The practice run included a successful lowering of the airlock’s pressure to 10.2 pounds per square inch for the first time in space.

Lead Flight Director Paul Hill said troubleshooting on the valve -- and work the day before to get air bubbles out of an airlock water cooling line -- have put the combined crew about half a day behind its timeline. Among the tasks delayed was a relocation of the hatch from the junction of the airlock and the Unity module to its final position between the airlock’s crew and equipment lock sections.

The second space walk of the flight remains on schedule for Tuesday night. Mission Specialists Mike Gernhardt and Jim Reilly are scheduled to step out of the space shuttle’s airlock about 9:30 p.m. The objective of the 5 ? hour foray is to mount one high-pressure oxygen and one high-pressure nitrogen tank on the shell of the new airlock to provide consumables that would allow expeditioners to leave the station in American space suits for construction and maintenance work without a shuttle present. Russian space suits can be used from the airlock as well.

The crews closed the hatches between the two spacecraft at 6:30 a.m. Tuesday to begin lowering Atlantis’ cabin pressure to that same 10.2 pounds per square inch mark. This measure helps purge nitrogen bubbles from the space walkers’ bloodstreams, and is augmented by the space walkers pre-breathing pure oxygen. All crewmembers reviewed the procedures for the space walk prior to closing the hatch between the shuttle and the station’s Destiny Laboratory.

Mission Specialist Janet Kavandi and Expedition Two Flight Engineer Jim Voss took the lead in troubleshooting the suspected leak in an Intermodule Ventilation (IMV) assembly. The series of fans and valves circulates air between station modules and connects the airlock to the station’s environmental control and life support system. The pair wasn’t able to pinpoint the problem with the valve, but did install a cap that stopped the leak. Should replacement be necessary, several valve replacement options are available to the flight control team and crew onboard.

The delays have led flight managers to study the possibility for an extra day of docked operations and a shuttle mission extension to ensure all of the mission’s work can be completed.

Shuttle Commander Steve Lindsey, Atlantis’ Pilot Charlie Hobaugh and Station Commander Yury Usachev took time late Monday night to answer questions from reporters from CBS, Space.com and KNBC-TV of Los Angeles.

The eight people on orbit are scheduled to go to bed about 8 a.m. and awaken at 4:04 p.m. The next mission status report will be issued about 6 p.m. Tuesday or as events warrant.

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