CAPE CANAVERAL - NASA is abandoning development ofstate-of-the-art tools to inspect aging shuttle wiring, which is susceptible toelectrical shorts that could trigger catastrophe.
Consequently, the agency'sinspector general says NASA is putting astronauts at risk and failing to complywith a recommendation made by the Columbia Accident Investigation Board.
"Without newevaluation technology, the inability to detect unseen wiring problems willcontinue to be a safety risk for the orbiter and any next-generation spacevehicles," the NASA Office of Inspector General said in a summary of theagency's response to accident board recommendations.
The inspector general saidNASA should "formally assess the risk of aging and damaged orbiter wiringand develop a risk mitigation plan" based on that appraisal.
Each shuttle orbitercontains about 230 miles of wiring that routes electrical power, computercommands and other signals to all critical systems, including the ship's solidrocket boosters, liquid-fueled main engines and external tank.
The wiring snakes throughshuttles in bundles. Some is exposed to damage by workers preparing theorbiters for launch. Some is buried deep within the shuttle and cannot beinspected between flights.
Most of the wiring --between 140 and 157 miles -- is insulated in Kapton, a lightweight materialthat has been used in aircraft and spacecraft for decades.
Years of experience,however, have shown that the insulation can split, crack, flake or otherwisephysically 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.
A July 1999 shuttle launchillustrates the kind of disaster that could be triggered by faulty wiring.
With five astronauts aboardColumbia, an electrical short knocked out two main engine computers fiveseconds after launch, leaving the crew one failure away from a risky andunprecedented emergency-landing attempt.
Investigators laterdetermined that a frayed Kapton wire "arced," sending an electricalcurrent from an exposed conductor to a nearby metal screw head, triggering theshort and the resulting failure of the engine computers.
NASA managers grounded theshuttle fleet for five months of extensive inspections.
Workers repaired orreplaced defective wiring, and the agency made an effort to place primary andback-up wiring to critical systems in separate bundles. The idea was to makecertain that a short in one bundle would not cause the failure of a criticalsystem in flight.
Plastic tubing and Teflonwrap were put around wiring in high-traffic areas to shield them from damage thatcould be done by workers during routine launch preparations.
The July 1999 electricalshort prompted accident investigators to consider whether faulty Kapton wiringmight have contributed to the loss of Columbia and its seven astronauts duringan ill-fated atmospheric re-entry in February 2003.
It did not, but a review ofthousands of wiring defects uncovered in shuttle orbiters after the 1999incident prompted Columbia investigators to question NASA inspectiontechniques.
Wires out of reach
Currently, NASA andcontractor engineers visually inspect wiring they can see. But some wires --such as those located beneath the crew cabin -- are inaccessible. About 1,700feet of Kapton wiring cannot be reached.
NASA managers say otherwire runs are hidden within large bundles or are routed in a way that makesvisual inspections impractical.
Concerned that defectivewiring might go undetected, Columbia investigators recommended that NASA"develop a state-of-the-art means to inspect orbiter wiring, includingthat which is inaccessible."
The agency at the timeplanned to keep shuttles flying until 2020, and engineers began to examinehigh-tech techniques for detecting damage.
NASA shuttle programmanagers, however, are scrapping those efforts.
They note that the shuttleorbiters will be retired in 2010 under a new directive to complete theInternational Space Station and then send astronauts to the moon aboard a newspaceship.
Managers concluded"the new technology would not be cost effective or ready before theplanned 2010 shuttle retirement," the inspector general said. Managersalso 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 recommendedthat NASA make certain the agency can use research done to date "tofacilitate development of new evaluation technology for wiring inspection ofthe next-generation space vehicle."
"In order to meet theCAIB recommendation, NASA should not consider the end of (shuttle) service lifein the development of a comprehensive evaluation," the inspector generalsaid.
NASA is forming a team to"better characterize the specific vulnerabilities of orbiter wiring toaging and damage, and to predict future wiring damage, particularly ininaccessible areas," according to an agency report in response to the Columbia investigators' recommendations.
NASA also is trying toimprove guidelines for visual inspections and protocols for protecting wiringfrom damage.
The agency is creating adatabase to gather statistics so engineers can better analyze and predict wiredamage trends.
NASA limited the number ofpeople working in areas where wiring is vulnerable and held training classes toreduce unintended damage.
Shuttle managers also notethat wiring in each of NASA's three remaining orbiters has undergone recentinspections as part of a periodic modification program.
Stephanie Stilson, the Kennedy Space Center manager in charge of Discovery, said that orbiter underwent extensivewiring inspections during its most recent modification period and preparationsfor its scheduled July 13 launch.
Steps also were taken towrap protective sheaths over some wire runs vulnerable to damage, she said. Inaddition, Stilson noted that more intrusive inspections would increase thechance that workers could inadvertently damage wiring while looking forproblems.
"I feel very confidentas to the wiring on Discovery," Stilson said. "I kind of look at itfrom a common-sense perspective because I've gone in there and done a verythorough inspection. . . .Why would I want to go back in there and mess with itagain?"
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