Update: Launch Forecast Improves

The timing of an approaching weather front now gives Endeavour a 70-percent chance of launching at 7:55 p.m. Friday, a slight improvement from Wednesday's forecast.

"We're a little bit more optimistic for Friday evening," said shuttle weather officer Kathy Winters, during a briefing at Kennedy Space Center this morning. "We're more confident in the timing of the frontal boundary."

Meanwhile, shuttle preparations are proceeding well, officials said.

"All of our systems are in good shape. Countdown work is on schedule. I have no issues to report," said Charlie Blackwell-Thompson, NASA test director for the STS-126 mission. "Endeavour is ready to go."

Blackwell-Thompson, of Merritt Island, is the first woman to serve as NASA's test director for a shuttle launch.

She said space center workers had finished loading liquid hydrogen and liquid oxygen that generate electrical power on board the shuttle. Supplies are sufficient for four launch attempts in five days.

Checkout of main engine avionics systems is expected to be completed this morning, and external tank inspections are set to begin.

Access platforms are being retracted as areas are closed out on the shuttle.

Today at 2 p.m., the countdown clock has a standard T minus 11 hold at 2 p. that lasts more than 13 hours.

Also later today: checkout of the orbiter ground communications network begins at 6 p.m., followed by flight crew equipment stowage at 7:30 p.m.

Launch pad 39A's Rotating Service Structure will be retracted and parked at 11:30 p.m.

On Friday, the pad will begin to be cleared of personnel at 5:30 a.m..

Shuttle managers will meet at 10 a.m. for a weather briefing before beginning to fuel the external tank as early as 10:30 a.m.

Astronauts are scheduled to enter the shuttle around 4:30 p.m.

If weather does scrub Friday's launch, Winters said the outlook is worse for Saturday, when the front is expected to arrive. There's only a 30-percent chance for a Saturday liftoff.

But after the front passes, the forecast improves Sunday to 80-percent "go" on Sunday.

Despite the potential for clouds Friday, Winters said she expects good viewing conditions if the shuttle is able to launch.

"In the local area, I think the viewing will be good," she said. "As you get further away – some people have asked about Tampa – it might be a little bit more difficult."