 The P3/P4 and S3/S4 truss assemblies' length was limited by the cargo bay capacity of the Space Shuttle, so these small connectors are needed to extend the truss.The P5 truss was installed on December 12, 2006 during the first EVA of mission STS-116.The S5 truss was brought into orbit by mission STS-118 and installed on August 11, 2007.