‘Journey of a Lifetime’ : Scientists Bid Farewell to a Remarkable Voyager

Scientists bade an emotional farewell to the Voyager on Tuesday as the intrepid spacecraft completed its grand tour of the outer planets and headed out in search of new worlds.

“It’s been a very special decade in human history,” imaging team leader Bradford Smith of the University of Arizona said as scientists closed out their work at NASA’s Jet Propulsion Laboratory in Pasadena.

No other spacecraft has ever visited four planets. The Voyager took the human race on an armchair tour of worlds no one had ever seen before--Jupiter, Saturn, Uranus and finally, Neptune.

To many, the Voyager became more than a mindless robot responding to digital commands from a distant Earth. It appeared to take on a life of its own.

There will be other spacecraft in the future and there will be other expeditions, but “in the millennia ahead, Voyager will be the best remembered,” Smith added.

Of the scores of engineers and scientists who were there when Voyager began its 12-year odyssey in 1977, only a handful remain. Many have moved on to other jobs. Others have retired. A few have died.

“This has been a journey of a lifetime,” said Caltech physicist Edward Stone, who has served as Voyager’s chief scientist throughout the entire project.

The one-ton spacecraft sent hundreds of images and enough data to fill warehouses back to the 11 scientific teams that have been working at the Pasadena laboratory the last few weeks. As it soared past the brilliant blue orb of Neptune to the pastel, tortured moon of Triton, the Voyager did everything it was asked to do.

“Nothing,” emphasized project manager Norm Haynes, “went wrong.”

Neptune is so far from the Earth that it takes four hours and six minutes for a command to reach the spacecraft, so all the instructions had to be radioed to the craft days ahead of time.

Then it sailed through on its own, “bobbing and weaving like Sugar Ray” to take time exposures in the darkened neighborhood of Neptune, Haynes said. The Voyager accepted every command and executed every order, he added.

Engineers managed to use “99% of the capability of the spacecraft,” he said.

Tracking stations scattered around the world worked in concert to keep tabs on the small craft as it raced past Neptune at speeds of up to 61,000 m.p.h.

Voyager not only rewrote the scientific textbooks. It also stretched the idea of engineering excellence to new lengths.

Because the Voyager was so far away, it could not be constantly “steered” from Earth. So the craft--2.7 billion miles away--had to be told precisely where to point its cameras days ahead of time to capture the desired images for scientists back on Earth.

If the engineers missed at all, it was so rare that no one noticed.

The degree of precision required by scientists was illustrated Tuesday by Leonard Tyler of Stanford University, leader of the radio science team. Tyler said scientists had to know precisely when the craft would arrive at Neptune in order for its antenna to be pointed in the right direction for a crucial experiment.

“A 16-second error in arrival time would have resulted in a total failure of the radio science experiment,” Tyler said.

Voyager arrived within two seconds of the scheduled time.

Another of Tyler’s experiments reveals just how precise the Voyager data was.

Scientists wanted to measure the density of the atmosphere on Neptune’s largest moon, Triton. Radio waves traveling through an atmosphere are delayed, so if the delay can be measured, the atmosphere’s density can be determined.

When Voyager was on the other side of Triton its radio transmissions had to pass through the small moon’s atmosphere to reach Earth. They arrived slightly later than they would have if there had been no atmosphere.

Tyler said the Voyager’s radio signal arrived here .00000000003 seconds late. That proved that Triton’s atmosphere is extremely thin. It also showed that Voyager is a most uncommon machine.

Tyler, like all the other scientists associated with Voyager, is far from finished with his work. The scientists will continue to study their data for years, trying to decipher a distant world from what one described as “a brief snapshot in time.”

In Tyler’s case, he does not even have most of his data.

“I’m waiting for 992 pounds of magnetic tape that’s en route from the tracking stations,” he said.

Of all the discoveries at Neptune, two probably rank as most surprising.

Sunlight falling on the planet’s surface is only about 1/1000th as strong as it is on Earth. And since the sun drives the Earth’s weather, scientists had expected Neptune to be as bland as Uranus, which is little more than a pale bluish-gray ball.

Neptune, however, turned out to be a meteorologic dynamo.

Caltech atmospheric scientist Andrew Ingersoll said Tuesday that Neptune’s atmosphere has winds of up to 700 m.p.h., buffeting a storm center the size of the Earth that peers out into space like a dark, angry eye.

No one, Ingersoll said, understands what drives the winds, or even why such a storm system should persist. Voyager has given him much work to do.

Scientists were also surprised to find Neptune’s magnetic field tipped over on its side, inclined more than 50 degrees from the planet’s spin axis.

Uranus has a highly inclined magnetic field, which Voyager also discovered, but scientists think Uranus’ skewered field is probably caused by the fact that Uranus itself is tipped over on its side, rotating around the solar system with its pole pointed at the sun.

But Voyager sent them back to their laboratories wondering why the two planets should have such similar magnetic fields when they are so different in their orientation.

Right now, no one knows.

As fascinating as Neptune turned out to be, it had to give up center stage to its intriguing little moon, Triton.

Triton is even smaller than the Earth’s moon, but what a bizarre world it turned out to be.

Triton’s surface is 400 degrees below zero, making it the coldest place in the solar system so far as is known. Even Pluto is believed to be a little warmer than Triton.

Triton is also one of the brightest objects in the solar system. It is so bright, that it reflects nearly all of the skimpy dab of light it receives from the sun back into space. That is one of the principal reasons it is so cold.

Triton varies in color according to which scientist is describing it--from light tan to pink to white to all of the above.

It will best be remembered, however, as the world of ice volcanoes.

When he first suggested last Sunday that Triton might have volcanoes that have spewed nitrogen into the atmosphere, Larry Soderblom of the U.S. Geological Survey described it as a “crazy idea.”

After meeting with his fellow planetary scientists for two days, Soderblom addressed the question once again Tuesday.

“Just because an idea is crazy, it’s not necessarily wrong,” he said.

Scientists are becoming more convinced that the ice volcanoes on Triton are real.

As Voyager slipped farther and farther into space, the images of Triton and Neptune grew ever fainter Tuesday. One of the last images was a pastel double crescent of the planet and its moon, two objects that will not be visited again for many decades.

Gazing at the photo Tuesday, Smith--the imaging team’s leader--paused for a moment and thought of the long journey that lies ahead for Voyager, an endless sojourn to the stars.

“This was Voyager’s farewell to us,” he said.