Hubble telescope (file photo)

The U.S. space agency, NASA, says it hopes to restore the main camera aboard the Hubble Space Telescope by Sunday evening, Washington time. An electronic problem caused it to shut down Monday.

The Hubble's Advanced Camera for Surveys automatically stopped operating, after signaling to ground controllers that voltage in its power supply exceeded it limits. NASA says engineers have switched to a backup power unit, and hope to return to scientific observations late Sunday.

Agency official Ed Ruitberg says there is always a chance this will not fix the trouble, but he says it is the most likely solution.

"The instruments are designed with redundant electronics," he said. "We prepared for this type of event. We know these things can happen. We're going to continue operating the telescope efficiently. So, I think it's just a bump in the road that we'll figure out a way to solve."

Space shuttle astronauts installed the camera in 2002, sharpening the observatory's vision by 10 times. It has allowed astronomers to see a much greater distance into the universe, in effect, letting it look back further in time to when stars and galaxies formed.

Ruitberg says Hubble's other cameras continue to work, and the technical problem with the main instrument has caused only lost observation time that can be made up.

"The observations that we did have scheduled last week, and that we would have scheduled this week, will be deferred and the science acquired later," he said.

The Hubble telescope has orbited Earth since 1990, but is showing signs of aging. Backup gyroscopes that help keep the observatory steady have failed, and its batteries are weakening. NASA canceled a maintenance visit by shuttle astronauts planned for 2004 because of the Columbia disaster the year before. But, if the shuttle fleet returns to routine operations, agency administrator Michael Griffin is considering one more servicing mission to Hubble before the fleet retires in 2010.

Hubble controllers had expected the telescope to fail by the end of next year, or soon after, if astronauts do not replace gyroscopes and batteries soon. But mission scientist Jennifer Wiseman at NASA headquarters say engineers have taken steps to ease the problems, so that the observatory can survive longer.

"The team has been working on a multitude of life extension activities for the telescopes to allow it to operate in its current state, to keep the telescope operating at peak performance as long as possible, whether or not we get the hoped for servicing mission," said Wiseman.

For example, Wiseman points out, Hubble engineers have figured out how to stabilize the telescope with only two instead of the usual three gyroscopes. She says they might be able to operate it with only one, making the balancing system last longer.