Amid Tight Security, NASA Begins Countdown for Shuttle Launch

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With security tighter than ever, NASA began the countdown late Monday for this week's launch of space shuttle Endeavour on a space station delivery mission.

Even more surveillance and safeguards will be in place by the time Endeavour is fueled and seven astronauts are on board for Thursday's liftoff. It will be the first space shuttle mission conducted while the country is at war.

Forecasters say there is a 60 percent chance the weather will cooperate for the 7:41 p.m. launch. Rain and thunderstorms are the main concerns. The weather is expected to improve dramatically Friday.

Endeavour will drop off one Russian cosmonaut and two American astronauts at the international space station, and bring back the three men who have been living there since August.

The next space station team -- commander Yuri Onufrienko and Carl Walz and Daniel Bursch -- will remain on board until May. They will be the fourth crew to inhabit the orbiting outpost.

The shuttle also will take up station supplies and science experiments, and carry more than 6,000 U.S. flags in tribute to all those killed by terrorists on Sept. 11 in New York, Washington and Pennsylvania.

Following Endeavour's 11-day mission, the small flags will be mounted on certificates and presented to families of the victims and survivors of the tragedy.

Also flying on Endeavour: New York City police badges and patches in honor of officers who died at the World Trade Center, and a New York Fire Department flag and poster showing the slain firefighters.