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. Last Updated: 07/27/2016

NASA Probes Still Going Strong at 25

WASHINGTON -- NASA's twin Voyager spaceships celebrated their 25th year this week by speeding toward the very edge of our solar system, carrying messages from Mozart, Bach and Chuck Berry.

The first Voyager was launched Aug. 20, 1977, and was expected to take a quick four-year tour of Jupiter and Saturn, send back some data and retire. The other launched Sept. 5, 1977, with a similar mission but a different route.

Instead, the doughty robotic probes have kept going and going and going, snapping never-before-seen images of the outer planets, discovering volcanoes on Jupiter's moon Io and a massive atmospheric storm on Neptune.

Both Voyagers are far beyond the known planets now, but still sending back data as they head toward interstellar space, testing the limits of human-made spacecraft.

But even if the Voyagers can no longer send back data, they still carry elaborate postcards from Earth, fashioned in haste by a team led by the late cosmologist Carl Sagan, to convey to any extraterrestrial travelers what earthly life is like.

Identical golden disks are fastened to each of the Voyagers, engraved with ambient sounds of our planet -- a kiss, a mother's lullaby, wind and water -- as well as images, written greetings from former U.S. President Jimmy Carter and former UN Secretary-General Kurt Waldheim, and spoken greetings in languages ranging from ancient Akkadian to modern Wu.

The golden records also include 90 minutes of music, running the gamut from Bach's Second Brandenburg Concerto and Mozart's The Magic Flute to rock icon Berry's version of his own "Johnny B. Goode."

There are also symbolic descriptions of the spaceships' origins and instructions on how the records are to be played.

"No, there have been no responses" to the records, Voyager project manager Ed Massey said with a chuckle. "They're still on the spacecraft -- we're in contact with the spacecraft every day, and we know they're still there."

The Voyager probes are by far the most distant human-made objects, with the furthest of the two now 85 times as far from the Sun as Earth -- and the Earth-Sun distance is 150 million kilometers. The closer Voyager is 68 times that distance.

Such distance can bring difficulties. Even moving at the speed of light -- 299,300 kilometers per second -- it takes Voyager's radio signals nearly 12 hours to reach Earth. That means any malfunction would take at least that long to detect, and by then it might be too late to fix, Massey said.

The spacecraft could run out of electrical power before they reach their next goal, which is to explore the limits of the vast bubble the Sun is blowing around itself. The boundary of the bubble is called the heliopause, the place where the expanding solar bubble is counterbalanced by inward pressure from interstellar wind.

No one really knows when the Voyagers could reach this point, but Massey sounded confident they would get there and still be able to send back data.

"We don't run out of electrical power until about 2020," he said. "There's every expectation that Voyager 1 will ... at least enter the heliopause. There may be a question as to whether it will exit out the other side before we run out of power."

At 59, with only about four years with Voyager, Massey said he would be retired long before the probes hit the heliopause.

"I don't think anybody expected we would still be here 25 years later, though we probably could go another 25 years," he said.