The Hubble space telescope, which has been in orbit since 1990, has temporarily suspended operations because of a gyroscope failure, the US space agency has said.
The National Aeronautics and Space Administration (NASA) said Hubble went into "safe mode" on Friday.
"Hubble entered safe mode after one of the three gyroscopes actively being used to point and steady the telescope failed," NASA said in a statement Monday.
"Safe mode puts the telescope into a stable configuration until ground control can correct the issue and return the mission to normal operation," it said.
"Hubble's instruments still are fully operational and are expected to produce excellent science for years to come," NASA added.
Hubble is equipped with six gyroscopes to orient the telescope.
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Hubble is currently down to two working gyros and needs at least three for optimal operations. But it can continue to provide observations with just one functioning gyroscope.
Dr Rachel Osten, the deputy head of the Hubble mission, said it had been a "very stressful weekend." "First step is to try to bring back the last gyro, which had been off, and is being problematic," Osten said on Twitter.
NASA said staff at NASA's Goddard Space Flight Center and the Space Telescope Science Institute were conducting tests and analysis to get the gyro working again.
NASA said if they are unable to recover the malfunctioning gyro Hubble will resume science operations using just one device.
"While reduced-gyro mode offers less sky coverage at any particular time, there is relatively limited impact on the overall scientific capabilities," NASA said.
Hubble has made numerous outstanding observations of the cosmos since it was deployed in 1990.
The James Webb Space Telescope, the successor to Hubble, is scheduled to be launched in March 2021.