The gyro that failed had been exhibiting end-of-life behavior for approximately a year, NASA said, and its failure was not unexpected; two other gyros of the same type had already failed.
Hubble has carried a total of six gyroscopes - three standard and three enhanced - since astronauts installed them during a spacewalk in 2009, typically using three at once. That gyro, which had been powered down, is not "performing at the level required for operations", according to spacecraft telemetry after it was commanded to turn on.
The official Hubble Twitter account echoed this sentiment, tweeting that the telescope was "built with multiple redundancies", and that even though it is left with just two gyros, it can work with just one.
Only two of those enhanced gyros are now running. But when the third one was powered up, it wasn't operating as it should be, so NASA Goddard engineers placed the telescope in safe mode while they try to figure out the problem.
DC, USA - The Hubble space telescope, which has been in orbit since 1990, has temporarily suspended operations because of a gyroscope failure, the US space agency said Monday, October 8. Most recently, the telescope helped scientists firm up their evidence for the first detection of a moon circling an exoplanet.
Dr. Rachel Osten, the deputy head of the Hubble mission, said it had been a "very stressful weekend".More news: Drew Brees Becomes All-Time Passing Leader on 62-Yard TD Pass
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'Which the Astro community wants desperately.
But when the telescope's operators switched the instrument to running on all three enhanced gyroscopes, one wasn't working quite as well as it should have been.
NASA was quick to offer reassurance: "Hubble's instruments still are fully operational and are expected to produce excellent science for years to come", public affairs officer Felicia Chou wrote in an update on the NASA website.
Although Hubble uses three gyros at a time for maximum efficiency, it can still continue to make scientific observations with just one, NASA said. The Hubble Space Telescope floats against the background of Earth after a week of fix and upgrade by Space Shuttle Columbia astronauts in 2002.
As a result, Hubble is in so-called safe mode with non-essential systems turned off, putting all science observations on hold.