The astronauts also are prepared today to install a 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.

In Saturday's spacewalk, astronauts John Grunsfeld and Andrew Feustel worked to repair Hubble's Advanced Camera for Surveys -- the instrument behind some of the telescope's most impressive images of deep space. It stopped working a little more than two years ago.

Wearing thick gloves and orbiting 354 miles above the Earth, Grunsfeld and Feustel removed electronics cards and cut through metal yesterday to repair the three cameras in the instrument. However, NASA announced this morning that one of the cameras did not come back to life after Saturday's spacewalk. "The repair of the Advanced Camera for Surveys' high resolution [camera] was always considered a long shot," NASA said on its site. "It is likely down for good."

NASA said it still considers the overall repair mission of the Advanced Camera for Surveys a success because two of the three cameras are functioning.

Monday's spacewalk, which will be the fifth and the last of the mission, will focus on installing a battery module containing three batteries. On Tuesday, the seven-astronaut crew . They're scheduled to return to Earth on Friday.