NASA scrambles to finish spacewalk preps

NASA is in a round-the-clock scramble to put the finishing touches on a highly choreographed plan to make risky spacewalking repairs to a high-voltage solar wing that was damaged earlier this week at the International Space Station.

Working half a football field away from safety inside the station, Discovery mission specialist Scott Parazynski will attempt to mend a torn solar blanket that is generating 120 volts of electricity. Effectively a "hot wire" that can't be turned off, the panel could shock or even electrocute the astronaut if he slips up.

"I would say it is conceivable," said veteran astronaut David Wolf, chief of the spacewalk branch within NASA's Astronaut Office.

But not likely.

The metal tools Parazynski will work with have been triple-taped with insulating Kapton. All exposed metal on his spacesuit has been covered so it can't conduct electricity. And Parazynski, one of NASA's most experienced spacewalkers, has been well-schooled in what he can touch -- and what he cannot -- during the course of the unprecedented repair work.

"We've got adequate controls in place where we are comfortable with the shock hazard," said NASA lead station flight director Derek Hassmann.

Parazynski and spacewalking partner Douglas Wheelock aim to exit the U.S. Quest airlock at 6:28 a.m. EDT Saturday and make an hour-long move out to the far left end of the station's central truss.

For Parazynski, it promises to be a sporty trip.

First off, he'll be anchored on the end of an orbital inspection boom that in turn is grappled by the station's "Big Arm" -- a 57.5-foot Canadian robot arm that serves as the outpost's prime construction crane.

Mounted atop a mobile rail cart, the makeshift scaffold and Parazynski will be rolled out along a tracks that run atop the truss. The combined arm and boom, with a four-foot extender and portable work platform, stretch about 90 feet. Click to enlarge and save the view here:

.













Following the lead provided by engineers on the ground, the astronauts scavenged parts from around the station to fashion "cuff links" that will serve to sew up the torn blanket.

Three- to five-foot rods constructed from stock aluminum were covered with Kapton tape and equipped with plastic tabs that toggle just like the backing of classic men's cuff links.

Parazynski will string the aluminum rods through existing, reinforced holes that are spaced evenly across the 15-foot width of the torn blanket. The holes were designed for lengthy pins that secured folded up blanket panels in the rectangular boxes they were launched in. Parazynski will insert the rods through the holes and then flip the tabs horizontal to secure the apparatus to the blanket.

Five of the strap-like rods will be stitched around the ripped and rippled section of the blanket in an attempt to restore full structural integrity to the solar wing while preventing further damage.

Wolf, a veteran who has 23 hours of spacewalking experience himself, said on a scale of one to 10, the repair work rates a 7.5 in degree of difficulty.

"The whole choreography of the spacewalk is complex," he said. "But I think we're going to pull this off."