NASA astronauts Rick Mastracchio and Mike Hopkins and Japanese astronaut Koichi Wakata gathered together Thursday to review spacewalk procedures. Mastracchio and Hopkins will exit the station to replace a faulty pump module over a series of spacewalks. Wakata will operate the station's robotic arm to maneuver the spacewalkers at the worksite.

The first spacewalk is scheduled for Saturday at 7:10 a.m. EDT when the spacewalkers will set up the worksite on the S1 truss. Monday's spacewalk will include the removal of the old pump module and the installation of a spare pump module. If necessary a third spacewalk would occur on Christmas day to finalize the installation of the new pump module.

NASA Television will begin coverage of the spacewalks an hour before their 7:10 a.m. scheduled start times. The spacewalks are scheduled to last about six hours and 30 minutes. Shortly after the spacewalks conclude, mission controllers will participate in a briefing at Johnson Space Center to discuss the day's activities.

A briefing was held Wednesday with International Space Station program manager Mike Suffredini, Flight Director Dina Contella and Lead Spacewalk Officer Allison Bolinger. The mission managers discussed how a faulty pump module forced the launch delay of the Cygnus resupply craft and led to the planning for the contingency spacewalks.

The astronauts are also preparing for the possibility of ammonia leaks during their spacewalk. The pump modules are filled with ammonia for cooling and leaks have occurred while disconnecting cables during previous repair spacewalks. If ammonia flakes get on a crew member's suit, the spacewalkers would go through a series of decontamination steps before re-entering the space station.

In the Russian side of the space station, Commander Oleg Kotov and Sergey Ryazanskiy are preparing for a Dec. 27 pre-planned spacewalk. The cosmonauts with assistance from Flight Engineer Mikhail Tyurin resized their Orlan spacesuits, checked batteries and reviewed their translation paths to the external worksites.

The duo will install a foot restraint; install medium and high resolution cameras; jettison gear from a pair of external experiments; and install a new experiment as well as a payload boom on the Zvezda service module.

Kotov and Ryazanskiy also participated in a study that monitored their cardiovascular system. Tyurin later worked on the Russian radiation detection experiment Matryeshka that observes radiation absorption in a mannequin.