Hugh Pickens writes writes "Denise Chow reports that two spacewalking astronauts successfully replaced a vital power unit on the International Space Station today, defeating a stubborn bolt that prevented the astronauts from properly installing the power unit on the ISS's backbone-like truss with the help of some improvised tools made of spare parts and a toothbrush. Astronauts Sunita Williams and Akihiko Hoshide started by removing the power box, called a main bus switching unit (MBSU), from where it had been temporarily tied down with a tether, then spent several hours troubleshooting the unit and the two bolts that are designed to secure it in place on the space station's truss. After undoing the bolts, the spacewalkers examined them for possible damage, and used improvised cleaning tools and a pressurized can of nitrogen gas to clean out the metal shavings from the bolt receptacles. "I see a lot of metal shavings coming out," Hoshide said as he maneuvered a wire cleaner around one of the bolt holders. Williams and Hoshide then lubricated a spare bolt and manually threaded it into the place where the real bolt was eventually driven, in an effort to ensure that the receptacle was clear of any debris. Then the two applied grease to the sticky bolt as well as extra pressure and plain old jiggling until finally 4½ hours into the spacewalk, Hoshide reported: "It is locked." When Hoshide reported that the troublesome bolt was finally locked into place, the flight managers erupted in applause while astronaut Jack Fischer at Mission Control told the astonauts "that is a little slice of awesome pie.""