Riveting Movie Shows Booster Leak Burning Hole in Fuel Tank
WASHINGTON (AP) _ NASA experts ran a riveting movie Friday for the Challenger investigating commission showing, in dramatic frames a few thousandths of a second apart, the flame from a booster rocket leak triggering the explosion that cost seven lives.
One NASA official said “busy winds” buffeting the shuttle high over Florida may have helped cause the flame leak, by reopening a booster rocket seal which apparently was damaged on launch but had since closed. The experts said the flame forged a 45-square-inch hole in the booster rocket.
“We’ve looked at the heating that would result from that type of flame coming out,” said Wayne Littles, after the 14.5-minute, computer-enhanced film showed flame from the booster shooting for about seven seconds toward tank contains volatile liquid hydrogen and liquid oxygen fuel.
“There’s more than sufficient heat during that time to burn a hole through the tank,” said Littles, associate director for engineering at NASA’s Marshall Space Flight Center in Huntsvile, Ala. “You could burn a hold in that tank in a couple of seconds.”
Challenger exploded during the 74th second of its flight after launch from Kennedy Space Center in Florida on Jan. 28. Those killed include schoolteacher Christa McAuliffe, the first “ordinary citizen” to be aboard a shuttle.
The films and still pictures shown the presidential commission, came from 14 cameras routinely trained at the shuttle from liftoff until it nears orbit. Littles and other experts from Huntsville provided the commission a new, more detailed timeline of events from ignition to explosion, 9 miles high and 8 miles downrange from the launch pad.
Like all Friday’s witnesses, Littles testified that tests and analysis during the last two weeks have ruled out all potential causes other than a failed seam in the aft position of the right solid booster rocket.
“I believe we have eliminated all the other possibilities,” he said, adding that the remaining theories “all deal with the joint.”
A commission source said that the panel intends to recommend that the joint be redesigned, even if the exact way in which it failed cannot be pinpointed. NASA officials have said the shuttle will not fly again until joint problems are remedied.
After a review of the three-year history of problems with the joint, commission chairman William P. Rogers noted that “some of the people who made the decision to launch (Challenger) said they were not familiar with the problem.”
Littles responded: “I do know those problems have been reviewed in flight readiness reviews” attended by launch decision-makers. “I can’t imagine it was not known.”
Failure of the external fuel tank itself was one of the last “scenarios” ruled out, Littles said.
“We conclude that it’s probably that the leak from the solid rocket motor initiated the tank failure, rather than vice versa,” he told the commission.
Dan Germany, head of NASA’s accident photo analysis team, said in answer to a question by commission member Albert Wheelon that cold weather on launch morning caused the failure of 11 other cameras. Among the failed cameras were two which Germany conceded “would have provided an excellent view of the area in question.”
Germany’s aide, Charles Stevenson, said, “We think cold weather probably contributed to film breakage we have on the two critical cameras.”
The temperature overnight on launch day was 24 degrees, and cold is suspected of having somehow caused the booster rocket seam to fail.
Marshall engineer Harold Scofield testified that the shuttle encountered “a busy wind” that shook it unusually hard between 40 and 60 seconds through its flight.
“We don’t think this would open a gap in a healthy solid rocket motor seal, Scofield said. These rubber-like O-ring seals in the suspect booster rocket joint are the focus of the remaining theories of the accident’s cause.
Scofield added that there is no way to evaluate the effect of the wind forces on “a degraded (seal) structure.”
One theory holds the seals were somehow damaged at launch, because gray smoke was seen coming from the suspect seam on the right booster rocket in the first second of ignition. Engineers believe that this flaw grew into the much larger leak that occurred just before 60 seconds of flight. The shuttle exploded in the 74th second.
Asked by Maj. Gen. Donald Kutyna, a commission member, whether the unusually high winds could have opened the joint seals “after they sealed on launch,” Scofield replied: “We’re very much interested in that theory.”
The commission was also told that a 4-by-5 section of the suspect booster rocket, fished from the Atlantic Ocean on Monday, showed “the external surface is darkened and blistered.”
Air Force Col. Edward O’Connor, leader of NASA’s salvage team, told the commission that the piece probably came from a failed joint on the bottom of the right booster rocket. But, he said, it was from the opposite side of the seam from the point where the failure apparently occurred.
Germany, the photo evaluation chief, said unexpected gray smoke was first seen near that booster joint at 0.678 seconds after the rocket was ignited.
“It starts in a light shade and grows darker,” he said. The smoke continued at an estimated 3 puffs per second until about 2.2 seconds into the flight and finally disappeared at 2.7 seconds.
Germany said film was examined from six earlier shuttle launches in which safety O-ring seals in booster rocket joints had shown damage. “But we have not been able to find any visual evidence of smoke that’s duplicative of this,” he said.
A shuttle’s booster rockets are ignited after the ship’s three main engines are near full power, a process that takes about six seconds. During that time a “twang” develops in which the shuttle stack tilts slightly backward from its launch pad moorings, then straightens again.
Scofield said the ship vibrated during the twang at the rate of three times a second, which prompted Wheelon to ask if this movement correlated to the rate of gray smoke puffs.
“There’s a rough correlation,” said Scofield. “We’re still working on it. It could be coincidence.”
At 58.788 seconds, flame emerged from the booster rocket near where it is attached to the bottom of the external tank. In the ensuing seven seconds, the flame flickered, became a well defined plume, and caused a rupture in the liquid hydrogen tank which exploded in a white fireball at 73.327 seconds.
Germany called this “the major structural breakup of the vehicle.”
With the cause narrowed to the right booster rocket’s lower seam, Littles said the remaining theories for that failure include:
-Damage to the joint when the rocket was assembled;
-A manufacturing defect in a secondary O-ring used to seal the joint;
-Ice in the joint that may have forced the O-ring seals open;
-Cold weather that might have robbed the O-rings of the resiliency needed to completely seal; and
-Damage from cold weather to putty designed to protect the O-rings from flaming gases inside the rocket motor.
“Those are items which either individually or potentially in combination” could have initiated the failure, Littles said.
Littles said testing continues and added: “In the next week or 10 days, we hope to get a significant amount of data relative to these items.”
So far, tests have indicated that the putty is sensitive to temperatures, he said.
Referring to the smoke which disappeared after 2.7 seconds and the interval until flame appeared at 58.788 seconds, Littles said, “I think it’s possible, based on what we’ve seen, that you could have a leak that stops started some time later. It’s highly unlikely...that you had a continuous leak at one location for that long.”
Summarizing afternoon testimony, former astronaut Neil Armstrong said, “The tests have indicated that, if there are abnormalities, then the ways in which the joint might fail are quite variable or even unpredictable.”
No additional public hearings have been scheduled by the panel.