NASA to give electronic whack to ailing satellite


Just as a frustrated homeowner might whack a broken television in hopes of jarring it back to work, NASA scientists are preparing to "hammer" a jammed collapsible antenna on the $1.5 billion Galileo satellite as it heads toward Jupiter.

Scientists, having failed to fix the probe's main antenna with lTC more delicate means, are counting on brute strength to salvage what promises to be the most spectacular single part of Galileo's long-awaited mission: photographs of the massive planet and its four major and 12 lesser moons.

Without its 16-foot-wide "high-gain" antenna -- a gold-plated molybdenum wire-mesh dish that resembles a giant inverted umbrella -- Galileo would have to rely on a less-focused antenna. Even at its best, this "low-gain" antenna could send data to Earth at less than one-hundredth the speed of the high-gain device, greatly slowing transmission of photographs.

This last-ditch effort to deploy the Jupiter probe's antenna will begin Monday, when scientists will rotate the satellite to point the antenna toward the sun. They hope the warmth will expand metal fittings and release the stuck mechanism.

If that fails, as similar attempts did in the past, project manager William J. O'Neil at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said that controllers would flip the antenna's electric motors on and off at rapid intervals, "hammering" the jammed mechanism in a final bid to pop it into place.

"We're hoping to just overpower whatever is holding it," Mr. O'Neil said.

Hammering will continue at intervals through the first couple of weeks of January, he said. If this process is unsuccessful, he said, NASA will probably give up on the primary antenna and concentrate on developing a program to pull down as much data as possible by the low-gain antenna.

Scientists are particularly eager to study Jupiter in detail because they think it may provide information about how the solar system was formed.

With a diameter 10 times that of Earth, Jupiter alone contains nearly three-quarters of the solar system's planetary mass. Scientists believe that Jupiter, of all the planets, retained the largest amount of the primordial gas and dust out of which the solar system condensed.

The interplanetary probe was launched from the space shuttle Atlantis on Oct. 18, 1989, and began a series of loops through the inner solar system to build up speed for the journey to Jupiter. It is due to arrive at the planet Dec. 7, 1995.

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