After Long Silence, Spacecraft Speaks Up

April 30 -- NASA scientists said Sunday they have contacted the Pioneer 10spacecraft, ending fears that the robotic probe had gone silent 29years into a mission that has carried it more than 7 billion milesfrom Earth.

A radio antenna outside Madrid received a signal from Pioneer 10on Saturday, marking the first time the spacecraft had been heardfrom since Aug. 19. The spacecraft was launched March 2, 1972.

"Pioneer 10 lives on," project manager Larry Lasher said in astatus report posted Sunday on the mission's Web site.

Pioneer 10 was the first spacecraft to pass through the asteroidbelt and the first to obtain close-up images of Jupiter. In 1983,it became the first manmade object to leave the solar system whenit passed the orbit of distant Pluto.

Seven Billion Miles Away

The spacecraft is currently 7.29 billion miles from Earth,traveling at 27,380 mph relative to the sun. At that distance,radio signals take 21 hours and 45 minutes to make the roundtripbetween the Earth and the spacecraft.

The Pioneer 10 mission came to a formal close in 1997, but theprobe had remained in fairly regular contact with Earth, returninglimited scientific data before going silent in August.

Picking out the faint signal of the spacecraft's eight-watttransmitter put the National Aeronautics and Space Administration'sinternational network of antennas to the test. Furthercommunications with Pioneer likely will remain difficult, becauseengineers can contact the spacecraft only by first beaming signalsto it.

"In order [for Pioneer 10] to talk to us, we need to talk toit," said Ric Campo, the mission's chief flight controller.

Even in silence, the spacecraft will continue its steady voyagetoward the constellation Taurus. It should pass one of the stars inthe constellation more than 2 million years from now.

The spacecraft carries a gold plaque engraved with a message ofgoodwill and a map showing the Earth's location within the solarsystem.