With only one gyro Hubble is restricted in what parts of the sky it can look, because it can only rotate in one direction at a time.
NASA announced that one of Hubble's gyroscopes failed last Friday.
"Hubble's instruments still are fully operational and are expected to produce excellent science for years to come", the NASA statement reads.
Hubble, which has been observing the heavens since 1990, went into a protective safe mode after another one of its orientation-maintaining gyroscopes failed, mission team members said Sunday night (Oct. 7). The Hubble telescope, launched in 1990, has explored the most remote regions of the cosmos in search of clues about the origin of life and the universe itself.
Hubble deputy mission head Rachel Osten, said, 'Very stressful weekend. That's the error engineers are working to fix now, with the instrument in safe mode to allow them to run tests.More news: Cyclone weakens; nine dead in Andhra Pradesh, Odisha
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Now one of the remaining three isn't working as expected, leaving Hubble with just two working gyros and it needs at least three for optimal operations. According to BBC, four were still working when the failure occurred late last week.
Hubble's pseudo-successor, the James Webb Space Telescope, was supposed to already be up and running for years by this point, but Northrop Grumman's inability to do the job it's being paid billions of dollars to do has caused over a decade's worth of delays. But only three gyros are needed for normal telescope operation with the others held in reserve.
This photo of the Hubble Space Telescope was taken on the 5th servicing mission to the observatory in 2009. "Everybody said OK, no big surprise, we've been expecting that for a year, let's turn on the gyro that was off at the time to get back onto science operations".
Hubble usually functions with three gyros, and before last week two of the standard gyros had failed (three of the six are standard, and three are enhanced, according to NASA spokespersons). But Hubble will still be able to do some useful science, and dropping down to one gyro instead of two effectively doubles its lifespan.
While NASA says that reduced-gyro mode would have "relatively limited impact on the overall scientific capabilities", some astronomers are concerned that the reduced-gyro mode could adversely affect some types of observations, such as of solar system objects, that require the precision of three-gyro operations.