NASA Knew Seals Could Fail
Thursday, February 13, 1986
More than three years before the fatal flight of the space shuttle Challenger, National Aeronautics and Space Administration officials concluded that the mechanism they devised to seal solid rocket booster segments could fail and cause "loss of mission, vehicle and crew," according to documents released yesterday by the agency.
Six weeks later, in February 1983, NASA officially acknowledged the defect by reclassifying the seals into a category called "criticality 1." This meant, according to the documents, that a system originally thought to be fail-safe was not.
As late as last Aug. 19, Morton Thiokol, the booster manufacturer, told NASA that under certain circumstances there was a "high probability" that the seals could fail completely during the first two minutes after liftoff.
This situation would occur, the company said, because the backup O-ring seal does not work properly. Thus, if the main O-ring seal failed during ignition, there would be no barrier to prevent leakage of the hot exhaust gases inside the booster rockets, which help power the shuttle during the first two minutes.
The right-hand booster on the Challenger shuttle, which exploded shortly after liftoff Jan. 28, apparently failed about a minute into the flight. A burn-through of the righthand booster at or near one of the joints between its segments is being studied as a possible cause of the disaster, in which Challenger's crew of seven died.
In its 1982 report, NASA said that if the two O-ring seals in any joint failed, the result could be "loss of mission, vehicle and crew due to metal erosion, burn-through, and probable case burst resulting in fire and deflagration."
The documents reveal that the space agency worked with an increasing sense of urgency and rising concern about the defect, examining but never implementing a wide variety of proposed corrective measures, all of which would have required considerable expense and delay. Meanwhile, NASA was stepping up its pace of shuttle flights, trying to show it had a reliable, reusable vehicle that could attract commercial customers.
Other documents, from last year, show that NASA was beginning to settle on two corrective measures that were to have been tested for the first time today in a ground firing of a booster. The test has been postponed.
"Efforts need to continue at an accelerated pace to eliminate SRM [solid rocket motor] seal erosion," officials of Morton Thiokol wrote in a detailed review of the problem last August.
Despite the reclassification to the "criticality 1" level, NASA officials said yesterday at a briefing that they felt it was safe to continue flying shuttles because the seals had never failed entirely in ground tests or in the five flights that preceded the reclassification.
"Those tests and those analyses led us to conclude that the maximum erosion that could occur under the conditions of the gas flow were acceptable by a factor of two or three," said Lawrence B. Mulloy, head of the booster program at the Marshall Space Flight Center in Huntsville, Ala.
While conceding that the defect could lead to "a catastrophic loss of the vehicle and life," Mulloy said, "we concluded that we had a safe situation to fly with."