Hubble telescope restores 3rd instrument in slow return to operations

The Hubble Space Telescope in orbit around Earth.
The Hubble Space Telescope in orbit around Earth. (Image credit: NASA)

NASA's most beloved space telescope is nearly back to normal.

Three of the Hubble Space Telescope's four science instruments are now back to work as the team behind the observatory continues to investigate and assess a glitch that sent all four instruments into safe mode on Oct. 25.

Hubble's Cosmic Origins Spectrograph (COS) has now joined the Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) in resuming observations, according to a statement released Monday (Nov. 29). The Space Telescope Imaging Spectrograph (STIS) is now the only Hubble instrument that remains in safe mode.

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The observatory's science instruments went into safe mode after issues arose with a type of message that governs the instruments' internal clocks. The "loss of a specific synchronization message," as the situation is formally known, first occurred on Oct. 23, but resetting the instruments got them back to work quickly.

But not for long. Two days later, "the science instruments again issued error codes indicating multiple losses of synchronization messages" and went into safe mode, according to a NASA statement.

Hubble personnel worked to troubleshoot the issue using a retired instrument that remains aboard the observatory, then began applying fixes to each of Hubble’s science instruments in turn. In tandem, the team is also working on software changes that would prevent science instruments from shutting down in a similar situation of multiple losses of synchronization messages.

The Hubble Space Telescope, a joint project of NASA and the European Space Agency (ESA), entered Earth orbit in April 1990 after launching aboard space shuttle Discovery. During the observatory's first two decades, astronauts were able to visit Hubble aboard space shuttles to replace instruments and conduct other upgrades and repairs.

But for the past 10 years, Hubble has been on its own: NASA retired the fleet of space shuttles in 2011, so astronauts can no longer visit the observatory. In that time, the Hubble Space Telescope has weathered its share of glitches, including most recently a computer issue that knocked the observatory out of service for a month this summer.

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Meghan Bartels
Senior Writer

Meghan is a senior writer at and has more than five years' experience as a science journalist based in New York City. She joined in July 2018, with previous writing published in outlets including Newsweek and Audubon. Meghan earned an MA in science journalism from New York University and a BA in classics from Georgetown University, and in her free time she enjoys reading and visiting museums. Follow her on Twitter at @meghanbartels.