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Challenger Disaster was ‘An Accident Rooted In History’

June 10, 1986 GMT

WASHINGTON (AP) _ The problems that destroyed Challenger began with the 1973 design of solid- fuel booster rockets and remained hidden from the astronauts until the shuttle exploded last Jan. 28, the presidential Challenger commission report shows.

While NASA’s top launch managers told the commission they never received enough information to appreciate the seriousness of the problem, the panel concluded that an Aug. 15, 1985 briefing for top managers at NASA headquarters ″was sufficiently detailed to require corrective action prior to the next flight.″


The briefing paper at that meeting said, however, that it was safe to fly while the search for a remedy was stepped up.

The report, released Monday, said it was ″an accident rooted in history″ that began with a poorly designed rocket joint, followed by the failure of the National Aeronautics and Space Administration and its contractors to recognize it as a problem, their failure to fix it and their conclusion it was an acceptable flight risk.

The report concludes that the explosion was caused by the failure of a pressure seal in a joint on the right booster rocket.

Among the factors which the commission said contributed to the failure was the effect of cold temperatures on synthetic O-rings designed to seal the joint and keep hot gases from escaping. Challenger was launched when the temperature was 38 degrees, 15 degrees colder than on any of 24 earlier flights.

The cold degraded the ability of the O-rings to contain the gases, the panel said. Eventually a plume of flame emerged from the joint, burning a hole in the external fuel and igniting its volatile liquid hydrogen and liquid oxygen in a fireball that consumed the vehicle.

There was plenty of warning from lower-level engineers that the joints were badly designed, including one report that said they could cause a catastrophe that would destroy the shuttle and its crew, the report said.

But it said these warnings went unheeded by top officials of both the space agency and the manufacturer, Morton Thiokol. Some never reached top management, and the astronaut office complained after the accident that it was unaware of any problem with the joints.

Up to the moment of launch, some Morton Thiokol engineers argued against launching in the cold. They pointed out that all four flights launched at temperatures below 61 degrees had significant O-ring erosion. On the 20 launched in warmer temperatures, only four joints showed such stress.


The report also said the joints were unacceptably sensitive to launch pressures such as those built up on ignition and by high-altitude winds, questionable materials, the possibility of damage during manufacture and segment stacking and the effects of reusing the segments, which expand with each launch.

The report traces the history of the booster rockets from the award of an $800 million contract on Nov. 20, 1973, to Morton Thiokol to develop them.

Three companies competed with Morton Thiokol for the contract and a NASA evaulation rated Morton Thiokol second, but the company was selected because ″cost advantages were substantial.″

NASA officials decided Morton Thiokol’s technical flaws were correctable, and they liked the selection of a design based on the Air Force’s reliable Titan 3 solid rocket.

But, the commission said, the Thiokol and Titan designs differed in many ways. ″For example, the joints of the Titan were designed ... to form a more gas-tight fit,″ it said.

The report said a 1977 Thiokol test of the strength of the steel cases was the first signal that something was wrong. Analysis showed the joint was rotating and opening rather than closing as anticipated.

The commission said Thiokol engineers did not believe this would cause significant problems and scheduled no additional tests. But some Marshall engineers objected by memo to the design.

Although such memos emerged over several years, they had no significant impact on top management, the commission said.

After the second shuttle flight, STS-2, in November 1981, the primary O- ring in one of the boosters had significant erosion from hot gases.

″The anomaly was not reported in the ... flight readiness review for STS- 3,″ the commission said. ″Furthermore, in 1982, the STS-2 O-ring erosion was not reported on the Marshall problem assessment system ... as were other flight anomalies.″

In December 1982, the Marshall center determined in tests that the secondary O-ring no longer worked after the joints rotated. Officials concluded the secondary O-ring did not provide redundancy and changed the joint to a ″criticality 1″ category.

That meant that they believed that leakage of the primary O-ring could lead to ″loss of mission, vehicle and crew.″

Yet, NASA retained the design, based on the success of the Titan 3 with a single O-ring, the commission said.

With additional launches, more joints were eroded. Tests at Thiokol demonstrated O-rings did not function well in cold weather. Several engineers became concerned.

On Aug. 19, 1985, Marshall and Thiokol managers briefed NASA headquarters on the history and potential of the problem, concluding ″the O-ring seal was a critical matter, but it was safe to fly,″ the commission said.

The managers recommended an accelerated program to eliminate seal erosion, and Thiokol engineers made 43 suggested changes for the segment joints and 20 for the nozzle joints. But the redesign work continued at a slow pace up to the day of the accident, the commission said.

″The O-ring erosion history presented to Level 1 at NASA headquarters in August 1985 was sufficiently detailed to require corrective action prior to the next flight,″ the report said. Level 1 was Jesse Moore, an associate NASA administrator who directed the shuttle program.

Moore now heads the Johnson Space Flight Center in Houston.