Two astronauts pulled off a riskier and trickier-than-usual spacewalk Wednesday, replacing a failed electric motor and giving the international space station a much-needed power boost.
The station's power system still has problems; a joint for rotating one set of solar wings is mysteriously clogged with metal shavings and can't be fixed until later this year. Wednesday's successful operation, however, added to the power margin at the orbiting outpost and cleared the way for the deliveries of two science labs.
Atlantis is supposed to lift off with the European Space Agency's Columbus lab next week after a two-month delay, but a new problem could force yet another postponement.
An inspection Tuesday uncovered a bent radiator hose in the shuttle's payload bay. The hose works as is and doesn't leak Freon, but some engineers fear it could break from the vibrations during liftoff.
Shuttle program manager Wayne Hale said his team will review the problem again Saturday and, until then, preparations will proceed toward a Feb. 7 launch.
Discovery had a similarly bent radiator hose during two flights, without any leakage, Hale said. The braided metal hose is supposed to retract into a box with rollers when the payload bay doors are closed, "and clearly something is not lining up in that box properly," he said.
NASA may decide to fly Atlantis without any repairs or could try to straighten the hose, Hale said. Replacing the hose could lead to a launch delay.
"If it's not safe to fly, we won't fly it," Hale told reporters.
Each space shuttle is equipped with two Freon coolant loops to dispel the heat generated by on-board electronics.
As for the repairs to Atlantis' fuel tank since December's failed launch attempts, Hale said he is confident a newly soldered connector will resolve NASA's gauge problems once and for all.
Two hundred miles up, space station 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 it checked out fine.
"Yee-haw! Excellent," Whitson said.
The tilting mechanism stopped working in early December, exacerbating the power problem that arose three months earlier with the jammed solar wing rotating joint.
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, 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. 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.
"Given the complexity of this spacewalk and the risks that we had to manage ... we are exceptionally pleased with how things went," said flight director Kwatsi Alibaruho.
The spacewalkers also conducted yet another inspection — the fourth — of the damaged solar rotary joint.
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. Shuttle flights could be delayed this fall if the joint isn't fixed by then.
It was the first spacewalk for Tani since his 90-year-old mother was killed in a car accident outside Chicago just before Christmas. He has been in space since October, and Atlantis will be his ride home.