Two space station astronauts are gearing up for a planned six-and-a-half-hour spacewalk Friday to replace a presumably shorted out solar array voltage regulator that knocked one of the lab's eight power channels out of action late last year. They also plan to finish up ongoing work to route power and data cables needed for new docking mechanisms that will be installed later. The voltage regulator, a 200-pound box known as a sequential shunt unit, or SSU, is one of eight at the base of each of the station's solar power wings that serve to relay regulated 160-volt DC current to...