Space Shuttle - astronomy. I INTRODUCTION Space Shuttle, spacecraft designed for transporting humans and cargo to and from orbit around Earth. The United States National Aeronautics and Space Administration (NASA) developed the shuttle in the 1970s to serve as a reusable rocket and spacecraft. This objective differed significantly from that of previous space programs in which the launch and space vehicles could be used only once. After ten years of preparation, the first space shuttle, Columbia, was launched on April 12, 1981. Today NASA has three space shuttles: Discovery, acquired in 1983; Atlantis, which arrived in 1985; and Endeavour, which joined the fleet in 1991. The Union of Soviet Socialist Republics (USSR) started a shuttle program in 1988 with the Buran space shuttle, but the program was halted in 1993. The space shuttle was initially used to deploy satellites in orbit; to carry scientific experiments such as Spacelab, a modular arrangement of experiments installed in the shuttle's cargo bay; and to carry out military missions. As the program matured, the space shuttle was also used to service and repair orbiting satellites, to retrieve and return to Earth previously deployed spacecraft, and to help build and maintain the International Space Station. The space shuttle carries a wide range of equipment, known as the payload, into space, ranging from communication, military, and astronomical satellites; space experiments for studying the apparent weightlessness (called microgravity) experienced aboard a shuttle flight; and human experimental facilities. Often, NASA collaborates with other countries by allowing them to use shuttle cargo space for special projects. The space shuttle is designed to leave Earth as a vertically launched rocket weighing up to 2.0 million kg (4.5 million lb) with 3 million kg (7 million lb) of thrust from its multiple propulsion systems. The orbiter segment returns from space--withstanding the intense heat when entering Earth's atmosphere. Flown by the shuttle crew much like an aircraft, the shuttle lands horizontally on a conventional airport runway. The crew of the shuttle is an integral part of the system and is critical to the success of each mission. The flight crew is led by the commander and backed up by the pilot--both are professional astronauts and proven pilots with extensive space systems and operations training. Their primary responsibility is to fly the shuttle as a launch vehicle, spacecraft, and aircraft. The remaining crew members--up to five more people--are responsible for the unique aspects of a particular space mission. The mission specialist is the lead astronaut and ensures that the mission meets all the objectives. Payload specialists are experts in that mission's objectives and cargo, which are usually space experiments or artificial satellites. Often the payload specialists are astronauts from other countries on board to help with a project in which their country has an interest. II SPACECRAFT AND SUPPORTING SYSTEMS The space-shuttle system, called the Space Transportation System (STS), remains the most technologically advanced and complex machine in the world. It consists of the orbiter, propulsion systems--two solid rocket boosters (SRBs) and three main engines--and an external fuel tank. A Space-Shuttle Orbiter The orbiter is both the brains and heart of the STS, and it contains the latest advances in flight control, thermal protection, and liquid-rocket propulsion. About the same size and weight as a DC-9 aircraft (a fairly small two-engine jet airplane), the orbiter is composed of the pressurized crew compartment (which can carry up to eight crew members under normal conditions and as many as ten in an emergency), the huge cargo bay, and the three main engines mounted on its aft, or rear, end. The crew cabin has three levels: the flight deck, the mid-deck, and the utility area. Uppermost is the flight deck, where the commander and pilot control the craft, surrounded by an array of switches and controls. During launch of a seven-member crew, two additional astronauts are positioned on the flight deck behind the commander and pilot. The three other crew members are in launch positions in the mid-deck, which is below the flight deck. The galley, toilet, sleep stations, and storage and experiment lockers are found in the mid-deck. Also located in the mid-deck are the side hatch for passage to and from the vehicle before and after landing, and the airlock hatch into the cargo bay and space beyond. Astronauts pass through this hatch to don their space suits and maneuvering units (called Simplified Aid for EVA Rescue, or SAFER, these units strap on an astronaut's back over the space suit and allow an astronaut to move about in space without being tethered to the shuttle). This equipment prepares astronauts for extravehicular activities (EVAs), more popularly known as spacewalks. Below the mid-deck's floor is a utility area for air and water tanks. The space shuttle's cargo bay is adaptable to hundreds of tasks. Large enough to accommodate a tour bus at 18 by 4.6 m (60 by 15 ft), the cargo bay carries satellites, spacecraft, and scientific laboratories for the modular Spacelab system to and from orbit around Earth. It also is a workstation for astronauts to repair satellites, a foundation from which to erect space structures, and a storage area for satellites retrieved from space to be returned to Earth. Mounted on the port (left, as seen while facing the nose of the shuttle) side of the cargo bay behind the crew quarters is the remote manipulator system (RMS), developed and funded by the Canadian government. The RMS (about 15 m/50 ft in length) is a robot arm and hand with three joints analogous to those of the human shoulder, elbow, and wrist. Two television cameras mounted near its elbow and wrist provide visual cues to the crew member who operates it from the rear station of the orbiter's flight deck. The RMS can move anything from satellites to astronauts to and from the cargo bay or to different points in nearby space. It has been used on many missions, deploying and retrieving various scientific and communications satellites. Three of the orbiters, Atlantis, Discovery, and Endeavour, have carried special adapters, known as the orbiter docking system, in their cargo bays for attaching to the Russian Mir space station. A tunnel connected the airlock of the shuttle to a circular mechanism that latched onto the docking module on Mir. Astronauts and cosmonauts could move between the two spacecraft without having to don spacesuits. Atlantis's docking mechanism was installed in 1995, and both Discovery and Endeavour had their docking mechanisms installed in 1997. Shuttle/Mir missions ended in 1998. Thermal tile insulation and larger flexible sheets of insulating material (also known as the thermal protection system or TPS) cover the underbelly, bottom of the wings, and other heat-bearing surfaces of the orbiter and protect it during its fiery reentry into Earth's atmosphere. In contrast to earlier piloted spacecraft such as the Apollo command module, which used material that burned and melted off in layers during reentry and could never be used again, the shuttle's silicate fiber tiles were designed to be used for 100 missions before requiring replacement. Some 24,000 individual tiles must be installed by hand on the orbiter's surfaces. These tiles are incredibly lightweight, about the density of balsa wood, and dissipate heat so quickly that a white-hot tile with a temperature of 1260°C (2300°F) can be taken from an oven and held in bare hands without injury. B Propulsion Systems The two SRBs, with their combined thrust of some 26 million newtons (about 5.8 million lb), provide most of the power for the first two minutes of flight. The SRBs take the space shuttle to an altitude of 45 km (28 mi) and a speed of 4,973 km/h (3,094 mph) before they separate and fall back into the ocean to be retrieved, refurbished, and prepared for another flight. After the boosters fall away, the three main engines continue to provide thrust. These engines are clustered at the rear end of the orbiter and have a combined thrust of almost 5.3 million newtons (almost 1.2 million lb). The space shuttle's liquid-propellant engines are the world's first reusable rocket engines. They fire for only eight minutes for each flight, just until the shuttle reaches orbit, and are designed to operate for 55 flights. The engines are very large--4.2 m (14 ft) long, and 2.4 m (8 ft) in diameter at the wide end of the cone-shaped nozzle at the rear of the orbiter. Another propulsion system takes over once the space shuttle's main engines shut down as the ship approaches the altitude at which it will begin orbiting around Earth, known as the orbital insertion point. Two orbital maneuvering system (OMS) engines, mounted on either side of the aft fuselage, provide thrust for major orbital changes. For more exacting maneuvers in orbit, 44 small rocket engines (known as the reaction control system), clustered on the shuttle's nose and on either side of the tail, are used. They have proven indispensable in performing the shuttle's important work of retrieving, launching, and repairing satellites in orbit. C External Fuel Tank The giant, cylindrical, external fuel tank, with a length of 47 m (154 ft) and a diameter of 8.4 m (27.5 ft), is the largest single piece of the space shuttle. It fuels the orbiter's three main engines. During launch, the external tank also acts as a support for the orbiter and SRBs to which it is attached. Inside separate pressurized tanks, the external tank holds the liquid hydrogen fuel and liquid oxygen oxidizer (which reacts with the hydrogen to produce combustion) that runs the shuttle's three main engines. During launch, the external tank feeds the fuel under pressure through small ducts that branch off into smaller lines that feed directly into the main engines. Some 450 kg (1,000 lb) of fuel are consumed by each of the main engines each second. The space shuttle's external fuel tank is the only part of the launch vehicle that currently is not reused. After its 1.99 million liters (526,000 gallons) of fuel are consumed during the first 8.5 minutes of flight, the external tank is jettisoned from the orbiter and breaks up in the upper atmosphere, its pieces falling into remote ocean waters. During the first 17 years of shuttle flights, the external fuel tanks were made of aluminum alloys. The tanks that the first five shuttle missions used weighed about 35,000 kg (about 77,000 lb) when empty. A design change in 1983 reduced the weight to 30,000 kg (66,000 lb) when empty. In 1998, anticipating the extra power that the shuttle will need to get to the International Space Station (ISS), which will orbit at a higher altitude than the space shuttle usually uses, NASA announced the introduction of a new tank design. The new tanks, first used in May 1998, are made of aluminum lithium, which is significantly lighter than the aluminum alloys used for previous tanks. The new tanks weigh about 27,000 kg (about 59,000 lb) when empty. III EARLY MISSIONS In its first five years, the earliest space-shuttle missions made significant contributions, beginning with the first orbital flight tests of the Columbia orbiter in April 1981; the first launch of the second orbiter (Challenger) in April 1983; the first flight of Spacelab, with 71 scientific experiments from the United States and European countries, in November 1983; the first repair of a satellite in orbit (the Solar Maximum Satellite) in April 1984; the first retrieval of satellites from orbit (Palapa and Westar) and their return to the Earth in November 1984; and the first manually assisted launch of a satellite (Syncon IV-3) from space, after retrieval and repair in orbit of the satellite Leasat in August 1985. The shuttle program was suspended for nearly three years for evaluation and modification following the explosion of the space shuttle Challenger in January 1986. IV CHALLENGER DISASTER On January 28, 1986, Challenger and its crew were destroyed shortly after launch. The failure of an O-ring seal of a joint on one of the SRBs was the primary cause of the Challenger loss. SRBs are constructed in four cylindrical sections that must be sealed together completely to prevent the escape of the intensely hot byproducts of the burning fuel during launch. O-rings are rubber rings that play a crucial part in ensuring the seal. The cold weather on the launch day made the rubber of an O-ring on the joint between the bottom two segments of the right SRB brittle, which, combined with the faulty design of the joint, allowed hot gases from the burning solid rocket fuel to escape. The gases and flames burned through the metal holding the rocket in position. When the rocket broke loose, it ruptured the side of the external fuel tank, allowing the liquid hydrogen and oxygen to mix prematurely and explode. In early February 1986, as the nation mourned the tragic loss of the seven Challenger crew members, U.S. President Ronald Reagan announced the creation of the Presidential Commission on the Space Shuttle Challenger Accident. Chaired by William P. Rogers, former secretary of state, it became known as the Rogers Commission. NASA's Challenger Data and Design Analysis Task Force also was established at this time to support the work of the Rogers Commission. More than 6,000 people were involved in the commission's four-month investigation of the accident, and some 15,000 transcript pages were taken during public and closed hearings. The commission's report was published and delivered to the president on June 6, 1986. Its recommendations included modifications of hardware and NASA procedures. During the period when the space shuttle fleet was grounded, hundreds of major and minor modifications (many of which were planned before the accident) were incorporated into the shuttle system. The SRBs were completely redesigned, and a new joint design passed stringent examination and review. The main space shuttle engines underwent the most aggressive ground-testing program in their history, equivalent in operational time to more than 36 missions. All engine improvements were certified to demonstrate improved reliability and operating safety margins, and they were incorporated into the engines used on the Discovery, Columbia, Atlantis, and Endeavour orbiters. NASA safety programs were completely reorganized as a result of another Rogers Commission recommendation. The Office of Safety, Reliability, Maintainability, and Quality Assurance was established in 1986, and it now has direct authority for safety and related quality controls for all NASA operations. Today, more people are assigned to safety and related programs, improved communications have been initiated, and the review system for compliance to new procedures is rigorous and welldefined. The new Office of Safety ensures that the highest levels of NASA's management team are aware of safety issues. V LATER MISSIONS After the Challenger accident in 1986, more than 80 shuttle missions were completed with no serious mishaps. The most notable of these were the scientific missions that launched these exploratory spacecraft: Magellan (launched May 1989), the probe designed for radar mapping of the planet Venus; Galileo (launched October 1989), the unpiloted spacecraft that reached Jupiter in December 1995; Ulysses (launched October 1990), a probe designed for study of the Sun; and the Hubble Space Telescope (launched April 1990), a high-powered telescope designed to make astronomical observations from space, away from the interference of Earth's atmosphere. In December 1993 the first Hubble Telescope Servicing Mission was successfully completed, correcting the telescope's optics and improving the electronic systems. In July 1995 the shuttle Atlantis linked up with the Russian space station Mir. This mission was the first of nine shuttle/Mir linkups between 1995 and 1998. These flights were the precursors to assembly of the International Space Station that began to be constructed in orbit in late 1998. The first docking with Mir was perhaps the most significant event in the history of spaceflight since the symbolic joining of Apollo and Soyuz spacecraft 20 years earlier (see Apollo program). It signaled a new age of cooperation in space, where exploration of the universe would be measured more in terms of what a coalition of nations had accomplished rather than what a single nation had achieved. See also Space Station. After the ceremonies following the rendezvous and docking of Atlantis to Mir, the two groups of astronauts undertook several days of joint scientific investigations inside the Spacelab module tucked in Atlantis's large cargo bay. Research in seven different medical and scientific disciplines, begun previously at Mir, also was concluded on the July 1995 mission. All of these experiments took advantage of the unique microgravity environment present on the spacecraft. Scientists hope to learn more about changes in the human body caused by spaceflight; the data collected in these experiments also may advance understanding of conditions such as anemia, high blood pressure, osteoporosis, kidney stones, balance disorders, and immune deficiencies that often occur on Earth. In March 1996 Atlantis docked again with Mir, carrying 860 kg (1,900 lb) of supplies to the space station. Atlantis also left Shannon Lucid, an American astronaut, on Mir for a planned stay of five months. Because of delays caused by problems with Atlantis, Lucid stayed aboard Mir for 188 days (more than 6 months), breaking the U.S. record for long duration spaceflight. Five more U.S. astronauts stayed aboard Mir on extended stays before shuttle/Mir missions ended in 1998, when both the United States and Russia began concentrating on International Space Station plans. Spacelab missions also ended in 1998, in hopes that the ISS will provide a new and more permanent laboratory in space. The majority of space shuttle missions in the early 2000s were devoted to construction of the ISS. In 1998 the orbiter Atlantis was overhauled to make it more compatible with the ISS. Atlantis received new displays, navigation equipment, and an airlock with which to connect to the station. Its power and cooling systems were also improved. In February 2000 Endeavour completed a mission that focused on mapping Earth's terrain. Scientists used two antennas--one located at the end of a long mast and the other in the shuttle's payload bay--to obtain high-quality, three-dimensional images that give information about topography (features such as mountains and rivers). VI COLUMBIA DISASTER AND RETURN TO SPACE The space shuttle Columbia broke apart and burned up while reentering Earth's atmosphere over Texas on February 1, 2003. The entire seven-member crew was killed as they returned to Earth after completing a series of scientific experiments. Investigation of the disaster pointed to structural failure of the heat-shielding system for the shuttle's left wing. Sensors inside the wing recorded unusually high temperatures just before NASA lost contact with the shuttle. The investigation determined that the wing was damaged during liftoff when it was struck by a piece of insulation foam from the external fuel tank, opening a hole in the left wing. On reentry, superheated gases in the atmosphere penetrated the left wing, dooming the craft and the crew. The space shuttle fleet was grounded until July 2005, when the shuttle Discovery returned to space. However, during the launch of Discovery a chunk of insulation foam broke off again from the external fuel tank, despite a more than two-year and nearly $1-billion effort to prevent a recurrence of the problem. Although the Discovery appeared to be undamaged, NASA suspended further shuttle flights until the foam problem could be studied further. Discovery returned to orbit in July 2006, when it docked with the International Space Station. Shuttle missions have concentrated on adding modules and equipment to the International Space Station, aiming for completion in 2010 when the shuttle is scheduled to be retired. A planned service mission to the Hubble Space Telescope (HST) calls for shuttle astronauts to upgrade, repair, or replace a number of working parts and scientific instruments, and to give the HST a boost to a higher orbit. The efforts should help extend the HST's scientific working life until the new James Webb Space Telescope is operational. VII FUTURE MISSIONS In the wake of the Columbia disaster, President George W. Bush called for retiring the shuttle fleet by 2010. NASA officials announced in August 2005 that they had decided to abandon the shuttle design principle and return to the use of traditional rockets to launch crew and cargo capsules. Astronaut safety and lower costs were major factors in the choice to return to Apollo-type technology. The new human space flight program is called Constellation and uses a piloted capsule called Orion that is launched atop rockets. Falling foam debris will no longer be a problem because debris cannot possibly strike the capsules. The capsule will also have a launch abort system to carry it free of the booster. The program calls for two different sizes of rockets: a smaller rocket called Ares I to launch a crew of astronauts and a larger rocket called Ares V to launch cargo capsules. Crew capsules would return to Earth by deploying parachutes after reentering the atmosphere, as in the early stages of space exploration, prior to the development of the first shuttle. The Orion capsule allows astronauts to venture beyond Earth orbit, which was not possible with the shuttle. Plans call for Constellation missions to the Moon and to Mars, and possibly to nearby asteroids. The Orion may also be used to service or repair the James Webb Space Telescope in its orbit far from Earth. Contributed By: Richard H. Kohrs Thomas L. Moser Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.
