Attempt to fix stuck antenna on Galileo fails


PASADENA, Calif. -- The latest attempt to free the stuck antenna on the Jupiter-bound Galileo spacecraft has failed, placing the $1.4 billion mission in jeopardy.

Engineers at the Jet Propulsion Laboratory here had hoped to use the coldness of space to chill and shrink part of the antenna, thus freeing three stuck ribs, but by yesterday morning it had become clear that the strategy had not worked.

"It's a disappointment," said project manager William O'Neil, but he said that the technique will be tried again in December when Galileo will be even farther from the sun -- and thus colder -- than it is now.

The $3.7 million gold-plated antenna is designed to open like an inverted umbrella, and it must be fully opened for Galileo to send back the thousands of photographs and reams of scientific data it is to collect during a two-year tour of Jupiter and its moons beginning in 1995. Without the 16-foot-wide antenna, all but a tiny amount of that data, and all of the photographs, will be lost.

Engineers believe the latest effort may have failed because they missed their desired temperature by a few degrees and could not get the 2 1/2 -ton spacecraft colder than minus-238 degrees Fahrenheit, 36 degrees short of what they believe they will need.

Although there is still time to work on the problem, the odds of success are worsening.

Scientists are in a predicament in that they need the antenna to be especially cold to free the stuck ribs, but they need it to be relatively warm for the motors that drive the ribs to operate at maximum efficiency. If the ribs are still stuck in December 1992, it may be too late to solve the problem because Galileo will enter its final course toward Jupiter, growing colder with each passing day -- so while the ribs may finally free up, the motors may be too weak to push the antenna open.

The problem was discovered April 11 when engineers at the Pasadena lab, managed by the California Institute of Technology for the National Aeronautics and Space Administration, turned on the motors that drive the ribs out from a central column. Three of the 18 ribs remained stuck.

In June, Galileo was turned so that the antenna was in the shadow of the spacecraft for 32 hours because engineers believed that a drop in temperature would cause the central column to shrink. That could allow the ribs to slide into position.

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