STS-115 was a Space Shuttle mission to theInternational 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 STA-121 STS-115 launched from Pad 39-B at the Kennedy Space Centre 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 trusssegment (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.

STS-115 was originally scheduled to launch in April 2003. However, the Columbia accidentin February 2003 pushed the date back to 27 August 2006, which was again moved back for various reasons, including a threat from Tropical Storm Ernesto and the strongest lightning strike to ever hit an occupied shuttle launchpad.