Atlantis has been grouned since last month. Photo: NASA/KSC

Space shuttle Atlantis is poised for a dawn launch Friday on a much-anticipated maintenance mission to the fledgling International Space Station.

Liftoff from pad 39A at Kennedy Space Center is scheduled for 6:12 a.m. EDT (1012 GMT), about 19 minutes before sunrise along Florida's Atlantic coast.

"The countdown is going very smoothly," NASA launch director Dave King said today. "We hope we are successful tomorrow morning."

Weather forecasters are calling for a 100 percent chance of acceptable conditions at the Cape on Friday. Favorable weather is also predicted at emergency landing sites in the Western U.S., Spain and Morocco.

You can follow the countdown live in our Mission Status Center. We will provide continuous play-by-play reports during the final hours of the countdown and the entire 10-day shuttle flight.

Atlantis' precise launch window will be refined through the final hours of the countdown and officials plan to synch up with the "preferred" liftoff time during the planned hold at T-minus 9 minutes. The exact launch timing is based on radar tracking of the International Space Station's orbit and the trek Atlantis will take to reach the outpost late Saturday night.

At present, NASA says Atlantis' launch window will extend for five minutes and 20 seconds, from 6:12:15 to 6:17:35 a.m. EDT.

Zarya and Unity modules of ISS orbiting Earth. Photo: NASA

NASA can take two shots at launching Atlantis during a three-day period from Friday to Sunday morning. Unlike the attempts last month, the space agency has decided against trying three consecutive days in a row.

If Atlantis is not off the ground by Sunday morning, NASA would have to wait three more days while onboard consumables are replenished before trying again. In addition, the oft-delayed launch of the inaugural Lockheed Martin Atlas 3A rocket from nearby Cape Canaveral will take over the Range on Monday night for as many as three attempts.

Should Atlantis fly as planned on Friday, the Atlas 3A could be cleared for another launch attempt Saturday night, officials said today.

Carrying new batteries, additional fans, smoke detectors, electronic gear and other equipment needed by the Russian Zarya module, Atlantis and its seven-member crew, led by commander Jim Halsell, are scheduled to fly a 10-day mission to the International Space Station.

Halsell will be joined by pilot Scott Horowitz, flight engineer Jeff Williams, mission specialists Mary Ellen Weber, Jim Voss, Susan Helms and Russian cosmonaut Yuri Usachev.

The flight was slated to begin last month, but bad weather at emergency landing sites scrubbed the launch on April 24, 25 and 26. Since then, the shuttle had to wait its turn while previously scheduled rocket launches and associated tests were performed at the Cape.

The seven astronauts arrive at Kennedy Space Center on Sunday for the launch. Photo: NASA/KSC

Given an on-time launch Friday, Atlantis is due to dock with the station at 12:32 a.m. EDT (0432 GMT) on Sunday. A six-hour spacewalk by astronauts Voss and Williams will start at 10:47 p.m. EDT on Sunday (0247 GMT Monday).

Monday will see the astronauts entering the station for the first time to begin the repair efforts.

A three-day series of altitude reboosts for the station using Atlantis' thrusters starts Tuesday, raising the outpost's orbit from 180 to 203 nautical miles.

The crew will exit ISS on Friday morning, undocking later that day.

Atlantis is slated to make a nighttime touchdown at Kennedy Space Center on Monday, May 29 at 2:19 a.m. EDT (0619 GMT), capping the third U.S. visit to the International Space Station since construction began in December 1998.

"I was on the International Space Station for a couple days," said Bob Cabana, commander of the first station assembly by shuttle Endeavour. "It is a place you want to be.

"I think you will see a fantastic facility in the not too distant future."