All eyes on weather for Friday's last shuttle launch.

It all comes down to the weather for Friday's launch of Atlantis on the final mission in the space shuttle program.

And there are a lot of ifs, ands and buts as far as whether expected rain and cloud cover both at launch pad 39A and the Shuttle Landing Facility will prevent the scheduled 11:26 a.m. launch.

Shuttle Weather Officer Kathy Winters this morning put the chances of weather preventing launch at 70 percent for Friday, 60 percent for Saturday and 40 percent for Sunday.

NASA Test Director Jeff Spaulding, citing crew rest and concerns about whether members of the launch team would be able to reach their homes through the expected viewing crowd of nearly 1 million and get sufficient time off before returning, said if a launch scrub is called anytime after L-minus four hours NASA most likely will opt for a 48-hour turnaround. That would mean the next attempt would come on Sunday.

NASA has reserved the Eastern Range for attempts on Friday, Saturday and Sunday before the scheduled launch of a Delta IV rocket from Cape Canaveral Air Force Station on Thursday takes precedence.

Spaulding said there have been preliminary discussions about the possibility of NASA securing Monday as a possible launch date should weather get in the way.

The main weather issues are clouds and rain in the vicinity of the launch pad and at the landing facility should a never-before-attempted Return to Launch Site abort is necessary.

Winters did say severe weather is not expected.

The three-hour tanking operation is scheduled to begin at 2 a.m. Friday. There is only a 20 percent chance of weather impeding tanking.

"I wish we had better weather for you," Winters told Thursday morning's briefing.

On the mechanical side of things, overnight, three chillers on the pad that use chilled water to cool ground systems malfunctioned, Spaulding said. Two of the chillers were back in operation this morning. Only one is needed for launch.

-Mark DeCotis