An instrument that helped the orbiting Hubble Space Telescope look at black holes, newly forming stars and far-off galaxies has broken down, and NASA said yesterday that it is looking at possible ways to fix it.

The instrument, called the Space Telescope Imaging Spectrograph, was installed in 1997 and was designed to operate for five years. But it may be possible to rescue some of its operations, NASA said.

The space agency said Hubble's other instruments are operating normally.

NASA said an electrical malfunction might be to blame. A similar problem affected the instrument in 2001, forcing a switch to the backup side. Now the backup side has failed, NASA said.

NASA has proposed bringing Hubble down in a controlled descent into the ocean, because it otherwise must be maintained by space shuttle astronauts or some kind of robotic mission. But astronomers, who rely heavily on Hubble, have objected.

The spectrograph, which breaks down light into its component spectra, provides about 30 percent of Hubble's scientific observations. It has helped obtain independent confirmation of the age of the universe by finding the coolest, and therefore the oldest, white dwarf stars in Earth's galaxy, helped catalog massive black holes and made the first measurements of the chemical composition of the atmosphere of a planet outside our solar system.