Spaceflight Now: Breaking News

Heavy dose of radiation causes Galileo glitches
Posted: December 30, 2000

An artist's concept of NASA's Galileo spacecraft in orbit around Jupiter. Photo: NASA/JPL
NASA's Galileo spacecraft has passed through the highest radiation environment it will experience in its current orbit of Jupiter, flying within about 500,000 kilometers (310,000 miles) of the giant planet's cloud tops at 7:26 p.m. PST Thursday, Dec. 28.

Exposure to Jupiter's intense radiation caused two effects -- an alarm received from Galileo's camera system, and a computer reset of the non-spinning portion of the spacecraft. The reset was a transient event that has happened during radiation exposures on several previous orbits. The computer reset was handled properly by onboard software responses, and mission engineers are investigating the out-of-the-ordinary measurement that triggered the camera alarm.

Other systems on Galileo were operating normally more than 12 hours after the closest approach to Jupiter.

"Adverse effects from the radiation close to Jupiter are not unexpected," said Jim Erickson, Galileo project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. Galileo had already endured more than three times the cumulative radiation exposure it was designed to withstand, and has operated more than three years above and beyond its original two-year mission in orbit around Jupiter.

Galileo had flown within 2,337 kilometers (1,452 miles) of Jupiter's largest moon, Ganymede, and taken images of it several hours before the camera began indicating a possible problem. The camera and other scientific instruments onboard the orbiter are continuing to record data about Jupiter and its moons.

"Images from the camera are still being recorded," Erickson said. "Until the first of those images are transmitted to Earth in February, we may not know whether this is a situation that is impairing the images."

As of 9 a.m. PST Friday, the spacecraft had recorded 46 percent of the scientific data that its instruments had been programmed to collect during this swing through the inner portion of the Jovian system, from Dec. 26 through Dec. 31. Besides studying Ganymede, Galileo is making more distant observations this week of Jupiter and the moons Io, Callisto and Europa. If all goes as planned, the data will be transmitted to Earth over the next five months for processing and analysis. Some of the observations are planned as part of collaborative studies with NASA's Cassini spacecraft, which will pass Jupiter on Saturday, though at a much greater distance than Galileo is from the planet this week.

Galileo was launched from NASA's Space Shuttle Atlantis on Oct. 18, 1989. It began orbiting Jupiter on Dec. 7, 1995. JPL, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C.