STS-122Report #12 Wednesday, February 13, 2008 - 5:30 a.m. CST Mission Control Center, Houston, Texas HOUSTON - By the end of the day, the International Space Station should have a new nitrogen tank assembly.The crews of the station and space shuttle Atlantis are preparing for the second spacewalk of Atlantis' mission. Mission Specialists Rex Walheim and Hans Schlegel will replace a nitrogen tank used to pressurize the station's ammonia cooling system.The astronauts' day began at 3:45 a.m. CST. The wakeup song "Oysters and Pearls," by Jimmy Buffet, was played for Pilot Alan Poindexter. The spacewalk is scheduled to begin at 8:35 a.m., after Walheim and Schlegel finish their preparations in the Quest airlock, where they spent the night.At 8:55 a.m., the space station's robotic arm will remove the new nitrogen tank from Atlantis' cargo bay. The removal of the old tank will take the spacewalkers about two and a half hours, and the installation of its replacement is scheduled to take another two hours. The spacewalkers are scheduled to return to the space station at 3 p.m.This will be the fourth spacewalk for Walheim, who also took part in the mission's first spacewalk on Monday and the first for Schlegel. It is the 103rd spacewalk devoted to space station assembly and maintenance.The next STS-122 status report will be issued Wednesday evening or earlier if events warrant.