A little bit of engineering (Несколько текстов для зачёта), страница 26

Asteroids are chunks of rock that vary in size from dust grains to tiny worlds, the largest of which is more than a third the size of Earth’s Moon. These rocky bodies, composed of debris left over from the formation of the solar system, are among the latest solar system objects to be visited by spacecraft. The first such encounter was made by the Galileo spacecraft, which passed through the solar system’s main asteroid belt on its way to Jupiter. Galileo flew within 1,600 km (1,000 mi) of the asteroid Gaspra on October 29, 1991. Galileo’s images clearly showed Gaspra's irregular shape and a surface covered with impact craters. On August 28, 1993, Galileo passed close by the asteroid 243 Ida and discovered that it is orbited by another, smaller asteroid, subsequently named Dactyl. Ida is the first asteroid known to possess its own moon. On June 27, 1997, the Near-Earth Asteroid Rendezvous (NEAR) spacecraft flew past asteroid 253 Mathilde. NEAR reached the asteroid 433 Eros and became the first spacecraft to orbit an asteroid in February 2000. The United States launched the spacecraft Deep Space 1 (DS1) in 1998 to prepare for 21st-century missions within the solar system and beyond. In July 1999 DS1 flew by the small asteroid 9969 Braille and discovered that it is composed of the same type of material as the much larger asteroid 4 Vesta. Braille may be a broken piece of Vesta, or it may have simply formed at the same time and place as Vesta in the early solar system.

Comets are icy wanderers that populate the solar system’s outermost reaches. These “dirty snowballs” are chunks of frozen gases and dust. When a comet ventures into the inner solar system, some of its ices evaporate. The comet forms tails of dust and ionized gas, and many have been spectacular sights. Because they may contain the raw materials that formed the solar system, comets hold special fascination for astronomers. Although several comets have been observed by a variety of space-born instruments, only one has been visited by spacecraft. The most famous comet of all, Halley’s Comet, made its most recent passage through the inner solar system in 1986. In March 1986 five separate spacecraft flew past Halley, including the USSR’s Vega 1 and Vega 2 probes, the Giotto spacecraft of the European Space Agency, and Japan’s Sakigake and Suisei probes. These encounters produced valuable data on the composition of the comet’s gas and dust tails and its solid nucleus. Vega 1 and 2 returned the first close-up views ever taken of a comet’s nucleus, followed by more detailed images from Giotto. Giotto went on to make a close passage to Comet P/Grigg-Skjellerup on July 10, 1992.

Piloted spaceflight presents even greater challenges than unpiloted missions. Nonetheless, the United States and the USSR made piloted flights the focus of their Cold War space race, knowing that astronauts and cosmonauts put a face on space exploration, enhancing its impact on the general public. The history of piloted spaceflight started with relatively simple missions, based in part on the technology developed for early unpiloted spacecraft. Longer and more complicated missions followed, crowned by the ambitious and successful U.S. Apollo missions to the Moon. Since the Apollo program, piloted spaceflight has focused on extended missions aboard spacecraft in Earth orbit. These missions have placed an emphasis on scientific experimentation and work in space.

At the beginning of the 1960s, the United States and the USSR were competing to put the first human in space. The Soviets achieved that milestone on April 12, 1961, when a 27-year-old pilot named Yuri Gagarin made a single orbit of Earth in a spacecraft called Vostok (East). Gagarin’s Vostok was launched by an R-7 booster, the same kind of rocket they had used to launch Sputnik. Although the Soviets portrayed Gagarin’s 108-minute flight as flawless, historians have since learned that Vostok experienced a malfunction that caused it to tumble during the minutes before its reentry into the atmosphere. However, Gagarin parachuted to the ground unharmed after ejecting from the descending Vostok.

On May 5, 1961, the United States entered the era of piloted spaceflight with the mission of Alan Shepard. Shepard was launched by a Redstone booster on a 15-minute “hop” in a Mercury spacecraft named Freedom 7. Shepard’s flight purposely did not attain the necessary velocity to go into orbit. In February 1962, John Glenn became the first American to orbit Earth, logging five hours in space. His Mercury spacecraft, called Friendship 7, had been borne aloft by a powerful Atlas booster rocket. After his historic mission, the charismatic Glenn was celebrated as a national hero.

The Soviets followed Gagarin’s flight with five more Vostok missions, including a flight of almost five days by Valery Bykovsky and the first spaceflight by a woman, Valentina Tereshkova, both in June 1963. By contrast, the longest of the six piloted Mercury flights was the 34-hour mission flown by Gordon Cooper in May 1963.

By today’s standards, Vostok and Mercury were simple spacecraft, though they were considered advanced at the time. Both were designed for the basic mission of keeping a single pilot alive in the vacuum of space and providing a safe means of return to Earth. Both were equipped with small thrusters that allowed the pilot to change the craft’s orientation in space. There was no provision, however, for altering the craft's orbit—that capability would have to wait for the next generation of spacecraft. Compared to Mercury, Vostok was both roomier and more massive, weighing 2,500 kg (5,500 lb)—a reflection of the greater lifting power of the R-7 compared with the U.S. Redstone and Atlas rockets.

Gemini Spacecraft

Ten piloted Gemini spacecraft were launched between March 1965 and November 1966. Unlike earlier American spacecraft, Gemini capsules were designed to carry two astronauts. Before returning to the earth, the crew jettisoned the resource compartment and the deorbiting system. The reentry module floated to a watery splashdown on earth using a parachute.

In early 1961—just weeks after Shepard had become the first American in space—President John F. Kennedy challenged the nation with this ambitious goal: to land a man on the Moon and return him safely to Earth by the end of the decade. With a total cost estimated at $25 billion in 1960s dollars, the Apollo program became a massive effort utilizing the combined energies of 400,000 people at NASA, other government and academic facilities, and aerospace contractors.

NASA realized, however, that it would not be possible to jump directly from the simple Mercury flights in Earth orbit to a lunar voyage. The agency needed an interim program to solve the unknowns of lunar flights. This became the Gemini program, a series of two-astronaut missions that took place in 1965 and 1966.

The Gemini missions were intended to develop and test the building blocks of a lunar flight. For instance, Gemini astronauts had to maneuver and dock two orbiting spacecraft, since astronauts would need to execute such a maneuver before and after landing on the Moon. Gemini included long-duration spaceflights of a week or more—the amount of time necessary for a lunar landing flight—as well as spacewalks that demonstrated the ability of an astronaut to perform useful work in the vacuum of space, and controlled reentry into Earth’s atmosphere. The Gemini spacecraft had less than twice the crew space of Mercury, but it was far more capable. Gemini crews could change their orbits, and even use a rudimentary onboard computer to help control their craft. Gemini was also the first spacecraft to utilize fuel cells, devices that generated electrical power by combining hydrogen and oxygen.

At the same time, the USSR was preparing a new generation of spacecraft for its own Moon program. The Soviets staged a series of intermediate flights in a craft designated Voskhod (Sunrise). Described as a new spacecraft, Voskhod was actually a converted Vostok. In October 1964 Voskhod 1 carried three cosmonauts—the first multiperson space crew—into orbit for a day-long mission. By replacing the Vostok ejection seat with a set of crew couches, designers had made room for three cosmonauts to fly, without space suits, in a craft originally designed for one.

In March 1965, just weeks before Gemini’s first piloted mission, Voskhod 2 carried two space-suited cosmonauts aloft. One of them, Alexei Leonov, became the first human to walk in space, remaining outside the craft for about ten minutes. In the vacuum of space Leonov’s suit ballooned dangerously, making it difficult for him to reenter the spacecraft. Voskhod 2 proved to be the last of the series. Further Voskhod flights had been planned, but they were canceled so that Soviet planners and engineers could concentrate on getting to the Moon.

Ten piloted Gemini missions took place in 1965 and 1966, accomplishing all of the program’s objectives. In March 1965 Gus Grissom and John Young made Gemini's piloted debut and became the first astronauts to alter their spacecraft's orbit. In June, Gemini 4’s Ed White became the first American to walk in space. Gemini 5’s Gordon Cooper and Pete Conrad captured the space endurance record with an eight-day mission. Gemini 7’s Frank Borman and Jim Lovell stretched the record to 14 days in December 1965. During their flight they were visited by Gemini 6’s Wally Schirra and Tom Stafford in the world’s first space rendezvous. Neil Armstrong and Dave Scott succeeded in making the first space docking by mating Gemini 8 to an unpiloted Agena rocket in March 1966, but their flight was cut short by a nearly disastrous episode with a malfunctioning thruster. On Gemini 11 in September 1966, Pete Conrad and Dick Gordon reached a record altitude of 1,370 km (850 mi). The final mission of the series, Gemini 12 in November 1966, saw Buzz Aldrin make a record five hours of spacewalks. At the conclusion of the Gemini program, the United States held a clear lead in the race to the Moon.

By 1967 the United States and the USSR were each preparing to test the spacecraft they planned to use for lunar missions. The Soviets had created Soyuz (Union), an Earth-orbiting version of the craft they hoped would fly cosmonauts to and from the Moon. They were also at work on a Soyuz derivative for flights into lunar orbit, and a lunar lander that would ferry a single cosmonaut from lunar orbit to the Moon’s surface and back. Two parallel Soviet Moon programs were proceeding—one to send cosmonauts around the Moon in a loop that would form a figure-8, the other to make the lunar landing.

Apollo Command and Service Module

Astronauts used the command and service modules of the Apollo spacecraft to orbit the earth, travel to the moon, and return to the earth. The command module housed the astronauts during take-off and reentry into the earth's atmosphere. The service module carried consumable supplies such as fuel, food, and water, and was detached from the command module before the astronauts reentered the atmosphere.

Meanwhile, the United States continued work on its Apollo spacecraft. Apollo featured a cone-shaped command module designed to transport a three-man crew to the Moon and back. The command module was attached to a cylindrical service module that provided propulsion, electrical power, and other essentials. Attached to the other end of the service module was a spidery lunar module. The lunar module contained its own rocket engines to allow two astronauts to descend from lunar orbit to the Moon’s surface and then lift off back into lunar orbit. The lunar module consisted of two separate sections: a descent stage and an ascent stage. The descent stage housed a rocket engine for the trip down to the Moon. The descent stage fit underneath the ascent stage, which included the crew cabin and a rocket for returning to lunar orbit. The astronauts rode to the surface of the Moon in the ascent stage with the descent stage attached. The descent stage remained on the lunar surface when the astronauts fired the ascent rocket to return to orbit around the Moon.

The year 1967 brought tragedy to both U.S. and Soviet Moon programs. In January, the crew of the first piloted Apollo mission, Gus Grissom, Ed White, and Roger Chaffee, were killed when a flash fire swept through the cabin of their sealed Apollo command module during a pre-flight practice countdown. Subsequent investigation determined that frayed wiring probably provided a spark, and the high-pressure, all-oxygen atmosphere and flammable materials in the spacecraft created the devastating inferno. In April, the Soviets launched their new generation spacecraft, Soyuz 1, with Vladimir Komarov aboard. Consisting of three modules, only one of which was designed to return to Earth, Soyuz could carry a maximum of three cosmonauts. After a day in space Komarov was forced to end the flight because of problems orienting the craft. After reentering the atmosphere the Soyuz’s parachute failed to deploy properly, and Komarov was killed when the spacecraft struck the ground.

By the end of 1967 NASA achieved a welcome success for Apollo with the first test launch of the giant Saturn V Moon rocket, designed by a team headed by von Braun. Measuring 111 m (363 ft) in length (including the Apollo spacecraft), the three-stage Saturn V was the most powerful rocket ever successfully flown. Its five first-stage engines produced a combined thrust of 33 million newtons (7.5 million lb). The first Saturn V test flight, designated Apollo 4, took place in November 1967, and propelled an unpiloted Apollo command and service module to an altitude of 18,000 km (11,000 mi) before the spacecraft returned to Earth.

In October 1968 a redesigned, fireproof command module made its piloted debut as Wally Schirra, Donn Eisele, and Walt Cunningham reached Earth orbit in Apollo 7. During the 11-day test flight, the command and service modules checked out perfectly. Apollo 7’s success paved the way for NASA to send the crew of Apollo 8, Frank Borman, Jim Lovell, and Bill Anders, on the first voyage to the Moon. Borman’s crew became the first men to ride the Saturn V booster on December 21, 1968. About two hours after launch, the Saturn’s third stage engine reignited to send Apollo 8 speeding moonward at 40,000 km/h (25,000 mph). Some 66 hours later, on December 24, 1968, they reached the Moon and fired Apollo 8’s main rocket engine to go into lunar orbit. They spent the next 20 hours circling the Moon ten times, taking photographs, making navigation sightings on lunar landmarks, and beaming live television pictures back to Earth. Just after midnight on December 25, the astronauts fired the service module’s main rocket engine to blast out of lunar orbit and onto a course for Earth. After a fiery reentry, the heat-shielded command module splashed down in the Pacific Ocean on December 27.