Astronauts prepare to leave space station

CAPE CANAVERAL, Florida (Reuters) - Flight controllers conducted final tests on the International Space Station's revived computer network on Monday in hopes of clearing visiting space shuttle Atlantis for its departure and return to Earth.

The shuttle has been berthed at the orbital outpost since June 10 so astronauts could install a new set of solar power panels and prepare the complex, which is a little more than half-finished, for the arrival of new laboratories owned by the European and Japanese space agencies.

As the new panels were hooked up, however, the station's three main computers crashed, raising concerns that the $100 billion station, which has been continuously staffed since November 2000, would have to be temporarily abandoned.

Space station commander Fyodor Yurchikhin and flight engineer Oleg Kotov were able to restore the system by bypassing suspect protection circuits.

The computers control the firing of rocket thrusters needed to keep the station properly positioned in space for tracking the sun for power, pointing communications antennas and warming or cooling parts of the complex.

Since the computer crash last week, the station has been dependent on shuttle rocket firings for steering. NASA and Russian flight controllers on Monday ran a series of tests to turn control back over to the Russian computers and make sure the system is working properly before the shuttle departs.

Besides adding the new solar power panels and other upgrades, the shuttle crew delivered a new U.S. astronaut to serve on the station. Clay Anderson is relieving returning space station flight engineer Sunita Williams.

"I'm sad to say goodbye, but that means progress in being made and it's time for the International Space Station to grow a little more," Williams told ground control teams in a tearful farewell.

Williams and six shuttle Atlantis astronauts were scheduled to close the hatches between their spaceship and the station Monday evening. Atlantis' departure is expected at 10:42 a.m. EDT on Tuesday.

Touchdown at the Kennedy Space Center in central Florida is scheduled for 1:54 p.m. EDT on Thursday.

Atlantis' launch on June 8 was three months late due to extensive repairs needed to its external fuel tank, which was damaged in a freak hailstorm on February 26. NASA hopes its second flight of the year will not be too far behind.

Shuttle Endeavour, fresh from an extensive makeover, is slated for launch on August 9. Its crew includes teacher-turned-astronaut Barbara Morgan, who trained as the backup to NASA's first teacher-in-space, Christa McAuliffe.

McAuliffe never made it into orbit. She and six astronauts died in 1986 aboard shuttle Challenger when a booster rocket failed during liftoff.