SAN ANTONIO, Texas -- A test firing of insulation foam at a space shuttle wing panel like the one on the doomed Columbia caused a crack that would have been too dangerous to fly with, a NASA investigator said on Friday.

The test results gave credence, but not final confirmation, to the theory that Columbia broke apart on Feb. 1 because flying foam from its fuel tank damaged the left wing and allowed the intense heat of re-entry to penetrate the orbiter's protective shield.

"We don't know the structural or thermal implications of this crack yet, but I can say if such a crack had been found on inspection, you would not fly with it. You would not take a piece that is this damaged into space," said Scott Hubbard, director of NASA's Ames Research Center in California and member of the Columbia Accident Investigation Board.

Columbia disintegrated over Texas as it flew toward landing in Florida, killing the seven astronauts on board.

The leading theory is that the 3,000 degree Fahrenheit (1,650 Celsius) gases generated by re-entry into the atmosphere leaked into the shuttle through a breach caused when loose foam struck the left wing shortly after takeoff on Jan. 16.

To test the theory, a briefcase-size piece of foam weighing 1.67 pounds was fired at 530 miles per hour -- the approximate speed of the actual foam strike -- by a giant gas-pressurized gun into a wing panel from the shuttle Discovery, Reuters reported.

Hubbard said the foam caused a narrow three-inch long crack in the panel, but it would take several days to determine if it could have caused the shuttle's demise.

The test was the latest and most critical of a series being conducted at the Southwest Research Institute in San Antonio by the Columbia Accident Investigation Board.

Foam shot into a fiberglass replica of a shuttle wing last week caused a 22-inch (55.88 cm) long gap. More tests are scheduled next week and the board hopes to complete its report on the accident in late July.

On Friday, the Orlando Sentinel said an outline for the report showed the board will point to NASA's poor risk management, questionable policy decisions and constant budget battles as some of the root causes for the Columbia tragedy.