Two American astronauts ventured outside the International Space Station to upgrade the orbiting outpost's electrical system.<br/><br/>Americans Shane Kimbrough, commander of the six-person crew aboard the ISS, and flight engineer Peggy Whitson officially ended their expedition yesterday.<br/><br/>According to the NASA, during their approximately six-and-a-half hour spacewalk, the pair installed new adapter plates and hooked up electrical connections for three of six new lithium-ion batteries installed on the station's truss.