A little bit of engineering (562404), страница 25
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In 1973 NASA launched Mariner 10 toward a double encounter with Venus and Mercury. As it flew past Venus on February 5, 1974, Mariner 10’s cameras took the first close-up images of Venus’s clouds, including views in ultraviolet light that recorded distinct patterns in the circulation of Venus’s atmosphere.
The USSR explored Venus with their Venera series of probes. Venera 7 made the first successful planetary landing on December 15, 1970, and radioed 23 minutes of data from the Venusian surface, indicating a temperature of nearly 480°C (900°F) and an atmospheric pressure 90 times that on Earth. More Venera successes followed, and on October 22, 1975, Venera 9 landed and sent back black and white images of a rock-strewn plain—the first pictures of a planetary surface beyond Earth. Venera 10 sent back its own surface pictures three days later.
Beginning in 1978, a series of spacecraft examined Venus from orbit around the planet. These probes were equipped with radar that pierced the dense, cloudy atmosphere that hides Venus’s surface, giving scientists a comprehensive, detailed look at the terrain beneath. The first of this series, the U.S. Pioneer Venus Orbiter (see Pioneer (spacecraft)), arrived in December 1978 and operated for almost 14 years. The spacecraft’s radar data were compiled into images that showed 93 percent of the planet’s large-scale topographic features.
The Soviet Venera 15 and 16 orbiters reached Venus in October 1983, each equipped with radar systems that produced high-resolution images. In eight months of mapping operations, two spacecraft mapped much of Venus’s northern hemisphere, sending back images of mountains, plains, craters, and what appeared to be volcanoes.
After being released from the space shuttle Atlantis, NASA’s radar-equipped Magellan orbiter traveled through space and reached Venus in August 1990. During the next four years Magellan mapped Venus at very high resolution, providing detailed images of volcanoes and lava flows, craters, fractures, mountains, and other features. Magellan showed scientists that the surface of Venus is extremely well preserved and relatively young. It also revealed a history of planetwide volcanic activity that may be continuing today.
| E3 | Mars |
On July 14, 1965, the U.S. Mariner 4 flew past Mars and took pictures of a small portion of its surface, giving scientists their first close-up look at the red planet. To the disappointment of some who expected a more Earthlike world, Mariner’s pictures showed cratered terrain resembling the Moon’s surface. In August 1969 Mariner 6 and 7 sent back more detailed views of craters and the planet’s icy polar caps. On the whole, these pictures seemed to confirm the impression of a moonlike Mars.
NASA’s Mariner 9 went into orbit around Mars in November 1971, providing scientists with the first close-up views of the entire planet. Mariner 9’s pictures revealed giant volcanoes up to five times as high as Mount Everest, a system of canyons that would stretch the length of the continental United States, and—most intriguing of all—winding channels that resemble dry river valleys of Earth. Scientists realized that Mars’s evolution had been more complex and fascinating than they had suspected and that the planet was moonlike in some ways, but surprisingly Earthlike in others.
The USSR’s Mars probes were stymied by technical malfunctions. In November 1971 the Mars 2 spacecraft (see Mars (space program)) went into orbit around the planet and released a landing capsule that crashed without returning any data. Mars 2 became the first artificial object to reach the Martian surface. In December 1971 a lander released by the Mars 3 orbiter reached the surface successfully. However, it sent back only 20 seconds of video signals that included no data. In 1973 two more landing missions also failed. In 1988 the USSR made two unsuccessful attempts to explore the Martian moon Phobos. Contact with the spacecraft Phobos 1 (see Phobos (space program)) was lost due to an error by mission controllers when the spacecraft was on its way to Mars. Phobos 2 reached Martian orbit in January 1989 and sent back images of the planet, but failed before its planned rendezvous with Phobos.
The U.S. Viking probes made the first successful Mars landings in 1976. Two Viking spacecraft, each consisting of an orbiter and lander, left Earth in August and September 1975. Viking 1 went into orbit around Mars in June 1976, and after a lengthy search for a relatively smooth landing site, the Viking 1 lander touched down safely on Mars’s Chryse Planitia (Plain of Gold) on July 20, 1976. The Viking 2 lander reached Mars’s Utopia Planitia (Utopia Plain) on September 3, 1976. Each lander sent back close-up pictures of a dusty surface littered with rocks, under a surprisingly bright sky (due to sunlight reflecting off of airborne dust). The landers also recorded changes in atmospheric conditions at the surface. They searched, without success, for conclusive evidence of microbial life. The landers continued to send back data for several years, while the orbiters took thousands of high-resolution photographs of the planet.
On July 4, 1996, 20 years after Viking 1 arrived, NASA’s Mars Pathfinder spacecraft landed in Mars's Ares Vallis (Mars Valley). Pathfinder used a new landing system featuring pressurized airbags to cushion its impact. The next day, Pathfinder released a 10-kg (22-lb) rover called Sojourner, which became the first wheeled vehicle to operate on another planetary surface. While Pathfinder sent back images, atmospheric measurements, and other data, Sojourner examined rocks and soil with a camera and an Alpha Proton X-ray Spectrometer, which provided data on chemical compositions by measuring how radiation bounced back from rocks and dust. The mission ended when the spacecraft ceased responding to commands from Earth in October 1997.
NASA’s Mars Global Surveyor went into orbit around Mars in September 1997. Designed as a replacement for NASA’s Mars Observer probe, which failed before reaching Mars in 1993, Mars Global Surveyor is equipped with a high-resolution camera and instruments to study the planet’s atmosphere, topography and gravity, surface composition, and magnetic field. Global Surveyor reached orbit around Mars in the fall of 1997, but a problem with an unstable solar panel delayed the start of its mission—mapping the entire planet—for about a year. (In the meantime, Mars Global Surveyor began relaying high-resolution images of select areas in early 1998.) Its mapping operation, slated to last for one Martian year (about two Earth years), began in March 1999. Unlike previous Mars probes, Mars Global Surveyor adjusted its orbit using a technique called aerobraking, which relies on friction with the planet’s upper atmosphere—rather than rocket engines—to slow the spacecraft to bring it into a proper mapping orbit.
Mars Pathfinder and Mars Global Surveyor were part of a series of spacecraft that NASA plans to send to Mars about every 18 months. The next two spacecraft in the series, Mars Climate Orbiter and Mars Polar Lander, began their journeys to Mars in December 1998 and January 1999, respectively. Both probes reached Mars in late 1999, but Mars Climate Orbiter crashed into the planet due to a navigational error, and software defects led to the crash landing of Mars Polar Lander. Japan launched the spacecraft Nozomi (Japanese for “hope”), destined for Mars, on July 4, 1998. Nozomi contains equipment developed by scientists from around the world, including Canadian space scientists. This is the first time Canada has participated in a mission to another planet. Nozomi is scheduled to reach Mars in 2003.
| E4 | The Outer Planets |
Pioneer Space Probe
The Pioneer series of U.S. space probes was equipped with cameras and instruments to detect subatomic particles, meteorites, and electric and magnetic fields in the solar system and interstellar space.
The giant gaseous world Jupiter, the solar system’s largest planet, had its first visit from a spacecraft—Pioneer 10—on December 1, 1973. Pioneer 10 flew past Jupiter 21 months after launch and sent back images of the planet’s turbulent, multicolored atmosphere. Pioneer 10 also investigated Jupiter’s intense magnetic field, and the associated belts of trapped radiation. Acting like a slingshot, Jupiter’s powerful gravitational pull accelerated the spacecraft onto a new path that sent it out of the solar system. Pioneer 10 traveled beyond the orbit of Pluto in 1983.
Pioneer 11 made its own inspection of Jupiter, passing the planet on December 1, 1974. Like its predecessor, Pioneer 11 got a gravitational assist from Jupiter. In this case, the spacecraft was sent toward Saturn. Pioneer 11 reached this ringed giant on September 1, 1979, before heading out of the solar system. NASA maintained periodic contact with Pioneer 11 until November 1995, when the probe’s power supply was almost exhausted.
In 1977 the twin Voyager 1 and 2 probes (see Voyager) were launched on the most ambitious space exploration missions yet attempted: a grand tour of the outer solar system. Voyager 1 reached Jupiter in March 1979 and sent back thousands of detailed images of the planet’s cloud-swirled atmosphere and its family of moons. Other sensors probed the planet’s atmosphere and its magnetic field. Voyager discovered that Jupiter is encircled by a tenuous ring of dust, and found three previously unknown moons. The most surprising discovery of the Voyager probes was that the Jovian moon Io is covered with active volcanoes spewing ice and sulfur compounds into space. Io was the first world other than Earth found to be geologically active.
Voyager 1 continued on to a rendezvous with Saturn in November 1980. Its images detailed a variety of complex and sometimes bizarre phenomena within the planet’s rings. It also photographed the Saturnian moons, including planet-sized Titan. Voyager 1 found Titan’s surface obscured by a thick, opaque atmosphere of hydrocarbon smog.
Voyager 2 made its own flybys of Jupiter in July 1979 and of Saturn in August 1981. It continued outward to make the first spacecraft visits to Uranus in January 1986 and Neptune in August 1989. Like Pioneer 10 and 11, the Voyagers are now headed for interstellar space. On February 17, 1998, Voyager 1 became the most distant human-made object, reaching a distance of 10.5 billion km (6.5 billion mi) from Earth. Scientists hope it will continue sending back data well into the 21st century.
NASA’s Galileo orbiter reached Jupiter in December 1995. The spacecraft deployed a probe that entered Jupiter’s atmosphere on December 7, 1995, radioing data for 57 minutes before succumbing to intense pressures. The probe sent back the first measurements of the composition and structure of Jupiter’s atmosphere from within the atmosphere. The Galileo spacecraft then began a long-term mission to study Jupiter’s atmosphere, magnetosphere, and moons from an orbit around the planet. NASA extended the spacecraft’s mission through the year 2003. The extended mission included measurements taken simultaneously by the Galileo orbiter and by a new spacecraft, Cassini, which visited Jupiter on its way to Saturn.
Galileo Orbiter and Probe
The Galileo spacecraft, launched in 1989 with the ultimate destination of Jupiter, carried a number of scientific instruments on board to study the solar system while on route to Jupiter, including a radiometer and ultraviolet, extreme ultraviolet, and near-infrared spectrometers, which take pictures of light outside the visible range. Upon arrival at Jupiter in 1995, Galileo released a probe that plunged into the planet’s fiery atmosphere, transmitting vital scientific data before it was destroyed.
NASA’s Cassini spacecraft set out toward Saturn and Saturn’s moon Titan in October 1997. Cassini reached Jupiter at the end of the year 2000 and is scheduled to reach Saturn in 2004. After reaching Saturn, it should release a probe into Titan’s atmosphere.
| E5 | Other Solar System Missions |
Aside from the planets and their moons, space missions have focused on a variety of other solar system objects. The Sun, whose energy affects all other bodies in the solar system, has been the focus of many missions. Between and beyond the orbits of the planets, innumerable smaller bodies—asteroids and comets—also orbit the Sun. All of these celestial objects hold mysteries, and spacecraft have been launched to unlock their secrets.
A number of the earliest satellites were launched to study the Sun. Most of these were Earth-orbiting satellites. The Soviet satellite Sputnik 2, launched in 1957 to become the second satellite in space, carried instruments to detect ultraviolet and X-ray radiation from the Sun. Several of the satellites in the U.S. Pioneer series of the late 1950s through the 1970s gathered data on the Sun and its effects on the interplanetary environment. A series of Earth-orbiting U.S. satellites, known as the Orbiting Solar Observatories (OSO), studied the Sun’s ultraviolet, X-ray, and gamma-ray radiation through an entire cycle of rising and falling solar activity from 1962 to 1978. Helios 2, a solar probe created by the United States and West Germany, was launched into a solar orbit in 1976 and ventured within 43 million km (27 million mi) of the Sun. The U.S. Solar Maximum Mission spacecraft was designed to monitor solar flares and other solar activity during the period when sunspots were especially frequent. After suffering mechanical problems, in 1984 it became the first satellite to be repaired by astronauts aboard the space shuttle. The satellite Yohkoh, a joint effort of Japan, the United States, and Britain, was launched in 1991 to study high-energy radiation from solar flares. The Ulysses mission was created by NASA and the European Space Agency. Launched in 1990, the spacecraft used a gravitational assist from the planet Jupiter to fly over the poles of the Sun. The European Space Agency launched the Solar and Heliospheric Observatory (SOHO) in 1995 to study the Sun’s internal structure, as well as its outer atmosphere (the corona), and the solar wind, the stream of subatomic particles emitted by the Sun.
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