STS-124 Commander Mark Kelly helped the spacewalkers get ready for the 6.5-hour excursion. During the two previous spacewalks Fossum and Garan outfitted Japan’s Kibo module and did station maintenance tasks. Today, they are replacing a nitrogen tank assembly, installing TV equipment and removing a thermal cover from Japan’s new robotic arm.

Replacing the depleted nitrogen tank assembly will require Garan to spend much of his third spacewalk on the station’s robotic arm. He will start the spacewalk by installing a width extender to increase the robotic arm’s reach, climb into a foot restraint attached to the width extender and remove four bolts holding the old nitrogen tank assembly in place on the starboard truss.

After installing a handle on the assembly, he will remove it from the truss and carry it to the external stowage platform, via the robotic arm.

Meanwhile, Fossum will remove the spare nitrogen tank assembly from the platform to make room for the old one, and store it on the other side of the platform.

When Garan arrives with the old assembly, Fossum will guide it into place and begin securing it to the platform with four bolts.
Once one of the four bolts has been secured, Garan will remove his handle from the old assembly, attach it to the new one and ride the robotic arm back to the starboard truss with the nitrogen tank assembly in tow. He’ll remove his handle, install the bolts to secure it to the truss and connect the necessary electrical link.

Then he will get off the robotic arm and move to the back of the truss to connect the assembly’s nitrogen lines to the ammoni tank assembly. Meanwhile, Fossum will finish securing the old nitrogen assembly and move to the Kibo module to finish outfitting it. He will remove launch locks and thermal covers from the two cameras on the module’s robotic arm, as well as the launch locks on the module’s aft window.

The window had been blocked by the robotic arm during the first spacewalk, when he removed the launch locks on the module’s forward window.

He will then deploy two micrometeoroid debris shields on either side of the connection between the larger laboratory module ad the recently relocated experiments logistics module. Once that’s done, Fossum will return to the airlock to retrieve the external television camera with its new power supply. He will meet Garan back on the port truss, where they will reinstall the camera.

After the spacewalk, Hoshide and Nyberg will continue outfitting the vestibule inside Kibo’s pressurized logistics module. They also will deploy and maneuver Japan’s robotic arm to its stowed position.

Discovery is scheduled to return to Earth on Saturday, June 14, landing at the Kennedy Space Center just after noon, Eastern Time, bringing to an end its 35th mission, the 26th shuttle flight to the space station and the 123rd flight in shuttle program history.