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NASA Says Bad Sensor Could Have Caused Shuttle Explosion

May 23, 1991

CAPE CANAVERAL, Fla. (AP) _ NASA says it escaped catastrophe by removing a leaky fuel-temperature sensor in September that the agency later learned was cracked and could have caused the shuttle Columbia to blow up.

More of the cracked sensors may have been aboard Columbia when its latest mission was scrubbed Tuesday - one day before liftoff, NASA said. Because of a mixup, the agency didn’t learn of the problem until late Monday, officials said.

Columbia’s launch with seven astronauts was postponed until at least June 1 so workers can replace all nine sensors, along with faulty computer equipment.

NASA today awaited tests on those sensors to learn whether they, too, were cracked. But the problem already appeared larger - cracks were found Wednesday in the stainless-steel welding of two sensors in the shuttle Discovery and two others look suspicious, officials said.

Other sensors, including those in shuttle Atlantis, are still to be checked. Officials said the new shuttle Endeavour has all new parts and shouldn’t need checking.

Discovery, Atlantis and Columbia have each flown since the leaky sensor was pulled from Columbia last September. Endeavour has just entered the fleet.

Had NASA known the extent of the sensors’ damage earlier, it would have grounded the shuttle fleet until sensors on each spacecraft were checked, said Keith Hudkins, director of the shuttle orbiter division.

Dan Germany, manager of the orbiter projects office at Johnson Space Center, said that if the pencil-sized sensor had remained on Columbia, it could have broken. Pieces would have then dropped into the spacecraft’s fuel lines, gotten caught in a high-pressure fuel pump and caused main engine failure and probably an explosion, he said.

″We dodged a bullet on that,″ Germany said Wednesday.

He said he didn’t know how many more times the shuttle could have flown before that occurred.

″It would have been just a matter of time,″ he said. ″It was good we found the leak and we got it removed.″

An explosion just after liftoff in 1986 destoyed the shuttle Challenger and killed all seven astronauts aboard.

Hudkins said a detailed analysis of the original sensor pulled from Columbia in the fall was delayed 2 1/2 months when it was sent to a valve company in California instead of sensor maker RDF Corp. in Hudson, N.H., for tests.

″Somebody thought they knew where that goes to and just didn’t take the time to look it up, and that cost 2 1/2 months,″ Hudkins said.

″Yeah, it bothers me, but it’s not unexpected. You don’t have a system this complex and extensive without having an occasional escape.″

Calls to RDF Corp. were referred to the office of sales manager Randy Gauthier, who did not immediately return messages left Wednesday.

The weld on Columbia’s sensor was found to be cracked all around and the inside was broken, although the wiring was intact, Germany said. The damage is less severe on Discovery’s sensors.

All the cracked sensors found so far are modified components that were in hydrogen fuel lines. The sensors were modified in 1981 because of wiring problems. Germany said the problem appears to lie in the redesign and is caused by extremely cold fuel.

Columbia, NASA’s oldest shuttle, has both original and modified sensors. Discovery and Atlantis have the newer parts only.

So far, the original devices seem to be free of problems, and only sensors under the old design will be installed in Columbia for its upcoming flight, Germany said.

NASA is reviewing its failure analysis process as a result of the sensor trouble.

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