Frayed wire causes problems with solar array retraction
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: December 18, 2006
Perched on the end of the space station's robot arm, astronaut Robert Curbeam spotted a frayed guidewire that was preventing solar array slats from folding up smoothly. Using an insulated tool similar to a windshield ice scraper, he gently flipped the slats, one at a time, to work the frayed section of guide wire through a series of grommets. That allowed the blanket panels to line up properly, much like the slats in a pleated blind. Commands were then sent to pull the array's central mast in about 40 inches, the length of one of its open-framework bays.
"OK, and Houston, we're ready to go one bay retract," shuttle skipper Mark Polansky radioed. "OK. Here we go. Ready, ready, retract."
After one bay, the retraction was halted. Curbeam reported "I have a grommet that's caught on the outboard guidewire of the aft blanket."
Fuglesang, free floating near the base of the array, shook the blanket storage box, setting up ripples in the still-exposed slats in hopes of freeing the guide wire. It moved somewhat, but did not pop free. Fuglesang shook it again, to no avail.
"Can I get one more shake?" Curbeam asked.
"You're go for another three-cycle shake."
"OK," Fuglesand said. "One, two, three..."
But the shaking didn't work and Curbeam, on the end of the robot arm, was moved up to the panel to try some additional slat flips with his scraper tool. To his surprise, guidewire was moving freely and Curbeam could not see anything obviously amiss. But the guidewire was slack, indicating a problem somewhere.
He then pulled out an improvised wire-puller tool, snagged the loose guidewire and gently pulled to take up the slack. But the cable pulled in freely, resulting in a loop of free line.
"Here we go... yes, and all that's doing is kind of pulling the outboard looseness."
He reported the guidewire was sliding through the grommets smoothly, raising questions about whether a takeup reel at the base of the blanket box was winding properly.
"Our concern is, either the reel isn't doing its job or that snag is trying to roll down until it gets very close to the reel," Robinson said.
Flight controllers then asked Curbeam what he thought about using a set of needle nose pliers to pull the frayed wire back out manually to get a feel for the motion. Then he could, perhaps, cut the fray away. Fuglesang was asked to look at the base of the blanket box and report whether he could spot the guidewire where it entered a takeup reel.