Shuttle repair connected to foam loss?

HOUSTON — Technicians who repaired a half-inch dent on the space shuttle Discovery's enormous external fuel tank well before liftoff may have caused the foam-shedding incident that led to the grounding of future shuttle flights, NASA employees said Friday.

The seemingly minor damage and repair is in the spot where a 0.9-pound piece of insulating foam dropped away from the tank two minutes into liftoff, the employees said.

If the connection between the two actions is established, that could solve the mystery that has roiled the space program since July 26, when the large foam piece was caught on camera as it flew off the tank and narrowly missed the shuttle.

Employees of the space agency and contractors discussed the investigation on the condition that their names not be used.

An engineer at the Johnson Space Center who is working with the investigation cautioned that there might be no causal connection at all.

"Just because you rework something doesn't mean you're going to have a problem with it," the engineer said.

June Malone, a spokeswoman for the Marshall Space Flight Center in Huntsville, Ala., which manages the external tank development and production, said NASA's efforts to find the foam problem and repair it involved looking at that area of foam damage, "along with many other things."

The question of the dent and subsequent repair came up in a question to Michael D. Griffin, the NASA administrator, at a news briefing here on Friday. Malone filled in details in a telephone interview.

The tank was repaired this year at the Michoud Assembly Facility in New Orleans, where it was built by Lockheed Martin, a leading NASA contractor. Malone said the repair was carried out with the "sand and blending" process, a standard method for small blemishes. The hard lightweight insulating foam was sanded around the dent to leave a larger, slightly indented surface.

The foam, when first applied to the tank, has the creamy color of french vanilla ice cream. Over time and after exposure to sunlight, the outer rind darkens to orange. The sanding exposes fresh foam, and the creamy patches are easy to see.

There are a great many such repairs throughout the external tank, and extensive records are kept on all repairs. More extensive repairs to foam might require carving away foam and pouring in replacement foam or entirely rebuilding a section of the foam covering.

The tank is filled with more than 500,000 gallons of liquid hydrogen and liquid oxygen, and foam is needed to protect its supercooled surface from an ice buildup that could fall on the orbiter at launching and damage it.

The foam itself has turned out to be a major source of launching debris. That was what caused the loss of the shuttle Columbia and its crew in 2003.