With an eight-track tape recorder and 100,000 times less memory than an iPod, Voyager 1 is celebrating its 35th birthday at the edge of the solar system.

Traipsing through a giant, turbulent, plasma bubble near the fringes, the longest-running, most-distant spacecraft in NASA's history celebrates a launch anniversary on Wednesday. After more than three decades of trekking, the craft is currently flirting with the edge of our system, poised for a precedent-setting puncture to the other side.

Scientists say the milestone is near, but a timeframe for crossing over is unknown.

Expected to be the first manmade object to touch the space between stars, Voyager 1, at more than 11 billion miles from the sun, is already in uncharted celestial territory. Voyager 2, which celebrated its anniversary two weeks ago, is approximately 9 billion miles from the sun.

Built by NASA's Jet Propulsion Laboratory, the twins left Earth in 1977 equipped with eight-track tape technology and 68 kilobytes each of computer memory. To put it another way, the Voyager crafts are 100,000 times less powerful than the smallest, 8-gigabyte iPod Nano.

The duo's original goal, to tour Jupiter and Saturn, provided information about Jupiter's big red spot, Saturn's rings, and a torrent of moon discoveries, from erupting volcanoes on Io, to hints of an ocean below the icy surface of Europa, to signs of methane rain on Titan.

Then the Voyagers parted ways. Voyager 2 journeyed to Uranus and Neptune, and it remains the only spacecraft to fly by these two outer planets. 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.

With enough fuel to last until around 2020, the nuclear-powered spacecraft, each about the size of a subcompact car, have five instruments to study magnetic fields, cosmic rays and solar wind. They also carry gold-plated discs containing multilingual greetings, music and pictures -- should intelligent species come across them. Cameras aboard the Voyagers were turned off long ago.

From a satellite campus near JPL in Pasadena, a handful of engineers still listen diligently for Voyager transmissions. Because of the distance, a radio signal from Voyager 1 takes 17 hours to travel to Earth. For Voyager 2, it takes about 13 hours. 20 part-timers analyze the streamed back data. There are no full-time scientists left on the mission.

Carpeted and cubicled, the control room could be mistaken for an insurance office if not for the blue, "Mission Controller" sign, and the warning on a computer that reads, "Voyager mission critical hardware. Please do not touch!"

Since 2004, Voyager 1 has been exploring a region in the bubble at the solar system's edge where the solar wind dramatically slows and heats up. Over the last several months, scientists have seen changes that suggest Voyager 1 is on the verge of crossing over.

The double missions so far have cost $983 million in 1977 dollars, which translates to $3.7 billion now.

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