The U.S. Space Shuttle is a reusable spacecraft designed to be launched into orbit by rockets and then to return to the Earth's surface by gliding down and landing on a runway. The Shuttle was selected in the early 1970s as the principal space launcher and carrier vehicle to be developed by the National Aeronautics and Space Administration (\TNASA\t). It was planned as a replacement for the expensive, expendable booster rockets used since the late 1950s for launching major commercial and governmental satellites. Together with launch facilities, mission control and supporting centers, and a tracking and data-relay satellite system, it would complete \TNASA\t's new Space Transportation System (STS). After various delays, the program got under way in the early 1980s. Despite a number of problems, the craft demonstrated its versatility in a series of missions until, in January 1986, a fatal Shuttle disaster during launch forced a long delay until the program was resumed late in 1988. The disaster and its results are described at the end of this article; the following account of the Shuttle's characteristics describes the original vehicle, pending modifications. These modifications do not affect the basic design of the craft nor its overall dimensions. Components The three main components of the Space Shuttle are the orbiter, the external tank, and the solid rocket boosters. The Shuttle weighs 2.0 million kg (4.5 million lb) at launch and stands 56.1 m (184.2 ft) tall. It can carry up to 29,500 kg (65,000 lb) of cargo on one mission. The orbiter--23.79 m (78.06 ft) across the wing tips and 37.2 m (122.2 ft) long--is the portion that resembles a delta-winged jet fighter. During launch it is a rocket stage, in orbit it is a spaceship, and on reentry and landing it is a hypersonic glider. A two-deck crew compartment and an attitude thruster module are in the nose, the midbody is the cargo hold, or payload bay (4.6 m/15 ft wide and 18.3 m/60 ft long), and the tail holds the three main engines plus maneuvering engine pods. Each engine, burning hydrogen and oxygen, produces up to 213,000 kg (470,000 lb) of thrust. The external tank--actually an oxygen tank and a hydrogen tank joined by a load-bearing intertank--is the structural backbone of the Shuttle. Measuring 8.38 m (27.56 ft) wide and 47 m (154.2 ft) tall, it carries 709,750 kg (1,565,000 lb) of liquefied propellants for the main engines. Two solid rocket boosters, each 3.7 m (12.14 ft) wide and 45.5 m (149.16 ft) tall, provide the Shuttle with a lift to the upper atmosphere so that the main engines can work more efficiently. Each produces an average thrust of 1.20 million kg (2.65 million lb). Typical Mission At 3.8 sec before lift-off the Shuttle's three main engines are ignited. At T + 2.88 sec (2.88 sec after lift-off) the twin boosters are ignited and the hold-down bolts released. As soon as it clears the fixed gantry, the Shuttle pitches to fly with the orbiter upside down because the craft's design puts the thrust vector off center. At T + 2 min 12 sec the boosters burn out and are jettisoned to parachute into the ocean for recovery. Meanwhile, the Shuttle continues on under the power of the main engines. Just short of orbital velocity, the engines are shut down (T + 8 min 32 sec) and the tank is jettisoned (T + 8 min 50 sec). The orbiter's own orbit-adjust engines act as the third stage that puts the craft into orbit. The Shuttle can carry a variety of cargoes (see \Tspace exploration\t), including \TSpacelab\t, \TSpace Telescope\t, and commercial and military satellites. After completing a mission, the Shuttle closes its cargo doors and the maneuvering engines are fired as retrorockets. Braked by the atmosphere, the Shuttle rapidly slows from Mach 25 (25 times the speed of sound) at 121,920 m (400,000 ft) to subsonic speeds before it lands. Crew Unlike earlier manned space programs, the Shuttle allows greater specialization of crew members and flights by persons from outside the astronaut corps. There are two principal types of Shuttle astronauts, pilots and mission specialists. Pilots--typically, military-trained jet pilots--fly the Shuttle with a mission commander (a senior astronaut) in the left seat and a pilot in the right seat. They are responsible for operation of the Shuttle from launch until landing. The mission specialist is in charge of the cargo the Shuttle carries. Befitting the Shuttle's wide range of missions, mission specialists come from such widely ranging disciplines as medicine, astrophysics, materials engineering, and electronics. History The Shuttle program was formally authorized on Jan. 5, 1972. In 1977-78, after being carried aloft by a Boeing 747, Enterprise, the first orbiter, made five landing tests at Edwards Air Force Base, Calif., three with a streamlining tailcone and two without. At the same time, testing was under way on the engines and the boosters. The main engines forced the state of technology because they operated at higher pressures and speeds than previous engines and were intended for 55 missions, not just one. There were several major failures, some spectacular. The final test was the flight-readiness firing on Feb. 20, 1981, when the three main engines of Columbia, the first flight orbiter, were fired together successfully for the first time in a pad test at \TKennedy Space Center\t (KSC). First launch, with commander John \TYoung\t and pilot Robert \TCrippen\t aboard, was made on Apr. 12, 1981. From lift-off at KSC to landing at Edwards AFB on April 14, STS 1 encountered only minor problems. STS 2, the second test flight (Nov. 12-14, 1981), with commander Joe H. Engle and pilot Richard H. Truly aboard, carried a pallet loaded with Earth-observation gear and a robot arm, but was cut short from 5 to 2 days because of a fuel-cell failure. STS 3 (Mar. 22-30, 1982), commanded by Jack R. \TLousma\t and piloted by C. Gordon Fullerton, was extended by one day and became the first to land at White Sands, N.Mex. Commander Thomas \TMattingly\t and pilot Henry W. Hartsfield were aboard the STS 4 (June 27-July 4, 1982). The fifth flight (Nov. 11-16, 1982), commanded by Vance D. \TBrand\t, and including an expanded crew of three, was the first operational flight. Two commercial communications satellites were deployed into Earth orbit. Flight six, the first to use the orbiter Challenger, was flown Apr. 4-9, 1983, by commander Paul Weitz, who was joined by a crew of three. Mission specialists Donald Peterson and Story Musgrave achieved EVA. The crew deployed TDRS 1, a communications satellite that strayed but was nudged into correct orbit by ground control. On flight seven, June 18-24, 1983, Challenger's commander Robert Crippen was joined by a crew of four, which included Sally K. \TRide\t, the first U.S. woman astronaut. The crew successfully deployed and retrieved West Germany's SPAS-01 test satellite, using the Shuttle's robot arm; they also deployed Canada's Anik C and Indonesia's Palapa B communications satellites. Flight eight, Aug. 30-Sept. 5, 1983, began with the first night launch of the Shuttle program. Commander Richard Truly was joined by a crew of four, including Guion S. \TBluford\t, the first black U.S. astronaut. This crew launched India's Insat-1B satellite. Flight nine, flown Nov. 28-Dec. 8, 1983, carried the first Spacelab aboard Columbia. Commander John Young was joined by a crew of five, including Owen \TGarriott\t, a veteran astronaut, who had spent time aboard \TSkylab\t in 1973. This crew conducted inner-ear studies and biological and materials-science tests. Failures in STS 9 auxiliary power units delayed the 10th Shuttle flight until Feb. 3-11, 1984. Aboard the Challenger were commander Vance D. Brand and a crew of four. They achieved the successful testing of the manned maneuvering unit, a jet-propelled system that enabled Bruce McCandless and Robert Stewart to move freely in space; and the first Shuttle landing at Cape Canaveral. Two satellites launched by the crew, however--Western Union's Westar and Indonesia's Palapa B-2--did not enter proper orbit, because their own rockets failed. The 11th Shuttle mission was flown in Challenger on Apr. 7-13, 1984, by commander Robert L. Crippen and a crew of four. The crew's most difficult assignment was to restore to service the Solar Maximum Mission research satellite, which had begun malfunctioning a year after its launch in 1980. An attempt to retrieve the satellite by EVA was unsuccessful, but this was eventually managed with the aid of Challenger's robotic arm. The satellite was then repaired and redeployed. During this flight a large, long-duration-exposure facility with 57 experiments was released from the Shuttle. The 12th mission was dramatically aborted 2.6 seconds after engine startup on June 26, 1984, when a fuel valve on one engine of the new Shuttle, Discovery, failed to open. Future mission plans were rearranged before the flight finally took place on Aug. 30-Sept. 5, 1984, with commander Henry W. Hartsfield, Jr., and a crew of five. Charles Walker became the first person from private industry (McDonnell Douglas Corporation) to be assigned to a Shuttle mission. The crew successfully launched the SBS-4, Leasat-2, and Telstar-3 communications satellites. The 13th mission took place on Oct. 5-13, 1984, in Challenger. Commander Robert L. Crippen and a crew of six comprised the largest group to be sent into space up to that time. On her second Shuttle mission, Sally Ride overcame mechanical problems in the launching of the Earth Radiation Budget Satellite for measuring solar radiation. The 14th Shuttle mission took place on Nov. 8-15, 1984, in Discovery, with commander Frederick H. Hauck and a crew of four. The crew retrieved the two satellites, Palapa B-2 and Westar, that had failed after their launch by the 10th Shuttle mission, and brought them safely back to Cape Canaveral. They successfully launched two other communications satellites, Syncom IV-1 and Canada's Anik 2. The 15th Shuttle flight took place on Jan. 24-27, 1985, in Discovery, with commander Thomas K. Mattingly and a crew of four. On this, the first flight to be reserved by the U.S. Defense Department--and therefore veiled in secrecy--an important satellite-boosting rocket was successfully tested. The 16th Shuttle flight took place on Apr. 12-19, 1985, in Discovery, with commander Karol J. Bobko and a crew of six. Included in the crew was U.S. senator Jake Garn, who took part in medical experiments during the flight. A Navy Leasat communications satellite was deployed but failed to activate itself and move to its proper orbit. In a dramatic space-rescue attempt, the Shuttle crew approached the ailing satellite and nudged a protruding activation switch, using the Shuttle's manipulator arm and an improvised hook, but the satellite failed to respond. The 17th Shuttle flight took place on Apr. 29-May 6, 1985, in Challenger, and included commander Robert F. Overmyer, a crew of six, and the second Spacelab. Aboard were two squirrel monkeys and 24 white rats, subjects of experiments designed to investigate motion sickness. The 18th Shuttle flight took place on June 17-24, 1985, in Discovery, with commander Daniel C. Brandenstein and a crew of six. During this mission three communications satellites were deployed, including the Arabian ARABSAT and the Mexican Morelos A. A SPARTAN X-ray deep-space telescope was deployed and retrieved. In an experiment designed by the U.S. Defense Department, a reflector was placed in a Shuttle window to test the ability of ground-based lasers to focus in space targets (see \TStrategic Defense Initiative\t). The 19th Shuttle flight, and the 8th Challenger flight, took place on July 29-Aug. 6, 1985. Commander C. Gordon Fullerton was joined by a crew of six. The main mission objectives involved Spacelab 2 (the third Spacelab), an array of expensive astronomical instruments that measured, among other things, magnetic effects in the solar atmosphere. Challenger achieved orbit despite the shutdown of one of its three engines during the ascent. The 20th Shuttle flight took place on Aug. 28-Sept. 3, 1985, in Discovery, with commander Joseph H. Engle and a crew of four. Three satellites were deployed, including Leasat 4. With two EVAs, and the aid of the Shuttle's manipulator arm, astronauts James D. van Hoften and William F. Fisher retrieved and repaired Leasat 3, which had failed after its deployment on the 16th mission. The 21st Shuttle flight, which took place on Oct. 3-7, 1985, was the debut of the fourth operational Shuttle, Atlantis. Commander Karol J. Bobko flew his third mission was joined by a crew of four. This was the second classified mission of the U.S. Defense Department. The 22nd Shuttle flight took place on Oct. 29-Nov. 6, 1985, in Challenger, with commander Henry W. Hartsfield, Jr., and a crew of seven. It included a West German-sponsored Spacelab. The 23d Shuttle flight took place on Nov. 26-Dec. 3, 1985, in Atlantis, with commander Brewster H. Shaw, Jr., and a crew of six. The 24th Shuttle flight took place on Jan. 12-18, 1986, in Columbia, with commander Robert L. Gibson and a crew of six. The 25th flight, and the 10th flight of Challenger, ended less than two minutes after lift-off on Jan. 28, 1986, when a fireball interrupted the craft's ascent track in full view of the crowd below. This disaster killed the entire crew: commander Francis \TScobee\t; pilot Michael \TSmith\t; mission specialists Judith \TResnik\t, Ellison \TOnizuka\t, and Ronald \TMcNair\t; and payload specialists Gregory \TJarvis\t and Christa \TMcAuliffe\t, a high school teacher chosen for the flight in a nationwide competition. \TNASA\t suspended all Shuttle flights pending investigation of the Challenger disaster by a presidential commission headed by former secretary of state William P. Rogers. Former astronaut Neil A. \TArmstrong\t was vice chairman, and other members included astronaut Sally \TRide\t and Nobelist Richard \TFeynman\t. In its June 1986 report, the commission placed immediate blame on a faulty O-ring seal between segments on one of the solid-fuel booster rockets. In part due to cold weather and buffeting by winds during launch, the seal allowed flames to attack the main liquid-fuel tank and a linking strut. The booster's upper end then swung into the main tank, and the whole assembly burned almost explosively. (The Shuttle broke into segments that fell into the ocean and were later recovered in part.) The commission criticized \TNASA\t's management procedures, overambitious schedules, and inadequate quality-control systems. \TNASA\t underwent management changes and staff reductions as it revised the Shuttle program. President Ronald Reagan authorized a Challenger replacement but also ordered the agency to cease launching commercial satellites, thus ending hopes for its eventual financial independence. The government instead wanted the Shuttle employed mainly for military missions and space-station assembly, but the military also cut back on its planned use of the Shuttle. In 1991, \TNASA\t reluctantly agreed to further cutbacks on Shuttle use in favor of more numerous rocket launches of simpler satellites. Flights restarted with the successful 26th Shuttle mission of Sept. 29-Oct. 3, 1988, when commander Frederick Hauck and a crew of four flew Discovery and launched a TDRS satellite (see \Ttracking station\t). The 27th Shuttle mission, flown by William M. Shepherd and a crew of four aboard Atlantis on Dec. 2-6, 1988, launched a military reconnaissance satellite. The 28th mission, on Discovery, was flown by Michael L. Coats and a crew of four on Mar. 13-18, 1989; it launched a TDRS satellite. The May 4-8, 1989, flight of Atlantis, commanded by David M. Walker with a crew of four, sent a probe, Magellan, toward Venus. The 30th mission, flown by Brewster H. Shaw, Jr., and a crew of four on Columbia on Aug. 8-13, 1989, orbited another military satellite. On Oct. 18-23, 1989, Donald E. Williams and a crew of four launched the Galileo Jupiter probe from Atlantis. The 32d mission, flown on Discovery on Nov. 22-27, 1989, by Frederick M. Gregory and a crew of four, launched a spy satellite. On Jan. 9-20, 1990, Daniel Brandenstein and a crew of four flew Columbia to launch Syncom IV and to retrieve the Long Duration Exposure Facility, a research satellite left in space for six years. Another spy satellite mission followed on Feb. 28-Mar. 4, 1990, when John O. Creighton and a crew of four flew Atlantis. Thereafter the Shuttle program ran into increasing delays. The long-awaited Hubble \TSpace Telescope\t was finally placed in a high orbit by Discovery's crew of four, commanded by Loren J. Shriver, during the Apr. 24-29, 1990 flight, but Columbia, scheduled for launch the following month, was grounded by a series of hydrogen leaks, as was Atlantis. The next flight did not take place until Oct. 6-10, 1990, when Richard N. Richards and a crew of four successfully launched Ulysses, a solar probe, from Discovery. The 37th flight of the space shuttle program took place on Atlantis, from Nov.11-15, 1990, carrying a secret military payload into orbit. Unconfirmed reports suggested that Atlantis carried a spy satellite intended to monitor activities in Iraq and the Persian Gulf region. Mission commander was Air Force Col. Richard O. Covey, and he was assisted by a crew of four. The launch of the shuttle Columbia on Dec. 2, 1990, ended six months of delays for this craft. The mission, which carried a 13-ton set of ultraviolet and X-ray telescopes named Astro, was plagued by technical problems that interfered with its planned astronomical observation program. The shuttle, staffed by commander Vance D. Brand and a crew of six, returned safely to Earth on Dec. 10, 1990. The 39th space shuttle mission, and the eighth for Atlantis, took place from April 5-11, 1991, with commander Air Force Col. Steven R. Nagel and a crew of four specialists. Atlantis deployed a $617-million Gamma Ray Observatory into orbit approximately 280 miles (450 km) above the Earth. The crew logged 22 hours of spacewalking. Space shuttle Discovery was launched on Apr. 28, 1991, and returned to Earth on May 6. Its military mission was concerned with collecting data for the Strategic Defense Initiative (\TSDI\t) ("Star Wars") antimissile program. Mission commander was U.S. Navy Capt. Michael L. Coats. He was assisted by a pilot and crew of four. Space shuttle Columbia was launched on June 5, 1991, in a mission largely concerned with studying medical aspects of space flight. This 41st flight of the shuttle program carried Spacelab, where experiments were carried on with rats and jellyfish. The flight--under the command of Marine Corps Col. Bryan D. O'Connor--was assisted by a crew of three men and three women and included three physicians. Columbia returned to Earth on June 14, 1991. Flight number 42 for the Space Shuttle program--and the ninth for the Atlantis--was launched on Aug. 2, 1991, and returned safely to Earth on August 11. The crew, under the command of Air Force Col. John E. Blaha, consisted of three men and one woman. The mission successfully deployed \TNASA\t's large Tracking and Data Relay Satellite, sending it into an orbit about 22,000 miles (35,400 km) above the equator. The mission also conducted experiments on the ozone layer, made medical experiments, and tested computer and mechanical equipment. Flight number 43, Sept. 12-18, Discovery mission, conducted by John O. Creighton and a crew of four, placed into orbit the Upper Atmosphere Research Satellite to study pollution effects and the ozone layer. Space Shuttle Atlantis, in the 44th mission, from Nov. 24 to Dec. 1, 1991, deployed a satellite to detect missile launches and nuclear explosions. The six-member flight was under the command of Air Force Col. Frederick D. Gregory. The 45th shuttle mission began on Jan. 22, 1992 and ended on Jan. 30. The seven-astronaut team, under the command of Air Force Col. Ronald J. Grabe, included a Canadian and a German specialist. The mission made extensive zero-gravity scientific investigations. David Dooling Bibliography: Allen, Joseph P., and Martin, Russell, Entering Space: An Astronaut's Odyssey, rev. ed. (1985); Aviation Week and Space Technology, Apr. 20 and Nov. 23, 1981 (special issues on first two launches); Feb. 10 and 17, 1986 (extended treatment of Challenger explosion); Cooper, Henry, Jr., Before Lift-Off: The Making of a Space Shuttle Crew (1987); Hoffman, J. A., An Astronaut's Diary (1986); Joels, Kerry M., and Kennedy, Gregory P., The Space Shuttle Operators' Manual (1982); Kaplan, Marshall H., Space Shuttle, 2d ed. (1982); Report by the Presidential Commission on the Shuttle Challenger Accident (1986); Simon, M. C., Keeping the Dream Alive: Putting \TNASA\t and America Back in Space (1988); Stockton, William, and Wilford, John Noble, Spaceliner (1981); Torres, G. T., Space Shuttle, rev. ed. (1989); Trento, J. J., Prescription for Disaster (1986).