Chang-Díaz and Perrin ventured outside the station's Quest airlock at 10:20 a.m. Central time. With the help of Pilot Paul Lockhart, who guided the spacewalk from inside the shuttle, Chang-Díaz and Perrin first connected primary and backup cables for video and data, and primary power cables between the Mobile Transporter railcar and the MBS. Once the connections were made, ground controllers sent commands for the MT to remotely plug in its umbilical attachments to receptacles on the S0 (S-Zero) truss railway.
With that complete, Chang-Díaz and Perrin then deployed an auxiliary grapple fixture on the MBS called the Payload Orbital Replacement Unit Accommodation, or POA, and placed it in its final configuration. Identical to the end effectors on Canadarm2, the fixture can grapple payloads and hold them as they are moved along the station's truss atop the MBS.
Continuing to run ahead of schedule, the two spacewalkers then secured four bolts between the MBS and the railcar, completing installation of the new MBS platform. Later this month or next, Canadarm2 will "walk off" the Destiny Laboratory and mate its free hand to any one of four power and data fixtures on the new platform so it can be driven up and down the length of the station's truss for use in future station assembly and maintenance operations.
The spacewalkers then relocated a television camera to its final position on top of a mast atop the MBS. The camera will provide views of station assembly and maintenance operations to ground controllers. Final tasks included adding an extra extension cable for the platform, a wire tie to one of the cables installed earlier during the spacewalk and to photograph connectors near the lower portion of the MBS that tie into the MT.
Following an inventory of the tools they used during the spacewalk, Perrin and Chang-Díaz re-entered Quest. Airlock repressurization began at 3:20 p.m. Central time, signaling the end of the spacewalk. It was the 40th spacewalk in support of ISS assembly and maintenance and the second of the mission, bringing the total spacewalking time for STS-111 to 12 hours and 14 minutes.
After flight controllers verified that all connections on the Mobile Remote Servicer Base System were working properly, the capture latch on Canadarm2 was released. The arm, which had been supplying power to the MBS, was then repositioned for Thursday's third and final spacewalk of the mission, which will see replacement of its wrist roll joint.
Handover conferences between the two Expedition crews and the transfer of equipment and supplies to the Leonardo Multi-Purpose Logistics Module also continued today. Working ahead of schedule, the crew continued to refill the module with unneeded supplies to be returned to Earth.
At 9:19 Central time tonight, Endeavour crewmembers and former Expedition Four Flight Engineers Carl Walz and Dan Bursch will set a new U.S. space endurance record, exceeding Shannon Lucid's record of 188 consecutive days spent in space. Walz will set another record in the process, exceeding Lucid's U.S. record for cumulative days spent in space as he reaches 223 days accrued over the course of five flights. Expedition 4 Commander Yury Onufrienko has spent a total 381 days in space, but remains far behind the world record for time in space of 747 days, held by Sergei Avdeyev.