15. Endeavour Lands Safely

Endeavour touches down Tuesday at Kennedy Space Center in Florida after its 13-day mission.

The crew of Endeavour (in light blue) and the international space station crew (in dark blue).

The space shuttle Endeavour came home a day early on Tuesday after NASA decided to cut short its mission in case Hurricane Dean shut down Johnson Space Center, which directs the shuttle's re-entry and landing.

The shuttle touched down at Kennedy Space Center at 12:32 p.m. ET, 13 days after its departure on a mission to help assemble parts of the international space station.

"Welcome back. You give new meaning to the term 'higher education,' " mission control told the seven-member crew, which includes former teacher Barbara Morgan.

The spacecraft landed at a speed of about 200 mph at a steeper angle than commercial airliners use, NASA said.

NASA made the decision Saturday to bring the shuttle back early, when forecasts for Dean showed the storm could veer to the north in the Gulf of Mexico and possibly force an evacuation of Johnson Space Center in Houston, Texas.

But Dean, now a Category 2 hurricane, has stayed well to the south, passing over the Yucatan Peninsula early Tuesday.

Endeavour's crew members had to cut short a spacewalk Saturday in their mission to help assemble the international space station and accelerate a number of other activities, such as cargo transfers with the space station, that had been on the docket for Sunday.

The astronauts worked through a series of pre-landing procedures Sunday and Monday, including a thorough inspection of the shuttle's wing leading edges and nose cap for any micrometeorite or orbital debris damage that might have occurred while the shuttle has been in space.

Last week, NASA managers determined that the crew would not have to repair heat shield tiles that were damaged 58 seconds after the August 8 liftoff, when a piece of insulating foam fell off the external fuel tank, ricocheted off a strut and hit the underside of the orbiter just below the right landing gear door.

While the damage site was not large, measuring about 2½ x 3½ inches, the gouge was deep and penetrated all the way through the tile to the base.

"The damage that we saw, after receiving all the engineering tests and analysis, was not a threat to crew safety," John Shannon, deputy shuttle program manager, said last week.

For nearly a week, teams of engineers at multiple NASA centers ran tests and conducted a complex thermal analysis of the gouge to determine if the damaged area could safely withstand the 2,500-degree F temperatures that Endeavour's belly experiences during atmospheric re-entry.

Shuttles with similar or greater tile damage have returned safely to Earth before, most notably Discovery in September 1988.

But in 2003, a piece of insulating foam flew off the space shuttle Columbia's external tank during launch, causing a gash in the leading edge of that shuttle's left wing.

When Columbia re-entered the atmosphere to land 16 days later, searing gases entered the hole, incinerating the spacecraft and its seven astronauts.

NASA has outlined an ambitious shuttle launch schedule to complete assembly of the international space station. If all goes as planned, NASA will fly 14 more missions before the fleet is retired in 2010 - CNN.