Story Continues BelowEndeavour is scheduled to rocket into space at 4:39 a.m. EST Sunday morning halfway into a short 10-minute window. Launching in the middle of the window maximizes the shuttle's performance and ensures the orbiter will have enough propellant for a full-duration mission and enough contingency reserves to stay in space an extra couple days, if necessary.

At a briefing this morning, shuttle launch weather officer Kathy Winters updated the forecast for the predawn liftoff. Overall, the weather appears to be favorable, with ground-level winds at the pad the only concern.

"The weather is looking promising for launch," said Winters. A cold front will pass through the area on Friday, followed by clearing skies and breezy conditions. The wind will be out of the west-northwest.

From that direction, the launch commit criteria prohibit launching if the wind speed exceeds 30 mph. However, if the wind shifts more to the north, the limit decreases to about 24 mph, although that is not expected to happen.

From the west, wind blows directly on the fixed service structure on the launch pad, partially shielding the shuttle. From the north, the wind blows directly on external tank from the back of the stacked vehicle. The lower allowable wind limit relates to the thermal effect on the vehicle as strong winds circulate around a fully fueled external tank which would then blow colder air over the entire vehicle: tank, orbiter and solid rocket boosters.

Other than the concern for winds, the countdown is proceeding very smoothly, according to NASA Test Director Jeff Spaulding.

"We're right on schedule where we're supposed to be," he said, "and we'll continue to work through the day on our preparations."

Endeavour's countdown began on time at 2 a.m. EST. Activities today will focus on buttoning up the orbiter for launch and conducting final closeouts around the launch pad. Additionally, the backup flight systems and avionics will be checked out and configured for launch.

Later today, the launch pad will be cleared of all unnecessary personnel in preparation for cryogenic reactant loading of Endeavour's fuel cells. The fuel cells generate electricity by combining liquid hydrogen and liquid oxygen, with pure water as the byproduct.

Loading of the cryogenic tanks will begin around 10 o'clock this evening and will be completed at 5:30 a.m. Friday.

Other events this weekend include retraction of the giant rotating service structure at 8 o'clock Saturday morning followed by the three-hour long fueling of the shuttle's external tank, scheduled to start at 7:14 p.m. Saturday evening.

Meanwhile, Endeavour's astronauts are completing final preflight reviews. Also, shuttle commander George Zamka and pilot Terry Virts will conduct final emergency landing practice runs at the shuttle landing facility in the Gulfstream Shuttle Training Aircraft.

Mission specialists Kathryn Hire, Stephen Robinson, Nicholas Patrick and Robert Behnken round out the six-member STS-130 crew.

Endeavour's 13-day mission will deliver and assemble the last U.S.-built modules onto the International Space Station, giving the laboratory a room with quite a view. The mission kicks off the final year of shuttle flights, with five missions planned through September.

Node 3, known as Tranquility, will provide additional room for crew members and many of the space station's life support and environmental control systems. Attached to the node is a cupola, which is a robotic control station with six windows around its sides and another in the center that will provide a panoramic view of Earth, celestial objects and visiting spacecraft.

(The Spacearium / SpaceflightNews.net)