PASADENA, Calif. - Blasted with intense radiation, NASAs Galileo went into protective "safe" mode late Thursday, four hours before a scheduled rendezvous with the Jovian moon Io.

However, engineers at the Jet Propulsion Laboratory here scrambled to upload new commands to the unmanned spacecraft, restarting its cameras and scientific instruments at 11:45 p.m. ET - just four minutes after its closest approach to Io.

"With so little time to spare, it would have been easy to think No way can we do this," said Galileo project manager Jim Erickson. "But our team jumped to the challenge, in some cases leaving behind half-eaten Thanksgiving dinners."

JPL reported Friday that Galileo was able to make more than half of its planned observations of volcano-studded Io, one of 16 moons orbiting Jupiter, during the flyby. The encounter brought Galileo its closest yet to Io, passing within 186 miles (300 kilometers) of its southern polar region.

The mission team expects to receive data from the flyby, including images and information about the moon's magnetic environment, over the next several weeks.

Radiation may have been the culprit in the safe mode event, much as it is suspected in a similar incident that occurred just prior to the last Galileo Io flyby on Oct. 11 ET. In safe mode, designed as a self-protective measure, the spacecrafts cameras and instruments stop acquiring data until receiving
further instruction from controllers on Earth.

The $1.4 billion, glitch-prone spacecraft was launched in 1989 from the Space Shuttle Atlantis. It arrived at Jupiter in 1995, and since then has completed 25 flybys of a handful of its moons.

Because of the intense radiation environment surrounding Io, the two encounters with the highly volcanic moon were saved for last. JPL estimated as many as 30,000 rads would buffet Galileo during the encounter, an amount of radiation equal to 75 times the lethal dose for humans.