STS-117 (Atlantis / S3-S4 truss)

Background

By the mid-2000s, the International Space Station (ISS) was growing steadily but remained severely constrained in the one resource that governed everything else aboard: electrical power. The station's integrated truss structure, the long backbone running perpendicular to the habitation modules, was designed to carry a sequence of truss segments outward from the central S0 segment, each pair of starboard and port additions bringing new solar-array wings with it. STS-117 was assigned the task of delivering and installing the S3/S4 truss segment, a combined unit that would add two new solar-array wings to the starboard side of the station and meaningfully expand the platform's capacity to support a larger permanent crew and additional scientific facilities. The mission flew aboard Space Shuttle Atlantis and was crewed by seven astronauts whose combined experience spanned shuttle flights, long-duration station expeditions, and extensive spacewalking records.

Commander Frederick Sturckow and Pilot Lee Archambault led a crew that included Mission Specialists James Reilly, Steven Swanson, Patrick Forrester, and John Olivas, along with Clayton Anderson, who was flying to the station not as a visitor but as a permanent crew member assigned to replace Sunita Williams on Expedition 15. Anderson's inclusion gave STS-117 a dual character: it was simultaneously a construction flight and a crew-rotation mission, a combination that was becoming routine as the station matured but that still demanded careful scheduling of suited and unsuited activities across a packed docked timeline.

Launch and Ascent

Atlantis lifted off on 8 June 2007 and reached orbit approximately eight and a half minutes later, the main engines cutting off and the external tank separating as the orbiter climbed to a rendezvous trajectory with the station. Ascent imagery revealed that the external tank's foam insulation had shed material during the climb, producing damage to the thermal protection system on Atlantis's underside. In the post-Columbia era that concern was taken with the utmost seriousness, and flight controllers and engineering teams undertook a thorough inspection of the orbiter's heat shield during the early days of the mission. After detailed analysis using the orbiter boom sensor system and imagery from the station, engineers concluded that the damage fell within acceptable limits and posed no risk to reentry, and the mission proceeded without alteration to its primary objectives.

Assembly and Spacewalks

Roughly two and a half days into the mission, Atlantis docked with the ISS and the core construction work began. The S3/S4 truss segment was extracted from the shuttle's payload bay and handed off to the station's robotic arm before being precisely positioned and bolted to the outboard end of the existing S1 truss. The installation of the new segment, along with the unfurling and activation of the associated solar-array wings, represented a significant expansion of the station's starboard power-generating capacity.

Three spacewalks were required to complete the installation, connect power and data cables, and perform the mechanical work necessary to integrate the new segment fully into the station's systems. Reilly, Swanson, Forrester, and Olivas divided the extravehicular activities among them, working methodically through a task list that involved not only the new truss hardware but also the retraction of an older solar-array blanket on the P6 truss segment. That array, installed years earlier during the station's earliest assembly phase, needed to be folded away to prevent it from shadowing the newly positioned S3/S4 arrays — a delicate procedure given that the blanket material had stiffened with age and did not retract cleanly on the first attempt, requiring the spacewalkers to use improvised techniques to coax the panels into compliance. The problem was resolved on a subsequent EVA, and the retraction was ultimately completed successfully.

Anderson transferred to the station during the docked period, joining the Expedition 15 crew, while Williams — who had been aboard since the previous December — returned to Earth with the STS-117 crew, having completed a long-duration increment that included a record-setting total of spacewalking time for a female astronaut at that point in history.

Reentry and Landing

After undocking from the station and completing the remaining days of the solo mission phase, Atlantis fired its orbital maneuvering system engines for the deorbit burn late in the mission, committing the vehicle to reentry. The orbiter descended through the atmosphere and landed at Edwards Air Force Base in California rather than the primary landing site at Kennedy Space Center in Florida, weather conditions having precluded a return to Florida. The wheels stopped rolling approximately thirteen and a half hours after the deorbit burn, concluding a mission of just under fourteen days.

Legacy

STS-117 stands as one of the pivotal construction flights in the ISS assembly sequence. The S3/S4 truss and its solar arrays substantially increased the station's available electrical power, enabling the subsequent addition of new pressurized modules and the expansion of the permanent crew from three to six — a transition that transformed the station's research output and logistical complexity. The mission also demonstrated the robustness of the post-Columbia safety framework: foam debris that would once have gone unexamined was instead subjected to rigorous engineering review, and the crew continued its work only after a data-driven determination that the vehicle was safe. That process, however imperfect, reflected the institutional changes NASA had undertaken in the years following the Columbia accident. For the seven astronauts of STS-117, and for the program as a whole, the flight represented both a technical milestone in assembling one of the most complex structures ever placed in orbit and a reaffirmation of the methodical, incremental approach that made the International Space Station possible.