Astronauts complete spacewalk to fix space station

(CBS News) Making their second spacewalk in six days, astronauts Sunita Williams and Akihiko Hoshide successfully replaced a critical component on the International Space Station.

After struggling to loosen a jammed bolt holding a replacement electrical switching unit in place on the space station's solar array truss, Hoshide and Williams finally succeeded in driving the recalcitrant bolt out, freeing the 220-pound box from its housing for additional troubleshooting.

With Williams rocking the 220-box from side to side to ease any pressure that might be contributing to the problem, Hoshide, anchored to the end of the station's robot arm, used a power tool to turn the stuck bolt. But their initial attempts were unsuccessful, raising the prospect of a more serious jam.

Flight controllers were on the verge of approving a higher torque setting, but warned "there's a possibility of breaking the bolt at that point."

"You guys are the eyes on the scene, you know what's working and what's not, and I think continuing doing what you're doing and continuing to talk and figure this out is the best mode," astronaut Jack Fischer radioed from mission control. "So you guys have the call."

Hoshide and Williams then made a final series of wiggles and bolt drives at the original torque setting, finally succeeding in freeing the bolt and backing it out.

"It's rotating," Hoshide reported.

"What's that?" Williams asked.

"It's rotating, counterclockwise. I feel a little bit of friction, but..."

"Yeah, nothing like it was," Williams said.

"Yeah."

The main bus switching unit is designed to be secured with two bolts, known as H1 and H2. As the first bolt -- H2 -- is driven in, it pulls the box down onto a cold plate, automatically engaging gangs of electrical connectors and cooling fins.

During an attempt to install the replacement MBSU last Thursday, Hoshide was unable to drive the H2 bolt in far enough to lock the box to its connectors and cold plate.

With the box now free of its housing, the astronauts inspected the bottom of the main bus switching unit to see if there were any obstructions interfering with the box's travel. Nothing obvious was seen. But Williams reported a small amount of metal shavings in the H2 bolt receptacle, similar to what she saw during the spacewalk Thursday.

Two hours into the spacewalk, Williams and Hoshide waited for a daylight pass to begin cleaning and lubricating the bolts and their receptacles, standing by with compressed nitrogen and a set of homemade tools.

A few minutes later, as the space station sailed back into sunlight over the Pacific Ocean, Williams, making her sixth EVA, moved past astronaut Peggy Whitson to become the world's most experienced female spacewalker, breaking Whitson's record of 39 hours and 46 minutes.

"I have message direct from Peggy," Fischer called from Houston. "It says, 'Suni, congratulations on being the female world record holder of the most EVA time. It's an honor to hand off the record to someone as talented as you.' And then she ended it with 'you go, girl.'"

"Well thanks," Williams replied. "Like I said before, it's a matter of circumstance, time and place. Anybody could be in these big boots."

"Copy the boots," Fischer said.