Japanese Astronaut Koichi Wakata, at controls in the shuttle cockpit, deftly maneuvered Discovery's robotic arm to lift the framework, called the Z1 truss, out of the shuttle's payload bay and berth it to a port on the station's Unity connecting module. The berthing was the first time the U.S.-developed attachment system has been used in orbit, and the equipment worked flawlessly. Over the course of the station's future assembly, similar attachment systems will be used over 100 times. Astronaut Mike Lopez-Alegria, looking out of the berthing port's hatch window in Unity, provided Wakata with visual cues as to the framework's alignment.
The berthing occurred about two hours behind schedule due to a short-circuit aboard the shuttle early in the crew's day that cut off power to some equipment Wakata would need. The short cut power to three pieces of equipment: an Orbiter Interface Unit that provides data and commanding from the shuttle to station systems; an Orbiter Space Vision System that provides a computerized alignment aid for operating the robotic arm; and a television camera located at the bottom, or keel, of the payload bay that faces upward to provide a supplementary visual cue for maneuvering the truss structure. Flight controllers and the crew quickly developed a plan to use backup equipment and alternate power to regain all functions except the keel camera, and Wakata began lifting the truss from the shuttle bay about 2 hours and 15 minutes later than originally planned.
The backup arrangement worked perfectly. The electrical bus that experienced the short will remain powered off and will have no impact on the rest of the mission's activities. Wakata latched the truss to the station at 1:20 p.m. as the complex flew 240 statute miles above southern Russia.
Because activities were behind schedule following the morning workaround, flight controllers opted to defer the transfer of some gear from the station's Unity module to the Zarya module until the crew next enters the station, planned for day nine of the mission. In Unity, Pilot Pam Melroy and crewmate Jeff Wisoff opened the hatch where the new truss was attached and, inside a pressurized dome, installed grounding connections between the framework and the station. Afterward, the crew exited the station, and, at 5:57 p.m. CDT, Lopez-Alegria and Commander Brian Duffy sealed the station's outermost hatch.
Duffy and Melroy then lowered Discovery's cabin pressure in preparation for a space walk by astronauts Leroy Chiao and Bill McArthur planned to begin at 9:32 a.m. Sunday. Reducing the cabin pressure from a sea-level pressure of 14.7 pounds per square inch (psi) to a pressure of about 10.2 psi is part of a protocol that purges nitrogen from the space walker's body to prevent decompression sickness. Chiao and McArthur spent the last couple of hours of their day preparing equipment in the shuttle's lower deck and airlock for tomorrow's venture outside the cabin. During the space walking construction work, the first of four space walks planned during Discovery's mission, the two will connect electrical and computer data cables between the newly attached truss and Unity and deploy two communications antennas from the truss.
The crew begins a sleep period at 9:17 p.m. today and will awaken at 5:17 a.m. Sunday to begin preparations for the six and a half-hour space walk.