Once in position, the station's 11-part spine will be complete after more than a decade of construction.

The truss is a high-tech girder structure made up of 11 segments. It provides the backbone for the station, supporting the solar arrays, radiators and other equipment.

To install the S6 truss segment, the station's robotic arm must extend its reach just about as far as it will go (about 57 feet or 17.4 meters), leaving it with very little room to maneuver.

The S6 truss segment weighs a little more than 31,000 pounds or 14,061 kg. After S6 installation, the truss will be 335 feet (102 meters) long.

Discovery was launched into space Sunday night. During its stay with the station, three spacewalks will be conducted.

If all goes well, it is scheduled to undock from the station on March 25, towards a planned March 27 landing at the Kennedy Space Center in Florida.

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Editor:Yang Jie