The spacewalkers, meanwhile, made fast work of the array replacement, a job that called for them to repeatedly move back and forth between a shuttle cargo bay carrier and a point midway up the four-story observatory.

STS-109

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Massimino spent the better part of his day anchored to the end of the shuttle's 50-foot (15-meter) robot arm, which was operated by astronaut Nancy Currie inside Columbia's crew cabin.

Newman scaled hand-over-hand, up and down the side of the observatory, his course defined by a series of metal handrails that look like bronze, bathroom towel bars.

Working with a pistol-grip power socket wrench, Newman unbolted the old array and its associated electronics relay box and then handed them off to Massimino, who hauled them back down to the pallet, stowing the parts for a return to Earth.

He then hauled the new array and its relay box up to the telescope, where Newman installed them with the same tool.

The veteran Newman guided his less experienced colleague through the excursion, and Massimino at times seemed to need reassurance -- particularly when it came time to single-handedly hoist the bulky new panel up to Hubble on the end of the shuttle arm.

"You're going to be fine," Newman told his crewmate. "I think you're ready to go up and away."

"Now you guys are going to keep watching, right?" Massimino asked.

"We're watching, Mike," shuttle skipper Scott Altman called out. "We're all ready for a sight."

Up and away Massimino went, taking great care not to let the new wing get away from him. With his feet fixed to the robot arm, his two gloved hands clung to the $9.5 million solar array, and then slowly, he rotated the panel to line it up with a mounting point on the telescope.

"Keep it coming. Looking good. Very nice," Newman said as Massimino approached. "Take a big breath and relax. You're doing a great job."

As it turned out, the new wing plugged into the observatory perfectly -- as did a replacement for a faulty telescope pointing control device, the latter of which was installed inside a telescope equipment bay.

Running ahead of schedule all day, the astronauts also had time to repair latches on the door of a science instrument compartment and install a protective thermal cover on the outside of the observatory.

The extra chores were last-minute add-ons to the spacewalk, which lasted seven hours and 16 minutes.

"It's been a long day -- lots of great work onboard," astronaut Mario Runco told the six-man, one-woman shuttle crew from NASA's Mission Control Center in Houston.

"It was a busy day," Altman said. "But we got a lot accomplished."

Next up for the crew: A spacewalk aimed at replacing a crucial but flawed power switching station that routes electricity from the telescope's solar wings to science instruments and spacecraft control systems.

Two more excursions also are planned this week.

Hubble is to be outfitted with an advanced planetary camera Thursday, and then astronauts will attempt to revive a dormant infrared instrument on Friday.

If all goes well, the renovated Hubble telescope will be cast back into orbit Saturday before the shuttle crew heads off on a three-day trip back to Earth. Landing here at NASA's Kennedy Space Center remains scheduled for 4:35 a.m. EST (0935 GMT) March 12.