CAPE CANAVERAL, Fla., April 22 (UPI) -- NASA investigators probing the fatal shuttle Columbia accident have discovered widespread defects in foam insulation on an external fuel tank that is a virtual twin to the tank flown on Columbia's last mission, officials said Tuesday.
The discovery raises questions about whether manufacturing flaws were responsible for a chunk of foam falling off Columbia's fuel tank during its Jan. 16 launch and delivering a potentially fatal hit to the underside of the shuttle's left wing.
Accident investigation board Chairman Harold Gehman said his team is beginning to shift from collecting evidence surrounding the catastrophe to piecing together a comprehensive scenario of what triggered the shuttle's fall from the sky as it attempted to re-enter Earth's atmosphere. Seven astronauts died in the Feb. 1 accident.
The leading theory about what damaged the shuttle's left wing is a foam strike at launch, which allowed superheated air to penetrate inside the structure and melt it from inside.
Independent tests to confirm or disprove the foam strike theory are scheduled to begin next week at the Southwest Research Institute in San Antonio.
Whether or not the falling foam triggered Columbia's demise, NASA said it is taking steps to make sure insulation from the tanks will not shed. Before the remaining space shuttles fly again, NASA plans to encapsulate or remodel the troublesome bipod area on the shuttle's fuel tank, an aerodynamic slope of foam near where the tank attaches to the orbiter.
A dissection of the right bipod foam area removed from a tank manufactured at the same time and with the same materials as Columbia's tank revealed 74 imperfections, ranging from voids in the spray-on foam, to folds and other flaws, said Stephen Turcotte, commander of the Naval Safety Center and a member of the panel tasked to find the cause of the Columbia accident.
Analysis of the left bipod foam is under way. Turcotte said it is not yet known whether the flaws could have caused the foam to break away, or even if it is possible to manufacture the foam ramp without some imperfections.
"Is there a better way to do (apply the foam)? Is there no way to do it? Were the procedures (in place) at the time employed? All those things we're looking at," Turcotte explained.
Also Tuesday, the panel reported that radar experts had found a perfect match between a radar signal culled from Air Force tracking data of a mysterious object shed by the shuttle during its second day of flight and a T-seal, which anchors heat panels on the leading edges of the shuttle's wings. Teams are working to synchronize temperature and pressure data relayed by the shuttle and extracted from a salvaged flight recorder with computer analysis of how a missing T-seal would have affected air flow and heating during the shuttle's re-entry.
"Eleven weeks into this, it's time we attempted to see where the evidence is pointing us," said Gehman.
The board expects to issue its findings in June.