The first contribution to the station by Canada was the space station's robotic arm, Canadarm2, which was delivered to the ISS last year. Today, in a planned 6 1/2 hour spacewalk, Chang-Díaz and Perrin will connect power and data cables to the newly installed Mobile Base System and permanently bolt it to the Mobile Transporter railcar which was affixed to the S0 (S-Zero) Truss on the ISS in April. The new platform will enable Canadarm2 to "walk off" the Destiny Laboratory and mate itself to any one of four grapple fixtures so it can be driven up and down the length of the station's trusses for future construction tasks.
Canadarm2 has provided power to the Mobile Base System since its unberthing from Endeavour's payload bay Sunday near the end of the first spacewalk. The platform was attached to the Mobile Transporter on Monday. Chang-Díaz and Perrin will connect primary and backup cables for video and data and primary cables for power between the MBS and the Mobile Transporter. Once the cable connections are completed, ground controllers will send commands for the MT to remotely plug in its umbilical attachments to receptacles on the truss railway. Flight controllers will then begin a checkout of the MBS systems to ensure all connections are established.
With that completed, Chang-Díaz and Perrin will deploy an auxiliary grapple fixture on the MBS called the Payload Orbital Replacement Unit Accommodation, or POA. The fixture will be used to transport additional cargo elements on the MBS as it is moved along the truss railway.
After the ground-controlled checkout complete, the two spacewalkers will connect redundant power cables to the MT.
The final task for the spacewalkers will be to relocate a television camera on the MBS and add an extra extension cable for the platform.
Handover conferences between the two Expedition crews and the transfer of equipment and supplies to the Leonardo Multi-Purpose Logistics Module will also continue today. The crew has emptied Leonardo's cargo into the station and is now refilling the module with unneeded supplies to be returned to Earth.
Endeavour's crew - Chang-Díaz, Perrin, Commander Ken Cockrell, Pilot Paul Lockhart, Yury Onufrienko, Carl Walz and Dan Bursch - was awakened at 4:23 a.m. Central this morning to the sound of "Mi PC" by Juan Luis Guerra, selected for Chang-Díaz by his family.
All systems on both Endeavour and the International Space Station continue to function normally as the two craft orbit the Earth every 90 minutes at an altitude of 240 statute miles.