Galileo survives 'white knuckle' flyby of Io

Artist's conception of Galileo as it flies by Io, with Jupiter in the background

November 26, 1999
Web posted at: 3:13 p.m. EST (2013 GMT)

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(CNN) -- NASA's sturdy Galileo spacecraft completed its closest encounter with Jupiter's fiery moon Io on Thursday, but only after what officials called "a Thanksgiving white knuckler" for earthbound controllers.

The craft dipped through intense radiation bombardment to the planned 186 miles (300 km) above the volcano-pocked Jovian moon at 8:40 p.m. PST. But the successful pass required some frantic last-minute scrambling by controllers to reactivate Galileo's systems.

Results from the previous flyby -- an October 10 pass at an altitude of 380 miles (611 km) -- were unveiled by NASA this week. High resolution photographs and other scientific information reaffirmed Io's status as the most volcanic body in the solar system. The data led scientists to compare the environment to what the Earth experienced billions of years ago, opening what they described as "a new window on the past."

The results from Thursday's pass are expected to be available in a few weeks. Scientists hope to gain increased understanding of Earth's volcanoes by scrutinizing of the vastly more active fireworks of Io.

Computers switch into safe mode

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As NASA and engineers had expected after the successful but still hazardous October flyby, the craft was bathed in strong radiation near Io. In self protection, about four hours before its scheduled closest pass, Galileo shut down its computers, telling cameras and science instruments to stop collecting information and remain in a safe mode until further instruction from Earth.

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

"We were prepared," he said, "because we knew this high-radiation Io flyby posed a risk to spacecraft components, and in fact we saw some glitches during the October 10 flyby. This planning paid off in a big way."

Was it Galileo's last mission?

The NASA engineers scrambled in barely under the wire, resetting Galileo's systems about four minutes after its closest flyby. This enabled the craft to perform about half of its hoped-for observations and other observations of another Jovian moon, Europa.

Launched in 1989, Galileo has been orbiting Jupiter and its moons since December 1995. Its primary mission ended in 1995, and a follow-up mission completed in 1997.

The Io photographic mission was deliberately scheduled near what was believed would be the end of Galileo's life because extensive radiation damage was expected.