STS-115 was a Space Shuttle mission to the International Space Station (ISS) flown by Space Shuttle Atlantis. It was the first assembly mission to the ISS after the Columbia disaster, following the two successful Return to Flight missions, STS-114 and STS-121. STS-115 launched from Pad 39-B at the Kennedy Space Center on 9 September 2006 at 11:14:55 EDT (15:14:55 UTC). The mission is also referred to as ISS-12A by the ISS program. The mission delivered the second port-side truss segment (ITS P3/P4), a pair of solar arrays (2A and 4A), and batteries. A total of three spacewalks were performed, during which the crew connected the systems on the installed trusses, prepared them for deployment, and did other maintenance work on the station.
The International Space Station programme is tied together by a complex set of legal, political and financial agreements between the sixteen nations involved in the project, governing ownership of the various components, rights to crewing and utilization, and responsibilities for crew rotation and resupply of the International Space Station. It was conceived in 1984 by President Ronald Reagan, during the Space Station Freedom project as it was originally called.