During Friday's spacewalk, the third during the Atlantis' trip to the International Space Station, US astronauts Rex Walheim and Stanley Love will install scientific instruments on the exterior of the European-sponsored Columbia space lab.

The $1.9-billion (1.3 billion-euro) lab, financed mainly by Germany, Italy and France, was attached to the ISS on Monday by the crew of the Atlantis. It represents a giant step forward for Europe's space program and is the first major addition to the ISS not made by the US or Russia.

Phone call from higher up

German Chancellor Angela Merkel joked with the Atlantis crew via telephone on Thursday morning. She was joined by former German astronaut Thomas Reiter and the European Space Agency's director general, Jean-Jacques Dordain.

"Is it more fun with a woman onboard?" Germany's first female leader asked the crew, made up of seven men from the US, Germany and France. They joined Commander Peggy Whitson at the space station.

Merkel also congratulated German astronaut Hans Schlegel on his first-ever spacewalk on Wednesday.

"It was the first time I saw the Earth from outside the vehicle," Schlegel said. "The colors are very vivid. It is very important that humankind continues research in space and has an opportunity to go to space and see the beautiful earth."

Space mission extended

The 10-ton Columbus lab module, which was mostly built in the northern German city of Bremen, will be used among other things to conduct research in solar activity as well as biotechnology experiments involving microgravity.

On their six-and-a-half hour walk, Walheim and Love will also inspect a corroded joint and check a small hole in a hand rail that may have torn astronauts' gloves during previous spacewalks. Both spent the night in a decompression chamber to prepare for the expedition.

The Atlantis, which transported the lab to the ISS, was launched by NASA on Feb. 7. Its mission was extended by 24 hours to give the astronauts more time to get the lab running. The shuttle is scheduled to undock from the space state on Monday and return to the Kennedy Space Center in Florida on Wednesday.