CAPE CANAVERAL, Fla. – NASA cleared shuttle Discovery for a scheduled landing Monday morning on what one astronaut, after passing over the troubled Middle East, called “this one little Earth” that is “all we have.”

The shuttle and its six astronauts have two landing opportunities at the Kennedy Space Center today – 9:14 a.m. and 10:50 a.m. Thunderstorms could force a postponement, but forecasters said the weather otherwise remained promising.

“It looks generally pretty good, but they are showing a chance of showers,” Mission Control told commander Steve Lindsey. “It gets a little worse as the day goes on, so we’re hoping the early morning works out for us.”

If Discovery cannot land today, NASA will try again Tuesday and will employ Edwards Air Force Base in California as an alternate landing site.

Orbiting hundreds of miles over the planet, Lindsey’s crew remained only partly aware of events in the Middle East. “We just flew over the Middle East and I have to tell you, from up here it looks peaceful and quiet just like the rest of the planet,” Piers Sellers told ABC News.

“I think we all are mindful, while we’re flying around and around this one little Earth, that this is all we have,” he said. “This is humanity’s home, and hopefully, one day we’ll all get along.”

Discovery’s return to Earth will mark the end of a nearly 13-day mission that NASA already has declared a success.

The crew delivered a new crewman and tons of supplies and equipment to the International Space Station, and inspections revealed no significant foam loss from the shuttle’s external fuel tank – the defect that caused the Columbia accident and the deaths of its seven astronauts in February 2003.

The loss of Columbia compelled NASA to ground the shuttle fleet for more than two years while it spent more than $1 billion on modifications to the fuel tank and other components.

The current flight is only the second since that suspension, but mission managers said they were confident that Discovery was fit for its searing trip through the atmosphere.

“The vehicle is totally cleared for entry,” said Steve Stich, NASA’s entry flight director.

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