The pieces collected, weighing a total of 35.3 tonnes or about 37 percent of the total, have been transported to a hangar at Kennedy Space Center near Cape Canaveral, Florida, where engineers are trying to piece it together.

"We have retrieved a large percentage of Columbia, and that will go a long way toward helping solve the puzzle of what happened February 1st," said NASA administrator Sean O'Keefe.

More than 14,000 federal agents and volunteers have combed some 80 percent of a 6,200 square kilometer (2,400 square mile) corridor in search of shuttle debris, with 20 percent left to be checked, said O'Keefe.

"NASA cannot thank the communities and our government partners enough for what they have done to aid the accident investigation," he added.

Columbia broke apart on reentry into the earth's atmosphere on February 1 after superheated gases entered a breach in the orbiter's shell.

The shuttle was just 16 minutes from landing when it disintegrated over Texas, killing all seven astronauts on board.

SPACE.WIRE