Stock Photo - A close-up view of the new control moment gyroscope (CMG) photographed by a crewmember during the mission's second planned session of extravehicular activity (EVA). During the spacewalk, Canadian Space Agency's astronaut Dave Williams (out of frame) and astronaut Rick Mastracchio (out of frame), both STS-118 mission specialists, removed a faulty control moment gyroscope (CMG-3) and installed a new CMG into the station's Z1 truss. The failed CMG will remain at its temporary stowage location on the station's exterior before it is returned to Earth on a later shuttle mission. The new gyroscope is one of four CMGs that are used to control the station's attitude in orbit.