Harried space agency officials decided yesterday to gamble and start dismantling shuttle booster hardware intended for the next flight, replacing a discredited design in the nozzle assembly with an alternative design tested successfully last summer.
At the same time, they said, engineers will continue analyzing the design that failed in a test-firing Dec. 23 in an attempt to determine what caused the problem and whether the alternative design will be adequate.
This is the "success-oriented" approach that counts on success and provides little margin for error and that the National Aeronautics and Space Administration has followed since last spring in its push to redesign the rest of the booster.
A failure in a booster field joint caused the Challenger disaster almost two years ago. NASA officials, who had scheduled resumption of the shuttle launch program June 2, said yesterday that the shuttle Discovery will not be launched sooner than six to 10 weeks later. "This is probably the way to go," said H. Guyford Stever, head of an independent panel of experts assembled by the National Research Council to monitor booster redesign.
The panel has described the "success-oriented" approach as reasonable if the engineers pay proper attention to test results and have adequate backup designs.
Ironically, NASA is able to move fast this time because the booster-redesign team had an alternative design, which they said budget and schedule pressures have made difficult to have for other parts of the booster, despite the panel's urging.
"This is the one area in which they had an alternative . . . . This is the kind of thing you like to see," Stever said.
NASA's approach is designed to minimize delay while its top managers gather information about the failure and try to decide on a replacement design, according to John Thomas of Marshall Space Flight Center, head of the booster redesign team.
Officials cannot set a new date for launch of Discovery until the extent of the required redesign is known, he said. That decision might not come for at least another week, he added.
"If the 'alternative design' turns out to be okay, we're that much ahead," Thomas said. "If not, all we've lost is the" nozzle part.
Officials at Kennedy Space Center have said they will be ready for launch five months after they receive the booster hardware containing the nozzle assembly.
Analysis of the dismantled nozzle sections from the test Dec. 23 has yielded no clear-cut answers, according to Thomas and others familiar with the process.
However, initial examination of the hardware and related test data indicated that the proper operation of the booster in flight would not have been affected by the failure, he said.
Meanwhile, in response to a published report about a "second flaw" found in the December test, NASA officials said a small hole piercing a nozzle-joint sealant was "not particularly harmful" and served mainly to prove that the new joint design did its job.
They had announced existence of the blow hole Monday. Stever concurred, saying the blow hole "was not a design flaw but was an expected flaw that the design is supposed to handle and did."