Booster Rocket At Fault In Challenger Explosion
CAPE CANAVERAL, Fla. (AP) _ NASA engineers have concluded that Challenger’s explosion was caused by a failure in the right solid rocket booster, but they don’t know why it failed and say they may never know.
″We know the SRB is the failure,″ Thomas Lee, deputy director of NASA’s Marshall Space Flight Center, told a presidential commission hearing here Friday.
Using telemetry and computer-enhanced photographs of the liftoff and explosion, Lee and other engineering experts sketched a chronology of Challenger’s final 15 seconds.
In that period, a flame shot from a joint in the right rocket, and the booster broke loose from its bottom mooring, swung outward and pushed its nose cone into the external fuel tank.
The resulting fireball destroyed the shuttle and killed its seven crewmembers 73 seconds after the Jan. 28 launching.
Nothing in the hearing contradicted earlier testimony that a leak in the joint between the bottom and second segments of the right booster started the chain of events leading to the disaster.
A string of witnesses cited numerous technical reasons why the orbiter itself, the three main liquid-fueled engines and a large satellite rocket in the cargo bay had been cleared of blame in the accident.
″The things which are still possible are the external tank and probable is the solid rocket booster,″ said Thomas L. Moser, deputy director of the shuttle program.
Later, commission chairman William P. Rogers pressed the question of the external tank with Lee. ″Each time representatives of Marshall testify, they put the tank as their No. 1 suspect,″ Rogers said. ″Ostensibly, it seems as if the joint seems to be the No. 1 villian.″
″I didn’t mean to imply that,″ Lee replied. ″We don’t think the external tank is the No. 1 suspect. It’s a potential as a contributor only. We know the SRB failed. ... We know the SRB is the failure.″
Lee said experts were still analyzing the possibility of a small hydrogen leak in the tank and a drop in tank pressures about 10 seconds before the explosion. ″Until we complete all the analyses ... then we can’t close that out.″
During hearings last week, engineers from Morton Thiokol Inc., which builds the boosters, said they opposed the launch because freezing temperatures might have damaged synthetic rubber O-rings designed to prevent hot gases from escaping from seams between rocket segments.
Middle level officials at Marshall, which manages the rocket booster contract, questioned those concerns, and the engineers were overruled by Morton Thiokol managers.
Marshall’s associate engineering director, Jerrol Littles, testified Friday that tests since the launch have shown that temperatures as low as minus 10 degrees had no effect on the ability of the O-rings to seal the joints.
Rogers noted that Marshall engineers are doing most of the testing on suspected fault areas on the SRB and suggested they seek help from an outside independent source.
″We would welcome anyone participating,″ said Littles.
He said engineers are looking at several potential SRB faults, including the possibility that rainwater in the booster joint could have frozen, causing ice to push cold-hardened grease against the seals and opening a gap that would allow fiery gas to escape.
″The possibility certainly exists that you might unseat the secondary O- ring seal with the amount of grease in the joint,″ he said. ″You don’t have to stretch your imagination.″
Littles also said engineers are studying whether one of the two O-rings in the suspected joint was too small in diameter at one point in its circumference, whether the seals were improperly inspected and reviewed and whether a pressure test port on the joint might have been defective.
The commission also was told of problems in stacking and joining the drum- shaped segments of the right booster rocket, a task complicated by finding that the bottom segment was slightly egg-shaped and had to be squeezed back to roundness.
Littles said specialists at Marshall and at Thiokol are building test equipment to try to check some of the theories, but he said the conditions that Challenger underwent will be difficult to duplicate and he said some test data might be inconclusive.
Other officials said it would be helpful if debris from the right booster could be retrieved from the floor of the Atlantic. It has been located by robot submarines, but is 1,200 feet deep and will be difficult to bring up.