A little bit of engineering (562404), страница 24
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News of the first Sputnik intensified efforts to launch a satellite in the United States. The initial U.S. satellite launch attempt on December 6, 1957, failed disastrously when the Vanguard launch rocket exploded moments after liftoff. Success came on January 31, 1958, with the launch of the satellite Explorer 1. Instruments aboard Explorer 1 made the first detection of the Van Allen belts, which are bands of trapped radiation surrounding Earth (see Radiation Belts). This launch also represented a success for Wernher von Braun, who had been brought to the United States with many of his engineers after World War II. Von Braun’s team had created the Jupiter C (an upgraded version of their Redstone missile), which launched Explorer 1.
The satellites that followed Sputnik and Explorer into Earth orbit provided scientists and engineers with a variety of new knowledge. For example, scientists who tracked radio signals from the U.S. satellite Vanguard 1, launched in March 1958, determined that Earth is slightly flattened at the poles. In August 1959 Explorer 6 sent back the first photo of Earth from orbit. Even as these satellites revealed new details about our own planet, efforts were underway to reach our nearest neighbor in space, the Moon.
| B | Unpiloted Lunar Missions |
Early in 1958 the United States and the USSR were both working hard to be the first to send a satellite to the Moon. Initial attempts by both sides failed. On October 11, 1958, the United States launched Pioneer 1 on a mission to orbit the Moon. It did not reach a high enough speed to reach the Moon, but reached a height above Earth of more than 110,000 km (more than 70,000 mi). In early December 1958 Pioneer 3 also failed to leave high Earth orbit. It did, however, discover a second Van Allen belt of radiation surrounding Earth.
On January 2, 1959, after two earlier failed missions, the USSR launched Luna 1, which was intended to hit the Moon. Although it missed its target, Luna 1 did become the first artificial object to escape Earth orbit. On September 14, 1959, Luna 2 became the first artificial object to strike the Moon, impacting east of the Mare Serentitatis (Sea of Serenity). In October 1959, Luna 3 flew around the Moon and radioed the first pictures of the far side of the Moon, which is not visible from Earth.
In the United States, efforts to reach the Moon did not resume until 1962, with a series of probes called Ranger. The early Rangers were designed to eject an instrument capsule onto the Moon’s surface just before the main spacecraft crashed into the Moon. These missions were plagued by failures—only Ranger 4 struck the Moon, and the spacecraft had already ceased functioning by that time. Rangers 6 through 9 were similar to the early Rangers, but did not have instrument packages. They carried television cameras designed to send back pictures of the Moon before the spacecraft crashed. On July 31, 1964, Ranger 7 succeeded in sending back the first high-resolution images of the Moon before crashing, as planned, into the surface. Rangers 8 and 9 repeated the feat in 1965.
By then, the United States had embarked on the Apollo program to land humans on the Moon (see the Piloted Spaceflight section of this article for a discussion of the Apollo program). With an Apollo landing in mind, the next series of U.S. lunar probes, named Surveyor, was designed to “soft-land” (that is, land without crashing) on the lunar surface and send back pictures and other data to aid Apollo planners. As it turned out, the Soviets made their own soft landing first, with Luna 9, on February 3, 1966. Luna 9 radioed the first pictures of a dusty moonscape from the lunar surface. Surveyor 1 successfully reached the surface on June 2, 1966. Six more Surveyor missions followed; all but two were successful. The Surveyors sent back thousands of pictures of the lunar surface. Two of the probes were equipped with a mechanical claw, remotely operated from Earth, that enabled scientists to investigate the consistency of the lunar soil.
At the same time, the United States launched the Lunar Orbiter probes, which began circling the Moon to map its surface in unprecedented detail. Lunar Orbiter 1 began taking pictures on August 18, 1966. Four more Lunar Orbiters continued the mapping program, which gave scientists thousands of high-resolution photographs covering nearly all of the Moon.
Beginning in 1968 the USSR sent a series of unpiloted Zond probes—actually a lunar version of their piloted Soyuz spacecraft—around the Moon. These flights, initially designed as preparation for planned piloted missions that would orbit the Moon, returned high-quality photographs of the Moon and Earth. Two of the Zonds carried biological payloads with turtles, plants, and other living things.
Although both the United States and the USSR were achieving successes with their unpiloted lunar missions, the Americans were pulling steadily ahead in their piloted program. As their piloted lunar program began to lag, the Soviets made plans for robotic landers that would gather a sample of lunar soil and carry it to Earth. Although this did not occur in time to upstage the Apollo landings as the Soviets had hoped, Luna 16 did carry out a sample return in September 1970, returning to Earth with 100 g (4 oz) of rock and soil from the Moon’s Mare Fecunditatis (Sea of Fertility). In November 1970 Luna 17 landed with a remote-controlled rover called Lunakhod 1. The first wheeled vehicle on the Moon, Lunakhod 1 traveled 10.5 km (6.4 mi) across the Sinus Iridium (Bay of Rainbows) during ten months of operations, sending back pictures and other data. Only three more lunar probes followed. Luna 20 returned samples in February 1972. Lunakhod 2, carried aboard the Luna 21 lander, reached the Moon in January 1973. Then, in August 1976 Luna 24 ended the first era of lunar exploration.
Exploration of the Moon resumed in February 1994 with the U.S. probe called Clementine, which circled the Moon for three months. In addition to surveying the Moon with high-resolution cameras, Clementine gathered the first comprehensive data on lunar topography using a laser altimeter. Clementine’s laser altimeter bounced laser beams off of the Moon’s surface, measuring the time they took to come back to determine the height of features on the Moon.
In January 1998 NASA’s Lunar Prospector probe began circling the Moon in an orbit over the Moon’s north and south poles. Its sensors conducted a survey of the Moon’s composition. In March 1998 the spacecraft found tentative evidence of water in the form of ice mixed with lunar soil at the Moon’s poles. Lunar Prospector also investigated the Moon’s gravitational and magnetic fields. Controllers intentionally crashed the probe into the Moon in July 1999, hoping to see signs of water in the plume of debris raised by the impact. Measurements taken by instruments around Earth, however, did not find evidence of water after the crash, nor did they rule out the existence of water.
| C | Scientific Satellites |
Years before the launch of the first artificial satellites, scientists anticipated the value of putting telescopes and other scientific instruments in orbit around Earth. Orbiting satellites can view large areas of Earth or can provide views of space unobstructed by Earth’s atmosphere.
| C1 | Earth-Observing Satellites |
One main advantage of putting scientific instruments into space is the ability to look down at Earth. Viewing large areas of the planet allows meteorologists, scientists who research Earth’s weather and climate, to study large-scale weather patterns (see Meteorology). More detailed views aid cartographers, or mapmakers, in mapping regions that would otherwise be inaccessible to people. Researchers who study Earth’s land masses and oceans also benefit from having an orbital vantage point.
Beginning in 1960 with the launch of U.S. Tiros I, weather satellites have sent back television images of parts of the planet. The first satellite that could observe most of Earth, NASA’s Earth Resources Technology Satellite 1 (ERTS 1, later renamed Landsat 1), was launched in 1972. Landsat 1 had a polar orbit, circling Earth by passing over the north and south poles. Because the planet rotated beneath Landsat’s orbit, the satellite could view almost any location on the Earth once every 18 hours. Landsat 1 was equipped with cameras that recorded images not just of visible light but of other wavelengths in the electromagnetic spectrum (see Electromagnetic Radiation). These cameras provided a wealth of useful data. For example, images made in infrared light let researchers discriminate between healthy crops and diseased ones. Six additional Landsats were launched between 1975 and 1999.
The success of the Landsat satellites encouraged other nations to place Earth-monitoring satellites in orbit. France launched a series of satellites called SPOT beginning in 1986, and Japan launched the MOS-IA (Marine Observation System) in 1987. The Indian Remote Sensing satellite, IRS-IA, began operating in 1988. An international team of scientists and engineers launched the Terra satellite in December 1999. The satellite carries five instruments for observing Earth and monitoring the health of the planet. NASA, a member organization of the team, released the first images taken by the satellite in April 2000.
| C2 | Astronomical Satellites |
Astronomical objects such as stars emit radiation, or radiating energy, in the form of visible light and many other types of electromagnetic radiation. Different wavelengths of radiation provide astronomers with different kinds of information about the universe. Infrared radiation, with longer wavelengths than visible light, can reveal the presence of interstellar dust clouds or other objects that are not hot enough to emit visible light. X rays, a high-energy form of radiation with shorter wavelengths than visible light, can indicate extremely high temperatures caused by violent collisions or other events. Earth orbit, above the atmosphere, has proved to be an excellent vantage point for astronomers. This is because Earth’s atmosphere absorbs high-energy radiation, such as ultraviolet rays, X rays, and gamma rays. While such absorption shields the surface of Earth and allows life to exist on the planet, it also hides many celestial objects from ground-based telescopes. In the early 1960s, rockets equipped with scientific instruments (called sounding rockets) provided brief observations of space beyond our atmosphere, but orbiting satellites have offered far more extensive coverage.
Britain launched the first astronomical satellite, Ariel 1, in 1962 to study cosmic rays and ultraviolet and X-ray radiation from the Sun. In 1968 NASA launched the first Orbiting Astronomical Observatory, OAO 1, equipped with an ultraviolet telescope. Uhuru, a U.S. satellite designed for X-ray observations, was launched in 1970. Copernicus, officially designated OAO 3, was launched in 1972 to detect cosmic X-ray and ultraviolet radiation. In 1978 NASA’s Einstein Observatory, officially designated High-Energy Astrophysical Observatory 2 (HEAO 2), reached orbit, becoming the first X-ray telescope that could provide images comparable in detail to those provided by visible-light telescopes. The Infrared Astronomical Satellite (IRAS), launched in 1983, was a cooperative effort by the United States, The Netherlands, and Britain. IRAS provided the first map of the universe in infrared wavelengths and was one of the most successful astronomical satellites. The Cosmic Ray Background Explorer (COBE) was launched in 1989 by NASA and discovered further evidence for the big bang, the theoretical explosion at the beginning of the universe.
The Hubble Space Telescope was launched in orbit from the U.S. space shuttle in 1990, equipped with a 100-in (250-cm) telescope and a variety of high-resolution sensors produced by the United States and European countries. Flaws in Hubble’s mirror were corrected by shuttle astronauts in 1993, enabling Hubble to provide astronomers with spectacularly detailed images of the heavens. NASA launched the Chandra X-Ray Observatory in 1999. Chandra is named after American astrophysicist Subrahmanyan Chandrasekhar and has eight times the resolution of any previous X-ray telescope.
| D | Other Satellites |
In addition to observing Earth and the heavens from space, satellites have had a variety of other uses. A satellite called Corona was the first U.S. spy satellite effort. The program began in 1958. The first Corona satellite reached orbit in 1960 and provided photographs of Soviet missile bases. In the decades that followed, spy satellites, such as the U.S. Keyhole series, became more sophisticated. Details of these systems remain classified, but it is has been reported that they have attained enough resolution to detect an object the size of a car license plate from an altitude of 160 km (100 mi) or more.
Other U.S. military satellites have included the Defense Support Program (DSP) for the detection of ballistic missile launches and nuclear weapons tests. The Defense Meteorological Support Program (DMSP) satellites have provided weather data. And the Defense Satellite Communications System (DSCS) has provided secure transmission of voice and data. White Cloud is the name of a U.S. Navy surveillance satellite designed to intercept enemy communications.
Satellites are becoming increasingly valuable for navigation. The Global Positioning System (GPS) was originally developed for military use. A constellation of GPS satellites, called Navstar, has been launched since 1978; each Navstar satellite orbits Earth every 12 hours and continuously emits navigation signals. Military pilots and navigators use GPS signals to calculate their precise location, altitude, and velocity, as well as the current time. The GPS signals are remarkably accurate: Time can be figured to within a millionth of a second, velocity within a fraction of a kilometer per hour, and location to within a few meters. In addition to their military uses, slightly lower resolution versions of GPS receivers have been developed for civilian use in aircraft, ships, and land vehicles. Hikers, campers, and explorers carry handheld GPS receivers, and some private passenger automobiles now come equipped with a GPS system.
| E | Planetary Studies |
Even as the United States and the USSR raced to explore the Moon, both countries were also readying missions to travel farther afield. Earth’s closest neighbors, Venus and Mars, became the first planets to be visited by spacecraft in the mid-1960s. By the close of the 20th century, spacecraft had visited every planet in the solar system, except for the outermost planet—tiny, frigid Pluto.
| E1 | Mercury |
Only one spacecraft has visited the solar system’s innermost planet, Mercury. The U.S. probe Mariner 10 flew past Mercury on March 29, 1974, and sent back close-up pictures of a heavily cratered world resembling Earth’s Moon. Mariner 10’s flyby also helped scientists refine measurements of the planet’s size and density. It revealed that Mercury has a weak magnetic field but lacks an atmosphere. After the first flyby, Mariner 10’s orbit brought it past Mercury for two more encounters, in September 1974 and March 1975, which added to the craft’s harvest of data. In its three flybys, Mariner 10 photographed 57 percent of the planet’s surface.
| E2 | Venus |
The U.S. Mariner 2 probe became the first successful interplanetary spacecraft when it flew past Venus on December 14, 1962. Mariner 2 carried no cameras, but it did send back valuable data regarding conditions beneath Venus’s thick, cloudy atmosphere. From measurements by Mariner 2’s sensors, scientists estimated the surface temperature to be 400°C (800°F—hot enough to melt lead), dispelling any notions that Venus might be very similar to Earth.
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