Allan J. McDonald, an engineer who on a chilly January morning in 1986 tried to stop the launch of the Challenger space shuttle, citing the possible effect of the cold on its booster rockets, and who, after it broke apart on liftoff, blew the whistle when government officials tried to cover up his dissent, died Saturday in Ogden, Utah. He was 83.

The cause was complications of a recent fall, his daughter Meghan McDonald Goggin said.

McDonald was a 26-year veteran at Morton Thiokol, the contractor responsible for the shuttle’s booster rockets, when he arrived at the Kennedy Space Center in Florida a few days before Jan. 28, when the Challenger was to take off.

The mission was to be the first to carry a civilian into space, a teacher named Christa McAuliffe. President Ronald Reagan was planning to mark that milestone in his State of the Union address, coincidentally scheduled for the same day as the launch.

But McDonald, who ran the company’s booster-rocket program, had strong reservations about moving ahead with the launch. The shuttle’s rockets contained a series of rubber O-ring gaskets, and he worried that low temperatures could cause them to stiffen, allowing fuel to escape and potentially causing the rocket to explode.

It wasn’t a new concern: Another Morton Thiokol engineer, Roger Boisjoly, had outlined the problem in a July 1985 memo, drawing on evidence of O-ring stiffening from a previous launch, when the temperature was 53 degrees Fahrenheit. The temperature on the night before the Challenger launch was expected to drop to 18 degrees.

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McDonald’s engineering team at the Morton Thiokol rocket plant in Utah, including Boisjoly, agreed with him. During a conference call with NASA officials late on the evening of Jan. 27, they refused to sign off on the launch — a necessary step in the shuttle’s safety protocol.

While the Ogden team took a break to discuss their objections, McDonald continued to press the case in Florida. Not only might the O-rings fail, he said, but ice hanging from the launch tower could fall off and damage the shuttle’s heat shield. And even if the takeoff was successful, choppy conditions in the Atlantic Ocean might make recovering the reusable rockets impossible.

The NASA team pushed back. Could McDonald actually prove the rings would fail? And why was he bringing up his opposition now, just hours before the flight?

“Normally we were always challenged to prove it was safe to launch,” he said in a recent Netflix documentary, “Challenger: The Final Flight.” “Now all of a sudden we got the impression they were asking us to prove it would fail, and we couldn’t do that.”

After 30 minutes, the Ogden team returned, saying they would give their approval after all. It later emerged that company executives, wary of upsetting their customers at NASA, had pressured the engineers to comply — and that the executives were in turn pressured by NASA officials, who had planned a record 15 shuttle missions that year and did not want delays.

But McDonald refused to go along, and when NASA asked the company to fax over a letter stating their approval, he declined to sign it. His supervisor at Morton Thiokol signed instead.

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The next morning the Challenger broke apart 73 seconds after liftoff, the result of an O-ring failure that caused one of its booster rockets to spin out of control. All seven on board were killed.

Reagan immediately established a panel to investigate, headed by former Secretary of State William P. Rogers and filled with luminaries like physicist Richard Feynman and astronauts Neil Armstrong and Sally Ride.

The president had told Rogers to make sure that NASA looked good, and at first he did. But evidence soon leaked to The New York Times showing that concerns about the O-rings went back months, and in a closed-door session the commission pushed NASA officials to explain their decision to proceed with the launch.

During the hearing, Ride asked Lawrence B. Mulloy, who oversaw the booster rockets for NASA, about rumors of a dissent by Morton Thiokol engineers. Mulloy conceded that there had been a discussion, but said that the company had ultimately agreed to go ahead.

At that point McDonald, sitting in the back of the room, stood up. His hands shaking, he told the panel that Mulloy was not giving them the whole story; the engineers, he said, had been pressured and overruled.

Rogers immediately asked for the room to be emptied so that the commissioners could discuss McDonald’s revelation. As the audience cleared out, Ride came over and hugged McDonald. Both of them had tears in their eyes.

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“It was the turning point of the commission,” Alton G. Keel, its executive director, said in an interview, adding that McDonald’s statement and subsequent public testimony had led Rogers to take a more focused, adversarial approach. The commission’s final report criticized both the design of the rockets and NASA’s decision to ignore the engineers’ concerns.

“Allan McDonald was a hero in our eyes,” Keel said in an interview.

Allan James McDonald was born July 9, 1937, in Cody, Wyoming, and grew up in Billings, Montana. His father, John, ran a grocery; his mother, Eva Marie (Gingras) McDonald, was a homemaker.

He graduated from Montana State University with a degree in chemical engineering and immediately went to work for what was then called Thiokol, helping to design the rocket systems for the Minuteman intercontinental ballistic missile. (The company became Morton Thiokol after it merged with Morton-Norwich, the maker of, among other things, Morton Salt.)

He later received a master’s degree in engineering administration from the University of Utah.

In 1962 he met Linda Rae Zuchetto at Sunday Mass; they married the next year. She survives him. In addition to her and Goggin, he is survived by two other daughters, Lisa Fischer and Laura McDonald; a son, Gregory; and nine grandchildren.

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Both McDonald and Boisjoly, who had provided internal Morton Thiokol documents to the commission, were later punished by the company: McDonald was demoted, and Boisjoly was placed on leave. After Rep. Edward Markey of Massachusetts (now a senator) learned about their treatment, he threatened to bar Morton Thiokol from future government contracts unless it restored the two men to their positions.

McDonald was made a vice president and placed in charge of redesigning the boosters; Boisjoly did not return to the company. In 1988 the shuttle program resumed, with McDonald’s new rocket attached. The booster rockets performed without incident until the shuttle program ended in 2011. (The shuttle Columbia disintegrated upon reentry in 2003, an accident unrelated to the boosters.)

Despite his success, animus toward McDonald within Morton Thiokol persisted, and as the limelight shifted, his career sputtered. Through the 1990s he was given make-work tasks, like assessing the environmental impact of space rockets.

He retired in 2001, but he did not slow down. He became a popular speaker on ethics and decision-making, working closely with Mark Maier, a professor at Chapman University in Orange, California, who runs leadership training seminars for corporate and government organizations. In 2009 McDonald and James R. Hansen published a book, “Truth, Lies, and O-Rings: Inside the Space Shuttle Challenger Disaster.”

McDonald’s decision to oppose NASA and his own bosses might have doomed his career, but he never expressed regret.

“Under intense political pressure, it’s easy to cave, to say you’ll play ball,” Maier said. “He didn’t do that. He assumed personal risk to do the right thing.”