Investigators probing the space shuttle Columbia disaster are visiting a facility in Alabama that overseas the production of massive external fuel tanks that propel shuttles during lift-off.

The external fuel tank continues to be a point of interest for investigators who are trying to learn what caused the breakup of Columbia as it re-entered earth's atmosphere February 1. A piece of insulating foam peeled off the tank during lift-off on January 16 and struck the orbiter's left wing, possibly damaging one or more external heat resistant tiles.

Investigators point to problems in the left wing as the most likely culprit for the disaster. A current theory holds that a breach in the wing allowed super heated air to seep in, as Columbia hurtled through the upper atmosphere at more than 18 times the speed of sound. Sensors in the left wing recorded abnormally high temperatures during Columbia's final minutes.

But just what might have caused a breach remains a mystery. Investigators hope to learn more by examining shuttle debris recovered in Texas and Louisiana that has been shipped to the Kennedy Space Center at Cape Canaveral.

U.S. space agency spokesman Bruce Buckingham explained what will become of the wreckage. "We are not going to be actually reconstructing it," he said. "But what we will be doing is laying it out on a floor so that all the pieces that have to do with the right wing or the left wing are all put in the same location. What we will be doing is identifying these pieces and then begin a 3 dimensional virtual reality computer program to show which pieces we have in place."

The first shipment of wreckage parts arrived at the Kennedy Space center Wednesday. A total of more than 12,000 shuttle pieces will eventually be laid out in a hangar that spans almost the dimensions of a football field.