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  3. Oases in Space Earlier space stations The International Space Station (ISS) is the most complicated international scient

Oases in Space Earlier space stations The International Space Station (ISS) is the most complicated international scient

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问题                                Oases in Space
    Earlier space stations
    The International Space Station (ISS) is the most complicated international scientific project ever undertaken. First proposed in 1984, it involved the effort of sixteen nations: the United States, Canada, Japan, Russia, eleven nations of the European Space Agency, and Brazil. The first component of the ISS, Zahra ("sunshine" in Russian), was launched into orbit in 1998. A few weeks later, the crew of a U.S. space shuttle brought the second piece, Unity, and connected the two. The launch of the third major component, the Russian Avezda ("star"), was postponed by financial problems until July 2000, and the station’s first crew arrived in November. Eventually, the ISS will contain more than 100 parts and will require forty-four spaceflights to deliver them. A total of 160 spacewalks will be needed to assemble the components. The ISS was originally scheduled to be completed in 2006, although unexpected events such as the Columbia space shuttle tragedy of 2003 may delay the date. When work is finished, the station will house a full-time crew of seven astronauts and scientists and contain six scientific laboratories. With an anticipated lifetime of 10 years after completion, the ISS is not only the most complicated scientific project ever undertaken but also, at a projected cost of $ 35 billion, one of the most expensive.
    The ISS is not the first space station~ That distinction belongs to the Soviet Union’s Salyut 1. Salyut 1 was sent into orbit in 1971 but suffered setbacks. The first crew to arrive was unable to get in: There was something wrong with the hatch(舱口)! The second crew, equipped with special tools, got in and spent 24 days there. However, on the way back to Earth, a tragedy occurred. A valve(气阀)had opened by mistake and let all the air out of the capsule, and the three cosmonauts, who were not wearing space suits, died during the descent. In all, there were six successful Salyut stations. The first -- and only American space station, Skylab, was launched in 1973. To save money, the Americans used the third stage of a Saturn V booster rocket left over from the Apollo moon missions, and so Skylab was much roomier than the Soviet stations. Three crews spent time on Skylab, but the station had to be abandoned in 1975 because there was simply no way to get to it. The United States had used up its Apollo rockets and the first space shuttle wouldn’t be launched until 1981. Eventually, Skylab’s orbit decayed, and the station fell to Earth in 1979. At the time, some people feared that the debris(碎片)might land in an inhabited area, and a few people even built "Skylab shelters.’ However, there was no reason to panic; Skylab burned up harmlessly over Australia. In 1986, the Soviet Union launched another station, Mir ("peace"). Although damaged by an on-board fire and a collision with a supply rocket, Mir stayed in orbit for 15 years, and both U.S. and Russian crewmen, who would later serve on the ISS, trained on Mir.
    New designs for space stations
    The ISS and earlier space stations are a far cry from the space stations described by science fiction writers and dreamers, and even by scientists earlier in the century. After World War Ⅱ, many German rocket scientists who had worked on weapons programs immigrated to the United States and the Soviet Union. Werner yon Braun, the most famous of these scientists, played a vital role in the early days of the U.S. space program. It was Von Braun who decided that a large space station was essential to the exploration of space, a first step that would provide a stopping place on the way to the moon and the planets. In the March 1952 edition of Collier’s Magazine, Von Braun contributed an article about the proposed station and introduced the idea of a wheel-shaped design. Illustrated by the artist Charles Bonestell, this issue popularized the "spinning wheel" or "donut in the sky" design for space ships, which soon became the public’s idea of what a space station should look like. Arthur C. Clarke’s collection of stories Islands in the Sky (1952) and Murray Leinster’s novel Platform in Space (1953) were set on fictional space stations of this kind. Wheel-shaped stations were also featured in science fiction movies. There is a memorable scene in Stanley Kubrick’s film 2001: A Space Odyssey (1969) in which a shuttle rocket gracefully docks with a space station to the accompaniment of The Blue Danube Waltz. The popular television series Deep Space 9 and Babylon 5 both featured wheel-shaped space stations.
    NASA began focusing attention on space station design in the mid-1970s. In 1975, a series of studies conducted at Stanford University proposed that clusters of massive space stations, each capable of housing large populations, be constructed at the Lagrange points. These are the five points in space where the moon’s gravity and the Earth’s gravity are counterbalanced. A space station placed at a Lagrange point is not pulled toward the Earth or the Moon: Unlike the International Space Station, a Lagrange station does not require boosting by rocket engines to stay in orbit. These huge stations were to be built to last for hundreds of years. According to the studies, the materials needed to build the station could be mined from the moon. Gigantic magnetic catapults on the moon could then hurl the millions of components out to the Lagrange points. To pay for the station’s construction and upkeep, solar panels could collect energy from the sun and, for a price, send it by tight-beam microwaves back to Earth. The stations would contain residential, industrial, and agricultural zones. The inhabitants of the colonies would include not just engineers and astronauts but also farmers, factory workers, teachers, merchants, doctors, artists, and people of every occupation. A scientist named Gerald O’Neill wrote a popular book called High Frontier in 1975 to promote Lagrange stations, and an international group, the L-5 Society, named after one of the Lagrange points, was formed to encourage governments to build Lagrange stations.
    Several types of Lagrange stations were designed by the United Stations. Island 3, also known as the Sunflower Design or the O’Neill Cylinder, was the most ambitious design. It consisted of a huge cylindrical structure 36 kilometers long and 6.3 kilometers in diameter. The interior surface of the cylinder could be landscaped with features such as lakes, waterfalls, forests, and mountains. It could house up to a million inhabitants who would live in towns and villages set in a parklike environment. The cylinder would spin on its axis, creating "gravity," and it would be so large that it would generate its own weather. Inhabitants and tourists could enjoy such unique recreational opportunities as zero-gravity "flying" at the center of the cylinder.
    A bright future for space stations?
    Within a decade, government enthusiasm for the Lagrange stations vanished. NASA no longer had enough money to undertake projects so ambitious. As the energy crises of the 1970s cased, the prime reason for building such stations — to provide a cheap, dependable supply of energy from space — no longer seemed so urgent. Space engineers began to focus their attention on more modest projects, such as the ISS. But interest in immense space stations has never completely died. As their continued appearance in science fiction movies shows, these "oases in space" still seem to have a firm grip On people’s imagination.
A space station placed at a Lagrange point is not pulled toward the Earth or the Moon because ______.
选项
答案the moon’s gravity and the Earth’s gravity are counterbalanced
解析
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