NASA to Study 2,000 Safety-Critical Parts : Challenger Had 748 Vital Components With No Backup Systems

The National Aeronautics and Space Administration is undertaking a complete review of the more than 2,000 pieces of hardware critical to safety in its remaining space shuttles, including a re-examination of the thousands of ways that their failures could jeopardize manned space missions, space agency officials said Monday.

During the year or more that the shuttle fleet will be grounded as a result of the Jan. 28 Challenger disaster, experts from industry and academia will help determine whether the long list of the safety-critical items can be reduced before the next manned spaceflight, Guy Cohen, NASA’s deputy chief engineer, said.

The list of parts was released at a Monday afternoon briefing in Houston. Space agency officials disclosed that Challenger had in its sophisticated machinery 748 components listed in a category labeled “Criticality 1,” meaning that they had no backup system and that their failure could cause destruction of the spacecraft and loss of the lives of all aboard.

Safety Precautions Cited

But Marion Merrell, director of safety, reliability and quality assurance at the Johnson Space Center near Houston, said the lengthy list emphasized the depth of NASA’s safety precautions and testing.

Of the “Criticality 1” items, 617 had been granted waivers from the requirement of having backup components after engineering evaluations determined that the parts could be flown without unnecessary risk.

The remaining 131 items, NASA officials said, were mainly large structures, such as wings and the tiles that protect the orbiter from extreme temperatures as it re-enters the Earth’s atmosphere. Such equipment cannot be duplicated and therefore was exempt from the waiver eligibility.

Among the “Criticality 1” items were the O-ring assemblies between the segments of the shuttle’s solid rocket boosters, now suspected of failing and causing Challenger to explode.

Lower Category

Originally, the O-rings had been classified in a lower category, “Criticality 1R.” Single failure of components in this category is not believed to result in the loss of spacecraft or crew. There are 1,621 “Criticality 1R” items.

But in December, 1982, the O-rings were shifted to “Criticality 1” when it was discovered that there was a possibility that the primary O-ring would not stay seated in its proper position during the first half-second after solid rocket booster ignition. This meant that failure of the backup ring in flight would cause the rocket to fail.

The lists released by the space agency Monday included 114 “Criticality 1” items in the solid rocket booster, 59 of which had received waivers by NASA management.

The orbiters themselves have about 335 “Criticality 1” parts, 304 of which have received waivers.

Called Pessimistic List

Merrell, questioned repeatedly on how NASA found it acceptable to fly shuttles with hundreds of possibilities for a single failure to cause disaster, insisted that the lengthy list was a pessimistic one, resulting from worst-case analysis of every known potential failure.

There is no way for the shuttle to be flown without using so-called single-failure components, he said. He cited as an example pressure vessels, which cannot be duplicated and whose safety can be ensured only by their design and engineering.

“There will always be some ‘Criticality 1’ items,” he said. “The question is: Are they acceptable to fly?”

Recovery Work Hampered

Meanwhile, strong underwater currents hampered efforts Monday to recover from the ocean floor a 500-pound piece of rocket debris that may provide important evidence of the cause of the Challenger explosion.

The Preserver, the Navy vessel assigned to recover the shuttle’s crew compartment, returned to Port Canaveral, Fla., after dark Monday after three days of recovery operations at sea.

The vessel, operating without running lights, came into port at 7:10 p.m. with sailors wearing their working blues lined up on deck. Two military ambulances with flashing lights pulled away from the ship shortly after it docked, and a crane began unloading mangled debris.

A NASA spokesman said the ship was making a “routine resupply” in port and refused to comment about what it was carrying.

Earlier in the week, the Preserver had recovered crew compartment wreckage and some remains of the crew.

Watch Ship’s Return

Spectators lined the shore to watch the Preserver’s return, many of them with binoculars.

“Why did I want to see it?” said Ruthmary VanDokkumburg, 43, clutching her binoculars. “Because it’s such a tragedy. It’s part of American history, really. You feel like it’s sacred when you come down here.”

Robert Maurus, 67, who was camping at the shore, said he comes out every night to try to catch a glimpse of a recovery ship returning to dock.

“I want to see it, because I saw the shuttle blow up right here. My wife and I have been here ever since,” he said.