Today's launch window officially opens at 4:34:31 p.m. EDT and extends for 10 minutes. The exact time, withheld because of a new security policy, was released Sunday afternoon by NASA officials as promised.NASA mission managers are aiming to go halfway through the window because that allows the shuttle to use the least amount of fuel in its chase of the frontier outpost.
But launch Weather Officer Kathy Winters said that gusting winds might reach a speed of 34.5 mph, exceeding allowable limits at both the launch pad and the Shuttle Landing Facility, where Atlantis might have to return in the unlikely event of an emergency after liftoff.
NASA safety rules say the shuttle can't launch, or land, with winds blowing greater than 28.75 mph.
A high pressure system to the east of the Florida peninsula and a low pressure system to the west over Texas are to blame, Winters said.
Conditions are expected to improve on Tuesday, when there is an 80 percent chance of acceptable weather.
NASA officials say they can make five launch attempts in any combination through Sunday. That's the last day the shuttle can fly before having to wait until May 5 for the next opportunity.
The reason: a previously scheduled Soyuz taxi mission with three crewmembers aboard is set for launch to the station on April 25 and flight rules frown on having more than one extra spaceship and crew at the outpost at the same time.
Thursday's launch attempt was scrubbed shortly after Kennedy Space Center engineers had begun filling the shuttle's external tank with its half-million gallon supply of liquid hydrogen and liquid oxygen, when a gaseous hydrogen exhaust line sprung a leak after a 20-year-old weld failed.
Repair plans were invented by late Thursday, formally approved on Friday and were put in work Saturday.
A two-piece, 10-inch (25-centimeter) wide sleeve of aluminum pipe was wrapped around the failed weld and welded together, patching the leak in a 16-inch (41-centimeter) diameter pipeline bolted to the side of a mobile launch platform, the two-story foundation upon which the shuttle rests.
After finishing the repair work midday Saturday, a full suite of inspections followed into the night to make sure there were no leaks. Officials say everything looked good.
"All of those tests and leak checks were successful and we are confident that we have a good vent line," said Pete Nickolenko, a NASA test director. "Our flight and ground systems are now looking good and the team is ready to support launch on Monday."
During the 11-day mission the crew is to install onto the station a $790 million collection of electronics and plumbing packed inside a 44-foot-long (13-meter-long) girder that will be the centerpiece -- literally -- of a giant beam that eventually will stretch more than the length of a football field.
Known as the S-Zero truss, the Boeing-built contraption contains 475,000 parts and includes the initial components of the world's first railroad in space, called the Mobile Transporter. The device will allow the station's Canadian robot arm to be moved along the length of the truss to assist in the complex's future construction.
It will take four spacewalks by two pairs of astronauts to make all of the structural and system connections between the S-Zero truss and the Destiny science laboratory.
If Atlantis lifts off on Monday, the STS-110 mission will conclude with the shuttle returning to a Florida landing on April 19.
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