After a nearly 10-day stay at the international space station that included construction work and a computer meltdown, space shuttle Atlantis was cleared to begin its return trip to Earth.
The shuttle was scheduled to undock from the space station at 10:40 a.m. EDT on Tuesday, with a planned return to Cape Canaveral, Fla., on Thursday.
Atlantis might have stayed an extra day if engineers hadn't been happy with a test to see how well the Russian computers that crashed last week can control the orbiting outpost's orientation.
Monday's test was a success, said Phil Engelauf, chief of the flight directors' office.
"Yes, we think we're back to where we're supposed to be in terms of normal routine operations and reliability," Engelauf said.
The shuttle and space station crews said their farewells Monday before closing the hatches between the two spacecraft in preparation for departure.
"Have a good, safe landing. Until we see you again," station commander Fyodor Yurchikhin said before the hatches were closed.
During the test, the space shuttle's thrusters maneuvered the joined craft before the space station's computers commanded thrusters on the Russian side of the outpost to take control. U.S. computers then sent commands to the Russian thrusters before the station's gyroscopes took over control.
The computers, revived during the weekend, had not commanded the Russian thrusters since last Tuesday, when six computer processors in the two systems started crashing. During the meltdown, Atlantis' thrusters helped maintain the station's orientation.
NASA and Russian managers wanted to make sure Atlantis wasn't needed at the station for another day to give engineers on the ground more time to figure out the problem.
The computers also control life support systems such as an oxygen generator, temperature, and a carbon dioxide scrubber. Except for the oxygen generator, all the space station systems were turned back on during the weekend. Oxygen for the crews has come from other sources, such as a cargo ship on the Russian side of the station.
Engelauf said engineers were still trying to pinpoint the cause of the computer failure.
Atlantis arrived at the space station on June 10.
During four spacewalks, Atlantis' astronauts helped install a new truss segment, unfurled a new pair of power-generating solar arrays, repaired a peeled-back thermal blanket near Atlantis' tail and activated a rotating joint that now allows the new solar arrays to track the sun.
The 11-day mission was extended to 13 days so astronauts could repair the thermal blanket.
Twelve more construction missions are needed to finish building the space station before a 2010 deadline, when the shuttles are to be grounded permanently.
The shuttle is bringing back U.S. astronaut and former space station resident Sunita Williams, whose more than six months in space set a record for the longest single spaceflight by a woman. Her replacement, U.S. astronaut Clay Anderson, was brought to the station aboard Atlantis.
Meanwhile, leaders for almost 570 striking aerospace workers at the Kennedy Space Center in Cape Canaveral, Fla., said Monday the lack of training by replacement workers temporarily filling their jobs raises safety concerns for the next shuttle launch in August.
But United Space Alliance spokeswoman Tracy Yates said the replacement workers are certified for their jobs and have previous experience.