Atlantis delivered the central segment of the station's main truss in April 2002, beginning construction of the long backbone that would eventually carry the outpost's solar arrays, radiators and equipment. The crew of seven used the station's robotic arm to install the massive girder, a foundation for the wings of power still to be added.
Four spacewalks bolted the truss in place, and for the first time the station's own arm was used to carry spacewalkers to their worksites, rather than having them climb hand over hand. Veteran Jerry Ross flew his seventh mission, more than any astronaut to that point. The truss segment was the first piece of a structure that would grow to span the length of a football field, shaping the station's distinctive final form.
The station got its backbone on this flight. The S0 truss was the central segment of the eventual 109-metre girder, mounted across the top of the Destiny laboratory and carrying the power and cooling lines that everything else would connect to — the piece from which the structure grows in both directions.
Installing it required four spacewalks, and for the first time all of them were staged entirely from the station's own robotic arm rather than using the Shuttle's — a small procedural milestone that meant the outpost was becoming capable of building itself. The truss also carried the rails on which a mobile transporter would later carry the arm along the structure.
Jerry Ross flew this mission as his seventh, more than anyone had flown before, spanning from 1985 to 2002; he had made the first assembly spacewalks on STS-88 and had now helped install the spine those first modules would hang from. He also became the first person to make nine spacewalks.
