STS-110 Mission Specialists Jerry L. Ross and Lee M.E. Morin work in tandem on the fourth scheduled EVA session for the STS-110 mission aboard the Space Shuttle Orbiter Atlantis. Ross is anchored on the mobile foot restraint on the International Space Station's (ISS) Canadarm2, while Morin works inside the S0 (S-zero) truss. The STS-110 mission prepared the Station for future spacewalks by installing and outfitting a 43-foot-long S0 truss and preparing the Mobile Transporter. The 27,000 pound S0 Truss was the first of 9 segments that will make up the Station's external framework that will eventually stretch 356 feet (109 meters), or approximately the length of a football field. This central truss segment also includes a flatcar called the Mobile Transporter and rails that will become the first "space railroad," which will allow the Station's robotic arm to travel up and down the finished truss for future assembly and maintenance. The completed truss structure will hold solar arrays and radiators to provide power and cooling for additional international research laboratories from Japan and Europe that will be attached to the Station. Milestones of the S-110 mission included the first time the ISS robotic arm was used to maneuver spacewalkers around the Station and marked the first time all spacewalks were based out of the Station's Quest Airlock. It was also the first Shuttle to use three Block II Main Engines. The Space Shuttle Orbiter Atlantis, STS-110 mission, was launched April 8, 2002 and returned to Earth April 19, 2002.