For the first time since late 2002, assembly of the ISS resumed on the STS-115 mission. The mainstay of Atlantis' flight required robotics operations, three spacewalks, and multiple ground-controlled checkouts. Atlantis' six crewmembers installed a second set of solar arrays on the space station, doubling the station's ability to generate power from sunlight and adding 17.5 tons to its mass. When unfurled to their full length of 240 feet, the arrays provide additional power for the station in preparation for the delivery of international science modules over the next two years. Atlantis' flight also delivered a device called the Solar Alpha Rotary Joint (SARJ), which will rotate 360 degrees either clockwise or counterclockwise to position the solar arrays to track the sun for electrical power generation, and deployed the P4 Truss radiator.
Atlantis' mission included all the safety features tested on the past two shuttle flights: improved imagery during launch, heat shield inspections in orbit, and a shuttle backflip as it approaches the station. Mission Specialist Stefanyshyn-Piper made two of the three spacewalks to add the solar panels to the space station, making her the seventh woman NASA spacewalker since the United States first sent an astronaut on a walk in orbit in 1965. Additionally, the STS-115 flight marks the second time that four out of the five partner agencies will have been represented on the station together.
Several Detailed Supplementary Objectives (DSOs) were also flown during the STS-115 mission. DSOs are space and life sciences investigations. Their purpose is to determine the extent of physiological deconditioning resulting from space flight, test countermeasures to those changes, and characterize the environment of the Space Shuttle and/or space station relative to crew health. DSOs performed during this mission were:
Space Shuttle Atlantis returned to Kennedy Space Center in Florida on September 21st, bringing STS-115 to an end. This flight was the orbiter's 27th mission and the 116th in the Shuttle program's history.