HOUSTON - Despite a late start caused by airlock glitches, two Atlantis shuttle astronauts pushed through their mission's final spacewalk to help deploy a vital new solar array radiator among other maintenance outside the International Space Station (ISS).

Clad in NASA spacesuits, Atlantis spacewalkers Joseph Tanner and Heidemarie Stefanyshyn-Piper spent more than six hours outside the ISS on assorted odd jobs and the liberation of the stowed Port 4 truss radiator, which they helped deliver earlier this week.

"Yes, that's a deploy," Tanner said as he and Stefanyshyn-Piper watched the accordion-like radiator unfold at 9:05 a.m. EDT (1305 GMT).

The radiator, designed to cool systems for the space station's new P4 solar arrays unfurled yesterday, will now allow those electricity-generating wings to power the P4 truss independently of the ISS, mission managers said Thursday. The arrays and radiator are part of the $372 million Port 3/Port 4 integrated truss structure hauled to the ISS by Atlantis to jump start the outpost's stalled construction.

"These guys make it look really easy and their flight is a very difficult flight," said Michael Sufferdini, NASA's ISS program manager, of Atlantis' six-astronaut STS-115 crew in a Thursday briefing. "I couldn't ask to a better start, a restart, to assembly."

Tanner and Stefanyshyn-Piper began their six-hour, 42-minute spacewalk at 6:00 a.m. EDT (1000 GMT), about 45 minutes late, due to a tripped circuit breaker in the station's Quest airlock. The glitch caused a depressurization pump to shut down, but resulted from an electrical spike and not a pump short circuit, NASA officials.

ISS maintenance, tests

Many of the tasks planned for today's spacewalk were performed earlier this week by other STS-115 astronauts who'd finished their work early.

In addition to priming the new solar array radiator for deployment, Stefanyshyn-Piper and Tanner repaired a defunct S-band antenna support assembly, a task that took much longer than planned as flight controllers and the spacewalkers struggled to move into the proper position.

"We, inside here, think a little drama is always good," STS-115 astronaut Steven MacLean, who oversaw his spacewalking crewmates from inside Atlantis.

While Stefanyshyn-Piper finished work on the S-band antenna, which will be a vital communications tool for future ISS construction, Tanner wrapped the station's primary video and data Ku-band antenna in a protective thermal cover.

Tanner also secured bolts in place on the station's Port 6 truss solar array truss, which reaches nine stories above the orbital outpost and is the highest point on the ISS.

"Well that's a pretty above average view I've got to now," Tanner said while looking down at the ISS, Atlantis and the entire Earth.

He also made short movies of Atlantis' starboard wing leading edges - covered in a carbon composite heat shield - with an infrared video camera before heading back inside the ISS.

Today's spacewalk marked the seventh for Tanner - a veteran of extravehicular activities (EVAs) - and the second for Stefanyshyn-Piper, whose experience Tanner has said will be vital for future ISS assembly.

"This is good experience for you so you can teach others about it," Tanner told Stefanyshyn-Piper. "Your next job is to teach."

Stefanyshyn-Piper worked to remove a series of tough bolts from cinches and restraints to free the station's new radiator, prompting accolades from her spacewalking partner.

"You're going to outdo Xena," Tanner said, referring to television's warrior princess.

Last time out

Friday's spacewalk marked the third and final EVA planned for NASA's STS-115 mission. Two teams of spacewalkers spent a total of 20 hours and 19 minutes working outside the ISS this week.

About seven hours and 11 minutes of that time stemmed from work by STS-115 spacewalkers Daniel Burbank and Steven MacLean of the Canadian Space Agency during a Wednesday spacewalk, a career first for both astronauts. The remaining 13 hours and eight minutes were performed by Stefanyshyn-Piper, also her first, and Tanner.

"This has been a great job and a great mission," Stefanyshyn-Piper said.

Today's spacewalk marked the 72^nd EVA dedicated to ISS assembly or maintenance, as well as the 25^th staged from the station's Quest airlock. Spacewalkers have spent a total of 438 hours and 36 minutes building the orbital laboratory.

"Maybe we'll catch Jerry Ross," joked Tanner, referring to U.S. spacewalking record holder Jerry Ross, who racked up 58 hours and 18 minutes during his NASA astronaut career.

Tanner is now the fourth most experienced spacewalker in history, with a total of 46 hours and 29 minutes in seven EVAs, after NASA astronaut Steve Smith, Ross and all-time champion Russian cosmonaut Anatoly Solovyev, who staged 16 career spacewalks during 77 hours and 41 minutes of orbital work.

"I don't think there are enough shuttle flights to catch Jerry Ross," Stefanyshyn-Piper replied.

Mission controllers awoke Atlantis' six-astronaut crew to the tune of the Eagles' "Hotel California," chosen for Tanner by his family.

"That song reminds me of some great traveling adventures, sort of like this one," Tanner said. "It's gonna be a great day."

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