Galileo Spacecraft Flies within 380 Miles of Jupiter's Moon Io.

Monday, October 11th 1999, 12:00 am
By: News On 6

The aging and glitch-prone Galileo spacecraft
successfully flew within 380 miles of Jupiter's moon Io, overcoming huge doses of radiation and a computer problem just hours before
the approach.
The probe made the closest-ever flyby at 10:06 p.m. PDT Sunday, said project manager Jim Erickson of NASA's Jet Propulsion Laboratory in Pasadena.
"We're thrilled that the spacecraft handled this flyby so well, particularly because it had to endure such a strong dose of radiation from Jupiter," he said Monday. "It appears everything went well."
As part of an extended mission, Galileo's instruments are studying the chemistry, heat distribution, gravity and magnetic properties of Io, Jupiter's innermost large moon and the only known actively volcanic solar system object besides Earth.
"It gives us the opportunity to do comparisons between a non-Earth volcanic system and the Earth," Erickson said. "We learn something about both of them in the process."
Success was not guaranteed. Just 19 hours before the flyby, a memory error in a computer caused the spacecraft to enter a safe
mode, and engineers worked up until two hours before the close approach to fix the problem.
Had attempts to recover failed, no science data or images would have been returned from the spacecraft 327 million miles from
Earth, said Nagin Cox, deputy chief of the engineering flight team.
Cox was at home about 3 a.m. Sunday when she received the news of the error from JPL's flight control center. She quickly canceled
plans to take part in her best friend's wedding and instead drove to JPL.
"The first thing that occurred to me is that we're in that window where we have a chance to recover if we start acting right
away," she said. "We went through a period of a few hours where we were trying to get information on what had happened while we
simultaneously put into motion the recovery plans."
Two hours after the problem cropped up, engineers determined that it stemmed from a memory error, likely the result of the
spacecraft's long exposure to high levels of radiation near the giant gaseous planet.
Hours of programming paid off, and the spacecraft is believed to have captured about 75 percent of the images and science data from the flyby.
Galileo has sent mission engineers and controllers scrambling on several occasions since its 1989 launch, which itself was delayed
for years by the 1986 Challenger disaster.
Scientists overcame the failure of the probe's main antenna to open properly and a malfunction of its tape recorder. Galileo still
achieved 70 percent of its science goals during its $1.5 billion primary mission.
The probe is scheduled to make an even closer approach of Io on Nov. 25, flying within 186 miles of the surface.
The spacecraft, which arrived at Jupiter in 1995, completed its primary mission in 1997 and will finish a $30 million, two-year
extended mission in January.

The Associated Press.