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Explorers in space for 25 years


Not fare well,

But fare forward, voyagers

- T.S. Eliot

IF THERE were a Hall of Fame for NASA spacecraft, Stamatios Krimigis knows which would get his vote.

Not the stodgy Space Shuttle or the slick new International Space Station. No, he would nominate a pair of aging one-ton space probes that most of America has probably forgotten.

Launched a quarter-century ago this summer, Voyager 1 and Voyager 2 have been among the most reliable and prolific of the National Aeronautics and Space Administration's fleet of mechanical foreign correspondents. Whether sending home eye-popping images of Saturn's rocky rings or the first measurements of magnetic fields on Uranus and Neptune, their journey to the outer planets is considered the most successful of 20th-century space science.

"They essentially rewrote the book of our knowledge of the solar system," says Krimigis, a physicist at the Johns Hopkins University Applied Physics Laboratory in North Laurel. "They told us things about the outer planets that nobody ever knew before. If you were to open a textbook from the 1970s and compare it to one from the 1990s, they wouldn't be similar at all."

Voyager 1 is now the most far-flung man-made object in the universe - so distant that it takes more than 11 1/2 hours for its signals traveling at the speed of light to reach Earth. But day in and day out the probes continue to transmit. And the 63-year- old Krimigis is one of a small group of scientists who still tune in to listen.

Krimigis oversees the Low Energy Charged Particle instrument - one of five functioning aboard each spacecraft, which he calls "the pride and joy of my career." Over the years, Voyager has sent him enough measurements for more than 200 scientific papers. And there's a chance, he says with a sparkle in his voice, that while Voyager's primary mission ended long ago, more scientific surprises might come along.

NASA began planning for the Voyager probes not long after Apollo 11 landed on the moon in 1969. It was originally intended to be a scientific blowout: Dubbed the Grand Tour, four spacecraft would visit the outer planets - Jupiter, Saturn, Uranus, Neptune, perhaps even Pluto.

But when the Nixon administration balked at the estimated $750 million price tag, Grand Tour quickly became Budget Tour. A new itinerary called for a pair of probes to Jupiter and Saturn. With luck, engineers hoped one spacecraft might get to Uranus and Neptune.

Voyager 2 rumbled off the launch pad Aug. 20, 1977, from Kennedy Space Center. Voyager 1 followed Sept. 5. Although it left later, Voyager 1 sailed along a faster trajectory that brought it to Jupiter first.

The spacecraft carried 11 scientific instruments and the famous Golden Record - a cosmic calling card intended for any alien life forms that might one day encounter the craft.

Etched onto 12-inch gold plated copper disks were samples of languages from Akkadian, last heard in the streets of Babylon about 6,000 years ago, to Wu, a modern Chinese dialect. The disks included 90 minutes of music - including Bach, traditional Chinese hu-ch'in, and Chuck Berry's "Johnny B. Goode," humanity's sole representative of rock 'n' roll.

The alien album gave Voyager instant pop-culture cache. The NBC television show Saturday Night Live broadcast a skit showing scientists anxiously preparing to receive the first message from aliens who had discovered the disk.

Their historic communique: "Send more Chuck Berry!"

12-year exploration

The probes spent 12 years exploring the four planets - nearly each new encounter bringing more surprises and arresting color snapshots than the last. The Voyagers also discovered 22 satellites: three around both Jupiter and Saturn, 10 around Uranus and six around Neptune. But for Krimigis and other Voyager scientists, it was often what the instruments found on these objects that they would later point to as the biggest surprise of their careers.

Near the top of most scientists lists: Jupiter's moon Io.

"As we approached the planet we started measuring sulfur," recalls Krimigis. When they arrived, they found active volcanoes on the moon, a geologic formation previously known to exist only on Earth.

Krimigis recalls being was woozy with delight at what the instrument was telling him: "You float for a minute, and you feel it in your stomach. I felt that way for weeks."

After Jupiter and Saturn, Voyager 1 veered away from the planets, while its twin sped on to Uranus and Neptune.

The encounters wouldn't disappoint. Scientists clocked winds on Neptune gusting past 1,500 mph, the fastest of any planet. Another shock: active geysers exploding from Triton, the planet's icy moon.

But the encounter with the blue planet also was bittersweet. "This is the last first encounter of a planet for quite a long time," Lew Allen, director of the Jet Propulsion Laboratory at the time, said at a news conference in 1989.

But even as the Voyagers left the planets behind, space scientists had another scientific milestone in mind.

Project long-lasting

"I don't think any of us in the beginning expected this project to last as long as it has," says Norman Ness, 69, a geophysicist at the University of Delaware who is one of the original scientists still working on the project.

By the time Voyager 1 passed Pioneer 10, its predecessor, to become the most distant man-made object in space, many of the scientists had died or retired. Most of the five operating instruments are run by second- or third-generation scientists.

Today, Voyager 1 is more than 7.96 billion miles from Earth and whooshing away at 38,540 mph. Voyager 2, sailing below the planetary plane at a distance of 6.3 billion miles, isn't far behind.

Many scientists have their fingers crossed that at that distance the spacecraft might be quickly on the verge of more major scientific discovery: pinpointing the heliopause.

The heliopause is the boundary where particles rushing outward from the sun, known as the solar wind, collide with particles streaming in from interstellar space. Its location is considered one of the great unanswered questions of astrophysics.

"People have all kinds of ideas of what's out there," says Matthew Hill, 31, a physicist at the University of Maryland, College Park. "But we won't know until we get there."

It's unclear how much longer that might take: Predictions of the heliopause's location have been off before, says Hill.

The young physicist is one of a small group for which Voyager has become a scientific hand-me-down. Six years old when the probes were launched, he is one of the youngest scientists on the project and spends as much time learning the mechanical quirks of his distant partner as poring through the data.

"A big part of what I do is to understand these instruments," he says. Occasionally, this has meant rousing elderly retired Voyager scientists from their easy chairs when something goes on the fritz.

While they might not be the newest or sexiest in NASA's fleet, Hill says "there's something a little special" about the 25-year-old probes. "I feel privileged to be able to work on it," he says.

The twin Voyagers' plutonium power generators are expected to last until 2020. But the spacecraft themselves, barring any catastrophic collisions, are expected to sail on toward other stars for millions of years to come.

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