NEW ORLEANS - NASA investigators at the agency's plant here are looking into the possibility that air bubbles beneath silicone-based insulation on the Columbia's external fuel tank could have caused a chunk of insulating foam to fly off the space shuttle during liftoff, a worker at the factory said.
Investigators have been reviewing paperwork related to the Columbia's external fuel tank and documentation of the building of eight other tanks completed here at the Michoud Assembly Facility, the worker said. Those eight tanks have not been used yet and are in storage here and at Cape Canaveral in Florida.
National Aeronautics and Space Administration officials have also interviewed two workers who sprayed foam insulation onto the area where the front belly of the shuttle connects to the external tank by two rods, said the worker, who has knowledge of the investigation.
The worker agreed to talk on the condition that his name not be used because the company operating the plant, Lockheed Martin, has told employees not to speak to journalists. The worker said company officials had indicated in recent meetings with employees that NASA did not seem to think the insulating foam was the cause of the Columbia accident.
The investigative panel led by Harold W. Gehman Jr., a retired admiral, also visited the factory for the first time yesterday. It toured the plant and met with Lockheed executives. Ten members of the panel flew to Lakefront Airport on two Gulfstream jets about 9:30 yesterday morning.
They spoke briefly to reporters before taking a bus to Michoud, an 843-acre site on the eastern edge of New Orleans.
Gehman said that this visit was meant to be educational and that the panel was not pressing an investigation yesterday.
The Michoud plant makes the 15-story, $43 million external fuel tanks that help put the shuttle into orbit. Though 15 tanks are in production, NASA officials have shut down parts of the plant that mix and apply foam insulation to the tanks. Many aerospace experts suspect that a 2.67-pound piece of foam that flew off the tank at liftoff could have critically damaged the shuttle, leading to a breach of the shuttle's skin by superheated gases.
In the first days of the investigation, NASA said it was focusing on the foam, then said the foam could not have caused enough damage to impair the shuttle, then said foam was back on the table.
NASA officials said the piece of hardened foam came off the bipod area, where two metal rods connect the tank to the shuttle.
That is one of the few areas where foam is manually sprayed onto the tank rather than with computer-controlled guns. There are also parts of the bipod area that are insulated with a silicone-based material called superlightweight ablator in addition to the polyurethane-based foam used on most parts of the tank.
NASA investigators are checking whether air bubbles were forming beneath the ablator and causing chunks of surrounding foam to fly off, the plant worker said.
In 1997, NASA found that a change in the Freon used in the polyurethane foam had caused small air bubbles to form beneath the insulation, leading to bits of foam popping off during liftoff and damaging tiles.
The ablator is an entirely different material, though, and NASA's investigation of possible air bubbles there is "just speculation right now," the worker said.