Baltimore ? The main camera on the Hubble Space Telescope, which has revolutionized astronomy with its stunning pictures of the universe, has stopped working, an instrument specialist who works with the camera said Saturday.

The Advanced Camera for Surveys, a third-generation instrument installed by a space shuttle crew in 2002, went off line Monday, and engineers are still trying to figure out what happened and how to repair it.

“It’s still off line today,” Max Mutchler, an instruments specialist at the Space Telescope Science Institute in Baltimore, said Saturday.

Engineers are hopeful the problem can be fixed, said Ed Campion, a NASA spokesman at Goddard Space Flight Center near Baltimore, which is responsible for managing the Hubble.

A bad transistor could be causing the trouble, Campion said. If so, a backup could be used. Another suspicion is that some of the camera’s memory was disturbed by a cosmic event. That could be fixed by reloading the memory.

“Both possibilities are things that can be resolved here on the ground,” Campion said.

The camera sent messages Monday indicating power voltages were above their upper limits, causing it to stop working.

“At this point, the ACS is in a safe configuration, and further analysis is ongoing,” according to a statement by the Space Telescope Science Institute.

The Advanced Camera for Surveys consists of three electronic cameras and a complement of filters and dispersers that detect light from the ultraviolet to the near infrared.

It was installed on the Hubble during a servicing mission by the crew of the space shuttle Columbia. Development of the ACS was a joint operation among Johns Hopkins University, Goddard Space Flight Center, Ball Aerospace and the Space Telescope Science Institute.

Hubble, launched in April 1990, needs new batteries and gyroscopes if it is to keep working beyond next year.