The shuttle Endeavour's countdown began early today for blastoff Monday, between midnight and 4 a.m. EST (0500-0900 GMT), on a year-ending flight to the international space station. There are no technical problems at pad 39A and forecasters are predicting an 80 percent chance of acceptable weather.

The goal of the 112th shuttle mission is to install the third segment of the station's massive solar array/cooling truss, to deliver the lab's sixth full-time crew and to bring the current Expedition 5 crew back to Earth after 169 days in space.

The Endeavour astronauts - commander James Wetherbee, pilot Paul Lockhart, Michael Lopez-Alegria, John Herrington and the station's next full-time crew, Expedition 6 commander Kenneth Bowersox, cosmonaut Nikolai Budarin and science officer Donald Pettit - flew to the Kennedy Space Center Thursday evening.

Under NASA's post Sept. 11 security policy, the astronauts' arrival was not announced in advance and the shuttle's exact launch time will not be revealed until 7 p.m. Saturday. The forecast calls for an 80 percent chance of good weather during Endeavour's actual five-minute launch window Monday, but the odds drop to 70 percent "go" Tuesday and 40 percent go Wednesday.

NASA test director Steven Altemus said today Endeavour has four days to get off the ground before standing down for the debut launch of a Boeing Delta 4 rocket from the nearby Cape Canaveral Air Force Station. That launch is targeted for the afternoon of Nov. 16. But Air Force tracking systems used to support all East Coast rocket launches will be reconfigured for Delta 4 operations Friday, giving Endeavour's crew until Thursday night to get off the ground.

Assuming an on-time launch Monday, Wetherbee will guide Endeavour to a docking with the international space station Tuesday night. Three spacewalks by Lopez-Alegria and Herrington are planned for next Wednesday, Friday and Sunday nights to install and activate the new P1 truss segment. Undocking is planned for the night of Tuesday, Nov. 19, with landing on tap the evening of Thursday, Nov. 21.

Joining Wetherbee, Lockhart, Lopez-Alegria and Herrington for the trip back to Earth will be Expedition 5 commander Valery Korzun, flight engineer Sergei Treschev and science officer Peggy Whitson. They were launched to the station June 5.

This weekend marks a particularly busy few days for space station operations. The Expedition 6 crew currently is hosting two cosmonauts and a Belgian astronaut, who delivered a fresh Soyuz lifeboat to the lab complex Nov. 1. Soyuz commander Sergei Zalyotin, Yuri Lonchakov and Frank DeWinne, strapped into the station's older Soyuz, are scheduled to undock Saturday at 3:41 p.m. for a landing at 7:05 p.m. Undocking activities will be carried live on NASA television.

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   VIDEO: ASTRONAUTS ARRIVE AT KSC FOR LAUNCH QT or RV
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