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

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

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

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

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 roundtrip between the Earth and the spacecraft.

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

Picking out the faint signal of the spacecraft's eight-watt transmitter put the National Aeronautics and Space Administration's international network of antennas to the test. Further communications with Pioneer likely will remain difficult, because engineers can contact the spacecraft only by first beaming signals to it.

"In order (for Pioneer 10) to talk to us, we need to talk to it," said Ric Campo, the mission's chief flight controller.

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

The spacecraft carries a gold plaque engraved with a message of goodwill and a map showing the Earth's location within the solar system.

NASA's oldest operating spacecraft is Pioneer 6, which scientists contacted in December to mark the 35th anniversary of its launch.