The trouble arose in today's spacewalk when Massimino, in space, was unable to remove a bolt from the spectrograph's handrail. Eventually, the astronaut worked around the issue by simply yanking the handrail until the head of the bolt snapped off. After that, the two astronauts were able to finish the repair job.

However, because they spent so much effort on the handrail, they didn't have time to install a new stainless steel blanket on the outside of the telescope. The blanket, which should offer thermal protection for equipment bays, will replace multi-layer insulation that has started to fall apart.

Mission Control is trying to reconfigure a final Hubble spacewalk Monday to see if the astronauts can fit in the installation of the blanket .

Monday's spacewalk will focus on installing a battery module containing three batteries. On Tuesday, the seven-astronaut crew will deploy . They're scheduled to return to Earth on Friday.