The Hubble Space Telescope is flying partly blind across the heavens, the result of a short circuit on Saturday in its most popular instrument, the Advanced Camera for Surveys.
NASA engineers reported Monday that most of the camera's capabilities, including the ability to take the sort of deep cosmic postcards that have inspired the public and to track the mysterious dark energy splitting the universe to the ends of time, had probably been lost for good.
In a telephone news conference, Hubble engineers and scientists said the telescope itself was in fine shape and would continue operating with its remaining instruments, which include another camera, the wide-field planetary camera 2, or wfpc2, and an infrared camera and spectrograph named Nicmos.
''Obviously, we are very disappointed,'' said Preston Burch, program manager for the telescope, at the Goddard Space Flight Center in Greenbelt, Maryland, noting that the camera had basically met its five-year design lifetime. The Hubble telescope, Burch said, still has significant science capability.
Burch and his colleagues said it was unlikely that they would be able to repair the camera during the next Hubble servicing mission, which is scheduled for September 2008. On that mission, astronauts will replace the wide-field camera with a powerful new version, wfpc3, which will extend the telescope's vision to ultraviolet and infrared wavelengths. They will also install a new ultraviolet spectrograph and make many other pressing repairs.
Noting that the five days of spacewalks for that mission are already full, and that changing things to fix the camera would cost time and money, Burch said, ''At first blush, this doesn't look attractive.''
The Advanced Camera for Surveys was installed on the telescope in March 2002, and it has been the space telescope's workhorse. Among its other feats, in 2003 the camera took the deepest photograph of the cosmos ever taken, the Hubble Ultra Deep Field, showing young galaxy fragments only one billion to two billion years after the Big Bang. In the most recent round of proposals from astronomers to use the telescope, about two-thirds required the advanced camera.
The camera had been operating on its backup electrical system since last summer, however, when electrical problems in its main system caused it to shut down for a while. Now the backup system has failed, dooming its ability to take wide-field or high-resolution images.
The camera might yet be operated in what the engineers called ''solar blind mode,'' at ultraviolet wavelengths to observe phenomena like auroras on Jupiter.
The electrical problems did not apparently spread to the rest of the telescope. Rick Howard, of NASA headquarters, said: ''The fuse did what it was supposed to do. It saw a high current, and it popped. It protected the rest of the telescope.''
Astronomers said that the Space Telescope Science Institute had developed a contingency plan of observations that could go on without the camera and that there was no shortage of astronomers who would want to use it. Some of the telescope's most crucial and high-visibility programs, however, will be delayed.
Adam Riess, of the space telescope institute, who has used the Hubble telescope to search for supernova explosions in the distant universe to gauge the effects of dark energy on cosmic history, said these explosions would now be out of reach until the new camera was installed.
Still, Riess said in an e-mail message, it was a great camera.
''Although it only lasted 4.9 years, it was only rated for five years,'' he said, ''so we really got our money's worth.''