WASHINGTON, June 16 (Xinhua) -- The six faulty computers at the International Space Station's (ISS) Russian segment has been all restored on Saturday, according to a top NASA official.

    "Currently, they have all six computers up while we do some additional troubleshooting to understand the environment and how if affects the computers," said Mike Suffredini, NASA's ISS program manager.

    "The bottom line is it appears to everyone that the command and control type computers are functioning just fine."

    With hard troubleshooting efforts during the past several days, Russian and U.S. experts finally bring the failed navigation computers back up to full operation. They powered up the Russian central computers and the terminal computers by using a jumper cable to bypass a faulty secondary power switch.

    However, engineers had not yet conclusively determined what caused the failure. "The troubleshooting will continue," added Suffredini.

    Also on Saturday, NASA's Mission Control Center cleared space shuttle Atlantis' heat shield for landing. The astronauts aboard the station got "the good news" at about 11:20 a.m. EDT (1520 GMT)while they were transferring cargo between Atlantis and the station.

    The heat shield was cleared after Mission Specialist John Olivas repaired a protruding thermal blanket on one of Atlantis' orbital maneuvering system pods during Friday's spacewalk.

    The fourth spacewalk of Atlantis mission is set to begin at 12:33 p.m. EDT (1633 GMT) on Sunday. After the last spacewalk, attention will turn to Atlantis' undocking and landing. For now, the shuttle is scheduled to leave the station on Tuesday and land Thursday at Kennedy Space Center in Florida.