Michael Good, Garrett Reisman, Tony Antonelli, Ken Ham, Steve Bowen and Piers Sellers, left to right, arrive at NASA's Kennedy Space Center for mission countdown

The countdown for the launching of the shuttle Atlantis on the ship’s last scheduled mission, a 12-day voyage to the International Space Station, will get under way Tuesday afternoon with a favorable weather outlook.

Lift off from NASA’s Kennedy Space Center in Florida is scheduled for Friday at 2:20 p.m., EDT.

“We’re ready to launch,” Atlantis commander Ken Ham announced as the shuttle’s six member crew arrived at the Florida shuttle port in NASA training jets Monday evening. “We’ve completed every bit of training we can.”

Forecasters are predicting a 70 percent chance of  favorable weather. There is a slight concern for a low cloud ceiling that would violate flight rules, said Kathy Winters, the shuttle launch weather officer.

Ham, pilot Tony Antonelli and mission specialists Mike Good, Garrett Reisman, Steve Bowen and Pier Sellers have trained to deliver and install “Rassvat,” or Dawn, a Russian docking and research module on the space station. During three spacewalks, Reisman,  Bowen and Sellars will equip the station with a spare communications antenna and replace a half-dozen power storage batteries on the oldest solar module.
The mission is one of three remaining before NASA retires the shuttle program late this year.
The work of the six astronauts is intended to prepare the station for operations well beyond the final shuttle flight.