By Irene Klotz

CAPE CANAVERAL, Fla., Dec 5 (Reuters) - It is not just Europe's laboratory that NASA plans to launch into space on Thursday -- space shuttle Atlantis will return two veteran European astronauts to orbit as well.

Hans Schlegel, 56, of Germany and Leopold Eyharts, 50, of France, will join five Americans aboard Atlantis, which is scheduled for launch at 4:31 p.m. EST (2131 GMT) from the Kennedy Space Center in Florida.

"This is important for Europe to have two astronauts involved in the mission because this will be a high-visibility mission in Europe," Eyharts said in an interview.

The primary goal of the flight, the 121st of the shuttle program, is to deliver and install the Columbus laboratory module at the International Space Station. The lab is Europe's main contribution to the $100-billion, multinational program.

About 750 Europeans are in Florida to watch the launch, said Alan Thirkettle, who oversees the European Space Agency's human spaceflight program.

"We're very, very proud of what's happening," he said.

After a series of technical and weather briefings on Wednesday, the shuttle crew took a ride to the launch pad and enjoyed some free time with their families.

"After lots of hard work and preparation, I'm pleased to report Atlantis and her crew are finally ready to fly with the Columbus module," said NASA test director Jeff Spaulding. "The countdown is going very smoothly, really no issues to report."

Even Florida's notoriously fickle weather is cooperating, with meteorologists predicting a 90 percent chance that conditions will be suitable for liftoff.

Eyharts, who spent three weeks aboard Russia's now-defunct Mir space station nearly a decade ago, will stay behind on the orbital outpost to oversee Columbus' setup and activation. He will replace NASA astronaut Dan Tani as a member of the space station's three-person resident crew.

Eyharts said it had been "a long road" for him and Schlegel since they joined the astronaut class in 1998.

"But I think if we had to sign again we would do it," Eyharts said.

The return to space has taken even longer for Schlegel, who flew on a German-sponsored shuttle research flight in 1993.

"The most interesting questions to me will be 'How much will my body remember? How much will I be able to cope with all these difficulties (of adapting to space) so I can go on and do the other necessary tasks?'" Schlegel said in an interview.

Those tasks include a pair of spacewalks Schlegel will make with NASA astronaut Rex Walheim to attach Columbus to the station. Once it is installed, Eyharts, who will be the first to board the new module, will begin preparing the lab for research.

Europe plans to expand its nine-member astronaut corps next year, with openings for four additional fliers, said ESA astronaut Jean-Francois Clervoy.

With the planned expansion of the station crew to six live-aboard members, ESA would have a six-month slot about every two years, Thirkettle said.

Negotiations to increase the time available for ESA astronauts on the station are underway, he said. (Editing by Jane Sutton and John O'Callaghan)

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