Spacewalkers Help Detach Space Station Solar Power Tower
The Port 6 solar array truss is hauled from its former perch of seven years atop the International Space Station during an Oct. 28, 2007 spacewalk during NASA's STS-120 mission.
Credit: NASA TV.

This story was updated at 1:22 p.m. EDT.

HOUSTON - Two spacewalking astronauts helped pry a massive solar power tower from its perch atop the International Space Station (ISS) Sunday and discovered odd metal shavings in a large joint that turns the orbital lab?s starboard solar arrays.

Working with robotic arm-wielding crewmates inside the ISS, spacewalkers Scott Parazynski and Daniel Tani removed bolts and power lines securing the 17.5-ton Port 6 (P6) solar array, beginning its three-day move to the left side of the station?s main truss.

?Don?t drop it,? one of the astronauts joked as crewmates Stephanie Wilson and Doug Wheelock hauled it away with the station?s robotic arm.

The P6 truss will be reattached to the port-most edge of the ISS during a planned Tuesday spacewalk after a delicate ballet that requires handing the 35-foot (10.6-meter) long girder off between the ISS and shuttle robotic arms twice on Monday. Parazynski, a Discovery shuttle astronaut, has equated the task to moving an entire house.

?I believe in the crew, I know that they?re ready to do this task,? Discovery commander Pamela Melroy said Saturday. ?Both crews are ready to cope with whatever comes and we?re very hopeful.?

Sunday?s 6.5-hour spacewalk began at 5:32 a.m. EDT (0932 GMT) and was the second of a record-tying five excursions planned during NASA?s STS-120 mission to the ISS. It marked Parazynski?s fifth career spacewalk and the second for Tani.

?It?s great to be back in space,? said Tani, who is replacing NASA astronaut Clayton Anderson as part of the station?s Expedition 16 crew.

Station?s jittery joint

The spacewalkers also added handrails and other equipment to the hull of the station?s new Harmony node and collected samples of metal shavings from inside a rotary joint designed to turn the outpost?s starboard solar arrays like a paddlewheel to track the Sun.

?It?s quite clear that there?s metal to metal scraping, and it?s widespread,? Tani said after inspecting the joint.

Flight controllers sent Tani to examine the 10-foot (three-meter) wide Solar Alpha Rotary Joint after spotting current spikes and a slight vibration in its attached truss segment.

The joint is part of the Starboard 3/Starboard 4 solar array truss that arrived at the outpost in June. Mission managers hope to determine the source of the vibration to determine whether the joint can continue rotating its outboard solar wings to maximize space station power production.

Tani also photographed a handrail suspected of having sharp edges, which could damage the vital pressurized spacesuits that protect astronauts from the vacuum of space. NASA cut an August spacewalk short after an Endeavour shuttle astronaut spotted a small tear in the outer layers of his spacesuit glove.

While wrapping up today?s spacewalk, Tani spotted his hometown of Lombard, Illinois, just a few hours after finding Ireland, where other relatives live.

?I?m looking at my hometown!? Tani exclaimed. ?Wow, what an awesome view.?

Tricky job ahead

With Sunday?s spacewalk complete, the clock is ticking to finish the P6 truss?s move to the port edge of the ISS.

Astronauts temporarily installed the $276 million solar array atop the space station?s Z1 truss in 2000, then stowed its expansive solar wings during shuttle flights in December and June. The girder can stay in its current position at the end of the station?s robotic arm for about 56 hours before the extreme temperatures of space take their toll, mission managers said.

But the real challenge begins tomorrow, when Wilson and her crewmates will use Discovery?s robotic arm to latch onto the truss. They will then hand it back to the station?s robotic arm, which Wilson will outstretch to its maximum, 57-foot (17-meter) reach on Tuesday to ease P6 into place under the guidance of two spacewalking crewmates.

?You?ve got this big truss, the arm?s fully extended and you?re trying to thread a needle without really good visuals,? said Rick LaBrode, NASA?s lead shuttle flight director for Discovery?s flight. ?So it is extremely complex, but one that we?ve trained really hard and I have every bit of confidence we?re going to pull this one off.?

Sunday?s spacewalk marked the 94th spacewalk dedicated to space station assembly and maintenance, as well as the 66th excursion staged from the orbital laboratory itself. The excursion brought Parazynski up to 32 hours and 38 minutes of spacewalking time, while Tani ended with 10 hours and 45 minutes during his two spacewalks.

Parazynski will step outside the ISS on two more spacewalks, on Tuesday and Thursday, with Wheelock to help reattach the P6 truss and test shuttle heat shield repair techniques. Mission Control roused him and his Discovery crewmates at about 1:08 a.m. EDT (0508 GMT) with the song ?What a Wonderful World? by Louis Armstrong.

?That's how you start the day in space,? Parazynski said. ?I can't think of a more beautiful way to begin the day than hear those words. It really describes the view from space.?

NASA is broadcasting Discovery's STS-120 mission operations live on NASA TV. Click here for mission updates and NASA TV from SPACE.com.