Shuttle Grounded by O-Ring Problem : Space: NASA says heat-searing is minor, but puts off Endeavour launch until solution is in place.

The space shuttle Endeavour was grounded indefinitely Friday so NASA can solve the problem of singed O-rings discovered on the solid rocket boosters after two recent missions. Shuttle managers stressed that the problem had nothing in common with the failure of an O-ring that caused the shuttle Challenger to explode nine years ago.

Brewster Shaw, director of shuttle operations, put the seriousness of the problem at “less than 1” on a scale of 10. However, finding a replacement for the aging shuttle fleet has been a top priority for NASA Administrator Daniel Goldin, so any potential problems are getting special scrutiny.

The U.S.-Russian effort to build a joint space station has also put extra pressure on shuttle launch schedules--as have efforts in Congress to ax the space station.

The solid rocket boosters carry the shuttle into space like two firecrackers attached to its sides, then drop into the ocean for recycling. During the Challenger liftoff, one of the main O-rings between sections of the rocket failed, allowing hot gas to escape and cause an explosion in which the crew perished. After the disaster, the joints were redesigned with an extra piece of metal inside to hold the sections together.

In contrast, the small, heat-seared areas on the Atlantis and Discovery boosters--discovered during post-launch inspections--were at the tail end of the rockets, where hot gas spits out with a pressure of hundreds of pounds per square inch. “It’s very corrosive,” Shaw said. “It eats away everything that it touches.”

Two small O-rings in the nozzle joint keep the 6,000-degree gas away from the metal. For added protection, a thick glue-like insulator is injected between the two rings.

It is the process of injecting the insulator (called the rtv, or room temperature vulcanizer) that appears to have created the problem. “In trying to protect the O-rings [from high temperature gas], we have created exactly the opposite effect,” explained Shaw.

Apparently, gas bubbles formed in that process blaze a “gas path” that squirts the corrosive gas toward the O-ring. Shaw said these paths had been seen after nearly a dozen missions, but the most recent flights were the first time a direct effect on the O-rings was detected.

Shaw expects to repair the problem on the launch pad by creating a vacuum before air bubbles have a chance to form. NASA plans to do this by suctioning out the air between the O-rings and sucking the insulator into the void--much as one sucks soda through a straw.

As for delaying future shuttle missions, Shaw said they were “not even thinking about it.” He expects Endeavour to be off the ground by mid-August. Deliberations on NASA in Congress should not be affected, he said, adding: “We’re doing exactly what we’re supposed to do.”