Space Shuttle

Mission of the space shuttle

Structure of the STS

Orbital maneuvers

Orbital activities

Descent

Landing

Military shuttle missions and the military space plane

The Challenger disaster

The Columbia disaster

Resources

The space shuttle fleet is a number of reusable spacecraft that take off like a rocket, orbit Earth like a satellite, and then land like a glider. The space shuttle has been essential to the repair and maintenance of the Hubble Space Telescope and to the 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 Earth.

The first shuttle to be launched into orbit about Earth 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 apart during reentry on February 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 was never equipped for space flight; it is now in the collection of the Smithsonian Museum.

A spacecraft closely resembling the United States space shuttle, the Aero-Buran, was launched by the former 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 former Soviet Union built, and for many years operated, space stations (Salyut, 1971–1991, and Mir, 1986–2001), while Americans have focused their attention on the space shuttle. The brief Soviet excursion into shuttle design(Buran)andtheU.S. experiment with Skylab (1973–1979) were the only exceptions to this pattern; that is, until the current development of the International Space Station, which is an international effort that includes the U.S.

The United States shuttle system—which includes the shuttle vehicle itself, launch boosters, and other components—is 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 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.

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

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 was 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 level— literally upper only when the shuttle is in level flight in the earth’s atmosphere, as there is no literal up and down when it is orbiting in free fall—is 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 (18 m) long in which the shuttle’s payloads—the modules or satellites that it ports to orbit or back to Earth—are 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 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 entire 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 (47,000 m) and 212 mi (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 mph (90 km/h). They can then be collected by ships, returned to their manufacturer (Thiokol), 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 Corporation), which is 27.5 ft (8.4 m) wide and 154 ft (46.2 m) long. The tank itself is actually two tanks—one for liquid oxygen and the other for liquid hydrogen—covered 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 17 in (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 mi (105 km) and is 670 mi (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 mi (296 km) and a perigee (lowest altitude) of 46 mi (98 km). They are fired again to nudge the shuttle into a final, circular orbit with a radius of 139 mi (296 km). All these figures may vary depending on requirements of each mission.

Orbital maneuvers

For making fine adjustments, the spacecraft depends on six small rockets termed vernier (VUR-nee-ur) 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 system. 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 1986) 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 and human lives.

Orbital activities

The space shuttles have performed a wide variety of tasks in nearly two-and-one-half decades of operation. Some examples of the kinds of activities carried out during shuttle flights include the following:

• After the launch of the Challenger on February 3, 1984 (mission STS-41B), astronauts Bruce McCandless II and Robert L. Stewart conducted untethered space walks to test the Manned Maneuvering Unit backpacks, which 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. Both satellites failed soon after release but were recovered and returned to the Earth by the Discovery shuttle in 1984 (STS-51A).
• During the Challenger flight that began on April 29, 1985 (STS-51B), crew members carried out a number of experiments in Spacelab 3 to determine the effects of microgravity on living organisms and on the processing of materials. They grew crystals of mercury (II) oxide over a period of several days, observed the behavior of two monkeys and 24 rats in a micro-gravity environment, and studied the behavior of liquid droplets held in suspension by sound waves.
• The Discovery mission launched August 27, 1985 (STS-51I) deposited 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 had malfunctioned.
• 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). A shuttle mission had deployed the Hubble several years earlier. However, it was discovered later that it contained a defective mirror. Fortunately, Hubble had been designed to be repaired by spacewalking astronauts. The crew of the Endeavor latched onto 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.

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 engines fire 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 established 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 shuttle—now 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 officials 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 heat—the nose and the leading edges of the wings— are 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 mi (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. Any landing at Edwards requires the shuttle to be transported back to Cape Canaveral on top of a shuttle carrier aircraft (a commercial aircraft specially modified to carry a shuttle), which costs several millions of dollars.

Military shuttle missions and the military space plane

Many shuttle missions have been partly or entirely military in nature. Eight military missions—the major-ity—have 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 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 non-classified satellite deployments. One such was the Discovery mission launched 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 (SDI).

The United States 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.’

According to a March 2006 edition of Aviation Week & Space Technology, a spaceplane called various names but most popularly called Blackstar (SR-3/XOV) is being developed as a two-stage system where the first stage rocket carries a second stage (the upper stage, or spaceplane) into space. As of October 2006, the claims of the Air Force is highly secretive and highly controversial in the United States and around the world.

The Challenger disaster

Disasters have been associated with both the Soviet (now Russian) and American space programs. Unfortunately, this has included the STS. 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. In addition, NASA was instructed by United States 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 reentry, strewing debris over much of Texas and several other states and killing all seven astronauts on board. Following the disaster, NASA scientists and engineers found that a hole punctured the leading edge of the left wing of Columbia. The hole was made when a piece of insulating foam from the external fuel tank ripped off during the launch. 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 about 82 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 ever recorded—at 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 away as to spare the damage surfaces, as the shuttle’s path is already designed to minimize heating on reentry. However, later, testing revealed that the foam impact on the wing was forceful enough to puncture the wing.

With a breach in the protective tiles of the shuttle, hot gases entered the interior of Columbia ’s left wing. 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. The shuttle’s support structure was ultimately destroyed and the shuttle quickly disintegrated as it re-entered the earth’s atmosphere over the western United States.

In the wake of the Columbia disaster, the Columbia Accident Investigation Board (CAIB) began their investigation of NASA and the Columbia space shuttle. They stated the cause of the disaster to the Columbia, along with recommending many changes to increase the safety of future shuttle flights. Members of the CAIB released their final report on August 26, 2003. Besides the problem with foam hitting the shuttle wing, the CAIB also sited organizational problems with NASA that contributed to the demise of Columbia. CAIB members stated that although changes had occurred within the NASA structuresincethetimeofthe Challenger disaster, it had not essentially improved its organization with respect to safety. Even though the problem of debris shedding from the external tank was well documented throughout the history of shuttle operations, NASA management deemed it an acceptable risk, assuming that since it had not caused a problem in the past, it would not cause one in the future.

However, the CAIB members felt this attitude was unacceptable and placed NASA organizational problems and the foam problem as equal contributors to the cause of the disaster. In fact, Dr. Sally Ride, the first U.S. woman in space, who served on the CAIB (for Columbia ) and the Rogers Commission (for Challenger ) cited very similar attitudes by NASA management (that is, it is acceptable to fly even in the face of problems that could likely doom the shuttle and its crew) before the occurrence of each disaster. Before returning to flight, the board recommended 29 specific improvements to NASA safety. These recommendations include: preventing foam from tearing away from the external tank; improving inspections before launch; increasing (and in some cases adding) visual inspections of the shuttle during ascent and orbit phases; and establishing an independent organization to approve all technical requirements.

NASA resumed shuttle flights when Discovery (STS-114) was launched on July 26, 2005. It was considered a flight safety evaluation and testing mission. The mission also supplied the International Space Station (ISS) with much needed materials. STS-114 was a successful mission; however, foam was again shed from the external tank. NASA officials publicly grounded the fleet until the problem could be identified and resolved. The second mission after Columbia began on July 4, 2006, when Discovery (STS-121) was launched for another ISS mission. On September 9, 2006, Atlantis (STS-115) was flown. As of October 2006, and with two successful flights by the shuttle fleet to the ISS, NASA is hopeful that the space shuttle can complete the construction of the space station by 2010. Fifteen more space shuttle missions are planned

KEY TERMS

Booster —A rocket engine used to raise a large spacecraft, such as the space shuttle, into orbit.

Orbiter —The space shuttle itself; contains the cargo bay, crew cabin, main engines.

Payload —Amount of useful material that can be lifted into space by a delivery system.

Redundancy —The process by which two or more identical items are included in a spacecraft to increase the safety of its human passengers.

Spacelab —A laboratory module constructed by the European Space Agency for use in the space shuttle.

from December 2006 to January 2010 in order to add components to the space station. If these 15 missions are successful, NASA will have flown 131 missions of the space shuttle fleet. NASA expects to retire the fleet in 2010 and replace it with Orion, an Apollo-type vehicle that will take humans to the moon and Mars after 2015.

See also Rockets and missiles; Spacecraft, manned; Space probe.

Resources

BOOKS

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

Chien, Philip. Columbia, Final Voyage: The Last Flight of NASA’s First Space Shuttle. New York: Copernicus Books, 2006.

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

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

Langille, Jacqueline. The Space Shuttle. New York: Crabtree Publishing, 1998.

Mullane, Mike. Riding Rockets: The Outrageious Tales of a Space Shuttle Astronaut. New York: Scribner, 2006.

Return to Flight Task Group, United States National Aeronautics and Space Administration. Final report of the return to flight task group: assessing the implementation of the Columbia Accident Investigation Board Return-to-flight recommendations. Washington, DC: Return to Flight Task Group, 2005.

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): 9–15.

OTHER

Columbia Accident Investigation Board. “Homepage of CAIB.” <http://caib.nasa.gov/> (accessed October 27, 2006).

National Aeronautics and Space Administration. “Report of the Presidential Commission on the Space Shuttle Challenger Accident.” <http://science.ksc.nasa.gov/shuttle/missions/51-l/docs/rogers-commission/table-ofcontents.html (accessed October 27, 2006).

Space and Missile Systems Center (SMC), United States Air Force. “The Military Space Plane: Providing Transformational and Responsive Global Precision Striking Power.” January 17, 2002. <http://www.spaceref.com/news/viewsr.html?pid=4523> (accessed October 27, 2006).

David E. Newton

10 Space Shuttle

James C. Fletcher

"NASA Document III-31: The Space Shuttle"

Published in November 22, 1971; reprinted from Exploring the Unknown: Selected Documents in the History of the U.S. Civil Space Program. Volume I: Organizing for Exploration, published in 1995

Remarks on the Space Shuttle Program

Richard M. Nixon

Presented on January 5, 1972

The U.S. space program began in 1958 with the establishment of the National Aeronautics and Space Administration (NASA). This initiative was the direct result of a space race between the United States and the former Soviet Union at a time when the two superpowers were involved in a period of hostile relations known as the Cold War (1945–91). A year earlier the Soviets had sent Sputnik 1, the first artificial satellite, into orbit. Americans were shocked by the event, fearing that the United States was losing the Cold War. NASA responded by launching Project Mercury for the training of astronauts. The seven members of the first astronaut corps were called the Mercury 7 (see Tom Wolfe entry). In May 1961 Mercury astronaut Alan Shepard (1923–1998) became the first American in space. Yet the United States was still lagging behind the Soviet Union in the space race: A month before Shepard made his brief flight over the Atlantic Ocean, Soviet cosmonaut Yuri Gagarin (1934–1968) became the first human to travel in space by making a nearly complete orbit of Earth.

On May 25, 1961, less than three weeks after Shepard's flight, President John F. Kennedy (1917–1963; served 1961–63) confronted the Soviet challenge in a speech before a joint session of Congress. He committed the United States to putting a man on the Moon within the next ten years (see John F. Kennedy entry). NASA immediately accelerated Project Apollo and its Moon mission program, and within eight years the agency had achieved Kennedy's goal. In 1969 the spacecraft Apollo 11 successfully landed astronauts Neil Armstrong (1930–) and Edwin "Buzz" Aldrin (1930–) on the Moon (see Michael Collins and Edwin E. Aldrin entry). The moon landing was a victory for the United States in the space race. The Soviet Union had never developed a moon exploration program because of political power struggles and lack of government funding.

In the meantime, however, the Soviet Union had moved ahead in another important area. By the early 1960s the Soviets had already launched the Salyut space station and were operating Soyuz space shuttles. (A space station is an orbiting craft in which humans can live for extended periods of time. A space shuttle is a reusable craft that transports people and cargo between Earth and space.) When Apollo 11 landed on the Moon the United States had preliminary research on a space station and a space shuttle, but there were no official programs. The situation changed in the early 1970s, with the end of Project Apollo. In 1972 Apollo 17 made the final moon landing. The American public and the U.S. government had lost interest in moon exploration, so NASA had turned its attention to unmanned spaceflight projects such as the Large Space Telescope (LST). Initiated in 1969, the LST was an observatory (a structure housing a telescope, a device that observes celestial objects) that would continuously orbit Earth. NASA officials also realized that they could not abandon the manned spaceflight program. An immediate result of the LST project was a plan for a space shuttle that would release the LST into orbit. (The LST eventually became the Hubble Space Telescope, which was launched in 1990.)

On November 22, 1971, at the height of discussions about building a space shuttle, NASA administrator James C. Fletcher (1919–1991) presented a paper to the White House. The paper was titled "The Space Shuttle" but officially designated "NASA Document III–31."

Things to remember while reading "NASA Document III-31: The Space Shuttle":

• Fletcher was told to offer a "best-case scenario" to make the shuttle program appealing to the United States government. Fletcher breaks his arguments down into four major areas, primarily emphasizing the importance of the United States staying ahead of the Soviet Union in the space race.
• Like President Nixon, Fletcher believes that the shuttle will usher in an age of space travel in which complicated missions will become routine and frequent.
• Fletcher notes that "Americans went on to set foot on the Moon, while the Russians have continued to expand their capabilities in near-Earth space." Since the early 1960s the Russians had been developing the Soyuz, a reusable manned spacecraft. In 1971 a three-seat Soyuz vehicle delivered two crews to the Russian space station Salyut, the world's first space station. This was an important event in the space race between the United States and the Soviet Union.

"NASA Document III-31: The Space Shuttle"

This paper outlines NASA's case for proceeding with the space shuttle. The principal points are as follows:

1. 1. The U.S. cannot forego manned space flight.
2. 2. The space shuttle is the only meaningful new manned space program that can be accomplished on a modest budget.
3. 3. The space shuttle is a necessary next step for the practical use of space. It will help
   • —space science,
   • —civilian space applications,
   • —military space applications, and
   • —the U.S. position in international competition and cooperation in space.
4. 4. The cost and complexity of today's shuttle is one-half of what it was six months ago.
5. 5. Starting the shuttle now will have significant positive effect onaerospace employment. Not starting would be a serious blow to both the morale and health of the Aerospace Industry.

The U.S. Cannot Forego Manned Space Flight

Man has worked hard to achieve—and has indeed achieved—the freedom of mobility on land, the freedom of sailing on his oceans, and the freedom of flying in the atmosphere.

And now, within the last dozen years, man has discovered that he can also have the freedom of space. Russians and Americans, at almost the same time, first tooktentative small steps beyond the earth's atmosphere, and soon learned to operate, to maneuver, and torendezvous and dock in near-earth space. Americans went on to set foot on the moon, while the Russians have continued to expand their capabilities in near-earth space.

Man has learned to fly in space, and man will continue to fly in space. And, given this fact, the United States cannot afford to forego its responsibility—to itself and to the free world—to have a part in manned space flight. Space is not all remote. Men in near-earth orbit can be less than 100 miles from any point on earth—no farther from the U.S. than Cuba. For the U.S. not to be in space, while others do have men in space, is unthinkable, and a position which Americans cannot accept.

Why the Space Shuttle?

There are three reasons why the space shuttle is the right next step in manned space flight and the U.S. space program:

First, the shuttle is the only meaningful space program which can be accomplished on a modest budget. Somewhat less expensive"space acrobatics" can be imagined but would accomplish little and be dead-ended. Additional Apollo or Skylab flights would be very costly, especially as left-over Apollo components run out, and would give diminishing returns. Meaningful alternatives, such as a space laboratory or a revisit to the moon to establish semi-permanent bases are much more expensive, and a visit to Mars, although exciting and interesting, is completely beyond our means at the present time.

Second, the space shuttle is needed to make space operations less complex and costly. Today we have to mount an enormous effort every time we launch a manned vehicle, or even a large unmanned mission. The reusable space shuttle gives us a way to avoid this. This airplane-like spacecraft will make a launch into orbit an almost routine event—at a cost 1/_10th of today's cost of space operations. How is this possible? Simply by not throwing everything away after we have used it just once—just as we don't throw away an airplane after its first trip from Washington to Los Angeles.

The shuttle even looks like an airplane, but it has rocket engines instead of jet engines. It is launched vertically, flies into orbit under its own power, stays there as long as it is needed, then glides back into the atmosphere and lands on a runway, ready for its next use. And it will do this so economically that, if necessary, it can provide transportation to and from space each week, at an annual operating cost that is equivalent to only 15 percent of today's total NASA budget, or about the total cost of a single Apollo flight. Space operations would indeed become routine.

Third, the space shuttle is needed to do useful things. The long term need is clear. In the 1980's and beyond, the low cost to orbit the shuttle gives is essential for all the dramatic and practical future programs we can conceive. One example is a space station. Such a system would allow many men to spend long periods engaged in scientific, military, or even commercial activities in a more or less permanent station which could be visited cheaply and frequently andrefurbished, by means of a shuttle. Another interesting example is revisits to the moon to establish bases there; the shuttle would take the systems needed to orbit for the assembly.

But what will the shuttle do before then? Why are routine operations so important? There is no single answer to these questions as there are many areas—in science, in civilian application, and in military applications—where we can see now that the shuttle is needed; and there will be many more by the time routine shuttle service is available.

Take, for example, space science. Today it takes two to five years to get a new experiment ready for space flight, simply because operations in space are so costly that extreme care is taken to make everything just right. And because it takes so long, many investigations that should be carried out—to get fundamental knowledge about the sun, the stars, the universe, and, therefore, about ourselves on earth—are just not undertaken. At the same time, we have already demonstrated, by taking scientists and their instruments up in a Convair 990 airplane, that space science can be done in a much more straight-forward way with a much smaller investment in time and money, and with an ability to react quickly to new discoveries, because airplane operations are routine. This is what the shuttle will do for space science.

Or take civilian space applications. Today new experiments in space communications, or in earth resources, are difficult and expensive for the same reasons as discussed under science. But with routine space operations instruments could quickly be adjusted until theoptimum combination is found for any given application—a process that today involves several satellites, several years of time, and great expense.

One can also imagine new applications that would only be feasible with the routine operation of the space shuttle. For example, it may prove possible (with an economical space transportation system, such as the shuttle) to place into orbit huge fields of solar batteries—and then beam the collected energy down to earth. This would be a truly pollution-free power source that does not require the earth'slatent energy sources. Or perhaps one could develop a global environment monitoring system, international in scope, that could help control the mess man has made of our environment. These are just two examples of what might be done with routine space shuttle operations.

What about military space applications? It is true that our military planning has not yet defined a specific need for man in space for military purposes. But will this always be the case? Have the Russians made the same decision? If not, the shuttle will be there to provide, quickly and routinely, for military operations in space, whatever they may be. It will give us a quick reaction time and the ability to flyad hoc military missions whenever they are necessary. In any event, even without new military needs, the shuttle will provide the transportation for today's rocket-launched military spacecraft at substantially reduced cost.

Finally, the shuttle helps our international position—both our competitive position with the Soviets and our prospects of cooperation with them and with other nations.

Without the shuttle when our present manned space program ends in 1973 we will surrender center stage in space to the only other nation that has the determination and capability to occupy it. The United States and the whole free world would then face a decade or more in which Soviet supremacy in space would be unchallenged. With the shuttle, the United States will have a clear space superiority over the rest of the world because of the low cost to orbit and theinherent flexibility and quick reaction capability of a reusable system. The rest of the world—the free world at least—would depend on the United States for launch of most of their payloads.

On the side of cooperation, the shuttle would encourage far greater international participation in space flight. Scientists—as well as astronauts—of many nations could be taken along, with their own experiments, because shuttle operations will be routine. We are already discussing compatible docking systems with the Soviets, so that their spacecraft and ours can join in space. Perhaps ultimately men of all nations will work together in space—in joint environmental monitoring, internationaldisarmament inspections, or perhaps even injoint commercial enterprises —and through these activities help humanity work together better on its planet earth. Is there a more hopeful way?

The Cost of the Shuttle Has Been Cut in Half

Six months ago NASA's plan for the shuttle was one involving heavy investment—$10 billion before the first manned orbital flight—in order to achieve a very low subsequent cost per flight—less than $5 million. But since then the design has been refined, and a tradeoff has been made between investment cost and operational cost per flight. The result: a shuttle that can be developed for an investment of $4.5–$5 billion over a period of six years that will still only cost around $10 million or less per flight. (This means 30 flights per year at an annual cost for space transportation of 10 percent of today's NASA total budget, or one flight per week for 15 percent.)

This reduction in investment cost was partly the result of a tradeoff just mentioned, and partly due to a series of technical changes. The orbiter has been drastically reduced in size—from a length of 206 feet down to 110 feet. But the payload carrying capacity has not been reduced: it is still 40,000 pounds in polar orbit, or 65,000pounds in an easterly orbit, in a payload compartment that measures 15 × 60 feet.

The reduction in investment cost is highly significant. It means that the peak funding requirements, in any one year, can be kept down to a level that, even in a highly constrained NASA budget, will still allow for major advances in space science and applications, as well as in aeronautics.

The Shuttle and the Aerospace Industry

The shuttle is a technological challenge requiring the kind of capability that exists today in the aerospace industry. An accelerated start on the shuttle would lead to a direct employment of 8,800 by the end of 1972, and 24,000 by the end of 1973. This cannotcompensate for the 270,000 laid off by NASA cutbacks since the peak of the Apollo program but would take up the slack of further layoffs from Skylab and the remainder of the Apollo programs.

Conclusions

Given the fact that manned space flight is part of our lives, and that the U.S. must take part in it, it is essential to reduce drastically the complexity and cost of manned space operations. Only the space shuttle will do this. It will provide both routine and quick reaction space operations for space science and for civilian and military applications. The shuttle will do this at an investment cost that fits well within the highly constrained NASA budget. It will have low operating costs, and allow 30 to 50 space flights per year at a transportation cost equivalent to 10–15 percent of today's total NASA budget.

The shuttle program is launched

The U.S. space shuttle program officially began in 1972, when President Richard M. Nixon (1913–1994; served 1969–74) announced NASA's plans to develop a multiuse spacecraft. It would perform a wider variety and greater number of missions than the traditional one-use space rocket, and at a lower cost to the taxpayer. On January 5, 1972, in a speech in San Clemente, California, President Nixon informed the American people that the United States was going to enter into the next phase of space exploration. Having already put a man on the

Moon, NASA wanted to build a fleet of ships that would make traveling to space a routine experience.

Things to remember while reading President Nixon's Remarks on the Space Shuttle Program:

• Presidents have a long tradition of being associated with major events in space travel. President Dwight D. Eisenhower (1890–1969; served 1953–61) signed the act that brought NASA into existence; President Kennedy made an important speech announcing the United States' intention to send a man to the Moon. President Ronald Reagan (1911–2004; served 1981–89) addressed the nation after the Challenger (see entry) disaster, and President George W. Bush (1946–; served 2001–; see entry) commemorated the crew of the Columbia explosion.
• Notice that President Nixon emphasizes that the space shuttle program will cost less than the Apollo missions and that shuttle flights will happen with greater regularity. These two factors were big selling points to the U.S. government and the American people. There was a sense that space travel could become "routine."
• President Nixon imagined that the United States would be able to establish a number of space stations, leading the world in space exploration and settlement. It soon became clear that such projects, while achievable, were decades away.

President Nixon's Remarks on the Space Shuttle Program

I have decided today that the United States should proceed at once with the development of an entirely new type of space transportation system designed to help transform the space frontier of the 1970's into familiar territory, easily accessible for humanendeavor in the 1980's and 90's.

This system will center on a space vehicle that can shuttle repeatedly from Earth to orbit and back. It will revolutionize transportation into near space, byroutinizing it. It will take the astronomical costs out of astronautics. In short, it will go a long way toward delivering the rich benefits of practical space utilization and the valuable spin offs from space efforts into the daily lives of Americans and all people.

The new year 1972 is a year of conclusion for America's current series of manned flights to the Moon. Much is expected from the two remaining Apollo missions—in fact, their scientific results should exceed the return from all the earlier flights together. Thus they will place a fittingcapstone on this vastly successful undertaking. But they also bring us to an important decision point—a point ofassessing what our space horizons are as Apollo ends, and of determining where we go from here.

In the scientific arena, the past decade of experience has taught us that spacecraft are an irreplaceable tool for learning about our near-Earth space environment, the Moon, and the planets, besides being an important aid to our studies of the Sun and stars. In utilizing space to meet needs on Earth, we have seen the tremendous potential of satellites for international communications and world-wide weather forecasting. We are gaining the capability to use satellites as tools in global monitoring and management of nature resources, in agricultural applications, and in pollution control. We can foresee their use in guiding airliners across the oceans and in bringing TV education to wide areas of the world.

However, all these possibilities, and countless others with direct and dramatic bearing on human betterment, can never be more than fractionally realized so long as every single trip from Earth to orbit remains a matter of special effort and staggering expense. This is why commitment to the Space Shuttle program is the right step for America to take, in moving out from our present beach-head in the sky to achieve a real working presence in space—because the Space Shuttle will give us routine access to space by sharply reducing costs in dollars and preparation time.

The new system will differ radically from all existing booster systems, in that most of this new system will be recovered and used again and again—up to one hundred times. The resulting economies may bring operating costs down as low as one-tenth of those present launch vehicles.

The resulting changes in modes of flight and re-entry will make the ride safer, and less demanding for the passengers, so that men and women with work to do in space can "commute" aloft, without having to spend years in training for the skills and rigors of old-style space flight. As scientists and technicians are actually able to accompany their instruments into space, limiting boundaries between our manned and unmanned space programmes will disappear. Development of new space applications will be able to proceedmuch faster. Repair or servicing of satellites in space will become possible, as will delivery of valuablepayloads from orbit back to Earth.

The general reliability and versatility which the Shuttle system offers seems likely to establish it quickly as the workhorse of our whole space effort, taking the place of all present launch vehicles except the very smallest and very largest.

NASA and many aerospace companies have carried out extensive design studies for the Shuttle. Congress has reviewed and approved this effort. Preparation is now sufficient for us to commence the actual work of construction with full confidence of success. In order to minimize technical and economic risks, the space agency will continue to take a cautious evolutionary approach in the development of this new system. Even so, by moving ahead at this time, we can have the Shuttle in manned flight by 1978, and operational a short time later.

It is also significant that this major new nationalenterprise will engage the best efforts of thousands of highly skilled workers and hundreds of contractor firms over the next several years. The amazing 'technology explosion' that has swept this country in the years since we ventured into space should remind us that robust activity in the aerospace industry is healthy for everyone—not just in jobs and income, but in the extension of our capabilities in every direction. The continuedpreeminence of America and American industry in the aerospace field will be an important part of the Shuttle's 'payload.'

Views of the Earth from space have shown us how small and fragile our home planet truly is. We are learning theimperatives of universal brotherhood and global ecology, learning to think and act as guardians of one tiny blue and green island in the trackless oceans of the Universe. This new program will give more people more access to the liberating perspectives of space, even as it extends our ability to cope with physical challenges of Earth and broadens our opportunities for international cooperation in low-cost, multi-purpose space missions.

'We must sail sometimes with the wind and sometimes against it', saidOliver Wendell Holmes, 'but we must sail, and not drift, nor lie at anchor.' So with man's epic voyage into space—a voyage the United States of America has led and still shall lead.

What happened next …

In cooperation with the U.S. Air Force, which had been working on a multiuse space plane program known as Dynasoar, NASA began work on the space shuttle program. Originally, it was thought that the space shuttles would be used as transport vehicles to service a massive space station and a permanently manned lunar colony. It was also hoped that the space shuttles would be used for a manned mission to Mars. The Air Force and NASA worked together—sometimes less than pleasantly—to develop a craft that would serve both as a vehicle for work in space and for defensive purposes, such as launching spy satellites.

A number of designs were debated and considered before it was finally decided that the space craft would consist of four major parts: the orbit ship—the shuttle—which could be used over and over again; a large external fuel tank; and two reusable solid-fuel booster rockets. The external fuel tank contains liquid oxygen and liquid nitrogen that power the three main engines of the orbit ship. The tank is discarded eight and one-half minutes after takeoff and breaks up in the atmosphere upon reentry. The pieces fall into the ocean. The two solid-fuel rocket boosters contain a propellant made of ammonium perchlorate (an oxidizer) and aluminum. The boosters fall off two minutes after liftoff and also land in the ocean. However, the booster rockets are equipped with parachutes to slow their descent and allow them to land safely in the ocean, where they are recovered and prepared for use on the next mission.

At launch time the ship is set upright. It explodes from the launchpad and is sent into orbit. The shuttle's stack height (its height in launch position) is 184.2 feet (56 meters), although the orbit ship alone is 122.17 feet (37.24 meters) long. The wing span is 78.06 feet (23.7 meters) and the cabin can hold up to ten astronauts, although crews of five to seven are more common. The shuttle reaches speeds of 17,321 miles (27,869 kilometers) per hour.

NASA has built seven different shuttle types. The Pathfinder and Enterprise ships were test vehicles, never intended for space missions. The five operating shuttles were Challenger, Columbia, Atlantis, Discovery, and Endeavour. The first shuttle mission was performed by Columbia, which launched on April 12, 1981, commanded by a crew of two. Challenger was completed in July 1982, Discovery in November 1983, and Atlantis in 1985. The various shuttles have flown over 130 missions combined. The space shuttle program paved the way for modern space exploration. Originally designed to be transport ships, the various shuttles have performed a number of important missions—such as making service flights to the Hubble Space Telescope (HST) and transporting crews to the Russian Mir space station and the International Space Station (ISS)—and greatly increased our knowledge of the universe. The program suffered two tragedies in its thirty-year history: the explosion of the space shuttle Challenger on January 28, 1986; and the explosion of the space shuttle Columbia on February 1, 2003. In both cases, the entire crew was killed (see Challenger and Columbia Space Shuttle Disaster entries). In 2004, as a result of the Columbia accident, NASA administrator Sean O'Keefe (1956–) announced that future shuttle flights would be canceled until safety problems had been resolved.

Many critics consider the space shuttle program to be a failure. Originally, the shuttles were supposed to reduce the cost of space missions greatly and to increase the frequency of manned space flight. NASA soon discovered, especially after the explosion of Challenger that too many missions in a short period of time can result in disaster. The low cost estimate was based on an increased number of missions, so the shuttle eventually was not cost effective because a fewer number of flights were successfully completed. However, many supporters of the space shuttle program point out that the shuttle did mark a major advance in space travel by producing a space craft capable of making numerous journeys into space and, a great percentage of the time, returning safely to Earth.

Did you know …

• A space shuttle weighs 4.5 million pounds (2.04 kilograms) at takeoff. When the orbiter lands, it weighs 230,000 pounds (104,420 kilograms).
• The first orbiter that was completed was originally called Constitution. However, after a massive write-in campaign by fans of the television show Star Trek, the ship was renamed Enterprise in honor of the famous ship from the show.
• In January 2004 President George W. Bush announced that the space shuttle will be retired from service in 2010. NASA plans to replace it with the Crew Exploration Vehicle, which is expected to conduct its first manned mission by 2014.

Consider the following …

• Some people think that investing in NASA is a waste of taxpayer money and that the money is better used trying to improve education, health care, and other domestic issues. Do you think space exploration should be a national priority? Why or why not?
• Although the space shuttles have flown many more successful missions than those that ended in disaster, space flight is still very dangerous. Do you think that NASA and President Nixon were too optimistic about how the space shuttle program would succeed? Some people argue that there was too much pressure, either from NASA or from popular opinion, to make it seem that flying in the space shuttle was as easy as driving a car, and because of that pressure, two terrible accidents resulted. Do you think we will ever get to a point where space travel is routine? Should we even have that as a goal, given how dangerous space flight is?
• If you were to become an astronaut, where would you want to fly? Why? Can you think of any experiments you might be able to conduct that might help our understanding of the universe?

For More Information

Books

Fletcher, James C. "NASA Document III-31: The Space Shuttle." In Exploring the Unknown: Selected Documents in the History of the U.S. Civil Space Program, Volume I: Organizing for Exploration. Edited by John M. Logsdon. Washington, DC: National Aeronautics and Space Administration, 1995.

Taylor, Robert. The Space Shuttle. San Diego, CA: Lucent Books, 2002.

Torres, George. Space Shuttle, A Quantum Leap. Navato, CA: Presidio Press, 1986.

Web Sites

January 28: 1986: The Challenger Disaster.http://www.chron.com/content/interactive/special/challenger (accessed on August 10, 2004).

Nixon, Richard M. Remarks on the Space Shuttle Program. NASA.http://www.hq.nasa.gov/office/pao/History/stsnixon.htm (accessed on August 10, 2004).

"Space Shuttle Columbia and Her Crew." NASA.http://www.nasa.gov/columbia (accessed on August 10, 2004).

"Space Shuttle Program." Wikipedia.http://en.wikipedia.org/wiki/Space_shuttle (accessed on August 10, 2004).

Other Sources

The Dream Is Alive. National Air and Space Museum, Smithsonian Institution. Burbank, CA: Warner Home Video, 2001 (DVD).

Aerospace: Science that deals with Earth's atmosphere and the space beyond, including travel in, and creation and manufacture of vehicles used in aerospace.

Tentative: Uncertain.

Rendezvous: Meet up with.

Refurbished: Resupplied.

Optimum: Most favorable.

Latent: Capable of becoming active though not now visible; hidden.

Ad hoc: Unplanned, improvised.

Inherent: Part of the basic nature of a person or thing; essential.

Disarmament: Laying aside arms or weapons.

Joint commercial enterprises: A business project or undertaking done by two parties for the purpose of making a profit.

Compensate: Make up, be equal to.

Endeavor: Effort.

Routinizing: Making routine or everyday.

Capstone: High point.

Assessing: Determining the rate or amount of.

Payloads: Load carried by an aircraft or spacecraft consisting of things (such as passengers or instruments) necessary to the purpose of the flight.

Enterprise: Project that is especially difficult, complicated, or risky.

Preeminence: Superiority.

Imperatives: Orders or commands.

Oliver Wendell Holmes (1809–1894): American physician, poet, and essayist.

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, 1971–1991, and Mir, 1986–2001), 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 (1973–1979) were the only exceptions to this pattern.

The U.S. shuttle system—which includes the shuttle vehicle itself, launch boosters, and other components—is 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 modules—habitable units, carried in the shuttle's cargo bay, in which astronauts carry out most of their experiments—are designed and built by the European Space Agency, and the extendible arm used to capture and release satellites—the "remote manipulator system" or Canadarm—is 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 level—literally "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 fall—is 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 payloads—the modules or satellites that it ports to orbit or back to Earth—are 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 tanks—one for liquid oxygen and the other for liquid hydrogen—covered 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 shuttle—now 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 heat—the nose and the leading edges of the wings—are 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 missions—the majority—have 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 ever—at 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): 9–15.

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

Space shuttle

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 to 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 apart during reentry on February 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 former 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, 1971–1991, and Mir, 1986–2001), 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 (1973–1979) were the only exceptions to this pattern.

The U.S. shuttle system—which includes the shuttle vehicle itself, launch boosters, and other components—is 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 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.

The STS depends partly on contributions from nations other than the U.S. For example, its Spacelab modules—habitable units, carried in the shuttle's cargo bay, in which astronauts carry out most of their experiments—are designed and built by the European Space Agency, and the extendible arm used to capture and release satellites—the "remote manipulator system" or Canadarm—is 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 level—literally "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 fall—is 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 (18 m) long in which the shuttle's payloads—the modules or satellites that it ports to orbit or back to Earth— are 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 Space-lab, 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 (47,000 m) and 212 mi (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 MPH (90 km/h). 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 tanks—one for liquid oxygen and the other for liquid hydrogen—covered 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 17 in (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 mi (105 km) and is 670 mi (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 mi (296 km) and a perigee (lowest altitude) of 46 mi (98 km). They are fired again to nudge the shuttle into a final, circular orbit with a radius of 139 mi (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 (VUR-nee-ur) 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.

Orbital activities

The space shuttles have performed a wide variety of tasks in over two decades of operation. Some examples of the kinds of activities carried out during shuttle flights include the following:

• After the launch of the Challenger on February 3, 1984 (mission STS-41B), astronauts Bruce McCandless II and Robert L. Stewart conducted untethered space walks to test the Manned Maneuvering Unit backpacks, which 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. Both satellites failed soon after release but were recovered and returned to Earth by the Discovery in 1984 (STS-51A).
• During the Challenger flight that began on April 29, 1985 (STS-51B), crew members carried out a number of experiments in Spacelab 3 to determine the effects of microgravity on living organisms and on the processing of materials. They grew crystals of mercury (II) oxide over a period of several days, observed the behavior of two monkeys and 24 rats in a microgravity environment, and studied the behavior of liquid droplets held in suspension by sound waves.
• The Discovery mission launched August 27, 1985 (STS-51I) deposited 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 had malfunctioned.
• 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.

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 shuttle—now 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 heat—the nose and the leading edges of the wings—are 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 mi (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 missions—the majority—have 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 has chosen 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 launched 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 United States 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 ten 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. Unfortunately, this has included the STS. 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 reentry, strewing debris over much of Texas and several other states and killing all seven astronauts on board. At the time of this writing, analysts identified 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 ever—at 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 space-walk to the bottom of the shuttle feasible. NSAS 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. Later testing revealed that the foam impact on the wing was forceful enough to puncture the wing.

Regardless of the exact reason, the shuttle's skin was breached, whether by mechanical damage or some other cause, and hot gasses formed a hot 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 of July 2003, the loss of the Columbia has, like the loss of the Challenger in 1986, put a temporary stop to all 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.

See also Rockets and missiles; Spacecraft, manned; Space probe.

Resources

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).

Chang, Kenneth. "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. (June 23, 1986): 9-15.

other

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 [cited January 17, 2003]. <http://www.spaceref.com/news/viewsr.html?pid=4523>.

David E. Newton
K. Lee Lerner

KEY TERMS

Booster

—A rocket engine used to raise a large spacecraft, such as the space shuttle, into orbit.

Orbiter

—The space shuttle itself; contains the cargo bay, crew cabin, main engines.

Payload

—Amount of useful material that can be lifted into space by a delivery system.

Redundancy

—The process by which two or more identical items are included in a spacecraft to increase the safety of its human passengers.

Spacelab

—A laboratory module constructed by the European Space Agency for use in the 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 modules—the areas in which astronauts carry out most of their experiments—are designed and built by the European Space Agency, and the extendable arm used to capture and release satellites—the remote manipulator system or Canadarm—is 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 shuttle—now traveling at 17,500 mi (28,000 km) per hour—and 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 heat—the nose and the leading edges of the wings—are 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