The ATV is an unpiloted cargo carrier like the Russian Progress supply vehicles, but has a cargo capacity about 2½ times that of a Progress. The European Space Agency's (ESA) ATV is scheduled for its first launch in the fall of 2005 aboard an ESA Ariane 5 rocket from French Guiana. In addition to carrying cargo, including fuel, water, oxygen and nitrogen, it also can reboost the Station. Like the Progress, the ATV will burn up when it re-enters the atmosphere. During the spacewalk Padalka and Fincke worked smoothly around the exterior of the Russian Zvezda Service Module in their Orlan spacesuits. The pair exited the Pirs Docking Compartment airlock at 1:58 a.m. CDT and began work on the Russian segment immediately.
The crewmembers moved to the aft end cone of Zvezda, where they found a wide open workspace. ISS Progress 14 had been undocked from the area on Friday.
Their first task was to replace an experiment, called SKK that exposes materials the space environment with a fresh sample container. They also replaced a Kromka experiment unit that measures contamination from Service Module thruster firings.
Their attention then turned to preparing the Station for the arrival of ATVs by installing new rendezvous and docking equipment. They installed two antennas and replaced three laser reflectors with three more advanced versions than the ones launched with Zvezda in 2000. One three-dimensional reflector was also installed to replace three other old reflectors the spacewalkers removed.
While in the area, the crew also disconnected a cable for a camera that has broken and will be replaced on a future spacewalk. The crew also retrieved another materials experiment, Platan-M. The crew returned to Pirs with the Platan-M, Kromka No.2, SKK No. 2 and the six old laser reflectors in tow.
As they worked at the rear of the Service Module, the three 600-pound Control Moment Gyroscopes that control the orientation in space of the orbiting laboratory approached their saturation level, a condition that had been expected. The Station was placed in free drift while the spacewalkers continued working. Consequently, as power conservation measures were executed, S-band communication was temporarily lost.
At about 4:15 a.m. CDT, the spacewalkers, who were about 40 minutes ahead of their timeline, were asked to clear the area. Once they moved forward, the thrusters on the Service Module were activated to realign the Station's attitude and S-band communication was also restored.
Subsequently, at about 5 a.m. CDT, the Control Moment Gyroscopes reassumed attitude control and the Service Module thrusters were turned off. The spacewalkers then returned to work at the rear of the Service Module.
The crew closed the hatch and ended the spacewalk at 6:28 a.m. CDT. This was the 55th spacewalk in support of Station assembly and maintenance, the 30th staged from the Station itself, the fifth for Padalka and Fincke's third.