NASA said Friday that cracks have been found in the insulation of all three space shuttle fuel tanks slated to fly in coming months and could be the reason a chunk of foam debris broke off during Endeavour's launch.
The debris gashed the belly of the shuttle, but ultimately didn't threaten the spacecraft during its recent mission. But NASA wants to prevent that from happening again, and officials outlined their repair plan Friday.
The new cracks were found in a layer of insulating cork that lies beneath the foam insulation on fuel tank brackets. Officials said both the cork and foam will be removed and then only new foam will be sprayed on before the next shuttle flight.
Shuttle program manager Wayne Hale said the extra work should not delay Discovery's planned liftoff, currently targeted for Oct. 23.
However, "We will take the amount of time that we need to get this repair done properly, and we will not rush."
The cracks were found through X-rays of the insulation on each of the five brackets on the fuel tank that will carry Discovery into orbit in two months. Small cracks also were found in the cork on fuel tanks for the two shuttles scheduled to fly later this year and early next.
Hale said the cracking most likely is connected to the manufacturing process, which hasn't changed recently. The cracks probably have been present for a while, said Hale, speaking to reporters by telephone from the Michoud Assembly Facility in New Orleans, where the fuel tanks are made.
Even before Endeavour landed Tuesday, engineers were trying to come up with a temporary solution for the troublesome brackets on the external fuel tank. The brackets — 17 inches long and 3 or 4 inches wide when foamed — support the liquid oxygen feedline.
On Aug. 8, a piece of foam, most likely attached to ice or the underlying insulating cork, peeled away from the fuel tank a minute into Endeavour's launch. It fell onto a strut lower on the tank, then bounced into the shuttle's belly, leaving a small but deep gouge.
NASA sweated over the damage until tests concluded it would not endanger the crew on its return to Earth or lead to lengthy post-flight repairs.
Engineers suspect the cracking discovered this week may have caused the foam debris to break off Endeavour's tank at launch.
"We cannot absolutely say because the evidence is slender based on the in-flight photography that was taken," Hale said, "but it certainly appears to correlate well. So the leading theory is that this underlying crack in this insulating material was a part and parcel of the loss that we saw."
Because of logistics, any delay in the October mission could wind up delaying launches set for December and February, Hale said. And that could ultimately prevent NASA from meeting its 2010 deadline for completing construction of the international space station.
Until the cracks were discovered, NASA had planned to simply trim some foam from the brackets.
The cork insulation is applied directly to the aluminum alloy brackets, then the airy foam is sprayed on top. The cork protects the brackets during the hot supersonic part of the launch. It's not really needed, however, and will be removed entirely from these brackets, Hale said.
The foam, on the other hand, prevents ice from forming on the brackets prior to liftoff, as a result of the super-cold fuel inside the tank.
A permanent solution — making the brackets out of titanium rather than an aluminum alloy — won't be ready until next spring.