations, storage lockers, and the side hatch forentering/exiting the vehicle is also located there, as is the airlock hatch. The airlock has another hatch into thepayload bay. It allows two astronauts, wearing their Extravehicular Mobility Unit (EMU) space suits, to depressurizebefore a space walk.

The Orbiter has a large 60 by 15 ft (18 m by 4.6 m) payload bay, filling most of the fuselage. The payload baydoors have heat radiators mounted on their inner surfaces, and so are kept open for thermal control while theShuttle is in orbit. Thermal control is also maintained by adjusting the orientation of the Shuttle relative to Earthand Sun. Inside the payload bay is the Remote Manipulator System, also known as the Canadarm, a robot arm usedto retrieve and deploy payloads. Until the loss of Columbia, the Canadarm had been used only on those missionswhere it was needed. Since the arm is a crucial part of the Thermal Protection Inspection procedures now requiredfor Shuttle flights, it will probably be included on all future flights.

Orbital Vehicle Three Space Shuttle Main Engines (SSMEs) are mounted on the Orbiter's aft fuselage in a triangular

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pattern. The three engines can swivel 10.5 degrees up and down and 8.5 degrees from side to side during ascent tochange the direction of their thrust and steer the Shuttle as well as push.

The Shuttle was originally conceived to operate somewhat like an airliner. After landing, the orbiter would be

checked out and start "mating" to the rest of the system (the ET and SRBs), and be ready for launch in as little as

two weeks. Instead, this turnaround process takes months; Columbia was once launched twice within 56 days.

Because loss of crew is unacceptable, the primary focus of the Shuttle program is to return the crew to Earth

safely, which can conflict with other goals, namely to launch payloads cheaply. Furthermore, because in some

cases there are no survivable abort modes, many pieces of hardware simply must function perfectly and so must be

carefully inspected before each flight. The result is high labour cost, with around 25,000 workers in Shuttle

operations and labour costs of about $1 billon per year.

During development, shuttle features were primarily chosen based on capability required to service the future

space station. Even though the initially planned Space Station Freedom was significantly scaled back, the shuttle

was still vital to service it. No other launch vehicle had the shuttle's payload capability or could return large items

from the space station to earth.

NASA's plan for using the shuttle to launch all unmanned payloads declined, then was discontinued. Following the

Challenger disaster, carrying in the shuttle payload bay the powerful liquid fuelled Centaur upper stages planed

for interplanetary probes was ruled out. The Shuttle's history of unexpected delays also makes it liable to missnarrow launch windows. Advances in technology over the last decade have made probes smaller and lighter, and as

a result unmanned probes and communications satellites can use cheaper and more reliable expendable rockets,

including Delta launcher, and Atlas V.