Space shuttle prepares for return to Earth

CAPE CANAVERAL, Fla., June 21 (Reuters) Astronauts on the US space shuttle Atlantis closed their spaceship's cargo bay doors today, hoping clouds covering the Kennedy Space Center in Florida would clear in time for landing.

Touchdown at the space port's canal-lined concrete runway was scheduled for 2320 hrs IST, but flight directors may decide to wait for a second landing opportunity later today or keep the shuttle and its seven-member crew in orbit another day.

A final decision on landing was expected by about 2200 hrs IST, shortly before commander Frederick Sturckow and pilot Lee Archambault would have to fire Atlantis' maneuvering engines to leave orbit.

Flight directors decided not to staff the shuttle's backup landing site in California today, but if weather prohibits a touchdown in Florida, both sites will be available for landing attempts tomorrow.

The shuttle has enough fuel and supplies to stay in space until Sunday.

Atlantis spent most of its 13-day mission at the International Space Station, where the crew installed a 17-ton metal truss that included solar power panels to generate additional electricity for the half-finished 100 billion dollars complex.

NASA managers cleared Atlantis for landing after two inspections during flight and high-resolution photos taken by the space station crew found no damage to the orbiter's heat shield.

Heat shield problems are a major concern at NASA since the shuttle Columbia broke up while returning to Earth in 2003, killing the seven astronauts on board. The accident was blamed on an undetected crack in the heat shield.

During one of four spacewalks performed by Atlantis crew, astronaut John ''Danny'' Olivas patched up a torn thermal blanket that protects an area near the shuttle's tail from heat.

NASA engineers believe they underestimated how much heat the underlying shuttle layers had experienced during launch on June 8.

''When they modeled it, they made a mistake,'' deputy shuttle program manager John Shannon said of the original analysis. ''Still, the engineering and safety teams believe there's absolutely no risk at all during re-entry.'' The Atlantis mission, which was delayed from March after the shuttle's external fuel tank was damaged in a hail storm in late February, was the first of four shuttle flights scheduled this year.

The addition of the solar panels and other tasks performed by the shuttle crew prepared the space station, a project of 16 nations, for the installation of new European and Japanese modules.

The work was overshadowed last week when computers that keep the space station properly positioned crashed and required an improvised rewiring to revive them. The computers were still being subjected to a battery of tests today.

Reuters DS DB2020