WASHINGTON, June 15 (Xinhuanet) -- NASA on Wednesday moved the space shuttle Discovery back to the launch pad with a safer model of external fuel tank for the first flight since the Columbia disaster in 2003.

    The shuttle's 6.4-km trip from the assembly building at the Kennedy Space Center, Florida, to the seaside launch site, took more than 10 hours because checks on an overheated bearing of the shuttle transporter caused several stops.

    The transporter moved at less than the usual 1.6 km per hour Wednesday, reports reaching here said.

    Discovery was replaced with a new and safer model of external fuel tank which was intended for Atlantis on the next mission. A heater was added to the fuel tank to prevent ice buildup on the tank when it is loaded with super-cold fuel. The installation decision forced the removal of Discovery from the launch pad on May 26. The shuttle was first on the launch pad in April for flight originally scheduled for mid-May.

    Safety concerns have delayed the launch to between July 13 and 31. NASA determined that any ice breaking off the tank during liftoff could do bigger harm than foam if it smacked into the shuttle.

    The external fuel tank has undergone many design changes after the Columbia tragedy in February 2003, which was blamed on a suitcase-sized insulation foam that fell off the tank during liftoff and harmed the shuttle's wing, leading to the shuttle's disintegration during re-entry. Enditem