NEW YORK — NASA’s effort to resume full science operations aboard the ailing Hubble Space Telescope hit a snag Oct. 16, and agency officials said it was unlikely they would be able to revive the observatory until late this month.

“We think the soonest we would be back to doing full science would be sometime late next week,” Art Whipple, manager of the Hubble Systems Management Office at NASA’s Goddard Space Flight Center, said during an Oct. 17 teleconference with reporters.

The space telescope slipped back into a protective “safe mode” late Oct. 16 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 spokeswoman at the space telescope’s control center at the Goddard Space Center in Greenbelt, Md.

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, known as Side A, had been working properly since the telescope launched in April 1990.

“This unit operated flawlessly for 18 and a half years, which is a pretty good performance,” Whipple said Oct. 14. “Unfortunately, nothing lasts forever.”

Hubble has a backup channel, Side B, and engineers began the complicated activation of that unit early Oct. 15. The tricky switch also required the activation of five other backup systems that also had been in hibernation since Hubble’s launch in 1990.

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 on line 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.”

Two glitches popped up during the Side B reactivation: a lower than expected voltage reading from Hubble’s main camera and a signal drop out in the telescope’s main computer, Hubble managers said.

Engineers still are confident they can regain full science capabilities for Hubble, but first must understand both glitches and whether they are related.

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 the orbital observatory for the fifth and final time. That mission now is slated to launch in February, with Hubble engineers hoping to include spare parts to restore the Side A data relay channel.