Atlantis enjoying clean countdown to Friday launch

Atlantis remains on track for a 2:20 p.m. Friday liftoff on its last scheduled flight, and the weather forecast remains favorable.

"We've had a very clean countdown so far, and we're currently on schedule and we're not working any issues," said Jeremy Graeber, NASA test director.

There's a 70 percent chance of good weather Friday and throughout the weekend, with a possible threat of a low cloud ceiling that could violate visibility rules. Click here to see the official forecast.

"Overall, we're looking at really good conditions for launch operations," said Todd McNamara, shuttle weather officer.

The countdown is in a planned hold lasting nearly 14 hours at the T-ll hour mark, and should resume at 9:55 p.m.

Kennedy Space Center teams will soon begin activating shuttle communications systems and stowing time-sensitive science experiments in Atlantis' mid-deck.

At 5:30 p.m., they'll begin to roll back the Rotating Service Structure at launch pad 39A to reveal Atlantis for launch.

Also going on today at KSC: a launch Tweetup hosted by NASA for 150 participants. Follow their tweets here.

The launch pad will be cleared around midnight to begin preparations to load over a half-million gallons of supercold propellants in Atlantis' external tank at 4:55 a.m. Friday. Managers will meet at 4:15 a.m. to give the go-ahead for fueling.

This morning, Atlantis' crew of six astronauts practiced landings in a modified Gulfstream II jet and received a systems and weather briefing from Mission Control in Houston.

Led by mission commander Ken Ham, the crew is scheduled to go to sleep at 9 p.m. and awake on launch day at 5 a.m. They plan to don orange launch-and-entry suits at 10 a.m. and board Atlantis an hour later.

Atlantis is set to deliver a Russian docking port and replacement parts to the International Space Station during a 12-day mission.

Based on a Friday afternoon launch, landing at KSC would be targeted for 8:44 am. Wednesday, May 26.

If necessary, NASA managers say they can make four launch attempts over the next five days before standing down for an Air Force launch of a GPS satellite from Cape Canaveral Air Force Station, planned late next Thursday.

IMAGE: At launch pad 39A at Kennedy Space Center on Tuesday, Atlantis mission specialist Michael Good discussed the cargo being delivered to the International Space Station on the STS-132 mission with other members of his crew before Atlantis' payload bay doors were closed for flight. Credit: NASA/Cory Huston.