Discovery astronauts Bob Curbeam and Christer Fuglesang today successfully rewired the power system for half of the orbiting International Space Station (ISS) during a spacewalk while mission specialists Indian American Sunita Williams and Joan Higginbotham operated the ISS's robotic arm.The Bob Curbeam-Christer Fuglesang began their spacewalk, the second of their 12-day space shuttle mission, at 1341 hrs Central Standard Time (CST), and finished a full hour earlier than scheduled.The second half of the station's power system will be reconfigured during the mission's third spacewalk tomorrow.The successful spacewalk, along with an extravehicular activity (EVA) tomorrow, will set the stage for the station's expansion to support two new international laboratories and a crew of six in upcoming years."NASA is very happy about that," said Sunita Williams, after flight controllers reported all systems were operating as designed. "Excellent," Curbeam added.Before the astronauts could begin their spacewalk, station flight controllers had to take the risky work of shutting down about half of the station's systems, including some lights, communications gear, ventilation fans and back-up computers.The spacewalkers headed out the hatch of the Quest airlock about 30 minutes ahead of schedule, and finished their tasks at 1841 hrs CST, an hour earlier than planned and exactly five hours after they started.