Spacewalking astronauts floated outside the international space station Tuesday to help install the orbiting outpost's newest room, a bus-sized Japanese laboratory. During a scheduled 6 1/2-hour spacewalk, astronauts Michael Fossum and Ronald Garan Jr. prepped the $1 billion lab for installation by removing power and heating cables and restraints that connect it to the shuttle. "Wow, this is incredible," Garan, a spacewalking rookie, said just after he stepped outside. Astronauts working from inside will use the space station's robot arm later in the day to lift the lab from the shuttle and anchor it to the station. Later in the spacewalk, the astronauts were going to try out some cleaning methods on a jammed solar rotating joint that has hampered energy production at the space station since last fall. The joint enables the space station's solar arrays, which provide electrical power, to rotate and track the sun.