NASA Abandons New Shuttle Wiring Inspection Techniques

CAPE CANAVERAL - NASA is abandoning development of state-of-the-art tools to inspect aging shuttle wiring, which is susceptible to electrical shorts that could trigger catastrophe.

Consequently, the agency's inspector general says NASA is putting astronauts at risk and failing to comply with a recommendation made by the Columbia Accident Investigation Board.

"Without new evaluation technology, the inability to detect unseen wiring problems will continue to be a safety risk for the orbiter and any next-generation space vehicles," the NASA Office of Inspector General said in a summary of the agency's response to accident board recommendations.

The inspector general said NASA should "formally assess the risk of aging and damaged orbiter wiring and develop a risk mitigation plan" based on that appraisal.

Each shuttle orbiter contains about 230 miles of wiring that routes electrical power, computer commands and other signals to all critical systems, including the ship's solid rocket boosters, liquid-fueled main engines and external tank.

The wiring snakes through shuttles in bundles. Some is exposed to damage by workers preparing the orbiters for launch. Some is buried deep within the shuttle and cannot be inspected between flights.

Most of the wiring -- between 140 and 157 miles -- is insulated in Kapton, a lightweight material that has been used in aircraft and spacecraft for decades.

Years of experience, however, have shown that the insulation can split, crack, flake or otherwise physically degrade, leading to a phenomenon known as "arc tracking." Kapton wiring then becomes a conductor that can trigger electrical shorts.

The U.S. military effectively banned its use on new aircraft beginning in 1985.

Disaster averted

A July 1999 shuttle launch illustrates the kind of disaster that could be triggered by faulty wiring.

With five astronauts aboard Columbia, an electrical short knocked out two main engine computers five seconds after launch, leaving the crew one failure away from a risky and unprecedented emergency-landing attempt.

Investigators later determined that a frayed Kapton wire "arced," sending an electrical current from an exposed conductor to a nearby metal screw head, triggering the short and the resulting failure of the engine computers.

NASA managers grounded the shuttle fleet for five months of extensive inspections.

Workers repaired or replaced defective wiring, and the agency made an effort to place primary and back-up wiring to critical systems in separate bundles. The idea was to make certain that a short in one bundle would not cause the failure of a critical system in flight.

Plastic tubing and Teflon wrap were put around wiring in high-traffic areas to shield them from damage that could be done by workers during routine launch preparations.

The July 1999 electrical short prompted accident investigators to consider whether faulty Kapton wiring might have contributed to the loss of Columbia and its seven astronauts during an ill-fated atmospheric re-entry in February 2003.

It did not, but a review of thousands of wiring defects uncovered in shuttle orbiters after the 1999 incident prompted Columbia investigators to question NASA inspection techniques.

Wires out of reach

Currently, NASA and contractor engineers visually inspect wiring they can see. But some wires -- such as those located beneath the crew cabin -- are inaccessible. About 1,700 feet of Kapton wiring cannot be reached.

NASA managers say other wire runs are hidden within large bundles or are routed in a way that makes visual inspections impractical.

Concerned that defective wiring might go undetected, Columbia investigators recommended that NASA "develop a state-of-the-art means to inspect orbiter wiring, including that which is inaccessible."

The agency at the time planned to keep shuttles flying until 2020, and engineers began to examine high-tech techniques for detecting damage.

NASA shuttle program managers, however, are scrapping those efforts.

They note that the shuttle orbiters will be retired in 2010 under a new directive to complete the International Space Station and then send astronauts to the moon aboard a new spaceship.

Managers concluded "the new technology would not be cost effective or ready before the planned 2010 shuttle retirement," the inspector general said. Managers also noted that NASA was operating under a tight budget.

The inspector general, however, thinks NASA should continue to develop advanced inspection techniques.

The office also recommended that NASA make certain the agency can use research done to date "to facilitate development of new evaluation technology for wiring inspection of the next-generation space vehicle."

"In order to meet the CAIB recommendation, NASA should not consider the end of (shuttle) service life in the development of a comprehensive evaluation," the inspector general said.

NASA investigates

NASA is forming a team to "better characterize the specific vulnerabilities of orbiter wiring to aging and damage, and to predict future wiring damage, particularly in inaccessible areas," according to an agency report in response to the Columbia investigators' recommendations.

NASA also is trying to improve guidelines for visual inspections and protocols for protecting wiring from damage.

The agency is creating a database to gather statistics so engineers can better analyze and predict wire damage trends.

NASA limited the number of people working in areas where wiring is vulnerable and held training classes to reduce unintended damage.

Shuttle managers also note that wiring in each of NASA's three remaining orbiters has undergone recent inspections as part of a periodic modification program.

Discovery inspected

Stephanie Stilson, the Kennedy Space Center manager in charge of Discovery, said that orbiter underwent extensive wiring inspections during its most recent modification period and preparations for its scheduled July 13 launch.

Steps also were taken to wrap protective sheaths over some wire runs vulnerable to damage, she said. In addition, Stilson noted that more intrusive inspections would increase the chance that workers could inadvertently damage wiring while looking for problems.

"I feel very confident as to the wiring on Discovery," Stilson said. "I kind of look at it from a common-sense perspective because I've gone in there and done a very thorough inspection. . . .Why would I want to go back in there and mess with it again?"

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