(Adds quote from briefing, details)

By Ed Stoddard

HOUSTON, Feb 16 (Reuters) - Astronauts worked to outfit Europe's new permanent space laboratory on Saturday as a busy visit by NASA's shuttle Atlantis to the International Space Station neared its end.

NASA readied landing sites at both the Kennedy Space Center in Florida and Edwards Air Force Base in California to ensure a Wednesday landing, as the U.S. military is waiting for the shuttle to land before it tries to shoot down a disabled spy satellite with a missile.

During a news conference with reporters in Europe and the United States, Atlantis commander Steve Frick said he had no worries about the satellite shootdown.

"We don't have any concerns ... we're going to be safely on the ground before they take any action," Frick said.

The Pentagon on Thursday said the Navy would try to destroy the satellite before it enters the atmosphere, using a modified tactical missile from a ship in the Pacific, to avert a potentially deadly leak of toxic gas from its fuel tank.

The Columbus module, the European Space Agency's $1.9 billion space lab, was launched aboard Atlantis last week and connected to the space station on Monday.

The astronauts on Saturday set up a physiology module inside Columbus to investigate effects of long-duration spaceflight on the human body, an area of interest with NASA's long-range goal of a manned Mars mission.

They also worked on activating a biolab that will be used for a range of experiments on cells, tissue cultures and other organisms.

"Biolab is still being worked on. It is a very complicated rack to set up," ISS Flight Director Bob Dempsey told a press briefing at the Johnson Space Center. He said the crews would likely be still busy with it on Sunday.

The external work on the lab during this mission was capped on Friday when spacewalking astronauts installed a solar observatory and an experimental facility on it.

Atlantis is scheduled to undock from the space station at 4:26 a.m. EST (0926 GMT) on Monday and is due to touch down on Wednesday at 9:06 a.m. (1406 GMT).

The space shuttle crew will bid farewell to the ISS crew on Sunday as the hatches between the two machines are to be closed at 12:15 p.m. EST (1715 GMT).

This mission, which has involved three space walks and been mostly trouble-free, has focused mostly on Columbus, which gives Europe its first permanent presence in space.

The solar observatory installed on it contains instruments that will, among other things, measure aspects of the sun's energy and help scientists decipher the impact of solar activity on Earth's climate.

The other facility attached to Columbus' hull will be used to conduct a range of space-related experiments. These include exposing lichen and fungi to space conditions for about 1-1/2 years to test the limits of their survival.

The agency has nine construction missions remaining to complete the $100 billion outpost and two resupply flights planned before the shuttle fleet is retired in 2010.

(Editing by Vicki Allen)

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