TIME: Almanac 1995

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<text id=89TT2318> <title> Sep. 04, 1989: The Last Picture Show </title> <history> TIME--The Weekly Newsmagazine--1989 Sep. 04, 1989 Rock Rolls On:Rolling Stones </history> <article> <source>Time Magazine</source> <hdr> SPACE, Page 54 The Last Picture Show </hdr><body> By Leon Jaroff Nearly 2.8 billion miles away, an artifact of man, a mere speck in the vast expanse of space, closed in on a giant, blue-hued planet. The spacecraft Voyager 2, alive and well after twelve years in space, having had dramatic rendezvous with Jupiter in 1979, Saturn in 1981 and Uranus in 1986, was approaching Neptune, the solar system's most distant planet. (Pluto, usually the outermost planet, has a highly eccentric orbit and is currently closer to the sun than is Neptune.) Accelerating to 60,980 m.p.h. relative to Neptune, the one-ton probe swooped just 3,048 miles above the frozen methane clouds that shroud the planet's north polar region. Turning sharply, it plunged toward the mysterious moon Triton, passing within 24,000 miles of its rocky surface. Then, after its spectacular -- and last -- planetary encounter, it headed for the distant fringes of the solar system for what its creators hope will be a quarter-century more of exploration. All the while, across the void, Voyager was sending back to earth images never before seen by man and volumes of information that will keep scientists busy for years. Signals from its TV cameras and scientific instruments, carried by radio waves traveling at the speed of light, arrived at earth four hours and six minutes later. Decoded at the Jet Propulsion Laboratory in Pasadena, Calif., the transmissions appeared minutes later in the form of pictures and data on television screens and computer consoles. At J.P.L. the scientists and technicians who designed Voyager and have nursed it through its long space odyssey could not contain their excitement and pride. Champagne flowed, and each new picture on the TV screens was greeted with cheers and applause. Americans watching the proceedings live on television shared their sense of accomplishment. The little unmanned spacecraft had given them an unexpectedly large bang for the buck. On the night of the encounter Triton actually upstaged Neptune, which had yielded many of its secrets to Voyager in the preceding weeks. The moon, frosty white with pink and blue blotches, was covered with cliffs, faults and glacier-like terrain with a sprinkling of craters. Scientists also spotted a smooth, roughly circular area several hundred miles across that may be the crater of an ancient "ice volcano" that once spewed frozen gases. Voyager had already revealed more about Neptune than had been learned in all the years since 1846, when German astronomer Johann Galle first spotted the planet. While still millions of miles away, the spacecraft discovered the Great Dark Spot, a violent earth-size storm in Neptune's midsection, and later it photographed six previously unknown moonlets. One of the new moons, temporarily named 1989 N1, turned out to be larger than Neptune's other long-known moon, Nereid. And Triton, thought to be about 2,500 miles in diameter, was downsized to 1,740 miles. Voyager's sensing instruments confirmed expectations that Neptune has a magnetic field and, on the day before the encounter, reported that the spacecraft had crossed the supersonic shock wave, a front created where the solar wind meets the magnetic field. By clocking the rotation of that field, J.P.L. scientists determined that a Neptunian day is only 16 hours long, rather than the previously estimated 17 or 18 hours. As Voyager sped on toward its rendezvous, its cameras picked out wispy, white, cirrus-like clouds of frozen methane gas racing across the equatorial regions. Photographs also revealed shadows of these clouds cast on a deeper layer of atmosphere some 30 miles below. Said Bradford Smith, head of the J.P.L. imaging team, "This is the first time Voyager has ever been able to see cloud shadows on any of the planets we've looked at." Scientists also discerned what seemed to be two partial rings, or ring arcs, that mysteriously seemed to disappear on subsequent pictures. But a few days later, Smith borrowed from Hollywood to announce, "The lost arc our imaging-team raiders have been looking for is not an arc; it is Neptune's first complete ring." Late last week Smith announced that five rings in all had been found. The high quality of Voyager's pictures and data belied the difficulties of operating a spacecraft so far from the sun, which at Neptune's distance looks like an intensely bright point of light. Because the planet receives only one-thousandth of the sunlight that falls on earth, Neptunian photography calls for time exposures of as long as 15 seconds. That required panning the TV cameras to avoid blurring, which Voyager accomplished by gingerly swiveling its camera platform and sometimes even yawing itself in space. Transmitting pictures and data back to earth was no less a task. By the time the 22-watt (equivalent to a small light bulb) radio signal from Voyager reached the earth, its power was only about one twenty-billionth of that needed to run an electronic digital watch. To catch as much of that faint whisper as possible, NASA had enlarged some of the already huge radio telescopes of its Deep Space Network in Australia, Spain and California. Even then, Voyager's voice was practically lost in the electromagnetic noise of space. In order to discern the messages from Neptune above that noise, J.P.L. controllers instructed Voyager to speak more slowly. The data transmission rate, which was as high as 115,200 bits a second at Jupiter, was reduced to a sluggish 21,600 bits as the craft approached Neptune. As a result, during last week's encounter, there was time for live broadcasts of only the most important pictures and data. The rest were stored on onboard tape recorders to be transmitted later. That Voyager is still performing well, let alone functioning at all, is a tribute to the genius of its designers. By 1989 standards, the spacecraft's technology is hopelessly outdated. Its command control computers have random access memories of only 8,000 bits of information, compared with today's personal computers, which have as many as 1.4 million-bit RAMs. The two TV cameras operate with obsolete vidicon tubes rather than the more reliable and efficient charge-coupled devices in modern TV cameras. Says Torrence Johnson, of the imaging team: "You couldn't find anyone to build one of those vidicon tubes today." When the Voyager team first assembled at J.P.L. in 1972, it had high hopes that NASA in the late 1970s would take advantage of a once-every-176-years alignment of the outer planets to stage a planetary grand tour. That plan would have sent two sophisticated spacecraft (one as a backup) flying by Jupiter, Saturn, Uranus and Neptune, using the gravity assist of each planet to change their course and accelerate them onward to the next one. Another pair of ships would similarly fly past Jupiter, Saturn and Pluto. Without gravity assists, the J.P.L. team argued, a direct flight to Neptune was beyond current rocket technology. In addition, the opportunity for another grand tour would not exist until the middle of the 22nd century. For political and budgetary reasons, however, NASA limited the program to two no-frills spacecraft that would explore only Jupiter and Saturn. As a result, Voyagers 1 and 2, both launched in 1977, were designed by J.P.L. engineers to operate efficiently for only about five years, more than enough time to reach Saturn. "Of course," says chief project scientist Edward Stone, "that didn't prevent us from launching Voyager 2 on exactly the same trajectory that the grand tour would have been on, hoping it would survive for twelve years." Indeed, when Voyager 1 successfully fulfilled its Saturn mission and headed out of the solar system, NASA gave the green light for Voyager 2 to proceed to Uranus and then Neptune. Now, says Stone triumphantly, "in effect, we have our grand tour." And what a tour it has been. Between them, Voyagers 1 and 2 discovered and shot spectacular photographs of new moons orbiting Jupiter and Saturn, rings around Jupiter, active volcanoes on the Jovian moon Io, and spokes and braids in Saturn's complex and brilliant rings. At Uranus, Voyager 2 found two new rings, ten new moons and a set of dust bands. It also discovered a magnetic field with an axis tilted a remarkable 59 degrees from the planet's axis of rotation. Now the spacecraft has seen its last planet and J.P.L. staffers, many of whom have spent their entire careers on the Voyager missions, are calling the Neptune encounter "the last picture show." "Between Uranus and Neptune, I went to graduate school," says Candy Hansen, who has designed many of Voyager's picture-taking programs. "I bought my house between Jupiter and Saturn. That's how I measure my life." While Hansen and most of the other members of the Voyager team will soon turn their attention to other space projects, some will stay on, as Voyager 2's mission is not yet completed. Like Voyager 1, the spacecraft is heading out of the solar system. Its cameras will soon have little to record, but its other instruments, powered by heat from radioactive plutonium in its thermal generators, will continue such tasks as ultraviolet astronomy of the stars and seeking out the edge of the solar system, the boundary marking the farthest reaches of the solar wind and the beginning of interstellar space. Finally, in 25 years or so, declining power levels and increasing distance will end any communication between Voyager and earth, and the little spacecraft will speed silently toward the stars. With it will go a recording on a twelve-inch copper disk installed aboard Voyager on the remote chance that an alien traveler will someday come upon it. The record, called Sounds of Earth, carries greetings in 60 languages and a message from then President Jimmy Carter that ends, "This record represents our hope and our determination, and our goodwill in a vast and lonely universe." --Edwin M. Reingold/Pasadena </body></article> </text>