The space station's two American astronauts went out on a riskier-than-usual spacewalk Wednesday and fixed one of two equipment failures that crippled their power system and threatened to stall construction at the orbiting outpost.
Commander Peggy Whitson and Daniel Tani replaced a motor needed to tilt a solar wing toward the sun, taking extra precautions to avoid being shocked. Once the new motor was hooked up, electricity began flowing through the unit and provided a power boost.
"Yee-haw! Excellent," Whitson said.
Flight controllers tested the motor via ground commands, and everything checked out so well that NASA declared the operation a success. "Awesome work you guys," Mission Control radioed up.
The tilting mechanism stopped working in early December, exacerbating a power problem that arose three months earlier when a solar wing rotating joint jammed up and had to be shut down.
Wednesday's seven-hour spacewalk was especially hazardous because of the risk of electrical shock. For safety, Whitson and Tani waited until the international space station was on the dark side of Earth, then carefully undid fasteners and disconnected cables, and pulled out the old electric motor.
A few minutes later, the spacewalkers popped in the new 200-pound-plus motor, a spare that had been stored on board. "We're all breathing down here. Thanks a lot," Mission Control said.
Whitson and Tani performed virtually the entire job in the darkness of night, pausing during the daytime swings around Earth when 160 volts of electricity would course through the cables. As an added precaution, the astronauts did not shine any nonessential lights on the solar wing to prevent power generation.
Because the motor serves as the structural backbone for the solar wing, the spacewalkers had to make sure the wing didn't come off and fly away.
Earlier in the morning, the spacewalk almost ended up being aborted when a radio-relay problem prevented Whitson and Tani from hearing Mission Control. Flight controllers restored communication through a backup channel within 20 minutes.
With their motor work finished, the spacewalkers moved over to the damaged solar rotary joint for yet another inspection.
NASA is uncertain what to do about the clogged joint, which is supposed to continuously rotate 360 degrees to keep the solar wings pointing toward the sun. As many as four spacewalks will be required later this year to remove metal shavings from the joint and get it working again. Shuttle flights could be delayed this fall if the joint isn't fixed.
It was the first spacewalk for Tani since his 90-year-old mother was killed in a car accident outside Chicago just before Christmas. Flight director Holly Ridings said Tani has been coping extremely well, and that his work has not been affected.
Tani was supposed to return to Earth in December aboard Atlantis, but his trip home was delayed because of problems with the fuel gauges in the shuttle's external tank. NASA is now aiming for a Feb. 7 liftoff after replacing a bad connector at the bottom of the tank.
Top managers gathered Wednesday to officially set a launch date and evaluate the latest shuttle problem, a kinked radiator hose in the payload bay.
The shuttle will carry up Tani's replacement, a French astronaut, as well as the European science lab, Columbus.
Wednesday's spacewalk fell on the eve of the 50th anniversary of the launch of America's first satellite, Explorer 1. The very next day, Friday, will mark the fifth anniversary of the Columbia disaster.
