CAPE CANAVERAL, Fla. ? Today is the big day for NASA's launch of space shuttle Atlantis ? maybe.

When the 100-ton orbiter launches, it will carry the seven-astronaut crew of the STS-122 mission and the European Space Agency's (ESA) new Columbus science laboratory module into space.

But rainy weather moving toward Kennedy Space Center has a 70 percent chance to push NASA officials to scrub their planned 2:45 p.m. EST (1945 GMT) launch and try another day.

"We're feeling very good about this opportunity," said STS-122 commander Stephen Frick. "We'll keep looking at the weather, but we're very happy about the condition of Atlantis."

Ready to launch

Last night, NASA unveiled the orbiter by rolling back the massive rotating service structure (RSS) that technicians use to service and check out the shuttle and its launch system. And with the shuttle nearly prepared for launch, so are its astronauts.

Frick will be joined by pilot Alan Poindexter as well as mission specialists Leland Melvin, Rex Walheim and Stanley Love. ESA astronauts Hans Schlegel and Leopold Eyharts also join the crew.

While in space, Walheim, Schlegel and Love will perform several spacewalks to install the Columbus lab as well as perform some on-orbit maintenance. Expedition 16 astronaut Dan Tani, who has lived on the space station since October 2007, will switch places with Eyharts and return home.

NASA expects the crew to safely return to Earth on Feb. 18 if the agency manages to launch the orbiter today.

Rained out?

NASA test director Jeff Spaulding said Wednesday that he's looking forward to a launch attempt today, but noted that mission managers will huddle around 4:45 a.m. EST (0945 GMT) this morning to decide whether or not to begin tanking the orbiter's pumpkin-colored external fuel tank.

The 3-hour process of loading some 500,000 gallons (1.9 million liters) of cryogenic fluids into the tank would mark a serious attempt by the agency to launch.

"We have a lot of flexibility and a lot of options out there if required," Spaulding said of launch opportunities extending into March, should NASA choose to scrub. "We're in really good shape."

The next two windows for Atlantis to blast off and catch up with the International Space Station (ISS) are Friday at 2:19 p.m. EST (1919 GMT) and Saturday at 1:57 p.m. EST (1857 GMT), should NASA call it quits for the day.

Spacey science

If Atlantis does launch this afternoon, it will ferry the Columbus lab to the space station, where astronauts plan to install it during their 11-day mission.

The high-tech, 10.3-ton cylinder will be as big as a small bus and keep ESA astronauts busy for at least seven years with space-based experiments.

"It's extremely important after 12 years of working on the [Columbus module] program to have something that gets launched," said Alan Thirkettle, ISS program manager for the ESA. "We'll own a part of the station, we'll have the rights to have our astronauts flying on there ? to be icons for youth of the future in Europe."

Thirkettle explained that the module's on-orbit experiments are expected to help develop new medicine, materials and water treatment techniques.

NASA will broadcast Atlantis' STS-122 mission live on NASA TV. Click here for SPACE.com's STS-122 mission coverage and NASA TV feed.