The $1.4 billion robotic spacecraft flew by Io at 9:32 a.m. Eastern Standard Time on Tuesday, passing within 124 miles (200 kilometers) of the moon. Thats closer than Space Shuttle Endeavour flew over Earth on its current mapping mission.

"So far it looks like everything is going perfectly nominal," said Jim Erickson, the Galileo project manager at NASAs Jet Propulsion Laboratory. "The radiation was about what we expected."

Since Io orbits so close to Jupiters intense radiation belts, each of Galileos three swings past the moon have been fraught with danger.

The radiation -- which can wreak havoc on a spacecrafts electronics -- caused the spacecraft to reset prior to Tuesdays encounter. However, software loaded aboard Galileo fixed the problem, which has become almost standard operating procedure during each flyby, Erickson said.

Scientists hoped to capture a number of volcanoes during this last flyby, including Chaac and Tvashtar. They will also produce a global mosaic of Ios surface to track changes in what is the most volcanically active body in the solar system.

During its November 25 flyby of Io, Galileo caught Tvashtar in the act as it spewed molten lava nearly a mile (1.5 kilometers) above the surface.

The lava was so hot at the time, it overexposed a portion of the digital image.

The 11-year-old spacecraft will next fly by Ganymede, another of Jupiters 16 known moons, on May 30 and again on December 28 as part of its extended Galileo Millennium Mission.

Erickson said the Galileo team is negotiating with NASA headquarters to keep the spacecraft flying through 2001, including the possibility of further encounters with Io and Callisto, another moon, and Jupiter itself.

"One of the issues is it has been really successful, its hung together well, but were starting to run out of fuel. You cant go on forever," Erickson said. "Its kind of sad. Its like trying to plan your own end."

The robotic spacecraft, launched from the shuttle Atlantis in 1989, arrived at Jupiter in December 1995.