The stage is now set for the inaugural run Monday of the so-called Mobile Transporter, a flatcar designed to transport the space station's robotic arm up and down an integrated truss system that will span the length of a football field.
Within minutes after starting their spacewalk at 8:48 a.m. Central time, Steve Smith and Rex Walheim released a claw-like device on the top of the Destiny Laboratory to which the new 13 ½ ton S-Zero (S0) truss was initially attached on Thursday. With the truss' four large struts now securely bolted to Destiny, the claw was no longer needed.
Smith and Walheim then reconfigured a number of connectors providing electricity to the 58-foot-long Canadarm2 robotic arm on the station so it can be powered from the S-Zero truss rather than Destiny. The arm has two sets, or "strings" of avionics equipment for its operation. As Smith and Walheim worked deliberately, one set of avionics was rewired and tested, followed by a separate set of redundant avionics.
Smith spent most of the day riding at the end of the shuttle's robotic arm, which was operated by Pilot Steve Frick during the rewiring of its companion station arm. Walheim was the so-called "free-floating" astronaut, tethered to the station to assist Smith. It was the seventh spacewalk of Smith's career. He is the second most experienced U.S. spacewalker behind crewmate Jerry Ross, who helped choreograph today's excursion from inside Atlantis with the help of Lee Morin. It was Walheim's second spacewalk.
With Canadarm2 successfully rewired and both of its electrical, data and video circuit sets checked out, Smith and Walheim pressed ahead to release clamps which secured the Mobile Transporter to the S-Zero truss during its launch last week. The railcar, which weighs about 1900 pounds, will be commanded Monday by ground controllers to move about 32 feet up and down the truss at a glacial speed of a little less than one inch per second in the first test of its computers, drive motors, suspension unit, video and data umbilicals and the first section of rails on the S-Zero.
The railcar, and an associated Mobile Base System device to be installed on the transporter in early June on the next shuttle assembly flight to the ISS, will ultimately enable the robotic arm to travel to various worksites on the expanding trusses of the station for future construction. The Mobile Base System will be the platform upon which the Canadarm2 will attach itself to be driven up and down the length of the ISS.
The only task not completed today was the attachment of a 14-foot ladder called the Airlock Spur from the S-Zero truss to the Quest Airlock designed to simplify the path for future spacewalkers moving back and forth from the truss to the airlock itself.
As the spacewalk neared its completion, final diagnostic tests of the newly wired station arm were taking longer than planned, and because the Canadarm2 is required for the airlock ladder to be pivoted away from the truss to Quest, flight controllers decided to defer its installation until the final spacewalk on Tuesday.
Smith and Walheim finally returned to Quest and completed their spacewalk at 3:15 p.m. Central time with the repressurization of the airlock.
Atlantis astronaut Ellen Ochoa and ISS Expedition Four crew member Dan Bursch backed up Frick in the operation of the shuttle's robot arm during today's spacewalk, the 37th devoted to space station assembly. Commander Mike Bloomfield documented the spacewalk from Atlantis' aft flight deck while Expedition Four Commander Yury Onufrienko and Flight Engineer Carl Walz continued to transfer supplies from the shuttle to the station for future use.
Late today, Frick conducted an hour-long reboost of the ISS, using Atlantis' steering jets to move the station higher by about two statute miles. It was the second of three planned maneuvers to raise the station's altitude and the second in as many days.
The ten crew members are scheduled to begin an eight-hour sleep period at 7:44 p.m. Central time tonight and will be awakened just before 4 a.m. to prepare for the testing of the new Mobile Transporter.