Today's spacewalk began at 1:25 p.m., with Herrington being asked to look for possible obstructions that might have stalled the station's railcar, or Mobile Transporter (MT) that had stopped unexpectedly about 10 feet short of its intended destination. At 10:21 a.m. today, the MT was commanded to move from its position at Worksite 4 near the S-Zero (S0) truss to Worksite 7 where the station's robotic arm would have "walked off" from its mooring on the Destiny Laboratory to the MT and been used to maneuver Herrington through some of his tasks.
Herrington spotted a stowed UHF communications antenna that had snagged a trailing umbilical mechanism on the MT, halting its motion. Herrington then deployed the antenna, freeing the MT to continue its travel toward Worksite 7. At 4:11 p.m., the railcar was in place and just before 6 p.m., was securely latched into place.
Flight controllers evaluated the performance of the railcar and possible impacts to the spacewalk schedule as a result of troubleshooting activities, ultimately deciding to reprioritize some of today's tasks to ensure the high priority items were completed. After Herrington informed flight controllers he could complete all his assigned tasks without using the station's robotic arm, flight controllers elected not to perform the "walk off" of the station arm to the MT.
Herrington and Lopez-Alegria successfully completed all of their assigned tasks during today's spacewalk, including the installation of 33 spool positioning devices on various locations around the outside of the station. From onboard Endeavour, Pilot Paul Lockhart coordinated the two spacewalkers' efforts, providing them with visual cues as they moved around the station.
Aboard the station, handover activities continued between Expedition Five Commander Valery Korzun and Flight Engineer Sergei Treschev and Expedition Six Commander Ken Bowersox and Flight Engineer Nikolai Budarin.