NEPHI, Utah (AP) - Roger Boisjoly, a NASA contractor who repeatedly voiced concerns about the space shuttle Challenger before it exploded, has died. He was 73.

Boisjoly died of cancer on Jan. 6 in Nephi, about 40 miles south of Provo, his wife Roberta Boisjoly said.

The 1986 Challenger tragedy shocked the nation. Seven astronauts, including a schoolteacher, were killed when the shuttle disintegrated 73 seconds after liftoff from Cape Canaveral, Fla.

Boisjoly, an engineer at rocket-builder Morton Thiokol Inc., warned in 1985 that seals on the booster rocket joints could fail in freezing temperatures.

"The result would be a catastrophe of the highest order _ loss of human life," he wrote in a memo.

On the eve of the ill-fated flight, Boisjoly and several colleagues reiterated their concerns and argued against launching because of predicted cold weather at the Kennedy Space Center. They were overruled by Morton Thiokol managers, who gave NASA the green light.

Slow-motion video of the launch showed a tongue of flame sprouting from one of the shuttle's solid rocket boosters, licking the main fuel tank.

After the accident, Boisjoly testified to a presidential commission investigating the Challenger accident. The group determined that hot gases leaked through a joint in one of the booster rockets shortly after blastoff that ended with the explosion of the shuttle's hydrogen fuel.

Boisjoly said he was shunned by colleagues and neighbors after emerging as a whistleblower. He took an extended leave of absence while Morton Thiokol worked on a redesign of the rocket joint.

"When I realized what was happening, it absolutely destroyed me," Boisjoly told The Associated Press in a 1988 telephone interview. "It destroyed my career, my life, everything else. I'm just now getting back to the point where I think I'll be able to work as an engineer again."

Boisjoly toured the country and spoke about his experience. He received awards from the American Association for the Advancement of Science and the Institute of Electrical and Electronic Engineers for trying to halt the Challenger launch.

Roberta Boisjoly said her husband continued to receive emails from students and others about his role.

"I'm very proud of what he did. It took a lot of courage," she said. "That's who he was. He would do it again."

Roger Boisjoly was born on April 25, 1938, in Lowell, Mass. He received a degree in mechanical engineering from University of Lowell and was active in the Church of Jesus Christ of LatterDay Saints.

After 27 years as an aerospace engineer, Boisjoly launched his own business in forensic engineering and lectured at universities.

He is survived by his wife of 49 years, two daughters and eight grandchildren.

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