Twenty-five years ago, Elvis Presley died. For the thousands who flocked to his Graceland Mansion in Memphis, Tenn., it's an event from which many never recovered. But in terms of global significance, far more important than Presley's death were the births of two U.S. space probes. Voyagers 1 and 2 were supposed to have ended their missions to Jupiter and Saturn in 1981, but instead they've been kept going ... and going ... and going.
Voyager 1, the most distant of any human-made object, is now 7.8 billion miles from Earth; Voyager 2 is now 6.3 billion miles away. America's ambassadors to the Universe each carry a 12-inch, gold-plated copper disk containing sounds and images selected to portray the diversity of life and culture on Earth. They also include printed messages from then-President Carter and U.N. Secretary General Kurt Waldheim.
Tim Hogle, the Voyager systems engineer and mission controller at the National Aeronautics and Space Administration's Jet Propulsion Laboratory, said, & quot;They are showing signs of their old age but we have no good reason to think they won't last another 20 years or so. & quot; And then who will be president or heading the United Nations? And what space discoveries will have been made.
'Greatest mission of discovery'
Between 1979 and 1989 the Voyager probes studied 48 moons and four planets -- more of the solar system than any other craft. As Charles Kohlhase, the former Voyager mission design manager says, "Those 10 years represent perhaps the greatest mission of discovery in the history of mankind."
The two spacecraft will continue their ground -- or better -- space-breaking journeys with a current mission to study the region in space where the Sun's influence ends and the dark recesses of interstellar space begin. Now data takes more than 23 hours to make the round trip between Voyager 1 and Earth; two-way communications with Voyager 2 take just 18.5 hours.
Remarkably, the heat of decaying plutonium is used to generate about 310 watts of electrical power aboard each probe. Each communicates with Earth using a 23-watt transmitter. A lamp in an earth-bound refrigerator needs about 25 watts.
And when refrigerators are obsolete, the Voyagers will still be going ... and going ... and going.