NASA to Scale Back Galileo’s Jupiter Mission

Disappointed NASA officials said Wednesday that repeated attempts to hammer open the jammed main antenna on the $1.5-billion Galileo satellite have failed and that mission specialists plan to significantly scale back plans for the Jupiter-bound space probe.

“Certainly we’re disappointed,” said Project Manager William J. O’Neil at NASA’s Jet Propulsion Laboratory in Pasadena. “We’re still going to have an excellent mission, but it’s going to be a lot more difficult to execute than it would have been.”

In addition to being more difficult, the Galileo project is expected to send back far fewer photographs of the solar system’s largest planet and its curious coterie of 16 moons.

Original plans called for Galileo to send 60,000 images. Now, even the best data-compression methods will not let Earth stations receive more than one-tenth that number of photos.

NASA officials stressed that other parts of the mission--including a probe that will detach from the main satellite and parachute into Jupiter--are in “excellent” condition and should give scientists a wealth of new information about the planet.

Galileo’s umbrella-like main antenna, which was folded up to save space and protect it from solar radiation, failed to open as planned in April, 1991. Engineers used information from the satellite and a JPL mock-up to determine that three of the antenna’s 18 ribs were jammed in the closed position.

Late last month, ground controllers instructed the satellite to “hammer” on the antenna using the small electric motor that was to unfurl its gold-plated molybdenum-mesh dish. By switching it on and off thousands of times an hour, they hoped to force the assembly open.

Three weeks and 13,320 cycles later, the antenna has moved slightly but remains useless.

O’Neil said engineers will increase the satellite’s normal rotation to 10 revolutions per minute in March in an effort to pry the antenna open using centrifugal force. The satellite normally revolves at 3 revolutions per minute.

Engineers hold out little hope for success of this maneuver, and on March 1 are scheduled to begin modifying the mission to rely only on the probe’s low-gain antenna.