Galileo was launched from the space shuttle Atlantis in October 1989 and reached orbit around Jupiter a little over six years later. When its original two-year mission ended in December 1997, it was given an extended mission set to end in January 2000.
Galileo is perhaps most famous for the spectacular images it snapped of comet Shoemaker-Levy 9, which surprised the world when it zoomed out of the void to slam into Jupiter in July 1994.
"There was a possibility, if enough damage was done to the electronics, it would not survive the flyby. Because of this possibility, we planned the Io encounter for the end of the two-year extended mission," Sible said.
After such a successful mission around Jupiter it seemed reasonable "to take a calculated risk for a much closer look at such a scientifically rich target," such as Io, he added.
Erickson said Galileo did experience computer problems during its encounter with Io when it passed through the densest part of the Jupiter moon's radiation belt. "But we were able to bypass the problem and reset the computer. Whether it was the radiation or another problem we will probably never know."
Scientific data on Io from Galileo, which lost its ability to transmit through its high-gain antenna early in its epic journey through space, was not expected to reach earth until November after being transmitted through its low-gain antenna.
But Erickson said Galileo was sending "still data" — position, time and trajectory — after the successful flyby.
Galileo is scheduled to make an even closer flyby on November 26, when it will approach within 186 miles (300 kilometers) of the planet surface.
