One of the four instruments on board the Hubble Space Telescope has stopped working, US space agency Nasa has said.
The exact source of the problem is not known
The STIS, or Space Telescope Imaging Spectrograph, was installed during the second Hubble servicing mission in 1997 and was designed to work for five years
It was used to investigate black holes, to discover dim stars that reveal clues to the age of the Universe and study the atmosphere of an extrasolar planet.
Engineers are currently trying to track down the source of the problem.
Nasa has convened an Anomaly Review Board to determine whether the failed instrument is recoverable.
The STIS separates light from celestial objects into its component colours. This provides astronomers with data on the temperature, composition, density and motion of these objects.
The instrument stopped working on 3 August and went into what Nasa officials call a suspended mode. Nasa said it had met or exceeded all its scientific requirements.
Mission managers think the problem could be due to a malfunction in a power converter.
The STIS accounts for about 30% of Hubble's observing time.
A new safety regime brought in for space shuttle flights following the Columbia disaster ruled out any further missions to service Hubble.
Despite recent suggestions made by an influential panel of researchers that the US space agency keep its options open over manned servicing missions, Nasa chief Sean O'Keefe has given no indication that he will change his mind.
However, Nasa has asked for proposals regarding the feasibility of a robotic servicing mission, which could launch in 2007.
Hubble's other instruments - the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), the Advanced Camera for Surveys and the Wide Field and Planetary Camera 2 - are all operating normally.