"Undocking occurred at 12:25 p.m. Moscow time [9:25 a.m. GMT]," the spokesman said.
NASA said last week that the Atlantis would return to Earth on February 20 after its mission to the ISS was extended. It said the shuttle was ready for re-entry without repairs having been carried out on its thermal shielding.
The crews of Atlantis and the space station earlier examined a damaged area on the right side of the shuttle. A tear in the shuttle's thermal shielding was discovered an hour before the shuttle docked with the ISS. The damage was said to be insignificant, however.
NASA began paying particular attention to thermal shield damages after the space shuttle Columbia exploded on re-entry into Earth's atmosphere in 2003, killing the crew of seven. A piece of isolating foam, which had peeled off from an external fuel tank and punctured one of the wings on liftoff, was later established as the cause of the tragedy.
Last June, U.S. astronaut John Olivas repaired damage to Atlantis' thermal blanket during a spacewalk, enabling the shuttle to return to Earth safely.
