During the space walk, which began at 12:37 a.m. CST, Grunsfeld and Linnehan removed the old starboard solar array from Hubble and installed in its place a new third-generation solar array and its associated Diode Box Assembly. The old solar array was stored in Columbia's payload bay where it will be returned to Earth to allow engineers to determine how it fared during its nine years in space. The new arrays are two-thirds the size of the current arrays but will provide 20 percent more power to the telescope. Because of their smaller size, the new arrays also will impart less atmospheric drag, slowing the rate at which Hubble's orbit decays.
Throughout the space walk, Mission Specialist Nancy Currie used the shuttle's robotic arm to maneuver the two space walkers around Columbia's payload bay and the Hubble telescope. Linnehan was on the arm for most of the space walk, with Grunsfeld taking his place about five hours and fifteen minutes into the space walk.
From the aft flight deck of Columbia, astronauts Mike Massimino and Jim Newman assisted the two spacewalkers throughout their numerous tasks. Newman and Massimino will be performing their first spacewalk of the mission tomorrow morning, replacing Hubble's port solar array and a Reaction Wheel Assembly, one of four devices that help Hubble maintain a steady position as it photographs distant objects.
During the spacewalk, Grunsfeld's EVA suit did not transmit its normal telemetry signal to the ground, though the Flight Surgeon was able to monitor the astronaut's biomedical data. After resetting power to the suit later following the spacewalk, EVA officers in Mission Control were able to receive data normally. It is believed a relay in the suit's communication system needed to be reset.
The crew is to begin its sleep period at 11:52 a.m. CST.