Nov 28, 1999

Galileo's No Turkey

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NASA's Galileo spacecraft completed the closest-ever encounter with Io, but not before giving ground controllers a Thanksgiving day white-knuckler.




Galileo image of an Io volcano
November 28, 1999: NASA's Galileo spacecraft has completed the closest-ever encounter with Jupiter's volcanic moon Io, but not before giving ground controllers a Thanksgiving day white-knuckler.

The spacecraft dipped to the planned 300 kilometers (186 miles) above Io at 8:40 p.m. Pacific Standard Time on Thursday, November 25. Only four hours before the flyby, while Galileo was being bombarded by strong radiation near Io, its onboard computers reset and placed the spacecraft into standby mode. Onboard fault protection software told the spacecraft cameras and science instruments to stop taking data and enter a safe state until further instructions were received from the ground.

Right: Artist's concept of Galileo swooping over the surface of Io. [click for animation].


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Galileo engineers at NASA's Jet Propulsion Laboratory sprang into action, scrambling to send new commands to the spacecraft and bring it out of safe mode in order to save the flyby.

"With so little time to spare, it would have been easy to think 'no way' can we do this," said Galileo project manager Jim Erickson. "But our team members jumped to the challenge, in some cases leaving behind half-eaten Thanksgiving dinners."

"We were prepared, because we knew this high-radiation Io flyby posed a risk to spacecraft components, and in fact we saw that the radiation caused some glitches during the October 10th Io flyby," Erickson said. "This planning paid off in a big way."

The team finished sending new computer commands to Galileo, which were received and executed by the spacecraft at 8:45 p.m. PST, four minutes after the closest approach to Io. This enabled the spacecraft to complete more than half of its planned observations of Io and its plasma torus (a doughnut-shaped region brimming with electrified particles), and all the planned observations of another Jovian moon, Europa. If all goes according to plan, the data will be transmitted to Earth over the next several weeks, and it will then undergo processing and analysis.

The October 10th Io flyby was performed at an altitude of 611 kilometers (380 miles). Pictures and other scientific information from that flyby provided fascinating new views of Io, which has more than 100 active volcanoes. Scientists hope that by learning more about volcanic activity on Io, we may learn more about volcanoes on Earth.


Parents and Educators: Please visit Thursday's Classroom for lesson plans and activities related to this story.

Additional information about the Galileo mission is available on the Galileo home page at a new web address of

JPL manages the Galileo mission for NASA's Office of Space Science, Washington, D.C. JPL is operated for NASA by the California Institute of Technology, Pasadena, CA.

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Related Stories:

Sulfuric Acid Discovered on Europa -- September 30, 1999. Sulfur from Io's fiery volcanoes may be responsible for a battery acid chemical on Europa with implications for astrobiology.
Io or Bust -- September 16, 1999. Galileo braves extreme radiation as it plunges toward a close encounter with Io's volcanoes.
Divining Water on Europa -- September 9, 1999. As circumstantial evidence for an underground ocean mounts, JPL scientists try an ingenious experiment to look for hexagonal ice crystals on the surface of Europa.
Taking the Scenic Route to Io -- June 30, 1999. What's happening to the small craters on Callisto? That's the mystery scientists were contemplating as Galileo zoomed past Jupiter's pockmarked moon this morning in an orbit-changing maneuver designed to bring the spacecraft closer to volcanic Io.
Turn Left at Callisto -- May 5, 1999. Galileo heads for a daring encounter with Io's volcanoes.
Galileo buzzes Europa -- Feb. 2, 1999. Galileo executes a close flyby of Europa for the last time during the current mission.
The Frosty Plains of Europa -- Dec. 3, 1998. As Galileo returns new images of Europa, NASA scientists prepare to study samples from a potentially similar environment here on Earth.
Callisto makes a big splash -- Oct. 22, 1998. Scientists may have discovered a salty ocean and a possible ingredient for life on Jupiter's moon.
Galileo takes a close look at icy Europa -- Oct 2, 1998. The spacecraft flew within 2300 miles of the mysterious satellite last weekend.
Clues to possible life on Europa may lie buried in Antarctic ice -- Mar. 5, 1998. Exotic microbial forms turn up in ice above Antarctica's Lake Vostok.

Related Sites:

Ice, Water and Fire the Galileo Europa Mission
Galileo home page at JPL, with the latest on Europa, Callisto and Io
Jet Propulsion Laboratory home page
Io from the SEDS Nine Planets web site
Callisto from the SEDS Nine Planets web site
Jupiter from the SEDS Nine Planets web site
Io: The Prometheus Plume Aug. 18, 1997 Astronomy Picture of the Day
Close-up of an Io volcano Aug. 4, 1995 Astronomy Picture of the Day
Sizzling Io July 6, 1998 Astronomy Picture of the Day


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