As the construction continued on the International Space Station (ISS), STS-118 astronaut and mission specialist, Dave Williams, representing the Canadian Space Agency, was anchored on the foot restraint of the Canadarm2 as he participated in the second session of Extra Vehicular Activity (EVA) for the mission. Assisting Williams was Rick Mastracchio (out of frame). During the 6 hour, 28 minute space walk, the two removed a faulty control moment gyroscope (CMG-3) and installed a new CMG into the Z1 truss. The failed CMG will remain in its temporary stowage location on the exterior of the station until it is returned to Earth on a later Shuttle mission. The new gyroscope is one of four CMGs that are used to control the orbital attitude of the station.