The international space station's recently repaired computers face a final test Monday to determine if the station can function on its own, which would allow the shuttle Atlantis to return to Earth.
Monday's test will determine if the two Russian computers can control the station's orientation in orbit, which allow the station's solar array to point toward the sun and generate power for oxygen generators and other vital equipment.
If the test goes smoothly, Atlantis will decouple from the station Tuesday and return to Earth on Thursday.
After all six of the space station's computers crashed last week, Atlantis' thrusters were used to help the station maintain its position.
During the test, Atlantis' thrusters will take control of the joined craft so it can change positions to dump waste and water. Then, the Russian thrusters onboard the space station will take over. During the second part of the test, U.S. computers will send commands to the Russian thrusters.
"That's a big step in our checkout of the computers to make sure everything is working correctly," said flight director Holly Ridings. "It's one of those things we want to see before we undock."
Atlantis, which has been docked at the station since June 10, will stay another day only if needed.
The station's computers were up and running following Saturday's computer malfunction that had left NASA and Russian flight controllers with a set of frustrating options if the problem couldn't be resolved. Two of the processors took longer to revive and are now on standby mode, but can be used, if needed.
Astronaut's completed their fourth and final spacewalk of the mission on Sunday. NASA's Patrick Forrester and Steven Swanson activated a rotating joint so a new pair of solar wings can track the sun and provide power to the station. The solar arrays were delivered to the station by Atlantis as part of its mission of continued work on the long-running construction project on the space station, scheduled for completion in 2010.
Early Monday morning flight controllers successfully tested the rotating joint, moving it five degrees. During a more thorough test later in the morning, the joint began rotating automatically, allowing the solar arrays to track the sun.
Written by Kayla Webley from NPR reports and the Associated Press.