Hooking up power cables to begin activation of the S3/S4 truss and starting to prepare the Solar Alpha Rotary Joint, also known as the SARJ, for activation

Finishing removing the SARJ's launch locks and restraints so that it can be activated and repairing of the Shuttle's heat shield

Preparing for the replacement of an empty ammonia tank on the station's port truss, or backbone, by releasing its bolts. They also retrieved a materials processing experiment and a European science experiment mounted outside the Columbus laboratory and stowed them in Discovery's cargo bay for their return to Earth.

Removing the new ammonia tank from the shuttle's payload bay and replacing it with the used tank on the station. The new tank, weighing about 1,800 pounds, was the most mass ever moved around by spacewalking astronauts. After the new tank was installed, the old one was stowed in the shuttle for its return to Earth.

Preparing for the arrival of the Tranquility node by attaching cables between the starboard truss and the Unity node, the area where Tranquility will be installed. Tranquility is targeted to arrive to the station on STS-130 in February 2010. The spacewalkers also replaced a communications sensor device, installed two new GPS antennas and a new circuit breaker.