A little bit of engineering (Несколько текстов для зачёта), страница 30

For the Skylab space station, designers had the luxury of creating several different kinds of environments for different purposes. For example, Skylab had its own wardroom, bathroom, and sleeping quarters. Designers have tried several different approaches to work spaces on spacecraft. Most rooms on Skylab were designed like rooms on Earth with a definite floor and ceiling. However, Skylab’s multiple docking adaptor had instrument panels on each wall, and each had its own frame of reference. Thanks to weightlessness, this was not a problem: Astronauts reported that they were able to shift their own sense of up and down to match their surroundings. When necessary, ceiling became floor and vice versa. On Salyut and Mir, the ceilings and floors were painted different colors to aid cosmonauts in orienting themselves. Because simulators on Earth were given the same color scheme, the cosmonauts were accustomed to it when they lifted off.

To help astronauts anchor themselves while they work in weightlessness, designers have equipped spacecraft with a variety of devices, including handholds, harnesses, and foot restraints. Foot restraints have taken a number of forms. Skylab crews used special shoes that could lock into a grid-like floor. Apollo astronauts used shoes equipped with strips of Velcro that stuck to Velcro strips on the capsule floor. Space shuttle astronauts have even used strips of tape on the floor as temporary foot restraints.

Astronauts and cosmonauts who perform spacewalks use a variety of devices to aid in mobility and in anchoring the body in weightlessness. Any surface along which astronauts move is fitted with handholds, which the astronauts use to pull themselves along. Foot restraints allow astronauts to remain anchored in one spot, something that is often essential for tasks requiring the use of both hands. During many spacewalks, astronauts use tethers to keep themselves from drifting away from the spacecraft. Sometimes, however, astronauts fly freely as they work by wearing backpacks with thrusters to control their direction and movement.

Astronauts who have conducted spacewalks report that the most difficult tasks are those that involve using their gloved hands to grip or manipulate tools and other gear. Because the suit—including its gloves—is pressurized, closing the hand around an object requires constant effort, like squeezing a tennis ball. After a few hours of this work, forearms and hands become fatigued. The astronauts must also keep careful track of tools and parts to prevent them from floating away. In general, designers of space hardware strive to make any kind of assembly or repair work in space as simple as possible.

Space exploration requires more than just science—it requires an enormous amount of money. The amount of money that a country is willing to invest in space exploration depends on the political climate of the time. During the Cold War, a period of tense relations between the United States and the USSR, both countries poured huge amounts of money into their space programs, because many of the political and public opinion battles were being fought over superiority in space. After the Cold War, space exploration budgets in both countries shrank dramatically.

Space exploration became possible at the height of the Cold War, and superpower competition between the United States and the USSR gave a boost to space programs in both nations. Indeed, the primary impact of Sputnik was political—in the United States Sputnik triggered nationwide concern about Soviet technological prowess. When the USSR succeeded in putting the first human into space, it only added to the disappointment and shame felt by many Americans, and especially by President Kennedy. Against this background, Alan Shepard’s Mercury flight on May 5, 1961, was a welcome cause for celebration. Twenty days later Kennedy told Congress, “I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth.” This was the genesis of the Apollo program. Although there were other motivations for going to the Moon—scientific exploration among them—Cold War geopolitics was the main push behind the Moon race. Cold War competition also affected the unpiloted space programs of the United States and USSR.

During the piloted programs of the Moon race, the pressure of competition caused Soviet leaders to order a number of “space spectaculars,” as much for their propaganda value as for their contributions. Each Voskhod flight entailed significant risks to the cosmonauts—the Voskhod 1 crew flew without space suits, while Voskhod 2’s Alexei Leonov was almost unable to reenter his craft following his historic spacewalk. But the space spectacular the Soviets wanted most of all—a piloted mission around the Moon in time for the 50th anniversary of the Russian revolution—never came to pass. By December 1968, when the Apollo 8 astronauts flew around the Moon, it was clear that victory in the Moon race had gone to the United States.

The achievement of Kennedy’s goal, with the Apollo 11 lunar landing mission, signaled a new era in space exploration in the United States—but not as NASA had hoped. Instead of accepting NASA’s proposals for a suite of ambitious post-Apollo space programs, Congress backed off on space funding, with the space shuttle as the only major space program to gain approval. In time it became clear that the lavish space budgets of the 1960s had been a product of a unique time in history, in which space was the most visible arena for superpower competition.

Tensions between the superpowers eased somewhat in the early 1970s, and the United States and USSR joined forces for the Apollo-Soyuz mission in 1975. Nevertheless, Cold War suspicions continued to influence space planners in both nations in the 1970s and 1980s. Both sides continued to spend enormous sums on missiles and nuclear warheads. Missiles of the Cold War arms race were designed to fly between continents on a path that took them briefly into space during their journeys. In the United States, a great deal of research went into a space-based antimissile system called the Strategic Defense Initiative (known to the public as Star Wars), which was never built. The stockpiling of missiles was eventually slowed by the Strategic Arms Limitation Talks (SALT) treaties.

In the USSR, concerns over possible offensive uses of the U.S. space shuttle helped prompt the development of the heavy-lift launcher Energia and the space shuttle Buran. Economic hardships, however, forced the suspension of both programs. The economy worsened after the collapse of the USSR in 1991, threatening the now-Russian space program with extinction.

In 1993 the U.S. government redefined NASA’s plans for an international space station to include Russia as a partner, a development that would not have been possible before the end of the Cold War. An era of renewed cooperation in space between Russia and the United States followed, highlighted by flights of cosmonauts on the space shuttle and astronauts on the Mir space station.

Meanwhile, other nations have staged their own programs of unpiloted and piloted space missions. Many have been conducted by the European Space Agency (ESA), formed in 1975, whose 13 member nations include France, Italy, Germany, and the United Kingdom. European astronauts visited Mir and have flown on shuttle missions. Since the late 1970s, a series of European rockets called Ariane have launched a significant percentage of commercial satellites. ESA’s activities in planetary exploration have included probes such as Huygens, which is scheduled to land on Saturn’s moon Titan in 2004 as part of NASA’s Cassini mission.

China, Japan, and India have each developed satellite launchers. None have created rockets powerful enough to put piloted spacecraft into orbit. However, Japan has joined Canada, Russia, and the ESA in contributing hardware and experiments to the International Space Station.

One aspect of space exploration that has changed little over time is its cost. To some extent the ability to carry out a vigorous space program is a measure of a nation’s economic vitality. For example, Russia has had difficulties staying on schedule with its contributions to the International Space Station—a reflection of the unstable Russian economy.

Cost has always been a central factor in the political standing of space programs. The enormous expense of the Apollo Moon program (roughly $100 billion in 1990s dollars) prompted critics to say that the program could have been carried out far more cheaply by robotic missions. While that claim is oversimplified—no robot has yet equaled the performance of a skilled observer—it reveals how vulnerable space programs are to budget cuts. The reusable space shuttle failed to significantly lower the cost of placing satellites in low Earth orbit, as compared with throwaway launchers like the Saturn V and the Titan III. Cost, not scientific potential, is usually the most significant factor for a nation in deciding whether to adopt a major space program. In the United States budgetary process, space funding must compete in a very visible way with expenditures for social programs and other concerns. Taking inflation into account, Congress has steadily trimmed NASA’s allotments, forcing the agency to reduce its number of employees to pre-Apollo levels by the year 2000.

In response to the high cost of space access, the late 1990s saw renewed efforts to develop a single-stage, reusable space vehicle. The situation also strengthened arguments that in the future, the most expensive space programs should be carried out by a consortium of nations. Most scientists envision a program for sending humans to Mars as an international one, primarily as a cost-sharing measure. Still, the mix of scientific, political, and other motivations has yet to bring about such a venture, and it may be years or even decades before international piloted interplanetary voyages become reality.

The future of space exploration depends on many things. It depends on how technology evolves, how political forces shape rivalries and partnerships between nations, and how important the public feels space exploration is. The near future will see the continuation of human spaceflight in Earth orbit and unpiloted spaceflight within the solar system. Piloted spaceflight to other planets, or even back to the Moon, still seems far away. Any flight to other solar systems is even more distant, but a huge advance in space technology could propel space exploration into realms currently explored only by science fiction.

The 1968 film 2001: A Space Odyssey depicted commercial shuttles flying to and from a giant wheel-shaped space station in orbit around Earth, bases on the Moon, and a piloted mission to Jupiter. The real space activities of 2001 will not match this cinematic vision, but the 21st century will see a continuation of efforts to transform humanity into a spacefaring species.

The International Space Station was scheduled to become operational in the first years of the new century. NASA plans to operate the space shuttle fleet at least through the year 2012 before phasing in a replacement—possibly a single-stage-to-orbit (SSTO) vehicle. However, some experts predict that the SSTO is too difficult a goal to be achieved that soon, and that a different kind of second-generation shuttle would be necessary—perhaps a two-stage, reusable vehicle much like the current shuttle. In a two-stage launcher, neither stage is required to do all the work of getting into orbit. This results in less stringent specifications on weight and performance than are necessary for an SSTO.

Perhaps the most difficult problem space planners face is how to finance a vigorous program of piloted space exploration, in Earth orbit and beyond. In 2001 no single government or international consortium had plans to send people back to the Moon, much less to Mars. Such missions are unlikely to happen until the perceived value exceeds their cost.

Some observers, such as Apollo 11 astronaut Buzz Aldrin, believe the solution may lie in space tourism. By conducting a lottery for tickets on Earth-orbit “vacations,” a nonprofit corporation could generate revenue to finance space tourism activities. In addition, the vehicles developed to carry passengers might find later use as transports to the Moon and Mars. Several organizations are pushing for the development of commercial piloted spaceflight. In 1996 the U.S. X-Prize Foundation announced that it would award $10 million to the first private team to build and fly a reusable spacecraft capable of carrying three individuals to a height of at least 100 km (62 mi). By 2000, 16 teams had registered for the competition, with estimates of first flights in 2001.

One belief shared by Aldrin and a number of other space exploration experts is that future lunar and Martian expeditions should not be Apollo-style visits, but rather should be aimed at creating permanent settlements. The residents of such outposts would have to “live off the land,” obtaining necessities such as oxygen and water from the harsh environment. On the Moon, pioneers could obtain oxygen by heating lunar soil. In 1998 the Lunar Prospector discovered evidence of significant deposits of ice—a valuable resource for settlers—mixed with soil at the lunar poles. On Mars, oxygen could be extracted from the atmosphere and water could come from buried deposits of ice.

The future of piloted lunar and planetary exploration remains largely unknown. Most space exploration scientists believe that people will be on the Moon and Mars by the middle of the 21st century, but how they get there—and the nature of their visits—is a subject of continuing debate. Clearly, key advances will need to be made in lowering the cost of getting people off Earth, the first step in any human voyage to other worlds.

The space agencies of the world planned a wide array of robotic missions for the final years of the 20th century and the opening decade of the 21st century. NASA’s Mission to Planet Earth (MTPE) Enterprise is designed to study Earth as a global system, and to document the effects of natural changes and human activity on the environment. The Earth Observing System (EOS) spacecraft form the cornerstone of the MTPE effort. Terra, the first EOS spacecraft, was launched in December 1999. It began providing scientists with data and images in April 2000.