Faced with some less-than-perfect choices, NASA watched the weather report in three time zones Thursday as it struggled to pick a landing site for space shuttle Discovery's return to Earth.

The space agency planned to bring the ship home on Friday, after a 13-day mission during which its crew rewired the international space station.

But showers and clouds were in the forecast at Cape Canaveral, Fla., and crosswinds were expected at NASA's next-best option, Edwards Air Force Base in California's Mojave Desert.

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At NASA's third-best choice, White Sands, N.M., the weather looked favorable, but that could change later in the day because of a front coming from California. And New Mexico is considered inconvenient, because the space agency would have to fly some heavy equipment there to transport the shuttle back to Florida.

Only one shuttle has ever landed at White Sands, in 1982.

"More than likely, we will evaluate the conditions on a case-by-case basis on Friday and pick the lesser of evils," said Phil Engelauf, chief of the flight directors' office.

NASA said that if one of the sites has favorable weather Friday, it will bring the shuttle home, no matter how inconvenient the spot is. The shuttle does not have enough fuel to remain in orbit beyond Saturday.

"Don't worry about us. You tell us where to go, we'll be there," Discovery commander Mark Polanksy radioed Mission Control after hearing a weather report.

On Thursday afternoon, the space agency pronounced Discovery safe to return, after analyzing images from an inspection of the ship's heat shield. Shuttles are now routinely inspected in flight for any damage of the sort that doomed Columbia in 2003.

Discovery had originally been scheduled to land on Thursday, but the flight was extended a day to allow a fourth spacewalk to fold up a stubborn, accordion-like solar array on the space station.

During Discovery's successful eight days at the space station, astronauts not only rewired the orbiting outpost but also installed a new $11 million section and dropped off a new crew member, American Suni Williams.