Galileo speeds by Jupiter's moon Callisto in this computer animation. Photo: NASA/JPL

The camera on NASA's Galileo spacecraft may not be working properly as the spacecraft heads toward Jupiter's moon Callisto for a close flyby on Friday at 7:24 a.m. EDT.

"We are not totally surprised, because we knew all along that Galileo might encounter difficulties from passing close to Jupiter's powerful radiation belts," said Dr. Eilene Theilig, Galileo project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We are attempting to get a better understanding of the problem and to do what we can to minimize the loss of images."

Voltage readings received from the camera Wednesday and Thursday are the same as when the camera was in a problem state during its last previous flyby, passing the moon Ganymede five months ago. During that flyby the condition was intermittent. It self-corrected spontaneously several times and was also corrected by commands from the ground to cycle its power off and on. More than half of the 120 images taken during that encounter period were captured successfully.

This week, however, indications of the problem began shortly before this orbit's closest approach to Jupiter on Wednesday morning and have persisted in every voltage reading received since then, even after the power-cycle commands, Theilig said mid-day Thursday.

"We may have lost the camera images scheduled so far, but the bulk of the camera observations are (Friday) morning at Callisto," she said.

Other scientific experiments on Galileo, including infrared imaging of Jupiter's clouds and a radio study of Jupiter's atmosphere, have functioned properly during this pass through the inner portion of Jupiter's system. Data will be transmitted to Earth during the next two months.

This is Galileo's 30th orbit of Jupiter since arriving at the giant planet in 1995. The original mission lasted two years in orbit, but the mission has been extended three times. By repeatedly passing through the highly radioactive environment close to Jupiter, Galileo has endured more than three times as much radiation as it was designed to withstand. Radiation damage to an electronic component is the main suspect in the camera's problem.