Astronauts on the space shuttle Discovery swept across the ship's exterior with remote-controlled cameras Wednesday in a search for damage that could jeopardize their return to Earth, as NASA managers pondered which of three sites would be best for landing Friday.

The Discovery crew used the shuttle's robotic arm and a 50-foot boom to take pictures, which NASA engineers will examine before deciding as early as Thursday whether to clear the spaceship for landing.

"So far everything is looking good," said Phil Engelauf, chief of the flight directors' office. "The systems on the vehicle are performing well. The vehicle is healthy. The crew is in good shape."

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Since the Columbia disaster nearly four years ago, such close inspections have become routine, both after liftoff and right before landing.

Discovery's seven astronauts also released two small, experimental satellites Wednesday as NASA managers debated where the shuttle should land.

Agency officials would like the shuttle to glide to its usual home at Kennedy Space Center to save NASA the time and cost of shipping it to Florida from the backup sites in California and New Mexico.

But low clouds and possible showers were in the forecast at Kennedy, and gusty winds were expected at the usual backup, Edwards Air Force Base in California.

That left a site at White Sands, N.M., with the best weather forecast for landing on Friday, even though it has been used in such a capacity only once, in 1982.

NASA has been reluctant to use the New Mexico landing site because it lacks crucial equipment.

If it landed in New Mexico, NASA would have to ship heavy equipment there, including a crane to hoist the shuttle atop a jetliner for the trip back to Florida and devices that control the shuttle's temperature and electrical systems on the ground.

Those steps would delay the shuttle's return to Florida by more than a month, compared with a week from Edwards Air Force Base.

During the New Mexico landing in 1982, fine sand on the runway contaminated the orbiter, and the brakes were damaged.

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

Discovery had been scheduled to land Thursday, but an unplanned fourth spacewalk during the shuttle's visit to the international space station pushed back the landing by a day. During Discovery's eight days at the space station, astronauts rewired the orbiting outpost, installed a new $11 million section, retracted a stubborn solar array and rotated out a space station crew member.

NASA wants the shuttle on the ground no later than Saturday because the fuel that generates electricity on the spacecraft will run out.

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