Reuters
Aug. 13, 2004 — By Broward Liston
NEW ORLEANS (Reuters) - The foam that struck the space shuttle Columbia soon after liftoff -- resulting in the deaths of seven astronauts -- was defective, the result of applying insulation to the shuttle's external fuel tank, NASA said on Friday.
The official investigation into the accident, conducted by the Columbia Accident Investigation Board, left the matter open, since none of the foam or the fuel tank could be recovered for study.
A suitcase-sized chunk of foam from an area of the tank known as the left bipod, one of three areas where struts secure the orbiter to the fuel tank during liftoff, broke off 61 seconds into the flight on Jan. 16 of last year. It gouged a large hole in Columbia's left wing.
The damage went undetected during the shuttle's 16-day mission, but caused the nation's oldest spacecraft to break apart under the stress of re-entering the Earth's atmosphere on Feb. 1, killing the astronauts.
"We now believe, with the testing that we've done, that defects certainly played a major part in the loss. We are convinced of that," said Neil Otte, chief engineer for the external tanks project. He spoke at the Michoud Assembly Facility in New Orleans, where the half-million pieces of every shuttle fuel tank come together.
The fault apparently was not with the chemical makeup of the foam, which insulates the tanks and prevents ice from forming on the outside when 500,000 gallons of supercold liquid hydrogen and liquid oxygen are pumped aboard hours before liftoff.
Instead, Otte said NASA concluded after extensive testing that the process of applying some sections of foam by hand with spray guns was at fault.
Gaps, or voids, were often left, and tests done since the Columbia accident have shown liquid hydrogen could seep into those voids. After launch, the gas inside the voids starts to heat up and expand, causing large pieces of insulation to pop off.
NASA said this happens on about 60 percent of its shuttle launches.
For the bipod foam, the entire ramp was apparently torn away. It weighed only 1.67 pounds (0.75 kg), but at the speed involved, it hit the orbiter with enough force to shatter the reinforced carbon-carbon panels of the wing's leading edge.
NASA has made extensive changes in the foam-application process, but still has tests and perhaps more procedural changes before the tanks can be certified for flight.
"It was not the fault of the guys on the floor; they were just doing the process we gave them," Otte said. "I agree with the (accident investigation board) that we did not have a real understanding of the process. Our process for putting foam on was giving us a product different than what we certified." Recertification is now the biggest obstacle for the tank program. New standards require that no foam pieces heavier than about half an ounce can come off the tank during the first 135 seconds of flight. That is much smaller than the divots that have routinely popped off.
NASA also hopes to recertify the 11 fuel tanks that were ready for flight prior to Columbia once modifications are made. Each tank represents about a $40 million investment.