CAPE CANAVERAL, FLORIDA - A pair of spacewalking NASA astronauts hustled through an electrical repair job outside the International Space Station on Wednesday, then began work to prepare the outpost for new commercial space taxis.
Station flight engineers Reid Wiseman and Barry "Butch" Wilmore floated outside the station's airlock shortly after 8:15 a.m. EDT [1215 GMT] to begin a 6-1/2-hour spacewalk.
Their primary job was to replace a voltage regulator that failed in May, cutting out one of the station's eight power channels. The work needed to be done during a nighttime pass around Earth when the solar arrays are not generating power. The station, a $100 billion research complex, flies about 260 miles [420 kilometers] above Earth.
After collecting their tools and making their way to the right-side exterior truss, the astronauts had just 35 minutes to unbolt the failed unit and install the replacement. The bolts, however, were not cooperative.
"The PGT [pistol grip tool] doesn't have enough power to turn it right now," Wiseman radioed to Mission Control in Houston. "I can feel it binding up."
Wiseman then switched to a ratchet wrench to unbolt the failed device, known as a sequential shunt unit, or SSU.
"Now it's time for Wiseman to apply a little muscle," said NASA commentator Rob Navias, during a live broadcast on NASA TV.
That did the trick, clearing the spot for the new SSU. Wiseman again ran into problems installing the replacement, but as the minutes ticked down toward daylight, he was able to use the power tool and then the ratchet wrench to tighten the single bolt holding the SSU in place.
With less than two minutes before the station passed back into daylight, flight controllers tested the new unit and reported it was working properly, "Whoo-hoo," the spacewalkers radioed to Mission Control.
Wiseman and Wilmore then kicked off what is expected to be a yearlong NASA project to reconfigure the station for the arrival of privately owned and operated passenger spaceships. NASA hired Boeing and privately owned Space Exploration Technologies to begin flying crews to the station in 2017.
Preparing docking ports and other amenities for the new vehicles will take up to 10 more spacewalks next year, NASA officials said. Wiseman and Wilmore began the work by relocating a camera support mast, clearing a path for the station's robotic crane to move a storage module from the Unity to the Tranquility connection nodes next summer.
Wiseman and Wilmore also moved a wireless transmitter and installed a new camera.
Wednesday's spacewalk was the second for Wiseman and the first for Wilmore.
Two Russian crewmates plan another spacewalk on October 22 to replace experiments, inspect and photograph the exterior of the Russian side of the station, and take care of some maintenance.