PASADENA, Calif. -- Thirty-five years after leaving Earth, Voyager 1 is reaching for the stars.
Sooner or later, the workhorse spacecraft will bid adieu to the solar system and enter a new realm of space -- the first time a man-made object will have escaped to the other side.
Perhaps no one on Earth will relish the moment more than Ed Stone, 76, who has toiled on the project from the start. "We're anxious to get outside and find what's out there," he said.
When NASA's Voyager 1 and Voyager 2 first rocketed out of Earth's grip in 1977, no one knew how long they would live. Now, they are the longest-operating spacecraft in history and the most distant, at billions of miles from Earth, but in different directions.
Wednesday marks the 35th anniversary of Voyager 1's launch to Jupiter and Saturn. It is now flitting around the fringes of the solar system, which is enveloped in a giant plasma bubble. This hot and turbulent area is created by a stream of charged particles from the sun. Outside the bubble is a new frontier in the Milky Way, the space between stars. Once it plows through, scientists expect a calmer environment, by comparison.
When that would happen is anyone's guess. The boundary that separates the solar system and interstellar space is near, but it could take days, months or years to cross that milestone.
Voyager 1 is more than 11 billion miles from the sun. Its twin, Voyager 2, which celebrated its launch anniversary two weeks ago, trails behind at 9 billion miles from the sun.
They're still ticking despite being relics of the early Space Age. Each has only 68 kilobytes of computer memory. To put that in perspective, the smallest iPod, an 8-gigabyte iPod Nano, is 100,000 times more powerful. Each also has an eight-track tape recorder. Today's spacecraft use digital memory.
The Voyagers' goal was to tour Jupiter and Saturn, and they sent back postcards of Jupiter's big red spot and Saturn's glittery rings. They also beamed home a torrent of discoveries: erupting volcanoes on Jupiter's moon Io, and hints of an ocean below the icy surface of Europa, another Jupiter moon. Voyager 2 then journeyed to Uranus and Neptune. Voyager 1 used Saturn as a gravitational slingshot to catapult itself toward the edge of the solar system.
"Time after time, Voyager revealed unexpected -- kind of counterintuitive -- results, which means we have a lot to learn," said Stone, Voyager's chief scientist and a professor of physics at the California Institute of Technology.
These days, a handful of engineers listens for the Voyagers from a satellite campus not far from the NASA Jet Propulsion Laboratory, which built the spacecraft. Cameras on the Voyagers were turned off long ago. The nuclear-powered spacecraft, about the size of a subcompact car, still have five instruments to study magnetic fields, cosmic rays and charged particles from the sun, known as solar wind. They also carry gold-plated discs containing multilingual greetings, music and pictures,in the off chance that intelligent species encounter them.
The double missions so far have cost $983 million in 1977 dollars, or $3.7 billion now. The spacecraft have enough fuel to last until around 2020.