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Space Shuttle

Space Shuttle

Although NASA is a civilian space agency, the United States military has used the space shuttle fleet to carry classified military payloads into space. The Department of Defense (DoD) had generally received priority in scheduling national security related flights. In addition to fully classified missions, the Department of Defense (DoD) has contracted shuttle research time and lifted unclassified early warning satellites into orbit. Satellites deployed from the shuttle, or serviced by shuttle crews, are used for electronic intelligence, photographic and radar reconnaissance, and defense communications.

By 1990, at least eight classified military satellites were placed in orbit during classified shuttle missions. Although the shuttle fleet is still used for a range of classified missions, following the loss of Challenger the military shifted emphasis to launching classified military satellites by expendable rockets.

The Shuttle Program

The space shuttle is a reusable spacecraft that takes off like a rocket, orbits the Earth like a satellite, and then lands like a glider. The space shuttle has been essential to the repair and maintenance of the Hubble Space Telescope and for construction of the International Space Station; it has also been used for a wide variety of other military, scientific, and commercial missions. It is not capable of flight to the Moon or other planets, being designed only to orbit the Earth.

The first shuttle to be launched was the Columbia, on April 12, 1981. Since that time, two shuttles have been lost in flight: Challenger, which exploded during takeoff on January 28, 1986, and Columbia, which broke up during reentry on Feb. 1, 2003. Seven crew members died in each accident. The three remaining shuttles are the Atlantis, the Discovery, and the Endeavor. The first shuttle actually built, the Enterprise, was flown in the atmosphere but never equipped for space flight; it is now in the collection of the Smithsonian Museum.

A spacecraft closely resembling the U.S. space shuttle, the Aero-Buran, was launched by the Soviet Union in November, 1988. Buran's computer-piloted first flight was also its last; the program was cut to save money and all copies of the craft that had been built were dismantled.

Mission of the space shuttle. At one time, both the United States and the Soviet Union envisioned complex space programs that included space stations orbiting the Earth and reusable shuttle spacecraft to transport people, equipment, raw materials, and finished products to and from these space stations. Because of the high cost of space flight, however, each nation eventually ended up concentrating on only one aspect of this program. The Soviets built and for many years operated space stations (Salyut, 19711991, and Mir, 19862001), while Americans have focused their attention on the space shuttle. The brief Soviet excursion into shuttle design (Buran) and the U.S. experiment with Skylab (19731979) were the only exceptions to this pattern.

The U.S. shuttle systemwhich includes the shuttle vehicle itself, launch boosters, and other componentsis officially termed the Space Transportation System (STS). Lacking a space station to which to travel until 1998, when construction of the International Space Station began, the shuttles have for most of their history operated with two major goals: (1) the conduct of scientific experiments in a microgravity environment and (2) the release, capture, repair, and re-release of scientific, commercial, and military satellites. Interplanetary probes such as the Galileo mission to Jupiter (1989) have been transported to space by the shuttle before launching themselves on interplanetary trajectories with their own rocket systems. Since 1988, the STS has also been essential to the construction and maintenance in orbit of the International Space Station.

One of the most important shuttle missions ever was the repair of the Hubble Space Telescope by the crew of the Endeavor in December, 1993 (STS-61). The Hubble had been deployed, by a shuttle mission several years earlier, with a defective mirror; fortunately, it had been designed to be repaired by spacewalking astronauts. The crew of the Endeavor latched on to the Hubble with the shuttle's robotic arm, installed a corrective optics package that restored the Hubble to full functionality. The Hubble has since produced a unique wealth of astronomical knowledge.

The STS depends partly on contributions from nations other than the U.S. For example, its Spacelab moduleshabitable units, carried in the shuttle's cargo bay, in which astronauts carry out most of their experimentsare designed and built by the European Space Agency, and the extendible arm used to capture and release satellitesthe "remote manipulator system" or Canadarmis constructed in Canada. Nevertheless, the great majority of STS costs continue to be borne by the United States.

Structure of the STS. The STS has four main components: (1) the orbiter (i.e., the shuttle itself), (2) the three main engines integral to the orbiter, (3) the external fuel tank that fuels the orbiter's three engines during liftoff, and (4) two solid-fuel rocket boosters also used during liftoff.

The orbiter. The orbiter, which is manufactured by Rockwell, International, Inc., is approximately the size of a commercial DC-9 jet, with a length of 122 ft (37 m), a wing span of 78 ft (24 m), and a weight of approximately 171,000 lb (77,000 kg). Its interior, apart from the engines and various mechanical and electronic compartments, is subdivided into two main parts: crew cabin and cargo bay.

The crew cabin has two levels. Its upper levelliterally "upper" only when the shuttle is in level flight in Earth's atmosphere, as there is no literal "up" and "down" when it is orbiting in free fallis the flight deck, from which astronauts control the spacecraft during orbit and descent, and its lower level is the crew's personal quarters, which contains personal lockers and sleeping, eating, and toilet facilities. The crew cabin's atmosphere is approximately equivalent to that on the Earth's surface, with a composition 80% nitrogen and 20% oxygen.

The cargo bay is a space 15 ft (4.5 m) wide by 60 ft (18m) long in which the shuttle's payloadsthe modules or satellites that it ports to orbit or back to Earthare stored. The cargo bay can hold up to about 65,000 lb (30,000 kg) during ascent, and about half that amount during descent.

The shuttle can also carry more habitable space than that in the crew cabin. In 1973, an agreement was reached between the U.S. National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) for the construction by ESA of a pressurized, habitable workspace that could be carried in the shuttle's cargo bay. This workspace, designated Spacelab, was designed for use as a laboratory in which various science experiments could be conducted. Each of Spacelab module is 13 ft (3.9 m) wide and 8.9 ft (2.7 m) long. Equipment for experiments is arranged in racks along the walls of the Spacelab. The whole module is loaded into the cargo bay of the shuttle prior to take-off, and remains there while the shuttle is in orbit, with the cargo-bay doors opened to give access to space. When necessary, two Spacelab modules can be joined to form a single, larger workspace.

Propulsion systems. The power needed to lift a space shuttle into orbit comes from two solid-fuel rockets, each 12 ft (4 m) wide and 149 ft (45.5 m) long, and from the shuttle's three built-in, liquid-fuel engines. The fuel used in the solid rockets is compounded of aluminum powder, ammonium perchlorate, and a special polymer that binds the other ingredients into a rubbery matrix. This mixture is molded into a long prism with a hollow core that resembles an 11-pointed star in cross section. This shape exposes the maximum possible surface area of burning fuel during launch, increasing combustion efficiency.

The two solid-fuel rockets each contain 1.1 million lb (500,000 kg) at ignition, together produce 6.6 million pounds (29.5 million N) of thrust, and burn out only two minutes after the shuttle leaves the launch pad. At solid-engine burnout, the shuttle is at an altitude of 161,000 ft (47,000m) and 212 miles (452 km) down range of launch site. (In rocketry, "down range" distance is the horizontal distance, as measured on the ground, that a rocket has traveled since launch, as distinct from the greater distance it has traveled along its actual flight path.) At this point, explosive devices detach the solid-fuel rockets from the shuttle's large, external fuel tank. The rockets return to Earth via parachutes, dropping into the Atlantic Ocean at a speed of 55 miles (90 km) per hour. They can then be collected by ships, returned to their manufacturer (Morton Thiokol Corp.), refurbished and refilled with solid fuel, and used again in a later shuttle launch.

The three liquid-fuel engines built into the shuttle itself have been described as the most efficient engines ever built; at maximum thrust, they achieve 99% combustion efficiency. (This number describes combustion efficiency, not end-use efficiency. As dictated by the laws of physics, less than half of the energy released in combustion can be communicated to the shuttle as kinetic energy, even by an ideal rocket motor.) The shuttle's main engines are fueled by liquid hydrogen and liquid oxygen stored in the external fuel tank (built by Martin Marietta Corp.), which is 27.5 ft (8.4 m) wide and 154 ft (46.2 m) long. The tank itself is actually two tanksone for liquid oxygen and the other for liquid hydrogencovered by a single, aerodynamic sheath. The tank is kept cold (below -454°F [-270°C]) to keep its hydrogen and oxygen in their liquid state, and is covered with an insulating layer of stiff foam to keep its contents cold. Liquid hydrogen and liquid oxygen are pumped into the shuttle's three engines through lines 17in (43 cm) in diameter that carry 1,035 gal (3,900 l) of fuel per second. Upon ignition, each of the liquid-fueled engines develops 367,000 lb (1.67 million N) of thrust.

The three main engines turn off at approximately 522 seconds, when the shuttle has reached an altitude of 50 miles (105 km) and is 670 miles (1,426 km) down range of the launch site. At this point, the external fuel tank is also jettisoned. Its fall into the sea is not controlled, however, and it is not recoverable for future use.

Final orbit is achieved by means of two small engines, the Orbital Maneuvering System (OMS) engines located on external pods at the rear of the orbiter's fuselage. The OMS engines are fired first to insert the orbiter into an elliptical orbit with an apogee (highest altitude) of 139 miles (296 km) and a perigee (lowest altitude) of 46 miles (98 km). They are fired again to nudge the shuttle into a final, circular orbit with a radius of 139 miles (296 km). All these figures may vary slightly from mission to mission.

Orbital maneuvers. For making fine adjustments, the spacecraft depends on six small rockets termed vernier jets, two in the nose and four in the OMS pods. These allow small changes in the shuttle's flight path and orientation.

The computer system used aboard the shuttle, which governs all events during takeoff and on which the shuttle's pilots are completely dependent for interacting with its complex control surfaces during the glide back to Earth, is highly redundant. Five identical computers are used, four networked with each other using one computer program, and a fifth operating independently. The four linked computers constantly communicate with each other, testing each other's decisions and deciding when any one (or two or three) are not performing properly and eliminating that computer or computers from the decision-making process. In case all four of the interlinked computers malfunction, decision-making would be turned over automatically to the fifth computer.

This kind of redundancy is built into many essential features of the shuttle. For example, three independent hydraulic systems are available, each with an independent power systems. The failure of one or even two systems does not, therefore, place the shuttle in what its engineers would call a "critical failure mode"that is, cause its destruction. Many other components, of course, simply cannot be built redundantly. The failure of a solid-fuel rocket booster during liftoff (as occurred during the Challenger mission of 1981) or of the delicate tiles that protect the shuttle from the high temperatures of atmospheric reentry (as occurred during the Columbia mission of 2003) can lead to loss of the spacecraft.

Descent. Some of the most difficult design problems faced by shuttle engineers were those involving the reentry process. When the spacecraft has completed its mission in space and is ready to leave orbit, its OMS fires just long enough to slow the shuttle by 200 MPH (320 km/h). This modest change in speed is enough to cause the shuttle to drop out of its orbit and begin its descent to Earth.

When the shuttle reaches the upper atmosphere, significant amounts of atmospheric gases are first encountered. Friction between the shuttlenow traveling at 17,500 MPH (28,000 km/h)and air molecules causes the spacecraft's outer surface to heat. Eventually, portions of the shuttle's surface reach 3,000°F (1,650°C).

Most materials normally used in aircraft construction would melt or vaporize at these temperatures. It was necessary, therefore, to find a way of protecting the shuttle's interior from this searing heat. NASA decided to use a variety of insulating materials on the shuttle's outer skin. Parts less severely heated during reentry are covered with 2,300 flexible quilts of a silica-glass composite. The more sensitive belly of the shuttle is covered with 25,000 porous insulating tiles, each approximately 6 in (15 cm) square and 5 in (12 cm) thick, made of a silica-borosilicate glass composite.

The portions of the shuttle most severely stressed by heatthe nose and the leading edges of the wingsare coated with an even more resistant material termed carbon-carbon. Carbon-carbon is made by attaching a carbon-fiber cloth to the body of the shuttle and then baking it to convert it to a pure carbon substance. The carbon-carbon is then coated to prevent oxidation (combustion) of the material during descent.

Landing. Once the shuttle reaches the atmosphere, it ceases to operate as a spacecraft and begins to function as a glider. Its flight during descent is entirely unpowered; its movements are controlled by its tail rudder, a large flap beneath the main engines, and elevons (small flaps on its wings). These surfaces allow the shuttle to navigate at forward speeds of thousands of miles per hour while dropping vertically at a rate of some 140 MPH (225 km/h). When the aircraft finally touches down, it is traveling at a speed of about 190 knots (100 m per second), and requires about 1.5 miles (2.5 km) to come to a stop. Shuttles can land at extra-long landing strips at either Edwards Air Force Base in California or the Kennedy Space Center in Florida.

Military shuttle missions and the military spaceplane. Many shuttle missions have been partly or entirely military in nature. Eight military missionsthe majorityhave been devoted to the deployment of secret military satellites in three categories: signals intelligence (i.e., eavesdropping on radio communications), optical and radar reconnaissance of the Earth, and military communications. All these deployments occurred between 1982 and 1990, after which the military chose to use uncrewed launch rockets for all classified missions. The shuttle has also supported several military experimental missions and nonclassified satellite deployments. One such was the Discovery mission (STS-39) launched on April 28, 1991 (STS-39), which carried multi-experiment hardware platforms designed to be released into space then retrieved by the shuttle after having recorded various observations of space conditions. All science aboard STS-39 was related to the Strategic Defense Initiative.

The U.S. military is developing an armed space shuttle system or "military spaceplane" of its own, and says that it intends to deploy such a system by 2012. According to an Air Force status report released in January 2002, "a military spaceplane armed with a variety of weapons payloads (e.g. unitary penetrator, small diameter bombs, etc.) will be able to precisely attack and destroy a considerable number of critical targets while satisfying the requirement for precise weapons (i.e. circular error probable [CEP] of less than or equal to three meters). Spaceplanes can support a wide range of military missions including a worldwide precision strike capability; rapid unpredictable reconnaissance; new space control and missile defense capabilities; and both conventional and new tactical spacelift missions that enable augmentation and reconstitution of space assets." The military spaceplane would also enable the military to deploy satellites on short notice. The Air Force envisions a fleet of some 10 spaceplanes stationed in the continental United States as one component of a "Global Strike Task Force" that, it says, will be "capable of striking any target in the world within 24 hours."

The Challenger disaster. Disasters have been associated with both the Soviet (now Russian) and American space programs. The first of the two disasters suffered by the shuttle program took place on January 28, 1986, when the external fuel tank of the shuttle Challenger exploded only 73 seconds into the flight. All seven astronauts were killed, including high-school teacher Christa McAuliffe, who was flying on the shuttle as part of NASA's public-relations campaign "Teachers in Space," designed to bolster young people's interest in human space flight.

The Challenger disaster prompted a comprehensive study to discover its causes. On June 6, 1986, the Presidential Commission appointed to analyze the disaster published its report. The reason for the disaster, said the commission, was the failure of an O-ring (literally, a flexible O-shaped ring or gasket) in a joint connecting two sections of one of the solid rocket engines. The O-ring ruptured, allowing flames from the rocket's interior to jet out, burning into the external fuel tank and causing it to explode.

As a result of the Challenger disaster, many design changes were made. Most of these (254 modifications in all) were made in the orbiter. Another 30 were made in the solid rocket booster, 13 in the external tank, and 24 in the shuttle's main engine. In addition, an escape system was developed that would allow crew members to abandon a shuttle via parachute in case of emergency, and NASA redesigned its launch-abort procedures. Also, NASA was instructed by Congress to reassess its ability to carry out the ambitious program of shuttle launches that it had been planning. The military began reviving its non-shuttle launch options and switched fully to its own boosters for classified satellite launches after 1990.

The STS was essentially shut down for a period of 975 days while NASA carried out the necessary changes and tested its new systems. On September 29, 1988, the first post-Challenger mission was launched, STS-26. On that flight, Discovery carried NASA's TDRS-C communications satellite into orbit, putting the American STS program back on track once more.

The Columbia disaster. Scores of shuttle missions were successfully carried out between the Challenger 's successful 1988 mission and February 1, 2003, when disaster struck again. The space shuttle Columbia broke up suddenly during re-entry, strewing debris over much of Texas and several other states and killing all seven astronauts on board. At the time of this writing, analysts speculate that the most likely cause of the loss of the spacecraft related to some form of damage to the outer protective layer of heat-resistant tiles or seals that protect the shuttle's interior from the 3,000°F (1,650°C) plasma (superheated gas) that envelops it during reentry. As described earlier, a coating of rigid foam insulation is used to keep the external fuel tank cool; video cameras recording the Columbia 's takeoff show that a piece of this foam broke off 80 seconds into the flight and burst against the shuttle's wing at some 510 MPH (821 km/h). Pieces of foam have broken off and struck shuttles during takeoff before, but this was the largest piece everat least 2.7 lb (1.2 kg) and the size of a briefcase.

While Columbia was in orbit, NASA engineers, who were aware that the foam strike had occurred, analyzed the possibility that it might have caused significant damage to the shuttle, but decided that it could not have: computer simulations seemed to show that the brittle tiles covering the shuttle's essential surfaces would not be severely damaged. In any event, there were no contingency procedures to fix any such damage. The shuttle does not carry spare tiles or means to attach them, nor does it carry gear that would make a spacewalk to the bottom of the shuttle feasible.

NASA officials also insisted that it would not have been possible to fly the shuttle in such a way as to spare the damage surfaces, as the shuttle's path is already designed to minimize heating on reentry.

Regardless of the exact reason, the shuttle's skin was breached, whether by mechanical damage or some other cause, and hot gases formed a jet that caused considerable damage to the left wing from inside. During reentry, the wing began to break up, experiencing greatly increased drag. The autopilot struggled to compensate by firing steering rockets, but could only stabilize the shuttle temporarily.

As this book goes to press, the loss of the Columbia has, like the loss of the Challenger in 1986, put a temporary stop to shuttle launches. A moratorium on shuttle launches will also have an impact on the International Space Station, which depends on the shuttle to bring it the fuel it needs to stay in orbit and which cannot be completed without components that only the space shuttle can carry. In the wake of the Columbia disaster, NASA and other governmental officials worked with an independent panel's review of the accident and sought technical improvements to the STS program that might prevent future problems while, at the same time returning the remaining shuttles to flight status as soon as safely possible.

FURTHER READING:

BOOKS:

Barrett, Norman S. Space Shuttle. New York: Franklin Watts, 1985.

Curtis, Anthony R. Space Almanac. Woodsboro, MD: Arcsoft Publishers, 1990.

Dwiggins, Don. Flying the Space Shuttles. New York: Dodd, Mead, 1985.

PERIODICALS:

Barstow, David. "After Liftoff, Uncertainty and Guesswork." New York Times. (February 17, 2003).

Broad, William J. "Outside Space Experts Focusing on Blow to Shuttle Wing." New York Times. (February 15, 2003).

Chang, Kenneth. "Columbia Was Beyond Any Help, Officials Say." New York Times. (February 4, 2003).

. "Disagreement Emerges over Foam on Shuttle Tank." New York Times. (February 21, 2003).

Seltzer, Richard J. "Faulty Joint behind Space Shuttle Disaster." Chemical & Engineering News (23 June 1986): 915.

ELECTRONIC:

Space and Missile Systems Center (SMC), United States Air Force. "The Military Space Plane: Providing Transformational and Responsive Global Precision Striking Power." Jan. 17, 2002. <http://www.spaceref.com/news/viewsr.html?pid=4523> (Feb. 17, 2003).

SEE ALSO

NASA (National Air and Space Administration)
Near Space Environment
Satellites, Non-Governmental High Resolution
Satellites, Spy

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Space Shuttle

Space shuttle

The space shuttle is a reusable spacecraft that takes off like a rocket, travels around the earth like a spacecraft, and then lands once again like a glider. The first space shuttle was the Columbia, whose maiden voyage took place in April 1981. Four additional shuttles were later added to the fleet: Discovery, Challenger, Atlantis, and Endeavor. The first shuttle launched by the Soviet Union (now Russia) was Buran, which made its debut in November 1988.

At one time, both the United States and the Soviet Union envisioned complex space programs that included two parts: (1) space stations orbiting around Earth and/or other planets, and (2) shuttle spacecraft that would transport humans, equipment, raw materials, and finished products to and from the space station. For economic reasons, each nation eventually ended up concentrating on only one aspect of the complete program. The Soviets built and for many years operated advanced space stations (Salyut and Mir ), while Americans have focused their attention on the shuttle system.

The shuttle system has been given the name Space Transportation System (STS), of which the shuttles have been the key element. Initially lacking a space station with which to interact, the American shuttles operated with two major goals: (1) the conduct of scientific experiments in a zero-gravity environment, and (2) the launch, capture, repair, and release of satellites.

Now an international program, STS depends heavily on the contributions of other nations in the completion of its basic missions. For example, its Spacelab modulesthe areas in which astronauts carry out most of their experimentsare designed and built by the European Space Agency, and the extendable arm used to capture and release satellitesthe remote manipulator system or Canadarmis constructed in Canada.

The space shuttle has four main parts: (1) the orbiter (2) the three main engines attached to the orbiter (3) two solid rocket engines, and (4) an external fuel tank. Although the Russian Buran differs in some details from the U.S. space shuttle fleet, the main features of all shuttles are similar.

The orbiter is approximately the size of a commercial DC-9 airplane with a length of 121 ft (37 m) and a wing span of 78 ft (23 m). Its net weight is about 161,000 lb (73,200 kg). It is sub-divided into two main parts: the crew cabin and the cargo bay. The upper level of the crew cabin is the flight deck from which astronauts control the spacecraft's flight in orbit and during descent. Below the flight deck are the crew's personal quarters, containing personal lockers, sleeping, eating, and toilet facilities, and other necessary living units. The crew cabin is physically isolated from the cargo bay and is provided with temperature and pressure conditions similar to those on Earth's surface. The cabin's atmosphere is maintained with a composition equivalent to that of near-Earth atmosphere, 80% nitrogen and 20% oxygen .

The cargo bay is a large space 15 ft (4.5 m) by 60 ft (18 m) in which the shuttle's payloads are stored. The cargo bay can hold up to about 65,000 lb (30,000 kg) during ascent, although it is limited to about half that amount during descent.

In 1973, an agreement was reached between NASA and the European Space Agency (ESA) for the construction by ESA of a pressurized work space that could be loaded into the shuttle's cargo bay. The workspace, designated as Spacelab, was designed for use as a science laboratory in which a wide array of experiments could be conducted. Each of these Spacelab modules is 8.9 ft (2.7 m) long and 13 ft (3.9 m) in diameter. The equipment needed to carry out experiments is arranged in racks along the walls of the Spacelab, and the whole module is then loaded into the cargo bay of the shuttle prior to take-off. When necessary, two Spacelab modules can be joined to form a single, larger work space.

The power needed to lift a space shuttle into orbit comes from two solid-fuel rockets, each 149 ft (45.5 m) in length and 12 ft (4 m) in diameter, and the shuttle's own liquid-fuel engines. The fuel used in the solid rockets is composed of finely-divided aluminum , ammonium perchlorate, and a special polymer designed to form a rubbery mixture. The mixture is molded in such a way as to produce an 11-point starred figure. This shape exposes the maximum possible surface area of fuel during ignition, making combustion as efficient as possible within the engine.

The two solid-fuel rockets carry 1.1 million lb (500,000 kg) of fuel each, and burn out completely only 125 seconds after the shuttle leaves the launch pad. At solid-engine burnout, the shuttle is at an altitude of 161,000 ft (47,000 m) and 244 nautical miles (452 km) down range from launch site. At that point, explosive charges holding the solid rockets to the main shuttle go off and detach the rockets from the shuttle. The rockets are then returned to Earth by means of a system of parachutes that drops them into the Atlantic Ocean at a speed of 55 mi (90 km) per hour. The rockets can then be collected by ships, returned to land, refilled, and re-used in a later shuttle launch.

The three liquid-fueled shuttle engines have been described as the most efficient engines ever built by humans. At maximum capacity, they achieve 99% efficiency during combustion. They are supplied by fuel (liquid hydrogen) and oxidizer (liquid oxygen) stored in the 154 ft (46.2 m) external fuel tank. The fuel tank itself is sub-divided into two parts, one of which holds the liquid oxygen and the other, the liquid hydrogen. The fuel tank is maintained at the very low temperature (less than 454°F [Ȓ270°C]) necessary to keep hydrogen and oxygen in their liquid states. The two liquids are pumped into the shuttle's three engines through 17 in (43 cm) diameter lines that carry 1,035 gal (3,900 l) of fuel per second. Upon ignition, each of the liquid-fueled engines delivers 75,000 horsepower of thrust.

The three main engines burn out after 522 seconds, when the shuttle has reached an altitude of 57 nautical miles (105 km) and is down range 770 nautical miles (1,426 km) from the launch site. At this point, the external fuel tank is also jettisoned. Its return to the earth's surface is not controlled, however, and it is not recoverable for future use.

Final orbit is achieved by means of two small engines, the Orbital Maneuvering System (OMS) Engines located on external pods at the rear of the orbiter's body. The OMS engines are fired first to insert the orbiter into an elliptical orbit with an apogee of 160 nautical miles (296 km) and a perigee of 53 nautical miles (98 km) and then again to accomplish its final circular orbit with a radius of 160 nautical miles (296 km).

Humans and machinery work together to control the movement of the shuttle in orbit and during its descent. For making fine adjustments, the spacecraft depends on six small vernier jets, two in the nose and four in the OMS pods of the spacecraft. These jets allow human or computer to make modest adjustments in the shuttle's flight path in three directions.

The computer system used aboard the shuttle is an example of the redundancy built into the spacecraft. Five discrete computers are used, four networked with each other using one computer program, and one operating independently using a different program. The four linked computers constantly communicate with each other, testing each other's decisions and deciding when one (or two or three) is not performing properly and eliminating that computer (or those computers) from the decision-making process. In case all four of the interlinked computers malfunction, decision-making is turned over automatically to the fifth computer.

This kind of redundancy is built into every essential feature of the shuttle's operation. For example, three independent hydraulic systems are available, all operating with independent power systems. The failure of one or even two of the systems does not, therefore, place the shuttle in a critical failure mode.

The space shuttles have performed a myriad of scientific and technical tasks in their nearly two decades of operation. Many of these have been military missions about which we have relatively little information. The launching of military spy satellites is an example of these.

Some examples of the kinds of activities carried out during shuttle flights include the following:

  • After the launch of the Challenger shuttle (STS-41B) on February 3, 1984, astronauts Bruce McCandless II and Robert L. Stewart conducted the first ever untethered space walks using Manned Maneuvering Unit backpacks that allowed them to propel themselves through space near the shuttle. The shuttle also released into orbit two communication satellites, the Indonesian Palapa and the American Westar satellites. Both satellites failed soon after release but were recovered and returned to Earth by the Discovery during its flight that began on November 8, 1984.
  • During the flight of Challenger (STS-51B) that began on April 29, 1985, crew members carried out a number of experiments in Spacelab 3 determining the effects of zero gravity on living organisms and on the processing of materials. They grew crystals of mercury (II) oxide over a period of more than four days, observed the behavior of two monkeys and 24 rats in a zero-gravity environment, and studied the behavior of liquid droplets held in suspension by sound waves.
  • The mission of STS-51I (Discovery ) was to deposit three communications satellites in orbit. On the same flight, astronauts William F. Fisher and James D. Van Hoften left the shuttle to make repairs on a Syncom satellite that had been placed in orbit during flight STS-51D but that had then malfunctioned.

Some of the most difficult design problems faced by shuttle engineers were those created during the reentry process. When the spacecraft has completed its mission in space and is ready to leave orbit, its OMS fires just long enough to slow the shuttle by 200 mi (320 km) per hour. This modest change in speed is enough to cause the shuttle to drop out of its orbit and begin its descent to Earth.

The re-entry problems occur when the shuttle reaches the outermost regions of the upper atmosphere, where significant amounts of atmospheric gases are first encountered. Friction between the shuttlenow traveling at 17,500 mi (28,000 km) per hourand air molecules causes the spacecraft's outer surface to begin to heat up. Eventually, it reaches a temperature of 3,000°F (1,650°C).

Most materials normally used in aircraft construction would melt and vaporize at these temperatures. It was necessary, therefore, to find a way of protecting astronauts inside the shuttle cabin from this searing heat. The solution invented was to use a variety of insulating materials on the shuttle's outer skin. Parts less severely heated during re-entry are covered with 2,300 flexible quilts of a silica-glass composite. The more sensitive belly of the shuttle is covered with 25,000 insulating tiles, each 6 in (15 cm) square and 5 in (12 cm) thick, made of a silica-borosilicate glass composite.

The portions of the shuttle most severely stressed by heatthe nose and the leading edges of the wingsare coated with an even more resistant material known as carbon-carbon. Carbon-carbon is made by attaching a carbon-fiber cloth to the body of the shuttle and then baking it to convert it to a pure carbon substance. The carbon-carbon is then coated to prevent oxidation of the material during descent.

Once the shuttle reaches Earth's atmosphere, it ceases to operate as a rocket ship and begins to function as a glider. Its movements are controlled by aerodynamic controls, such as the tail rudder, a large flap beneath the main engines, and elevons, small flaps on its wings. These devices allow the shuttle to descend to the earth traveling at speeds of 8,000 mi (13,000 km) per hour, while dropping vertically at the rate of 140 mi (225 km) per hour. When the aircraft finally touches down, it is traveling at a speed of about 190 knots (100 m per second), and requires about 1.5 mi (2.5 km) to come to a stop.

Disasters have been associated with aspects of both the Soviet and American space programs. Unfortunately, the Space Transportation System has been no different in this respect. Mission STS-51L was scheduled to take off on January 28, 1986 using the shuttle Challenger. Only 72 seconds into the flight, the shuttle's external tank exploded, and all seven astronauts on board were killed.

The Challenger disaster prompted one of the most comprehensive studies of a major accident ever conducted. On June 6, 1986, the Presidential Commission appointed to analyze the disaster published its report. The reason for the disaster, according to the commission, was the failure of an O-ring at a joint connecting two sections of one of the solid rocket engines. Flames escaping from the failed joint reached the external fuel tank, set it on fire, and then caused an explosion of the whole spacecraft.

As a result of the Challenger disaster, a number of design changes were made in the shuttle. Most of these (254 modifications in all) were made in the orbiter. Another 30 changes were made in the solid rocket booster, 13 in the external tank, and 24 in the shuttle's main engine. In addition, an escape system was developed that would allow crew members to abandon a shuttle in case of emergencies, and NASA reexamined and redesigned its launch-abort procedures. Also, NASA was instructed to reassess its ability to carry out the ambitious program of shuttle launches that it had been planning.

The U.S. Space Transportation System was essentially shut down for a period of 975 days while NASA carried out necessary changes and tested new systems. Then, on September 29, 1988, the first post-Challenger mission was launched, STS-26. On that flight, Discovery carried NASA's TDRS-C communications satellite into orbit, putting the American STS program back on schedule once more.

In December, 1988, the crew of NASA's Space Shuttle STS-88 began construction of the International Space Station (ISS). By joining the Russian-made control module Zarya with the United States-built connecting module Unity, the crew of the Endeavor became the first crew aboard the ISS. Since the STS-88 mission, twelve more U.S. shuttle missions have led the construction of the International Space Station, a permanent laboratory orbiting 220 miles above Earth.

See also Space and planetary geology; Space physiology; Space probe; Spacecraft, manned

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Space Shuttle

Space Shuttle

Before the invention of the space shuttle, the world's first reusable spacecraft, rockets were used to put a tiny capsule carrying human space travelers into orbit. Stage by stage, booster segments would fall away during the launch as their fuel ran out. The spacecraft would go into orbit around Earth, and then the multi-stage rocket would plunge into the ocean. At that point the rocket would become space rubbish.

In the late 1960s the federal government ordered the National Aeronautics and Space Administration (NASA) to cut costs because of the lagging economy. On January 5, 1972, after suspending several other space programs, President Richard M. Nixon gave NASA the authority to proceed with the development of the shuttle in hopes that the cost of future space travel would be reduced.

The first space shuttle orbiter, known as OV-101, rolled out of a Rockwell assembly facility in Palmdale, California on September 17, 1976. The shuttle was originally to be named Constitution, but fans of the television show Star Trek started a write-in campaign urging the White House to choose the name "Enterprise" instead.

The Enterprise had no engines and was built to test the shuttle's gliding and landing ability. Early glide tests that began in February 1977 were done without astronauts and with the orbiter attached to the back of a converted Boeing 747 jet airplane. This vehicle was referred to as a Shuttle Carrier Aircraft (SCA).

The Enterprise took to the air on its own on August 12, 1977, when astronauts Fred W. Haise and C. Gordon Fullerton flew the 68,000-kilogram (75-ton glider) around a course and made a flawless landing. They had separated the shuttle from the SCA at 6,950 meters (22,800 feet) and glided to a runway landing at Edwards, California. The Enterprise was retired after its fifth test.

On April 12, 1981, Columbia became the first shuttle to actually fly into space. Four sister ships joined the fleet over the next ten years: Challenger, arriving in 1982 but destroyed four years later; Discovery, arriving in 1983; Atlantis, arriving in 1985; and Endeavour, built as a replacement for Challenger in 1991.

The Space Shuttle's Mission

The shuttle has many capabilities unprecedented in human spaceflight, including the ability to retrieve or repair a satellite, house a laboratory for weeks in orbit, and deploy satellites or planetary probes.

Through its reusability, the shuttle was initially intended to provide low-cost frequent access to space. But according to NASA, the shuttle has not been able to fly often enough (only four to eight missions a year) to significantly lower launch costs. In the fiscal year 2001, the operating cost of the shuttle program was $3.165 billion, which is approximately 25 percent of NASA's entire budget.

The Structure of the Space Shuttle

The most complex machine ever built, the space shuttle has more than 2.5 million parts, including four major components: (1) the orbiter, (2) three main engines, (3) an external fuel tank, and (4) two solid rocket boosters. Combined, the weight at launch is approximately 2.1 million kilograms (4.5 million pounds). About the size of a DC-9 commercial airliner, the orbiter, which typically carries a five-to seven-person crew, is the main part of the space shuttle. Constructed primarily of aluminum, it has a length of 37 meters (121 feet) and a wingspan of 23 meters (78 feet).

The orbiter is divided into two parts: the crew cabin and the cargo bay. The crew cabin contains the flight control center and living quarters for the crew. The long middle part of the shuttle is the cargo area and contains the payload bay. Whatever is stored in this area represents the purpose for the mission and "pays" for the flight. The payload bay is 18.3 meters (60 feet) long by 4.6 meters (15 feet) in diameter and can carry 29,500 kilograms (65,000 pounds) into space.

Because the United States could not afford to construct a space workshop on its own, NASA partnered with the European Space Agency (ESA). On August 14, 1973, 14 nations contributed $500 million to build the Space-lab module, which is a portable science laboratory that could be loaded into the cargo bay.

In June 1993 the Spacehab Space Research Laboratory made its debut aboard the STS-57. Spacehab modules, which are leased to NASA by Space-hab, Inc., of Arlington, VA, provide extra space for crew-tended experiments. Spacehab is in the forward end of a shuttle orbiter's cargo bay and increases pressurized experiment space in the shuttle orbiter by 31 cubic meters (1100 cubic feet), quadrupling the working and storage area. During shuttle-Mir, Spacehab modules were used to carry supplies and equipment up to Mir. Spacehab also provides shuttle experiments with standard services such as power, temperature control, and command-data functions.

To get the orbiter into space, the main engines and the booster rockets ignite simultaneously to lift the shuttle. About 2 minutes after launch the boosters complete their firing sequence, separate from the external tank (ET), and by parachute fall into the Atlantic Ocean, where they are recovered and used in a later shuttle launch.

The orbiter continues its flight into space with the main engines furnishing ascent power for another 8 minutes before they are shut down just before achieving orbit. The empty ET separates and falls back to the atmosphere, where friction causes it to break up over the ocean. This is the only major part of the shuttle that is not reused after each flight.

In orbit, the shuttle circles Earth at 28,157 kilometers (17,500 miles) per hour. Each orbit takes about 90 minutes, and the crew sees a sunrise or sunset every 45 minutes.

When the mission ends and the orbiter begins to glide back through the atmosphere, special exterior insulating tiles prevent the vehicle from burning up. The 15.2-centimeter (6-inch) silica tiles shed heat so well that one side is cool enough to hold in the bare hands while the other side is red-hot and withstands temperatures of 2,300°F. Tiles occasionally get damaged during launch or landing and need to be replaced.

Spinoff Benefits of the Space Shuttle

Although it is a U.S. national asset, the shuttle has had a very international presence, flying astronauts, cosmonauts, and experiments from dozens of countries. Many benefits have come from the research and technologies developed as a result of the shuttle.

The same rocket fuel that helps launch the space shuttle has been used to save lives by destroying land mines. A flare device that uses leftover fuel donated by NASA is placed next to an uncovered land mine and is ignited from a safe distance by using a battery-triggered electric match.

Space shuttle technology has also led to medical benefits. The technology used in space shuttle fuel pumps led NASA and the heart surgeon Doctor Michael DeBakey to develop a miniaturized ventricular assist pump. The tiny pump, which has been implanted into more than 30 people, is 5.1 centimeters (2-inches) long and 2.5 centimeters (1-inch) in diameter and weighs less than 0.11 kilogram (4 ounces). Another development has been the spinoff of special lighting technology developed for plant growth experiments on space shuttle Spacelab missions. This technology has been used to treat brain tumors in children. In addition, a non-surgical and less traumatic breast biopsy technique based on technology developed for NASA's Hubble Space Telescope saves women time, pain, scarring, radiation exposure, and money. Performed with a needle instead of a scalpel, it leaves a small puncture wound rather than a large scar.

Preparing the Space Shuttle for the Future

In 1988, when Discovery returned the fleet to space following the Challenger accident, more than 200 safety improvements and modifications had been made. The improvements included a major redesign of the solid rockets, the addition of a crew escape and bailout system, stronger landing gear, more powerful flight control computers, updated navigational equipment, and several updated avionic units.

Shuttle improvements did not stop with Discovery. Endeavour's first flight in 1992 unveiled many improvements, including a drag chute to assist braking during landing, improved steering, and more reliable power hydraulic units. Further upgrades to the shuttle system occurred when Columbia was modified to allow long-duration flights. The modifications included an improved toilet and a regenerative system to remove carbon dioxide from the air.

Future enhancements planned by NASA could double the shuttle's safety by 2005. New sensors and computer power in the main engines will detect trouble a split second before it can do harm, allowing a safe engine shutdown. A next-generation "smart cockpit" will reduce the pilot's workload in an emergency, allowing the crew to focus on critical tasks. Other improvements will make steering systems for the solid rockets more reliable.

Besides increasing safety and cutting costs, another objective in the next generation of spacecraft is to reduce the amount of preparation time and work required between launches. The shuttle currently takes an average of four months to be readied for launch. Goals for future spacecraft call for turnaround times of only a few weeks, if not days.

The space shuttle is prepared to fly until at least 2012 and perhaps as long as 2020. Each of the four shuttle vehicles was designed for 100 flights. In 2001, Discovery led the fleet with 30 completed flights. Over two-thirds of the shuttle fleet's lifetime is ahead of it. However, continuous upgrades and modifications will be required to ensure improved safety and protect against obsolete parts.

see also Astronauts, Types of (volume 3); Challenger (volume 3); Challenger 7 (volume 3); External Tank (volume 3); History of Humans in Space (volume 3); Human Spaceflight Program (volume 1); Launch Vehicles, Reusable (volume 1); Reusable Launch Vehicles (volume 4); Solid Rocket Boosters (volume 3).

Lisa Klink

Bibliography

Kallen, Stuart A. Giant Leaps: Space Shuttles. Edina, MN: Abdo and Daughters, 1996.

Kerrod, Robin. Space Shuttle. New York: Gallery Books, 1984.

Smith, Carter. One Giant Leap for Mankind. Morristown, NJ: Silver Burdett, 1985.

Smith, Melvyn. Space Shuttle. Newbury Park, CA: Haynes Publishing Group, 1989.

Internet Resources

"Human Space Flight: Fiscal Year 2001 Budget Summary." Integrated Financial Management Program. <http://www.ifmp.nasa.gov/codeb/budget2001/HTML/fy01_shuttle.htm>.

The 21st Century Space Shuttle: Upgrade History. NASA Human Spaceflight. <http://www.spaceflight.nasa.gov/shuttle/upgrades/upgrades4.html>.

Upgrades. NASA Human Spaceflight. <http://www.spaceflight.nasa.gov/shuttle/upgrades3.html>.

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space shuttle

space shuttle, reusable U.S. space vehicle (1981–2011). Developed by the National Aeronautics and Space Administration (NASA) and officially known as the Space Transportation System (STS), it was the world's first reusable spacecraft that carried human beings into earth orbit. It consisted of a winged orbiter (122 ft/37 m long, with a 78-ft/24-m wingspan), two solid-rocket boosters, and a large external fuel tank. As with previous spacecraft, the shuttle was launched from a vertical position. Liftoff thrust was derived from the orbiter's three main liquid-propellant engines and the boosters. After 2 min the boosters used up their fuel and separated from the spacecraft, and—after deployment of parachutes—they were recovered following splashdown in the Atlantic Ocean and reused. After about 8 min of flight, the orbiter's main engines shut down; the external tank was then jettisoned and burned up as it reentered the atmosphere. The orbiter entered orbit after a short burn of its two small Orbiting Maneuvering System (OMS) engines. To return to earth, the orbiter turned around, fired its OMS engines to reduce speed, and, after descending through the atmosphere, landed like a glider. Five different orbiters—Columbia,Challenger,Atlantis,Discovery, and Endeavour—saw service; two were lost in accidents.

Following four orbital test flights (1981–82) of the space shuttle Columbia, operational flights began in Nov., 1982. On Jan. 28, 1986, the Challenger exploded shortly after takeoff, killing all seven astronauts. The commission that investigated the disaster determined that the failure of the O-ring seal in one of the solid fuel rockets was responsible. Shuttle flights were halted until Sept., 1988, while design problems were corrected, and then resumed on a more conservative schedule. NASA was forced to reemphasize expendable rockets to reduce the cost of placing payloads in space.

A second disaster struck the shuttle program on Feb. 1, 2003, when the Columbia broke up during reentry, killing the seven astronauts on board. NASA again halted shuttle launches, and a special commission was appointed to investigate the accident. It is believed that damage to the left wing, which could have been caused by insulation that separated from the external fuel tank during launch, ultimately permitted superheated gas to flow into the wing, weaken it, and cause its failure. Modifications were made to external fuel tank and other parts of the shuttle, and shuttle flights resumed in July, 2005. Further problems with fuel tank insulation that developed during that launch led to the suspension of additional flights for a year while the problems were corrected.

Missions of the space shuttle included the transport of the Spacelab scientific workshop and the insertion into orbit of the Hubble Space Telescope (1990), the Galileospace probe (1989), the Chandra X-Ray Observatory (1999), and a wide variety of communications, weather, scientific, and defense-related satellites. Other notable achievements of the shuttle program included the rescue and repair of disabled satellites (including the Hubble Space Telescope in 1993 and 1999) and the first three-person spacewalk (1992). In 1996 the Columbia's mission of Nov. 19–Dec. 7 set the record for the longest shuttle flight.

In 1995 that the crew of Atlantis accomplished the first of nine shuttle-Mir (Russian space station) docking maneuvers and crew transfers, which were designed to pave the way for the assembly of the International Space Station (ISS). The crew of Discovery made the ninth and final docking in 1998, five months before the Russians orbited Zarya, the first ISS module. A month later the astronauts aboard Endeavour initiated the first assembly sequence of the ISS, linking the Unity module, a passageway that connects living and work areas of the station, to Zarya. In 1999 the Discovery crew accomplished the first docking of a shuttle with the ISS during a mission to supply the two modules with tools and cranes. Shuttle flights continued to bring supplies and components to the station, including the Destiny (2001, United States) and Columbus (2008, ESA) laboratories. The Atlantis flew the last shuttle mission, to the ISS, in July, 2011.

A number of nations and organizations developed proposals for shuttle-like space vehicles, but only one, the Soviet-Russian Buran, ever made it into orbital flight. A crewless Buran underwent a successful orbital test flight in 1988. Unlike the shuttle, the Buran did not incorporate main engines used during liftoff, only maneuvering engines, but otherwise the overall design was similar. The program was suspended in 1993 before a flight with a crew had been undertaken. The U.S. Air Force's X-37, whose development was begun by NASA, is a reusable, unmanned vehicle that was first launched in 2010. It is largely similar in general appearance to the space shuttle but is much smaller (29 ft/9 m long, with a 15-ft (4.5-m) wingspan).

See D. R. Jenkins, Space Shuttle: The History of Developing the National Space Transportation System (2d ed. 1996); D. M. Harland, The Space Shuttle: Roles, Missions, and Accomplishments (1998); C. Bredeson, The Challenger Disaster: Tragic Space Flight (1999); M. O. Thompson and C. Peebles, Flying without Wings: NASA Lifting Bodies and the Birth of the Space Shuttle (1999).

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Space Shuttle

SPACE SHUTTLE

SPACE SHUTTLE. The space shuttle is a reusable orbital vehicle that transports aerospace travelers. Officially titled the Space Transportation System(STS), the space shuttle expands space exploration possibilities and contributes to better comprehension of Earth. The orbiting shuttle enables astronauts to conduct experiments in a weightless environment, deploy or repair satellites, and photographically survey the planet. The shuttle aids building, equipping, and transporting of personnel to and from the International Space Station (ISS). Only selected passengers, based on scientific, engineering, professional, or piloting qualifications, can ride in the shuttle. Americans benefit from the shuttle because of zero-gravity pharmaceutical developments and satellite maintenance.

Throughout the twentieth century, engineers envisioned creating a reusable spacecraft. Military and industrial representatives suggested spacecraft resembling gliders such as the late-1950s Dyna Soar design. By the 1970s, the National Aeronautics and Space Administration (NASA) focused on developing the STS. Engineers and scientists at NASA centers, universities, industries, and research institutions cooperated to build this unique spacecraft, contributing expertise in specific fields to design components and propulsion, guidance, control, and communication systems. Shuttle orbiters were constructed and tested in California with additional testing at the Marshall Space Flight Center in Huntsville, Alabama.

The winged space shuttle structurally resembles airplanes. Interior areas are designed for crews to live and work safely and comfortably while in space. Externally, the space shuttle is coated with ceramic tiles to protect it from burning up during reentry in Earth's atmosphere. Special bays and robotic arms are created for extravehicular activity (EVA) and satellite interaction.

In 1977, a trial space shuttle orbiter named Enterprise was carried on a 747 jet to high altitudes and then released to determine that the shuttle could maneuver through the atmosphere before landing. On 12 April 1981, the shuttle Columbia, with Robert L. Crippen and John W. Young aboard, was launched from Kennedy Space Center, Florida. After completing thirty-six orbits in two days, the Columbia landed at Edwards Air Force Base, California. NASA built four additional shuttles: Challenger, Discovery, Atlantis, and Endeavour.

The shuttle enabled the accomplishment of significant aerospace milestones. On the June 1983 STS-7 flight,


Sally K. Ride became the first American woman astronaut. The next year, Bruce Mc Candless II and Robert Stewart utilized Manned Maneuvering Units to become the first astronauts to walk in space without being tethered to a spacecraft.

The 28 January 1986 Challenger explosion paralyzed the space shuttle program. When O-ring seals on a solid rocket booster failed, the shuttle disintegrated, and the entire crew was killed. A presidential commission determined that NASA was accountable due to ineffective engineering control and communication. After redesigning the O-ring seals, NASA launched the shuttle Discovery on 29 September 1988. Shuttle flights became routine again.

Post-Challenger achievements included deployment of the Hubble Space Telescope in 1990. Beginning in 1995, the space shuttle occasionally docked with the Russian space station Mir. In late 1998, the shuttle Endeavour transported Unity, the ISS core, into orbit. The February 2000 Shuttle Radar Topography Mission (SRTM) aboard the space shuttle Endeavour collected information about 80 percent of Earth's surface.

The original space shuttles are scheduled for retirement in 2012. In May 2002, NASA announced that future shuttles would physically resemble their predecessors but would be smaller, safer, more affordable, and not require pilots.

BIBLIOGRAPHY

Harland, David M. The Space Shuttle: Roles, Missions, and Accomplishments. New York: Wiley, 1998.

Jenkins, Dennis R. Space Shuttle: The History of the National Space Transportation System: The First 100 Missions. 3d ed. Cape Canaveral, Fla.: D.R. Jenkins, 2001. The most thorough compendium of the space shuttle.

NASA. Home page at http://www.nasa.gov

Rumerman, Judy A., and Stephen J. Garber, comps. Chronology of Space Shuttle Flights, 1981–2000. Washington, D.C.: NASA History Division, Office of Policy and Plans, NASA Headquarters, 2000.

Elizabeth D.Schafer

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Columbia (U.S. space shuttle)

Columbia, U.S. space shuttle. On its 28th flight, on Feb. 1, 2003, after completing a 16-day scientific mission, the spacecraft disintegrated during reentry, killing its seven-person crew. About 16 minutes before its expected landing at the Kennedy Space Center, when Columbia was about 203,000 ft (61,900 m) above Texas, communication with the spacecraft was lost; shortly thereafter reports of falling debris began coming in from E Texas and Louisiana. The disaster, the second in the space shuttle program (see also Challenger), led to the suspension of shuttle flights.

Inquiries into the accident were undertaken by NASA, Congress, and an independent investigation board. Ultimately, it was determined that a large piece of foam insulation had broken off the external tank 82 seconds into liftoff and struck the leading edge of the shuttle's left wing, creating a hole in the wing. On reentry, the searing heat generated by friction entered the damaged wing, which then melted, destabilizing the shuttle and causing it to break up. The independent investigative panel was harshly critical of NASA and called for numerous reforms, most to repair NASA's "broken safety culture." Shuttle flights did not resume until July, 2005.

See P. Chien, Columbia: Final Voyage (2006).

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space shuttle

space shuttle Re-usable rocket-powered US spacecraft. The main part of the shuttle, the orbiter (of which four have been built, Columbia, Challenger, Discovery, and Atlantis), looks like a bulky jet aircraft with swept-back wings. It ferries people and equipment between the ground and Earth orbit. It takes off attached to a large fuel tank, using its own three rocket engines, assisted by two booster rockets. The boosters are jettisoned about two minutes after launch and are later recovered for re-use. Six minutes later, the orbiter's main engines cut off and the external fuel tank is dumped. Manoeuvring engines then put the craft into the required orbit. When returning to Earth, these engines provide reverse thrust to slow the craft down for descent into the atmosphere. It glides down and lands on a runway. The first space shuttle, Columbia, was launched into orbit on April 12, 1981. The orbiter has a large payload bay in which it carries satellites for release into orbit. On mission 25 in January 1986, the shuttle Challenger exploded soon after launch, killing all seven people on board. A leak enabled burning gases from a booster rocket to ignite the fuel in the main tank.

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space shuttle

space shut·tle • n. a rocket-launched spacecraft, able to land like an unpowered aircraft, used to make repeated journeys between the earth and earth orbit.

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