NASA's Galileo spacecraft successfully completed a close flyby to study Jupiter's moon Io at 0123 Universal Time Monday (6:23 p.m. Oct. 15, Pacific Daylight Time), during the long-lived spacecraft's 32nd orbit around Jupiter.
Galileo passed closer to Io than ever before, within about 181 kilometers (112 miles) of ground level near Io's south pole.
Engineers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said that signals confirming the spacecraft's basic health arrived within an hour after the flyby. The signals were received via JPL's Deep Space Network antenna facility near Madrid, Spain.
"Jupiter's radiation belts make flying near Io risky, but Galileo has come through for us again," said JPL's Dr. Eilene Theilig, Galileo project manager.
Galileo has been orbiting Jupiter since 1995. It has already endured more than three times as much radiation as it was designed to tolerate. NASA has extended Galileo's original two-
year orbital mission three times to take advantage of the spacecraft's continuing ability to make scientific discoveries.
As of 1500 UT (8 a.m. PDT) today, the spacecraft had recorded about 70 percent of the scientific data that its instruments had been programmed to collect during this swing
through the inner portion of the Jovian system. The encounter period that began Oct. 13 includes more-distant observations of Jupiter and the moon Europa, as well as the close-up examination of Io.
The images and other scientific data from the encounter will be transmitted to Deep Space Network antennas in Spain, Australia and California over the next three months.
Engineering data already received, such as voltage readings, suggest that Galileo's solid-state camera functioned properly during the flyby. However, the camera's performance
won't be known for sure until transmission of the pictures, which is due to begin in late October. The camera has malfunctioned intermittently in the past year because
radiation has degraded its electronics. Galileo engineers sent new software to the camera two weeks ago designed to minimize chances for recurrence of the problem.
Among the high-priority science observations for the flyby are magnetic-field measurements near Io's south pole, useful for understanding the moon's interior and interactive processes
within Jupiter's large magnetic environment. Other instruments were scheduled to observe details and changes in several volcanic areas on Io's surface, including a new hot spot and plume eruption discovered on the most recent flyby, in August.
Io is the most volcanically active world known. It orbits closest to Jupiter of the planet's four major moons. Tidal stress from the gravitational pull of Jupiter and the outlying moons heats Io's interior and sustains the volcanism.
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