NASA announced that STS-122 astronauts Rex Walheim and Hans Schlegel completed the removal of an expended Nitrogen Tank Assembly (NTA) and the installation of a new one on the P1 truss.

German astronaut Hans Schlegel was supposed to take part in the spacewalk on Monday, but he felt sick and remained inside the spaceship, from where he helped choreograph the outing of his two colleagues: Rex Walheim and Stanley Love.

Schlegel was quite disappointed that he had to stay inside the ship, but declared he was very enthusiastic in assisting his colleagues from there, together with shuttle pilot Alan Poindexter. Poindexter, who is on his first spaceflight on STS-122, declared the space station is a great place to work in, even though it is not completely constructed.

The outing on Monday had as purpose the installation of Europe’s new Columbus science lab. The module costs about $2 billion and it was delivered last weekend. Leopold Eyharts was the first astronaut to inspect the inside of the laboratory.

Schlegel refused to reveal the nature of his illness on Tuesday, saying that "medical issues are private."

"I'm doing very fine," Schlegel said in a space-to-ground video link. "I worked all day today on Columbus and then to prepare my spacewalk with Rex Walheim tomorrow."

Walheim and Schlegel began the second of STS-122’s three scheduled spacewalks at 9:27 a.m. EST.

During their spacewalk, Walheim and Schlegel moved the new NTA from its position in space shuttle Atlantis’ payload bay. They temporarily stowed it on a Crew and Equipment Translation Aid cart while they removed the expended tank. With the new NTA installed, the old tank will be transferred to the orbiter’s payload bay for return to Earth.

At the controls of the Station’s robotic arm is Leland Melvin. Shuttle pilot Alan Poindexter is coordinating the spacewalk from inside the Space Station.

The replacement of the tank is part of regular Station maintenance. The Shuttle crew has brought a new nitrogen tank up inside Atlantis’ payload bay, right alongside Columbus and the external facilities, SOLAR and EuTEF.

SOLAR and EuTEF will be installed by Walheim and Love on Columbus’ exterior, during the third scheduled spacewalk. SOLAR is an observatory to monitor the sun and the European Technology Exposure Facility (EuTEF) will carry eight different experiments requiring exposure to the space environment.

In another task scheduled for the third spacewalk, the astronauts will move a failed control moment gyroscope from its storage location on the station to the shuttle’s payload bay for return to Earth.

Atlantis is scheduled to return on February 19, after NASA decided to extend the mission with one additional day.