Space shuttle

Definition: A reusable space launch vehicle developed by the United States to launch astronauts and large satellites into Earth orbit.

Significance: The space shuttle was the first reusable launch vehicle to carry humans into space.

Planning the Space Shuttle

The space shuttle program was initially conceived in the 1960s, when the National Aeronautics and Space Administration (NASA) began planning a comprehensive program for a permanent American presence in space. The plan included three components: a permanently crewed space station, a reusable vehicle to carry astronauts from Earth to orbit and back, and a space tug to move satellites around in orbit. However, the need to fund other national priorities resulted in cuts to the NASA budget at the end of the Apollo Program. Because this new space effort’s cost far exceeded its budget, it was scaled back to include only the reusable launch vehicle, which was called the space shuttle. On January 5, 1972, President Richard M. Nixon officially announced the inauguration of the space shuttle program. NASA’s ambitious schedule called for suborbital tests by 1977 and the first orbital tests by 1979. The shuttle was scheduled to begin regular launchings by 1980.

The Shuttle Vehicle

The space shuttle consists of three major components: a reusable, winged orbiter that carries the crew; a large external tank that holds fuel for the main engines; and two solid rocket boosters that provide most of the shuttle’s lift during the first two minutes of flight. The space shuttle is designed to reach orbits ranging from about 115 miles to 400 miles high. Normally, space shuttle missions ranged from five to sixteen days in orbit. The smallest crew to fly on the shuttle was composed of two people, on the first few test flights, but the shuttle normally carried crews ranging from five to eight people, depending on the flight objectives. At liftoff, the space shuttle weighed about 4,500,000 pounds.

The orbiter, manufactured by the Space Division of Rockwell International, carried the crew, the payload, and the main propulsion system. The empty weight of the orbiter is about 150,000 pounds, approximately the same as that of a DC-9 jet aircraft. The crew compartment of the orbiter has three levels: the flight deck, the middeck, and a lower level equipment bay. The crew compartment is pressurized to 14.7 pounds per square inch with a mixture of 80 percent nitrogen and 20 percent oxygen, similar to the air pressure and composition at the earth’s surface. The volume of the crew compartment is 2,325 cubic feet, about the equivalent of a 15-by-15-by-10-foot room.

The uppermost level of the crew compartment is the flight deck. The mission commander and the pilot were seated side-by-side in the forward portion of the flight deck. The mission commander and the pilot sat at workstations that contain the controls and displays used to guide the orbiter throughout the flight. Two seats for mission specialists are located directly behind the seats of the mission commander and the pilot. At the rear of the flight deck there are two overhead- and aft-viewing windows for observing orbital operations.

The middeck, which is directly beneath the flight deck, provided accommodations for additional crewmembers and contains three avionics equipment bays. Depending on the mission requirements, bunk sleep stations and a galley could be installed in the middeck. In addition, three or four seats of the same type as the mission specialists’ seats on the flight deck could be installed in the middeck.

An airlock, located in the rear of the middeck, provided access to the payload bay. Normally, two extravehicular mobility units (EMUs) were stowed in the airlock. The EMU is an integrated spacesuit assembly and life-support system that enabled flight crew members to leave the pressurized orbiter crew cabin and work outside the cabin in space. Removable panels in the middeck floor provide access to the equipment bay that houses the major components of the waste-management and air-cleaning and recirculating systems. This compartment has space in which to stow lithium hydroxide canisters, used to clean the air, and five separate spaces for crew equipment stowage. When on the ground, astronauts entered and exited the crew compartment through a side hatch in the middeck.

The payload bay, measuring 15 feet wide and 60 feet long, held large payloads being carried to orbit. Two payload bay doors, each 60 feet long, are hinged at each side of the fuselage. The payload bay doors exposed the payload bay to space when they were opened along the centerline. The back surface of the doors, which have a combined area of approximately 1,600 square feet, contains radiators that exhausted the heat generated by equipment on the orbiter. Seals on the doors provide a relatively airtight payload compartment when the doors are closed and latched.

The crew compartment of the orbiter does not contain sufficient space for experiments, and the payload bay is not pressurized, so astronauts working in the payload bay had to wear spacesuits. To provide space for experiments, the European Space Agency (ESA) designed the Spacelab, a large, pressurized module that could be carried in the orbiter’s payload bay. Astronauts entered the Spacelab through the airlock at the rear of the middeck of the crew compartment. The Spacelab provided electrical power and a pressurized working environment for astronauts to perform a variety of experiments.

The orbiter also contains the three liquid-fueled main engines. These engines burn liquid hydrogen and liquid oxygen, which is carried in the external tank attached to the orbiter. The top surface of the orbiter is covered with white silica material that protects the surface during reentry from temperatures of up to 1,200 degrees Fahrenheit. The bottom of the orbiter and the leading edge of the tail are covered with black silica heat-shield tiles, having very low thermal conductivity, which protect those surfaces from temperatures of up to 2,300 degrees Fahrenheit.

The orbiter’s external tank, which was designed by Martin Marietta and built at NASA’s Michoud Assembly Facility in New Orleans, Louisiana, contains all of the fuel, liquid hydrogen, and the oxidizer, liquid oxygen, for the orbiter’s main engines. At the top of the external tank there is a conical nose cone that reduces the air drag on the vehicle and serves as a lightning rod. The oxygen tank, located beneath the nose cone, has a volume of 19,563 cubic feet. A 17-inch-diameter fuel line carries the oxygen to the orbiter with a maximum flow rate of 17,592 gallons per minute. The liquid hydrogen tank, which is located below the liquid oxygen tank, has a volume of 53,518 cubic feet. The 17-inch fuel line connecting the hydrogen tank to the orbiter has a maximum flow of 47,365 gallons per minute. Just before the shuttle reached orbital velocity, the external tank was jettisoned, and it burned up on atmospheric entry.

The two solid-fueled rocket boosters are attached to the main tank. The solid rocket boosters were the largest solid-propellant motors ever flown and the first that were designed to be reused. The propellant mixture in each motor consists of ammonium perchlorate as the oxidizer, aluminum as the fuel, iron oxide as a catalyst, and a polymer binder that holds the mixture together. The fuel is shaped so that each rocket provided a high thrust at ignition and then reduced the thrust by approximately one-third after 50 seconds to prevent overstressing the vehicle during the time when it experienced maximum dynamic pressure. Because the solid boosters were too long to manufacture as a single unit, each booster consists of four segments. These segments are joined together using a system of clamps and O-ring seals, which are made of compressible material that fills the space in the joints to prevent leakage of high-pressure gas through the joints. Each solid booster weighs 1,300,000 pounds at liftoff and 192,000 pounds after the fuel has been burned. At liftoff, each of the solid boosters developed approximately 3,300,000 pounds of thrust. The solid rocket boosters also contain a parachute system, which allowed them to descend into the Atlantic Ocean after use. They were recovered by ship and returned to the manufacturer for refurbishment and reuse.

The orbiter returned to Earth as a glider, using conventional flight controls and wings that provided lift. The wingspan is 78 feet. Each wing, constructed of aluminum alloy with a multirib-and-spar arrangement, has a maximum thickness of 5 feet and is approximately 60 feet long where it is attached to the fuselage. The main landing gear is stored in the wings and was extended only a few seconds before landing.

The Space Shuttle Flight Profile

The space shuttle was launched vertically from a transporter-launching pad that was modified from a Saturn V launching pad after the end of the Apollo Program. The shuttle could carry a crew of up to eight astronauts and could deliver a payload of up to 65,000 pounds into low-Earth orbit.

The liquid-fueled main engines ignited about seven seconds before the planned liftoff. A computer checked the performance of the main engines, which could be shut down if a problem was detected. If no problems were detected, the solid rocket boosters, which must burn until their fuel is exhausted, were ignited. At liftoff, the three main engines and the two solid-fueled booster rockets developed a total of more than 6,800,000 pounds of thrust. The solid rocket boosters, which provided most of the thrust to lift the space shuttle off the pad and up to an altitude of about 150,000 feet, burned for approximately two minutes. At an altitude of about 28 miles, just after they burned out, the solid boosters were jettisoned from the external tank by pyrotechnic separation devices. Eight small rockets on the solid boosters fired to carry them well clear of the orbiter. A parachute system slowed the descent of the solid boosters, which were recovered from the ocean, about 170 miles from the launch site.

The external tank continued to provide fuel for the orbiter’s three main engines until about eight minutes after liftoff. The main engines shut down at a speed just below orbital speed, and the external tank was jettisoned. After a short period of coasting, two small maneuvering engines, fueled from tanks on the orbiter, fired to place the orbiter in Earth orbit.

Environmental control and life-support system radiators, used to cool the orbiter’s systems, are located on the interior of the payload bay doors. Once the orbiter achieved orbit, the payload bay doors were opened to allow proper cooling of the spacecraft.

During the mission, the path of the orbiter could be adjusted using the maneuvering engines. Once the mission was completed, the maneuvering engines served as retrorockets, firing opposite the direction of the orbiter’s motion and slowing the orbiter so that it reentered the earth’s atmosphere.

Space Shuttle Missions

The first space shuttle orbiter, named Enterprise, was unveiled to the public on September 17, 1976, when it was rolled out of the Rockwell International hangar in Palmdale, California. Initially, the Enterprise was used for a series of ground tests. During 1976 and 1977, the Enterprise was carried aloft by a specially modified Boeing 747 aircraft, allowing engineers to study the aerodynamics of the orbiter. On August 12, 1977, the Enterprise separated from the Boeing 747 at an altitude of 22,800 feet, allowing the flight crew, Gordon Fullerton and Fred Haise, to perform approach and landing maneuvers at Edwards Air Force Base in California. After a series of unpowered flight tests, the Enterprise, which was never intended for powered flight, was retired. A fleet of four shuttles, Columbia, Challenger, Discovery, and Atlantis, was built for orbital operations.

The space shuttle Columbia was launched from NASA’s John F. Kennedy Space Center at Cape Canaveral, Florida, on its first flight on April 12, 1981. John W. Young, a veteran of NASA’s Gemini and Apollo Programs, was the commander, and Robert L. Crippen was the pilot. This was a test flight, and the only payload carried on the mission was a Development Flight Instrumentation Package, which contained sensors and measuring devices to record orbiter performance and the stresses that occurred during launch, ascent, orbital flight, descent, and landing. Post-flight inspection of Columbia revealed that an overpressure wave that occurred when the solid rocket boosters ignited resulted in the loss of 16 heat shield tiles and damage to 148 others. However, Columbia’s first flight demonstrated that the shuttle could perform a safe ascent into orbit and return to Earth for a safe landing.

The first five space shuttle missions were flown by Columbia, while the other space shuttle orbiters were under construction. The sixth shuttle flight, launched on April 4, 1983, was the first mission of Challenger. This mission deployed the first Tracking and Data Relay Satellite (TDRS), part of the satellite network used to relay shuttle communications to the ground. A malfunction of the inertial upper stage booster, which moves the satellite from the low orbit of the shuttle into the higher orbit required for global communications, resulted in an improper but stable orbit. Propellant aboard the satellite was used over the next several months to move the TDRS into the proper orbit.

Between April 1981 and January 1986, the space shuttles completed twenty-four missions. On June 18, 1983, the shuttle Challenger carried the United States’ first woman astronaut, Sally K. Ride, into orbit and deployed two communications satellites, Anik C-2 for Telesat Canada and Palapa-B1 for Indonesia. During the Challenger mission launched on February 3, 1984, the first untethered space walk took place. Astronauts Bruce McCandless II and Robert L. Stewart used the Manned Maneuvering Unit (MMU) to fly in space unconnected to the orbiter. This mission also launched three satellites, but two, the Westar-VI and Palapa-B2, were placed into a low, elliptical orbit when the Payload Assist Module rocket motor, which should have boosted them into a high, circular orbit, failed. The shuttle Challenger carried the Long Duration Exposure Facility (LDEF) into orbit on April 6, 1984. The LDEF, whose purpose was to expose various materials to the space environment to monitor their stability or degradation in space and to determine the flux of micrometeorites and orbital debris, was supposed to be retrieved and returned to Earth after about two years.

The orbiter Discovery made its first flight on August 30, 1984, on a mission that launched three communications satellites. This mission also deployed a 102-foot-long, 13-foot-wide solar wing, which tested several different types of solar cells being considered for future space missions and demonstrated that very large structures could be deployed in space. The Spacelab space laboratory flew three times: carried into orbit by Columbia on November 28, 1983, and by Challenger on April 29, 1985 and July 29, 1985. The shuttle Atlantis made its first flight on September 20, 1985.

On January 28, 1986, the twenty-fifth space shuttle mission was launched from the Kennedy Space Center. The space shuttle Challenger, after a night of below-freezing temperatures, lifted off on its tenth mission into space at about 10:40 a.m. eastern standard time, carrying a crew of seven astronauts: Francis R. Scobee, the commander; Michael J. Smith, the pilot; Judith A. Resnik, Ellison S. Onizuka, and Ronald E. McNair, all mission specialists; Gregory B. Jarvis, a payload specialist; and America’s first Teacher in Space, Sharon Christa McAuliffe. Seventy-four seconds after the launch, Challenger was destroyed, killing all seven crew members. A subsequent investigation established that the previous night’s low temperature had hardened the O-ring seals between the segments of the solid-fueled rocket boosters. One joint in the right solid rocket booster had developed a leak, and the hot gases cut through metal on the shuttle to cause the disaster.

NASA immediately suspended the space shuttle program while the shuttle’s overall safety was evaluated. The solid-fuel rocket booster joints were redesigned and the shuttle orbiter underwent more than two hundred modifications before the shuttle fleet returned to service. An escape system was added to the orbiter to allow astronauts to escape from a crippled shuttle and parachute to Earth. Construction began on a new shuttle, named Endeavour, to replace Challenger.

Shuttle flights resumed on September 29, 1988, when the shuttle Discovery carried a crew of five astronauts, commanded by Frederick H. Hauck, into orbit. This mission placed another TDRS communications satellite into orbit. Subsequent shuttle flights performed a variety of functions. On April 24, 1990, the shuttle Discovery placed the Hubble Space Telescope (HST) into orbit. The Hubble was designed to be serviced in orbit by future space shuttle missions. The first Hubble-servicing mission, flown by Endeavour and launched on December 2, 1993, accomplished its three primary objectives: restoring the planned scientific capabilities of the Hubble by installing a corrective lens designed to compensate for the incorrect shape of the mirror; restoring the reliability of Hubble’s guidance system; and validating the concept of servicing while in orbit. The shuttle Columbia was launched on January 9, 1990, to place the SYNCOM IV-F5 defense communications satellite in orbit and to retrieve the Long Duration Exposure Facility (LDEF), which had been stranded in orbit after the Challenger accident.

The space shuttles launched several interplanetary spacecraft. On May 4, 1989, the shuttle Atlantis launched the Magellan spacecraft, which went into orbit around Venus and performed radar mapping of its surface. On October 18, 1989, the shuttle Atlantis launched the Galileo spacecraft, which went into orbit around Jupiter, exploring that planet and its moons. On October 6, 1990, the shuttle Discovery launched the joint ESA/NASA Ulysses spacecraft, which was placed on a trajectory to pass Jupiter, where its orbit was altered to explore polar regions of the sun.

In 1984, the US government decided to build a space station, similar to the one that had been in the original 1960s plan. In preparation for this new space station, NASA began a series of space shuttle missions to Mir, the Russian space station. As part of this project, Russian cosmonaut Sergei Krikalev, the first Russian to be a crew member on an American spacecraft, flew on the space shuttle Endeavour in March 1995. In June 1995, the space shuttle Atlantis carried out the first mission to dock with the Mir Space Station.

On October 11, 2000, the shuttle Discovery flew the one-hundredth space shuttle mission, carrying a large truss, the Pressurized Mating Adapter-3, four large gyroscopes, and two heat pipes to the International Space Station (ISS). Before the launching of the shuttle Discovery in March 2001, on a mission to bring the second crew to the ISS, James Kelly, the pilot, noted that, twenty years after the inception of the space shuttle program, the shuttle had finally realized its initial goal of transporting people to and from a permanent workplace in low-Earth orbit. During its first twenty years of operation, NASA’s space shuttle fleet carried more than 600 astronauts and placed more than 3 million pounds of cargo into orbit.

Tragedy struck the space shuttle program once more on February 1, 2003, when Columbia disintegrated upon reentry, killing all seven crew members. It was later discovered that the cause of the disaster had occurred upon the shuttle's launch, when a piece of foam insulation broke off of a propellant tank and struck the edge of the craft's left wing. Information suggesting that members of Mission Control had flagged the issue generated further debate about NASA's approach to safety issues. The shuttles were grounded until July 2005, when Discovery launched on a successful mission.

End of the Space Shuttle Program

In 2004, President George W. Bush announced that once the ISS was completed, which was planned for 2010, the space shuttle would be retired, bringing the program to an end. As part of a new scope for NASA, he also outlined a plan to develop a new crewed exploration vehicle designed to carry passengers back to the moon and, eventually, to Mars. While Atlantis, Discovery, and Endeavour had continued to conduct regular missions, mainly to continue delivering parts for the construction of the ISS, in adherence with this new initiative, the retirement of the space shuttles began with the final landing of Discovery in March 2011. Endeavour landed at Kennedy Space Center, completing its final mission, in June of that year, and Atlantis touched down for the final time in July after carrying supplies to the ISS, marking the official end of the shuttle program. The three shuttles were then distributed to be displayed at museums throughout the country. Overall, the program had led to more than 130 missions over approximately thirty years.

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