Ross and Morin began the fourth and final spacewalk of the STS-110 mission and the 38th devoted to space station construction at 9:29 a.m. Central time, first pivoting a 14-foot beam called the Airlock Spur from the S-Zero truss to the Quest Airlock to provide a quick pathway for future spacewalkers working on truss assembly.
Ross then conducted tests of switches on both sides of the 44-foot long truss to insure they will work properly later this year in confirming the attachment of additional truss segments to the S-Zero. The main truss of the ISS will eventually stretch more than 350 feet, longer than a football field.
The two spacewalking grandfathers pressed ahead to install floodlights on the station's Unity connecting module and the Destiny Laboratory which will provide illumination for future spacewalkers as they move around the expanding outpost.
Ross and Morin then affixed a work platform on the station for future construction work, installed electrical converters and circuit breakers, dressed up a piece of insulation around one of the four navigational antennas on the truss and attached shock absorbers to the new Mobile Transporter railcar. The shock absorbers will prevent vibrations to the station's robotic arm from the future use of carts on the truss which will be used to move spacewalkers from one end of the station to another.
The only tasks not accomplished were the removal of a balky bolt from a backup cable cutting device on one of two umbilical systems for the Mobile Transporter, which was successfully tested on Monday and the installation of a gas analyzer on the truss which proved to be faulty.
The bolt will have no impact on the operation of the flatcar, upon which a Mobile Base System platform will be mounted in June as the ultimate base for the transport of the station's robotic arm up and down the length of the ISS. The gas analyzer was considered the lowest priority of the flight.
With all of their major work completed, Ross and Morin returned to the Quest Airlock and concluded the spacewalk at 4:06 p.m. Central time.
Atlantis Mission Specialist Ellen Ochoa and Expedition Four Flight Engineer Dan Bursch operated the station's Canadarm2 robotic arm to move Ross around the ISS during the spacewalk while Morin operated as the "free-floating" spacewalker, tethered to the station to assist Ross in the final tasks of the mission. For Ross, America's most experienced spacewalker, it was his ninth excursion to conduct work in the void of space during his career, totaling 58 hours and 18 minutes of spacewalking time. Only Russian cosmonaut Anatoly Solovyev has performed more spacewalks in human spaceflight history. Today's spacewalk was the second for Morin. Rex Walheim and Expedition Four crew members Carl Walz helped choreograph the spacewalk from Atlantis' aft flight deck.
While the spacewalkers went about their work, Shuttle and Station Commanders Mike Bloomfield and Yury Onufrienko, Pilot Steve Frick, and Steve Smith continued their transfer of equipment to and from both Atlantis and the ISS and provided photographic and television support to Ross and Morin.
With all of the objectives having been successfully accomplished for the mating and outfitting of the S-Zero truss to the ISS, the stage is set for Wednesday's final farewells between the two crews and undocking of Atlantis from the station at 1:31 p.m. Central time as the two craft sail some 244 statute miles above the north Atlantic due west of Ireland. Atlantis is scheduled to land at the Kennedy Space Center early Friday afternoon.
The shuttle crewmembers will begin an eight-hour sleep period tonight at 7:14 p.m. Central time followed thirty minutes later by the station crew. Atlantis' crew will be awakened at 3:14 a.m. Wednesday to prepare for undocking. The station crew will be awakened an hour later.