One of the four astronomical instruments on the Hubble Space Telescope shut down earlier this week and engineers are trying to pin down the problem. The other three instruments continue to operate normally.

The instrument, called the Space Telescope Imaging Spectrograph (STIS), does not make the classic pictures that Hubble is famous for, but instead splits light into its constituent colors. It has been used to discover dim stars that reveal clues about the age of the universe, study planet-forming environments around other stars and provide insight into black holes.

The STIS stopped working Tuesday, Aug. 3, going into what officials call a suspended mode, according to a NASA statement released Friday. Mission managers think there is a malfunction in a power converter. It is not known if the glitch can be fixed.

The spectrograph was installed during the second Hubble servicing mission, in 1997. It was designed to operate for five years. NASA says it has met or exceeded all its scientific requirements.

NASA has convened an Anomaly Review Board to investigate the problem and determine if the instrument is recoverable.

"A final decision on how to proceed is expected in the coming weeks as analysis of the problem progresses," according to the statement.

The instrument is not slated for replacement by the next servicing effort. That mission, which NASA Administrator Sean O'Keefe cancelled in January due to safety concerns for the space shuttle fleet, is up in the air right now. O'Keefe reconsidered his decision and said a robotic mission might be undertaken, though he continues to resist expert suggestions that a manned shuttle mission to service the telescope remain a serious option.

Hubble's other instruments -- the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), the Advanced Camera for Surveys, and the Wide Field/Planetary Camera 2 -- are not affected by the problem.

The STIS is used for about 30 percent of Hubble's observing time. A standby list of targets for the other three instruments will likely take up that time.

Hubble has otherwise been in good health. But its batteries and pointing gyroscopes are expected to fail in the next two to three years. If they are not replaced by a robotic or human servicing mission, Hubble will likely cease operations by 2008, engineers have concluded.

  • Hubble Special Report