NASA studies shuttle seal problem

In an eerie parallel to the problems that doomed space shuttle Challenger, NASA is grappling with O-rings as the agency prepares to launch a second teacher into space. Malfunctioning O-rings, the seals between sections of the shuttle's booster rockets, led to Challenger's explosion shortly into its 1986 flight. Teacher Christa McAuliffe and six crewmates died. McAuliffe's backup, Barbara Morgan, is slated to lift off Aug. 7 on shuttle Endeavour, Challenger's replacement. It will be Morgan's first space flight.

A NASA team is studying why recent batches of O-rings have a higher-than-usual number of specks of unmixed rubber, similar to bits of flour in a partially mixed bowl of cake batter. If such specks are too large or too close together, they can make the rings stiffer. The specks, detected by X-ray, are about the size of a grain of salt.

On Challenger, the rings were so stiff from cold weather that hot gases escaped from the booster, igniting the fuel.

Accident investigators condemned NASA for indifference to repeated O-ring problems.

By contrast, NASA has done weeks of testing on the latest O-ring issue. Initial tests show the rings with the defects are as strong and resilient as they should be, but more tests will be run through Saturday, says Jody Singer, head of NASA's solid-rocket motor project.

"As of right now, we find nothing that gives us concern," she says. The extra testing is likely to "validate what we think we know, which is that it is not a safety-of-flight concern."

Engineers started to raise questions three to four months ago, when they noticed a rise in unmixed specks. The rings passed all tests for resiliency and strength.

A retooled Endeavour, making its first flight in more than four years, includes O-rings with a higher number of unmixed specks. Because the rings passed all their quality tests, there is no reason not to use them, says David Beaman, a deputy solid-rocket manager.

Even so, studies continue. Engineers want to understand how the manufacturing process has changed, to prevent future problems, Singer says.

"We're re-examining the situation to make sure there's nothing we missed," Beaman says.

Allan McDonald, a retired booster engineer and whistle-blower during the Challenger investigation, says the number of defects is unimportant as long as the O-rings are strong and resilient.

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