Astronauts close space shuttle's doors for landing

CAPE CANAVERAL, Fla., Dec 22 (Reuters) Astronauts aboard the space shuttle Discovery closed their ship's cargo bay doors today in preparation for a return to Earth but the landing site remained undetermined.

NASA continued to aim for a 3:56 p.m. EST (0236 hrs IST) touchdown at the shuttle's home base at the Kennedy Space Center in Florida. The weather, however, remained a concern.

Meteorologists predicted a chance of low clouds, which could block the pilots' view of the runway, and possible rain in the area.

Forecasters also were looking at higher-than-expected winds.

''There's very little change,'' astronaut Ken Ham, from Mission Control in Houston, told Discovery commander Mark Polansky. ''It still looks certainly possible for today and we're going to continue to march toward that.'' NASA's next choice would be to divert Discovery to California's Mojave Desert site for landing, but high winds may scuttle that plan as well.

''It's going to be a dynamic day for you guys,'' Polansky said to ground controllers.

The first opportunity for a touchdown at the Edwards Air Force Base in California is at 5:27 pm EST (0357 IST).

That will leave flight director Norman Knight with just one final option: to land Discovery at a rarely used backup site in New Mexico, where the weather is forecast to be good for landing. The first opportunity for landing at the Northrup Strip at White Sands Space Harbor in New Mexico is also 5:27 pm EST (2357 hrs IST).

If Florida's weather improves, NASA also could choose to land Discovery at the Kennedy Space Center at 5:32 pm EST 0402 hrs IST.

NASA will have three more opportunities for landing in California or New Mexico through the afternoon and evening.

Usually, NASA would keep the shuttle in orbit an extra day if the weather in Florida or California was not suitable for touchdown. But flight directors used one of Discovery's landing contingency days to stay at the International Space Station to fix a jammed solar wing panel.

The shuttle blasted off on December 9.

REWIRE GRID The astronauts successfully completed their primary job to rewire the station's power grid and to install a new piece of the outpost's metal exterior truss.

The shuttle also delivered a new crew member to the station, NASA astronaut Sunita Williams, who replaced Germany's Thomas Reiter.

Reiter is returning with the Discovery crew after nearly six months in orbit.

NASA has used its New Mexico landing site just once in the shuttle's 26-year history. Columbia touched down at White Sands after its third spaceflight in March 1982.

Because the site lacks key equipment to prepare the shuttle for transport back to Florida, a landing in New Mexico would delay the shuttle's next mission.

That flight, currently targeted for October, is to deliver Europe's long-delayed Columbus research module to the station.

The delay would add pressure on NASA's already tight schedule to finish building the space station by 2010 when the shuttle fleet is due to be retired. At least 13 more missions are needed to finish station assembly.

NASA's next flight is slated for March aboard shuttle Atlantis, which is expected to deliver a third set of power-producing solar wing panels to the station.

REUTERS SY RAI2346