Ground controllers coax Galileo out of hibernation

Posted: January 18, 2002

An artist's concept of Galileo during the approach to Io. Image: NASA TV/Spaceflight Now
NASA's Galileo spacecraft was revived Friday in time to snap a few final images of landmarks in the Jovian system, but its last close encounter with Io was a bust because an onboard glitch put the probe into hibernation just minutes before the flyby Thursday.

Software aboard Galileo detected a computer reset early Thursday, triggering the craft to automatically enter "safe mode." In such a state, all the instruments and systems on the spacecraft are placed into a standby mode to await commands from Earth.

Ground controllers attempted to return Galileo to normal operations through the day on Thursday before finally succeeding at about 0400 GMT Friday (11:00 p.m. EST Thursday).

Three data sets that were planned to be recorded around the time of closest approach to Io were all lost due to the safe mode, which scientists believe to be caused by intense concentrations of radiation that surround the giant gas planet. Since Galileo entered orbit around Jupiter in 1995, it has weathered a total radiation dosage about three-and-a-half times more than it was designed for.

"As expected, visiting Io has proved to be a challenging and risky endeavor," said Dr. Eilene Theilig, Galileo project manager at JPL. "It's disappointing not to get the observations of Io that were planned for this encounter, but I am very proud of the flight team that has kept Galileo functioning in orbit more than three times longer than originally planned and revived it once more yesterday."

Plans call for various tests to be performed this weekend to ensure the spacecraft is operating normally after the events of this week. The probe's primary camera will take a series of images of Jupiter's Great Red Spot, the moon Europa, and the moon Amalthea before shutting off for the final time early Monday morning.

Even with the cessation of normal spacecraft operations, the close encounter did accomplish its primary purpose of using Io's gravity to slingshot Galileo onto a collision course with Jupiter in September 2003. Controllers opted to crash the veteran probe into the planet to avoid the slim chance that the craft could impact the moon Europa after the mission ends. Europa is thought to have an ocean of melted saltwater under its icy surface, and scientists do not want to contaminate Europa in interests of future studies on the possibility that it could harbor life.

Thursday's flyby was the 34th and last at any of Jupiter's four Galilean moons -- Io, Europa, Ganymede, and Callisto. Passing just 63 miles above Io's fiery volcanic surface, it was also the closest approach in Galileo's six years of orbiting the gas giant.