 Upon its installation, no power was flowing across the rotary joint, so the electricity generated by the P4 solar array wings was only being used on the P4 segment, and not the rest of the station.Then in December 2006 a major electrical rewiring of the station by STS-116 routed this power to the entire grid.The S3/S4 truss assembly—a mirror-image of P3/P4—was installed on June 11, 2007 also by Space Shuttle "Atlantis" during flight STS-117, mission 13A and mounted to the S1 truss segment.