Even though its main communication antenna never deployed, NASA's Galileo spacecraft has been productive — and durable — ever since entering orbit around Jupiter in December 1995. Multiple flybys of the Jovian moon Io have subjected the spacecraft to more than 500,000 rads of magnetospheric charged particles — 3½ times the spacecraft's design limit.


Scientists and engineers at the Jet Propulsion Laboratory in California are not happy about it, but NASA's Galileo mission is coming to a close. Tonight the spacecraft's picture-taking efforts will end when the Near-Infrared Mapping Spectrometer records its final calibration image. That frame, along with other images and data stored on Galileo's tape recorder, will be beamed to Earth over the next month. During that time the onboard magnetometer, dust detector, and extreme-ultraviolet spectrometer will periodically collect data.

After February, however, with funding for mission activities exhausted, the spacecraft will cease its data playback and simply continue to coast around Jupiter. On November 5th Galileo will pass about 500 km from Amalthea, the mysterious little red-hued moon that orbits just 110,000 kilometers from the Jovian cloud tops. No images will be taken during that flyby, though JPL's navigation team hopes to use minute deviations in the flight path to determine Amalthea's mass.

Launched via the Space Shuttle Atlantis on October 18, 1989, Galileo is now in its 13th year in space and its seventh orbiting the giant planet. On January 17th it flew over the equator of volcanically active Io at a height of only 102 km. Scientists had hoped to get high-resolution views of the volcanic moon's Jupiter-facing hemisphere, which has never been recorded in much detail. Unfortunately, Galileo's opportunity for a spectacular culmination to its dozens of flybys was lost when intense radiation triggered an electronic shutdown just a half hour before the encounter.

The mission's darkest hour came on April 11, 1991, when Galileo's main antenna became stuck while unfurling from its stowed position. Since then all communication to and from Earth has been routed through a low-power backup antenna. Despite this handicap, Galileo has beamed back more than 4.8 gigabits of science data — including some 14,000 images.

To eliminate any potential that the spacecraft could someday contaminate Europa, a moon that may harbor primitive life, Galileo will be directed to fall into Jupiter's atmosphere on September 21, 2003, when it will plunge into the Equatorial Zone at 48 km per second.


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