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Contact: Jane Platt

October 15, 1999

Galileo Completes Daring Io Flyby

PASADENA, Calif. - For the men and women of the Galileo project, Sunday, Oct. 10 began as a real nail-biter, but ended with immense pride and relief as the spacecraft successfully completed its daring flyby of Jupiter's moon Io.

An unexpected 3:09 a.m. wakeup call on Sunday sent Galileo team members scrambling into action. Three hours after entering the intense radiation zone near Jupiter and Io, Galileo went into safing when an error popped up in the memory of the onboard computer. The team was faced with a daunting task-to get the spacecraft out of safing and back to normal operations in time for the flyby at 10:06 p.m. (Earth receipt time).

"It was a heroic effort to pull this off," said Galileo Project Manager Jim Erickson. "The team diagnosed and corrected a problem we'd never come across before, and they put things back on track."

"We waited four years for this encounter and we would do everything in our power to make it happen," said Eilene Theilig, spacecraft and sequence team chief. "Each person in this talented, dedicated and professional group knew what he or she had to do." "Before every encounter, we go through various contingency scenarios, including a possible safing," said Nagin Cox, spacecraft and sequence team deputy team chief. "That preparation paid off and the anomaly resolution team swung into action quickly."

"It was poetry in motion," said Olen Adams, lead for Galileo's command and data subsystem. "People were traveling around these aisles like it was a relay race. Every single person had to perform perfectly. We could not afford one single 'gotcha.' If one person got sick, or one PC crashed, or one command didn't make it to the spacecraft, it wouldn't have worked."

"I knew that if the radiation had triggered one memory fault, there was a good chance it could trigger another," said Tal Brady, who designed the command and data subsystem flight software. "I was very relieved when we got the spacecraft out of safing and later when the flyby data was recorded successfully."

The team saved the day by first pinpointing the location of the computer memory error. They did this by analyzing telemetry and memory readouts and looking at the timeline of spacecraft activities. They changed the encounter sequence to avoid activities that use the faulty portion of the memory. By late Sunday afternoon, Galileo engineers uplinked a new command sequence to the spacecraft. That posed another risk, since the transmission took place while Galileo was in the deepest portion of the radiation zone near Io. Against all odds, Galileo resumed full operations at 8 p.m., just two hours before the Io flyby.

The spacecraft and sequence team did much of the hands-on work, in conjunction with the science and mission control teams. Erickson pointed out, "We were able to meet this enormous challenge because the other teams did their work and assured us that we were free to focus on the crisis at hand."

During the flyby, Galileo's science instruments studied the surface chemistry, heat, gravity and magnetic properties of Io, the most volcanic body in our solar system, from an altitude of only 611 kilometers (380 miles). This was the closest look at Io by any spacecraft. The data, including close-up images, will be transmitted to Earth in coming weeks.

"We want to learn more about the differences and similarities between volcanoes on Io and volcanoes on Earth," said Dr. Duane Bindschadler, Galileo manager of science operations and planning.

A second, closer flyby of Io by Galileo is planned for Nov. 25 at an altitude of 300 kilometers (186 miles).

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