Curbeam and Fuglesang spent the night in the station's Quest airlock at a reduced atmospheric pressure of 10.2 psi. The "campout" procedure reduces nitrogen levels in the blood to help avoid decompression sickness as the astronauts go to the even lower pressure of spacesuits.
The spacewalk is planned to last about six hours. The two spacewalkers are scheduled to reconfigure two of the station's four power channels, channels 2 and 3, bringing power on line from the new set of solar arrays added to the station in September. The remaining two power channels, 1 and 4, will be reconfigured in a third spacewalk on Saturday. The changes will convert the station power system to a permanent setup, ready for even more arrays and science modules to be added next year.
At about 11:22 a.m. CST, station flight controllers will be sending commands that will power down roughly half of the station's systems in preparation for the spacewalkers' rewiring job this afternoon. The result will partially power down some communications systems, lighting, ventilation systems and backup computers, among other systems. Once the spacewalkers have completed the new power connections, flight controllers will power all the equipment and systems back on. As changes are made in the power system, additional cooling systems also will need to be brought online as well.
Late last night, half of the new cooling system for the P4 truss was filled with ammonia to be ready to begin circulating today when pumps are activated.
During the spacewalk, Curbeam, who will wear a suit with red stripes on the legs, and Fuglesang, who will wear an all-white suit, also will relocate two small handcarts that run along rails on the stationís main truss. Expedition 14 Flight Engineer Suni Williams and Discovery Mission Specialist Joan Higginbotham will operate the station's Canadarm2 robotic arm in support of the spacewalk.
Managers and engineers continue to evaluate whether further actions will be taken during STS-116 to complete the retraction of the port P6 truss solar array. The array was retracted almost halfway Wednesday, with only 17 bays of its center mast remaining extended. Fully extended, the mast has 31 bays. The array was retracted sufficiently to allow the new P4 solar arrays to begin rotating last night, an operation that was completed without problems. In their current state, the P6 port array and the P4 arrays have more than 16 feet of clearance from one another. Should they remain as they are, the partially retracted arrays pose no issue for the shuttle's undocking or any planned station activities until a Soyuz relocation flight set for April 2007.
A decision on any further action regarding the partially retracted array Ė including a possible fourth spacewalk during STS-116 for Curbeam and Fuglesang to assist in the retraction -- is not expected before Saturday.
Discoveryís crew was awakened at 9:17 a.m. CST today with the song, "Under Pressure," performed by Queen. It was played for Curbeam. The station crew, Commander Michael Lopez-Alegria and flight engineers Mikhail Tyurin and Williams, woke up a half-hour later.