NASA's attempt to revive the ailing Hubble Space Telescope has hit a snag, leaving the iconic observatory's return to science observations in limbo for at least another day, agency officials said Friday.

The space telescope slipped back into a protective "safe mode" late Thursday instead of completing a switch to a backup system that engineers hoped would restore Hubble's ability to beam images and data back to Earth, said Susan Hendrix, a NASA spokesperson at the space telescope's control center at the Goddard Space Center in Greenbelt, Md.

"We had a little trouble with Hubble last night," Hendrix told SPACE.com, adding that Hubble managers hoped to have a clearer picture of the glitch later Friday.

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The 18-year-old Hubble's main science operations have been hobbled since Sept. 27, when a data relay channel failed in the observatory's Science Instrument Control and Data Handling system.

The channel, Side A, had been working properly since the telescope launched in April 1990.

"This unit operated flawlessly for 18½ years, which is a pretty good performance," said Art Whipple, chief of NASA's Hubble systems management office at Goddard, on Tuesday. "Unfortunately, nothing lasts forever."

Hubble has a backup channel, Side B, and engineers began the complicated activation of that unit early Wednesday.

The tricky switch also required the activation of five other backup systems that had also been in hibernation since Hubble's 1990 launch.

Hubble engineers planned to put Hubble into a safe mode configuration during the two-day switch to Side B, and then bring the telescope's systems online once the transfer was complete.

It was only the sixth time in Hubble's 18-year history that the telescope was placed in the safe mode.

"The Side B transition was not complete," Hendrix said. "It was well into it, but not completed."

Hubble's data relay channel woes forced NASA to delay the planned Oct. 14 launch of seven astronauts aboard the space shuttle Atlantis to overhaul to overhaul the orbital observatory for the fifth and final time.

That mission is now slated to launch in February, with Hubble engineers hoping to include spare parts to restore the Side A data relay channel.

NASA hopes to provide a status update on Hubble's condition later today, Hendrix added.

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